3 Radiation Protection in Brachytherapy

SECOND EDITION

The GEC ESTRO Handbook of Brachytherapy

PART I: THE BASICS OF BRACHYTHERAPY 3 Radiation Protection in Brachytherapy Panagiotis Papagiannis, Jack Venselaar

Editors Erik Van Limbergen Richard Pötter

Peter Hoskin Dimos Baltas

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3 Radiation Protection in Brachytherapy Panagiotis Papagiannis, Jack Venselaar

1. Summary 3 2. Introduction: The international recommendations for a system of radiological protection 3 3. Design considerations of brachytherapy facilities 5 4. Brachytherapy facility shielding 7

5. Radiation protection issues associated with specific techniques 6. Source storage and transportation

9

11 12 14 15

7. Organizational issues

8. Key messages 9. References

1. SUMMARY

effects on human health, i.e.: global / regional radiation expo- sures, evidence of radiation-induced health effects in exposed groups including atomic bomb survivors, and advances in the understanding of biological mechanisms involved in the occur- rence of radiation-induced health effects (21,29,40). Updated general recommendations for a system of radiological protec- tion are prepared by the ICRP. These are further disseminated internationally through the publication of basic safety standards in the IAEA safety series and European Atomic Energy Commu- nity (Euratom) directives, which are based heavily on ICRP rec- ommendations. 1 Ultimately, these recommendations need to be transformed into national regulations and legislation, and they are further particularized by national and international scientific and professional bodies. An example of the dynamic aspect of this process can be seen in Table 3.1. According to ICRP terminology, a brachytherapy program is a source leading to planned exposure situations that involve the deliberate introduction and operation of the program, and are characterized by the ability to predict the magnitude and extent of the exposures and plan the radiological protection. It must be optimization and the application of exposure limits) in the context of brachytherapy. This is followed by an overview of design aspects and equipment prerequisites of brachytherapy departments. Particular focus is given to the calculation of material thickness to meet a set of structural shielding design goals, providing reference to sources of relevant data in the literature as well as the ESTRO website. Besides technique specific aspects of a radiation protection program for low- and high-dose rate applications, including practical infor- mation for source management, storage, and transportation, organizational issues are also discussed. These comprise the elements of a radiation protection program within a com- prehensive quality management system to ensure optimized patient treatments, while minimizing risks of radiation acci- dents as well as staff and general public exposure. The im- portance of written procedures and proper training of the members of the brachytherapy team cannot be overstressed.

This chapter aims to summarize technical and procedural information to aid the process of optimization of protection in brachytherapy, and to highlight some key elements of this process by elaborating on aspects of radiation protection in practice. Although based on the system for radiation protection de- veloped, and periodically re-evaluated, through expert con- sensus at an international level, national legislation may vary. Information in this chapter is therefore informative only and it should be carefully checked against local regulations prior to adoption. The chapter begins by discussing the general principles of the international system for radiation protection (justification,

2. INTRODUCTION: THE INTERNATIONAL RECOMMENDATIONS FOR A SYSTEMOF RADIOLOGICAL PROTECTION

Radiological protection, in general, is based on consensus de- veloped by international committees and organizations to pro- tect the individual from the harmful effects of radiation. This relates to occupational exposure, public exposure, and medical exposure of patients as well as their comforters and caregiv- ers. These independent international bodies have developed recommendations for a comprehensive system of radiologi- cal protection pertinent to all applications of radiation. These recommendations stem mainly from work performed by the International Committee on Radiological Protection (ICRP), and two members of the United Nations family of entities, the Scientific Committee on the Effects of Atomic Radiation (UN- SCEAR) and the International Atomic Energy Agency (IAEA). Such work forms a dynamic process based on the continuous review of studies and publications on ionizing radiation and its

1 At the time of writing, the ICRP Publication 103 (2007) (24) had replaced the previous recommendations (ICRP 1991) (17), which in turn led to the publication of revised IAEA Basic Safety Standards (IAEA 2014 (15) replacing IAEA 1996 (8)) and a new European Union basic safety Directive (Council Directive 2013/59/EURATOM of 5 December 2013 (3) replacing Directive 96/29/Euratom of 13 May 1996 (4)).

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emphasized that planned exposure situations include both nor- mal exposures that are reasonably expected to occur (i.e., medical exposures of patients, medical exposures of comforters or public exposures in permanent low dose rate (LDR) implants, occupa- tional exposures in applications involving source handling), and potential exposures that may result from deviation from normal operating procedures (i.e., accidents). Although the focus of this chapter is on brachytherapy planned exposures, during their operation emergency exposure situations might occur due to the operation itself or malevolent action (i.e. breach of source secu- rity). Emergency exposure situations cannot be predicted; they may require urgent protective actions, and they could even lead to existing exposure situations in the form of prolonged exposure situations following emergencies. In terms of biological dose response to radiation, determinis- tic effects are characterized by dose thresholds so that there is absence of risk for harmful tissue reactions at low doses (lower than about 100 mSv; updated information on dose thresholds in the form of dose resulting in about 1% incidence are provided in ICRP 2007 (24)). Although the introduction of a practical dose threshold has been proposed for stochastic effects, it is deemed that current data support that at low doses (e.g., below 100 mSv) the incidence of cancer and heritable effects rises proportionally to the increase of radiation dose over the background. The adop- tion of this so-called Linear No Threshold model (LNT) implies that a finite risk is associated with any exposure to radiation, however small, and protection must include considerations of what level of risk is deemed acceptable. Hence, any system of radiological protection is based on the following three funda- mental principles: justification, optimization, and application of dose limits. 2.1 Justification ICRP 2007 points out that any decision that alters the radiation exposure situation should do more good than harm (24). This principle is source related and applies to all exposure situations. With regard to occupational and public exposures, planned ex- posures such as those from a brachytherapy program should not be introduced if a net benefit to individuals or the society is not warranted, and any decision to reduce further exposures from emergency and existing exposure situations should be justified in the sense that more good than harm will come from it. Justi- fication in the above situations is a broad process wherein radi- ation detriment serves as one of the many necessary inputs. For medical exposures, brachytherapy planned situations are justi- fied at a first level since the medical use of radiation is widely accepted as doing more good than harm. At a second level, the potential of new brachytherapy techniques to improve treatment should be justified by competent national and international professional bodies and authorities. At the third level, referral criteria and patient groups must be established to facilitate the justification of medical exposure to any particular individual by physicians, who should be well aware of the risks and benefits of particular brachytherapy procedures as well as potential treat- ment alternatives. 2.2 Optimization of protection According to ICRP 2007, the likelihood of incurring exposure, the number of people exposed, and the magnitude of their in- dividual doses should all be kept as low as reasonably achiev-

able, taking into account economic and societal factors (the ALARA principle) (24). This is also a source related and uni- versal principle, i.e. it applies to all exposure situations that have been justified. It is the cornerstone of any system for radiological protection and its application involves a process of prospective and iterative character with the aim of preventing or reducing future exposures. This process includes the review of an expo- sure situation, the restriction of doses likely to be delivered to a named individual, the listing of options available for protection, the selection of the best option(s) under the circumstances using quantitative methods and cost-effect analysis, the implementa- tion of the optimization option decided and its dynamic evalu- ation. Dose restriction is applied in the form of dose constraints for planned exposure situations (except for medical exposure of patients), and reference levels for emergency and existing expo- sure situations which represent upper bounds of dose predicted in optimising protection from a particular source. These must be defined in the planning stage of optimization. Exceeding these constraints and reference levels in such an analysis should trig- ger an investigation and optimisation of protection should aim at establishing acceptable dose levels below them. For medical exposures of patients, optimisation assumes the form of a set of measures to ensure that dose is in accordance with the medical purpose. For diagnosis, reference dose levels are set that are not individual patient dose constraints but levels of dose indicating that patient dose is neither too high nor too low for a particular procedure. Patient dose management informa- tion for equipment and imaging techniques used in conjunction with brachytherapy, such as fluoroscopically guided interven- tional procedures, computed tomography and digital radiology, are provided in the literature (18, 19,20). Reference dose levels do not apply to radiation therapy itself, where optimization in- volves the delivery of the prescribed dose to the target while also planning the protection of healthy tissues (16). This is related to quality assurance procedures and accident prevention that are dealt with in other publications; see also (12, 22, 41) and several AAPM reports. 2.3 Application of dose limits Again quoting from ICRP 2007 “…the total dose to any individ- ual from regulated sources in planned exposure situations other than medical exposure of patients should not exceed the appro- priate limits specified by the Commission…” (24). In contrast to the previous two principles, this one is individual related and applies to planned exposure situations only (except for medical exposures of patients). ICRP recommendations for dose limi- tation are summarized in Table 3.1. Regulatory dose limits are set by national competent authorities taking into account these recommendations, and variations from country to country may occur (32). Members of the public involved in patient comforting and care giving are not subject to the dose limit for public exposure (but a prospectively defined, reference level should apply). For female workers who declare pregnancy, additional controls must be im- plemented to ensure protection for the embryo similar to that for the public. Dose limitation is a means of regulatory control to prevent the occurrence of deterministic effects and confine the risk of sto- chastic effects to levels currently deemed acceptable. The im-

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lations appropriate to their individual countries. Information in this chapter should therefore be considered for information only and carefully checked against local regulations prior to adoption.

Table 3.1: Dose limits recommended by the ICRP (24)

PUBLIC EXPOSURE

OCCUPATIONAL EXPO- SURE 20 mSv per year averaged over 5 years and less than 50 mSv in any single year

Effective dose limit:

1 mSv per year

3. DESIGN CONSIDERATIONS OF BRACHYTHERAPY FACILITIES

Eye lens equivalent dose limit: Skin equivalent dose limit: Hands and feet equiv- alent dose limit:

15 mSv

150 mSv*

A brachytherapy program normally requires the availability of physical plant facilities that include an operating room, ra- diograph imaging room, patient treatment room, and/or a hot lab, as described in the IAEA TecDoc 1040 (12). Each of these facilities has its own functionality and plays a unique role in a brachytherapy program. For radiation protection purposes, they may need to be designated controlled or supervised areas (24). Controlled areas are those where specific protection measures are required to control normal exposures and prevent/limit po- tential exposures. These measures include a clear delineation of the area, appropriate labelling, access restriction, radiological surveillance and the establishment of written procedures and working instructions. Supervised areas, often surrounding con- trolled areas, are those where protection measures are not nor- mally needed but occupational exposures are kept under review. Areas may be designated according to the magnitude of expected exposure, i.e. in the UK and several other countries. Areas where annual dose could be greater than 6 mSv and 1 mSv are designat- ed controlled and supervised areas, respectively (11). Brachytherapy treatment rooms and source preparation/storage rooms (“hot labs”), as well as imaging rooms, are controlled ar- eas. Operating rooms could fall into a designated area category depending on application and source loading procedure, and high dose rate (HDR) and pulsed-dose rate (PDR) treatment consoles are supervised areas. The operating room is used for catheter/applicator placement and sometimes for radioactive source “hot loading”. Depending on the type of brachytherapy procedure, the operating room may require sterilization condi- tions. The availability of an imaging room/equipment is critical to the success of a brachytherapy program. The radiograph imag- ing room/equipment is typically used to acquire patient 2D/3D images on which the target volumes, critical organs, and/or cath- eters/applicators can be localized for accurate dosimetry calcu- lations and treatment planning. A CT/MR scanner room can be used for this purpose although it is important to bear in mind that catheters/applicators compatible with the imaging modality are desirable to avoid image artifacts. A conventional 2D simu- lator is a reasonable option although it is difficult or impossible to identify soft tissue target volumes from the images. In some cases, a C-arm type fluoroscopy machine is used in the operating room to ensure precise placement of brachytherapy instruments. The images acquired with the C-arm machine can be directly used for dosimetry calculations and treatment planning. Patient treatment rooms must be designed and prepared appro- priately for a brachytherapy program. The requirements for the treatment room are different for LDR and HDR/PDR programs. A hot lab should be designed and made available for long-term or temporary storage of radioactive sources. In addition, many physics related procedures, such as seed assay and preparation, wipe test, etc., should be conducted in the hot lab. The hot lab should be equipped with a well shielded source storage cabinet,

50 mSv

500 mSv

-

500 mSv

*After review of epidemiological evidence suggesting threshold doses might be lower than previously considered, irrespective of rate of dose delivery, ICRP issued a statement on tissue reactions (25) and an equivalent dose limit for the lens of the eye of 20 mSv in a year, averaged over defined periods of 5 years, was recommended for occupational exposure in planned exposure situations. This recommendation, which is significantly lower than corre- sponding ICRP 103 (24) recommendations, was adopted in the IAEA Basic Safety Standards (15) and will very likely be implemented in national dose limits in the coming years.

portance of optimization cannot be overstressed. Source specific dose constraints and reference levels for planned exposures of workers and members of the public cannot be greater than dose limits and are an aid to ensuring that the latter will not be ex- ceeded due to exposure from different sources. 2.4 General comments on the recommendations The introduction of remote afterloading devices has brought a radical change in brachytherapy practice as a whole, as well as in radiation protection in particular. Occupational doses have been drastically reduced by technical advances (7) to levels com- parable to those in external beam therapy. Still, brachytherapy reserves its special niche due to the storage of sealed sources emitting radiation constantly, permanent implants, and the need for source manipulation in permanent implant applications (i.e. for prostate treatment) or, less frequently, applications involv- ing manual source loading (i.e. eye plaque applicators for ocu- lar melanoma treatment, or use of pin and wire sources). For example, the use of sealed radionuclides for brachytherapy and unsealed radionuclides for radiopharmaceutical therapy are col- lectively identified as radionuclide therapy in the NCRP 155 re- port which offers guidance for the management of radionuclide therapy patients (36). Neither the above summary of the internationally adopted ra- diological protection system and its recommendations, nor the remainder of this chapter seeks to replace the need for a thor- ough review of the literature, in the form of published articles as well as reports from the cited international bodies and national or international professional societies, and their implementa- tion in brachytherapy. This chapter merely aims to summarize selected technical and procedural information to aid the process of optimisation of protection in brachytherapy, and to highlight some key elements of this process by elaborating on aspects of radiation protection in practice. A word of caution is in order. This chapter does not attempt to summarize regulatory or licens- ing requirements. This would be impractical since international bodies leave it to national protection bodies to formulate regu-

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3.2 HDR brachytherapy treatment room Since HDR (and, as stated, PDR) brachytherapy procedures normally deliver a large dose to patient target volumes within a relatively short period of time, many safety features and meas- ures have to be taken into consideration in the design of a HDR treatment room. Treatment rooms have to be properly shielded in construction (see next section). The shielding design should follow the rec- ommendations of international/national organizations that are recognized for providing scientific basis for radiation protection and safety. A radiation exposure survey needs to be performed by qualified physicists after the construction is completed, to en- sure that the radiation exposure levels do not exceed the limits laid down by government agencies. Safety interlocks, such as a door interlock, power interlock and backup system, and procedure interruption systems, should be installed. The procedure interruption systems should be placed where they can be easily reached by the medical staff members during a treatment. Almost all commercially available HDR systems (see e.g. Fig. 3.1, with the cover removed) are equipped with interruption systems and these should be periodically checked and evaluated. Radiation monitoring systems, which are independent of the HDR unit, should be installed inside an HDR treatment room and at the door of the room to monitor the ra- diation levels. It is preferable that monitoring systems inside the room are muted, giving out clearly visible signals (e.g., a flash- ing light) when the radiation exposure exceeds a certain level. On the other hand, it is preferable that the monitoring systems installed at the door should give out both visible and audible sig- nals to ensure awareness in case of potential loss of a radioactive source from the HDR unit. A warning sign should be installed at the room entrance to show clearly that a HDR procedure is in progress. This type of system can be placed right above or beside the room door and should be automatically turned on when a HDR treatment starts. It is important to include a video monitoring system and an in- tercom audio system in the design of a HDR treatment room

lead bricks, leaded glass, and other accessories. It is desirable to install a radiation area monitor in the hot lab to constantly mon- itor the radiation level. Radiation survey meters with different levels of sensitivity should be included in the facility design and budget. These sur- vey meters are important to ensure the integrity and accuracy of radiation safety and documentation. Depending on the type of brachytherapy procedure, consideration should be given to sur- vey meters that can also be used for particles other than photons. Emergency radiation safety kits, such as a lead container, should be also available for a brachytherapy program (12). Aspects of brachytherapy facility design are reviewed in the lit- erature (5, 9,11,12,26,36). Some important features are given be- low for LDR and HDR treatment rooms. In general all aspects of radiation safety with HDR equipment are equally valid for use of PDR equipment and here when HDR is used in this text one may substitute HDR/PDR. 3.1 LDR brachytherapy treatment room LDR brachytherapy procedures can be performed in one of two ways: 1) placement of applicators first in an operating room, then loading radioactive sources into the applicators after the com- pletion of dosimetry calculations and treatment planning; 2) loading the radioactive sources directly into or around the target volumes with or without applicators in the operating room. Most temporary brachytherapy procedures follow the first of these to minimize unnecessary radiation exposures to the members of medical staff. On the other hand, many permanent brachyther- apy procedures, such as prostate implants, are performed by di- rectly implanting radioactive sources into the target volume in the operating room. As discussed previously, for temporary LDR brachytherapy procedures, the radioactive sources are most likely to be loaded into the afterloaders in a patient treatment room. The treatment room should be suited for patient procedures that will usually last for hours to days. This treatment room does not have to be dedicated to brachytherapy procedures alone. It can be used as a regular in-patient room when there are no brachytherapy procedures. However, the room should be carefully selected in terms of its location to minimize radiation exposures to other patients, the general public, and medical staff, especially for the brachytherapy procedures that involve high energy photon emit- ting sources (the most commonly applied source types in LDR, 137 Cs and 192 Ir, are high energy photon emitting sources!). It is ideal to select a room that is located in a corner or a room that is remote from populated areas. In many cases, the brachyther- apy treatment room will need thicker walls than a normal room to reduce the radiation levels in the surrounding areas or other patient rooms. In some cases, solutions can be found by using mobile (lead) shields which are positioned close to the bed of the patient, depending on the lay-out of the room and its surround- ings. These mobile shields can be stored in a near-by room when not needed, but they can be very heavy due to the lead thickness required for high energy photon emitting sources. An intercom audio system, and sometimes a video monitoring system, is useful to avoid unnecessary time spent near the im- planted patient, hence reducing staff exposure.

Fig. 3.1 The tungsten container for the safe position of the high dose rate iridium-192 source in a high dose rate afterloader is clearly visible when the covers are removed. (Courtesy: Elekta AB, Sweden)

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so that during HDR treatments, patient and treatment proce- dure can be constantly monitored and a verbal communication channel is always available between the patient and medical staff members. Other requirements are the direct availability of emergency equipment such as a cutting device, long forceps and a storage container in case of a source obstruction during treatment. Writ- ten emergency procedures must be available on site. Emergency response practice should be conducted periodically to ensure emergency preparedness of the staff members. It is quite common for a conventional external beam treatment room to be used as a HDR room, especially for clinics where HDR procedures are relatively rare and/or budget/space is limit- ed. If a conventional external beam treatment room is used as a HDR treatment room, the room shielding is normally adequate although a careful radiation survey is highly recommended and the room may need to be modified to be equipped with all the above-mentioned safety and interlock features. When time and distance are not adequate to ensure acceptable levels of protection, recourse to the third option for radiation protection in practice, shielding, has to be made. This can be simply described as the process where one needs to calculate the thickness of a particular material that must be interposed in a radiation field, to achieve a reduction of the expected exposure to a shielding design goal exposure at a point of interest (POI). The shielding design goal exposure at a POI cannot be greater than the regulatory dose limits for occupational and public ex- posure expressed in mSv per year (see Table 3.1). As an example, UK recommendations for controlled and public areas are 6 mSv and 0.3 mSv, respectively (11). Other countries may have defined different shielding design goals (33, 34). With the assumption of a 50 week working year and a brachytherapy facility workload that is evenly distributed in time, weekly derivative shielding de- sign goals are traditionally used (i.e. 0.12 mSv/week and 6 μSv/ week in controlled and public areas, respectively, in the UK). Given the source strength and the treatment duration, the air kerma can used for the calculation of the shielding requirements at the POI. The expected exposure at a reference point, common- ly referred to as the facility workload, needs to be determined in units of air kerma per week of operation. In order to estimate the workload, one needs the reference air kerma rate ( RAKR ) of the source(s) in units of Gym 2 h -1 , as well as an estimate of the number of patients treated per week and the average treatment time, so that the product will yield the workload in units of Gy per week at 1 m from the source(s). The estimate of the num- ber of patients should be based on reliable data (such as average national figures available) and as a minimum meet the viability standards set by the hospital management or national regula- tions. For example, the NHS in UK suggests that a brachytherapy centre patient throughput should, at minimum, be 50 patients per year overall, further elaborated to at least 10 intrauterine insertions, 10 of each of low throughput treatment sites (head and neck interstitial, bronchial and oesophageal intraluminal, 4. BRACHYTHERAPY FACILITY SHIELDING

breast and rectal interstitial and cervical applicator insertions), or 25 permanent prostate interstitial implants, as applicable (31). High-volume departments should use their own, higher, esti- mates. Treatment time is of course site and technique specific. It should be noted that the workload estimate should also include periodic quality control procedures and measurements. The workload should be appropriately weighted for the distance from the source to the POI using the inverse square law. This distance should be the shortest one (if applicable) and the POI is usually taken at 30 cm behind any physical barrier/wall. Since we are not seeking to protect the area but the most exposed indi- vidual occupying it, the workload must also be weighted by the appropriate occupancy factor which corresponds to the average fraction of working time during which the POI is occupied by the single person who spends the most time there. The occu- pancy factor is usually determined by facility employees and as- sumes a value of 1 for controlled areas (for a list of indicative oc- cupancy factors for shielding calculations refer to (11) or (35)). In summary, the reduction factor, R , by which the expected ex- posure at a POI must be reduced to comply with a shielding de- sign goal exposure, is given by: where: • P is the shielding design goal in units of effective or equivalent dose per week (Sv per week) for the POI, • W is the facility workload in units of air kerma per week at 1 m from the source(s) (Gym 2 per week where air kerma can be conservatively assumed equal to effective or equivalent dose, i.e. Gy≈Sv), • F is the occupancy factor at the POI (usually denoted by the capital letter T , not used here to avoid confusion with the trans- mission factor, T = R -1 , defined in the following), • d is the distance from the source(s) to the POI (m), The weekly workload is obtained from the multiplication of the source air kerma strength RAKR (in Gym 2 h -1 ), the number of sources or source positions used in procedures and the dwell time t (in h) summed over all used sources or dwell positions, and the estimate of the number of treatments per week. For exceedingly low workloads the assumption made above of a workload evenly distributed in time does not apply. Shielding calculations using Eq. 3.1 might therefore prove inadequate due to high instantaneous dose rates. For example, due to the time necessary for catheter placement and the limited availability of operating rooms, brachytherapy treatment rooms are not used as frequently as those for external beam treatments, and while the average workload might be low, the dose rate will be zero most of the time and high during treatment sessions. In order to accomodate such scenarios, additional regulatory shielding de- sign goals may also have been set for the instantaneous dose rate ( IDR ), the dose per hour over a given time interval. Having calculated the reduction factor, R , or equivalently the transmission factor, T = R -1 , defined as the ratio of air kerma rate at a POI with and without the interposition of a shielding barrier, this transmission must be translated into a shielding thickness for a given material. Care must be taken to use the transmission R = Pd 2 WF (3.1)

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Fig. 3.3 169 Yb radiation transmission factor T for a lead shielding barrier in broad beam geom- etry conditions. Note the change of slope in the transmission curve at small thickness due to the combined effect of increased attenuation of the lower photon energy emissions by 169 Yb and build up. The transmission curve for monoenergetic photons of energy close to the maximum energy emitted by 169 Yb is also presented for comparison. (Courtesy: P. Papagiannis)

Fig. 3.2 60 Co radiation transmission factor T for a lead shielding barrier in narrow and broad beam geometry conditions. (Courtesy: P. Papagiannis)

data from the literature for the correct (realistic) broad beam geometry. As shown in Fig. 3.2, the use of narrow beam con- ditions employing material attenuation coefficients (i.e. solving the equation: T(x) =I(x)/I0 =exp (-μx) for x in which I stands for the intensity of the radiation beam) is unacceptable due to the build-up factor. In order to augment outdated experimental transmission data for selected brachytherapy radionuclide/material combinations in broad beam conditions, the numerical method of Monte Carlo simulation has been employed in a series of publications (6, 27, 37). This approach however produces discrete values of trans- mission versus material thickness in tabular form or graphs, thus necessitating interpolations. Often recourse is made to the use of transmission curve indices such as the half and tenth value layer ( HVL and TVL , respectively) for particular radionuclide-mate- rial combinations (11, 36). These indices however do not remain constant due to spectral variation with increasing shielding bar- rier thickness (27, 37). An example is shown in Fig. 3.3. It has been suggested (11) that the first HVL or TVL at small R (or large T ) and HVL e or TVL e at large R (or small T ), should be used for the calculation of material shielding thickness to achieve a given R or T value. HVL e and TVL e , called “hard” or equilibrium values, correspond to that penetrating region where the radiation directional and spectral distributions are practical- ly independent of thickness so that a single value of the HVL or TVL is valid. This suggestion however has been shown to intro- duce potentially significant errors (37). It is therefore both con- venient and accurate to fit an ad hoc analytical representation to transmission data for use in practical dose calculations and shield designs. Within the framework of a BRAPHYQS activity, (BRAPHYQS, a physicists’ working group within GEC-ESTRO) Monte Carlo simulation was used to generate photon radiation broad beam transmission data for various radionuclide-materi- al combinations ( 60 Co, 137 Cs, 198 Au, 192 Ir, 169 Yb, 170 Tm, 131 Cs, 125 I,

and 103 Pd photons through concrete, stainless steel, lead, as well as lead glass and baryte concrete). Besides the tabulation of first and equilibrium HVL/TVL values, a three-parameter analytical expression was fitted to results to facilitate accurate and simple radiation shielding calculations (37). The Monte Carlo calcu- lated data sets, as well as fitting coefficient results, are available online at http://www.estro.org/about/governance-organisation/ committees-activities/radiation-protection. Indicative data are presented in Fig. 3.4. This figure also provides a hint on the se- lection of shielding material. A high-Z/high-density material such as lead would require a smaller shielding thickness which could be favorable if space is limited. Depending on the facility workload and layout however, support issues might ensue that could be dealt with by using a combination of materials (i.e. con- crete and lead or stainless steel sheets) or a maze to reduce door shielding. Cost, time to completion, and other technical aspects are also pertinent; the solution to the shielding problem is nei- ther unique nor generally applicable. Two more publications prepared within the framework of BRA- PHYQS activities present data useful for the structural shielding of brachytherapy facilities. Zourari et al. (42) present a method for calculating the transmission of any broad photon beam with a known energy spectrum in the range of 20–1090 keV, through concrete and lead, based on the superposition of corresponding monoenergetic data obtained from Monte Carlo simulation. This method is complemented with a simple program, incorporating a graphical user interface, to facilitate the superposition of monoen- ergetic data, the graphical and tabular display of broad photon beam transmission curves, and the calculation of material thick- ness required for a given transmission from these curves. Pujades et al. (39) present the adaptation of the NCRP 151 meth- odology (35) for estimating the air-kerma rate at the door in BT facilities using Monte Carlo simulation in actual brachytherapy

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facility designs with a maze. This study also includes illustrative Monte Carlo results of air-kerma rate distributions in the five facilities studied, for both 192 Ir and 60 Co sources. See Fig. 3.5. The responsibility for shielding design goes beyond the calcu- lation of required thickness of a given material and includes the supervision of construction (i.e. the materialization of the shielding as planned needs to be verified in general, and particu- larly: ducts for cable, plumbing and ventilation, concrete com-

position and density that varies with local aggregate, etc) and post-construction survey. More information can be found in (5, 11,26,36).

5. RADIATION PROTECTION ISSUES ASSOCIATEDWITH SPECIFIC TECHNIQUES

Although both LDR and HDR brachytherapy procedures are treatments of patients with radioactive sources, LDR procedures differ from HDR (and PDR, with sources usually 1/10 of the strength of an HDR source) procedures in several aspects: 1) Dose rates at prescription points are significantly different. These dose rates in LDR brachytherapy procedures range from 4 cGy/hr to 200 cGy/hr while the dose rates in HDR procedures are higher than 1200 cGy/hr. 2) LDR brachytherapy can be permanent or temporary while HDR treatments are always temporary. 3) Temporary LDR brachtherapy may require continuous treat- ment for hours or days while HDR treatments usually take several minutes and will only rarely last more than 1 hour (PDR treatments usually mimic the overall treatment time of LDR, with multiple pulses). 4) Patients treated with LDR brachytherapy may be released with implanted radioactive sources while HDR patients should never be released with the radioactive source(s). These differences should be taken into account in radiation pro- tection and should be addressed specifically. 5.1 LDR brachytherapy In many LDR brachtherapy treatments, radioactive sources need to be ordered specifically for the treatments in terms of source strength and source quantity. Wipe test should be first performed after source delivery to check the source integrity. The sources should also be carefully assayed independently from manufacturers before the start of treatment to ensure the accu- racy of source strength and quantity. For radioactive sources of long half-life in storage (e.g., 137 Cs, possibly used only for con- stancy checks of measurement equipment) a periodical wipe test and assay should be conducted. Patients should be surveyed before LDR treatment to establish a radiation baseline. During the treatment procedures, the sourc- es –if not in an afterloader- need to be visually checked so that they are all accounted for. After a procedure, radiation surveys should be performed in the treatment rooms to prevent source loss. The survey should cover the entire room, while trash bins, equipment, and outfits of medical staff members should not be removed from the room without a check with the survey moni- tor. Since the source strength or the energy levels of emitted par- ticles from the sources can be relatively low, a highly sensitive radiation detector may be needed for this purpose. A radiation survey should also be conducted to evaluate whether it is safe to release the patient. If the patient is to stay in a room, such as a treatment room, recovery room or designated inpatient room, for a period of time, a radiation survey should be performed af- ter the patient moves into the room and radiation signs and safe- ty instructions for visitors, patient and medical staff should be posted on the room door. During the patient’s stay, it should be clearly documented in the patient chart that the patient is under-

a.

b.

Fig. 3.4 Radiation transmission factor T for a lead (a) and a concrete (b) shielding barrier in broad beam geometry conditions for selected radionuclides employed in brachytherapy. Presented lines correspond to a fit of the three parameter model introduced by Archer et al . (1) to the Monte Carlo simulation calculated data. Data and fitting results are available online at http://www.estro.org/about/governance-organisation/committees-activities/radiation-protec- tion for various radionuclide-shielding material combinations. (Courtesy: P. Papagiannis)

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Fig. 3.5 Air-kerma rate distribution on the plane parallel to the floor and containing the source for five different facility designs for 192 Ir (left column) and 60 Co (right column) of a given strength. See the original article for more details. (Courtesy: M.C. Pujades)

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6. SOURCE STORAGE AND TRANSPORTATION

going brachytherapy treatment and labels with radiation signs should be attached to the patient. Radiation emergency equip- ment should be placed in the room in case of unexpected events. After the completion of treatment, additional radiation surveys should be conducted for patient, equipment, and room. Related radiation signs should be then removed from the room and pa- tient. For temporary implants, the removed sources should be counted, logged, and returned to storage in the hot lab. For per- manent implants, patients should be surveyed before release to ensure the implanted radioactive sources do not pose potential radiation risks to the general public. The criteria for the patient release are that -based on the patient radiation survey- the expo- sure to the public from the implanted radioactive source should not exceed the corresponding annual limit. Radiation safety instructions should be provided to the patients, including spe- cial instructions to protect pregnant women and children from being exposed to excessive radiation levels. The patients should be advised to minimize contacts with pregnant women and chil- dren. The patients should also be provided contact information so that radiation related questions can be answered after their discharge from hospital. These may concern, for example, fur- ther post-implantation surgery (TURP), autopsy or cremation. More information can be found in ICRP and NCRP documents (23, 36). Some practical data on radiation exposures to family and household members after prostate brachytherapy can be found in Michalski et al . (28) who used radiation monitors to measure dose values with mean lifetime doses to a spouse from her husband of 0.1 mSv for 29 125 I patients and 0.02 mSv for 15 103 Pd patients. Cattani et al . (2) recorded a mean dose rate after implants of 6.4 µSv/h at 0.5m distance for 200 125 I cases and 1.7 µSv/h for 16 103 Pd cases. From such data it can be estimated that the realistic lifetime exposures are well below the limits. 5.2 HDR brachytherapy The HDR, and similarly the PDR, source is periodically replaced. The frequency of replacement is based on the source half-life. For an HDR 192 Ir source type with a half-life of 74 days the inter- val between source changes is usually 3 or 4 months. Wipe tests should be performed for both new and old sources during the re- placement. Source strength should be independently measured during the source replacement and periodically thereafter. Since most HDR procedures are delivered with computerized systems, accuracy of source strength decay should be manually checked and confirmed before each treatment. Emergency procedure instructions should be posted in the con- trol area. Radiation monitors and safety interlocks and interrup- tion buttons should be checked before each treatment. Patients should be surveyed prior to treatment to establish a radiation baseline. Radiation emergency safety equipment should be read- ily available before the start of treatment and throughout the treatment procedure. The patient and the treatment procedure should be closely and continuously monitored via video mon- itors and audio communication devices. After the treatment is completed, patient and equipment should be surveyed to ensure that the HDR radioactive source has returned to the HDR unit safe. More information can be found in IAEA publications (9, 12).

Sources are delivered to the brachytherapy department in spe- cially designed containers that are clearly marked (isotope, activ- ity, transport index) and accompanied by appropriate shipping documents, all subject to international regulations for their safe transport (13). Beginning with the acceptance of the sources by authorized personnel, specific measures must be taken to ensure both optimal radiation protection and source security. For ra- diation protection, these measures consist of facility design el- ements, the configuration of specific procedures, and the use of appropriate instrumentation, all based on the three basic rules for radiation protection in practice (exposure time reduction, in- crease of distance from a source, use of shielding). Source securi- ty is ensured by exercising continuous accountability and control of the sources through appropriate procedures for the safe ex- change and movement of radioactive sources within the institu- tion and controls to prevent theft, loss, unauthorized withdrawal or damage of sources, or entrance of unauthorized personnel to controlled areas (38). Source exchange should be performed by well trained staff only, often by the service engineer of the com- pany and a radiation safety officer of the hospital. Written proce- dures should be available. HDR brachytherapy procedures using remote afterloaders do not require source preparation. The source is safely stored in the afterloader when not used for treatment since most afterloaders are certified as transportable radioactive containers (9). In terms of source security, the afterloader is usually kept in the treatment room which is a controlled area and consequently access is re- stricted. See also the last paragraph of section 7. A cutting device, a set of long forceps or tongs, and an emergen- cy source container (sufficiently large to accept the entire appli- cator assembly containing the source) must be available in the treatment room in case of source retraction failure during use. A dedicated storage room might still be required if unused sources are temporarily kept in the department to decay to safe levels. This room is also a controlled area subject to all requirements for appropriate labeling, access restriction, radiological surveil- lance and the establishment of written procedures and working instructions (24, 38). A dedicated source preparation and storage room (commonly called a “hot” lab) is an essential prerequisite for LDR and man- ual brachytherapy. The hot lab must include: an area where all LDR sealed sources can be safely stored in an orderly fashion, space and facilities for receiving and returning sources, source inventory, source calibration and quality control, space and equipment for source preparation for treatments, adequate space for QA and treatment aids and, if necessary, for storage of short- lived sources or temporary storage of unused long-lived sources (36). A work area should also be available, in or near the hot lab, where records can be prepared and stored without danger of radioactive contamination (36). Following their acceptance, sources and source containers should be marked using a unique identification scheme, entered in the department’s source register (listing the id, location, activity of all sources, as well as dates and results of checks and periodic inven- tories) and put in a storage safe (38). Different safes are used for different source types. These must be fire resistant, equipped with a lock and shielded. Regulations will generally require a maxi-

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results documented (38). For HDR and PDR units, these wipe tests are obviously performed on the afterloading drive assembly and not the high activity sources. The hot lab is of course a controlled area (24, 38). It should be locked at all times and a latch to automatically lock the door is recommended (36). An area radiation monitor should be visi- ble on entering the room, and while manipulating the sources radiation protection measures and their effectiveness should be periodically reevaluated and periodic area surveys should be performed around the room (12, 38). The hot lab, and treat- ment, treatment planning, operating and patient rooms must be located as close as possible to each other to reduce distances over which patients and sources have to be transported, particularly avoiding the use of elevators (12). Source transport should be made using a mobile, shielded con- tainer which reduces exposure to less than 2 mSvh -1 in contact and 1 mSvh -1 at 1 m (41) or as required by national regulations. The transport container should be clearly marked for its radio- active content, never left unattended, and surveyed both before and after brachytherapy procedures. The movement of sourc- es should be entered in a source movement log with a signed record of the date of removal from the safe, patient name and the return of the source (38). Besides access restriction, source registry and periodic inventories, additional measures for source control might be in order according to the specific applications. For example, HDR brachytherapy patients should be surveyed to ensure source return to its safe, all linen, dressing, clothing, equipment and refuse collectors should not be removed from the brachytherapy patient room until they are checked for stray sources and results are documented, and a filter should be used wherever there is a risk of loss of a source through a drain (i.e applicator cleaning, LDR seed dislodging from the prostate). Old sources (‘orphan’ sources), such as unused 125 I seeds or de- cayed 192 Ir wires, can be stored in the storage room before dispos- al according to national and international regulations. Among other aspects of setting up a brachytherapy program, a radiation protection program must be established to ensure compliance with regulations for radiation safety and protection produced by government agencies (9, 12). The radiation pro- tection program should be designed and developed to ensure the doses to medical staff and the general public are as low as is reasonably achievable (see Introduction). A qualified radia- tion safety officer, who is responsible for implementing the ra- diation protection program, should be identified and officially appointed. The radiation safety officer should be given sufficient administrative authority, in writing, to supervise the program. A radiation safety committee should also be established if the institution plans to start a brachytherapy program that involves multiple types of procedures and multiple types of radioactive sources. The committee should include an authorized user of each type of use permitted by the license, the radiation safety officer, a representative of the nursing service, and a representa- tive of management. The committee may include other members whom the licensee considers appropriate. 7. ORGANIZATIONAL ISSUES

Fig. 3.6 Example of the shielding on a preparation table in the storage room of a brachytherapy department. (Courtesy: J. Venselaar)

mum exposure rate of less than 1 μSvh -1 at 10 cm distance from the container surface and most commercially available equip- ment ensures a surface dose rate of about 25 μSvh -1 (41). Their functionality and their place in the room should ensure that oc- cupational doses are maintained as low as reasonably achievable. For example, a safe for a particular source type should be close to the area reserved for the manipulation of the sources for prepa- ration or quality control purposes, and a diagram on the source safe showing the exact location of each source within it helps to reduce the time to locate and identify a source (38). Source manipulation, for any purpose, should be made using forceps or tongs and never directly by hand (38). The use of lead gloves or other protective garments serves little to reduce expo- sure from high energy sources and might unnecessarily prolong the manipulation time (41). However, personnel shielding such as a lead “L-block” or a structure made from interlocking lead blocks must be provided, including a leaded window of sufficient thickness (36) or at least a mirror system. See the example in Fig. 3.6. A magnifying viewer might be required in the shielded preparation area since sources for manual brachytherapy must be inspected visually for damage after each use, especially if they are subject to possible damage from heat, abrasion, chemical attack and mechanical stress for cleaning and sterilization pur- poses (38). In general, sources should never be left on prepara- tion surfaces and the work surface should be easily cleaned and brightly lit to facilitate finding dropped sources (12, 38). Espe- cially for 192 Ir wires, equipment for cutting and handling should be properly decontaminated and any radioactive waste collected and stored (12, 38). Wipe tests for source leakage and prepara- tion area contamination need to be periodically performed and