Proton theraPy sPecial feature: full PaPer a planning study of focal dose escalations to multiparametric Mri- defined dominant intraprostatic lesions in prostate proton radiation therapy

potential clinical impact of different treatment schemes for prostate DIL dose escalation reported for both photon EBRT and high-dose rate (HDR) brachytherapy. photon intensity- modulated radiation objectives: The purpose of this study is to investigate the dosimetric effect and clinical impact of delivering a focal radiotherapy boost dose to multiparametric MRI (mp- MRI)- defined dominant intraprostatic lesions (DILs) in prostate cancer using proton therapy. Methods: We retrospectively investigated 36 patients with pre- treatment mp- MRI and CT images who were treated using pencil beam scanning (PBS) proton radiation therapy to the whole prostate. DILs were contoured on co- registered mp- MRIs. Simultaneous integrated boost (SIB) plans using intensity- modulated proton therapy (IMPT) were created based on conventional whole- prostate- irradiation for each patient and optimized with additional DIL coverage goals and urethral constraints. DIL dose coverage and organ- at- risk (OAR) sparing were compared between conventional and SIB plans. Tumor control probability (TCP) and normal tissue complication probability (NTCP) were estimated to evaluate the clinical impact of the SIB plans. results: Optimized SIB plans significantly escalated the dose to DILs while meeting OAR constraints. SIB plans were able to achieve 125, 150 and 175% of prescription dose coverage in 74, 54 and 17% of 36 patients, respec-tively. This was modeled to result in an increase in DIL TCP by 7.3–13.3% depending on α / β and DIL risk