Sector analysis of dosimetry of prostate cancer patients treated with low-dose-rate brachytherapy

PurposeBrachytherapy is an effective single treatment modality for low- and intermediate-risk prostate cancer. Here, we compare the radiation doses in different prostate sectors between the preimplant planning images and the postimplant dosimetry.Methods and MaterialsTwo hundred fifteen consecutive patients treated for prostate cancer by ¹²⁵I seed brachytherapy were assessed. Pretreatment plans using transrectal ultrasound images of the prostate were compared with the dose calculated on posttreatment MRI and CT scans obtained 1 month after seed implantation. Twelve sectors were generated by dividing the prostate base, midgland, and apex into four quadrants each. Pretreatment and posttreatment dosimetry were compared between the 12 different sectors of the prostate.ResultsAverage V₁₀₀ (percentage of prostate volume that receives 100% of the prescribed dose) in the preimplant planning images of the prostate was 99.9 ± 0.25% compared with postimplant V₁₀₀ of 94.8 ± 3.77% (p < 0.0001). Prostate V₁₀₀ in the postimplant dosimetry was >91% in all sectors, except the anterior base sector, in which it was 64.87 ± 20.96%. Average 1-month D₉₀ (the dose to 90% of the prostate volume) was 114.5 ± 10.55%. D₉₀ at 1 month compared with preimplant planning was lower in the prostate base and higher in the prostate apex (p < 0.001).ConclusionsOur results show that in ¹²⁵I seed brachytherapy, prostate base receives a lower dose and apex receives a higher dose compared with preimplant planned dose coverage.