Abstract Book

S67

ESTRO 37

results were compared with the clinic’s internal RTT requirement profile and the ESTRO RTT benchmarking.

postgraduate professional education in treatment specific knowledge domains.

Results Except for

target delineation (physicians), plan

Poster Viewing : Poster viewing 3: Dosimetry

optimization and approval of the plan (medical physicists and physicians), activities of the RTTs were detected in every step of the workflow. In case of Documentation the main tasks are the recordings during the insertion of the BT-implant and treatment-delivery. Beside the documentation of the used applicator, the records contain a clinical/technical drawing of the positions and insertion depths of the needles to simplify the reconstruction of the implant. The preparation of these drawings requires advanced knowledge about anatomical structures and different versions and sizes of the predominantly used VIENNA applicators and needles. Radiographs in ap and lateral direction are produced to identify the needles in the patient body and give a better overview for the implant reconstruction and verify the catheter labelling. The 3D-Imaging for treatment planning realized using MRI appeared as a complex matter from the RTTs’ point of view. In our department the MR scanner is directly located in the BT clinical area. In addition to the basic understanding of the image modality, a close cooperation between BT RTT and MR operators is required to adjust the MRI acquisition to achieve optimal image quality. Also a fundamental knowledge about the applicator structure and application technique is required by all RTTs involved in the imaging process. In case of Treatment-planning the basic tasks contain the case administration and import of the required image data. As it is nowadays our standard to treat patients with combined intracavitary and interstitial implants, RTTs are trained to routinely performing the MR-only based applicator reconstruction, aided by specialised physicists in case of more complex implants . In addition RTTs prepare all basic treatment plan parameters and create a standard dose plan, which is later optimized by the physicists and radiation oncologists. The delineation process of the OARs on MR images is currently done by physicians. RTTs are currently trained to support this task in the future. The right Treatment-delivery is the RTT’s field of responsibility. The basic tasks include the loading of the patient specific treatment plan, the correct connection between patient and the after-loader and the handling of the device. The advanced role of the RTT provides that in addition to the patient data also the plausibility of treatment parameters like source strength, treatment time and total reference air kerma are checked. This induces an advanced knowledge and sense for dose parameters. The RTT serves as last validation instance of the correct preparation of the patient, like bladder filling and state of urinary catheter. In several cases the preparations were also performed by RTTs. Finally the last optical control and preparation of the in-vivo- measurement of OAR (bladder and rectum) are in RTT’s responsibility. Prior to delivery of the 2 nd fraction, a new MRI is acquired and registered with planning MRI from day one based on the intracavitary applicator position by the RTT. Based on the registration the interdisciplinary team assesses implant stability, variation of the anatomy relative to the implant and decides if treatment adaptation is necessary. Documentation, Imaging, Treatment-planning and Treatment-delivery require knowledge of anatomy, medical physics and BT-specific medical engineering, beyond basic RT skills. Clinics which perform complex treatment forms shall schedule extra time for training and offer Conclusion RTTs specific roles in

PV-0136 Comparison of secondary cancer risks of whole and various partial breast irradiation techniques N. Hoekstra 1 , E. Fleury 1 , P. Van der Baan 1 , A. Bahnerth 1 , M. Hoogeman 1 , J.P. Pignol 1 1 Erasmus Medical Center Rotterdam Daniel den Hoed Cancer Center, Radiotherapy, Rotterdam, The Netherlands Purpose or Objective With the increased detection of breast cancer at an early stage, the overall survival has steeply increased, so preventing radiation-induced secondary cancers is becoming an important issue. There is concern that total body radiation exposure from new radiotherapy techniques might result in increased secondary cancer risks. These new techniques include accelerated partial breast irradiation (APBI), delivered as VMAT, stereotactic radiotherapy or HDR brachytherapy. The aim of this study is to compare the risk of secondary cancer of whole breast irradiation (WBI) and various APBI techniques. Material and Methods We conducted a phantom study using a Rando-Alderson anthropomorphic phantom that was modified to hold realistic tissue-equivalent breasts. Treatment plans were generated for 3D-conformal WBI (42.56 Gy in 16 fractions), 3D-conformal APBI (38.5 Gy in 10 fractions), VMAT APBI (38.5 Gy in 10 fractions), multicatheter HDR brachytherapy (34 Gy in 10 fractions), balloon-based HDR brachytherapy (34 Gy in 10 fractions) and Cyberknife stereotactic APBI with the Iris collimator or the MLC (both 38.5 Gy in 10 fractions). We measured organ dose with Li-powder TLDs and Gafchromic EBT3 films. All experiments were repeated three times. We calculated the lifetime attributable risk (LAR) for secondary cancer in the lungs, contralateral breast, esophagus, thyroid, colon, ovaries and uterus with the online RadRAT calculation tool (available at https://radiationcalculators.cancer.gov/radrat), which is based on the BEIR VII formalism. We also calculated the relative risk (RR) as compared to a non-exposed population of the same age. Results The mean organ doses for the various techniques are shown in table 1. There was good agreement between the measurements demonstrated by the small standard deviations. Figure 1 shows the LARs for exposure at the age of 50 years, which is the standard threshold age for APBI. WBI resulted in the highest total LAR with 6070 cases per 100,000 exposed persons. This translated into a RR of 1.22 compared to non-exposed persons of the same age. The multicatheter brachytherapy technique had the lowest total secondary cancer risk with 1880 cases and a RR of 1.07. LARs for the other APBI techniques were: 3D- conformal APBI 3330 cases, VMAT APBI 5390 cases, balloon-HDR 2970 cases, Cyberknife-Iris 4200 cases and Cyberknife-MLC 4160 cases. The relative risks ranged from 1.11 to 1.20. Lung tumors accounted for 84 – 94% of the secondary cancers.