Introduction
To verify the dose sparing effect of hydrogel spacer (SpaceOAR™) on rectal dosimetry for prostate brachytherapy, and to determine whether prostate and rectal dosimetry was affected by the time gap between hydrogel spacer injection and brachytherapy dosimetry.

Material and methods
The 103Pd brachytherapy dosimetry of 174 consecutive intermediate- and high-risk patients injected with hydrogel was compared with a dosimetry of 174 contemporaneous patients without hydrogel injections. Of the SpaceOAR™ patients, 91 had hydrogel injected upon completion of brachytherapy implant, while the remaining 83 patients had hydrogel placed prior to external beam radiation therapy (EBRT), followed 2-10 weeks later by brachytherapy. Brachytherapy implants were either planned with the prostate undistorted by any hydrogel or planned with hydrogel in place. Dosimetry of the prostate and tissues at risk was determined from CT imaging on the day of brachytherapy implant.

Results
SpaceOAR™ significantly reduced mean and maximum rectal doses as well as rectal wall V50, but there was a statistically significant reduction of planning target volume (PTV) D90 to 121.1% of the prescribed dose in hydrogel patients compared to 123.3% in the non-hydrogel patients. Rectal dosimetry was similar between patients injected with hydrogel after brachytherapy and those with spacer injected prior to EBRT. However, patients who had hydrogel placed prior to EBRT had statistically significantly higher dosimetry indices of PTV and urethra relative to those with spacer placed at the completion of brachytherapy.

Conclusions
There was a significant rectal dose sparing in the cohort with hydrogel spacer compared to a reference group without spacer injection. The rectal dose sparing effect was similar in the sub-group of patients injected with hydrogel prior to EBRT and the sub-group injected with hydrogel at the conclusion of brachytherapy.



中文翻译：

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水凝胶垫片放置时间对低剂量率近距离放射治疗植入物前列腺和直肠剂量测定的影响

简介
验证水凝胶垫片 (SpaceOAR™) 对前列腺近距离放射治疗直肠剂量测定的剂量节省效果，并确定前列腺和直肠剂量测定是否受到水凝胶垫片注射和近距离放射治疗剂量测定之间的时间间隔的影响。

材料与方法
将 174 名连续注射水凝胶的中高风险患者的 103Pd 近距离放射治疗剂量测定与 174 名未注射水凝胶的同时期患者的剂量测定进行了比较。在 SpaceOAR™ 患者中，91 名患者在完成近距离放射治疗植入后注射了水凝胶，而其余 83 名患者在外照射放疗 (EBRT) 之前放置了水凝胶，然后在 2-10 周后进行近距离放射治疗。近距离放射治疗植入物要么计划使用任何水凝胶未扭曲的前列腺，要么计划使用适当的水凝胶。前列腺和危险组织的剂量测定是在近距离放射治疗植入当天通过 CT 成像确定的。

结果
SpaceOAR™ 显着降低平均和最大直肠剂量以及直肠壁 V50，但水凝胶患者的计划目标体积 (PTV) D90 显着降低至规定剂量的 121.1%，而非水凝胶患者为 123.3%耐心。近距离放射治疗后注射水凝胶的患者与 EBRT 前注射间隔物的患者的直肠剂量学相似。然而，与在近距离放射治疗完成时放置垫片的患者相比，在 EBRT 之前放置水凝胶的患者 PTV 和尿道的剂量学指数显着更高。

结论
与没有注射间隔物的参考组相比，使用水凝胶间隔物的队列中有显着的直肠剂量节省。在 EBRT 前注射水凝胶的患者亚组和近距离放射治疗结束时注射水凝胶的患者亚组的直肠剂量节省效果相似。