Calibration of dosemeters used in mammography with different X ray qualities: EUROMET project no. 526.

The effect of different X ray radiation qualities on the calibration of mammographic dosemeters was investigated within the framework of a EUROMET (European Collaboration in Measurement Standards) project. The calibration coefficients for two ionization chambers and two semiconductor detectors were established in 13 dosimetry calibration laboratories for radiation qualities used in mammography. They were compared with coefficients for other radiation qualities, including those defined in ISO 4037-1, with first half value layers in the mammographic range. The results indicate that the choice of the radiation quality is not crucial for instruments with a small energy dependence of the response. However, the radiation quality has to be chosen carefully if instruments with a marked dependence of their response to the radiation energy are calibrated.

Comparison of two methods of therapy level calibration at 60Co gamma beams.

The accuracy and traceability of the calibration of radiotherapy dosimeters is of great concern to those involved in the delivery of radiotherapy. It has been proposed that calibration should be carried out directly in terms of absorbed dose to water, instead of using the conventional and widely applied quantity of air kerma. In this study, the faithfulness in disseminating standards of both air kerma and absorbed dose to water were evaluated, through comparison of both types of calibration for three types of commonly used radiotherapy dosimeters at 60Co gamma beams at a few secondary and primary standard dosimetry laboratories (SSDLs and PSDLs). A supplementary aim was to demonstrate the impact which the change in the method of calibration would have on clinical dose measurements at the reference point. Within the estimated uncertainties, both the air kerma and absorbed dose to water calibration factors obtained at different laboratories were regarded as consistent. As might be expected, between the SSDLs traceable to the same PSDL the observed differences were smaller (less than 0.5%) than between PSDLs or SSDLs traceable to different PSDLs (up to 1.5%). This can mainly be attributed to the reported differences between the primary standards. The calibration factors obtained by the two methods differed by up to about 1.5% depending on the primary standards involved and on the parameters of calculation used for 60Co gamma radiation. It is concluded that this discrepancy should be settled before the new method of calibration at 60Co gamma beams in terms of absorbed dose to water is taken into routine use.

Cancer risk among staff at two radiotherapy departments in Denmark.

In comparison with the general Danish population, the relative risk (RR) for cancer among staff members employed in two radiotherapy departments in Denmark during 1954-1982 and alive on 1 April 1968 was assessed by linkage to the Danish Cancer Registry. All staff had been monitored with film dosimeters for exposure to radiation. The study cohort consisted of 4151 persons, accruing 49553 person-years at risk. The collective radiation dose was 76.54 manSv and the mean dose 18.4 mSv. A total of 163 cancer cases were observed with 152.3 expected. The risks for cancers usually considered to be radiogenic were not elevated. A significant excess of prostatic cancer was observed (five cases, relative risk, 6.02; 95% confidence interval, 1.94-14.06); this is likely to be a chance finding. No relation was observed between radiation dose or years of exposure and cancer risk, but a weak non-significant increase in risk with time since first exposure was seen.

Anaphylactic reaction to orthoiodohippurate.

A case of an anaphylactic reaction following administration of 125I- and 131I-o-iodohippurate in a 32-year-old woman is reported. The patient had a renography performed because of hematuria. She was known to react to an intravenous pyelography previously performed with an anaphylactic shock. The importance of reporting all adverse reactions to radiopharmaceuticals for central registration is stressed.

Intercomparison of Nordic exposure secondary standards for soft roentgen rays.

An intercomparison of exposure secondary standards for soft roentgen rays in use in the Nordic countries is reported. One of the standards was used as a reference standard against which all the other standards were calibrated. The statistical uncertainty in the calibrations was estimated to be 0.8 per cent (at the 95% confidence level) and the maximum systematic uncertainty in the intercomparison was estimated to be 0.8 per cent. The observed differences, at most about one per cent, were not considered significant. It was concluded that for this type of chambers a period of about five years is acceptable between recalibrations against a primary standard unless stability checks indicate otherwise.

Spectral measurements and Monte Carlo calculations of scattered radiation from therapeutic radiation sources.

Spectral measurements have been made on scattered radiation in a perspex phantom in various depths from a kilocurie 60Co unit and a 6 MeV linear accelerator using a NaI crystal spectrometer. The measurements are compared to Monte Carlo calculations and a good agreement is obtained. The measured total photon distributions make the basis for calculations of absorbed dose and track length distributions in LET and their average values for the different depths and fields.