RADIATION RISK OF MAMMOGRAPHY RELATED TO BENEFIT IN SCREENING PROGRAMS - A FAVORABLE BALANCE

Objectives-To estimate the number of breast cancer deaths induced by l ow dose radiation in breast cancer screening programmes compared with numbers prevented. Methods-A computer simulation model on the natural history of breast cancer was combined with a model from BEIR-V on indu ced breast cancer mortality from low levels of radiation. The improvem ent in prognosis resulting from screening was based on the results of the Swedish overview of the randomised screening trials for breast can cer and the performance of screening in the Netherlands. Different sce narios (ages and intervals) were used to explore the objectives. Sensi tivity analyses were carried out for latency period, dose of mammograp hy, sensitivity of the screening test, early detection by screening of induced breast tumours, and new 1996 risk estimates by Howe and McLau ghlin. Results-For a screening programme, age group 50-69, two year in terval, 2 mGy per view, the balance between the number of deaths induc ed versus those prevented was favourable: 1:242. When screening is exp anded to the age group 40-49 with a one or two year interval the resul ts may be less favourable, that is, 1:66 and 1:97. According to these scenarios and with the Dutch scenario as reference, one breast cancer death from radiation may be expected to occur to save eight extra deat hs from breast cancer. If screening was equally effective in young wom en as in women aged 50-69, the marginal value was 1:+/-30. Assuming de tection of induced cancers by screening could influence the ratios by about 30%, but did not substantially change the conclusions. The new r isk estimates by Howe and McLaughlin resulted in five times to eight t imes favourable ratios breast cancer deaths induced to prevented. Besi des age group of screening, dose of mammography is the other determina nt of risk. Conclusions-For screening under the age of 50, the balance between the number of breast cancer deaths prevented by screening com pared with the number induced by radiation seem less favourable. Credi bility intervals were however wide, because of many uncertainties of r adiation risk at very low doses.