ESTRO 2024 - Abstract Book

S1571

Clinical - Lower GI

ESTRO 2024

Preoperative short-course radiation therapy: data from clinical practice for protons and photons

Nikita Kataev 1 , Nikolay Vorobyov 1 , Alexei Mikhaylov 1 , Natalia Berezina 2

1 MIBS, Radiation Oncology, Saint Petersburg, Russian Federation. 2 MIBS, administrative, Saint Petersburg, Russian Federation

Purpose/Objective:

Total neoadjuvant treatment (TNT) is an established treatment modality in locally advanced rectal cancer. A short course of high-dose radiation is an important part of the whole course.Traditionally, such a course has been performed using 3D conformal radiation therapy. High conformal techniques may minimize acute toxicity, which in turn likely impacts favorably on the tolerability to subsequent chemotherapy. The aim of this study is a dosimetric comparison between two high-conformal tehniques of RT: with photons (VMAT) and protons (IMPT) in real world settings

Material/Methods:

Between september 2021 and september 2021 total 62 patients with rectal cancer recived shourt course radiation therapy as part of TNT for locally advanced rectal cancer. 25 of them were proton and 37 photon. All of them were treated according RAPIDO arm B study protocol. We compared patient's plans according to our constraints, loads on organs at risk, and volume of low bath doses.

Our analyses included: Volume, Dmax, Dmin and Dmean. Absolute bowel bag volume receiving 19,5 Gy and bladder wall receiving 18,3 Gy were assessed.

Results:

Dose-volume histogram analysis revealed that radiation therapy with protons significantly reduced radiation dose to organs compared with photons at risk such as bladder wall (V18,3 Gy 25.3 cc in protons compared with 44,2 cc in photons p<0,05) , bowel bag (V19,5 Gy 117cc in protons compared with 230 cc in photons p<0,05) Proton plans had least low-dose bath in abdomen (Dose of 5,0 and 10,0 Gy for abdominopelvical caviry).

Morover it was easier to achieve our goals of radiation volume coverage when using proton beam therapy (D100%/V100%) without excessive strain on healthy organs.

Conclusion:

Preoperative proton beam radiotherapy can significantly reduce the dose to normal tissue compared to photon radiotherapy, even though a highly conformal irradiation technique is used. The dosimetric advantages may lead to tangible clinical benefit in these patients. We also plan to analyse acute toxicity in this group of patients

Keywords: Rectal, proton, TNT