Pilot Dosimetric Comparison of Dynamic ARC Proton Therapy Versus Helical Tomotherapy for Complex Skin Cancer

Document Type

Conference Proceeding

Publication Date

9-2026

Publication Title

International Journal of Particle Therapy

Abstract

Background and Aims: To compare Dynamic ARC proton therapy (DARC) and helical tomotherapy (TOMO) for a complex skin cancer case and to assess DARC’s robustness under combined setup and range uncertainties. Methods: This retrospective, single-case pilot study used the planning CT dataset with a custom bolus from a previously treated TOMO patient. The patient received 55 Gy in 20 fractions to circumferential scalp squamous cell carcinoma, placing the brain at high risk for unwanted dose. A comparative DARC plan was generated on the same CT dataset in RayStation (research version 2024A) using a single partial arc with a 270° couch rotation and a 4 cm WET range shifter. The DARC plan was robustly optimized on the CTV using setup uncertainty (±3mm) and range uncertainty (±3.5%). Both DARC and TOMO plans were normalized such that CTV D99% equaled 99% of 55 Gy(RBE). Plan evaluation included target coverage, homogeneity index, brain near-maximum dose, brain V5Gy, and doses to adjacent OARs (brainstem, optic structures, lenses, lacrimal glands, and cochleae). Integral dose (ID) was computed for the body contour by excluding the CTV. Results: Nominally, both techniques achieved comparable target homogeneity (HI: DARC 0.04 vs TOMO 0.03). Compared with TOMO, DARC reduced brain dose metrics, including a 23.7% reduction in brain D0.03cc (41.22 vs 54.00 Gy[RBE]), a 63.3% reduction in brain D1% (16.85 vs 45.92 Gy[RBE]), and a 27.1% reduction in brain V5Gy (24.30% vs 33.31%). DARC also demonstrated favorable sparing for other OARs (brainstem, optic structures, lenses, lacrimal glands, and cochleae) compared with TOMO. Under robustness evaluation (total of 12 scenarios combining ±3 mm/±3.5%), DARC worst-scenario target coverage (D95%:52.38 Gy [RBE]) met the acceptability criterion (D95%≥52.25Gy[RBE]). DARC reduced the ID by 38.3% compared with TOMO (38.58 vs 62.58 Gy·L). Conclusions: To our knowledge, this is the first report of DARC planning and robustness evaluation for a complex skin cancer case. In this pilot comparison, DARC maintained worst-scenario robust target coverage while reducing brain dose, brain V5Gy, and ID relative to TOMO, with comparable target homogeneity. These dosimetric improvements may reduce the risk of radiation-related brain toxicity in skin cancer patients and support further evaluation of DARC in a larger cohort.

Volume

21

Issue

Suppl

First Page

101604

Last Page

101604

Comments

PTCOG 64 Particle Therapy Co-Operative Group 64th Annual Conference, June 8-13, 2026, Deauville, France

DOI

10.1016/j.ijpt.2026.101604

Link to Full Text

Share

COinS