ESTRO 2022 - Abstract Book

S1287

Abstract book

ESTRO 2022

Results CTV volumes differed with a median (range) of 650 cm 3 (418–757 cm 3 ) for CTV-E and 56 cm 3 (25–79 cm 3 ) for the boost. Mean doses to all OARs were significantly lower with protons compared to photons except for spinal cord, due to the posterior beams and for pancreas which for one patient had a higher mean dose with photons, (Figure 1). For left and right kidney, a reduction from 4.9 Gy to 3.3 Gy and 4.7 Gy to 2.6 Gy (p=0.03; p=0.03) was seen, respectively. Mean dose to body outline was reduced from 3.9 Gy to 1.9 Gy (p=0.03). The excess absolute risk (EAR) of secondary cancer was reduced from 46 to 23 per 10.000 persons per year (PY) for photon vs proton plans (p=0.03) but with considerable variation between opposing IMRT fields and VMAT. VMAT resulted in a higher EAR due to the low dose bath from the VMAT technique.

Conclusion For all patients, the mean dose to delineated OAR were reduced with protons compared to photons except for the spinal cord and pancreas. Likewise, the radiation dose to all OARs and thereby the risk of secondary cancer was reduced; this was

especially pronounced comparing proton planning to VMAT planning. Robust IMPT is a favorable treatment option for seminoma patients.

PO-1508 Bone versus soft tissue setup in proton therapy for patients with oesophageal cancer

M. Shamshad 1,2 , D. Sloth Møller 2,3 , H. Mortensen 1 , M. Lykkegaard Ehmsen 1 , M. Fuglsang Jensen 1 , L. Hoffmann 2,3

1 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark; 2 Aarhus University Hospital, Department of Medical Physics, Aarhus, Denmark; 3 Faculty of Health Sciences, Aarhus University, Department of Clinical Medicine, Aarhus, Denmark Purpose or Objective Proton therapy (PT) may reduce dose to organs-at-risk compared to photon therapy (RT) which makes PT favourable for oesophageal tumours where anatomical changes and respiratory motion risk imposing target dose deterioration. The aim of this study was to investigate the effect of patient (pt) positioning based on bone versus soft tissue setup for PT in