Pieters Bradley R, van de Kamer Jeroen B, van Herten Yvonne R J, van Wieringen Niek, D'Olieslager Greet M, van der Heide Uulke A, Koning Caro C E
Department of Radiation Oncology, Academic Medical Center/University of Amsterdam, Amsterdam, The Netherlands.
Radiother Oncol. 2008 Jul;88(1):46-52. doi: 10.1016/j.radonc.2008.02.023. Epub 2008 Apr 2.
The two main modalities to deliver high dose to the prostate and prevent high doses to neighboring organs are intensity modulated radiotherapy (IMRT) or external beam radiotherapy combined with brachytherapy. Because of the different biological effectiveness the physical dose distributions were converted to 3-dimensional linear quadratic dose at 2 Gy per fraction (EQD(2)). From the latter, cumulative EQD(2)-volume histograms were determined for comparison of the modalities.
An IMRT plan was made on the contoured planning target volume (PTV1) and organs at risk (OAR) of 20 patients (IMRT-only). A dose of 70 Gy was prescribed on the PTV1 with a concomitant boost to a total of 76 Gy on a subvolume (PTV2). Also a 46 Gy IMRT plan was made combined with either a pulsed dose-rate (PDR) or a high dose-rate (HDR) brachytherapy boost. The EQD(2) on the PTV1 of the combined IMRT-PDR and IMRT-HDR plans were made equivalent to the EQD(2) of the 70 Gy IMRT-only plan. The alpha/beta-ratio for prostate was set to 1.5 Gy and 10 Gy. For normal tissues an alpha/beta-ratio of 3.0 Gy was taken. Several EQD(2)-volume histogram parameters were calculated for comparison and analyzed by two-way ANOVA.
The mean EQD(2) to 95% of the prostate volume was slightly higher for the IMRT-only plan than for the brachytherapy modalities (P<0.001), in contrast to the mean EQD(2) to 50% of the prostate volume in which the opposite was the case (P<0.001). Rectum and bladder doses for IMRT-only are significantly higher (P<0.001). The urethra dose for IMRT-HDR was much higher than the other modalities only when the alpha/beta-ratio for prostate was 10 Gy.
Because of the high doses within an implant, the dose in 50% of the prostate volume is much higher with the brachytherapy modalities than IMRT-only which may have clinical consequences. With brachytherapy the doses to the OAR are lower or similar to IMRT-only. Dose escalation for prostate tumors is more easily achieved with brachytherapy than with IMRT alone. Therefore, brachytherapy might be the preferred modality to achieve further dose escalation.
将高剂量精准投送至前列腺并避免对邻近器官造成高剂量照射的两种主要方式是调强放疗（IMRT）或外照射放疗联合近距离放疗。由于生物效应不同，物理剂量分布被转换为每分次2 Gy的三维线性二次剂量（EQD(2)）。据此确定累积EQD(2) - 体积直方图，以比较不同方式。
针对20例患者的轮廓化计划靶区（PTV1）和危及器官（OAR）制定IMRT计划（单纯IMRT）。PTV1处方剂量为70 Gy，同时对一个子体积（PTV2）追加剂量至总计76 Gy。还制定了46 Gy的IMRT计划，并联合脉冲剂量率（PDR）或高剂量率（HDR）近距离放疗追加剂量。使IMRT - PDR和IMRT - HDR联合计划中PTV1的EQD(2)等同于单纯70 Gy IMRT计划的EQD(2)。前列腺的α/β比值设定为1.5 Gy和10 Gy。对于正常组织，α/β比值取3.0 Gy。计算多个EQD(2) - 体积直方图参数进行比较，并通过双向方差分析进行分析。
单纯IMRT计划中前列腺体积95%的平均EQD(2)略高于近距离放疗方式（P < 0.001），而前列腺体积50%的平均EQD(2)情况则相反（P < 0.001）。单纯IMRT的直肠和膀胱剂量显著更高（P < 0.001）。仅当前列腺的α/β比值为10 Gy时，IMRT - HDR的尿道剂量远高于其他方式。
由于植入体内的剂量较高，近距离放疗方式下前列腺体积50%的剂量远高于单纯IMRT，这可能会产生临床后果。采用近距离放疗时，对危及器官的剂量低于或类似于单纯IMRT。与单纯IMRT相比，近距离放疗更容易实现前列腺肿瘤的剂量递增。因此，近距离放疗可能是实现进一步剂量递增的首选方式。
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