Endorectal contact radiation boosting: Making the case for dose AND volume reporting

Evert J Van Limbergen, Colien Hazelaar, Femke Vaassen, Murillo Bellezzo, An-Sofie Verrijssen, Yves Willems, Alexandra J Stewart, Ben Vanneste, Jeroen Buijsen, Gabriel Paiva Fonseca, Jeroen Leijtens, Ane L Appelt, Frank Verhaegen, Maaike Berbee*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

INTRODUCTION: The various rectal endoluminal radiation techniques all have steep, but different, dose gradients. In rectal contact brachytherapy (CXB) doses are typically prescribed and reported to the applicator surface and not to the gross tumor volume (GTV), clinical target volume (CTV) or organs at risk (OAR), which is crucial to understand tumor response and toxicity rates. To quantify the above-described problem, we performed a dose modeling study using a fixed prescription dose at the surface of the applicator and varied tumor response scenarios.

METHODS: Endorectal ultrasound-based 3D-volume-models of rectal tumors and the rectal wall were used to simulate the delivered dose to GTV, CTV and the rectal wall layers, assuming treatment with Maastro HDR contact applicator for rectal cancer with a fixed prescription dose to the applicator surface (equivalent to 3 × 30 Gy CXB) and various response scenarios.

RESULTS: An identical prescribed dose to the surface of the applicator resulted in a broad range of doses delivered to the GTV, CTV and the uninvolved intestinal wall. For example, the equieffective dose in 2 Gy per fraction (EQD2) D90% of the GTV varied between 63 and 231 Gy, whereas the EQD2 D2cc of the rectal wall varied between 97 and 165 Gy.

CONCLUSION: Doses prescribed at the surface are not representative of the dose received by the tumor and the bowel wall. This stresses the relevance of dose reporting and prescription to GTV and CTV volumes and OAR in order to gain insight between delivered dose, local control and toxicity and to optimize treatment protocols.

Original languageEnglish
Pages (from-to)887-895
Number of pages9
JournalBrachytherapy
Volume21
Issue number6
Early online date18 Sept 2022
DOIs
Publication statusPublished - 2022

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