Cancer risk from professional exposure in staff working in cardiac catheterization laboratory: insights from the National Research Council's Biological Effects of Ionizing Radiation VII Report.

BACKGROUND: Occupational doses from fluoroscopy-guided interventional procedures are the highest ones registered among medical staff using x-rays. The aim of the present study was to evaluate the order of magnitude of cancer risk caused by professional radiation exposure in modern invasive cardiology practice. METHODS: From the dosimetric Tuscany Health Physics data bank of 2006, we selected dosimetric data of the 26 (7 women, 19 men; age 46 +/- 9 years) workers of the cardiovascular catheterization laboratory with effective dose >2 mSv. Effective dose (E) was expressed in milliSievert, calculated from personal dose equivalent registered by the thermoluminescent dosimeter, at waist or chest, under the apron, according to the recommendations of National Council of Radiation Protection. Lifetime attributable risk of cancer was estimated using the approach of Biological Effects of Ionizing Radiation 2006 report VII. RESULTS: Cardiac catheterization laboratory staff represented 67% of the 6 workers with yearly exposure >6 mSv. Of the 26 workers with 2006 exposure >2 mSv, 15 of them had complete records of at least 10 (up to 25) consecutive years. For these 15 subjects having a more complete lifetime dosimetric history, the median individual effective dose was 46 mSv (interquartile range = 24-64). The median risk of (fatal and nonfatal) cancer (Biological Effects of Ionizing Radiation 2006) was 1 in 192 (interquartile range = 1 in 137-1 in 370). CONCLUSIONS: Cumulative professional radiological exposure is associated with a non-negligible Lifetime attributable risk of cancer for the most exposed contemporary cardiac catheterization laboratory staff.

Dependence of brain DTI maps of fractional anisotropy and mean diffusivity on the number of diffusion weighting directions.

The rotational variance dependence of diffusion tensor imaging (DTI) derived parameters on the number of diffusion weighting directions (N) has been investigated by several Monte Carlo simulation studies. However, the dependence of fractional anisotropy (FA) and mean diffusivity (MD) maps on N, in terms of accuracy and contrast between different anatomical structures, has not been assessed in detail. This experimental study further investigated in vivo the effect of the number of diffusion weighting directions on DTI maps of FA and MD. Human brain FA and MD maps of six healthy subjects were acquired at 1.5T with varying N (6, 11, 19, 27, 55). Then, FA and MD mean values in high (FAH, MDH) and low (FAL, MDL) anisotropy segmented brain regions were measured. Moreover, the contrast-to-signal variance ratio (CVRFA, CVRMD) between the main white matter and the surrounding regions was calculated. Analysis of variance showed that FAL, FAH and CVRFA significantly (p < 0.05) depend on N. In particular, FAL decreased (6%-11%) with N, whereas FAH (1.6%-2.5%) and CVRFA (4%-6.5%) increased with N. MDL, MDH and CVRMD did not significantly (p>0.05) depend on N. Unlike MD values, FA values significantly vary with N. It is noteworthy that the observed variation is opposite in low and high anisotropic regions. In clinical studies, the effect of N may represent a confounding variable for anisotropy measurements and the employment of DTI acquisition schemes with high N (> 20) allows an increased CVR and a better visualization of white matter structures in FA maps.

Comparison between remnant and red-marrow absorbed dose in thyroid cancer patients submitted to 131I ablative therapy after rh-TSH stimulation versus hypothyroidism induced by L-thyroxine withdrawal.

OBJECTIVE: In thyroidectomized patients, increased levels of thyroid stimulating hormone (TSH) are necessary to maximize I uptake. Traditionally, this has been achieved by withdrawing L-thyroxine (L-T4) for 4-6 weeks, inducing hypothyroidism in patients. The availability of a genetically engineered version of the recombinant human TSH (rh-TSH) provides an alternative tool to enhance the TSH serum level without inducing hypothyroidism. In this paper the I remnant and red-marrow doses calculated in differentiated thyroid cancer (DTC) patients pre-treated with rh-TSH are compared to those calculated in patients in hypothyroidism induced by L-T4 withdrawal. METHODS: Forty-six DTC patients, submitted to I ablative therapy, were randomly divided in group A (pre-treated with rh-TSH) and group B (treated after L-T4 withdrawal for 30 days). The red-marrow absorbed dose per unit administered activity and the remnant cumulated activity per unit administered activity were calculated for both groups. RESULTS: The red-marrow dose in 17 rh-TSH treated patients is 0.06+/-0.02 mGy.MBq; that in 14 hypothyroid patients is 0.09+/-0.03 mGy.MBq (two-tailed unpaired t-test P=0.003). The remnant cumulated activity per unit administered activity in 10 rh-TSH treated patients is 0.9+/-0.8 h; that calculated in 21 hypothyroid patients is 1.55+/-1.05 h (two-tailed unpaired t-test P=0.063). This last result is mainly due to the difference between the maximum uptake (U) in rh-TSH (U=0.01+/-0.01) and hypothyroid patients (U=0.03+/-0.02) (two-tailed unpaired t-test P=0.019). CONCLUSION: The rh-TSH pre-treated patients seem to have a lower uptake compared to those in hypothyroidism induced by L-T4 withdrawal. On the other hand their red-marrow absorbed dose seems to be lower.

A study of the possibility of curing Graves' disease based on the desired reduction of thyroid mass (volume) as a consequence of 131I therapy: a speculative paper.

PURPOSE: The possibility of predicting the final volume of Graves' disease thyroids submitted to 131I therapy could allow the physician to decide what activity to administer based on the desired volume reduction instead of on a fixed value of the thyroid radiation absorbed dose. In this paper the relationship between maximum uptake of 131I, fractional reduction of thyroid volume and outcome of Graves' disease is discussed. METHODS: The results are based on ultrasonography thyroid volume measurements before administration of therapy and at the moment of recovery from Graves' disease (thyroid stimulating hormone >0.3 microIU x ml(-1) in the absence of anti-thyroid drug therapy) and on measurements of 131I uptake in 40 patients. It is shown that the possibility of curing Graves' disease may be individually related to the final volume of the patient's thyroid. An equation is presented to calculate the 'optimal' final thyroid volume. RESULTS: A comparison between the traditional method, based on absorbed dose, and the final method, based on volume, has been carried out retrospectively. In the first case a median activity of 529 MBq has been administered; in the second, a median activity of 394 MBq (non-parametric Wilcoxon test, P<0.05) should be administered. The corresponding thyroid median absorbed doses are, respectively, 353 Gy and 320 Gy (non-parametric Wilcoxon test, P<0.02). CONCLUSION: A method to evaluate individually the 'optimal' final thyroid mass is presented and discussed. The method based on 'volume reduction' could probably reduce the activity and the thyroid absorbed dose compared to the method based on 'empirical' calculations, thus allowing the administration of 131I therapy to be optimized.

[Sustainability of medical imaging in cardiology]. / La sostenibilità della diagnosi per immagini in cardiologia.

Every year, 5 billion imaging testing are performed worldwide, and about 1 out of 2 are cardiovascular examinations. According to recent estimates, 30 to 50% of all examinations are partially or totally inappropriate. This represents a potential damage for patient undergoing imaging (who takes the acute risks of a stress procedure and/or a contrast study without a commensurable benefit), an exorbitant cost for the society and an excessive delay in the waiting lists for other patients needing the examination. Economic induction, medico-legal concern, and specialist guidelines, which do not quantitate the potential benefits against the risks of a given procedure, boost inappropriateness of all imaging techniques. In case of ionizing tests, the reduction of useless imaging testing would improve the quality of care also through abatement of long-term risks, which are linked to the dose employed. The radiation dose equivalent of common cardiological imaging examinations corresponds to more than 1000 chest x rays for a thallium scan and to more than 500 chest x-rays for a multislice computed tomography. Although a direct evaluation of incidence of cancer in patients submitted to these procedures is not available, the estimated risk (often ignored by cardiologists) of cancer according to the latest 2005 Biological Effects of Ionizing Radiation Committee VII is about one in 500 exposed patients for a Thallium scintigraphy scan, and one in 750 for a CT scan. Such a risk is probably not acceptable when a scintigraphic or radiological procedure is applied for mass screening (when the risk side of the risk-benefit balance is not considered) or when a similar information can be obtained by other means. By contrast, it is fully acceptable in appropriately selected groups as a filter to more invasive, risky and costly procedures (for instance, coronary angiography and anatomy-driven revascularization). At this point, the cardiological community, that faces the reality of limited resources, should do every effort in order to minimize inappropriate testing, since they induce an exorbitant increase in health care costs with no improvement, and possibly with a reduction in care quality.

A predictive mathematical model for the calculation of the final mass of Graves' disease thyroids treated with 131I.

Substantial reductions in thyroid volume (up to 70-80%) after radioiodine therapy of Graves' hyperthyroidism are common and have been reported in the literature. A relationship between thyroid volume reduction and outcome of 131I therapy of Graves' disease has been reported by some authors. This important result could be used to decide individually the optimal radioiodine activity A0 (MBq) to administer to the patient, but a predictive model relating the change in gland volume to A0 is required. Recently, a mathematical model of thyroid mass reduction during the clearance phase (30-35 days) after 131I administration to patients with Graves' disease has been published and used as the basis for prescribing the therapeutic thyroid absorbed dose. It is well known that the thyroid volume reduction goes on until 1 year after therapy. In this paper, a mathematical model to predict the final mass of Graves' diseased thyroids submitted to 131I therapy is presented. This model represents a tentative explanation of what occurs macroscopically after the end of the clearance phase of radioiodine in the gland (the so-called second-order effects). It is shown that the final thyroid mass depends on its basal mass, on the radiation dose absorbed by the gland and on a constant value alpha typical of thyroid tissue. Alpha has been evaluated based on a set of measurements made in 15 reference patients affected by Graves' disease and submitted to 131I therapy. A predictive equation for the calculation of the final mass of thyroid is presented. It is based on macroscopic parameters measurable after a diagnostic 131I capsule administration (0.37-1.85 MBq), before giving the therapy. The final mass calculated using this equation is compared to the final mass of thyroid measured 1 year after therapy administration in 22 Graves' diseased patients. The final masses calculated and measured 1 year after therapy are in fairly good agreement (R = 0.81). The possibility, for the physician, to decide a therapeutic activity based on the desired decrease of thyroid mass instead of on a fixed thyroid absorbed dose could be a new opportunity to cure Graves' disease.

A dosimetric approach to patient-specific radioiodine treatment of Graves' disease with incorporation of treatment-induced changes in thyroid mass.

The traditional algorithms (Marinelli-Quimby and MIRD) used for the absorbed dose calculation in radionuclide therapy generally assume that the mass of the target organs does not change with time. In radioiodine therapy for Graves' disease this approximation may not be valid. In this paper a mathematical model of thyroid mass reduction during the clearance phase (30-35 days) after 131I administration to patients with Graves' disease is presented. A new algorithm for the absorbed dose calculation is derived, taking into account the reduction of the mass of the gland resulting from the 131I therapy. It is demonstrated that thyroid mass reduction has a considerable effect on the calculated radiation dose. Either the model of the thyroid mass reduction or the new equation for the absorbed dose calculation depend on a parameter k for each patient. This parameter can be calculated after the administration of a diagnostic amount of radioiodine activity (0.37-1.85 MBq). Thus, thyroid absorbed dose and thyroid mass reduction during the first month after therapy can be predicted before therapy administration. The absorbed dose values calculated by the new algorithm are compared to those calculated by the traditional Marinelli-Quimby and MIRD algorithms.