MSOR02 Presentation Time: 8:05 AM

Abstract

Purpose

Earlier it was demonstrated that lack of standardization in dose reporting is hampering progress in the field of rectal brachytherapy (Verrijssen et al 2019). Standardization of dose reporting and thus treatment data would allow for better comparison of results between patient cohorts of different studies and also allow for NTCP or TCP modelling. A prerequisite for standardized dose reporting is standardization of target volume and organ at risk (OAR) delineation. As there is currently a lack of guidelines for target volume definition and organ at risk delineation in image-guided rectal HDR brachytherapy, this project is aimed at solving this issue. The collaboration involves members of GEC ESTRO and the ABS.

Materials and Methods

The target volume consensus process consists of several steps: Step 1: Selection of an expert group and evaluation group (including radiation oncologists and physicists from Europe/Canada/India). Step 2: Survey regarding target volume delineation in each institution. Step 3: Delineation of 3 rectal cancer (RC) cases with different clinical stages using the FALCON platform. Step 4: First expert group meeting to create a draft guideline. Step 5: Redelineation by the expert group using the draft guideline. Step 6: Second expert group meeting to evaluate the redelineations and optimize the draft guideline. Step 7: Redelineation by the evaluation group and finalization of the guideline.

Results

The current project involves radiation oncologists and physicists from 10 countries in Europe/Canada/India and has currently finalized step 2. Ten out of 17 respondents indicated that they don't have their own delineation guidelines. There is clear variation in the CTV definitions used, for example some use margins and some prescribe to the GTV. Eleven respondents don't use PTV margins. There is no consensus on which OAR need to be delineated and how.

Conclusions

Our survey has shown that target volume delineation and OAR definition varies widely between institutions. Here we describe the methodology to come to international standardization in dose reporting for rectal brachytherapy. The next step is to evaluate the consensus and differences in target and OAR delineation between the different centers using test cases, prior to contouring guideline development.