MRI Guided SBRT for Localized Prostate Cancer

This study utilizes advanced imaging techniques (mpMRI prostate scan) to select and stratify patients for two different radiotherapy regimens based on the presence/absence of identifiable intraprostatic lesions. In patients without identifiable prostate cancer lesions, SBRT to the prostate in 5 sessions (fractions) will be administered. In patients with MRI-identified lesion(s), pelvic IMRT in 25 fractions will be administered followed by an SBRT prostate boost while simultaneously treating the prostate cancer lesion(s) to a higher dose in 3 fractions.

Radiotherapy (RT) is considered standard of care treatment for prostate cancer. Conventional RT regimens consist of 8-9 weeks of daily RT. Recent data support the use of hypofractionated RT (5-6 weeks) due to similar disease control in a contracted treatment time. This study combines the benefits of RT dose escalation while shortening the overall RT treatment course. In this protocol, patients will undergo a pretreatment mpMRI prostate scan and be stratified to two separate SBRT regimens depending on whether prostate lesions are present. For patients without any positive mpMRI lesions, an SBRT monotherapy (36.25 Gy in 5 fractions) approach will be utilized. Patients with an equivocal or positive mpMRI lesion(s), will receive IG-IMRT (45 Gy in 25 fractions) to prostate and seminal vesicle +/- lymph nodes followed by a SBRT whole prostate boost (18 Gy in 3 fractions) with a simultaneously integrated boost (SIB) (21 Gy in 3 fractions) to intraprostatic lesion(s) only. Patients will be regularly assessed every 3 months for the first 2 years and then every 6 months, indefinitely. Side effects will be monitored using the standardized international prostate symptom score (I-PSS) and Sexual Health Inventory of Men (SHIM) questionnaires at baseline and subsequent follow-up appointments. Hypothesis: MRI-guided treatment planning and delivery can selectively target high-risk prostate cancer nodules and deliver a higher effective RT dose, to achieve maximal tumor control without increasing toxicity, all in a shortened treatment duration.