Intensity-Modulated vs. Conformal Radiotherapy after Prostate Seed Implant Brachytherapy Regarding Summed Rectal Dose

Purpose: To disclose effectiveness of substitution of conformal radiotherapy (CRT) with intensity-modulated radiotherapy (IMRT) in combined with 125I permanent seed brachytherapy(BT) in reducing a rectal dose-volume parameter recently proven to be correlated with late rectal bleeding after the combined radiotherapy. Materials/Methods: A CT image set obtained a month after BT was used for CRT and tentative IMRT planning as well as dosimetry of BT (post plan). Physical dose of each DICOM-RT was converted to biologically effective dose under α/β of 3(Gy3) for three dimensional summation of rectal volume exposed to 150 Gy3 (rV150 (3)). Alteration of the value along BT, BT combined with CRT (BT+CRT), and BT combined with IMRT (BT+IMRT) was traced individually, and the mean value were statistically compared between the modalities. Results: The elevation rate of rV150 (3) from BT to BT+CRT is proportional to their rV150 (3) of BT. All rV150 (3) was decreased from BT+CRT to BT+IMRT except 3 cases with smaller rV150 (3) at BT+CRT. The mean rV150 (3) values of BT, BT+CRT, and BT+IMRT were 0.06 ± 0.09 cc, 1.41 ± 0.88, and 1.18 ± 0.75 cc, respectively, showing significant differences between all values. Conclusions: The substitution of CRT with IMRT in conjunction with seed implant brachytherapy reduces the rectal dose predisposing bleeding. Avoiding rectal exposure to high doses during BT is important even in BT+IMRT. Short Communication Intensity-Modulated vs. Conformal Radiotherapy after Prostate Seed Implant Brachytherapy Regarding Summed Rectal Dose Ryuji Nakamura1*, Koyo Kikuchi1, Satoshi Yamaguchi1, Hisao Kakuhara1, Jun Sugawara2, Hirobumi Oikawa1, and Hisanori Ariga1 1Department of Radiology, Iwate Medical University, Japan 2Department of Radiology, Iwate Prefectural Chubu Hospital, Japan