Asymmetric breast dose in coronary angiography.

The purpose of this study was to demonstrate asymmetric radiation dose distribution to the breasts in coronary angiography. Gafchromic XR-QA2 film was used as an area dosimeter to capture the asymmetric dose distribution to the breasts at various tissue depths in an anthropomorphic phantom. A selection of tube angulations were used under a controlled experiment and during a mock coronary angiography procedure. The Gafchromic XR-QA2 film was able to confirm the asymmetric distribution of radiation dose to the breast and provide a normalized breast dose value. The right breast received the majority of dose for most of the tube angulations in the controlled experiment. However the left breast received the most radiation dose during the mock procedure. Asymmetric dose distribution to the breasts is normally not observed if Monte Carlo based simulations are performed because individual breast dose calculations are not available. The application of a typical coronary angiogram determined in the experiment showed the normalized left breast dose is 0.16 mGy/ Gy.cm2 and the right breast dose is 0.08 mGy/ Gy.cm2.

Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians.

OBJECTIVE: To assess the cancer risk in children and adolescents following exposure to low dose ionising radiation from diagnostic computed tomography (CT) scans. DESIGN: Population based, cohort, data linkage study in Australia. COHORT MEMBERS: 10.9 million people identified from Australian Medicare records, aged 0-19 years on 1 January 1985 or born between 1 January 1985 and 31 December 2005; all exposures to CT scans funded by Medicare during 1985-2005 were identified for this cohort. Cancers diagnosed in cohort members up to 31 December 2007 were obtained through linkage to national cancer records. MAIN OUTCOME: Cancer incidence rates in individuals exposed to a CT scan more than one year before any cancer diagnosis, compared with cancer incidence rates in unexposed individuals. RESULTS: 60,674 cancers were recorded, including 3150 in 680,211 people exposed to a CT scan at least one year before any cancer diagnosis. The mean duration of follow-up after exposure was 9.5 years. Overall cancer incidence was 24% greater for exposed than for unexposed people, after accounting for age, sex, and year of birth (incidence rate ratio (IRR) 1.24 (95% confidence interval 1.20 to 1.29); P<0.001). We saw a dose-response relation, and the IRR increased by 0.16 (0.13 to 0.19) for each additional CT scan. The IRR was greater after exposure at younger ages (P<0.001 for trend). At 1-4, 5-9, 10-14, and 15 or more years since first exposure, IRRs were 1.35 (1.25 to 1.45), 1.25 (1.17 to 1.34), 1.14 (1.06 to 1.22), and 1.24 (1.14 to 1.34), respectively. The IRR increased significantly for many types of solid cancer (digestive organs, melanoma, soft tissue, female genital, urinary tract, brain, and thyroid); leukaemia, myelodysplasia, and some other lymphoid cancers. There was an excess of 608 cancers in people exposed to CT scans (147 brain, 356 other solid, 48 leukaemia or myelodysplasia, and 57 other lymphoid). The absolute excess incidence rate for all cancers combined was 9.38 per 100,000 person years at risk, as of 31 December 2007. The average effective radiation dose per scan was estimated as 4.5 mSv. CONCLUSIONS: The increased incidence of cancer after CT scan exposure in this cohort was mostly due to irradiation. Because the cancer excess was still continuing at the end of follow-up, the eventual lifetime risk from CT scans cannot yet be determined. Radiation doses from contemporary CT scans are likely to be lower than those in 1985-2005, but some increase in cancer risk is still likely from current scans. Future CT scans should be limited to situations where there is a definite clinical indication, with every scan optimised to provide a diagnostic CT image at the lowest possible radiation dose.

The implementation of diagnostic reference levels to Australian radiology practice.

At the present time, there is no national surveillance of the increasing ionising radiation dose to the population from diagnostic imaging procedures. As the number of procedures undertaken is increasing, it is expected that the population dose will also increase. A substantial component of that contribution is from multi-detector computed tomography (MDCT) systems. The Australian Radiation Protection & Nuclear Safety Agency (ARPANSA) estimates that the growth in MDCT scans, based on Medicare Benefits Schedule data, is increasing at approximately 9% per annum, with over 2 million MDCT scans being performed in 2009. The caput effective dose (mSv) from this modality is expected to be approaching 1.2 mSv per annum. If current dose-detriment models are accurate, the risk of induction of carcinogenic detriment from current MDCT scanning patterns is a significant public health issue that requires a concerted and ongoing response. For the application of ionising radiation in medicine, the International Commission on Radiological Protection recommends the conservative philosophy of Justification and Optimisation via the measurement of 'Diagnostic Reference Levels' to limit the potential overexposure of patients and decrease the overall population burden. The Australian government has commissioned ARPANSA to survey, calculate and construct representative national diagnostic reference levels for diagnostic imaging modalities that use ionising radiation. This will be achieved in close consultation with the professional organisations who represent the professionals responsible for the use of ionising radiation in diagnostic imaging.

Multidetector CT dose: clinical practice improvement strategies from a successful optimization program.

PURPOSE: The aims of this study were to collect data relating to radiation dose delivered by multidetector CT scanning at 10 hospitals and private practices in Queensland, Australia, and to test methods for dose optimization training, including audit feedback and didactic, face-to-face, small-group teaching of optimization techniques. METHODS: Ten hospital-based public and private sector radiology practices, with one CT scanner per site, volunteered for the project. Data were collected for a variety of common adult and pediatric CT scanning protocols, including tube current-time product, pitch, collimation, tube voltage, the use of dose modulation, and scan length. A one-day feedback and optimization training workshop was conducted for participating practices and was attended by the radiologist and medical imaging technologist responsible for the project at each site. Data were deidentified for the workshop presentation. During the feedback workshop, a detailed analysis and discussion of factors contributing to dose for higher dosing practices for each protocol occurred. The postoptimization training data collection phase allowed changes to median and spread of doses to be measured. RESULTS: During the baseline survey period, data for 1,208 scans were collected, and data from 1,153 scans were collected for the postoptimization dose survey for the 4 adult protocols (noncontrast brain CT, CT pulmonary angiography , CT lumbar spine, and CT urography). A mean decrease in effective dose was achieved with all scan protocols. Average reductions of 46% for brain CT, 28% for CT pulmonary angiography, 29% for CT lumbar spine, and 24% CT urography were calculated. It proved impossible to collect valid pediatric data from most sites, because of the small numbers of children presenting for multidetector CT, and phantom data were acquired during the preoptimization and postoptimization phase. Substantial phantom dose reductions were demonstrated at all sites. CONCLUSION: Audit feedback and small-group teaching about optimization enabled clinically meaningful dose reduction for a variety of common adult scans. However, access to medical radiation physicists, assistance with time-consuming data collection, and technical support from a medical imaging technologist were costly and critical to the success of the program.