TH‐A‐BRA‐04: Evaluation of Three IGRT Approaches for Prostate Cancer Treatment

Purpose: To evaluate two online IGRT and one hybrid adaptive modification for prostate cancertreatment with onboard CBCTimager.Methods: Two online IGRT and one hybrid adaptive modification were simulated and evaluated retrospectively using daily CBCTimages obtained from 5 prostate cancer patients treated with total dose 64Gy in 20 fractions. For each daily treatment, two CBCTs obtained at the pre‐ and post‐treatment delivery were used in the study. Online IGRT techniques include (1) Online‐ correction: a pre‐treatment IMRT plan with 3mm CTV‐to‐PTV margin was delivered following the CBCTimaging and online target position correction; and (2) Online‐planning: an online inverse plan designed on the pre‐ treatmentCBCTimage with 3mm target margin was accomplished and delivered. The Hybrid‐adaptation consists of the online prostate position correction and delivery of a pre‐treatment IMRT plan with no target margin for the first week of the treatment, and an offline adaptive inverse planning with using the planning CT and the first week of post‐treatment CBCTimages for the remaining treatment.Treatment dose for all 3 approaches were constructed using all the post‐treatment CBCTimages. Evaluations were all performed using the treatment dose distribution in organs of interest for all patients. Results: The minimal delivered dose (D99) in CTV (prostate + seminal vesicle) is in the range of [51.6, 65.6]Gy for Online‐ correction; [63.2, 66.1]Gy for Online‐planning; and [62.8, 66.1]Gy for the Hybrid‐adaptation. The rectal volume with 62.6Gy, V62.6, for Online‐ correction, Online‐planning, Hybrid‐adaptation are 0.7+/−1.0%, 0.4+/−0.2%, 0.5+/−1.0%; the rectal V59.4 are 2.1+/−1.8%, 1.5+/‐1.1%, 1.6+/−1.9%; and V56.5 are 4.0+/−3.2%, 3.0+/−2.2%, 3.5+/−3.2%. The bladder volume dose, V64.1, are 2.3+/−2.2%, 0.5+/−0.6%, 0.4+/−0.3%, and V59.4 are 5.2+/−3.6%, 2.0+/−1.1%, 1.6+/−0.8% respectively for the 3 approaches. Conclusions: Both Online‐planning and Hybrid‐adaptation achieved comparable target coverage and normal tissue sparing, and were superior to Online‐correction. However, Hybrid‐adaptation is more efficiency in clinical practice. This research was partially supported by Elekta.