ESTRO 2024 - Abstract Book

S3798

Physics - Image acquisition and processing

ESTRO 2024

[1] T. Park, A. A. Efros, R. Zhang, J.-Y. Zhu, Contrastive learning for unpaired image-to-image translation, in: Computer Vision–ECCV 2020: 16th European Conference, Glasgow, UK, August 23–28, 2020, Proceedings, Part IX 16, Springer, 2020, pp. 319–345. [2] C. Kurz, F. Kamp, Y.-K. Park, C. Zöllner, S. Rit, D. Hansen, M. Podesta, G. C. Sharp, M. Li, M. Reiner, et al., Investigating deformable image registration and scatter correction for CBCT-based dose calculation in adaptive IMPT, Medical physics 43 (2016) 5635–5646.

Acknowledgement: DFG 399148265

754

Digital Poster

An audit of a compensation technique for cord and brainstem doses in head and neck reirradiation

David Nash 1 , Sarah Muscat 1 , Chelmis Thiong'o 2 , Eliana Vasquez Osorio 2,3 , Antony L Palmer 1

1 Portsmouth Hospitals University NHS Trist, Department of Medical Physics, Portsmouth, United Kingdom. 2 University of Manchester, Division of Cancer Sciences, Manchester, United Kingdom. 3 The Christie NHS Foundation Trust, Medical Physics, Manchester, United Kingdom

Purpose/Objective:

Reirradiations are increasing in clinical practice. However, determining dose constraints for individual patients is still challenging and often relies on conservative estimates. Different techniques have been proposed to determine constraints [1], but few have been verified in an independent system. Here we present the results of a retrospective audit aiming at verifying our novel technique for determining patient specific dose constraints for the spinal cord and brainstem in head and neck cancer reirradiation patients. We also present spinal cord and brainstem side-effect data.

Material/Methods:

Ten reirradiation patients from a single centre, categorised as type 1 according to the recently published ESTRO/EORTC consensus [2], were considered. As part of clinical practice, the planning CT scan of the previous treatment was deformably registered in Pinnacle (Philips, NL) or ProSoma (Medcom, France) to the reirradiation CT scan, mapping the dose of the previous treatment into the reirradiation CT scan. Contours corresponding to multiple isodoses levels were created to establish local dose constraints. These contours started at the maximum dose to the cord PRV/brainstem PRV of the previous treatment and progressed downwards in 5-10 Gy steps to 10-25 Gy. The cord and/or brainstem was then divided into segments using these isodose contours. Maximum dose constraints for each of these segments were calculated based on a maximum safe, cumulative, dose of 60 Gy equivalent dose in 2 Gy fractions (EQD2) to the cord [3] and 54 Gy to the brainstem [4], using the linear quadratic model and α/β=2 Gy. The original and reirradiation physical doses, with EQD2 values, were collected and reported to the treating physician at the time.