ESTRO 2022 - Abstract Book

S859

Abstract book

ESTRO 2022

These features make LC-CRT a local treatment that can be tailored to tumor presentation and treatment goals, compared to SCRT which is a ‘one fits all’ treatment that, regardless of tumor presentation, does not allow dose differentiation, escalation or adaptation. Interval: several studies on LC-CRT have shown that prolonging the interval between CRT and surgery leads to an increase in tumor response with pCR rates of up to 30%, 95% of which occur 10 weeks after the end of CRT. Delaying surgery after SCRT resulted in a better tumor response rate with pCR of 11%, which is still lower than those obtained with preoperative LC-CRT. CT intensification: the addition of consolidation CT to LC-CRT demonstrated an increased complete response rate and improved DFS. Although the RAPIDO trial demonstrated better pCR DFS of LCRT and FOLFOX compared to adjuvant LC-CRT +/- CT, the two arms are unbalanced in both treatment intensity and the interval between RT and surgery. Despite these differences, local control still favored LC-CRT. More robust results are expected from ongoing studies comparing LCRT regimens with SCRT and consolidation CT versus LC-CRT and consolidation CT with the same interval between preoperative RT and surgery.

SP-1009 For the motion (rebuttal)

C. Marijnen

The Netherlands Abstract not available

SP-1010 Against the motion (rebuttal)

C. Rödel

Germany Abstract not available

Symposium: Spatial and spatio-temporal fractionation

SP-1012 Biology of spatial and spatiotemporal fractionation

J Scott

USA Abstract not available

SP-1013 Clinical implementation of spatial-fractionated radiotherapy

V. Gonzalez Perez 1 , M.C. Banos-Capilla 2 , J.D. Lago-Martin 2

1 Fundación Instituto Valenciano de Oncología, Medical Physics Department, Valencia, Spain; 2 Vithas Valencia Consuelo, Medical Physics Department, Valencia, Spain Abstract Text The spatially fractionated radiation therapy (SFRT) technique uses high spatial dose modulation to create dose profiles with valleys and peaks that increase the tolerance of healthy tissue, in addition to activating biological processes by stimulating the immune response. Currently, the most established uses of SFRT are ablative irradiation for tumor debulking or as boost treatment. Bystander and abscopal effects are achieved in certain tumors, but the immunological response caused by SFRT is still under active investigation. This presentation focuses on the commissioning of SFRT with conventional LINACS, which allows the treatment using SFRT with the techniques of GRID (both with physical block and with the use of MLC modulation) and lattice therapy, with spheres of very high dose distributed inside the GTV or an inward margin structure LTV (Lattice Tumor Volume), and where PTV periphery receives the dose in a conventional fractionation without increasing the toxicity to adjacent OARs. The knowledge of these techniques is based on the experience of a few centers, which have reported parameters on the dose, fractionation, peak-to-valley dose contrast and spatial frequency, and physics quality assurance (QA). In this talk, we will review published articles that cover these topics. A recent publication of a white paper by the physics working group of the Radiosurgery Society on photon GRID RT is presented. It provides consensus recommendations on dose prescription, treatment planning, response modeling and dose reporting. It recommends commissioning with water phantom measurements with microionization chamber and transverse and radial dose profiles, as well as film dosimetry and Monte Carlo simulation before clinical use of the GRID collimator. For MLC-generated GRID dose distributions, it is recommended film dosimetry in solid-water slabs. Furthermore, criteria are established for the dose prescription and the treatment report.

The experience published by single institutions on commissioning for both GRID with physical block and MLC-based is also