Real-Time Image-Guided Ablative Prostate Cancer Radiation Therapy: Results from the TROG 15.01 SPARK Trial.

PURPOSE: Kilovoltage Intrafraction Monitoring (KIM) is a novel software platform implemented on standard radiation therapy systems enabling real-time image-guided radiation therapy (IGRT). In a multi-institutional prospective trial, we investigated whether real-time IGRT improved the accuracy of the dose prostate cancer patients received during radiation therapy. METHODS AND MATERIALS: Forty-eight patients with prostate cancer were treated with KIM-guided Stereotactic Ablative Radiation Therapy (SABR) with 36.25 Gy in five fractions. During KIM-guided treatment the prostate motion was corrected for by either beam gating with couch shifts or multileaf collimator tracking. A dose reconstruction method was used to evaluate the dose delivered to the target and organs at risk with and without real-time IGRT. Primary outcome was the effect of real-time IGRT on dose distributions. Secondary outcomes included patient-reported outcomes and toxicity. RESULTS: Motion correction occurred in >/=1 treatment for 88% of patients (42/48) and 51% of treatments (121/235). With real-time IGRT, no treatments had prostate CTV D98% dose 5% less than planned. Without real-time IGRT, 13 treatments (5.5%) had prostate CTV D98% doses 5% less than planned. The prostate CTV D98% dose with real-time IGRT was closer to the plan by an average of 1.0% (range -2.8% to 20.3%). Patient outcomes show no change in the 12-month patient reported outcomes compared with baseline and no grade >/=3 GU or GI toxicities. CONCLUSION: Real-time IGRT is clinically effective for prostate cancer SABR.