Dosimetric impact of accidental irradiations on radiotherapy facility workers and considerations on personal monitoring

摘要

The possibility of an accidental irradiation of a linac-based radiotherapy facility worker always exists if an operator remains in avertedly within the treatment room when the radiation beam is turned on.Two distinct irradiation situations can be identified: (1) the operator passes partially within the primary radiation beam, (2) the operator only receives secondary radiation (mainly head leakage and patient scatter radiation).This work estimates, by theoretical calculation and experimental verification, the resulting effective doses derived in these situations for different conservative irradiation scenarios and discusses the resulting implications for occupational dose monitoring.A number of relevant conclusions can be mentioned:• These accidental irradiations can never pose a deterministic radiation effect on the worker due to the fractionated nature of the radiotherapy treatment scheme.• It can be seen that for case (1) situations, being this the worst irradiation condition, the effective dose will most likely be below the 1CRP annual dose limit for normal working conditions (20mSv). In these situations the whole body personal dosimetry monitoring device will give extremely inexact results due to the highly inhomogeneous nature of the volume irradiation. Careful consideration must be given to these cases in order avoid misinterpretations of the personal dosimeter readings. A reconstruction of the specific irradiation conditions will most likely be needed in order to arrive at a good theoretical estimate of the effective dose.• For case (2) situations, calculated values range from 4mSv to O.lmSv under conservative working hypothesis. Nevertheless, experimental measurements have showed a number of factors that lower these estimates, causing a large number of the irradiation situations to go dosimetrically unnoticed by the personal dosimetry monitoring system due to their low magnitude (<0.1mSv). This may lead the uninformed radiation protection officer or operator to unjustifiably distrust the results of the personal dosimetry system.