ESTRO 2025 Congress Report I Brachytherapy track

In the treatment of rectal cancer, there is a shift towards organ preservation. Organ preservation could have a significant impact on quality of life and is crucial for individuals who are either unable to undergo surgery or wish to avoid the toxicity associated with surgery, including stoma. An increasing number of trials are being conducted in this area. At this year’s ESTRO congress, Corrie Marijnen (radiation oncologist, the Netherlands)  shared the promising 12-month results of the phase II/III STAR-TREC trial. During the panel discussion entitled “Rectal cancer is the new anal cancer: organ preservation in focus”, Emmanouil Fokas (radiation oncologist, Germany) showed a new German guideline with two separate treatment algorithms: intended organ preservation vs. non intended organ preservation.

Compared with external beam radiotherapy (EBRT), due to the steep dose fall-off around the tumour target, high-dose-rate (HDR) brachytherapy to rectal targets enables more selective dose delivery – and thereby potential dose escalation – to the tumour and better sparing of the surrounding normal tissues. 

For this reason, it may be an appropriate (or even preferable) alternative to EBRT, or a valuable addition to it.

Now, however, a lack of international guidelines is hampering treatment quality and progress in the field of rectal HDR brachytherapy. Standardisation of dose reporting would allow for better comparison of clinical results between patient cohorts and for normal tissue complication probability or tumour control probability modelling.

That is why the gastrointestinal GEC-ESTRO working group initiated the HDR rectal brachytherapy project. The first step was to create a consensus guideline on target volume and organs-at-risk (OAR) definition, as this is a fundamental prerequisite for standardised dose and volume reporting.

The guideline has been developed using a modified Delphi approach. The development process included the selection of international experts (30 members from nine countries), a survey on current practices, delineation of three patient cases, and three consensus meetings to discuss the findings and to draft the guideline.

The survey and first delineation round showed marked variation in treatment preparation as well as in definition and delineation of target volumes and OARs. This further highlighted the importance of having clear guidelines.

Consensus was reached on the prerequisites for adequate delineation. Target volumes were defined: gross tumour volume of the primary tumor at the time of brachytherapy (GTVp_BT), a dose reporting structure (GTVp_BTev05), and any macroscopic lymph nodes at the time of brachytherapy (GTVn_BT). Recommendations on OAR selection and delineation were made.

The delineation guideline will be implemented in clinical practice and used for the development of the dose reporting guideline, which is the second part of the gastrointestinal GEC-ESTRO rectal brachytherapy project. Together, these two guidelines are intended to standardise dose reporting to its full extent. Also, we anticipate a third guideline, which will provide recommendations on patient selection, treatment preparation, dose prescription, treatment planning, and follow-up.

Anne Valkenburg

Department of Radiation Oncology (Maastro)
GROW Research Institute for Oncology and Reproduction
Maastricht University Medical Centre+
Maastricht, The Netherlands 

Anne.valkenburg@maastro.nl