ESTRO 2022 - Abstract Book

S149

Abstract book

ESTRO 2022

Conclusion This multi-parameter selection strategy for HL protontherapy, taking simultaneously into consideration patient clinical characteristics and national treatment capacity, allows flexible patient selection in case of IMPT availability shortage and might be readily implemented for other tumor types.

PD-0173 Deep Inspiration breath-hold in gastric lymphomas.

P. Meidal Petersen 1 , L.A. Rechner 2 , L. Specht 3

1 Rigshospitalet, University of Copenhagen, Department of Oncology , Copenhagen, Denmark; 2 Rigshospitalet, University of Copenhagen, Department of Oncology, Section of Radiotherapy, Copenhagen, Denmark; 3 Rigshospitalet, University of Copenhagen, Department of Oncology, Copenhagen, Denmark Purpose or Objective The aim of this study was to assess the effect of the two components of assumed reduction to the dose levels to organs at risk with deep inspiration breath-hold (DIBH) compared with free breathing (FB): 1) the change of anatomy and 2) the possibility of planning target volume (PTV) reduction. Materials and Methods Radiation therapy plans were made for each of the15 patients using DIBH and FB scans. Clinical target volume (CTV) was the stomach plus 1cm margin. The heart and surrounding organs at risk (OAR) were contoured. We kept the variables constant separately and compared: 1) FB with 1 cm margin CTV to PTV margin in all directions vs FB with an additional 5mm margin in cranio-caudal direction. 2) DIBH and FB with same CTV to PTV margin. Datasets were analysed with Wilcoxon signed rank test for non-parametric paired data. Results Target coverage was kept equal between FB and DIBH, while a little reduction of the estimated dose to the heart was seen with the margin reduction and a more substantial reduction with DIBH. Margin reduction causes a minor reduction of estimated mean dose to the liver, duodenum, pancreas and spinal cord while the effect of DIBH varies in between patients and between OAR’s (Table 1 and figure 1).