Cancer is a major societal public health and economic problem, responsible for one in every six deaths. Radiotherapy is the main technique of treatment for more than half of cancer patients. To achieve a successful ou...Cancer is a major societal public health and economic problem, responsible for one in every six deaths. Radiotherapy is the main technique of treatment for more than half of cancer patients. To achieve a successful outcome, the radiation dose must be delivered accurately and precisely to the tumor, within ± 5% accuracy. Smaller uncertainties are required for better treatment outcome. The objective of the study is to investigate the uncertainty of measurement of external radiotherapy beam using a standard ionization chamber under reference conditions. Clinical farmers type ionization chamber measurement was compared against the National Reference standard, by exposing it in a beam 60Co gamma source. The measurement set up was carried out according to IAEA TRS 498 protocol and uncertainty of measurement evaluated according to GUM TEDDOC-1585. Evaluation and analysis were done for the identified subjects of uncertainty contributors. The expanded uncertainty associated with 56 mGy/nC ND,W was found to be 0.9% corresponding to a confidence level of approximately 95% with a coverage factor of k = 2. The study established the impact of dosimetry uncertainty of measurement in estimating external radiotherapy dose. The investigation established that the largest contributor of uncertainty is the stability of the ionization chamber at 36%, followed by temperature at 22% and positioning of the chamber in the beam at 8%. The effect of pressure, electrometer, resolution, and reproducibility were found to be minimal to the overall uncertainty. The study indicate that there is no flawless measurement, as there are many prospective sources of variation. Measurement results have component of unreliability and should be regarded as best estimates of the true value. .展开更多
目的:对常用4种新型进口及国产医用诊断X射线剂量仪的能量响应特性进行比较研究。方法:在国际原子能机构(IAEA)北京二级标准剂量学实验室(SSDL)的标准辐射场中,采用替代法分别完成10种管电压为60~150 k V、管电流为10 m A、用2.5 mm Al...目的:对常用4种新型进口及国产医用诊断X射线剂量仪的能量响应特性进行比较研究。方法:在国际原子能机构(IAEA)北京二级标准剂量学实验室(SSDL)的标准辐射场中,采用替代法分别完成10种管电压为60~150 k V、管电流为10 m A、用2.5 mm Al(毫米铝)做附加过滤的X射线诊断辐射线质进行比对测量。结果:国产RD-98诊断剂量仪与进口剂量仪的能量响应性能,在60~150 k V的X射线范围内,不同能量对剂量的响应均在±5%以内。结论:4种新型诊断X射线剂量仪的能量响应特性均良好,半导体探测器的诊断剂量仪与空气电离室剂量仪,不同能量对剂量的响应均符合国际电工委员会(IEC)的要求。展开更多
文摘Cancer is a major societal public health and economic problem, responsible for one in every six deaths. Radiotherapy is the main technique of treatment for more than half of cancer patients. To achieve a successful outcome, the radiation dose must be delivered accurately and precisely to the tumor, within ± 5% accuracy. Smaller uncertainties are required for better treatment outcome. The objective of the study is to investigate the uncertainty of measurement of external radiotherapy beam using a standard ionization chamber under reference conditions. Clinical farmers type ionization chamber measurement was compared against the National Reference standard, by exposing it in a beam 60Co gamma source. The measurement set up was carried out according to IAEA TRS 498 protocol and uncertainty of measurement evaluated according to GUM TEDDOC-1585. Evaluation and analysis were done for the identified subjects of uncertainty contributors. The expanded uncertainty associated with 56 mGy/nC ND,W was found to be 0.9% corresponding to a confidence level of approximately 95% with a coverage factor of k = 2. The study established the impact of dosimetry uncertainty of measurement in estimating external radiotherapy dose. The investigation established that the largest contributor of uncertainty is the stability of the ionization chamber at 36%, followed by temperature at 22% and positioning of the chamber in the beam at 8%. The effect of pressure, electrometer, resolution, and reproducibility were found to be minimal to the overall uncertainty. The study indicate that there is no flawless measurement, as there are many prospective sources of variation. Measurement results have component of unreliability and should be regarded as best estimates of the true value. .
文摘目的:对常用4种新型进口及国产医用诊断X射线剂量仪的能量响应特性进行比较研究。方法:在国际原子能机构(IAEA)北京二级标准剂量学实验室(SSDL)的标准辐射场中,采用替代法分别完成10种管电压为60~150 k V、管电流为10 m A、用2.5 mm Al(毫米铝)做附加过滤的X射线诊断辐射线质进行比对测量。结果:国产RD-98诊断剂量仪与进口剂量仪的能量响应性能,在60~150 k V的X射线范围内,不同能量对剂量的响应均在±5%以内。结论:4种新型诊断X射线剂量仪的能量响应特性均良好,半导体探测器的诊断剂量仪与空气电离室剂量仪,不同能量对剂量的响应均符合国际电工委员会(IEC)的要求。
