Towards the clinical implementation of intensity-modulated proton therapy for thoracic indications with moderate motion: Robust optimised plan evaluation by means of patient and machine specific information

Cássia O Ribeiro; Sabine Visser; Erik W Korevaar; Nanna M Sijtsema; R Melissa Anakotta; Margriet Dieters; Stefan Both; Johannes A Langendijk; Robin Wijsman; Christina T Muijs; Arturs Meijers; Antje Knopf

doi:10.1016/j.radonc.2021.01.014

Towards the clinical implementation of intensity-modulated proton therapy for thoracic indications with moderate motion: Robust optimised plan evaluation by means of patient and machine specific information

Radiother Oncol. 2021 Apr:157:210-218. doi: 10.1016/j.radonc.2021.01.014. Epub 2021 Feb 3.

Affiliations

¹ Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, The Netherlands. Electronic address: c.oraboni.ribeiro@umcg.nl.
² Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, The Netherlands.
³ Department of Radiation Oncology, University Medical Center Groningen, University of Groningen, The Netherlands; Division for Medical Radiation Physics, Carl von Ossietzky University Oldenburg, Germany.

PMID: 33545257
DOI: 10.1016/j.radonc.2021.01.014

Abstract

Purpose: Compared to volumetric modulated arc therapy (VMAT), clinical benefits are anticipated when treating thoracic tumours with intensity-modulated proton therapy (IMPT). However, the current concern of plan robustness as a result of motion hampers its wide clinical implementation. To define an optimal protocol to treat lung and oesophageal cancers, we present a comprehensive evaluation of IMPT planning strategies, based on patient 4DCTs and machine log files.

Materials and methods: For ten lung and ten oesophageal cancer patients, a planning 4DCT and weekly repeated 4DCTs were collected. For these twenty patients, the CTV volume and motion were assessed based on the 4DCTs. In addition to clinical VMAT plans, layered rescanned 3D and 4D robust optimised IMPT plans (IMPT_3D and IMPT_4D respectively) were generated, and approved clinically, for all patients. The IMPT plans were then delivered in dry runs at our proton facility to obtain log files, and subsequently evaluated through our 4D robustness evaluation method (4DREM). With this method, for each evaluated plan, fourteen 4D accumulated scenario doses were obtained, representing 14 possible fractionated treatment courses.

Results: From VMAT to IMPT_3D, nominal D_mean(lungs-GTV) decreased 2.75 ± 0.56 Gy_RBE and 3.76 ± 0.92 Gy_RBE over all lung and oesophageal cancer patients, respectively. A more pronounced reduction was verified for D_mean(heart): 5.38 ± 7.36 Gy_RBE (lung cases) and 9.51 ± 2.25 Gy_RBE (oesophagus cases). Target coverage robustness of IMPT_3D was sufficient for 18/20 patients. Averaged dose in critical structures over all 4DREM scenarios changed only slightly for both IMPT_3D and IMPT_4D. Relative to IMPT_3D, no gain in IMPT_4D was observed.

Conclusion: The dosimetric superiority of IMPT over VMAT has been established. For most thoracic tumours, our IMPT_3D planning protocol showed to be robust and clinically suitable. Nevertheless, accurate patient positioning and adapting to anatomical variations over the course of treatment remain compulsory.

Keywords: 3D robust optimisation; 4D robust optimisation; 4D robustness evaluation; Intensity-modulated proton therapy; Lung cancer; Oesophageal cancer.

MeSH terms

Carcinoma, Non-Small-Cell Lung*
Humans
Lung Neoplasms* / radiotherapy
Organs at Risk
Proton Therapy*
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted
Radiotherapy, Intensity-Modulated*