ESTRO 2023 - Abstract Book

S287

Sunday 14 May 2023

ESTRO 2023

Conclusion Target coverage loss, overdose of OARs, and reduced target homogeneity were commonly found when GI air content increased, particularly for midline tumours. Simulating scenarios with -500 HU during plan evaluation may help identify PT plans where variation in bowel filling could impact key dose metrics, such as dose to kidneys. MO-0385 Relapse patterns after local and residual metastatic irradiation in high risk neuroblastoma E. Recalde 1 , M. Ramos 1 , S. Micó 1 , J. Giralt 1 1 Vall d'Hebron Hospital, Radiation Oncology, Barcelona, Spain Purpose or Objective Metastatic High Risk Neuroblastoma (HRNB) die after disease progression despite multimodal intensive treatment. Radiation Therapy (RT) to the primary tumor after induction is a standard practice, but there is still controversy about irradiation of residual metastatic (RM) locations. We evaluated HRNB pediatric patients treated with RT to local and metastatic sites to evaluate the local control and relapse patterns. Materials and Methods Retrospective analysis of 15 patients treated at our institution from 2011 and 2019, which were HRNB stage M at diagnosis, that had received intensive systemic chemotherapy (ISC) and had 1-3 residual metastasis (RM) after induction. All patients received 21Gy after ICS to primary tumor site and the RM sites. We analyzed site and time to relapses, as well as mortality. Results A total of 15 patients and 24 RM locations were irradiated. See table 1 for detail. All patients received RT to primary and 1-3 RM sites (1 site 53%, 2 sites 33%, 3 sites 13%), there were no RM that were not irradiated. All RM were MIBG avid except from two (one missing data, the other was a palpable soft tissue RM). Predominant irradiated RM site was appendicular skeleton (50%). Mean follow up (FO) was 56 months (range 13-135 months). There is no available FO data about 1 patient. 8 patients (53%) presented relapse. 100% of relapses were at least at distant sites. 2 patients (13%) presented both primary tumor and distant failure. 4 out of 8 metastatic relapses were at previously irradiated RM and 3 at non-irradiated sites. Of 24 total RM that were irradiated, only 5 (20.8%) presented relapse. 3 patients (20%) were dead at the end of follow up. Mean time to relapse or death was 33.5 months (median 24 months, ED28 months).

Conclusion With the limitations of this study, our results suggest that RT to 1-3 RM for HRNB patients seems feasible as most progressions occur at distant sites that were not previously irradiated. Relapse still happens in half of the patients and prospective data including more patients should be added. MO-0386 MRI-based inter- and intra-fraction motion of the spleen/pancreatic tail in neuroblastoma patients F. van Ommen 1 , G.A. le Quellenec 1 , M.E. Willemsen-Bosman 1 , M.M. van Noesel 2 , E. Seravalli 1 , P.S. Kroon 1 , G.O. Janssens 1 1 University Medical Center Utrecht, Radiotherapy, Utrecht, The Netherlands; 2 Princess Máxima Center for Pediatric Oncology, Solid Tumors, Utrecht, The Netherlands Purpose or Objective In state-of-the-art radiotherapy treatment planning, dose constraints to the spleen/pancreatic tail in pediatric patients with neuroblastoma and renal tumors are applied. An analysis of MRI-based inter- and intrafraction motion of the spleen/pancreatic tail is performed to estimate the potential dose reduction using an adaptive MR-linac (MRL) workflow.

Materials and Methods