Prostate radiotherapy in the setting of bilateral hip prostheses: All commonly used photon-based radiation approaches are feasible

Abstract

The prevalence of hip prostheses is increasing. Prostate radiation delivery in the setting of hip prostheses is complicated by both imaging artifacts that interfere with volume delineation and dosimetric effects that must be addressed in the planning process. We hypothesized that with specialized planning, any photon-based definitive prostate radiotherapy approach may be utilized in patients with bilateral hip prostheses. Imaging data from sequential patients with prostate cancer and bilateral hip prostheses treated definitively with radiation were retrospectively reviewed. Bimodality imaging was used to define targets and organs at risk (OARs) along with specialized MRI sequences and/or orthopedic metal artifact reduction (OMAR) for MRI and CT artifact suppression, respectively. Multiple VMAT plans were generated for each set of patient images to include three fractionation schemes (conventional, hypofractionated, and SBRT), each with hip avoidance and with simulated normal hip. The ability to meet standard dose constraints was assessed for each plan type. Differences in target and OAR dosing between plans accounting for prosthetic hips via avoidance vs plans with simulated absence of prosthetic hip were also assessed. T-tests were used to compare dosimetric parameters. Ten patients with bilateral hip prostheses were identified, and 6 plans were created for each patient for a total of 60 radiation plans. Prosthetic hip avoidance did not result in failure to meet dose constraints for any patient. Hip avoidance resulted in minimal increases in high dose to the rectum and bladder (increases in mean V80%, V90%, and V95% ranged from 0.1% to 2.4%). Larger increases were seen at lower dose levels, with rectal V50% significantly increased in all three plan types with hip avoidance (conventional: 26.0% [standard deviation, SD 13.9] vs 16.9% [SD 10.2, p = 0.003]; hypofractionation: 26.4% [SD 13.3] vs 17.1% [SD 10.1, p = 0.002]; SBRT: 18.3% [SD 10.7] vs 10.5% [SD 6.9, p = 0.008]). Similarly, hip avoidance resulted in increases in bladder V50% to 31.7% (SD 16.8) vs 23.3% (SD 14.0, p = 0.001), 31.3% (SD 17.0) vs 23.3% (SD 13.8, p = 0.002), and 22.7% (SD 12.3) vs 16.5% (SD 12.6, p < 0.001) for conventional, hypofractionated, and SBRT plans, respectively. Hydrogel spacer resulted in reductions in rectal dose. For example, V70% for hip avoidance plans decreased with spacer presence to 8.3% (SD 6.7) vs 21.1% (SD 5.8, p = 0.021), 8.6% (SD 6.5) vs 21% (SD 5.7, p = 0.022), and 3.7% (SD 3.2) vs 15% (SD 8.2, p = 0.010) for conventional, hypofractionated, and SBRT plans, respectively. Any photon-based definitive prostate radiotherapy approach can be used with bimodality imaging for target and OAR definition and planning techniques to avoid dose attenuation effects of hip prostheses. Hydrogel spacer is a useful adjunct.

Keywords: Hip implant; IMRT; Rectal constraint; Rectal tolerance.