Independent Verification Framework for Directspr Commissioning In Dect-Based Proton Therapy Planning
Abstract
Purpose
Stopping power ratio (SPR) estimation from dual-energy CT (DECT) may improve proton range accuracy by eliminating conventional HU calibration uncertainties. Commercial proprietary algorithms, such as DirectSPR, necessitate independent verification methods during commissioning. We developed a commissioning framework using DEEDZ-SPR as an independent verification tool to validate DirectSPR implementation against our clinical single-energy CT (SECT) workflow.
Methods
A head-and-neck patient underwent DECT (100kVp/Sn150kVp) scanning and treatment using 100 kVp images. The clinical plan was recalculated on DirectSPR (Siemens Syngo.via) and DEEDZ-SPR images. SPR distributions within the 10% dose region were compared using the Kolmogorov-Smirnov (KS) test. Dosimetric evaluation compared D95%, V95%, conformity index (CI), and homogeneity index (HI). Gamma analysis (3%/3mm, 10% threshold), robustness evaluation (±3mm/±3.5%), and range difference (R90) along a beam traversing heterogeneous anatomy were assessed
Results
SPR distributions differed significantly (p-value) between image sets (KS: DirectSPR(D=0.124), DEEDZ-SPR(D=0.254)), reflecting inherent differences between DECT and HU-calibration methods. However, these differences did not translate to clinically significant dose deviations. Target coverage was equivalent across
Methods
CTV70 D95% ranged 70.37–70.48 Gy (criterion ≥66.5 Gy); V95% exceeded 99.97% for all targets. CI and HI differences were negligible. Gamma passing rates were 99.26% (DirectSPR) and 98.14% (DEEDZ-SPR). Robust evaluation confirmed consistent target coverage across all 28 uncertainty scenarios. Along a beam traversing tissue, bone and air, LET (DirectSPR: -0.166 keV/μm, DEEDZ-SPR: -0.253keV/μm) and R90 (DirectSPR: 1.64 mm, DEEDZ-SPR: 2.73 mm) differences were observed.
Conclusion
We developed and validated a commissioning framework for DECT-based proton therapy planning using DEEDZ-SPR as an independent verification method for proprietary DirectSPR algorithms. Both DECT-SPR methods demonstrated dosimetric equivalence to clinical SECT planning despite inherent SPR distribution differences. DirectSPR showed marginally higher gamma agreement. This framework enables institutions to independently verify commercial DECT-SPR implementations while confirming that current SECT-based range margins adequately accommodate SPR uncertainties.