ESTRO 2022 - Abstract Book

S1422

Abstract book

ESTRO 2022

Film exposures Three 25x25 cm2 Grafchromic EBT3 films were irradiated (Varian 21EX, 6MV) in a RW3 phantom with an open beam of 20x20 cm2 size at film plane. The calculated dose (Varian Eclipse with AAA) at central axis were 72 cGy, 144 cGy and 287 cGy, respectively, The films were digitalized 24-hours after exposure using a multi-channel flatbed scanner Epson Expression 10000XL. The films belonged to a lot previously calibrated using [E.1]. Image to dose conversion was performed applying the calibration curves for single-channel (SC) dosimetry. Correction factors were then calculated using the proposed method. The effectiveness of the "corrected single-channel" (CSC) dosimetry in accounting for LRA effect was evaluated against the central axis dose profiles extracted perpendicularly to scan direction. Results The proposed method showed an evident mitigation of LRA for the central axis dose profiles extracted perpendicularly to scan direction (fig. 1). In table 1 the maximum values of measured/expected dose ratio among different channels were reported.

Conclusion The proposed method provided a more reliable dosimetry respect to single-channel dosimetry,

PO-1631 Feasibility of low-dose 4DCBCT for patient setup and motion measurement

J. Lindsay 1 , A. Bryce-Atkinson 1 , S. Meara 2 , C. Faivre-Finn 1 , C. Eccles 2 , M. Aznar 1 , M. van Herk 1

1 The University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom; 2 The Christie NHS Foundation Trust, Clinical Oncology, Manchester, United Kingdom

Purpose or Objective