Fröhlich Georgina, Kovács Kinga Dóra, Major Tibor, Polgár Csaba
National Institute of Oncology, Centre of Radiotherapy, Ráth György Street 7-9, Budapest H-1122, Hungary.
Eötvös Loránd University, Faculty of Science, Pázmány Péter mall 1/A, Budapest H-1117, Hungary.
Rep Pract Oncol Radiother. 2019 Mar-Apr;24(2):158-164. doi: 10.1016/j.rpor.2019.01.004. Epub 2019 Feb 14.
To investigate the feasibility of in vivo rectal dosimetry in image-guided adaptive brachytherapy of cervical cancer.
Error of measurement of dose rate in a semiconductor diode probe was investigated depending on the distance and angle in water, and on temperature in a polymethyl methacrylate phantom using an Ir-192 source. Furthermore, the difference between the measured and calculated dose was analysed in the interstitial brachytherapy of 30 cervix cancer patients. The relationship between in vivo measured dose, calculated dose in the point of the diode, calculated maximal dose in the point of the diodes and calculated maximal dose of the rectum were examined.
The dosimeter measured with 85% accuracy at more than 5 cm from the source, but within a closer distance the accuracy decreased significantly. At 45-90° angle, the device measured with a 15% error. The error increased with the temperature, 22% at 35 °C. In 8 cases (26.7%) the maximal dose was measured in the correct diode. The device measured 73% of the calculated dose in the point of the diode. The maximum of the calculated doses of diodes was 60% of the calculated maximal dose. The in vivo measured dose was 35% of the calculated maximal dose.
Under treatment conditions, the semiconductor diode does not provide reliable measured data. The probe pushes the rectal wall closer to the high dose areas and underestimates the dose of it. Semiconductor probe is not recommended for in vivo dosimetry of the rectum in image-guided brachytherapy of cervical cancer.
探讨在宫颈癌图像引导下的自适应近距离放射治疗中进行体内直肠剂量测定的可行性。
使用铱 - 192源，在水模中研究半导体二极管探头剂量率测量误差与距离、角度的关系，以及在聚甲基丙烯酸甲酯体模中研究其与温度的关系。此外，分析了30例宫颈癌患者组织间近距离放射治疗中测量剂量与计算剂量之间的差异。研究了体内测量剂量、二极管位置的计算剂量、二极管位置的计算最大剂量与直肠计算最大剂量之间的关系。
剂量计在距离源超过5 cm处测量精度为85%，但在更近的距离内精度显著下降。在45 - 90°角度时，该设备测量误差为15%。误差随温度升高而增加，在35°C时为22%。在8例（26.7%）中，在正确的二极管中测量到最大剂量。该设备在二极管位置测量到计算剂量的73%。二极管计算剂量的最大值为计算最大剂量的60%。体内测量剂量为计算最大剂量的35%。
在治疗条件下，半导体二极管不能提供可靠的测量数据。探头将直肠壁推向高剂量区域并低估其剂量。不建议在宫颈癌图像引导近距离放射治疗中使用半导体探头进行直肠的体内剂量测定。
