Okamoto Hiroyuki, Aikawa Ako, Wakita Akihisa, Yoshio Kotaro, Murakami Naoya, Nakamura Satoshi, Hamada Minoru, Abe Yoshihisa, Itami Jun
Department of Radiation Oncology, National Cancer Center Hospital, 104-0045, Tokyo, Japan.
J Radiat Res. 2014 Jul;55(4):780-7. doi: 10.1093/jrr/rru001. Epub 2014 Feb 23.
The influence of deviations in dwell times and source positions for (192)Ir HDR-RALS was investigated. The potential dose errors for various kinds of brachytherapy procedures were evaluated. The deviations of dwell time ΔT of a (192)Ir HDR source for the various dwell times were measured with a well-type ionization chamber. The deviations of source position ΔP were measured with two methods. One is to measure actual source position using a check ruler device. The other is to analyze peak distances from radiographic film irradiated with 20 mm gap between the dwell positions. The composite dose errors were calculated using Gaussian distribution with ΔT and ΔP as 1σ of the measurements. Dose errors depend on dwell time and distance from the point of interest to the dwell position. To evaluate the dose error in clinical practice, dwell times and point of interest distances were obtained from actual treatment plans involving cylinder, tandem-ovoid, tandem-ovoid with interstitial needles, multiple interstitial needles, and surface-mold applicators. The ΔT and ΔP were 32 ms (maximum for various dwell times) and 0.12 mm (ruler), 0.11 mm (radiographic film). The multiple interstitial needles represent the highest dose error of 2%, while the others represent less than approximately 1%. Potential dose error due to dwell time and source position deviation can depend on kinds of brachytherapy techniques. In all cases, the multiple interstitial needles is most susceptible.
研究了（192）铱高剂量率后装近距离放疗中驻留时间和源位置偏差的影响。评估了各种近距离治疗程序的潜在剂量误差。使用井型电离室测量（192）铱高剂量率源在不同驻留时间下的驻留时间偏差ΔT。源位置偏差ΔP通过两种方法测量。一种是使用校验尺装置测量实际源位置。另一种是分析驻留位置之间间隙为20mm的情况下，用射线照相胶片照射后的峰值距离。使用以ΔT和ΔP作为测量值的1σ的高斯分布计算复合剂量误差。剂量误差取决于驻留时间以及从感兴趣点到驻留位置的距离。为了评估临床实践中的剂量误差，从涉及圆柱形容器、串形卵形体、带组织间针的串形卵形体、多根组织间针以及体表模具施源器的实际治疗计划中获取驻留时间和感兴趣点距离。ΔT和ΔP分别为32ms（不同驻留时间中的最大值）以及0.12mm（校验尺测量值）、0.11mm（射线照相胶片测量值）。多根组织间针代表的最高剂量误差为2%，而其他的代表误差小于约1%。由于驻留时间和源位置偏差导致的潜在剂量误差可能取决于近距离治疗技术的种类。在所有情况下，多根组织间针最敏感。
