Pencil beam scanning proton therapy for mediastinal lymphomas in deep inspiration breath-hold: a retrospective assessment of plan robustness

• Published in: Acta oncologica Vol. 63; no. 1; pp. 62 - 69
• Main Authors: Hörberger, Filip, Andersson, Karin M, Enmark, Marika, Kristensen, Ingrid, Flejmer, Anna, Edvardsson, Anneli
• Format: Journal Article
• Language: English
• Published: Sweden MJS Publishing on behalf of Acta Oncologica 28.02.2024; Medical Journals Sweden
• Subjects: Clinical Medicine; deep inspiration breath- hold; Humans; Klinisk medicin; Lymphoma - diagnostic imaging; Lymphoma - radiotherapy; mediastinal lymphomas; Mediastinal Neoplasms - diagnostic imaging; Mediastinal Neoplasms - radiotherapy; Medical and Health Sciences; Medicin och hälsovetenskap; Original; Proton Therapy; Radiologi och bildbehandling; Radiology, Nuclear Medicine and Medical Imaging; repeated verification CTs; Reproducibility of Results; Retrospective Studies; Robust optimization
• ISSN: 0284-186X; 1651-226X; 1651-226X
• DOI: 10.2340/1651-226X.2024.23964

The aim of this study was to evaluate pencil beam scanning (PBS) proton therapy (PT) in deep inspiration breath-hold (DIBH) for mediastinal lymphoma patients, by retrospectively evaluating plan robustness to the clinical target volume (CTV) and organs at risk (OARs) on repeated CT images acquired throughout treatment.  Methods: Sixteen mediastinal lymphoma patients treated with PBS-PT in DIBH were included. Treatment plans (TPs) were robustly optimized on the CTV (7 mm/4.5%). Repeated verification CTs (vCT) were acquired during the treatment course, resulting in 52 images for the entire patient cohort. The CTV and OARs were transferred from the planning CT to the vCTs with deformable image registration and the TPs were recalculated on the vCTs. Target coverage and OAR doses at the vCTs were compared to the nominal plan. Deviation in lung volume was also calculated. The TPs demonstrated high robust target coverage throughout treatment with D98%,CTV deviations within 2% for 14 patients and above the desired requirement of 95% for 49/52 vCTs. However, two patients did not achieve a robust dose to CTV due to poor DIBH reproducibility, with D98%,CTV at 78 and 93% respectively, and replanning was performed for one patient. Adequate OAR sparing was achieved for all patients. Total lung volume variation was below 10% for 39/52 vCTs. PBS PT in DIBH is generally a robust technique for treatment of mediastinal lymphomas. However, closely monitoring the DIBH-reproducibility during treatment is important to avoid underdosing CTV and achieve sufficient dose-sparing of the OARs.