Purpose: According to the American Cancer Society report in 2022, one in eight men will develop prostate cancer during their lifetime. With the prevalence of the total hip replacement surgery, it is expected that the number of patients with bilateral hip prostheses receiving prostate radiotherapy will increase steadily in the future. This work investigates the treatment planning for advanced prostate cancer patients (pelvic irradiation) with dual hip replacements and evaluates the dosimetric quality of different VMAT planning strategies in comparison with IMRT.
Methods: Three patients with bilateral prosthetic hips were included in this study. Two VMAT planning strategies, avoidance sector (skip arcs) and automated structure avoidance using MLC, were employed to ensure no irradiation of the target volume through the prostheses. For each patient, IMRT plans with 7-9 coplanar beams were also created. Plan quality were compared between VMAT and IMRT plans in the aspects of PTV/CTV coverage, OAR doses, 90%Rx and 105%Rx volumes outside PTV, skin dose, and femoral head dose. Plan robustness were also evaluated for VMAT with structure avoidance by using MLC to block the expanded prostheses with 3/5mm margin to account for the setup uncertainty.
Results: Compared to skip arcs and IMRT, VMAT with avoiding prostheses overall demonstrates improved PTV/CTV coverage and sparing of rectum, bladder, bowels and femoral head. With the presence of lateral beams, structure avoidance technique also greatly reduces the skin dose and high dose volumes outside PTV resulted from nontarget irradiation. Moreover, VMAT plan with structure avoidance shows its robustness in PTV/CTV coverage against prosthesis misalignment (PTV coverage drops from 99.2% to 98.4% and 97.6% and CTV from 99.8% to 99.6% and 98.4% for 3mm and 5mm margins, respectively).
Conclusion: This study demonstrates VMAT with structure avoidance is most favorable for pelvic irradiation planning for prostate patients with dual hip replacements.
Prostate Therapy, Prosthetics, Dose Volume Histograms
TH- External Beam- Photons: treatment planning/virtual clinical studies