(Sunday, 7/14/2019) 2:00 PM - 3:00 PM
Room: Stars at Night Ballroom 1
Purpose: Dual-energy computed tomography (DECT) have been shown to provide reduced error in SPR estimation. Dual source (DS) designs provide good temporal and spatial registration between scans and minimize voxel mismatch for computing SPR compared to single-source sequential scans. The methodology for validating DS-DECT calculated SPR and the advantages of using DS-DECT scans with reduced margins is presented for proton planning.
Methods: All CT images used in this study were acquired on a Siemens SOMATOM Drive DS scanner. Dual energy scans were obtained simultaneously using 80kVp and Sn filtered 140kVp energy settings using the kernel Qr32. Single energy CT (SECT) images were obtained using 120kVp with kernel Br32. A dual energy stoichiometric method was used to derive the SPR from DECT scans calibrated with the Gammex 467 phantom. The SPR map was converted to a Synthetic CT with the SPR-to-HU lookup table of the SECT SPR calibration for the inner 32 cm. Validation was performed using animal tissue irradiation with film. Margin reduction and irradiated dose distribution between SECT and DS-DECT plans were quantified for 10 Head and Neck (H&N) patients. The proton plans were robustly optimized for CTV target coverage on SECT and DECT using 3.5% and 2% range uncertainty respectively with 3mm isocenter shifts.
Results: Film measurements with animal tissue for DECT SPR were within 1mm. For H&N plans, the average reduction in the 50%, 70%, and 90% isodose volumes were 6.8%, 7.3%, and 13.3% respectively. An average decrease in esophagus max of 3.0Gy, constrictor mean 1.2Gy, and parotid mean 0.3Gy were achieved with DECT plans.
Conclusion: A DS-DECT was deployed for proton SPR calculation and validated using animal tissue measurements. The reduction in SPR uncertainty leads to lower irradiated normal tissue volumes for head and neck treatments.
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