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A new method is presented to decouple the parameters of the incident e− beam hitting the target of the linear accelerator, which consists essentially in optimizing the agreement between measurements and calculations when the difference filter, which is an additional filter inserted in the linac head to obtain uniform lateral dose-profile curves for the high energy photon beam, and flattening filter are removed from the beam path. This leads to lateral dose-profile curves, which depend only on the mean energy of the incident electron beam, since the effect of the radial intensity distribution of the incident e− beam is negligible when both filters are absent. The location of the primary collimator and the thickness and density of the target are not considered as adjustable parameters, since a satisfactory working Monte Carlo model is obtained for the low energy photon beam (6 MV) of the linac using the same target and primary collimator. This method was applied to conclude that the mean energy of the incident e− beam for the high energy photon beam (18 MV) of our Elekta SLi Plus linac is equal to 14.9 MeV. After optimizing the mean energy, the modelling of the filters, in accordance with the information provided by the manufacturer, can be verified by positioning only one filter in the linac head while the other is removed. It is also demonstrated that the parameter setting for Bremsstrahlung angular sampling in BEAMnrc (‘Simple’ using the leading term of the Koch and Motz equation or ‘KM’ using the full equation) leads to different dose-profile curves for the same incident electron energy for the studied 18 MV beam. It is therefore important to perform the calculations in ‘KM’ mode. Note that both filters are not physically removed from the linac head. All filters remain present in the linac head and are only rotated out of the beam. This makes the described method applicable for practical usage since no recommissioning process is required.

Monte Carlo based treatment planning of two different patient groups treated with step-and-shoot IMRT (head-and-neck and lung treatments) with different CT resolutions and scoring methods is performed to determine the effect of geometrical and scoring voxel sizes on DVHs and calculation times. Dose scoring is performed in two different ways: directly into geometrical voxels (or in a number of grouped geometrical voxels) or into scoring voxels defined by a separate scoring grid superimposed on the geometrical grid. For the head-and-neck cancer patients, more than 2% difference is noted in the right optical nerve when using voxel dimensions of 4 × 4 × 4 mm3 compared to the reference calculation with 1 × 1 × 2 mm3 voxel dimensions. For the lung cancer patients, 2% difference is noted in the spinal cord when using voxel dimensions of 4 × 4 × 10 mm3 compared to the 1 × 1 × 5 mm3 calculation. An independent scoring grid introduces several advantages. In cases where a relatively high geometrical resolution is required and where the scoring resolution is less important, the number of scoring voxels can be limited while maintaining a high geometrical resolution. This can be achieved either by grouping several geometrical voxels together into scoring voxels or by superimposing a separate scoring grid of spherical voxels with a user-defined radius on the geometrical grid. For the studied lung cancer cases, both methods produce accurate results and introduce a speed increase by a factor of 10–36. In cases where a low geometrical resolution is allowed, but where a high scoring resolution is required, superimposing a separate scoring grid on the geometrical grid allows a reduction in geometrical voxels while maintaining a high scoring resolution. For the studied head-and-neck cancer cases, calculations performed with a geometrical resolution of 2 × 2 × 2 mm3 and a separate scoring grid containing spherical scoring voxels with a radius of 2 mm produce accurate results and introduce a speed increase by a factor of 13. The scoring grid provides an additional degree of freedom for limiting calculation time and memory requirements by selecting optimized scoring and geometrical voxel dimensions in an independent way.

The purpose of this study was to assess the absorbed dose in and around lung tissue by performing radiochromic film measurements, Monte Carlo simulations and calculations with superposition convolution algorithms. We considered a layered polystyrene phantom of 12 × 12 × 12 cm³ containing a central cavity of 6 × 6 × 6 cm³ filled with Gammex RMI lung-equivalent material. Two field configurations were investigated, a small 1 × 10 cm² field and a larger 10 × 10 cm² field. First, we performed Monte Carlo simulations to investigate the influence of radiochromic film itself on the measured dose distribution when the film intersects a lung-equivalent region and is oriented parallel to the central beam axis. To that end, the film and the lung-equivalent materials were modelled in detail, taking into account their specific composition. Next, measurements were performed with the film oriented both parallel and perpendicular to the central beam axis to verify the results of our Monte Carlo simulations. Finally, we digitized the phantom in two commercially available treatment planning systems, Helax-TMS version 6.1A and Pinnacle version 6.2b, and calculated the absorbed dose in the phantom with their incorporated superposition convolution algorithms to compare with the Monte Carlo simulations. Comparing Monte Carlo simulations with measurements reveals that radiochromic film is a reliable dosimeter in and around lung-equivalent regions when the film is positioned perpendicular to the central beam axis. Radiochromic film is also able to predict the absorbed dose accurately when the film is positioned parallel to the central beam axis through the lung-equivalent region. However, attention must be paid when the film is not positioned along the central beam axis, in which case the film gradually attenuates the beam and decreases the dose measured behind the cavity. This underdosage disappears by offsetting the film a few centimetres. We find deviations of about 3.6% between Monte Carlo and the superposition convolution algorithm of Pinnacle behind the lung region, for both field configurations. Pinnacle is quite accurate in the lung region. Deviations up to 5.6% for the small field are found in the lung region between Monte Carlo and the superposition convolution algorithm of Helax-TMS. Behind the lung region, Helax-TMS is in better agreement with Monte Carlo. Radiochromic film measurements or Monte Carlo simulations are reliable methods to establish the dose in and around lung tissue.

Two Monte Carlo dose engines for radiotherapy treatment planning, namely a beta release of Peregrine and MCDE (Monte Carlo dose engine), were compared with Helax-TMS (collapsed cone superposition convolution) for a head and neck patient for the Elekta SLi plus linear accelerator. Deviations between the beta release of Peregrine and MCDE up to 10% were obtained in the dose volume histogram of the optical chiasm. It was illustrated that the differences are not caused by the particle transport in the patient, but by the modelling of the Elekta SLi plus accelerator head and more specifically the multileaf collimator (MLC). In MCDE two MLC modules (MLCQ and MLCE) were introduced to study the influence of the tongue-and-groove geometry, leaf bank tilt and leakage on the actual dose volume histograms. Differences in integral dose in the optical chiasm up to 3% between the two modules have been obtained. For single small offset beams though the FWHM of lateral profiles obtained with MLCE can differ by more than 1.5 mm from profiles obtained with MLCQ. Therefore, and because the recent version of MLCE is as fast as MLCQ, we advise to use MLCE for modelling the Elekta MLC. Nevertheless there still remains a large difference (up to 10%) between Peregrine and MCDE. By studying small offset beams we have shown that the profiles obtained with Peregrine are shifted, too wide and too flat compared with MCDE and phantom measurements. The overestimated integral doses for small beam segments explain the deviations observed in the dose volume histograms. The Helax-TMS results are in better agreement with MCDE, although deviations exceeding 5% have been observed in the optical chiasm. Monte Carlo dose deviations of more than 10% as found with Peregrine are unacceptable as an influence on the clinical outcome is possible and as the purpose of Monte Carlo treatment planning is to obtain an accuracy of 2%. We would like to emphasize that only the Elekta MLC has been tested in this work, so it is certainly possible that alpha releases of Peregrine provide more accurate results for other accelerators.

A new accurate Monte Carlo code for IMRT dose computations, MCDE (Monte Carlo dose engine), is introduced. MCDE is based on BEAMnrc/DOSXYZnrc and consequently the accurate EGSnrc electron transport. DOSXYZnrc is reprogrammed as a component module for BEAMnrc. In this way both codes are interconnected elegantly, while maintaining the BEAM structure and only minimal changes to BEAMnrc.mortran are necessary. The treatment head of the Elekta SLiplus linear accelerator is modelled in detail. CT grids consisting of up to 200 slices of 512 × 512 voxels can be introduced and up to 100 beams can be handled simultaneously. The beams and CT data are imported from the treatment planning system GRATIS via a DICOM interface. To enable the handling of up to 50 × 10⁶ voxels the system was programmed in Fortran95 to enable dynamic memory management. All region-dependent arrays (dose, statistics, transport arrays) were redefined. A scoring grid was introduced and superimposed on the geometry grid, to be able to limit the number of scoring voxels. The whole system uses approximately 200 MB of RAM and runs on a PC cluster consisting of 38 1.0 GHz processors. A set of in-house made scripts handle the parallellization and the centralization of the Monte Carlo calculations on a server. As an illustration of MCDE, a clinical example is discussed and compared with collapsed cone convolution calculations. At present, the system is still rather slow and is intended to be a tool for reliable verification of IMRT treatment planning in the case of the presence of tissue inhomogeneities such as air cavities.

This study reports on the optimization of the labelling procedure of clinical grade 123Irhannexin V and on the investigation of the biodistribution and dosimetry of 123Irhannexin V, a tracer proposed for the study of apoptosis in mice and humans. Research grade 123Irhannexin V was prepared as described previously, whereas clinical grade 123Irhannexin V was prepared according to a modified IodoGen method. NMRI mice, 3–4 weeks of age, received research grade 123Irhannexin V 74.0 3.7 kBqmouse by intravenous i.v. injection and killed at preset time points. Afterwards, the collected organs, blood, urine and faeces were counted for radioactivity and determined as IDg tissue or ID over time. Secondly, six volunteers with normal liver and kidney function underwent wholebody scans up to 21 h after i.v. injection of clinical grade 123Irhannexin V 345 ±38 MBq. Timeactivity curves were generated for the organs of interest, e.g., thyroid, heart, liver, kidneys and whole body, by fitting the organ specific geometric mean counts, obtained from region of interest analysis of acquired images in humans. The MIRD formulation was applied to calculate the absorbed radiation doses for various organs. Clinical grade 123Irhannexin V was obtained in radiochemical yields of 87.0 6.5 and radiochemical purities >98. In mice, research grade 123Irhannexin V accumulated primarily in liver, kidney, stomach and lung tissue, limiting its usefulness for imaging of ongoing apoptosis in the abdominal and thoracic region. Clearance was predominantly urinary. In humans, acquired images with the clinical grade radioligand showed low lung uptake, resulting in good imaging conditions for the thoracic region. On the other hand, delayed imaging of the abdominal region was impeded due to extensive bowel activity. The highest absorbed doses were received by the thyroid, the kidneys, the heart wall, the liver and bone surfaces. The average effective dose of 123Irhannexin V was estimated to be 0.02 mSv·MBq1. The amount of 123Irhannexin V required for in vivoimaging, results in an acceptable effective dose to the patient.

Several authors have demonstrated the good tolerance of hepatic intra-arterial 131I-Lipiodol therapy and report survival rates of 21-25 after 1 year in inoperable patients. This study explored the possibility that more selective hepatic arterial instillation could be a strategy for increasing tumoural uptake and response of 131I-Lipiodol. Between June 1999 and September 2001 we selected 24 patients: 14 received a selective instillation of 131I-Lipiodol to the proper hepatic artery (SEL group); and 10 received a hyperselective instillation in the right or left hepatic artery (HYP-SEL group). The individual 131I-Lipiodol activity as a per cent of the injected activity per millilitre of tumour (IAml tumour) was correlated with the selectivity of instillation in 28 tumours and with tumour response in 24 tumours. Differences in tumour response or tumour uptake between the SEL and HYP-SEL groups were not significant. In general, we observed a IAml tumour of 0.05-2.6 for the uptake of 131I-Lipiodol. The uptake was significantly higher in responsive disease than in stable or progressive disease (P0.002). A large tumour volume was invariably related to low uptake of 131I-Lipiodol and progressive disease (P0.008). In conclusion, our study does not support the general use of hyper-selective or super-selective intra-arterial administration of 131I-Lipiodol. This result may be extrapolated to similar types of intra-arterial, loco-regional hepatic radionuclide therapy.

A new component module (CM), called MLCE, has been implemented in the BEAM program. The CM takes into account the particular &lquot;tongue-and-groove&rquot; design of the Elekta multi-leaf collimator (MLC) and the air gap between the leaves. The model was validated by two series of measurements and simulations. The first benchmarking series focuses on the interleaf leakage and the intraleaf transmission. The measurement showed a total transmission through the MLC of 1.42&percent; of the open field dose. Two Monte Carlo (MC) simulations were made, the first with the new CM MLCE (inclusive of air gap) and the second with the CM MLCQ (exclusive of air gap), which is available in the BEAM distribution. When the air gap between the leaves was determined by varying the parameters of the leaf geometry within tolerance limits on the technical drawing, the total measured transmission of 1.42&percent; was well reproduced by the CM MLCE. In contrast, MC simulations with MLCQ showed that the transmission through the MLC calculated without the interleaf leakage is only 44&percent; of the total transmitted radiation. The relevance of the detailed MLC modelling was demonstrated also by studying the &lquot;adjacent&rquot; tongue-and-groove effect, where two adjacent (not opposing) leaves are complementary, opened or closed. The two complementary leaf settings were simulated both with the CM MLCE and MLCQ. A comparison with measurements was made. In regions covered by two or more leaves, the dose increased by 14&percent; for two leaves and by 40&percent; for more than two leaves when the interleaf leakage was included in the transmission. The tongue-and-groove effect was perfectly reproduced by the MLCE module.

The micronucleus (MN) assay already applied to the biomonitoring of radiation workers is a relatively easy and fast technique allowing assessment of the individual chromosomal radiosensitivity status of radiation workers on a large scale. A pilot study was set up to evaluate the chromosomal radiosensitivity in a group of 99 male radiation workers from the nuclear power plant Doel in Belgium. Heparinized blood samples of the workers were divided into three parts: one served for the assessment of a possible effect of occupational exposure on the number of micronuclei, the two others served for the assessment of individual chromosomal radiosensitivity by the increase of the number of micronuclei after 1 and 2 Gy in vitro γ-irradiation. For each worker, date of birth, smoking habit and previous medical exposures were registered. Furthermore the external radiation burden accumulated over the last 10 years was calculated from the personnel dosimetry records. Concerning the MN frequency as a biomarker for effect, the present study confirms the strong increase of MN frequency with age and the tendency of an increase with an accumulated radiation burden, observed in previous studies. Using the MN frequency after in vitro irradiation as a biomarker for chromosomal radiosensitivity, the data of the present study do not support a lowered radiosensitivity in radiation workers due to the adaptive response mechanism induced by occupational exposure. As the overall in vitro radiation induced MN frequency distributions can be represented by a normal distribution without a high frequency tail, none of the workers can be considered as exceptionally by radiosensitive with the test. Further validation of the MN assay as a radiosensitivity assay for a population of workers is necessary.

AimThe aim of the study was to determine the equivalent total body dose (ETBD) using the cytokinesis-blocked micronucleus assay in 22 131I-meta-iodobenzylguanidine (131I-MIBG) therapies (18 neuroblastoma, mean 5097 MBq, SD 1591; and four carcinoid tumours, mean 7681 MBq, SD 487). The results are correlated with the total body radiation dose according to the Medical Internal Radiation Dosimetry (MIRD) formalism.MethodsFor each patient, blood samples were taken immediately before and 1 week after 131I-MIBG therapy. The first blood sample was irradiated in vitrowith 60Co γ-rays to determine the dose-response curve. Micronuclei were scored in 1000 binucleated cells. By using the dose-response curve the ETBD was derived from the increase in micronuclei after 131I-MIBG therapy (second blood sample). Based on three consecutive biplanar scans taken at 3, 6 and 9 days post-administration respectively, the total body dose following the MIRD formalism was calculated.ResultsThe micronucleus assay was evaluable in only 14 out of 22 131I-MIBG therapies due to cell division inhibition caused by previous chemotherapy treatments and lymphocyte dilution due to blood transfusions given shortly after 131I-MIBG therapy. For these 14 therapies, the mean micronucleus yield after 131I-MIBG therapy was significantly increased (P<0.01) with a mean of 92 (SD 77) for neuroblastoma patients and with a mean of 35 (SD 8) for carcinoid patients. The increase observed in the present study is greater than previously observed after 131I therapy and 89Sr therapy but much lower than after external beam radiotherapy. For all patients treated with multiple therapies, the initial increase in micronucleus yield had at least partially recovered by the time of the next therapy. This might be explained by an increased turnover of lymphocytes. A mean ETBD of 0.95 Gy (SD 0.55) for neuroblastoma patients and a mean of 0.46 Gy (SD 0.09) for carcinoid patients was calculated. A reasonable correlation (R0.87) between the ETBD and the MIRD dose was obtained. The slope value of 0.75 can be explained by the low dose rate effect.ConclusionsThe observation in the present study of important inter-individual variability in the total body dose, with the possibility of high dose values, suggests the necessity of individual dosimetry when administering 131I-MIBG therapy, especially considering that generally more than one therapy is given to each patient.

The use of X-rays in cardiac interventional radiology has the potential to induce deterministic radiation effects on the patient's skin. Guidelines published by official organizations encourage the recording of information to evaluate this risk, and the use of reference values in terms of the dose-area product (DAP). Skin dose measurements were made with thermoluminescent dosemeters placed at eight different locations on the body. In addition, DAP was recorded in 100 patients for four types of interventional radiology procedures. Mean, median and third quartile for these results are presented. Maximum skin dose values found were 412 mGy, 725 mGy, 760 mGy and 1800 mGy for coronary catheterization, coronary catheterization with left ventricle investigation, and percutaneous transluminal angiography without and with stenting, respectively. Median DAPs for these same procedures were, respectively, 5682 cGy cm2, 10,632 cGy cm2, 10,880 cGy cm2 and 13,161 cGy cm2. The relationship between DAP and skin dose was investigated. We found a poor correlation of DAP with maximum skin dose (r = 0.77) and skin dose indicator (r = 0.78). Using conversion factors derived from Monte Carlo simulations, skin dose distributions were calculated based on the measured DAPs. Agreement between the calculated skin dose distribution, using DAP values averaged over a group of patients who underwent coronary catheterization and left ventricle investigation, and the measured skin dose averaged over the same group of patients was very good. However, there were large differences between the calculated skin doses using the individual DAP data per patient and measured skin doses for individual patients (r = 0.66). Hence, calculation of individual skin doses based on the specific DAP data per patient is not reliable and therefore measuring skin dose is preferable.

We studied the synthesis of 57Co-EDTA (Eγ 122 keV), its biodistribution in Wistar rats and its blood and urinary elimination compared with that of 51Cr-EDTA. We added 6 μmol EDTA diluted in 3-5 ml isotonic phosphate buffer (Na2HPO4) to a commercial 57CoCl2radioactive tracer solution. The incubation period was 15 min. Quality control was performed using TLC and HPLC. Six healthy Wistar rats underwent 57Co-EDTA renography for 30 min. In one rat, additional TLC and HPLC was performed on blood (one sample only) and urine samples (n3) obtained 30 min, 30 min, 2 h and 4 h following injection of 18.5 MBq 57Co-EDTA and 51Cr-EDTA respectively. Radioisotope quantification was done by means of a germanium detector. 57Co was chelated to EDTA at high yield (Kstab10E36). No free or protein-bound 57Co was found. The ratio of 51Cr-EDTA to 57Co-EDTA remained constant (P0.133, n4). 57Co-EDTA was rapidly cleared from the blood pool (heart), and prompt and high target-to-background ratios for both kidneys were obtained (mean 8.4, range 7-12). At the end of the acquisition, activity remaining in the body excluding kidney and bladder was 45±5.2. No specific activity uptake was noted in any other organ or tissue. We conclude that 57Co-EDTA is a promising radioligand for simultaneous clearance and separate renal function estimation. Its preparation is straightforward and, in rats, no free or protein-bound 57Co was found.

A multicentre study was undertaken to assess the cytogenetic damage to peripheral blood lymphocytes in 31 patients treated with 131I for thyrotoxicosis using the cytokinesisblocked micronucleus assay. The results were compared to those for eight thyroid carcinoma patients using the same method. For each patient, blood samples were taken immediately before and 1 week after iodine administration. The first blood sample was divided into three fractions and each fraction was subsequently irradiated in vitrowith 0, 0.5 and 1 Gy 60Co gamma rays, respectively. After blood culture for 70 h, cells were harvested, stained with RomanowskyGiemsa and the micronuclei scored in 1000 binucleated cells. For both patient groups, a linearquadratic doseresponse curve was fitted through the data set of the first blood sample by a least squares analysis. The mean increase in micronuclei after 131I therapy second blood sample was fitted to this curve and the mean equivalent total body dose ETBD calculated. Surprisingly, in view of the large difference in administered activity between thyroid carcinoma patients and thyrotoxicosis patients, the increase in micronuclei after therapy mean ± S.D. 32 ± 30 and 32 ± 23, respectively and the equivalent total body dose 0.34 and 0.32 Gy, respectively were not significantly different P> 0.1. The small number of micronuclei induced by 131I therapy 32 ± 29, compared with external beam radiotherapy for Hodgkin's disease 640 ± 381 or cervix carcinoma 298 ± 76 1, gave a cancer mortality estimate of less than 1. This also explains why late detrimental effects in patients after 131I treatment have not been reported in the literature.

Caspase 3 has been shown to be actively involved in the apoptotic process in thymocytes after γ-irradiation. We examined caspase 3 activation in mature peripheral blood lymphocytes (PBL) after γ irradiation. Since the activation of caspase 3 is generally prceded by a decrease in mitochondrial membrane potential (ΔΨm) and cytochrome c release, these two parameters were also examined. Apoptosis in PBL after a 5-Gy γ irradiation, is characterized by a decrease in ΔΨm, but surprisingly no release of cytochrome-c and only a weak caspase 3 activation was noticed. In contrast, staurosporin treated PBL showed a decrease in ΔΨm with cytochrome-c release and a clear caspase 3 activation. We were unable to block the decrease in ΔΨm with the caspase-inhibitors zVAD-fmk or zDEVD-fmk after γ irradiation, but DNA fragmentation as measured by the TUNEL assay was partially inhibited. Therefore, in γ irradiated mature PBL, caspase-dependent and -independent pathways, but not cytochrome c, seem to be involved in the apoptotic process.

Resting lymphocytes are sensitive to radiation damage and die by apoptosis. We investigated the effect of caspase-inhibitors on radiation induced apoptosis in human peripheral blood lymphocytes. Lymphocytes were irradiated in vitro with 5 Gy 60Co-γ-rays and cultured for 24 hours in the presence or absence of the caspase-inhibitors zVAD-fmk and zDEVD-fmk. Cell death was evaluated by electron microscopy. Irradiation in the absence of the inhibitors resulted in about 30% dead cells, almost all showing typical apoptotic morphologies. Addition of either one of the inhibitors could not rescue cells from death. Part of the dead lymphocytes (about 65%) still showed typical nuclear characteristics of apoptotic cells: sharply marginated, condensed chromatin, clumped into one sphere or into a crescent shaped mass. The remaining part of the dead cells had ultrastructural characteristics, aberrant from apoptic cells: clumping of the chromatin was less pronounced and less sharply marginated. Irregular clumps were formed. Data indicate that part of the lymphocytes go in apoptosis in a caspase-independent way. The other part shows caspase-dependent apoptosis with respect to the nuclear events.

Abstract.: This study reports on the distribution and radiation dosimetry of iodine-123 labelled trans-Z-iodomethyl-N,N-diethyltamoxifen (123-ITX), a promising radioligand for prediction of the therapeutic efficacy of unlabelled tamoxifen in human breast carcinoma. Whole-body scans were performed up to 24 h after intravenous injection of 123-ITX (mean: 146 MBq, range: 142–148 MBq) in five female volunteers, four with and one without thyroid blockade. Blood samples were taken at various times up to 24 h after injection. Urine was also collected up to 24 h after injection, allowing calculation of renal clearance and interpretation of whole-body clearance. Time-activity curves were generated for the thyroid, heart, brain, breasts, liver and gallbladder by fitting the organ-specific geometric mean counts, obtained from regions of interest. The MIRD formulation was applied to calculate the absorbed radiation doses for various organs. The images showed rapid hepatobiliary excretion, resulting in good imaging conditions for the thoracic region, whereas imaging of the abdominal region was impeded by extensive bowel activity. The breast to non-specific uptake ratio increased over time. 123-ITX was cleared by both the kidneys and the gastrointestinal tract. At 50 h p.i. the mean excretion in the urine was 89.4% (SD 5.7%). If the thyroid was not blocked, it was one of the critical organs. The highest absorbed doses were received by the excretory organs, i.e. the urinary bladder wall, the lower and upper large intestine, and the gallbladder wall. The average effective dose of 123-ITX was estimated to be 0.0084 mSv/MBq. The amount of 123-ITX required for adequate imaging of tumoral uptake results in an acceptable effective dose to the patient.

Small fields where electronic equilibrium is not achieved are becoming increasingly important in clinical practice. These complex situations give rise to problems and inaccuracies in both dosimetry and analytical/empirical dose calculation, and therefore require other than conventional methods. A natural diamond detector and a Markus parallel plate ionization chamber have been selected for clinical dosimetry in 6 MV photon beams. Results of simulations using the Monte Carlo system BEAM/EGS4to model the beam geometry have been compared with dose measurements. A modification of the existing component module for multileaf collimators (MLCs) allowed the modeling of a linear accelerator SL 25 (Elekta Oncology Systems) equipped with a MLC with curved leaf‐ends. A mechanical measurement method with spacer plates and a light‐field edge detection technique are described as methods to obtain geometrical data of collimator openings for application in the Monte Carlo system. Generally a good agreement is found between measurements and calculations of depth dose distributions and deviations are typically less than 1%. Calculated lateral dose profiles slightly exceed measured dose distributions near the higher level of the penumbras for a 10×2cm2field, but agree well with the measurements for all other cases. The simulations are also able to predict variations of output factors and ratios of output factors as a function of field width and field‐offset. The Monte Carlo results demonstrate that qualitative changes in energy spectra are too small to explain these variations and that especially geometrical factors affect the output factors and depth dose curves and profiles.

Objective The aim of this study was to evaluate the healing of artificially induced bony defects in dogs by means of demineralized allogenous bone powder (DBP) implants covered with polyhydroxy lactic acid (PLA) casts compared with DBP implants without the casts.Design Prospective animal study.Setting Research university.Sample Following a pilot study in which two dogs were used, four mongrel dogs between the ages of 18 and 24 months and weighing approximately 20 kg were used as subjects.Interventions Each experimental animal had bilateral maxillary alveolar clefts created. In a later procedure, each defect was repaired with a DBP implant, half of which were covered with a PLA96matrix. Each animal also had a circular defect created in each parietal bone that was immediately covered with DBP implants, half of which were similarly covered with a PLA96disk.Main outcome measure Repeated technetium-99m methylene-diphosphate (99mTC MDP) uptake measurements were performed to evaluate bone metabolism during the healing period, while at relevant intervals, radiographs were taken of the healing alveolar cleft defects to register bone repair. After 1 year, the animals were euthanized for macroscopic and histologic evaluation.Results Histologically, the grafts covered with PLA96were at a more advanced stage of healing than those without, and the cranial defects similarly were more advanced in the healing process than the alveolar defects. Uptake of 99mTC MDP into the cranial implants was at its maximal level after 1 week and then gradually decreased until, after 7 weeks, it was not significantly different from zero. Cranial defects covered with a PLA96-enhanced implant showed a mean maximum count rate of 275, while the plain DBP side showed a mean maximal count rate of 150. Alveolar defects with the plain DBP implant showed a maximum count rate in the first week; those with the PLA96enhanced implant showed maximum uptake during the second week. On both sides, there was a gradual decrease to the base value in the seventh week. The mean maximum count on the PLA96-enhanced side was 285, while on the plain DBP side, the corresponding value was 320.Conclusion Although an advantage of the combination was established for parietal cranial defects, no advantage was seen for alveolar cleft defects in this experimental setup.

Radiation effects on the RNA and glycosaminoglycan (GAG) synthesis of embryonic cartilaginous tibiae were studied in vitro during a 4- or 7-day culture period. Before being cultured, tibiae received single radiation doses of 20, 50 or 100 Gy. The counterparts served as sham-irradiated controls. At different times after irradiation, irradiated and control tibiae were pulse-labelled for 2 h with [3H]uridine or [3H]glucosamine. The incorporated radioactivity was measured by liquid scintillation counting. Histochemical demonstration of acid phosphatase (AP), a lysosomal enzyme, was carried out using β-glycerophosphate as substrate. A limited, dose-dependent immediate effect on RNA and GAG synthesis was found. This effect was unchanged for 2 days. After this period a time-dependent delayed effect was observed. For each radiation dose, and for each precursor, the same time-related pattern was found. At the end of the culture period AP activity, an early indicator for apoptosis, was higher in the irradiated tibiae than in the controls. No other morphological ultrastructural differences were observed at this time. We conclude that the metabolic alterations are probably due to stimulation of the initial stages of the apoptotic process in the irradiated cartilage cells.

A large scale cytogenetic study of the radiation damage in nuclear power plant workers and medical workers handling X-ray machines (269 individuals) was undertaken using the micronucleus assay for peripheral blood lymphocytes. The micronucleus frequency was found to increase systematically with donor age. After correction for the age-dependence, no correlation of the micronucleus frequency with smoking habits, expressed as cigarette-years and cigarette consumption per day, could be observed. Compared to the group of administrative workers receiving doses below 1 mSv/year, limit recommended by the ICRP for public exposure, the micronucleus frequency was slightly increased in the group of radiation workers, exposed occupationally. However, applying the Mann-Whitney test, the observed differences are not statistically significant. After correction of the dose accumulation pattern for the turn-over of the lymphocyte pool, a weak correlation between the micronucleus frequency and the equivalent dose accumulated over the 10 years preceding the study was obtained. For clear-cut conclusions on the radiation damage of low-dose worker cohorts, an increase in the sensitivity of the assay, e.g., by analysis of the micronuclei for the presence of centromeres is necessary.

One of the early events occurring at the cell membrane during apoptosis is the translocation of phosphatidylserine from the inner side of the plasma membrane to the outer layer. These phosphatidylserine groups can be bound by fluorescein isothiocyanate (FITC)-labelled annexin V. The aim of this study was to evaluate the power of the annexin V flow cytometric assay in detecting apoptosis in γ irradiated peripheral blood lymphocytes and in differentiating between apoptosis and primary necrosis in these cells. Therefore, 5Gy and 20Gy γ irradiated peripheral blood mononuclear cells (PBMCs) were examined after a 24-h culture period. The terminal deoxynucleotidyl transferase-mediated dUTP–biotin nick end labeling (TUNEL) technique was performed as well. A comparison with an electron microscopic (EM) evaluation was made. EM is based on established morphological criteria allowing the classification of cells into four groups: viable, early apoptotic, secondary necrotic and primary necrotic cells. EM performed on annexin V positive sorted cells proved that a 5Gy γ irradiation of PBMCs mainly causes apoptosis, whereas a 20Gy γ irradiation mainly induces primary necrosis. Neither the annexin V flow cytometric assay nor the TUNEL assay were able to distinguish between primary and secondary necrotic cells. These results illustrate that if quantification of apoptosis is required, one should be careful in interpreting flow cytometric results obtained by annexin V or TUNEL staining in peripheral blood lymphocytes. Although in general primary necrotic cells show an increased forward scatter due to cellullar swelling, both early apoptotic and necrotic (primary or secondary) lymphocytes show a decreased forward scatter signal. Moreover, both primary and secondary necrotic lymphocytes are annexin V and propidium iodide (PI) positive and therefore indistinguishable. We conclude that if a new experiment focusing on apoptosis is set up, an initial EM evaluation is mandatory. If EM shows that the apoptosis inducing agent used in the design of the experiments is not causing primary necrosis, than the annexin V flow cytometric assay can provide rapid and quantitative information about apoptosis.

Chick down feather bulbi can be cultured in different culture systems. Morphological analysis and3H-thymidine incorporation measurements prove that the majority of cells are viable epithelial cells.

Chick feather bulbi cultured in vitro showed an increased DNA synthesis and a delayed keratinization after treatment with ketanserin, a serotonin2antagonist with wound-healing properties. In contrast, serotonin stimulates keratinization of the keratinocytes in the bulbus.

The effects of ionizing radiation on the glycosaminoglycan synthesis of cartilaginous tibiae of 6.5 day old chick embryos have been studied in vitro over a 3 day period. As a parameter for the glycosaminoglycan synthesis, the incorporation of 3H-glucosamine is evaluated by liquid scintillation counting. A radiation induced inhibition ranging from 6% at 20 Gy to 68% at 200 Gy is observed. Light microscopical autoradiographs reveal that the secretion of the newly synthesized glycosaminoglycans is not affected significantly by ionizing radiation up to 150 Gy. Electron microscopical pictures confirm this observation and show that the chondrocytes in the irradiated tibiae remain viable. At 200 Gy most cells are necrotic. The results indicate that the radiation effects on the synthesis of the extracellular matrix components are determined by the damage of the RNA transcription.

Here we compared the effectiveness of neutrons (〈E〉 = 5·5 MeV) versus 60Co γ-rays in producing micronuclei (MN) in human lymphocytes. To obtain dose-response data, blood samples of six donors were irradiated with doses ranging from 0·1 to 5 Gy for γ-rays and 0·1-3 Gy for neutrons. A linear dependence of MN yield with dose was found for fast neutrons while for γ-rays a nonlinear dependence existed. For both radiation qualities no significant interindividual differences were found. Derived relative biological effectiveness values decreased with increasing dose. The MN frequency distributions were overdispersed with respect to the Poisson distribution, with neutrons showing higher dispersion values than with γ-rays. To compare the repair kinetics of both radiation qualities split-dose experiments were performed. A dose of 4 Gy γ-rays (3 Gy neutrons) was delivered either as a single exposure or in two equal fractions separated by time intervals ranging from 30 min to 10h (30 min to 7h for neutrons). The data showed for γ-rays a significant decline (30% ± 10%) in MN yield with interfraction time due to repair of DNA damage. This repair is a continuous process starting almost immediately after the first of the two doses and lasting 3-5h. For fast neutrons no decline was observed indicating irreparable damage.

The genetic damage present in peripheral blood lymphocytes of patients treated with fractionated partial-body radiation therapy for cervical cancer or Hodgkin's disease was followed during treatment by means of the cytokinesis-block micronucleus assay. For each patient a dose - response relationship with respect to the number of micronuclei after in vitro irradiation of blood samples pretreatment was also determined. Comparing the individual in vivo-in vitro data, the micronucleus yields after the equivalent whole-body dose during radiotherapy were found to differ substantially from the in vitro dose - response. Contrary to the linear - quadratic dose dependence after in vitro irradiation the initial increase in the micronucleus yield during radiotherapy levelled off at elevated doses. The observed differences cannot be attributed only to the effects of interphase death and the partial irradiation of the lymphocyte pool. The correlation between the micronucleus yield and the equivalent whole-body dose for values up to 2 Gy, observed for the pooled data of the first part of the radiotherapy treatment, demonstrates the suitability of the cytokinesis-block micronucleus assay as a biological dosemeter after accidents involving partial-body irradiation.

The performance characteristics of a 50 μm. niobium filter and a copper filter of equivalent thickness (0.15 mm) were compared for postero-anterior chest X-ray examination. Radiographs of 20 patients obtained using an automatic exposure control device showed no significant differences in image quality and exposure setting between the filters. Radiation dose distributions measured in a Rando phantom revealed a higher reduction in the patient dose with the niobium filter. The reduction in the effective dose equivalent, produced by the addition of the niobium and copper filters to the standard filter of 2.5 mm aluminium, of 17% and 10%, was relatively small compared with the reductions in the entrance surface dose of 31% and 26%. Our study confirms that drastic alterations in the patient dose by the addition of a dose reduction filter to the usual filtration cannot be expected.

Human peripheral blood lymphocytes, irradiated in vitro , die by an apoptotic process. The number of apoptotic cells after in vitro gamma -irradiation (0, 0.1, 0.2, 1, 2 and 5 Gy) was measured by flow cytometry using Annexin V and DiOC6 (a cationic dye) after 24 and 48 h incubation. The mean dose-response curves for apoptosis of six healthy volunteers obtained with both methods were steep below 1 Gy and flatter at higher doses. A slightly higher number of apoptotic cells was observed with DiOC6 , compared to Annexin V. This can be assigned to a minor DiOC6-int/PI population. Forty-eight hour cultures contained higher numbers of apoptotic cells compared with 24 h cultures. For both culture times, DiOC6 and Annexin V detected a statistically significant difference between a control sample and a 0.1 Gy irradiated one, illustrating the high sensitivity of the methods.

To study the possible mechanism of the age-dependent involution of the notochord, isolated mesenchymefree notochords of chick embryos were cultured in vitro and compared with their counterparts in vivo. Two different aspects were evaluated: (1) DNA synthesis measured by [3H]thymidine incorporation and visualized by autoradiography and (2) cell death quantified by counting the number of pyknotic nuclei. The results demonstrate that [3H]thymidine uptake by notochords shows an age-dependent decrease in vitro as well as in vivo. The number of [3H]thymidine-labelled notochord cells, however, is higher in vitro than in vivo. At the same time, there is an age-dependent increase in pyknosis in the notochord in vivo and in vitro. So, during the aging process, the number of both pyknotic nuclei and of [3H]thymidine-labelled nuclei suggest a high turnover of notochord cells in vitro. From these results, we can conclude that the process of involution in aging notochord seems to be controlled by a programmed intrinsic process, which might be influenced partially by the microenvironment in vivo.

This paper reports the effects of changes in dose-rate and dose-fractionation on the micronucleus (MN) yield in human lymphocytes exposed to 250 kV X-rays. For the investigation of dose-rate effects whole blood samples of four healthy donors were irradiated with doses ranging from 1 to 4 Gy given at various dose-rates between 0·2 and 40 Gy/h. For the higher doses (3 and 4 Gy) a decline in the MN yield became apparent when the dose-rate was reduced below 1·6 Gy/h. This effect was enhanced systematically by a further lowering of the dose-rate. For lower doses (1 and 2 Gy) the reduction in the MN yield was less pronounced: only a small effect was observed for two donors when a dose of 2 Gy was administered at a dose-rate of 0·2 Gy/h. In the split-dose experiment a dose of 4 Gy was delivered either as a single exposure or in two fractions of 2 Gy, separated by time intervals ranging from 30 min to 10 h. A continuous decrease of the MN yield with increasing interfraction time is observed: after an initial fast decline a further slight reduction in the MN yield occurs. The observed dose-rate and split-dose effects on the MN yield can be attributed to repair of sublethal damage.

One of the major drawbacks of the in vitro micronucleus MN assay for human lymphocytes is its reduced sensitivity for the detection of damage induced by low radiation doses, due to the high variability among the spontaneous MN frequencies. In this paper we investigated the enhancement of the sensitivity of the MN assay by analysing spontaneous and radiation-induced MN for the presence of centromeres. For this, in situ hybridization FISH with the human pancentromeric DNA probe, p82H, was performed. Our results revealed that a high percentage 73 of the spontaneous MN contain a centromere. These centromerepositive MN indicate the presence of a whole chromosome chromatid. After in vitro irradiation with low doses 0 1-2 Gy 60 Co-rays mainly centromere-negative MN were induced while only a very small number of additional centromerepositive MN were formed. This demonstrates that radiationinduced MN mainly contain acentric fragments, pointing to the clastogenic action of ionizing radiation. Furthermore, our data show that the sensitivity of the MN assay for low dose detection is increased by scoring only centromere-negative MN. .

The uptake and retention of [methyl-11C]thymidine in organs and tissues after intravenous injection were studied using positron emission tomography scanning of patients. In addition, clearance of 11C-activity from the blood was determined directly by measurements of blood-samples. 5 min after administration the activity level was already reduced to 5% of the initial activity after injection. Preferential uptake of 11C-activity was present in the liver and kidneys. A less pronounced uptake was observed in the skeletal muscle tissue, heart wall, lungs and salivary glands. The retention in these organs and tissues has a long half-life compared with the physical half-life of 11C. The absorbed dose per unit activity administered was calculated for all critical organs following the Medical Internal Radiation Dose Committee formalism. Averaging over the patients, values of 37 and 28 μGy MBq−1were obtained for the liver and the kidneys respectively. The committed effective dose after a [methyl-11C]thymidine scan with 740 MBq, a commonly applied amount of activity for this type of scan, is 2.8 mSv.

The Thetis research pool reactor (with a nominal power of 150 kW) of the Ghent University was operational from 1967 till December 2003. The first phase of the decommissioning of the reactor, the removal of the spent fuel from the site, took place in 2010. The cumulative dose received was only 404 man · µSv. During the second phase, the transition period between the removal of the spent fuel in 2010 and the start of the decommissioning phase in March 2013, 3-monthly internal inspections and inspections by Bel V, were performed. The third and final decommissioning phase started on March 18, 2013. The total dose received between March 2013 and August 2013 was 1561 man · µSv. The declassification from a Class I installation to a Class II installation was possible by the end of 2015. The activated concrete in the reactor pool will remain under regulatory control until the activation levels are lower than the limits for free release.

The evaluation of the health risks associated with low dose radiation exposure relies on the verification of exposure history. Retrospective biodosimetry based on frequencies of chromosome translocations is well established for exposure to low LET radiation and has proved a valuable tool for validating doses in epidemiological studies. For high LET irradiation, such as that from internally deposited α-emitting radionuclides, the relationship between chromosome aberration frequencies in blood lymphocytes and dose is more difficult to establish. In recent years, in vitro studies have highlighted the complexity of chromosome aberrations induced by α-irradiation. Moreover, exposure to densely ionising radiation is predicted to result in a lower ratio of inter- to intra-chromosomal exchanges (F ratio) than exposure to low LET radiation. However, the majority of cells with complex aberrations will be unstable and will not undergo cell division to give viable descendant cells. Therefore, the quantification of chromosome biomarkers of α-irradiation must take into account the distribution and transmissibility of the different aberration types if it is to provide information that is relevant to the interpretation of in vivo frequencies. The profile of chromosome damage induced by α-particle irradiation was examined using sFISH and mBAND. Lymphocytes in their first in vitro division following exposure to 213Bi α-particles were analysed by sFISH and genomic aberration frequencies derived. Cell stability status was established by analysing the whole genome for unstable aberrations. The majority of aberrant stable cells contained a single simple translocation. The dose response for translocations in stable cells for doses up to 200mGy was 7.90 ± 0.98 x 10-2 per Gy. Aberrations involving the number 5 chromosomes were identified using mBAND. Exchanges involving aberrant chromosomes 5 were classed as inter- or intrachanges and further classified into simple and complex. F ratios were 1.4 and 2.4 for 0.2 and 0.5Gy α-particles and 5.5 for 1.5Gy γ-rays. Although α-particles induced more intrachanges, their association with complex exchanges, which are likely to be unstable and nontransmissible through cell division, will limit their applicability as a marker of past in vivo exposure. This work has failed to demonstrate a unique chromosome biomarker which would discriminate between different qualities of radiation in workers with historical exposures but has confirmed that stable cells with a single translocation do arise in significant numbers in a dose dependent fashion following α-particle irradiation.

In case of a large radiation accident, when hundreds of people may be exposed, it is very important to distinguish the severely exposed individuals, who require early medical treatment, from those less exposed. In such a situation, specific biological indicators should promptly indicate whether the whole-body dose received by the victims exceeded 1Gy, the level above which it is necessary to provide medical care. Once the exposed population has undergone such an early triage, a second step may be indicated for a more accurate assessment of the exposure. Up to now, scoring of dicentrics is the reference to estimate the dose received in case of individual overexposures. However, to obtain a reliable dose estimate, 500 metaphases should be screened for the presence of dicentrics, a very time consuming procedure, that can only be applied to small populations of exposed individuals. The aim of our study was to develop a quick population triage method based on automated micronucleus (MN) scoring. Automated MN scoring was performed using a MN software module specifically developed by Metasystems for the Metafer4 platform. Standard dose response curves were established for manual, automated and semi-automated MN scoring. To this aim, blood samples of 10 individuals were irradiated with in vitro doses of 0-0,2-0,5-1-2-3Gy Co-60 γ-rays. Whole blood cultures were set up and cells were harvested after 70h, applying rigorous culture/harvest conditions. Cells were stained with DAPI for manual and automated scoring. For both scoring methods 500 binucleated (BN) cells were counted. The reproducibility, accuracy and sensitivity of the manual versus automated scoring procedure were analyzed. A comparison between manual and automated scoring of the same slides, revealed a drop in the MN yield for the automated scoring procedure. However, the automated scores were as reproducible as the manual scores and both scores were highly correlated. Scoring of 500 BN cells allows us to detect a dose of 0,5 Gy, with 95% confidence, for both manual and automated MN scoring procedures (Mann-Whitney U test, p<0.05). The semi-automated scoring procedure, taking into account false positives and false negatives in the MN class, didn’t result in a better accuracy or reproducibility. With the automated MN scoring procedure, about 80 slides (500 BN cells) can be scored in 1 day with the Metafer4. In conclusion, our preliminary results show that automated MN scoring is a quick and reliable method, useful for a first population triage in case of large radiation accidents.

Breast cancer patients are characterised by an enhanced chromosomal radiosensitivity pointing to a defect in the repair of DNA double strand breaks (dsb). In mammalian cells, radiation induced dsb are mainly repaired by the non homologous end-joining (NHEJ) repair pathway, a pathway in which the Ku70/Ku80 heterodimer plays a key role as it binds to the broken DNA ends. In this study we wanted to investigate the radiosensitizing effect of Ku70/80 knockdown, by lentivirus-mediated RNAinterference, in a spontaneous immortalised human mammary epithelial cell line (MCF10A). Several endpoints for measuring radiosensitivity were taken into acount: micronucleus formation (chromosomal radiosensitivity), cell survival, apoptosis and senescence. For all endpoints, MCF10A cells were infected with lentiviral vectors for RNAi of Ku70 (pLVTHM/shKu70/GFP). Western blot analysis showed that the Ku70 lentiviral vector was effective in silencing the expression of both Ku70 and Ku80. When a satisfactory knockdown was obtained (70-90% vs. mock-infected (pLVTHM/GFP) cells), the cells were used to perform radiation experiments. For the in vitro MN assay, cells were irradiated with doses of 2 and 4 Gy 60Co gamma-rays. A significantly higher radiation-induced MN yield was obtained in the Ku70/80 knock down cell line compared to the mock-infected cell line, pointing to an increased chromosomal radiosensitivity. This increased chromosomal radiosensitivity demonstrates that the repair genes, Ku70 and Ku80, are involved in the repair of DNA double strand breaks, which are the main DNA lesions resulting in chromosomal aberrations such as micronuclei. Besides chromosomal radiosensitivity we also investigated radiosensitivity at the cellular level by cell survival experiments. Cells were irradiated with doses ranging between 0 and 8 Gy and cultured for 5 days before being analysed. The results of the cell survival assay show that Ku70/80 knockdown cells have a lower survival yield after irradiation compared to mock-infected cells, pointing to an enhanced cellular radiosensitivity. Analysis of the cell death pattern showed that MCF10 cells (Ku70/80 knockdown and mock-infected) do not undergo apoptosis but go into cellular senescence. In conclusion, we can state that knockdown of Ku70 and Ku80 by RNAi of Ku70 resulted in an increased chromosomal and cellular radiosensitivity in an immortalised MCF10 human mammary cell line after irradiation with low LET 60Co gamma-rays. These results may further support the role of DNA dsb repair genes in breast cancer.

INTRODUCTION

The aim of present study was to investigate the relation between physical dose related parameters and single nucleotide polymorphisms (SNPs) in DNA DSB repair genes XRCC3 (c.-1843 A>G, c.562-14 A>G, c.722 C>T), Rad51 (c.-3429 G>C, c.-3392 G>T), Lig4 (c.26 C>T, c.1704 T>C), Ku70 (c.-1310 C>G) and Ku80 (c.2110-2804 G>A) and development of acute normal tissue RT reactions. The study population consisted of 89 head and neck cancer patients treated with IMRT. All RT reactions were scored using the CTCAE scale for mucositis, dermatitis and dysphagia. The population was subdivided in a group with low and moderate radiosensitivity (CTC0-2) and a group with high radiosensitivity (CTC3) for each acute normal tissue effect. The polymorphic regions were analysed by PCR- RFLP or single base extension analysis (PCR- Snapshot). Analyses showed that if we compare the CTC0-2 and the CTC3 group, the mean dose to the oral cavity is significantly associated with the development of mucositis (p= 0.042). For dysphagia a statistically significant relation was found with the dose of the upper, mid and lower constrictor pharyngeus (CP) muscles. These physical factors are considered as confounding factors in the radiogenomics analyses of this study. The SNPs in the coding region of the XRCC3 gene (c.722 C>T) and in the 5’ UTR region of the Ku70 gene (c.-1310 C>G) were significantly associated with the risk of developing severe dysphagia (CTC3) and can therefore be considered as risk alleles. Heterozygous carriers of the variant allele had a respectively 4.47 (p= 0.033) and 4.17 (p=0.014) increased risk to develop acute swallowing problems. We developed a risk analysis model using logistic regression analysis to predict patients probability to suffer from severe dysphagia as a result of the RT treatment. In this model the CP dose and the information regarding XRCC3 c.722 C>T and Ku70 c.-1310 C>G genotypes were included. Using a cut off value of two times the median, the model provided us a sensitivity of 78.6% and a specificity of 77.6% for prediction of severe dysphagia. No association between the investigated polymorphisms and the development of mucositis or dermatitis was found. Considering the dose to the CP muscles as confounding factor in a logistic regression model, presence of the variant allele of XRCC3 c.722 and Ku70 c.-1310 is significantly associated with development of dysphagia. Using the paramount physical and biological parameters, we developed a risk model for prediction of patients risk for severe dysphagia.

Enhanced chromosomal radiosensitivity (CR) has been observed in a significant number of breast cancer patients. Since ionising radiation induces double-strand breaks (DSB), polymorphisms in DSB repair genes could be involved in genetic predisposition to breast cancer. A family history of breast cancer is a well known risk factor for the disease. Other risk factors are also associated with breast cancer, such as early age of first menarche, nulliparity or late first childbirth, and late menopause. The principle culprit common for these risk factors is said to be the prolonged exposure to elevated levels of estrogens. As non homologous end-joining (NHEJ) is the major DSB repair pathway in mammalian cells, we investigated the association of 5 SNPs in 3 different NHEJ genes with breast cancer in a population-based case-control setting. The total patient population was composed of a selected group of patients with a family history of the disease and an unselected group. CR was previously studied in both patient groups. SNP analysis showed that the c.2099-2408G>A SNP (Ku80) has a significant odds ratio (OR) of 2.81 (95% confidence interval (CI): 1.30-6.05) for the heterozygous (He) and homozygous variant (HV) genotypes in the group of familial patients. The He+HV genotypes of the c.2099-2408G>A SNP (Ku80) also showed high and significant ORs in the group of radiosensitive, familial breast cancer patients (OR=4.62 ,95%CI: 1.28-16.74). For the c.-1310 C>G SNP (Ku70) a significant OR of 1.85 (95%CI: 1.01-3.41) was found for the He genotype in the unselected patient group. For the radiosensitive, unselected patients, increased, but non-significant ORs were observed. The c.-1310 C>G SNP (Ku70) SNP exhibits significant results in the unselected patient group only, indicating an influence of other, environmental factors besides genetic factors. As breast epithelium is exposed to endogenous oxidative stress through increased estrogen exposure, the possible effect of hormone exposure was examined in an enlarged, unselected patient population (OR enlarged population =1.68, 95%CI:1.09-2.60). The ORs of the c.-1310 C>G SNP (Ku70) SNP for patients with a longer estrogen exposure were high and significant (early menarche: OR=1.85, 95%CI:1.20-2.92; late menopause: OR=1.94, 95%CI:1.08-3.51) while the ORs for patients with a short hormone exposure were lower and non-significant. These results provide preliminary evidence that the variant allele of c.-1310C>G (Ku70) and c.2099-2408G>A (Ku80) are risk alleles for breast cancer as well as CR. Furthermore, the association of c.-1310C>G (Ku70) with breast cancer risk was stronger in women with a long estrogen exposure.

BD-PND bubble detectors from Bubble Technology Industries (BTI) were used to conduct a study of the life span of these detectors. The manufacturer guarantees an optimum detector performance for three months after receipt. Nevertheless, it is important to know the evolution of their characteristics with time, also after those three months. On a standard set-up with a 252Cf source the bubble detectors were irradiated until they reached the end of their life span. During this period, the evolution in sensitivity was monitored. The temperature compensating system seems to be the limiting factor with time for the use of the BTI bubble detectors. The change in temperature dependence with age was determined. The same parameters were also checked with several batches of detectors that were used in practice.

The first results are presented of a study of the BD-PND bubble detector. A large batch of these neutron detectors was tested for their main characteristics by irradiation with a 252Cf source. This included an investigation on the reproducibility, the batch uniformity of the results and linearity with dose equivalent. The change in sensitivity after activation of the detector is another parameter investigated. Over a large temperature range (14 to 47 oC) the extent to which the BD-PND bubble detectors are really temperature independent was investigated. Probably due to a limited lifetime of the temperature compensation, a progressive rise of sensitivity with temperature was found. Checks were also made for any change in sensitivity during the lifetime of the detectors and a few parameters that could influence this sensitivity were studied.