Introduction
The purpose of this technical note was to investigate correlation of total reference air-kerma (TRAK) with volume enclosed by the prescription isodose surface in vaginal cylinder high-dose-rate (HDR) brachytherapy.

Material and methods
Treatment plans of 175 gynecological cancer patients treated at our institution with iridium-192 (192Ir) HDR brachytherapy using a single-channel vaginal cylinder applicator were retrospectively reviewed. Applicator size in diameter ranged from 20 mm to 40 mm. Treatment length ranged from 30 mm to 90 mm (median, 50 mm). Brachytherapy fractional dose was 5 Gy (DoseRef) prescribed to 5 mm distance from cylinder surface. Parameters TRAK (cGy), source activity during treatment (Ci), total treatment time (s), and prescription isodose surface volume ISVRef (cm3) were recorded from individual treatment plans. In each case, vaginal tissue volume (VVT) enclosed by prescription isodose was calculated by subtracting cylinder volume enclosed by the prescription isodose from ISVRef.

Results
Total reference air-kerma correlated with the total volume enclosed by the prescription isodose via ISVRef = 4768 × (TRAK/DoseRef)1.47. TRAK related linearly to the volume of vaginal tissue enclosed by the prescription dose via VVT = ((138.3 × TRAK) – 8.2). Secondarily, TRAK related to the treatment time through time (s) = 882 (s/cGy) × TRAK (cGy), where 882 is (1/air-kerma strength) for 10 Ci apparent activity of 192Ir source.

Conclusions
The correlation of TRAK to the vaginal tissue volume encompassed by the prescription dose surface yields a useful predictive equation. The TRAK treatment time relationship enables quick verification of planned treatment time by knowing TRAK in any HDR brachytherapy application.



中文翻译：

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总参考空气比释动能 (TRAK) 与阴道圆柱高剂量率近距离放射治疗中处方等剂量表面积的相关性

简介
本技术说明的目的是研究总参考空气比释动能 (TRAK) 与阴道圆筒高剂量率 (HDR) 近距离放射治疗中处方等剂量表面所包围的体积的相关性。

材料与方法
回顾性回顾了在我们机构使用单通道阴道圆筒涂药器接受铱-192 (192Ir) HDR 近距离放射治疗的 175 名妇科癌症患者的治疗计划。直径的涂抹器尺寸范围为 20 毫米至 40 毫米。治疗长度范围从 30 毫米到 90 毫米（中位数，50 毫米）。近距离放射治疗分次剂量为 5 Gy (DoseRef)，距离圆柱体表面 5 毫米。参数 TRAK (cGy)、治疗期间的源活动 (Ci)、总治疗时间 (s) 和处方等剂量表面体积 ISVRef (cm3) 从各个治疗计划中记录下来。在每种情况下，处方等剂量所包含的阴道组织体积 (VVT) 是通过从 ISVRef 中减去处方等剂量所包含的圆柱体体积来计算的。

结果
通过 ISVRef = 4768 × (TRAK/DoseRef)1.47，总参考空气比释动能与处方等剂量所包含的总体积相关。TRAK 通过 VVT = ((138.3 × TRAK) – 8.2) 与处方剂量所包围的阴道组织体积线性相关。其次，TRAK 与治疗时间相关（s）= 882（s/cGy）× TRAK（cGy），其中 882 是（1/空气比释动能强度），用于 192Ir 源的 10 Ci 表观活性。

结论
TRAK 与处方剂量表面所包含的阴道组织体积的相关性产生了一个有用的预测方程。TRAK 治疗时间关系可以通过在任何 HDR 近距离放射治疗应用中了解 TRAK 来快速验证计划的治疗时间。