Dosimetric and Radiobiological Comparison of Volumetric Modulated Arc Therapy, High-dose-rate Brachytherapy and Low-dose-rate Permanent Seeds Implant for Localized Prostate Cancer

Abstract

To assess the dosimetric and radiobiological differences among volumetric modulated arc therapy (VMAT), high-dose-rate (HDR) brachytherapy, and low-dose-rate (LDR) permanent seeds implant treatment of localized prostate cancer. Ten patients with localized prostate cancer were retrospectively selected for this study. Volumetric modulated arc therapy, high-dose-rate brachytherapy and low-dose-rate permanent seeds implant plans were created for each patient. For volumetric modulated arc therapy, planning target volume (PTV) was created by adding a margin of 5 mm to the clinical target volume. Bladder, rectum, femoral heads, urethra, and pelvic tissue were considered as organs at risk. 78 Gy in 39 fractions were prescribed for PTV. The dose prescription was D90 of 34 Gy in 8.5 Gy per fraction and 145 Gy to clinical target volume for HDR (192Ir) and LDR (125I), respectively. The dose and dose volume parameters were evaluated for target and organs at risk. Physical dose were converted to dose based on 2-Gy fractions (equivalent dose in 2 Gy per fraction, EQD2) for comparison of three techniques. All three techniques could achieve the prescribed dose to the target and clinically satisfactory plans. The volume of rectum and bladder exposed to 30-70 Gy (EQD2) was reduced for LDR and HDR when compared with VMAT. The sparing of normal tissue and femoral heads was also significantly improved in LDR and HDR compared with VMAT. The mean dose to urethra was lower in HDR than LDR. Brachytherapy techniques were clearly superior in terms of bladder, rectum, femoral heads and normal tissue sparing compared with VMAT. HDR could further improve the sparing of urethra compared with LDR.