Aggregated Plan Robustness Analyses for Spot-Scanned Pancreatic Stereotactic Body Proton Therapy

Abstract

minimum dose of at least 39.2 GyE was achieved in 95% of the plans. Multicomparative and 2-sample t-tests were used. Results: The median GTV and CTV volumes were 43.9 and 56.9 cc, respectively. With median minimum separation from GTV of 0.15 cm (range, 0.0-1.6 cm), the duodenum was the most difficult organ-at-risk (OAR) for meeting dosimetric constraints, especially in the CTV+7 mm cases. For CTV+5 mm planning, selected IMRT and SBPT dosimetric values are shown in Table; P-values were calculated across all 4 proton groups. The integral dose was significantly better for proton vs. IMRT plans (V5Gy, 1663 vs. 3285 cc, P Z 0.0064), as for multiple other OARs. While most proton plans were acceptable, 4-mm spot plans gave slightly less dose to the OAR structures owing to a smaller spot size, but the binary differences (vs. 6-mm spot) were not statistically significant in most cases. Conclusions: Benchmarked against IMRT planning, pancreatic SBPT offers comparable duodenal sparing with significant improvements in most OAR dosimetric metrics considered, which represents an attractive therapeutic option. Under static proton planning considerations, MFO vs. SFO differences were generally not statistically significant. As expected, smaller spot size trended for better OAR sparing. Further proton plan robustness evaluations are warranted to determine the optimal combination of spot size, optimization technique, and target volume for spot placement in spotscanned SBPT. Author Disclosure: T.T. Sio: None. E.J. Tryggestad: None. J.B. Ashman: None. C.J. Beltran: None. W.S. Harmsen: None. K.A. Hoeft: None. S.K. Wurgler: None. R.C. Miller: None.