Knaup Courtney, Mavroidis Panayiotis, Stathakis Sotirios, Smith Mark, Swanson Gregory, Papanikolaou Niko
Cancer Therapy & Research Center, University of Texas Health Science Center at San Antonio, USA.
J Contemp Brachytherapy. 2011 Sep;3(3):125-30. doi: 10.5114/jcb.2011.24818. Epub 2011 Sep 30.
This study evaluates low dose-rate brachytherapy (LDR) prostate plans to determine the biological effect of dose degradation due to prostate volume changes.
In this study, 39 patients were evaluated. Pre-implant prostate volume was determined using ultrasound. These images were used with the treatment planning system (Nucletron Spot Pro 3.1(®)) to create treatment plans using (103)Pd seeds. Following the implant, patients were imaged using CT for post-implant dosimetry. From the pre and post-implant DVHs, the biologically equivalent dose and the tumor control probability (TCP) were determined using the biologically effective uniform dose. The model used RBE = 1.75 and α/β = 2 Gy.
The prostate volume changed between pre and post implant image sets ranged from -8% to 110%. TCP and the mean dose were reduced up to 21% and 56%, respectively. TCP is observed to decrease as the mean dose decreases to the prostate. The post-implant tumor dose was generally observed to decrease, compared to the planned dose. A critical uniform dose of 130 Gy was established. Below this dose, TCP begins to fall-off. It was also determined that patients with a small prostates were more likely to suffer TCP decrease.
The biological effect of post operative prostate growth due to operative trauma in LDR was evaluated using the concept. The post-implant dose was lower than the planned dose due to an increase of prostate volume post-implant. A critical uniform dose of 130 Gy was determined, below which TCP begun to decline.
本研究评估低剂量率近距离放射治疗（LDR）前列腺计划，以确定由于前列腺体积变化导致的剂量降解的生物学效应。
本研究评估了39例患者。植入前使用超声确定前列腺体积。这些图像与治疗计划系统（Nucletron Spot Pro 3.1(®)）一起用于使用（103）Pd种子创建治疗计划。植入后，使用CT对患者进行成像以进行植入后剂量测定。从植入前和植入后的剂量体积直方图（DVH）中，使用生物有效均匀剂量确定生物学等效剂量和肿瘤控制概率（TCP）。该模型使用RBE = 1.75和α/β = 2 Gy。
植入前和植入后图像集之间的前列腺体积变化范围为-8%至110%。TCP和平均剂量分别降低了高达21%和56%。观察到TCP随着前列腺平均剂量的降低而降低。与计划剂量相比，植入后肿瘤剂量通常观察到降低。确定了130 Gy的临界均匀剂量。低于此剂量，TCP开始下降。还确定前列腺较小的患者更有可能出现TCP降低。
使用该概念评估了LDR中手术创伤导致的术后前列腺生长的生物学效应。由于植入后前列腺体积增加，植入后剂量低于计划剂量。确定了130 Gy的临界均匀剂量，低于该剂量TCP开始下降。
