Background This study reports the single-institution clinical experience of multifield pencil beam scanning (PBS) intensity-modulated proton therapy (IMPT) and dosimetric comparison to proton arc for uveal melanoma (UM) in a regular PBS gantry room. Methods Eleven consecutive UM patients were treated with IMPT to 50 Gy in 5 fractions. A customized gaze-fixation device attached to the thermoplastic mask was used to reproduce the globe position for each patient. IMPT plans were robustly optimized with perturbations of 3 mm setup and 3.5% range uncertainties using 3–4 fields without apertures. Each plan was robustly reoptimized (using the same perturbation parameters) using two non-coplanar arc fields in the RayStation treatment planning system. Treatment quality for both plans was evaluated daily using CBCT-generated synthetic CT. Target coverage, conformity, and mean/maximum doses to adjacent organs were assessed. Results Proton arc plans provided comparable plan quality compared to IMPT plans. Similar target coverage was achieved, with an average GTV D95% equal to 101.1% <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13014_2025_2621_Article_IEq1.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:\pm\:\)</EquationSource> </InlineEquation> 1.0% and 101.4% <InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13014_2025_2621_Article_IEq2.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:\pm\:\)</EquationSource> </InlineEquation> 0.4% for IMPT and proton arc plans, respectively. Proton arc improves the conformity index (RTOG) compared to IMPT plans (average 0.96 <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13014_2025_2621_Article_IEq3.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:\pm\:\)</EquationSource> </InlineEquation> 0.23 vs. 0.88 <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13014_2025_2621_Article_IEq4.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:\pm\:\)</EquationSource> </InlineEquation> 0.18, p = 0.11). Both modalities met all the clinical goals for organs-at-risk (OARs), while proton arc significantly reduced the maximum dose for the retina from, on average, 54.5 <InlineEquation ID="IEq5"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13014_2025_2621_Article_IEq5.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:\pm\:\)</EquationSource> </InlineEquation> 0.7 to 53.2 <InlineEquation ID="IEq6"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="13014_2025_2621_Article_IEq6.gif" Format="GIF" Height="13" Rendition="HTML" Resolution="72" Type="Linedraw" Width="18" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:\pm\:\)</EquationSource> </InlineEquation> 0.3 Gy (p < 0.01). Treatment evaluation on synthetic CT showed that the doses received by patients were highly consistent with the planned doses, with a relative target coverage (D95%) difference within 3.5% for IMPT and 3.1% for proton arc, and the D95% of actual delivery exceeding 98.7% and 98.2%, respectively. The doses delivered to OARs did not exceed clinical constraints. Conclusions This is a novel report on proton arc for ocular tumors and gantry-based multifield PBS proton treatment for these tumors. This study demonstrated that both modalities can meet the clinical goals. The IMPT is currently clinically implanted, and 2-field non-coplanar proton arc plans can achieve comparable dosimetric metrics to those of IMPT plans when the deliver technique is matured.

Gantry-based pencil beam scanning proton therapy for uveal melanoma: IMPT versus proton arc therapy

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2025年4月2日

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Hang Qi,
Lei Hu,
Sheng Huang,
Yen-Po Lee,
Francis Yu,
Qing Chen,
Yunjie Yang,
Minglei Kang,
Huifang Zhai,
Milo Vermeulen,
Andy Shim,
Peter Park,
Xuanfeng Ding,
Jun Zhou,
David H. Abramson,
Jasmine H. Francis,
Charles B. Simone 2nd,
Christopher A. Barker,
Haibo Lin

摘要

Background

This study reports the single-institution clinical experience of multifield pencil beam scanning (PBS) intensity-modulated proton therapy (IMPT) and dosimetric comparison to proton arc for uveal melanoma (UM) in a regular PBS gantry room.

Methods

Eleven consecutive UM patients were treated with IMPT to 50 Gy in 5 fractions. A customized gaze-fixation device attached to the thermoplastic mask was used to reproduce the globe position for each patient. IMPT plans were robustly optimized with perturbations of 3 mm setup and 3.5% range uncertainties using 3–4 fields without apertures. Each plan was robustly reoptimized (using the same perturbation parameters) using two non-coplanar arc fields in the RayStation treatment planning system. Treatment quality for both plans was evaluated daily using CBCT-generated synthetic CT. Target coverage, conformity, and mean/maximum doses to adjacent organs were assessed.

Results

Proton arc plans provided comparable plan quality compared to IMPT plans. Similar target coverage was achieved, with an average GTV D95% equal to 101.1% \(\:\pm\:\) 1.0% and 101.4% \(\:\pm\:\) 0.4% for IMPT and proton arc plans, respectively. Proton arc improves the conformity index (RTOG) compared to IMPT plans (average 0.96 \(\:\pm\:\) 0.23 vs. 0.88 \(\:\pm\:\) 0.18, p = 0.11). Both modalities met all the clinical goals for organs-at-risk (OARs), while proton arc significantly reduced the maximum dose for the retina from, on average, 54.5 \(\:\pm\:\) 0.7 to 53.2 \(\:\pm\:\) 0.3 Gy (p < 0.01). Treatment evaluation on synthetic CT showed that the doses received by patients were highly consistent with the planned doses, with a relative target coverage (D95%) difference within 3.5% for IMPT and 3.1% for proton arc, and the D95% of actual delivery exceeding 98.7% and 98.2%, respectively. The doses delivered to OARs did not exceed clinical constraints.

Conclusions

This is a novel report on proton arc for ocular tumors and gantry-based multifield PBS proton treatment for these tumors. This study demonstrated that both modalities can meet the clinical goals. The IMPT is currently clinically implanted, and 2-field non-coplanar proton arc plans can achieve comparable dosimetric metrics to those of IMPT plans when the deliver technique is matured.