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SBRT has been established as a safe and effective treatment for prostate cancer. SBRT requires high accuracy to reduce treatment margins. Metal hip prostheses create image artifacts, distorting pelvic imaging and potentially decreasing the accuracy of target/organ at risk identification and radiation dose calculations. Data on the safety and efficacy of SBRT after hip replacement is limited. This single-institution study sought to evaluate the safety and local control following SBRT for prostate cancer in men with hip replacements.

Twenty-four patients with localized prostate cancer and a history of pre-treatment hip replacement, treated with SBRT from 2007-2017 at MedStar Georgetown University Hospital, were included in this retrospective analysis. Minimum follow-up was three years. Treatment was delivered using the CyberKnife with doses of 35-36.25 Gy in 5 fractions. The target and OARs were identified and contoured by a single experienced Radiation Oncologist. In treatment planning, care was taken to avoid treatment beams that directly traversed the hip replacement(s). Toxicities were recorded and scored using the Common Terminology Criteria for Adverse Events version 4.0. Local recurrence was confirmed by magnetic resonance imaging and/or prostate biopsy.

The median follow-up was 8 years. The patients were elderly (Median age = 71.5 years) with a high rate of comorbidities (Carlson Comorbidity Index > 2 in 25%). Four patients had bilateral hip replacements.  The majority were low to intermediate risk (91.7%) according to the D’Amico classification.  Median pre-treatment PSA was 6.3 ng/mL.  12.5% received upfront ADT.  Ten were treated with 35 Gy and 14 were treated with 36.25 Gy.  The rates of late > Grade 3 GU toxicity and late > Grade 2 GI toxicity were 8.3% and 4.2%, respectively, with no Grade 4 or 5 toxicities.  Six patients (25%) developed a local recurrence at a median time of 7.5 years. Of these six patients, four had unilateral hip replacements and two had bilateral. Three underwent salvage cryotherapy and three received salvage ADT. 

Local recurrence and high-grade late toxicity are uncommon following prostate SBRT in the general population. However, in this cohort of patients with prior hip replacements, prostate SBRT had higher than expected rates of both.  In the opinion of the authors, such patients should be counseled on these elevated risks and treatment alternatives. Brachytherapy, with its ultrasound guidance, circumvents CT image artifact interference, while moderately-hypofractionated/conventionally-fractionated IMRT utilizes larger treatment margins and is therefore less susceptible to target miss. Both represent preferable radiation options in this patient population. If these patients are treated with SBRT, they should be monitored for local recurrence so early salvage can be performed. It is hoped that recent advances in metal artifact reduction techniques and dose-calculation algorithms will improve future outcomes.