Proton Versus CyberKnife Therapy Planning for Hypofractionated Treatment of Prostate With Focal Boost.

Purpose: To compare intensity-modulated proton therapy with CyberKnife (CK) therapy for hypo-fractionated treatments of prostate with focal boost, as a first planning study for prostate with dose escalation to a dominant intraprostatic lesion (DIL). Materials and Methods: Ten patients who possess one DIL in their prostate and their CK plans that were used to treat the planning target volume of prostate were chosen. Six of the plans were further escalated to DIL. Intensity-modulated proton therapy plans were created for the patients with robust optimization, accounting for setup and range uncertainties for the clinical target volume (CTV) of prostate. The CK plans were then compared with the proton plans. Results: In the worst scenario of the robust evaluation, the proton plans reasonably met all objectives and constraints used in CK planning for both CTV coverage and organs-at-risk (OAR) sparing. Under the nominal scenario of the robust optimization, the proton plans produced dosimetric values comparable to those by the CK plans for both CTV and DIL coverage. The average dose to CTV, outside DIL and urethra, was found lower in the proton plans than in the CK plans due to the uncertainties. A similar trend was observed for the dose conformity to CTV. These two findings, however, were not planning objectives. Regarding organs-at-risk sparing, the proton plans in the nominal scenario were comparable to the CK plans for doses >18.125 Gy; for doses below it, the proton performed better. This study offers a basis for a clinical trial of treatment of prostate cancer by proton that may be transferred from the CK system in our center. Conclusion: The dosimetric objectives and constraints used in the CK plans were achieved with the proton plans.