ESTRO 2021 Abstract Book

S1288

ESTRO 2021

Conclusion SuperART protocol shows a limited increase of late rectal toxicity and negligible risk for surrounding organs. As a future step, we will assess through the TCP model published by our group (XXXX et al) the complete response with SuperART treatment, with the potential of individually predict pCR and possibly skipping surgery a priori. The result regarding late rectal toxicity are encouraging in the case of surgery omission. PO-1564 CT on rails versus in-room CBCT for online daily adaptive proton therapy K. Nesteruk 1 , M. Bobić 1,2 , A. Lalonde 1 , H. Lee 1 , G. Sharp 1 , J. Verburg 1 , B. Winey 1 , A. Lomax 3,2 , H. Paganetti 1 1 Massachusetts General Hospital and Harvard Medical School, Department of Radiation Oncology, Boston, USA; 2 ETH Zurich, Department of Physics, Zurich, Switzerland; 3 Paul Scherrer Institute, Center for Proton Therapy, Villigen, Switzerland

Purpose or Objective To compare the efficacy of CT on rails versus in-room CBCT for daily adaptive proton therapy.

Materials and Methods Cone-Beam CT (CBCT) is the primary imaging modality considered for daily adaptation due to its low cost, compactness, and thus wide availability. However, there are proton therapy centers equipped with a CT on rails or considering installation of such scanners for the so-called “near-treatment-position” imaging. The necessity of moving the patient after a CT scan leads to an increased treatment execution uncertainty

, where �� i

is the uncertainty of the iso-center matching between the CT is the couch-motion-induced movement of the patient. We analyze a

scanner and treatment unit, and �� m