Dose inhomogeneities for photons and neutrons near interfaces

Perturbations of charged particle equilibrium (CPE) at interfaces of materials of different atomic composition can lead to considerable differences in the energy deposition by photons and neutrons. Specific examples of these interface perturbations are encountered during irradiation of body cavities and soft tissue adjacent to bone or metallic implants and irradiation of cells in monolayer on the bottom of culture dishes. Another example is the build-up of CPE at air-tissue interfaces, referred to in radiotherapy as the skin sparing effect. For photon irradiation excess production of secondary electrons in high-Z materials, such as glass, bone or gold, will induce appreciably higher doses and decreased cell survival compared to the equilibrium situation. The energy dissipation of fast neutrons in biological materials occurs through recoil protons, heavy recoil nuclei and products of nuclear reactions. Owing to the large contribution from recoil protons to the neutron kerma, the hydrogen content of the biological material mainly determines the energy deposition. For neutron irradiation of cells in monolayer, CPE can be established or deliberately avoided by mounting tissue-equivalent plastic or carbon discs in front of the cells, respectively. This approach makes it possible to distinguish the biological effects of the low- and high-LET radiation components.

Patient and staff dose during CT guided biopsy, drainage and coagulation

Patient and staff dose during CT guided coagulation of osteoid osteoma, tissue biopsy and abscess drainage were evaluated retrospectively on a conventional CT scanner and prospectively on a scanner equipped with fluoroscopic CT. The computed tomography dose index (CTDI) and the individual dose equivalent, i.e. the penetrating dose for workers at a depth of 10 mm tissue, were measured. Evaluation of CTDI enabled effective dose and maximum skin entrance doses for the patient to be determined. Doses were assessed for 96 CT guided interventions, including 16 drainages with average effective doses of 13.5 mSv and 9.3 mSv for the conventional CT scanner and the scanner with spiral CT fluoroscopy, respectively, 49 biopsies (effective doses of 8 mSv and 6.1 mSv, respectively), and 31 coagulations of osteoid osteoma (effective doses of 2.1 mSv and 0.8 mSv, respectively). Effective doses to patients were in the same range as those observed for regular diagnostic CT examinations. Entrance skin doses were well below the 2 Gy threshold for deterministic skin effects on the CT scanner equipped with fluoroscopic function (0.03-0.33 Gy), whilst skin doses on the conventional scanner were considerably higher (0.09-1.61 Gy). This is mainly owing to the fact that on the conventional scanner mAs was rarely reduced for scans evaluating needle position whereas low mAs per rotation was selected on the scanner with the fluoroscopy option. The maximum dose to a worker measured outside the lead apron was 28 microSv for one single procedure. The mean dose per procedure was below 10 microSv for radiologists and below 1 microSv for radiographers. Correcting for attenuation of the lead apron, the doses to workers are very low.

Protocol for X-ray dosimetry in radiobiology

PURPOSE

To harmonize X-ray dosimetry in radiobiology to allow a direct comparison of radiobiological studies performed at institutes cooperating within the framework of the European Late Effects Project Group (EULEP).

MATERIALS AND METHODS

The 1985 EULEP protocol for X-ray dosimetry and exposure arrangements employed for studies of late somatic effects in mammals required serious revision, e.g. due to the replacement of calibration of dosemeters in terms of exposure by calibration in terms of air kerma free-in-air. An action group established by EULEP and the European Radiation Dosimetry Group (EURADOS) updated the 1985 protocol.

RESULTS

The new EULEP-EURADOS protocol for X-ray dosimetry in radiobiology including the code of practice for irradiation of small animals and related dosimetry. The present protocol includes the changes in calibration procedures and dosimetric concepts for irradiation with medium energy X-rays since 1985. Accuracy and precision are replaced by the concept of combined (standard) uncertainty. The revised supplements provide more detailed background information. New appendices contain definitions of general terms used for measurements and mathematical expressions of the relative variances.

CONCLUSION

Adherence to the present protocol will result in improved dosimetry and facilitates the comparison of results of radiobiological experiments obtained at different institutes.

Apoptosis is present in the primate macula at all ages

BACKGROUND

It has become increasingly clear that apoptosis is a main event in photoreceptor cell death in a variety of retinal degenerations. We investigated the role of apoptosis in the physiologically aging primate macula.

METHODS

Twenty maculae of rhesus monkeys, aged 6-34 years, were investigated. Apoptosis was determined in formalin-fixed, paraffin-embedded eyes using the TUNEL (TdT-mediated dUTP-biotin nick end labeling) method and quantitatively analyzed. Morphology of TUNEL-positive cells was studied by confocal laser microscopy and transmission electron microscopy. The thickness of the outer nuclear layer (ONL) was determined by image analysis. Furthermore, expression of apoptosis-regulating proteins Bcl-x, Fas and Fas Ligand was studied by immunohistochemistry.

RESULTS

TUNEL-positive nuclei showed apoptotic features on confocal laser microscopy. They were scattered and sparsely found in the macula, most frequently in the ONL. The thickness of the ONL decreased with increasing age. Apoptosis was found equally distributed at all ages, although in the two oldest maculae up to 13 times more apoptosis was found. Expression of Bcl-x, Fas and Fas Ligand was equal at all ages.

CONCLUSION

Our findings indicate that apoptosis in the primate macula occurs at all ages at similar rates, possibly increasing in the oldest age group, and may account for the decreasing thickness of the primate macula with age.

Long-term effects of total-body irradiation on the kidney of Rhesus monkeys

PURPOSE

To investigate the long-term effects of total-body irradiation (TBI) on kidneys in non-human primates.

METHODS AND MATERIALS

The kidneys of Rhesus monkeys were histologically examined at 6-8 years after TBI with low single doses of 4.5-8.5Gy or two fractions of 5.4Gy. The kidneys of age-matched non-irradiated monkeys served as controls. Irradiation was performed on adult monkeys aged about 3 years; 6-8 years later animals were sacrificed and the kidneys removed and processed for histology. A semi-quantitative scoring system was used to evaluate overall histological damage. Glomerular changes were also morphometrically analysed according to previously published criteria. In selected dose groups (pro)thrombotic and inflammatory changes were investigated by immunostaining cryosections with antibodies against von Willebrand factor (vWF), leukocytes and macrophages.

RESULTS

Histological changes were generally mild and only seen in kidneys irradiated with doses higher than 7 Gy. Glomerular changes were characterized by increased mesangial matrix and capillary dilatation. Tubulo-interstitial changes included hypercellularity, fibrosis and mild tubular atrophy. The mean glomerular area expressing vWF protein in the irradiated kidneys was not different from that in the age-matched controls. Numbers of infiltrating leukocytes were not significantly different between irradiated kidneys and controls. However, slightly increased numbers of macrophages were present in the renal cortex after irradiation.

CONCLUSIONS

Renal damage after TBI of Rhesus monkeys with single doses of 4.5-8.5 Gy or two fractions of 5.4 Gy was mild, even after follow-up times of 6-8 years.

The effects of fractionated gamma irradiation on induction of mammary carcinoma in normal and estrogen-treated rats

The effects of dose fractionation on induction of mammary carcinoma were studied in normal and estrogen-treated female rats of the inbred WAG/Rij strain. Groups of 40 animals received total-body doses of 1 or 2 Gy of (137)Cs gamma radiation, administered in fractions of 2.5, 10 or 40 mGy with intervals of 12 h, or in fractions of 10 mGy with intervals of 2, 5 or 24 h. The irradiations were started at the age of 8 weeks. Estrogen treatment was accomplished by implantation of a pellet containing estrogen at the age of 6 weeks. All mammary tumors were resected and classified histologically as carcinoma or fibroadenoma. The age-specific incidence of mammary carcinoma was compared with that in control groups of unirradiated normal or estrogen-treated rats and was expressed as excess normalized risk, using lifetime statistical analysis with both parametric and nonparametric methods. The data were also compared to the results of single-dose experiments reported in previous papers. Fractionated irradiation increased the risk of mammary cancer in both normal and estrogen-treated rats compared to the corresponding unirradiated control group. The excess normalized risk per unit of total dose was approximately equal with or without estrogen treatment. Without estrogen treatment, the effects of the single-dose and fractionated irradiations were approximately equal. In estrogen-treated animals, however, single-dose irradiation was up to 15 times more carcinogenic than the fractionated exposures. This fractionation effect appeared to vanish for total doses below approximately 0.3 Gy. With estrogen treatment, the excess normalized risk was significantly higher for dose fractions of 40 mGy than for fractions of 10 mGy. The risk was also markedly higher for fractionation intervals of 2 or 5 h than for intervals of 12 or 24 h. The results of these experiments show that the effects of dose fractionation on the induction of mammary carcinoma may depend on hormonal status, the total dose delivered, the dose per fraction, and the fractionation interval.

The carcinogenic risk of high dose total body irradiation in non-human primates

PURPOSE

High dose total body irradiation (TBI) in combination with chemotherapy, followed by rescue with bone marrow transplantation (BMT), is increasingly used for the treatment of haematological malignancies. With the increasing success of this treatment and its current introduction for treating refractory autoimmune diseases the risk of radiation carcinogenesis is of growing concern. Studies on tumour induction in non-human primates are of relevance in this context since the response of this species to radiation does not differ much from that in man.

MATERIALS AND METHODS

Since the early sixties, studies have been performed on acute effects in Rhesus monkeys and the protective action of bone marrow transplantation after irradiation with X-rays (average total body dose 6.8 Gy) and fission neutrons (average dose 3.4 Gy). Of those monkeys, which were irradiated and reconstituted with autologous bone marrow, 20 animals in the X-irradiated group and nine animals in the neutron group survived more than 3 years. A group of 21 non-irradiated Rhesus monkeys of a comparable age distribution served as controls. All animals were regularly screened for the occurrence of neoplasms. Complete necropsies were performed after natural death or euthanasia.

RESULTS

At post-irradiation intervals of 4-21 years an appreciable number of tumours was observed. In the neutron irradiated group eight out of nine animals died with one or more malignant tumours. In the X-irradiated group this fraction was 10 out of 20. The tumours in the control group, in seven out of the 21 animals, appeared at much older age compared with those in the irradiated cohorts. The histogenesis of the tumours was diverse with a preponderance of renal carcinoma, sarcomas among which osteosarcomas, and malignant glomus tumours in the irradiated groups.

CONCLUSIONS

When corrected for competing risks, the carcinogenic risk of TBI in the Rhesus monkeys is similar to that derived from the studies of the Japanese atomic bomb survivors. The increase of the risk by a factor of 8, observed in the monkeys, indicates that patients are likely to develop malignancies more frequently and much earlier in life after TBI than non-exposed individuals. This finding underlines the necessity of regular screening of long-term surviving patients subjected to TBI and BMT.

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.

Aspects of fetal thyroid dose following iodine-131 administration during early stages of pregnancy in patients suffering from benign thyroid disorders

Detrimental effects on the thyroid of the developing fetus as a result of iodine-131 treatment for thyrotoxicosis of the mother in the first trimester of pregnancy are discussed. Dose estimations under typical clinical circumstances yield a fetal thyroid dose of 100- 450 Sv. This dose may increase considerably if the blood concentration of (131)I in the mother remains high. Under such circumstances there may be fetal thyroid dysfunction, which can lead to severe abnormalities.

Effects of total-body irradiation on growth, thyroid and pituitary gland in rhesus monkeys

PURPOSE

To investigate the effect of total-body irradiation (TBI) on growth, thyroid and pituitary gland in primates.

METHODS AND MATERIALS

Thirty-seven rhesus monkeys (mean age 3.1+/-0.6 years) received either a low-dose (4-6 Gy) TBI (n = 26) or high-dose (7-12 Gy) TBI (n = 11) and were sacrificed together with 8 age-matched controls after a post-irradiation interval of 5.9+/-1.5 years. Anthropometric data were collected: thyroid and pituitary glands were examined; serum levels of thyroid stimulating hormone (TSH), free thyroxin (FT4), insulin-like growth factor-I (IGF-I) and its binding protein-3 (IGFBP-3) were measured.

RESULTS

Decrease in final height due to irradiation could not be demonstrated. There was a dose-dependent decrease in body weight, ponderal index, skinfold thickness and thyroid weight. The latter was not accompanied by elevation of TSH or decrease in FT4. Structural changes in the thyroid gland were found in 50% of the irradiated animals. Levels of IGF-I and IGFBP-3 did not differ between the dose groups, but the high-dose group had a lower IGF-1/IGFBP-3 ratio.

CONCLUSION

Total body irradiation had a negative effect on body fat. There was no evidence of (compensated) hypothyroidism, but dose-dependent decrease in thyroid weight and changes in follicular structure suggest some effect of TBI on the thyroid gland. The decreased IGF-I/IGFBP-3 ratio in the high-dose group can indicate that the somatotrophic axis was mildly affected by TBI. These results show that TBI can have an effect on the physical build and thyroid gland of primates even in the absence of cytostatic agents or immunosuppressive drugs.

Late ophthalmological complications after total body irradiation in non-human primates

PURPOSE

To investigate the long-term effects of total body irradiation (TBI) on the incidence and time course of ocular complications.

MATERIALS AND METHODS

Rhesus monkeys treated with TBI photon doses up to 8.5 Gy and proton doses up to 7.5 Gy were studied at intervals up to 25 years post-irradiation. They were compared with control groups with a similar age distribution. Cataract formation and ocular fundus lesions were scored according to a standardized protocol. Fluorescein angiography and histopathology was performed in selected animals.

RESULTS

Cataract formation occurred after a latent period of 3-5 years. Significant cataract induction was observed for photon-doses of 8 and 8.5 Gy and beyond 20 years after proton irradiation. The severity of the lesions represents significant impairment of vision and would require cataract surgery if similar results occurred in human bone marrow transplant patients. Fluorescein angiography demonstrated a normal pattern of retinal vessels in 13 out of 14 animals (93%) from the irradiated group and in eight out of nine animals (89%) from the control group. No additional lesions apart from age-related degenerative changes could be demonstrated. Histological evaluation revealed no radiation-associated vasculopathy.

CONCLUSIONS

Radiation alone for doses up to 8.5 Gy of photons does not carry a potential risk for fundus pathology, whereas clinically important cataract induction should be anticipated within 5 years after photon doses of 8.0 and 8.5 Gy and proton doses in excess of 2.5 Gy.

Long-term effects of X-irradiation on gastrointestinal function and regulatory peptides in monkeys

PURPOSE

To investigate the long-term effects of X-irradiation on different aspects of gastrointestinal function in the non-human primate (Macaca mulatta).

MATERIALS AND METHODS

Animals were exposed to X-radiation (5 or 6 Gy) or not (sham) and gastrointestinal function was investigated 4-6 years after exposure. Basal and agonist-stimulated short circuit current (Isc) responses were measured in isolated jejunum. Intestinal tissue was taken for histological analysis as well as for determination of mucosal marker enzyme activities and gastrointestinal regulatory peptide levels. Vasoactive intestinal peptide receptor characteristics were determined as well as VIP-stimulated Isc responses. GI peptides were also measured in plasma.

RESULTS

Few differences were seen in basal electrical parameters or tissue morphology but there was a tendency for reduced basolateral membrane enzyme activity. VIP-stimulated Isc responses were reduced in irradiated animals as were VIP-stimulated adenylate cyclase responses. Plasma and tissue (ileal and colonic muscle layers) gastrin releasing peptide levels were increased in irradiated animals. In contrast circulating gastrin levels were lower.

CONCLUSIONS

Late effects of total-body irradiation on GI function in monkeys showed altered circulating and tissue levels of some GI peptides. In addition the biological effects of vasoactive intestinal peptide were modified.

Somatic effects in nuclear medicine and radiology

Probable risks for the occurrence of somatic effects due to diagnostic radiology and nuclear medicine are summarised. The biological background of radiation carcinogenesis and epidemiological results are discussed. At the Leiden University Medical Centre the average effective dose per examination due to diagnostic radiology and nuclear medicine amount to 0.95 and 4.4 mSv, respectively. These values correspond well with the average values of 0.82 and 3.0 mSv reported for The Netherlands as a whole. Since radiological examinations are performed at a much larger frequency than nuclear medicine the relative collective dose for the first type of examinations is higher than the latter. Risk for occurency of malignancies are at least one order of magnitude lower than the hypothetical risk due to the background radiation typical of The Netherlands.

Induction of mammary tumors in rats by single-dose gamma irradiation at different ages

The effect of age at exposure on induction of mammary tumors was studied in female rats of the inbred WAG/Rij strain. Groups of 40 animals were exposed to a single total-body dose of 1 or 2 Gy of 137Cs gamma radiation at ages of 8, 12, 16, 22, 36 or 64 weeks and were observed for life. Mammary tumors, identified as nodules persisting and growing for 6 weeks, were resected and classified histologically as carcinoma or fibroadenoma. The age-specific incidence of mammary carcinoma was compared with that in a group of 120 unirradiated control rats, using lifetime statistical analysis with both parametric and nonparametric methods. The excess normalized risk of carcinoma was 0.9 for 1 Gy and 2.2 for 2 Gy in age groups 8-36 weeks, with no significant differences between the age groups. However, irradiation at 64 weeks yielded fewer carcinomas than in the controls, the excess normalized risk being -0.7 and -0.3 for 1 and 2 Gy, respectively. The occurrence of one or more fibroadenomas did not influence the incidence of carcinoma. The present data agree closely with the results reported previously for rats irradiated at age 8 or 17 weeks with a dose of 1.2 Gy. The reduced risk of radiation exposure at midlife is consistent with the available epidemiological data for exposed women. Although our findings have been obtained with a single total-body dose that is several orders of magnitude higher than the multiple doses delivered to the mammary gland during mammography, it is suggested that radiological screening for mammary cancer after the age of menopause will not increase the normal incidence of breast cancer.

The influence of estrogen treatment on induction of mammary carcinoma in rats by single-dose gamma irradiation at different ages

The effect of age at exposure on induction of mammary carcinoma was studied in female rats of the inbred WAG/Rij strain that were treated with estrogen. Groups of 40 animals were exposed to a single total-body dose of 1 or 2 Gy of 137Cs gamma radiation at age 8, 10, 12, 15, 22, 36 or 64 weeks. Hormone levels in the animals were increased by implantation of a pellet containing Estradiol-17beta 2 weeks prior to irradiation. Animals were killed when moribund. All mammary tumors were resected and classified histologically as carcinoma or fibroadenoma. The age-specific incidence of mammary carcinoma was compared with that in control groups of unirradiated estrogen-treated rats using lifetime statistical analysis with both parametric and nonparametric methods. The excess normalized risk of carcinoma was 7.7 for both 1 and 2 Gy in the age groups 8-15 weeks, with no significant differences between the age groups. However, in the age groups 22-64 weeks, the excess normalized risk decreased with increasing age at exposure. Irradiation at 64 weeks yielded fewer carcinomas than in the controls, with an excess normalized risk of -0.6 for both 1 and 2 Gy. The excess normalized risk was 10-80 in estrogen-treated controls compared to untreated rats. The present data agree with the results reported previously for estrogen-treated rats irradiated at ages 8 or 17 weeks with doses of 0.3 or 1.2 Gy. The reduced risk of radiation exposure at midlife observed in this study in hormone-treated rats has also been reported for animals not treated with estrogens. The present findings support the earlier conclusion that radiological screening for mammary cancer after the age of menopause will not increase the normal incidence of breast cancer. Estrogen treatment at midlife may increase the risk of breast cancer in women using replacement estrogens during and after menopause.

Dosimetry for total body irradiation of rhesus monkeys with 300 kV X-rays

PURPOSE

To obtain more accurate information on the dose distribution in rhesus monkeys for total body irradiation with orthovoltage X-rays.

MATERIALS AND METHODS

Dose measurements were performed with an ionization chamber inside homogeneous cylindrical and rectangular phantoms of various dimensions and in phantoms containing lung-equivalent material. The irradiations were carried out with reference to a monitor ionization chamber placed alongside the phantom or the irradiation cage.

RESULTS

Correction factors for mass and lung dose relative to the average dose in a homogeneous reference phantom, showed linear relationships with the effective diameter of the monkey. The lung dose correction factor relative to the homogeneous phantom was about 1.12 for a 3.5 kg monkey. The stated values for the average absorbed dose in the animal of standard weight should be multiplied by a factor of 0.93 for experiments performed before 1983. All publications on total body irradiations of monkeys at TNO after 1983 contain the corrected dose values.

CONCLUSION

Dose distributions are reported for phantoms of different diameters and of cylindrical or rectangular shape. The new dosimetry has also resulted in a revised statement of the LD50 for the occurrence of bone marrow syndrome after X-irradiation; 4.9 Gy instead of 5.3 Gy.

Detection of total- and partial-body irradiation in a monkey model: a comparative study of chromosomal aberration, micronucleus and premature chromosome condensation assays

PURPOSE

To investigate the efficacy of three cytogenetic methods (dicentrics, micronuclei (MN) and premature chromosome condensation (PCC) analysis) for assessment of the unirradiated fraction and the persistence of damage after total-body (TB) and partial-body (PB) irradiation of rhesus monkeys (Macaca mulatta).

MATERIALS AND METHODS

Animals were exposed to X-rays (5 Gy), either TB or PB, with about 6% of marrow cells shielded. Blood samples were collected at different times after exposure, i.e. 1, 3 and 7 days, and cultures were set up for the different cytogenetic endpoints. In addition, blood count analysis was performed before and after irradiation.

RESULTS

Blood count analysis was not suitable for discriminating between TB and PB exposure. By using Poisson or overdispersion distribution as the basis, it was not possible to distinguish TB from PB irradiation when dicentric chromosomes and MN were analysed. PCC analysis, in contrast, showed a Poisson distribution after TB exposure and overdispersion after PB exposure. Using the PCC assay, reliable dose estimates could be obtained up to 7 days after irradiation.

CONCLUSIONS

For dicentrics and MN, shielding of 6% of bone marrow cells was found to be too small to estimate the unirradiated fraction accurately. The PCC technique was useful for dose assessment and the inhomogeneous exposure of 6% was detected within a short period of time after exposure.

A comparison of patient dose for examinations of the upper gastrointestinal tract at 11 conventional and digital X-ray units in The Netherlands

The objective of this study was to derive the effective dose to patients from examinations of the upper gastrointestinal (GI) tract at 11 X-ray units in 10 Dutch hospitals. Entrance dose and entrance dose rate were measured at the surface of a homogeneous PMMA phantom and at the entrance surface of the image intensifier. Dose-area products (DAPs) were assessed during examinations of patients. The patients (334 females and 256 males) ages were 18-95 years (average 52 years). Effective dose was assessed from DAP using Monte Carlo computer calculations for male and female mathematical anthropomorphic phantoms. The DAPs measured during the survey showed substantial variations, i.e. an overall average value of 21 Gy cm2 and a range of average DAP per X-ray unit varying from 7 to 56 Gy cm2. Variations in the number of images (8-28) and the fluoroscopy time (1.7 min-7.0 min) were also large. A DAP to effective dose conversion factor of 0.32 mSv Gy cm-2 was derived for upper GI studies. The dose survey yielded an overall average effective dose of 6.7 mSv. At one location an examination involving as many as 28 projections was performed, whilst maintaining a DAP well below 15 Gy cm2 and an effective dose below 6 mSv. This was achieved using modern equipment (i.e. high frequency generator, digital spot films) with 0.2 mm additional copper filtration and a relatively high tube voltage. For examinations of the upper GI tract, the application of a reference value of 30 Gy cm2 for the DAP will ensure that, in general, the effective dose to individual patients will not exceed 15 mSv.

Diagnostic nuclear medicine and risk for the fetus

The possible detrimental effects on the developing embryo subsequent to irradiation are discussed. The doses to the embryo or fetus encountered for the most common procedures in diagnostic nuclear medicine are evaluated with respect to the threshold doses and the risks per cGy. The threshold dose for fatal and non-fatal malformations or other defects is, at the lowest estimate, 5-10 cGy. The dose which the embryo or fetus receives from diagnostic nuclear medicine is below 1 cGy. For the induction of fatal cancer and for genetic defects no threshold dose is assumed. The risk for the induction of cancer is 0.03%-0.05% per cGy. The risk for the induction of genetic defects is even lower (0.024%-0.099% per cGy). It is concluded that for common diagnostic nuclear medicine procedures the risk of detrimental effects on the embryo or fetus due to radiation is negligible. On the basis of present knowledge there are no radiation safety indications for abortus provocatus as a consequence of a diagnostic nuclear medicine study.

Recent EULEP dosimetry intercomparisons for whole body irradiation of mice. European Late Effects Project group

PURPOSE

To foster quality assurance of dosimetry among the institutes involved in joint studies on late effects of ionizing radiation.

MATERIALS AND METHODS

The participants in the dosimetry intercomparison received for each facility two mouse phantoms loaded with LiF thermoluminescent dosemeters (TLD) and a control badge. The participants were requested to irradiate the test phantoms in the actual arrangement used for whole body irradiation of mice, such that the dose in the centre of the test phantoms was 2 Gy and the dose distribution was uniform. The readout of the TLD and the dose evaluation were made at the organizing institute.

RESULTS

Ten institutes operating 14 exposure facilities in four countries took part in the intercomparison. For one facility a dose deviation between 5 and 10% was found, whereas for two others the deviation exceeded 10%. The requirement for uniform dose distribution in a mouse phantom was not fulfilled by six exposure facilities. The causes for the dose discrepancies were found for two participants whereas for one participant the problems were only partly resolved. Non-uniform dose distributions are mainly related to unilateral irradiations.

CONCLUSION

The seven EULEP dosimetry intercomparisons clearly show the need for quality assurance of dosimetry in radiobiology.

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.

Protection of the maternal and fetal thyroid from radioactive contamination by the administration of stable iodide during pregnancy. An experimental evaluation in chimpanzees

The safety and efficacy of the administration of stable iodide to protect the fetal thyroid from exposure to radioactive iodide were investigated in chimpanzees in weeks 19 to 21 of pregnancy. The mean 24-h uptake of iodide in the fetal thyroid, determined with 123I-, was 1.8%. Administration of stable potassium iodide (KI), 0.65, 1.95 or 6.5 mg per kg body weight, 1 h before tracer injection reduced the fetal uptake satisfactorily. Only the higher doses were effective after 20 h. Excess iodide may impair a child's thyroid status. However, adverse effects were not found during the 11 days the animals ingested these doses. Tracer concentrations in the amniotic fluid were 30- to 130-fold lower than in the urine. The dose to the fetus from radioactivity in the maternal bladder was estimated by computer simulation. The potential increment of the risk from this dose during the ingestion of stable iodide is smaller than the reduction of risk achieved by inhibiting the uptake of radioactive iodide by the fetal thyroid. The conclusion of the experiments is that stable iodide can be used safely and effectively to protect the fetal thyroid against contamination with radioactive iodine.

Protection of the infant thyroid from radioactive contamination by the administration of stable iodide. An experimental evaluation in chimpanzees

Protection of the thyroid from radioactive contamination by the administration of stable iodide was investigated in chimpanzees aged 2 to 98 weeks. The uptake of iodide in the thyroid was measured with 123I-. The animals were subjected to a control measurement first, and subsequently the thyroid uptake of 123I- was determined twice; once at the start and once at the end of 11 days of ingestion of 0.5, 1.5 or 5.0 mg of stable iodide per kg body weight per day. The three doses of iodide reduced the control thyroid iodide uptake of 10 to 30% to lower than 1% when ingested 1 h before exposure to the tracer and to 2-4% when ingested 20 h before exposure. In the latter experiments 0.5 mg iodide/kg was less effective than doses of 1.5 mg/kg or higher. The physiological state of the thyroid of control infant chimpanzees does not differ from that of human infants. Incidentally, an increased level of TSH was found during the ingestion of iodide, but with unaltered thyroxine levels. Therefore, it is concluded that a daily dose of 1.5 mg stable iodide/kg body weight and higher offers optimal protection of the thyroid against exposure to radioactive iodine in infants and that, when used during 10 days, it leaves the thyroid unaffected.

Survey of CT techniques and absorbed dose in various Dutch hospitals

The purpose of this study was to make an inventory of the radiation dose from CT in the Netherlands and to relate the dose to the way the examination was performed. Details were obtained from approximately 3000 CT examinations carried out in 18 hospitals (22 CT scanners). Effective dose was calculated for each examination using CTDI-to-effective dose conversion factors. For most scanners, the conversion factors were available from the literature, for some they had to be derived with a computer model using a Monte Carlo algorithm. The data on effective dose, examination parameters and patient population are presented on a per hospital basis. Mean effective doses from brain CT were 0.8-5 mSv, from lumbar spine CT 2-12 mSv, from chest CT 6-18 mSv and from abdominal CT 6-24 mSv. The general indications for the various CT examinations were as follows: for the brain ischaemia and malignancy, for the lumbar spine disc herniation and for the chest and abdomen a known malignancy. This explains the relatively advanced age of the patients. In many hospitals intravenous contrast is used less than is recommended in current literature.

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.

[Radiation risks in dental and medical radiography]

Biological effects of exposure to ionizing radiation in diagnostic dental and medical radiology are stochastic effects such as carcinogenesis and genetical effects. Today, radiation exposure due to an x-ray or nuclear medicine examination varies from less then 0.001 mSv to more then 10 mSv effective dose. The background level of natural radiation in the Netherlands is about 2 mSv. Assuming that an appropriate indication for the examination exists, it can be stated that generally the diagnostic information obtained outweighs by far the risks involved in the exposure to radiation.

Long-term consequences of high-dose total-body irradiation on hepatic and renal function in primates

Radiation effects in non-human primates were studied in order to define the long-term risk of total-body irradiation (TBI) for bone marrow transplantation patients. The long-term effects of TBI could be investigated by keeping 84 monkeys of different ages, from an experiment on acute effects, under continuous observation for a period up to 25 years. The control group consisted of non-irradiated monkeys with a comparable age distribution and identical housing conditions. Since radiation was the common toxic agent, the different age groups provided the possibility to investigate the occurrence of deterministic effects after TBI. In the present study emphasis was placed on the assessment of hepatic and renal function and the associated histopathology. The values of the liver function parameters, such as alkaline phosphatase and gamma glutamyl transferase in the irradiated group were significantly increased after TBI (p < 0.05). Also the parameters of kidney dysfunction, e.g. haematocrit and blood urea nitrogen showed a significant change in the irradiated old-aged (post-irradiated interval > 15 years) cohort (p < 0.005). The impairment of the liver and renal functions, did not lead to clinical symptoms and were only associated with mild morphologic changes in the irradiated group of monkeys. In the population of bone marrow transplant patients treated with TBI, alterations in hepatic and renal function parameters after a post-irradiated interval of > 10 years can be anticipated. This could have consequences for the tolerance and toxicity of a broad range of drugs to be administered as additional medications.

General ion recombination for ionization chambers used under irradiation conditions relevant for diagnostic radiology

General ion recombination has been studied under irradiation conditions relevant for diagnostic radiology and with four different ionization chambers. When the exposure time is appreciably shorter than the ion transit time, the exposure can be designated as pulsed irradiation. On the contrary, for relatively long irradiation times, the term continuous irradiation can be applied. Recombination was estimated by measuring the collected charge at various collecting potentials of the ionization chamber. This is a well-known method in radiotherapy, but unfortunately it cannot be used in diagnostic radiology with typical exposure meters, since they do not offer the option of varying the collecting potential. For exposures with diagnostic x-ray units, an alternative approach is to vary the exposure or exposure rate over a wide range at a constant collecting potential. Experimental and theoretical estimates of ion recombination did not yield similar values. This might be due to several causes, such as differences between the actual and the nominal dimensions and volumes of the ionization chambers, due to errors and uncertainties in the physical parameters used in the theoretical models or due to deviations of the shape of the ionization chambers from the perfect cylindrical or parallel plate geometry. For better accuracy, corrections for recombination losses should therefore be based on experimental verification rather than on theoretical models.

Radiation exposure in standard and high-resolution chest CT scans

It has been suggested that radiation doses due to high-resolution computed tomography (HRCT) of the chest are considerably higher than those from conventional CT. We compared the effective dose (E, mSv) in conventional chest CT (10-mm contiguous slices) and HRCT (1.5-mm slices, gap 10 mm). In our study, the effective dose from a HRCT (0.98 mSv) is about 6.5 times less than the effective dose from a standard CT scan (6.5 mSv), and only a factor 12 higher than from a conventional chest examination (0.085 mSv).

Carcinogenic risk in diagnostic nuclear medicine: biological and epidemiological considerations

During the last decade new data have become available on the mechanism of carcinogenesis and on cancer induction by ionizing radiation. This review concentrates on these two items in relation to the use of radiopharmaceuticals in diagnostic nuclear medicine. On the basis of reports of expert committees, the concept of radiation risk is elucidated for high and low doses. Mortality risk factors due to ionizing radiation are put in perspective to other risks. The extra risk for patients who undergo a scintigraphic examination for fatal cancer is very small and is of the order of 1.4 x 10(-4). It is most unlikely that this figure can even be verified by actual measurement since the majority of nuclear medicine patients will die of other causes before the radiogenic cancer manifests itself.

Neoplastic transformation of C3H 10T1/2 cells: a study with fractionated doses of monoenergetic neutrons

As most occupational and environmental exposures to ionizing radiation are at low dose rates or in small dose fractions, risk estimation requires that the effects of the temporal distribution of dose are taken into account. Previous in vitro studies of oncogenic transformation, as well as in vivo studies of carcinogenesis induced by high-LET radiation, yielded controversial results concerning the presence of an inverse dose-rate effect. The present study tested the influence of one scheme of dose fractionation of monoenergetic neutrons on neoplastic transformation of C3H 10T1/2 cells. Neutrons of 0.5, 1.0 and 6.0 MeV were used. Cells were exposed to doses of 0.25 and 0.5 Gy, given acutely or in five fractions at 2-h intervals. The acute and fractionated irradiations with each energy were done on the same day. No significant difference between the two irradiation modes was found for both cell inactivation and neoplastic transformation at all energies. These results are in agreement with our data for fractionated fission-spectrum neutrons from the RSV-TAPIRO reactor.

Comparison of two methods for assessing patient dose from computed tomography

Radiation exposure of the patient during routine computed tomography (CT) examinations is known to be relatively high. In this study organ doses were determined using two methods and these served as a basis to calculate the effective dose. Thermoluminescence dosemeters (TLDs) were used to measure organ doses in an anthropomorphic Rando Alderson phantom. In addition organ doses were obtained from measurement of the computed tomography dose index (CTDI) and the application of published organ dose conversion factors. Effective dose values obtained with the Rando phantom for CT head examinations are about 1-2 mSv. For CT examinations of thorax and abdomen the estimation of effective doses with the Rando phantom yielded values of 18 and 24 mSv respectively. Effective doses determined from CTDI values were similar for CT head examinations (1-2 mSv) but were smaller for the CT thorax scan (11-15 mSv) and the CT abdomen scan (15-20 mSv). In this study effective dose values are relatively high compared with the results of other investigators who indicate effective doses and effective dose equivalents of 7-9 mSv for CT of the thorax and of 4-16 mSv for CT of the abdomen. Discrepancies between our results and those from other studies could be attributed to differences in the selected CT protocols and to differences in the phantoms employed. Measurements in an anthropomorphic phantom were laborious and time-consuming. Assessment of organ doses from CTDI values and organ dose conversion factors will therefore be the preferable method for future dose intercomparisons at different locations in The Netherlands. It should be realized, however, that this method tends to yield up to 40% lower effective dose values compared with the assessment of effective dose with a Rando phantom.

PCDOSE: an interactive software system to calculate internal radiation dose on a personal computer

An interactive, menu directed, software system to calculate committed dose equivalents for individuals with different physiques after inhalation, ingestion or injection of radionuclides has been developed. The calculations are based on ICRP 26/30 methods. The programs are written in PASCAL and can be implemented on a personal computer with a MS-DOS operating system and a hard disk with a storage capacity of at least 20 Mb. This paper describes the development and features of the system.

AMBER and conventional chest radiography: comparison of radiation dose and image quality

The authors compared the radiation dose to the patient and the image quality in advanced multiple-beam equalization radiography (AMBER) with those in conventional chest radiography. Organ doses were estimated for an anthropomorphic phantom from measurements with thermoluminescence dosimeters. These measurements were supplemented with area-air kerma products obtained during chest examinations of 223 patients. Image quality was determined by means of a contrast-detail image evaluation test. An improvement in image quality in regions of high absorption and an increased dose to the patient were found for the AMBER technique compared with the conventional technique. However, for both techniques, the radiation exposure was relatively low compared with other reported values of patient dose during chest radiography. The estimated effective dose for an average-size patient during chest radiography with posteroanterior and lateral projections is 0.085 mSv for the conventional and 0.14 mSv for the AMBER technique.

Dosimetry of ruthenium-106 eye applicators

In view of the importance of clinical applications of ruthenium-106 beta-ray sources for the treatment of choroidal melanoma, experimental, and theoretical approaches are presented for the dosimetry of such sources. The absolute dose and percentage depth dose of ruthenium applicators have been measured with an extrapolation ionization chamber. For a special flat applicator the absolute dose could be measured with an accuracy of +/- 5%, which is determined by the collection efficiency of the extrapolation chamber. The percentage depth dose of concave applicators, employed in the clinical situation, could only be measured at a distance larger than 5 mm due to their geometry and the outer dimensions of the extrapolation chamber. A computer simulation was therefore developed for the absorption and scattering of electrons, taking into account the geometry and materials of the applicator, to predict the percentage depth dose at distances smaller than 5 mm. The calculated and experimentally determined depth doses are in good agreement. With the aid of the computer simulation a depth dose determination for concave applicators can be made for clinically relevant distances less than 10 mm from the source surface with an absolute accuracy of +/- 10%.

Relative biological effectiveness for neutron carcinogenesis in monkeys and rats

The risks of total-body irradiation with large doses of X rays (average dose 6.7 Gy) and fission neutrons (average dose 3.4 Gy) were investigated by keeping a group of long-term surviving monkeys from an experiment on acute effects under continuous observation. On the basis of the number of animals developing tumors in each group as a function of the total observation period and the average absorbed dose, relative biological effectiveness (RBE) values between 4 and 5 have been derived at these high dose levels. In experiments on mammary carcinogenesis in rats the highest RBE values are observed for neutrons with energies of 0.43 to 1 MeV as produced by the p + T reaction or by the fission process. Based upon linear dose-response curves for neutrons and X rays, a maximum RBE value of 15 was observed for induction of adenocarcinomas in WAG/Rij rats. Appreciably higher RBE values would be obtained if the results of the gamma-ray exposure, indicating a nearly quadratic dose-response relationship, were used as a baseline. For radiation protection applications it should be realized, however, that such an increase will be caused by the lower efficiency of low-linear-energy-transfer radiation rather than by an increase in efficiency of the neutron irradiation at low doses.

Flow cytometric DNA measurement and cytomorphometric analysis of formalin fixed rat mammary tumours

Archival paraffin embedded material was used to examine whether additional quantitative criteria would be helpful to discriminate between histologically benign and malignant rat mammary tumours. To this end nuclear DNA content expressed as DNA ploidy index (DI) was measured using flow cytometry (FCM). A total of 63 benign and malignant mammary tumours were investigated. Thirteen out of 38 (34%) mammary carcinomas were DNA aneuploid against 0 out of 25 benign mammary tumours. Aneuploidy was not significantly increased in tumours showing histological signs of greater malignancy such as cribriform-comedo type or invasive growth. In addition to DI other quantitative criteria indicative for malignancy, such as mitotic count and nuclear morphometric characteristics, were estimated in 24 benign and malignant tubulopapillary tumours, a category where the histological classification may be difficult. It appeared that five out of nine noninvasive tubulopapillary carcinomas and six out of seven invasive carcinomas had abnormal values for either DI, mitotic count or nuclear area or for a combination of these parameters. Each single parameter however was abnormal only in a minority of the malignant tumours. In this respect our data are in accordance with the fact that rat mammary carcinomas are clinically and histologically less malignant than their human counterparts.

Monoclonal gammapathies in long-term surviving rhesus monkeys after lethal irradiation and bone marrow transplantation

Late effects of total body irradiation and subsequent autologous bone marrow transplantation on the development of age-related monoclonal gammapathies (MG) were studied in 14 long-term surviving Rhesus monkeys. Together with 27 untreated control monkeys, they have been followed up for more than 20 years. In contrast with the control group, the experimental monkeys developed MG with aging in higher frequencies, earlier and mainly of the benign MG category. One experimental monkey developed a multiple myeloma, the first observed in the nonhuman primates so far. These results indicate an accelerated senescence of the immune system in the experimental monkeys as a late consequence of tissue or cell damage during irradiation.

Dosimetric aspects of exposure of the population to ionizing radiation

Radiation carcinogenesis is generally considered to be the most important detrimental effect of exposure to ionizing radiation. The collective effective dose-equivalent values due to medical procedures amount to values between 10 and 20 per cent of the doses received from natural radiation. Risk factors have been derived up to the present from three large epidemiological studies, notably atomic bomb survivors, spondylitis patients and female patients treated for cancer of the cervix. The assessment of the absorbed doses received by the inhabitants of Hiroshima and Nagasaki has received continuous attention and the latest estimates are summarized. On the basis of original radiotherapy records the absorbed doses in organs adjacent to the primary treatment field can be derived from computerized dosimetry and this source of information should be further exploited. European co-operation has been established to investigate dosimetric problems for medical applications and radiation protection. The risk factors obtained up to the present are derived at relatively high dose levels (in excess of 0.3 Gy). The uncertainties in the extrapolation of these values to the area of low doses administered at low dose rates are discussed.

Dosimetry for radiation accidents: present status and prospects for biological dosemeters

The induction of chromosome aberrations in human peripheral blood lymphocytes is still the most useful dosimetry system for accidental whole-body irradiation; however, in the case of a very large number of casualties the micronuclei technique might provide advantages. For partial-body irradiations, determination of hair diameter and chromosome aberrations in skin fibroblasts and hair might be advantageous, since better information on dose distribution might be obtained. The latter cytological techniques are complex and require considerable culture time. Flow cytometry for determination of chromosome aberrations, a staining technique for hair follicles and an immunochemical method for quantitative detection of persistent DNA damage in mammalian cells might be applicable in the future.