Mehta Shahil, Farnia Benjamin, de la Zerda Alberto, Rahimi Robabeh, Wolfson Aaron, Portelance Lorraine
Department of Radiation Oncology, Sylvester Comprehensive Cancer Center/University of Miami Miller School of Medicine, Miami, FL, United States.
Department of Radiation Oncology, Jackson Memorial Hospital/University of Miami Miller School of Medicine, Miami, FL, United States.
J Contemp Brachytherapy. 2019 Dec;11(6):584-588. doi: 10.5114/jcb.2019.90435. Epub 2019 Dec 6.
Smit sleeves are used to facilitate insertion of the intrauterine tandem during brachytherapy for cervical cancer. When a tandem and ovoids system is used the base of the Smit sleeve displaces the ovoids distally. The dosimetric impact of this displacement is not known. Herein we performed a dosimetric analysis to quantify this impact on the integral dose and dose delivered to the organs at risk (OARs).
Eleven high-dose-rate brachytherapy plans in which a Smit sleeve was used with a tandem and ovoids were reviewed. A second set of plans was generated modifying the position of the ovoids to simulate absence of the Smit sleeve. The high-risk clinical tumor volume (HR-CTV) dose coverage was maintained the same for both sets of plans by appropriately rescaling the dwell times of the simulated plan. The mean integral dose, D to the OARs (bladder, bowel, sigmoid and rectum) and the ICRU rectum point dose were compared between the original and modified plans using a paired two-sample -test.
Simulating removal of the Smit sleeve was associated with an average reduction in the mean integral dose of 6.1% ( < 0.001) and an average reduction of 10.9% ( = 0.004) to the rectal D. Doses to the remaining OARs decreased to a lesser magnitude with only that of the sigmoid being statistically significant.
The use of a Smit sleeve with a tandem and ovoids system could lead to the delivery of a higher mean integral dose to achieve similar HR-CTV coverage. In addition, it could increase the dose to surrounding OARs, primarily the rectum. The clinical significance of these findings is unknown, but the potential dosimetric impact of using a Smit sleeve should be taken into consideration during the planning when this device is used.
施密特套管用于在宫颈癌近距离放射治疗期间便于插入子宫内串联装置。当使用串联和卵圆体系统时，施密特套管的底部会将卵圆体向远侧移位。这种移位对剂量学的影响尚不清楚。在此，我们进行了剂量学分析，以量化这种对总剂量和输送到危及器官（OARs）的剂量的影响。
回顾了11个使用施密特套管与串联和卵圆体的高剂量率近距离放射治疗计划。生成了第二组计划，通过修改卵圆体的位置来模拟施密特套管不存在的情况。通过适当重新调整模拟计划的驻留时间，使两组计划的高危临床肿瘤体积（HR-CTV）剂量覆盖保持相同。使用配对双样本t检验比较原始计划和修改后计划之间OARs（膀胱、肠道、乙状结肠和直肠）的平均总剂量、D以及ICRU直肠点剂量。
模拟移除施密特套管与平均总剂量平均降低6.1%（P<0.001）以及直肠D平均降低10.9%（P = 0.004）相关。输送到其余OARs的剂量降低幅度较小，只有乙状结肠的剂量降低具有统计学意义。
使用带有串联和卵圆体系统的施密特套管可能会导致输送更高的平均总剂量以实现相似的HR-CTV覆盖。此外，它可能会增加对周围OARs的剂量，主要是直肠。这些发现的临床意义尚不清楚，但在使用该装置进行计划时，应考虑使用施密特套管的潜在剂量学影响。
