ESTRO 2024 - Abstract Book

S1134

Clinical - Haematology

ESTRO 2024

A retrospective analysis of TYA lymphoma patients treated at the national centres between December 2021 and September 2023 was undertaken. Demographic, planning and toxicity data were captured from prospectively filled electronic records, clinic letters, on-treatment notes and ARIA planning systems.

Results:

Twenty patients received PBT for lymphoma, with a median age of 20.5 years (range 17-26) and male:female ratio of 8:12. Tumour subtypes and treatment details are shown in Table 1.

All patients were referred via the national PBT portal. Accepted patients were discussed in PBT MDTs and seen in a ‘one - stop assessment’ for initial review and PBT planning. Average time from PBT portal acceptance to initial clinic visit was 17 days (range 2-48.) The long range was due to deferral of PBT till completion of chemotherapy. Mean travel distance to PBT centre was 39.8 miles (range 1.6-121.) Those from further afield stayed in PBT dedicated accommodation for the planning process and treatment duration. Average time from first clinic appointment to treatment was 23 days (range 14-34). PBT planning CT (with and without contrast) and MR scans were performed on the day of, or day after first clinic appointment. Customised Vacbag or a thermoplastic head & neck shell were used for immobilisation, where appropriate, with an emphasis on shoulder and clavicle immobilisation to prevent minimal change notably affecting dosimetry. 4DCT was utilised for mediastinal treatment sites.

All contours were delineated according to ILROG (1) guidance and along with final plans were prospectively peer reviewed.

Plans were created through an iterative process. Beam number, angles, and range shifter were chosen to optimise target coverage and minimise organs at risk (OAR) dose. Uncertainties of 3.5% were used to account for error in the CT calibration from Hounsfield units to relative stopping power. All plans were within 95% robustness tolerance, an average 97.77 % (range 95.38-98.86.)

OAR doses were acceptable. These were comparable to, if not better than comparative photon plans. See figure 1.