Targeting Prostate Cancer through High Dose Rate Brachytherapy
Abstract
While prostate cancer is not typically an aggressive disease, it can be lethal for some patients. Treatment of the disease has proven to be effective; however, when the disease recurs locally it does so most commonly at the site of the dominant intraprostatic lesion (DIL). An effective treatment method for prostate cancer is high dose rate brachytherapy (HDR-BT). This is a radiation therapy where a radioactive seed is interstitially inserted into the patient to deliver the radiation dose. It was the goal of this work to utilize preprocedural imaging and pathological data from radical prostatectomy specimens to investigate methods to dose escalate DILs. The first objective was to establish a baseline range of doses that DILs would receive within clinically standard whole-gland HDR-BT treatment plans. To execute this objective, DILs were retrospectively registered within previously implemented HDR-BT plans to analyze DIL dose. The next objective was to investigate targeting mpMRI and PSMA-PET DILs and to determine if this would translate to escalated dose to the pathologically defined cancer. This was performed by retrospectively developing mpMRI and PSMA-PET DIL targeted treatment plans and comparing the doses delivered to co-registered digital histology between targeted and whole-gland plans. The final investigation that was performed aimed to determine an optimal margin to be added to the mpMRI DILs to increase dose to the pathologically confirmed cancer . To do so, we created mpMRI targeted HDR-BT treatment plans with varying margins added to the DIL and analyzed the dose that would have been delivered to the pathologically confirmed cancer. The results of this work demonstrated that while most DILs would receive the prescription dose during HDR-BT, up to 26% may receive less than the intended dose . Secondly, it was shown that by targeting predefined DILs on mpMRI or PSMA-PET with a boost of 130% of the 15-Gy prescription resulted in an average increase of 1.3 Gy to the pathologically defined high-grade disease in comparison to standard whole-gland plans. Lastly, there is the potential to further increase the dose to the pathologically confirmed disease by adding an expansion margin of 1 mm to the mpMRI-defined DILs.