Abstract Book

S66

ESTRO 37

SP-0134 Treatment planning in brachytherapy A.L. Soares 1 1 Instituto Português de Oncologia do Porto Francisco Gentil- EPE, Radioterapia Externa, Porto, Portugal Abstract text The IPOPFG-Porto Brachytherapy Service has been a progressive and continuous differentiation since its creation in 1974. Over the last ten years, Brachytherapy has developed gradually from an empirical art to a diversified subject, scientifically based. Naturally, the practices evolved and, with the evolution of technology, new procedures were introduced in the treat ment of different pathologies, with indication to Brachytherapy. Examples of advantages taken from this evolution are the use of advanced planning systems that allow an individualized clinical dosimetry for each patient, and the introduction of computed tomography (CT) images that allow the delineation of both target volumes and organs at risk, three-dimensional calculation of dose, dose distribution and dose-volume histogram evaluation, as well as reporting. However, not all Brachytherapy dosimetry plans are based on CT images, so dose prescriptions refer not to volumes but to geometrically defined points, according to the ICRU38 and ICRU 58 recommendations. Besides, the most calculation algorithms are not used to calculate the radiation interaction with the tissues, and with the applicators which constitute the vector material to the movement of the radiation source. At the moment, the calculation of the dose distribution obtained by the treatment planning system is based on the TG-43 formalism introduced by AAPM10-12 for cylindrical and symmetric sources. However, this formalism only takes into account the dose distribution around the sealed source, considering the surroundings as water. Besides this technological evolution, the role and importance of the Radiotherapist, as well as his/her skills and responsibilities, have become fundamental throughout the course of the patient and in the therapeutic act. At the same time, research projects are developed with the involvement of a multidisciplinary team, aiming to offer a continuous improvement in the health care provided to the cancer patient. SP-0135 The RTT´s advanced role in image guided adaptive brachytherapy for cervix cancer in clinical routine B. Wisgrill 1 , N. Nesvacil 1 , D. Berger 1 , M. Schmid 1 , A. Osztavics 1 1 Universitätsklinik für Strahlentherapie, Brachytherapy, Wien, Austria Image guided adaptive brachytherapy for cervix cancer is a complex and extensive treatment-option which requires the collaboration between physicians, medical physicists and RTTs. The purpose of the presentation is to point out the role of the RTTs in the different steps of the workflow and outline specific knowledge and skills. Material and Methods The workflow chart out of Applicator based-image registration to support image guided adaptive cervix brachytherapy in clinical routine published by J. Bör et al. served as base for the survey of RTTs’ required skills and knowledge. For this purpose the activities of the RTTs were recorded in every step of the workflow for a total of ten treatments. Afterwards the results were allocated into the main fields of duties Documentation, Imaging, Treatment-planning and Treatment-delivery. In addition the collected information was divided into basic and advanced skills and knowledge. In the last step the Abstract text Purpose/Objective

Symposium: Brachytherapy - RTT advanced roles

SP-0133 Modern Imaging for Brachytherapy: MRI, US R. Schokker 2 , E. Kaljouw 1 1 Academic Medical Center,Academic Physics, Amsterdam, The Netherlands 2 UMC Utrecht, Radiotherapy, Utrecht, The Netherlands Abstract text Imaging has become an essential part of brachytherapy treatment. In the recent years the role of MRI and US as imaging modalities has extended a lot. This lecture will highlight the three parts of the brachytherapy treatment where modern imaging plays an important role. To start an interstitial brachytherapy procedure well prepared, it is useful to have imaging in advance. Dependent on target volume, adjacent OAR and brachytherapy technique there are different possibilities for pre-treatment imaging. The use of ultrasound in pre-treatment planning for prostate I125 is a proved method, to correctly measure the prostate volume and check for pubic arch interference. Based on the pre-treatment volume and source activity, the number of sources needed for treatment can be determined. When needles are implanted, the prostate architecture gets disturbed and the zones within the prostate and tumour lesions are less visible on MRI. Therefore an MRI made before the insertion of needles can be used to determine the positions of the needles. In the case of interstitial brachytherapy of a vaginal or anal carcinoma, a pre-operative MRI with cylinder can be made. This scan can be used to design an individual template, with the desired needle configuration in advance. An MRI scan made in one of the final weeks of external beam radiotherapy for cervical cancer, to assess possible tumour regression, can be used to determine subsequent positioning of the applicator and interstitial needles. Applicator positioning is another moment during the brachytherapy procedure where imaging is nowadays used. Instead of checking the position of the applicator when the procedure is finished, real time imaging supports accurate placement in the OR. Abdominal ultrasound can improve the placement of the intrauterine applicator. The ultrasound can be used to visualise the uterus in the OR and guide the positioning of the tandem. Dependent on the position of the needles an abdominal, rectal or vaginal positioning of the ultrasound probe can visualise the target volume and adjacent OAR together with the insertion of the needles. Imaging has always been important for treatment planning, but with modern imaging we are able to have quality control of the dose delivery. With online treatment planning for prostate I125, based on ultrasound imaging, it is possible to adjust the plan to the definite position of the seeds. This makes it possible to further optimise the treatment planning based on possible needle positions (interactive treatment planning) and seed placement (dynamic dose calculation). The use of MRI for treatment planning in intrauterine applicator cases, has improved the treatment planning based on 3D information and volume histogram parameters. With the introduction of MRI imaging dose escalation in the target volume is realised with acceptable dose to the OAR. The visibility of the needles in combination with target volume and OAR on MRI for interstitial cases, makes optimisation of the treatment planning more accurate.