4D strategies for lung tumors treated with hypofractionated scanning proton beam therapy: Dosimetric impact and robustness to interplay effects

Edoardo Mastella; Silvia Molinelli; Andrea Pella; Alessandro Vai; Davide Maestri; Viviana Vitolo; Guido Baroni; Francesca Valvo; Mario Ciocca

doi:10.1016/j.radonc.2020.02.025

4D strategies for lung tumors treated with hypofractionated scanning proton beam therapy: Dosimetric impact and robustness to interplay effects

Radiother Oncol. 2020 May:146:213-220. doi: 10.1016/j.radonc.2020.02.025. Epub 2020 Mar 26.

Authors

Edoardo Mastella¹, Silvia Molinelli², Andrea Pella², Alessandro Vai², Davide Maestri², Viviana Vitolo², Guido Baroni³, Francesca Valvo², Mario Ciocca²

Affiliations

¹ CNAO, National Center for Oncological Hadrontherapy, Pavia, Italy. Electronic address: edoardo.mastella@cnao.it.
² CNAO, National Center for Oncological Hadrontherapy, Pavia, Italy.
³ CNAO, National Center for Oncological Hadrontherapy, Pavia, Italy; Politecnico di Milano, Italy.

PMID: 32222489
DOI: 10.1016/j.radonc.2020.02.025

Abstract

Purpose: To investigate the impact of four-dimensional robust optimization (4DRO) on dose delivered to lung cancer patients in pencil beam scanning proton therapy.

Methods and materials: 2 strategies were compared for 20 lung cancer patients, using a different number of breathing phases of the reconstructed 4D computed tomography (CT) included in the plan optimization problem. In the restricted approach combined with gating, only 3 phases close to reference end-exhale were considered instead of the whole breathing cycle. The prescribed dose was 60 Gy(RBE) in 10 fractions. Target coverage (D98%) and dose to healthy tissues were evaluated using Wilcoxon signed-rank test. To assess the robustness against interfractional anatomical and respiratory variations, the optimized plans were recalculated on re-evaluation 4DCTs. To compare the sensitivity of both strategies to interplay effects, we implemented an end-to-end test with a home-made heterogeneous moving phantom and ionization chambers measurements. Robustly optimized plans with prescription doses of 6 Gy(RBE) were delivered in different dynamic conditions.

Results: Both 4D robustly optimized plans reached the same target coverage (p = 0.56), while a statistically significant decrease of the homolateral lung dose was observed using the restricted approach (p < 0.0001). Plan recalculations within 15 days from the treatment simulation showed the same robustness of target D98% against interfractional variations (p = 0.48), with an average decrease of approximately 3 Gy(RBE). Phantom measurements confirmed the delivery accuracy of the restricted approach (mean dose deviations <5%). Higher deviations were found for ungated full 4DRO and larger motion amplitude.

Conclusion: The restricted approach combined with gating improved normal tissue sparing and was shown to be more robust to single fraction deliveries and large motion amplitude.

Keywords: 4D robust optimization; Gating; Lung cancer; Pencil beam scanning; Proton therapy; Quality assurance.

MeSH terms

Four-Dimensional Computed Tomography
Humans
Lung Neoplasms* / radiotherapy
Proton Therapy*
Radiometry
Radiotherapy Planning, Computer-Assisted