ESTRO 2022 - Abstract Book

S1262

Abstract book

ESTRO 2022

Conclusion SSPI significantly improves localization of paediatric tumours in comparison to classic setup of skin/cradle marks. This reduction in the setup margin treated with SSPI could also have significant clinical implications for second malignancies and acute and late radiation induced toxicities. Better results are expected once the learning curve flattens. A larger prospective trial is ongoing using a robotic couch for correcting setup errors in six degrees of freedom.

PO-1487 Inter-fraction prostate bed motion during salvage radiation therapy within the PERYTON-trial

F. Staal 1 , C.L. Brouwer 1 , J. Janssen 1 , S. Krishnapillai 1 , J.A. Langendijk 1 , J.F. Verzijlbergen 2 , I.J. de Jong 3 , R.J. Smeenk 4

1 University Medical Center Groningen, Department of Radiation Oncology, Groningen, The Netherlands; 2 Radboud University Medical Center, Department of Nuclear Medicine, Nijmegen, The Netherlands; 3 University Medical Center Groningen, Department of Urology, Groningen, The Netherlands; 4 Radboud University Medical Center, Department of Radiation Oncology, Nijmegen, The Netherlands Purpose or Objective The PERYTON-trial, a phase III RCT, investigates the role of hypofractionation in salvage radiotherapy (SRT) for patients with a biochemical recurrence after prostatectomy. In hypofractionation, accurate dose delivery is crucial. We aim to analyze the inter-fractional displacement (IFD) of the CTV in SRT. Materials and Methods The first 12 patients treated in the PERYTON-trial were retrospectively analyzed, six patients received the conventional schedule (35x2Gy) and six patients received the hypofractionated schedule (20x3Gy). The PTV margin used was 8 mm. Each patient underwent a planning-CT and MRI. Patients were instructed to show with a comfortably full bladder, no rectal preparation was applied. Prior to each fraction a CBCT was obtained. CBCTs were matched with the planning-CT using a bony verification mask, translations only. Rectum and bladder were contoured for each CBCT. The anterior rectal wall represents the posterior border of the CTV and the bladder wall represents the anterior border of the CTV. To analyze