Multi-parametric MRI guided dose escalated radiotherapy for treatment of localized prostate cancer (PCa): Initial toxicity results of a prospective phase II trial.

25Background: Multi-parametric MRI (mpMRI) of PCa uses advanced sequences to detect aggressive, high grade and bulky lesions. Given known advantages of hypofractionated radiotherapy (RT) to treat PCa (low a/b ratio), we conducted a phase II trial to escalate a high dose to mpMRI lesion(s) via Image-Guided (IG)-RT/Volumetric Arc Therapy (VMAT)/Stereotactic Body Radiotherapy (SBRT) technology. We present the acute toxicity results of this novel approach. Methods: 22 pts with mpMRI lesion(s) were prospectively treated to a course of IGRT/VMAT to the prostate & seminal vesicle +/- pelvic lymph nodes (PLN) to a dose of 45 Gy in 25 fractions followed by SBRT boost, 18 Gy in 3 fraction to the prostate with a simultaneous integrated boost 21 Gy in 3 fractions (EQD2 = 85.2 Gy using a/b 3 or 93.4 Gy using a/b 1.5) to the mpMRI prostatic lesion(s). Placement of 3 polymer based fiducial markers visible in both CT and MRI for image co-registration and treatment guidance was performed. Genitourinary (GU) and gastrointe...