ESTRO 2023 - Abstract Book

S935

Digital Posters

ESTRO 2023

Aim of this study is to describe the experience gained at our institute with a dedicated EPID-based couch coupled for delivering a volumetric modulated arc therapy (VMAT )-based TBI. Materials and Methods Selected patients underwent a total body CT in prone and supine position two weeks before treatment. A vacuum positioning cushion was used for immobilization. An experienced radiation oncologist was responsible for delineating the treatment target (whole body) and organs at risk. To limit the mean lung dose below 10 Gy, customized lung shields were produced for each patient using a 3D printer. Subsequently, a highly customized plan was calculated using Pinnacle TPS (Philips Radiation Oncology Systems, Fitchburg, WI). A dedicated couch with integrated EPID panels for performing online setup imaging and accurately positioning the printed lung blocks was used before delivering TBI, in supine and prone position. The prescribed dose was 12 Gy in twice daily fractionation (2 Gy per fraction), delivered by single modulated sweeping-arc technique. Results A total of 16 patients (median age: 33 years, range: 8 – 56) were treated at our Institute from April 2021 to April 2022. Conditioning chemotherapy before TBI was given to 11 out of 16 patients, in the remaining cases it was performed after radiation therapy. The dedicate couch with integrated EPID panel allowed a reproducible patients and lung shields positioning in all cases. The treatment was completed correctly by the totality of the proposed patients, and it was well tolerated overall. During three days of TBI treatment 2/16 patients developed parotitis G1, 6/16 patients developed nausea G1, 5/16 patients developed asthenia G1, G1 diarrhoea was described in a single case. All patients had leukopenia G2-3, mainly due to the previous chemotherapy conditioning regimen. Hematopoietic stem cell transplantation was performed successfully for all patients. With a median follow-up of 7 months (range: 2 – 14), no cases of disease relapse have been reported. Conclusion The dedicated EPID-based couch VMAT TBI and the 3D-printed blocks proved to be a valid and feasible technique with well manageable side effects that allowed us to achieve excellent reproducibility while keeping patient discomfort to a minimum. A prolonged follow-up will be needed for evaluation of late toxicities Purpose or Objective MR-guided daily adaptive radiotherapy (MR-ART) is a modality that could be advantageous for patients with gastric lymphoma due to the improved soft tissue contrast for daily image guidance, possibility of tracking and gating on internal anatomy, and the ability to account for large daily anatomical variations. The purpose of this study is to report a preliminary analysis from an ongoing protocol for MR-ART for patients with gastric lymphoma and investigate if daily adaption with MR ART improves target coverage relative to no adaption. Materials and Methods Two patients with gastric lymphoma were recruited to participate in our protocol for MR-ART and provided written informed consent. Both patients were planned in (comfortably deep) inspiration breath-hold on the MR-linac (MRIdian, ViewRay) using IMRT for the base plan. PTV margins were 5 mm superiorly near the heart and 8 mm otherwise and the prescription dose was 24 Gy in 12 fractions. Both patients were treated on the MR-linac with MR-ART, with internal gating on the superior region of the stomach near the heart. Results Daily adaption with MR-ART improved target coverage for both patients relative to the predicted plan (base plan recalculated on the daily anatomy) (Figure 1). For example, the dose to 95% of the PTV (D95%) improved from 77% to 95% of the prescription dose for the predicted plan compared to the reoptimized adapted plan for patient 1 and from 72% to 98% for patient 2 (mean of all fractions). The results for the volume (cubic centimeters) of the heart and kidneys receiving 5 Gy or 10 Gy (V5Gy or V10Gy) were mixed when comparing the predicted plan to the reoptimized adapted plan but were acceptable (Figure 2). PO-1170 Preliminary results from ongoing protocol of MR-guided adaptive radiotherapy for gastric lymphoma L. Rechner 1 , R.H. Hansen 1 , K. Boye 1 , L. Specht 1 , P.M. Petersen 1 1 Copenhagen University Hospital, Rigshospitalet, Department of Oncology, Copenhagen, Denmark