Clinical Verification of in vivo Range and 3D Dose Reconstruction Using a Multi-Slit Prompt-Gamma Camera In Spot-Scanning Proton Therapy
Abstract
Purpose
In proton therapy, precise beam range measurement and dose verification are critical to overcome range uncertainty and ensure patient safety. This study developed and evaluated a technique to reconstruct and visualize in vivo dose distribution from spot scanning proton therapy using the beam range information acquired by a multi-slit prompt-gamma camera (MSPGC).
Methods
The MSPGC measures the prompt gamma distribution to determine the in vivo proton beam range. Using the measured beam ranges, the 3D dose distribution is reconstructed and visualized via a superposition-based method using a precomputed dose dataset containing planned and range-shifted dose distributions. The MSPGC was applied to clinical cases of glioblastoma and skull-base tumor patients treated at the National Cancer Center, Korea. We evaluated range discrepancies, defined as the difference between the measured and planned ranges, and inter-fractional variations. The agreement between the visualized and the planned dose was also evaluated using gamma index analysis and dose-volume histogram (DVH).
Results
The developed technique reduced the range confidence interval by approximately 75% compared to the treatment safety margin. The analysis of inter-fractional variations confirmed that target coverage was consistently maintained across all fractions. The visualized dose distributions demonstrated high agreement with the treatment plans. Specifically, the 2%/2 mm gamma passing rates exceeded 95% in all cases (95.16%, 95.77% for glioblastoma, 95.43% for skull-base), and DVH analysis confirmed minimal deviation (<0.03 Gy for CTV D98% and brainstem D50%, D90%).
Conclusion
The proposed MSPGC-based technique demonstrated a significant reduction in range uncertainty and verified target coverage. Additionally, the visualized dose distributions showed high agreement with treatment plans. These results validate the developed technique as an effective tool for enhancing treatment precision and patient safety in proton therapy, paving the way for adaptive proton therapy.