Proton beam radiotherapy versus three-dimensional conformal stereotactic body radiotherapy in primary peripheral, early-stage non-small-cell lung carcinoma: a comparative dosimetric analysis.

Purpose: Proton radiotherapy (PT) and stereotactic body radiotherapy (SBRT) have the capacity to optimize the therapeutic ratio. We analyzed the dosimetric differences between PT and SBRT in treating primary peripheral early-stage non-small-cell lung cancer.
Methods and Materials: Eight patients were simulated, planned, and treated with SBRT according to accepted techniques. SBRT treatments were retrospectively planned using heterogeneity corrections. PT treatment plans were generated using single-, two-, and three-field passively scattered and actively scanned proton beams. Calculated dose characteristics were compared.
Results: Comparable planning target volume (PTV) median minimum and maximum doses were observed between PT and SBRT plans. Higher median maximum doses 2 cm from the PTV were observed for PT, but higher median PTV doses were observed for SBRT. The total lung mean and V5 doses were significantly lower with actively scanned PT. The lung V13 and V20 were comparable. The dose to normal tissues was lower with PT except to skin and ribs. Although the maximum doses to skin and ribs were similar or higher with PT, the median doses to these structures were higher with SBRT. Passively scattered plans, compared with actively scanned plans, typically demonstrated higher doses to the PTV, lung, and organs at risk.
Conclusions: Single-, two-, or three-field passively or actively scanned proton therapy delivered comparable PTV dose with generally less dose to normal tissues in these hypothetic treatments. Actively scanned beam plans typically had more favorable dose characteristics to the target, lung, and other soft tissues compared with the passively scanned plans. The clinical significance of these findings remains to be determined.