Impact of additional PRV constraint to Direct OAR robust optimization in IMPT for targets near serial organs at risk.

Authors

Sham Sundar, Srinivas Chilukuri, Manikandan Arjunan, Rajesh Selvaraj, Aishwarya Guruvaiah, Dayananda Shamurailatpam Sharma

Published in

Radiation oncology (London, England). Jul 04, 2026. Epub Jul 04, 2026.

Abstract

In intensity-modulated proton therapy (IMPT), the benefit of adding planning organ-at-risk volume (PRV)-like nominal constraints to direct robust optimization for serial organs at risk remains uncertain when target-OAR separation is minimal. Using paraspinal chordoma as a model, we evaluated whether an additional nominal canal/thecal sac (PRV-like) constraint improves OAR sparing or compromises target coverage.
Ten patients with paraspinal chordomas were planned using two IMPT strategies: direct cord robust optimization alone (Cord-RO) and direct cord optimization with additional nominal canal/thecal sac constraint (Canal-RO). PTV-based helical tomotherapy (HT) was generated as a secondary benchmark. Prespecified institutional criteria were used for planning, prioritizing OAR constraints over coverage; when standard coverage goals were not achieved, GTV D98 ≥ 59 Gy(RBE) was accepted as the fallback criterion. Endpoints included target coverage, cord/canal doses, and robustness. Statistical comparisons used Wilcoxon signed-rank, Friedman, and Cochran's Q tests, two-sided, p < 0.05.
All plans met plan-specific OAR constraints. Cord-RO achieved superior target coverage (median HR-CTV D98 [Gy(RBE)]: 63.05 vs. 57.38 vs. 59.46; p ≤ 0.002) and met the fallback objective (GTV D98 ≥59 Gy[RBE]) in 10/10 cases versus 4/10 and 7/10 (p=0.011) in Canal-RO and HT respectively. Robustness favored Cord-RO (median worst-case CTV D95: 90% vs 85%, p=0.018). Nominal cord D0.03cc was similar; worst-case cord D0.03cc was slightly lower with Canal-RO.
When targets abut serial OARs, our results suggest that direct OAR-based robust optimization without additional PRV-like constraints improve target coverage and robustness while maintaining acceptable OAR doses. PRV constraints may be reserved for re-irradiation or when target-OAR separation is adequate.

PMID:
42401967
Bibliographic data and abstract were imported from PubMed on 05 Jul 2026.

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