Assessment of a carcinogenic risk for treatment of Graves' ophthalmopathy in dependence on age and irradiation geometry.

In view of the probable carcinogenic risk due to the irradiation of Graves' ophthalmopathy in young patients the effective dose was assessed for two geometries. Adjusting the field to the conical outline of the orbit resulted in appreciable reduction in dose to uninvolved areas such as brain and bone marrow. In Leiden and in Essen the initial target dose was 20 Gy in 10 fractions of 2 Gy. Since 1996 the target dose in Essen was lowered to 10 fractions of 1.6 Gy with equal positive results. The combined effect of field optimization and 20% reduction in target dose has lowered the effective dose from 65 to 34 mSv. The attributable lifetime risk for fatal malignancies of 0.3% as a population average will be considerably reduced when the exposure occurs at older age.

Patient dose due to colon examination: dose assessment and results from a survey in The Netherlands.

PURPOSE: To determine the effective dose to the patient during radiographic colon examination. MATERIALS AND METHODS: The integral dose-area product was measured during colon examination in 1,733 patients aged 18-94 years. The effective dose was estimated from the dose-area product through computer simulations of radiation transport in anthropomorphic phantoms. The relation between patient dose and imaging or radiographic technique was considered. Patient dose from a biphasic colon examination was compared to that from a double-contrast examination. RESULTS: The factors for converting dose-area product to effective dose were 0.29 mSv x Gy(-1) x cm(-2) and 0.27 mSv x Gy(-1) x cm(-2) for the biphasic and the double-contrast studies, respectively. The average dose-area product for the biphasic colon examination was 21 Gy x cm2, of which 13 Gy x cm2 was attributed to the double-contrast views. The average dose-area product was 29 Gy x cm2 (range, 18-53 Gy x cm2); the average effective dose was 4.7 mSv (range, 2.7-8.4 mSv). CONCLUSION: Careful selection of the radiologic technique resulted in a surprisingly low dose during the biphasic colon examination. It is recommended that additional filtration of at least 0.1-mm copper be applied and that a screen-film combination with a speed class of at least 400 be used. Dose reduction when using digital techniques is often not realized in clinical practice.

Simulation of measurements of uptake of 123I-iodide in the thyroid of fetal chimpanzees.

The quantitative assessment of the uptake of 123I-iodide (123I-) in the fetal thyroid in vivo was simulated in phantom measurements. First, the relationship between the depth of the fetal thyroid phantom and the two-peak ratio, the ratio of the counts in the gamma-ray and the X-ray energy windows of the registered spectrum, was determined. Subsequently, the attenuation of the gamma-ray signal in relationship to the depth of the fetal thyroid phantom was determined. Finally, the relationship between the two-peak ratio and the attenuation of the gamma-ray signal was deduced. For a reliable correlation, the signal recorded from the radioactivity surrounding the fetal thyroid phantom has to be subtracted from that obtained with the fetal thyroid phantom present. A correction curve was generated to be applied to the in vivo measurements. It is concluded that with this method determination of uptake of 123I- in the fetal thyroid is feasible.

Probable risk of tumour induction after retro-orbital irradiation for Graves' ophthalmopathy.

Retrobulbar irradiation for Graves' ophthalmopathy is considered as a safe treatment and has recently been recommended as the initial treatment for patients with moderately severe eye problems. However, calculations using risk factors presently known reveal a theoretical risk of radiation-induced cancer of 1.2%. Therefore, the authors suggest that this treatment should be reserved for the elderly patient, for example above the age of 40-50 years.

Risk- and cost-benefit analyses of breast screening programs derived from absorbed dose measurements in The Netherlands.

Risk- and cost benefit analyses for breast screening programs are being performed, employing the risk-factors for induction of breast cancer from six extensive follow-up studies. For women of the age group above 35 years and for a risk period of 30 years after a 10-year latency period, a factor of extra cases of 20 X 10(-6) mGy-1 can be estimated. This factor is by coincidence the same as the factor estimated by the Committee on the Biological Effects of Ionizing Radiations and by United Nations Scientific Committee on the Effects of Atomic Radiation for women above 20 years, and would have been about a factor 2 lower for the category older than 35 years. Measurements are being performed in Dutch hospitals to determine the mean absorbed tissue dose. These doses vary from 0.6 to 4.4 mGy per radiograph. For a dose of 1 mGy per radiograph (which can easily be achieved) and yearly screening of women between 35 and 75 years, the risk of radiogenic breast cancer is about 1% of the natural incidence (85,000 per 10(6) women) in this group. A recommended frequency of screening has to be based on medical, social and financial considerations. The gain in woman years and in completely cured women is being estimated for screening with intervals of 12 instead of 24 months. This estimation is based on the frequencies of the tumour diameters after 12 and 24 months intervals and the survival percentages for these tumour diameters. The medical and social benefit is 1,520 years life-time and 69 more cases completely cured per 1,000 breast cancer patients. The financial profit of a completely cured instead of an ultimately fatal cancer can be roughly estimated at 55,000 guilders. In addition the costs per gained woman-year are about 5,000 guilders (1 US $ = 3.60 guilders). In consequence, the extra costs of annual additional rounds of mammographic screening are balanced by the benefit.