Exhibit Hall | Forum 4
Purpose: Mitigation of proton range uncertainties (RU) is essential for plan robustness. The current standard-of-care entails the expansion of the dose cloud beyond the diseased volume to account for RU. Associated with this approach is an increase in surrounding healthy-tissue dose. Previous phantom studies have demonstrated that dual-energy CT (DECT) provides more accurate stopping power ratios (SPR). This study quantifies dosimetric differences between single-energy CT (SECT) and DECT for patients treated with intensity modulated proton therapy (IMPT).
Methods: Under IRB approval, SECT and DECT scans of 30 IMPT patients (15 head and neck, 15 pelvis) were acquired using Siemens Somatom Definition Edge scanner. SECT and DECT SPR images were imported to a commercial treatment planning system. Clinical plans were generated on the SECT images, and recomputed on the DECT image-set using SPR calibration curve. Target coverage, mean and maximum organs at risk (OAR) doses were compared for both image sets.
Results: Systematic differences in target D95%, and V100 were observed. For pelvis patients, DECT indicated that V100 was overestimated by up to 6% when SECT was used for planning. For head and neck (HN) patients, variations as high as 3% in target D99% were seen with DECT indicating target under-dosage. Since all clinical plans were optimized robustly to meet V95% coverage, D95 (HN: 99.6±1.2%, pelvis: 99.7±0.4%) and V95% (HN: 99.8%±0.4%, pelvis: 100.0±0.4%) were in higher agreement (<1%). In most cases, DECT indicated higher OAR maximum doses (D1%); Mean brainstem dose difference for HN cases was 3.8% with maximum differences as high as 11.0%.
Conclusion: The reduction in RU associated with DECT implies the potential for more conformal proton plans. Moreover, utilization of DECT images in treatment planning provides more accurate target coverage and OAR doses, thereby improving overall treatment quality.