High Dose Rate Prostate Brachytherapy: Dose Escalation to Dominant Intra-prostatic Nodule

Overview

This study will investigate the feasibility of using technology of ultrasound guided HDR brachytherapy to focally increase dose to regions within the prostate that are heavily infiltrated with cancer. Such regions, referred to as dominant intraprostatic lesions (DIL) can be visualized using diffusion contrast enhanced MRI employing an endo-rectal coil. The magnetic resonance (MR) images can be fused with the planning transrectal ultrasound (TRUS) prior to the brachytherapy procedure to design a dose distribution that will encompass the malignant volume with higher than the prescription dose. By its nature, brachytherapy has subvolumes that receive (for example)125% of the prescription dose or 150% of the prescription dose. With TRUS-guided and TRUS-planned HDR these areas can be manipulated to coincide with the DIL. The limit of dose escalation has been reached at whole prostate external beam doses of 81-86 Gy and still failure rates for intermediate and high risk disease are unacceptable. There is much interest in focal dose escalation and TRUS-guided HDR brachytherapy is perfectly suited to achieving this.

Methods: If a dominant nodule is visualized on dynamic contrast enhanced (DCE) MRI, it will be contoured in 3D and the images fused to the planning TRUS study that is done in preparation for brachytherapy (of any type: seeds or HDR). The patient's treatment will consist of the standard combined external beam (4600 centiGray (cGy) in 23 fractions) and HDR brachytherapy boost (2 fractions of 1000 cGy given on days 5 and 15 of the external beam course). During each HDR treatment the plan will be manipulated such that the normally occurring high dose regions (125%, 150%) are positioned at the site of the identified disease. Normally approximately 60% of the prostate volume receives 125% of the dose and 30% receives 150%. By ensuring that the inherent dosimetry favors treatment of the known cancer, no region of the prostate would be "underdosed". HDR treatments are performed under general anesthesia as an out patient procedure. Statistical Analysis: This is a feasibility study and the data reported will be descriptive including the frequency with which the DIL can be visualized in this population, the DIL volume compared to total prostate volume, and the isodose that can encompass the DIL without violating dose constraints to adjacent organs (urethra and bladder). Toxicity will be monitored and efficacy will be assessed by repeat DCE MRI at 12 months and biopsy at 30 months.