ESTRO 2023 - Abstract Book

S715

Monday 15 May 2023

ESTRO 2023

Long lasting experience with image-guidance in clinical practice of brachytherapy resulted in a new state of the art for this treatment modality. It is based on the clinical needs for an image showing the location of the dose delivery device (source path defined by an implant), target volumes and organs at risk in one image, considered as the relevant “room” of brachytherapy dose delivery. Such imaging data serve as a basis for an online planning concept. Variations and uncertainties exists intra-fractional as well as between fractions in terms of one implant for more HDR fractions or PDR pulses. Also for fractionated treatments several workflows have been presented integrating repetitive imaging for verification and potential replan or plan of the day approaches. The use of MRI in definitive brachytherapy treatment is based on more than 20 decades including the clinical application of MRI only workflows. Also the use of ultrasound (US), with a soft tissue contrast that allows in several disease sites similar target volume definition accuracy as with MRI has its place in brachytherapy. The combination of imaging modalities as MRI, US, CT and new developed cone-beam CT devices is beneficial for some workflows. However, the registration between imaging techniques is fundamentally different to external beam techniques, related to the brachytherapy set-up “room” showing the depicted applicators fixed to the surrounding anatomy. Intensity modulation is an intrinsic characteristic of brachytherapy especially applying the stepping source technology of afterloaders. In combination with manual forward planning based on risk adapted target volumes or inverse planning approaches highly heterogeneous dose distributions can be achieved. Brachytherapy dose painting benefits from high dose gradients for focal treatment as well as risk adapted target dose variation and organ sparing. Modern approaches combine TCP/NTCP findings but also source loading patterns analyzed from clinical trials with intensity modulation. However, daily clinical application often remains cumbersome. Here automated planning workflows could results in clinical relevant benefits, both in terms of accuracy and resources. The use of AI is increasingly applied in brachytherapy, by now within research settings. AI can assist in the before mentioned automation of the treatment planning process, but also in several other areas. While dose prediction, automated contouring, outcome analysis and decision support might be similar as in radiation oncology in general, image registration, applicator reconstruction and the online planning approach is different for brachytherapy. Here AI developments could results in a huge benefit, but would also need joint efforts from centers, researchers and the industry.

SP-0862 Image-guidance, intensity-modulation and AI in EBRT G. Meijer

Abstract not available

Debate: This house believes that there is no role for the plan libraries approach in the era of real-time adaptive radiotherapy

SP-0864 For the motion L. Kildegård Johansen 1 1 Rigshospitalet, Department of Oncology, Copenhagen, Denmark

Abstract Text As a consequence of daily image guidance in the world of radiotherapy, we have expanded our knowledge regarding the everchanging human anatomy. It can be a struggle to handle this knowledge, because while the margins can be reduced, the target and organs at risk should ideally remain static intra- and inter-fractional during the entire treatment course. As we are all human beings, and especially when treating in the pelvic region, this is nearly impossible. Some of the strategies to cope with this could be having a Library of Plans to choose from or using real-time adaptation. The patients spend more time on the couch when they are treated with online adaptive radiotherapy, and they have to get something in return. In the first part of this debate, I will do my best to provide the evidence, based on the advantages found in both literature and experience, that the real-time adaptation strategy is indeed the way going forward.

SP-0865 Against the motion A. Le 1 1 Royal North Shore Hospital, Northern Sydney Cancer Centre , ST LEONARDS, Australia

Abstract Text Against the motion

Plan library approaches for adaptive radiotherapy treatments are easy to set up and allow for an efficient workflow.1 In pelvic radiotherapy sites such as the bladder, majority of patients will only require three treatments plans to be developed. These were large, medium, and small bladder plans and were able to keep V95% prescription dose to over 99% of CTV over 96.3% of the time.2 Plan library approaches for adaptive radiotherapy have been shown to be effective, well-tolerated and feasible with up to 82% of patients retaining disease-free bladders at 3 years after treatment.3 There is no data yet to prove benefits of real time adaption for the additional time they spend on the couch. Real time daily adaption does not consider intrafraction motion.4 Bladder filling can increase in volume up to 150cm3 within a treatment session.4 Lengthier times required on the treatment couch during online adaptive therapy will increase the risk of bladder expanding out of target fields.5 Against the motion: rebuttal Daily real time adaption is expensive and won’t be applicable and accessible to all patients. Generally, oART requires specialist staff such as a Radiation Oncologist (RO), dosimetrist and Radiation Oncology Medical Physicist (ROMP) to be present in addition to the RTT treatment team. Human resources and training are clearly barriers to widespread implementation of oART6