Inter-fraction motion robustness and organ sparing potential of proton therapy for cervical cancer

• Published in: Radiotherapy and oncology Vol. 154; pp. 194 - 200
• Main Authors: Gort, Elske M., Beukema, Jannet C., Matysiak, Witold, Sijtsema, Nanna M., Aluwini, Shafak, Langendijk, Johannes A., Both, Stefan, Brouwer, Charlotte L.
• Format: Journal Article
• Language: English
• Published: Ireland Elsevier B.V 01.01.2021
• Subjects: Cervical cancer; Female; Humans; inter-fraction motion; intra-fraction motion; OAR sparing; Organs at Risk; pencil beam scanning proton therapy; Proton Therapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy, Intensity-Modulated; robustness evaluation; Uterine Cervical Neoplasms - radiotherapy; volumetric arc therapy; inter-fraction motion; pencil beam scanning proton therapy; OAR sparing; volumetric arc therapy; intra-fraction motion; Cervical cancer; robustness evaluation
• ISSN: 0167-8140; 1879-0887
• DOI: 10.1016/j.radonc.2020.09.022

[Display omitted] •Proton therapy can be as robust as photon therapy to inter-fraction motion.•Proton therapy significantly reduces organ at risk doses compared to photon therapy.•Two ITV-based treatment planning techniques for PBS-PT presented. Large-field photon radiotherapy is current standard in the treatment of cervical cancer patients. However, with the increasing availability of Pencil Beam Scanning Proton Therapy (PBS-PT) and robust treatment planning techniques, protons may have significant advantages for cervical cancer patients in the reduction of toxicity. In this study, PBS-PT and photon Volumetric Modulated Arc Therapy (VMAT) were compared, examining target coverage and organ at risk (OAR) dose, taking inter- and intra-fraction motion into account. Twelve cervical cancer patients were included in this in-silico planning study. In all cases, a planning CT scan, five weekly repeat CT scans (reCTs) and an additional reCT 10 min after the first reCT were available. Two-arc VMAT and robustly optimised two- and four-field (2F and 4F) PBS-PT plans were robustly evaluated on planCTs and reCTs using set-up and range uncertainty. Nominal OAR doses and voxel-wise minimum target coverage robustness were compared. Average voxel-wise minimum accumulated doses for pelvic target structures over all patients were adequate for both photon and proton treatment techniques (D98 > 95%, [91.7–99.3%]). Average accumulated dose of the para-aortic region was lower than the required 95%, D98 > 94.4% [91.1–98.2%]. With PBS-PT 4F, dose to all OARs was significantly lower than with VMAT. Major differences were observed for mean bowel bag V15Gy: 60% [39–70%] for VMAT vs 30% [10–52%] and 32% [9–54%] for PBS-PT 2F and 4F and for mean bone marrow V10Gy: 88% [82–97%] for VMAT vs 66% [60–73%] and 67% [60–75%] for PBS-PT 2F and 4F. Robustly optimised PBS-PT for cervical cancer patients shows equivalent target robustness against inter- and intra-fraction variability compared to VMAT, and offers significantly better OAR sparing.