Patient doses in gamma-intracoronary radiotherapy: the Radiation Burden Assessment Study

PURPOSE

To determine accurately the radiation burden of both patients and staff from intracoronary radiotherapy (IRT) with (192)Ir and to investigate the importance of IRT in the patient dose compared with interventional X-rays.

METHODS AND MATERIALS

The Radiation Burden Assessment Study (RABAS) population consisted of 9 patients undergoing gamma-IRT after percutaneous transluminal coronary angioplasty and 14 patients undergoing percutaneous transluminal coronary angioplasty only as the control group. For each patient, the dose to the organs and tissues from the internal and external exposure was determined in detail by Monte Carlo N-particle simulations. Patient skin dose measurements with thermoluminescence dosimeters served as verification. Staff dosimetry was performed with electronic dosimeters, thermoluminescence dosimeters, and double film badge dosimetry.

RESULTS

With respect to the patient dose from IRT, the critical organs are the thymus (58 mGy), lungs (31 mGy), and esophagus (27 mGy). The mean effective dose from IRT was 8 mSv. The effective dose values from interventional X-rays showed a broad range (2-28 mSv), with mean values of 8 mSv for the IRT patients and 13 mSv for the control group. The mean dose received by the radiotherapist from IRT was 4 microSv/treatment. The doses to the other staff members were completely negligible.

CONCLUSION

Our results have shown that the patient and personnel doses in gamma-IRT remain at an acceptable level. The patient dose from IRT was within the variations in dose from the accompanying interventional X-rays.

DOSSCORE: an accelerated DOSXYZnrc code with an efficient stepping algorithm and scoring grid

DOSSCORE is an accelerated version of DOSXYZnrc that allows photons to cross voxel boundaries of the same medium and utilizes a separate scoring grid superimposed on the geometrical grid. Two different stepping algorithms, the hownear method and the scaling method are implemented in DOSSCORE. The hownear method allows particles to travel larger distances in homogeneous regions where there is no interest in the dose deposition of these particles, whilst the scaling method utilizes a stepping algorithm in which particles are only slowed down by the boundaries of the geometrical voxels and not by the boundaries of the scoring voxels. For CT-based phantoms, only photon ray tracing is applied, which results in a rather modest speed gain of factor 1.2 compared to DOSXYZnrc. The hownear method and scaling method do not increase the speed for CT-based phantoms, but only for homogeneous phantoms and phantoms with a limited number of small heterogeneities. In cases where a small number of scoring voxels are needed, the hownear method performs better than the scaling method, whilst the opposite is true for cases when many scoring voxels are needed. The photon transport is accelerated by almost a factor of 2 for all phantoms (homogeneous, heterogeneous with much homogeneity and CT-based phantoms) compared to DOSXYZnrc. For a small number of scoring voxels, the hownear method is up to a factor of 2.6 and 1.9 faster than DOSXYZnrc for homogeneous and heterogeneous phantoms in the case of photon beams. For an electron beam, a speed gain of factor 2.4 is obtained. For a full scoring grid like the one used in DOSXYZnrc, the scaling method is up to a factor of 2.2 and 1.7 faster than DOSXYZnrc for homogeneous and heterogeneous phantoms in the case of photon beams. For an electron beam, a speed gain of factor 2 is obtained. A speed increase without biasing the results is very relevant. The use of two separate grids, the more efficient stepping algorithms and the accelerated photon transport can be applied to every EGS-based or other Monte Carlo code.

The use of EBV-transformed cell lines of breast cancer patients to measure chromosomal radiosensitivity

To investigate the chromosomal radiosensitivity of lymphocytes in cancer patients the micronucleus (MN) assay is often used and performed on freshly drawn peripheral blood lymphocytes. The use of Epstein-Barr virus (EBV)-transformed lymphoblastoid cell lines may have a lot of advantages (e.g. large pool of cells) compared with fresh blood samples. In this study we have investigated whether the response of EBV-transformed lymphoblastoid cell lines to irradiation in the G1/S/G2 phases of the cell cycle is the same as in concordant whole blood cultures where primary lymphocytes were irradiated in the G0 phase of the cell cycle. For this study the MN assay (2 Gy) was performed on EBV-transformed cell lines of breast cancer patients and a group of healthy women. Those breast cancer patients were selected who showed an elevated chromosomal radiosensitivity in fresh blood samples in a previous study. The results demonstrated that the enhanced chromosomal radiosensitivity observed in fresh blood cultures of breast cancer patients is not present in EBV-transformed cell lines derived from the same blood samples. Therefore, care must be taken when EBV cell lines are used to assess chromosomal radiosensitivity in breast cancer patients.

Radiolabeling, biodistribution, and dosimetry of (123)I-mAb 14C5: a new mAb for radioimmunodetection of tumor growth and metastasis in vivo

This study reports on the in vitro evaluation, biodistribution, and dosimetry of (123)I-labeled monoclonal antibody (mAb) 14C5, a new antibody-based agent proposed for radioimmunodetection of tumor growth and metastasis in vivo.

METHODS

(123)I-mAb 14C5 was prepared by direct iodination and tested for stability in vitro. Binding assays were performed on human SK-BR-3 and HeLa carcinoma cells to investigate the antigen expression, antibody affinity, and kinetics of tracer binding. For the biodistribution and dosimetry study, 3- to 4-wk-old NMRI mice were injected intravenously with (123)I-mAb 14C5 (148.0 +/- 7.4 kBq per mouse) and killed at preset time intervals. Organs, blood, urine, and feces were counted for radioactivity uptake, and the data were expressed as the percentage injected dose per gram tissue (%ID/g tissue) or %ID. The MIRDOSE3.0 program was applied to extrapolate the estimated absorbed radiation doses for various organs to the human reference adult.

RESULTS

(123)I-mAb 14C5 was obtained in radiochemical yields of 85.0% +/- 2.5% and radiochemical purities were >97%. The iodinated antibody demonstrated good in vitro stability with 93.6% +/- 0.1% of (123)I-mAb 14C5 remaining intact at 24 h after radiolabeling. (123)I-mAb 14C5 bound to SK-BR-3 cells (dissociation constant [K(d)] approximately 0.85 +/- 0.17 nmol/L) and HeLa cells (K(d) approximately 1.71 +/- 0.17 nmol/L) with nanomolar affinity and high specificity, whereas both cell types exhibited a high CA14C5 antigen expression (maximum number of binding sites [B(max)] = 40.6 +/- 5.2 and 57.1 +/- 9.6 pmol/L, respectively). In mice, (123)I-mAb 14C5 accumulated primarily in lungs (20.4 %ID/g), liver (15.1 %ID/g), and kidneys (11.1 %ID/g) within 5 min after injection. A delayed uptake was observed in stomach (12.8 %ID/g) and urinary bladder (8.7 %ID/g) at 3 and 6 h, respectively, after injection. Radioactivity clearance was predominantly urinary, with 44.9 +/- 4.5 %ID excreted during the initial 48 h after administration (cumulative amount). The highest absorbed radiation doses determined for the human reference adult were received by the urinary bladder wall (0.1200-0.1210 mGy/MBq), liver (0.0137-0.0274 mGy/MBq), uterus (0.0196-0.0207 mGy/MBq), and lower large intestine wall (0.0139-0.0258 mGy/MBq). The average effective dose resulting from a single (123)I-mAb 14C5 injection was estimated to be 0.017-0.022 mSv/MBq.

CONCLUSION

(123)I-mAb 14C5 shows good in vitro biologic activity and favorable biodistribution properties for imaging carcinomas of different origin and provides an acceptable radiation dose to the patient.

Chromosomal aberrations and in vitro radiosensitivity: intra-individual versus inter-individual variability

In order to assess the applicability of the micronucleus (MN) and G2 assays as biomarkers of in vitro radiosensitivity and cancer susceptibility, we investigated the inter- and intra-individual variation of these endpoints. For the MN assay unstimulated blood cultures from 57 healthy donors were exposed in vitro to 3.5 Gy Co gamma-rays and for the G2 assay PHA stimulated cultures were irradiated with a dose of 0.4 Gy Co gamma-rays in the G2 phase of the cell cycle. For 14 donors, 2-15 repeat samples were tested over a period of 3 years. The repeat experiments revealed that the intra-individual variability was not significantly different from the inter-individual variability for both G2 and MN assays. As the intra-individual variability determines the reproducibility of the assay, our results highlight the limitations of these endpoints in detecting reproducible differences in radiation sensitivity between individuals within a normal population. Due to the high intra-individual variability and no significant difference with the inter-individual variability found in our study we conclude that care has to be taken when results obtained with chromosomal aberration assays based on one blood sample are used to assess the individual radiosensitivity. Multiple blood sampling may be necessary to draw reliable conclusions. Although more validation studies on the reliability of the G2 and MN assay will be required before they can be used in a confident way as biomarkers of individual radiosensitivity or cancer susceptibility the assays are very valuable to examine population radiosensitivity and the relationship between radiosensitivity, cancer predisposition and genotype.

Biologic dosimetry of 188Re-HDD/lipiodol versus 131I-lipiodol therapy in patients with hepatocellular carcinoma

One approach to treatment of primary hepatocellular carcinoma (HCC) is intraarterial injection of (131)I-lipiodol. Although clinical results have been positive, the therapy can be improved by using (188)Re instead of (131)I as the radionuclide. (188)Re is a high-energy beta-emitter, has a shorter half-life than (131)I, and has only low-intensity gamma-rays in its decay. The present study compared the cytotoxic effect of the radionuclide therapy in HCC patients treated with (131)I-lipiodol and (188)Re-4-hexadecyl 2,2,9,9-tetramethyl-4,7-diaza-1,10-decanethiol (HDD)/lipiodol. To this end, dicentric chromosomes (DCs) were scored in metaphase spreads of peripheral blood cultures. The equivalent total-body dose was deduced from the DC yields using an in vitro dose-response curve.

METHODS

Twenty (131)I-lipiodol treatments and 11 (188)Re-HDD/lipiodol treatments were performed on, respectively, 16 and 7 patients with inoperable HCC. Patients received a mean activity of 1.89 GBq of (131)I-lipiodol or 3.56 GBq of (188)Re-HDD/lipiodol into the liver artery by catheterization. For each patient, a blood sample was taken during the week before therapy. A blood sample was also taken 7 and 14 d after administration for the patients treated with (131)I-lipiodol and 1 or 2 d after administration for the patients treated with (188)Re-HDD/lipiodol.

RESULTS

The mean DC yield of (188)Re-HDD/lipiodol therapy (0.087 DCs per cell) was significantly lower than that of (131)I-lipiodol therapy (0.144 DCs per cell) for the administered activities. Corresponding equivalent total-body doses were 1.04 Gy for (188)Re-HDD/lipiodol and 1.46 Gy for (131)I-lipiodol. Data analysis showed that, in comparison with (131)I-lipidol, (188)Re-HDD/lipiodol yielded a smaller cytotoxic effect and a lower radiation exposure for an expected higher tumor-killing effect.

CONCLUSION

(188)Re is a valuable alternative for (131)I in the treatment of HCC with radiolabeled lipiodol, and a dose escalation study for (188)Re-HDD/lipiodol therapy is warranted.

The effect of caspase-inhibitors on radiation induced apoptosis in human peripheral blood lymphocytes: an electron microscopic approach

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 60 Co-gamma-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 apoptotic 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.

Dose reduction in patients undergoing chest imaging: digital amorphous silicon flat-panel detector radiography versus conventional film-screen radiography and phosphor-based computed radiography

OBJECTIVE

We sought to compare the radiation dose delivered to patients undergoing clinical chest imaging on a full-field digital amorphous silicon flat-panel detector radiography system with the doses delivered by a state-of-the-art conventional film-screen radiography system and a storage phosphor-based computed radiography system. Image quality was evaluated to ensure that the potential reduction in radiation dose did not result in decreased image acuity. SUBJECTS AND METHODS. Three groups of 100 patients each were examined using the amorphous silicon flat-panel detector, film-screen, or computed radiography systems. All patient groups were matched for body mass index, sex, and age. To measure the entrance skin dose, we attached 24 calibrated thermoluminescent dosimeters to every patient. The calculation of the effective dose, which represents the risk of late radiation-induced effects, was based on measurements on an anthropomorphic phantom. Image quality of all three systems was evaluated by five experienced radiologists, using the European Quality Criteria for Chest Radiology. In addition, a contrast-detail phantom study was set up to assess the low-contrast detection of all three systems.

RESULTS

The amorphous silicon flat-panel detector radiography system allowed an important and significant reduction in both entrance skin dose and effective dose compared with the film-screen radiography (x 2.7 decrease) or computed radiography (x 1.7 decrease) system. In addition, image quality produced by the amorphous silicon flat-panel detector radiography system was significantly better than the image quality produced by the film-screen or computed radiography systems, confirming that the dose reduction was not detrimental to image quality.

CONCLUSION

The introduction of digital flat-panel radiography systems based on amorphous silicon and cesium iodide is an important step forward in chest imaging that offers improved image quality combined with a significant reduction in the patient radiation dose.

In vitro evaluation of 213Bi-rituximab versus external gamma irradiation for the treatment of B-CLL patients: relative biological efficacy with respect to apoptosis induction and chromosomal damage

External source radiotherapy and beta radioimmunotherapy (RIT) are effective treatments for lymphoid malignancies. The development of RIT with alpha emitters is attractive because of the high linear energy transfer (LET) and short path length, allowing higher tumour cell kill and lower toxicity to healthy tissues. We assessed the relative biological efficacy (RBE) of alpha RIT (in vitro) compared to external gamma irradiation with respect to induction of apoptosis in B chronic lymphocytic leukaemia (B-CLL) and induction of chromosomal damage in healthy donor B and T lymphocytes. The latter was measured by a micronucleus assay. 213Bi was eluted from a 225Ac generator and conjugated to CD20 antibody (rituximab) with CHX-A"-DTPA as a chelator. B-CLL cells from five patients were cultured for 24 h in RPMI/10% FCS while exposed to 213Bi conjugated to CD20 antibody or after external 60Co gamma irradiation. Binding assays were performed in samples of all patients to calculate the total absorbed dose. Apoptosis was scored by flow cytometric analyses of the cells stained with annexin V-FITC and 7-AAD. Apoptosis was expressed as % excess over spontaneous apoptosis in control. Full dose range experiments demonstrated 213Bi-conjugated CD20 antibody to be more effective than equivalent doses of external gamma irradiation, but showed that similar plateau values were reached at 10 Gy. The RBE for induction of apoptosis in B-CLL was 2 between 1.5 and 7 Gy. The micronucleus yield in lymphocytes of healthy volunteers was measured to assess the late toxicity caused by induction of chromosomal instability. While gamma radiation induced a steady increase in micronucleus yields in B and T cells, the damage induced by 213Bi was more dramatic, with RBE ranging from 5 to 2 between 0.1 Gy and 2 Gy respectively. In contrast to gamma irradiation, 213Bi inhibited mitogen-stimulated mitosis almost completely at 2 Gy. In conclusion, high-LET targeted alpha particle exposure killed B-CLL cells more effectively than did external gamma irradiation at a low dose (RBE=2), while a plateau was reached at a high dose. Long-term toxicity on healthy B and T lymphocytes was systematically higher for the alpha emitter (RBE=5 to 2).

Biodistribution and dosimetry study of 123I-rh-annexin V in mice and humans

This study reports on the optimization of the labelling procedure of clinical grade 123I-rh-annexin V and on the investigation of the biodistribution and dosimetry of 123I-rh-annexin V, a tracer proposed for the study of apoptosis in mice and humans. Research grade 123I-rh-annexin V was prepared as described previously, whereas clinical grade 123I-rh-annexin V was prepared according to a modified IodoGen method. NMRI mice, 3-4 weeks of age, received research grade 123I-rh-annexin V (74.0+/-3.7 kBq/mouse) 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 %ID/g tissue or %ID over time. Secondly, six volunteers with normal liver and kidney function underwent whole-body scans up to 21 h after i.v. injection of clinical grade 123I-rh-annexin V (345+/-38 MBq). Time-activity 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 123I-rh-annexin V was obtained in radiochemical yields of 87.0+/-6.5% and radiochemical purities >98%. In mice, research grade 123I-rh-annexin 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 123I-rh-annexin V was estimated to be 0.02 mSv.MBq-1. The amount of 123I-rh-annexin V required for in vivo imaging, results in an acceptable effective dose to the patient.

The value of radiochromic film dosimetry around air cavities: experimental results and Monte Carlo simulations

In this study we investigate radiochromic film dosimetry around air cavities with particular focus on the perturbation of the dose distribution by the film when the film is parallel to the beam axis. We considered a layered polystyrene phantom containing an air cavity as a model for the air-soft tissue geometry that may occur after surgical resection of a paranasal sinus tumour. A radiochromic film type MD-55 was positioned within the phantom so that it intersected the cavity. Two phantom set-ups were examined. In the first case, the air cavity is at the centre of the phantom, thus the film is lying along the central beam axis. In the second case, the cavity and film are located 2 cm offset from the phantom centre and the central beam axis. In order to examine the influence of the film on the dose distribution and to interpret the film-measured results, Monte Carlo simulations were performed. The film was modelled rigorously to incorporate the composition and structure of the film. Two field configurations, a 1 x 10 cm2 field and a 10 x 10 cm2 field, were examined. The dose behind the air cavity is reduced by 6 to 7% for both field configurations when a film that intersects the cavity contains the central beam axis. This is due to the attenuation exerted by the film when photons cross the cavity. Offsetting the beam to the cavity and the film by 2 cm removes the dose reduction behind the air cavity completely. Another result was that the rebuild-up behind the cavity for the 10 x 10 cm2 field, albeit less significant than for the 1 x 10 cm2 field, could only be measured by the film that was placed offset with respect to the central beam axis. Although radiochromic film is approximately soft-tissue equivalent and energy independent as compared to radiographic films, care should be taken in the case of inhomogeneous phantoms when the film intersects air cavities and contains the beam central axis. Errors in dose measurement can be expected distal to the air cavity due to attenuation in the film itself. This attenuation would not occur in the absence of the film. Both experiments and Monte Carlo computations support this conclusion.

Intra-arterial radionuclide therapy for liver tumours: effect of selectivity of catheterization and 131I-Lipiodol delivery on tumour uptake and response

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 (%IA/ml 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 %IA/ml 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 (P=0.002). A large tumour volume was invariably related to low uptake of 131I-Lipiodol and progressive disease (P=0.008). 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.

Monte Carlo model of the Elekta SLiplus accelerator: validation of a new MLC component module in BEAM for a 6 MV beam

A new component module (CM), called MLCE, has been implemented in the BEAM program. The CM takes into account the particular 'tongue-and-groove' 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% 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% 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% of the total transmitted radiation. The relevance of the detailed MLC modelling was demonstrated also by studying the 'adjacent' 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% for two leaves and by 40% 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.

Chromosomal radiosensitivity in breast cancer patients with a known or putative genetic predisposition

The chromosomal radiosensitivity of breast cancer patients with a known or putative genetic predisposition was investigated and compared to a group of healthy women. The chromosomal radiosensitivity was assessed with the G2 and the G0-micronucleus assay. For the G2 assay lymphocytes were irradiated in vitro with a dose of 0.4 Gy (60)Co gamma-rays after 71 h incubation, and chromatid breaks were scored in 50 metaphases. For the micronucleus assay lymphocytes were exposed in vitro to 3.5 Gy (60)Co gamma-rays at a high dose rate or low dose rate. 70 h post-irradiation cultures were arrested and micronuclei were scored in 1000 binucleate cells. The results demonstrated that the group of breast cancer patients with a known or putative genetic predisposition was on the average more radiosensitive than a population of healthy women, and this with the G2 as well as with the high dose rate and low dose rate micronucleus assay. With the G2 assay 43% of the patients were found to be radiosensitive. A higher proportion of the patients were radiosensitive with the micronucleus assay (45% with high dose rate and 61% with low dose rate). No correlation was found between the G2 and the G0-micronucleus chromosomal radiosensitivity. Out of the different subgroups considered, the group of the young breast cancer patients without family history showed the highest percentage of radiosensitive cases in the G2 (50%) as well as in the micronucleus assay (75-78%).

Patient dosimetry for 131I-MIBG therapy for neuroendocrine tumours based on 123I-MIBG scans

Pre-therapeutic metaiodobenzylguanidine (MIBG) scans can be performed using labelling with either iodine-123 or iodine-131. (123)I-MIBG scans provide better image quality and count statistics, while (131)I-MIBG allows registration of tracer kinetics over a longer period. The aim of this study was to determine how much information about the (131)I-MIBG therapy total body dose according to the MIRD formalism can be gathered from (123)I-MIBG pre-therapy scans. Thirty-eight (131)I-MIBG therapies administered to a total of 15 patients suffering from neuroblastoma ( n=6), carcinoid tumours ( n=5), phaeochromocytoma ( n=3) and medullary thyroid carcinoma ( n=1) were included. The mean administered activity was 5.3 GBq (SD 2.4 GBq). Three biplanar (123)I-MIBG total body scans were taken only once before a series of therapies while three biplanar (131)I-MIBG scans were taken after each therapy. Attenuation correction was performed taking into account the difference in attenuation between (123)I and (131)I. Using the MIRD formalism, the total body dose to the patient was calculated on the basis of: (1) a single exponential fit drawn through the data from the (123)I-MIBG pre-therapy scans, (2) a bi-exponential fit through the combined data of (123)I-MIBG pre-therapy and (131)I-MIBG post-therapy scans. The mean total body dose calculated in our study was significantly higher for patients suffering from neuroblastoma (mean+/-SD 0.37+/-0.21 mGy/MBq) than for patients suffering from phaeochromocytoma (0.08+/-0.02 mGy/MBq), carcinoid tumours (0.07+/-0.01 mGy/MBq) and medullary thyroid carcinoma (0.09 mGy/MBq). The correlation coefficient between the dose calculated on the basis of the (123)I-MIBG pre-therapy scans and the subsequent (131)I-MIBG therapy was 0.93 when a correction factor of 1.26 was taken into account. When considering all following therapies, the correlation was 0.85 and the correction factor, 1.20. Our results show that it is feasible to use data from pre-therapy (123)I-MIBG scans to calculate the total body dose of the subsequent (131)I-MIBG therapy.

Chromosomal radiosensitivity study of temporary nuclear workers and the support of the adaptive response induced by occupational exposure

PURPOSE

To study chromosomal radiosensitivity in a population of radiation workers and investigate the possibility of an adaptive response in lymphocytes of workers after short-term occupational exposure to ionizing radiation.

MATERIALS AND METHODS

The studied group comprised 41 workers temporarily employed at the Nuclear Power Plant Doel (Belgium) for reactor maintenance. A blood sample was taken before and directly after the exposure period of about 1 month. Chromosomal radiosensitivity was assessed in vitro by the G2 assay and the G0 micronucleus (MN) assay. For the MN assay, a low dose-rate (LDR) in vitro irradiation protocol was applied in addition to high dose-rate (HDR) irradiation of the blood samples in order to determine the dose-rate sparing (DRS) effect.

RESULTS

No statistically significant effect of the occupational exposures (up to 10 mSv) on the baseline MN frequencies without in vitro irradiation was observed. A comparison of the number of chromatid aberrations pre- and post-exposure shows no effect of the occupational exposure. On the other hand, the G0-MN assay with the LDR irradiation protocol reveals a systematic reduction in chromosomal radiosensitivity by the exposure, increasing with dose. For workers who received the highest dose (4-10 mSv) a statistically significant (p <0.05) decrease of the in vitro induced MN yields and increase of the dose-rate sparing was observed.

CONCLUSIONS

Short-term low-dose occupational exposure may act as an in vivo adaptive dose and stimulate repair in G0 lymphocytes.

Parameter dependence of the MCNP electron transport in determining dose distributions

In this paper, a detailed study of the electron transport in MCNP is performed, separating the effects of the energy binning technique on the energy loss rate, the scattering angles, and the sub-step length as a function of energy. As this problem is already well known, in this paper we focus on the explanation as to why the default mode of MCNP can lead to large deviations. The resolution dependence was investigated as well. An error in the MCNP code in the energy binning technique in the default mode (DBCN 18 card = 0) was revealed, more specific in the updating of cross sections when a sub-step is performed corresponding to a high-energy loss. This updating error is not present in the ITS mode (DBCN 18 card = 1) and leads to a systematically lower dose deposition rate in the default mode. The effect is present for all energies studied (0.5-10 MeV) and depends on the geometrical resolution of the scoring regions and the energy grid resolution. The effect of the energy binning technique is of the same order of that of the updating error for energies below 2 MeV, and becomes less important for higher energies. For a 1 MeV point source surrounded by homogeneous water, the deviation of the default MCNP results at short distances attains 9% and remains approximately the same for all energies. This effect could be corrected by removing the completion of an energy step each time an electron changes from an energy bin during a sub-step. Another solution consists of performing all calculations in the ITS mode. Another problem is the resolution dependence, even in the ITS mode. The higher the resolution is chosen (the smaller the scoring regions) the faster the energy is deposited along the electron track. It is proven that this is caused by starting a new energy step when crossing a surface. The resolution effect should be investigated for every specific case when calculating dose distributions around beta sources. The resolution should not be higher than 0.85*(1-EFAC)*CSDA, where EFAC is the energy loss per energy step and CSDA a continuous slowing down approximation range. This effect could as well be removed by determining the cross sections for energy loss and multiple scattering at the average energy of an energy step and by sampling the cross sections for each sub-step. Overall, we conclude that MCNP cannot be used without a caution due to possible errors in the electron transport. When care is taken, it is possible to obtain correct results that are in agreement with other Monte Carlo codes.

Micronucleus assay reveals no radiation effects among nuclear power plant workers

The micronucleus assay was applied as biomarker for exposure effect and radiosensitivity in a group of 99 radiation workers of the Nuclear Power Plant Doel (Belgium). The difference in micronucleus frequency between the group of radiation workers with annual dose exceeding 2 mSv and a non-exposed control population was statistically not significant. With respect to the micronucleus frequency after an in vitro challenge dose of 2 Gy, which can be considered as biomarker for radiosensitivity, the data of present study can be represented by a normal distribution without a high frequency tail. This means that a subpopulation of workers with elevated radiosensitivity could not be identified in the population under study.

Thyroid uptake and radiation dose after 131I-lipiodol treatment: is thyroid blocking by potassium iodide necessary?

In radionuclide therapy with iodine-131 labelled pharmaceuticals, free (131)I may be released and trapped by the thyroid, causing an undesirable radiation burden. To prevent this, stable iodide such as potassium iodide (KI) can be given to saturate the thyroid before (131)I is administered. The guidelines of the European Association of Nuclear Medicine do not, however, recommend special precautions when administering (131)I-lipiodol therapy for hepatocellular carcinoma. Nevertheless, some authors have reported (131)I uptake in the thyroid as a consequence of such therapy. In this study, the influence of prophylactic KI on the thyroid uptake and dose (MIRD dosimetry) was prospectively investigated. (131)I-lipiodol was given as a slow bolus selectively in the proper hepatic artery or hyperselectively in the right and/or left hepatic artery. Patients were prospectively randomised into two groups. One group received KI in a dose of 100 mg per day starting 2 days before (131)I-lipiodol administration and continuing until 2 weeks after therapy (KI group; n=31), while the other group received no KI (non-KI group; n=37). Thyroid uptake was measured scintigraphically as a percentage of administered activity 7 days after (131)I-lipiodol ( n=68 treatments). The absorbed radiation dose to the thyroid was assessed by scintigraphy after 7 and 14 days using a mono-exponential fitting model and MIRD dosimetry ( n=40 treatments). The mean activity of (131)I-lipiodol administered was 1,835 MBq in a volume of 2 ( n=17) or 4 ( n=51) ml. Thyroid uptake was lower in the KI group, being 0.23%+/-0.06% of injected activity ( n=31) compared with 0.42%+/-0.20% in the non-KI group ( n=37); the mean thyroid dose was 5.5+/-1.6 Gy in the KI group ( n=19) versus 11.9+/-5.9 Gy in the non-KI group ( n=21). These differences were statistically significant ( P<0.001). No effect of the amount of added cold lipiodol (4 vs 2 ml total volume) or selectivity of (131)I-lipiodol administration was evident ( P>0.1). (131)I-lipiodol is associated with a generally low thyroid uptake and dose that may be significantly decreased by KI premedication. Given the low cost and the very good tolerance of the KI treatment, we believe the use of KI should be recommended in the majority of the patients.

Towards a standardization of biological dosimetry by cytogenetics

When individuals are accidentally overexposed to ionising radiations, follow-up investigations may include dose assessment by cytogenetics. Scoring of unstable chromosome aberrations (dicentrics, centric rings and acentrics) in peripheral blood lymphocytes is regarded as the most specific method to estimate the exposure dose. It has acquired, in some countries, a medico-legal recognition. Paradoxically, there is no universally adopted technique and so important variations occur in methods and these may influence the quality of results. The only published documents supplying some standardization background are International Atomic Energy Agency (IAEA) Technical Reports No 260 (1986) and 405 (2001). Even they do not address crucial areas such as the organization of service laboratories and the need for quality assurance programmes. The significant role of biological dosimetry in many countries has proved the need for a standardized technique that is compatible with national radiological protection programmes. Thus, an International Standards Organization working group for the standardization of biological dosimetry by cytogenetics was created. This group comprises 13 scientists from 11 countries plus an IAEA representative. On the basis of a group consensus, a text defining minimal constraints on all the steps of the process was proposed. A working draft was submitted to ISO in 2001 and its structure is presented here.

Dose distributions for 90Y intravascular brachytherapy sources used with balloon catheters

The dose distribution around an intravascular brachytherapy 90Y line source with centering balloon catheters was measured with a plastic scintillator, TLD and radiochromic film. The absolute dose rates measured with the three detectors in a solid water phantom at 1, 2 and 3 mm distance from the centering balloon surfaces are in agreement within 3.5%, when the detectors are calibrated with the same 90Sr/90Y source. The dose rates measured with the plastic scintillator in the solid water phantom are in agreement with those directly measured in water. The measured relative dose distributions can be reproduced by Monte Carlo calculations. Also, the influence of the balloon diameter on the dose rate can be reproduced by the calculations. The dose rate calibration routinely performed with the plastic scintillator was checked for fifty-one sources with a well chamber and with another dedicated dose rate checking device. These measurements show that the consistency of the calibration of these sources was better than 10%. In a previous paper absolute dose rates for five other 90Y sources measured with TLD and radiochromic film in a solid water phantom were compared with those obtained with the plastic scintillator in water [Piessens and Reynaert, "Verification of absolute dose rates for intravascular beta sources," Phys. Med. Biol. 45, 2219-2231 (2000)]. Differences of 25 to 41%, depending on the balloon diameter, were reported. In this paper we show the evidence for three main reasons for these previously observed discrepancies: an inconsistency between a detector calibration performed with a 6 MeV electron beam and with a calibrated 90Sr/90Y source from NIST (16%), inaccuracies of the measuring distances in the solid water phantom (maximum 7.5%) and a time instability of the plastic scintillator, probably due to radiation damage (6%).

Underdosage of the upper-airway mucosa for small fields as used in intensity-modulated radiation therapy: a comparison between radiochromic film measurements, Monte Carlo simulations, and collapsed cone convolution calculations

Head-and-neck tumors are often situated at an air-tissue interface what may result in an underdosage of part of the tumor in radiotherapy treatments using megavoltage photons, especially for small fields. In addition to effects of transient electronic disequilibrium, for these small fields, an increased lateral electron range in air will result in an important extra reduction of the central axis dose beyond the cavity. Therefore dose calculation algorithms need to model electron transport accurately. We simulated the trachea by a 2 cm diameter cylindrical air cavity with the rim situated 2 cm beneath the phantom surface. A 6 MV photon beam from an Elekta SLiplus linear accelerator, equipped with the standard multileaf collimator (MLC), was assessed. A 10 x 2 cm2 and a 10 x 1 cm2 field, both widthwise collimated by the MLC, were applied with their long side parallel to the cylinder axis. Central axis dose rebuild-up was studied. Radiochromic film measurements were performed in an in-house manufactured polystyrene phantom with the films oriented either along or perpendicular to the beam axis. Monte Carlo simulations were performed with BEAM and EGSnrc. Calculations were also performed using the pencil beam (PB) algorithm and the collapsed cone convolution (CCC) algorithm of Helax-TMS (MDS Nordion, Kanata, Cahada) version 6.0.2 and using the CCC algorithm of Pinnacle (ADAC Laboratories, Milpitas, CA, USA) version 4.2. A very good agreement between the film measurements and the Monte Carlo simulations was found. The CCC algorithms were not able to predict the interface dose accurately when lateral electronic disequilibrium occurs, but were shown to be a considerable improvement compared to the PB algorithm. The CCC algorithms overestimate the dose in the rebuild-up region. The interface dose was overestimated by a maximum of 31% or 54%, depending on the implementation of the CCC algorithm. At a depth of 1 mm, the maximum dose overestimation was 14% or 24%.

Assessment of genotoxic effects related to chronic low level exposure to ionizing radiation using biomarkers for DNA damage and repair

The first objective of our study was to analyse whether biomarkers for genotoxic effects (DNA breaks and alkali-labile sites and micronucleus and non-disjunction frequencies) could be fully validated for biomonitoring workers chronically exposed to ionizing radiation (IR). Blood samples of controls and individuals chronically exposed to IR were analysed. The interindividual variation was reduced when the comet data were adjusted for interexperimental variation, but remained statistically significant. No differences were found between groups, either for smoking or for exposure status. The second objective was to determine whether the Comet assay can be used to evaluate global repair phenotype as a susceptibility biomarker for IR-induced DNA damage in nuclear workers. A pilot study was performed and blood from workers exposed or not to radiation was submitted to a challenging dose of gamma-rays. The repair kinetics of each individual donor were analysed by Comet assay at different time points and compared with the frequencies of biomarkers of genotoxic effects. There was a statistically significant interaction between biomarkers assessing the same damage (micronucleus and Comet assays). Multivariate analysis showed that micronucleus frequencies were positively influenced by age and the percentage of residual tail length was negatively influenced by the interaction between smoking and exposure status. The general conclusions from our study are: (i) a positive correlation exists between mechanistically related biomarkers; (ii) multivariate regression analysis confirmed that the interaction between smoking and exposure to IR negatively and statistically significantly influenced residual tail length; (iii) use of the Comet assay for the estimation of global repair phenotype with respect to IR is recommended because it is simple, fast and differences in in vitro repair capacity can be detected.

The micronucleus and G2-phase assays for human blood lymphocytes as biomarkers of individual sensitivity to ionizing radiation: limitations imposed by intraindividual variability

As part of a program to assess the applicability of the micronucleus (MN) and G2-phase assays as biomarkers of cancer susceptibility, we investigated the inter- and intraindividual variations of these end points. For the MN assay, unstimulated blood cultures from 14 healthy donors were exposed in vitro to 3.5 Gy 60Co gamma rays; for the G2-phase assay, PHA-stimulated cell cultures were irradiated with a dose of 0.4 Gy 60Co gamma rays in the G2 phase of the cell cycle. Two of the 14 volunteers were assayed 9 times over a period of 1 year. The repeat experiments revealed that the intraindividual variability was not significantly different from the interindividual variability for both the G2-phase and MN assays. Since the intraindividual variability determines the reproducibility of the assay, our results highlight the limitations of these end points in detecting reproducible differences in radiation sensitivity between individuals within a normal population. For example, one donor of the population was identified as being radiosensitive (based on the 90th percentile criterion) but turned out to be normal when the assay was repeated twice. We conclude that the determination of individual radiosensitivity with these two cytogenetic assays is unreliable when based on one blood sample.

Induction and disappearance of G2 chromatid breaks in lymphocytes after low doses of low-LET gamma-rays and high-LET fast neutrons

PURPOSE

To determine by means of the G2 assay the number of chromatid breaks induced by low-LET gamma-rays and high-LET neutrons, and to compare the kinetics of chromatid break rejoining for radiations of different quality.

MATERIALS AND METHODS

The G2 assay was performed on blood samples of four healthy donors who were irradiated with low-LET gamma-rays and high-LET neutrons. In a first set of experiments a dose-response curve for the formation of chromatid breaks was carried out for gamma-rays and neutrons with doses ranging between 0.1 and 0.5 Gy. In a second set of experiments, the kinetics of chromatid break formation and disappearance were investigated after a dose of 0.5 Gy using post-irradiation times ranging between 0.5 and 3.5 h. For the highest dose of 0.5 Gy, the number of isochromatid breaks was also scored.

RESULTS

No significant differences in the number of chromatid breaks were observed between low-LET gamma-rays and high-LET neutrons for the four donors at any of the doses given. The dose-response curves for the formation of chromatid breaks are linear for both radiation qualities and RBEs = 1 were obtained. Scoring of isochromatid breaks at the highest dose of 0.5 Gy revealed that high-LET neutrons were, however, more effective at inducing isochromatid breaks (RBE = 6.2). The rejoining experiments further showed that the kinetics of disappearance of chromatid breaks following irradiation with low-LET gamma-rays or high-LET neutrons were not significantly different. Half-times of 0.92 h for gamma-rays and 0.84 h for neutrons were obtained.

CONCLUSIONS

Applying the G2 assay, the results demonstrate that at low doses of irradiation, the induction as well as the disappearance of chromatid breaks is independent of the LET of the radiation qualities used (0.24 keV x microm(-1) 60Co gamma-rays and 20 keV x microm(-1) fast neutrons). As these radiation qualities produce the same initial number of double-strand breaks, the results support the signal model that proposes that chromatid breaks are the result of an exchange process which is triggered by a single double-strand break.

Absorbed dose to water based dosimetry versus air kerma based dosimetry for high-energy photon beams: an experimental study

In recent years, a change has been proposed from air kerma based reference dosimetry to absorbed dose based reference dosimetry for all radiotherapy beams of ionizing radiation. In this paper, a dosimetry study is presented in which absorbed dose based dosimetry using recently developed formalisms was compared with air kerma based dosimetry using older formalisms. Three ionization chambers of each of three different types were calibrated in terms of absorbed dose to water and air kerma and sent to five hospitals. There, reference dosimetry with all the chambers was performed in a total of eight high-energy clinical photon beams. The selected chamber types were the NE2571, the PTW-30004 and the Wellhöfer-FC65G (previously Wellhöfer-IC70). Having a graphite wall, they exhibit a stable volume and the presence of an aluminium electrode ensures the robustness of these chambers. The data were analysed with the most important recommendations for clinical dosimetry: IAEA TRS-398, AAPM TG-51, IAEA TRS-277, NCS report-2 (presently recommended in Belgium) and AAPM TG-21. The necessary conversion factors were taken from those protocols, or calculated using the data in the different protocols if data for a chamber type are lacking. Polarity corrections were within 0.1% for all chambers in all beams. Recombination corrections were consistent with theoretical predictions, did not vary within a chamber type and only slightly between different chamber types. The maximum chamber-to-chamber variations of the dose obtained with the different formalisms within the same chamber type were between 0.2% and 0.6% for the NE2571, between 0.2% and 0.6% for the PTW-30004 and 0.1% and 0.3% for the Wellhöfer-FC65G for the different beams. The absorbed dose results for the NE2571 and Wellhöfer-FC65G chambers were in good agreement for all beams and all formalisms. The PTW-30004 chambers gave a small but systematically higher result compared to the result for the NE2571 chambers (on the average 0.1% for IAEA TRS-277, 0.3% for NCS report-2 and AAPM TG-21 and 0.4% for IAEA TRS-398 and AAPM TG-51). Within the air kerma based protocols, the results obtained with the TG-21 protocol were 0.4-0.8% higher mainly due to the differences in the data used. Both absorbed dose to water based formalisms resulted in consistent values within 0.3%. The change from old to new formalisms is discussed together with the traceability of calibration factors obtained at the primary absorbed dose and air kerma standards in the reference beams (60Co). For the particular situation in Belgium (calibrations at the Laboratory for Standard Dosimetry of Ghent) the change amounts to 0.1-0.6%. This is similar to the magnitude of the change determined in other countries.

Thyroidal uptake and radiation dose after repetitive I-131-MIBG treatments: influence of potassium iodide for thyroid blocking

BACKGROUND

In I-131-MIBG therapy, I-131-iodide can be released from the I-131-MIBG molecule. Hypothyroidism might result from the undesirable irradiation of the thyroid gland. To prevent this, stable iodide such as potassium iodide (KI) is given to oversaturate the thyroid before I-131-MIBG is administered.

PROCEDURE

In the present study, the incidence of hypothyroidism (elevated TSH) was correlated with the thyroidal uptake of I-131 and dose (MIRD dosimetry) after 35 individual treatments in ten patients. Iodine-131-MIBG therapy was performed using a modified dosage of 1.9-11.1 GBq (50-300 mCi) IV. Premedication with KI was done as recommended with a dose of 100 mg KI orally from 2 days before until 4 weeks after I-131-MIBG.

RESULTS

The absorbed thyroidal dose amounted to a very variable range of 0.2 (patient # 1) up to 30.0 (patient 3) Gy with 7.1 +/- 7.9 Gy per treatment and 24.1+/- 19.2 Gy per patient (mean+/- SD), despite the same and compliantly taken KI premedication protocol. Up to now, 4/10 or 40% of patients have developed hypothyroidism after a mean follow-up period of 11 months and a mean total administered dose of 18.7 GBq (505 mCi). A trend towards higher thyroidal doses was seen in the hypothyroid patients.

CONCLUSIONS

This study observes a general high inter- and intra-individual variability in radio-iodide uptake in the thyroid after I-131-MIBG therapy despite KI premedication, as well as possible occurrence of hypothyroidism. A dose-response relationship needs confirmation on a larger cohort of patients to reach statistical value. An alternative thyroid cytoprotection strategy for possible long-term survivors may be considered.

Interphase death in human peripheral blood lymphocytes after moderate and high doses of low and high LET radiation: an electron microscopic approach

Peripheral blood lymphocytes irradiated with low and moderate doses of low linear energy transfer (LET) gamma-rays are known to die by an apoptotic process. In the present study, the type of interphase death occuring after administration of moderate and high doses of low LET gamma-rays and high LET fast neutrons was investigated. Lymphocytes were irradiated in vitro with radiation doses of 5 and 20 gray (Gy) of both radiation qualities. They were cultured for 24 or 48 hours and the type of cell death induced was determined by electron microscopy. After neutron irradiation, a slight increase in the incidence of apoptosis from 5 to 20 Gy was found, whereas after gamma-irradiation, the incidence of apoptosis was lower at 20 Gy as compared to 5 Gy. However, unlike the other radiation doses, the 20 Gy dose of gamma-rays, besides apoptosis also induced oncosis (classical necrosis). According to our experiments, membranes are probably an important target for the induction of interphase death. It is suggested that a great amount of ionisations distributed all over the cell surface, as caused by high doses of gamma-rays, lead to a high influx of Ca++ which induces oncosis instead of apoptosis.

Biodistribution and dosimetry of (99m)Tc-RP527, a gastrin-releasing peptide (GRP) agonist for the visualization of GRP receptor-expressing malignancies

The aim of this study was to determine the human biodistribution and radiation dosimetry of (99m)Tc-RP527, a promising radioligand for the visualization of gastrin-releasing peptide (GRP) receptor-expressing human malignancies.

METHODS

Whole-body scans were obtained up to 48 h after intravenous injection of 555 MBq (99m)Tc-RP527 in each of 6 subjects. Blood samples were taken at various times up to 48 h after injection. Urine was collected up to 48 h after injection for calculation of renal clearance and whole-body clearance. Time-activity curves were generated for the thyroid, heart, breasts in women, testes in men, and liver by fitting the organ-specific geometric mean counts, obtained from regions of interest, on the respective images as a function of the time after injection. The MIRD formulation was applied to calculate the absorbed radiation dose for various organs.

RESULTS

The serial whole-body images showed rapid hepatobiliary excretion, resulting in low background and potentially high-contrast imaging of the thoracic region. Imaging of abdominal tumors may prove problematic, however, because of the extensive bowel activity. (99m)Tc-RP527 was predominantly cleared by the kidneys and to a lesser extent by the gastrointestinal tract. The mean excretion in the urine (+/-SD) at 48 h after injection was 58.3 +/- 5.4 percentage of the injected activity corrected for decay to the time of injection. The highest absorbed doses were received by the excretory organs (i.e., the urinary bladder and gallbladder wall). The average effective dose of (99m)Tc-RP527 was estimated to be 0.0095 mSv/MBq.

CONCLUSION

The biodistribution of (99m)Tc-RP527 revealed low lung, myocardial, and liver uptake, which allowed early imaging of the supradiaphragmatic region with a favorable dosimetry (including effective dose) for administered activities required for SPECT imaging.

Translocation frequencies measured in patients one year after radioactive iodine therapy for thyrotoxicosis

PURPOSE

To investigate the incidence of translocations induced by iodine-131 therapy in thyrotoxicosis patients 1 year after the administration of the radiolabelled compound.

MATERIALS AND METHODS

Tricolour FISH with whole-chromosome-specific probes for chromosomes 2, 4 and 8 was used for scoring translocations. From the genomic translocation frequencies, derived using the Lucas formula, equivalent whole-body doses were calculated, based on the in vitro (60)Co gamma-ray dose-response curve.

RESULTS

A total of 101 translocations were observed in 4864 metaphases, 63% being of the two-way type. In the control group used for obtaining dose-response data, nine translocations were observed in 5278 metaphases, 55% being two-way translocations. No correlation was found between the observed frequency of translocations and administered radioactivity. Using the in vitro dose-response, an estimated average dose for the group of nine patients of 0.79 +/- 0.22Gy was obtained. Compared with frequencies following the assumption that the involvement of a particular chromosome in a two-break exchange-type aberration is proportional to its DNA content, chromosome 4 was more frequently involved and chromosomes 2 and 8 less frequently involved in chromosomal rearrangements.

CONCLUSION

This study shows that (131)I therapy for thyrotoxicosis patients induced translocations, especially in chromosome 4, which could be detected 1 year after the administration of the radiolabelled compound.

Biodistribution and dosimetry of 99mTc-ciprofloxacin, a promising agent for the diagnosis of bacterial infection

This study reports on the biodistribution and dosimetry of technetium-99m ciprofloxacin, a radio-ligand developed for the visualisation of bacterial infection. Whole body scans were performed up to 24 h after intravenous injection of 370 MBq 99mTc-ciprofloxacin in three male and three female volunteers. 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, liver and whole body 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, predominantly urinary excretion of 99mTc ciprofloxacin, with low to absent brain, lung and bone marrow uptake and low liver uptake and excretion. Accordingly, imaging conditions are excellent for both the thoracic and the abdominal region, even at early time points (60 min) post injection. In none of the volunteers was the gallbladder visualised. Approximately 60% of the injected activity was recovered in urine by 24 h post injection. The highest absorbed doses were received by the urinary bladder wall, the thyroid, the upper large intestine, the lower large intestine and the uterus. The estimated mean effective dose for the adult subject, taking into account the weight factors of the ICRP60 publication, was 0.0083 mSv/MBq. The amount of 99mTc ciprofloxacin required for adequate planar and tomographic imaging results in an acceptable effective dose to the patient.

Experimental p(wall) and p(cel) correction factors for ionization chambers in low-energy clinical proton beams

Current dosimetry protocols for clinical protons using ionization chambers do not take into account ionization chamber-dependent perturbation correction factors. In the present investigation, the relative response of 17 cylindrical ionization chambers was evaluated at three proton beam qualities: at two points in a modulated beam and one point in a non-modulated beam, all with an incident energy of 75 MeV. Thirteen of the ionization chambers had a Farmer-type geometry but consisted of different combinations of wall and central electrode materials. All ionization chambers were calibrated in terms of air kerma as well as in terms of absorbed dose to water in a 60Co beam. The relative response of the ionization chambers was compared with results of Monte Carlo simulations of proton and secondary electron transport in the phantom and the ionization chamber geometry. The results of the measurements for cylindrical ionization chambers show relative perturbation effects that are limited to 0.5-1%, resulting in perturbation correction factors that are larger than unity compared with an NE2571 ionization chamber. The experimental relative wall and total perturbation correction factors agree with Monte Carlo calculated values, indicating that the differences between the responses of different ionization chambers are due to secondary electron effects. This conclusion is supported by the comparison of our results with those from other investigators after re-analysis of their data. The central electrode perturbation correction factor for an aluminium electrode in a Farmer-type geometry was found to be unity within the experimental uncertainties.

A higher micronucleus yield in B-versus T-cells after low-dose gamma-irradiation is not linked with defective Ku86 protein

PURPOSE

To elaborate the B-cell micronucleus (MN) response in the low-dose region in detail and to investigate the postulated deficiency in DNA-PK in B-cells.

MATERIALS AND METHODS

Lymphocytes of five healthy volunteers were irradiated with low LET gamma-rays and high LET fast neutrons with doses ranging between 0.01 and 2 Gy. After post-irradiation incubation, B- and T-cells were isolated via CD3 and CD19 immunomagnetic microbeads. MN were analysed in both subpopulations. To study the underlying mechanism of chromosomal radiosensitivity, cell extracts prepared from purified B- and T-cells were subjected to SDS-electrophoresis and electroblotting using antibodies directed against the DNA-PK repair enzymes Ku70/86 and DNA-PKcs. Activity measurements were performed using the SignaTECT DNA-dependent protein kinase assay. DNA double-strand break (DSB) induction and rejoining was determined using constant-field gel electrophoresis.

RESULTS

For low LET gamma-rays a higher MN yield was observed in B-cells than in T-cells, but only in those samples exposed to doses < 1 Gy. For 1 Gy, the MN yields were comparable and for 2Gy even lower in B-cells compared with T-cells. After high LET neutron irradiation no significant differences in MN yields were observed between both subsets. The results of the DNA-PK experiments demonstrate that there is no difference between T- and B-cells in the basal expression and activity of DNA-PK repair proteins. No differences in DNA DSB induction and rejoining were found between T- and B-cells using constant-field gel electrophoresis.

CONCLUSIONS

From the results, it was concluded that the enhanced chromosomal radiosensitivity in B-cells is restricted to low doses (<1 Gy) of low LET radiation and that the chromosomal behaviour of B-cells to low LET radiation cannot be attributed to aberrant forms of the DNA-PK components. A type of chromosomal induced radioresistance (IRR) may be a possible explanation for the observed effect.

Dosimetry of 192Ir sources used for endovascular brachytherapy

An in-phantom calibration technique for 192Ir sources used for endovascular brachytherapy is presented. Three different source lengths were investigated. The calibration was performed in a solid phantom using a Farmer-type ionization chamber at source to detector distances ranging from 1 cm to 5 cm. The dosimetry protocol for medium-energy x-rays extended with a volume-averaging correction factor was used to convert the chamber reading to dose to water. The air kerma strength of the sources was determined as well. EGS4 Monte Carlo calculations were performed to determine the depth dose distribution at distances ranging from 0.6 mm to 10 cm from the source centre. In this way we were able to convert the absolute dose rate at 1 cm distance to the reference point chosen at 2 mm distance. The Monte Carlo results were confirmed by radiochromic film measurements, performed with a double-exposure technique. The dwell times to deliver a dose of 14 Gy at the reference point were determined and compared with results given by the source supplier (CORDIS). They determined the dwell times from a Sievert integration technique based on the source activity. The results from both methods agreed to within 2% for the 12 sources that were evaluated. A Visual Basic routine that superimposes dose distributions, based on the Monte Carlo calculations and the in-phantom calibration, onto intravascular ultrasound images is presented. This routine can be used as an online treatment planning program.

A survey of guidelines in 27 EANM associated societies by the EANM Task Group on Quality Assurance and Standardisation. European Association of Nuclear Medicine

The main aim of the EANM Task Group on Quality Assurance and Standardisation is to develop harmonised clinical procedures that are accepted within Europe. In order to achieve an evidence-based analysis of guidelines in the 27 EANM member societies, a survey was conducted. A questionnaire in mid 1999 investigated three major questions: (1) current status of national guidelines in EANM member societies, (2) specification of the cover and level of these national guidelines, and (3) future desires for national, EANM and SNM guidelines. The complete response rate was 96% (26/27). Guidelines are required by 19 of 27 member societies and have been initiated by 16 member societies. Guidelines are provided by 13 member societies, generally in the national language. In ten societies, specialists other than nuclear medicine physicians, mostly physicists and radiopharmacists, take the lead on some guidelines. Moreover, in some national societies there is active collaboration with other medical societies when writing guidelines, particularly cardiology societies. Currently, only 18% of the necessary procedure guidelines are covered. Compared with a survey conducted in 1993 by the EANM Committee on Quality Assurance and Standardisation, slow progress has been made in this regard, but compared with a survey conducted by the same committee in 1996 in 23 EANM member societies, the number of member societies providing guidelines has approximately doubled. Moreover, 26 of 27 member societies share a commitment for future development of guidelines and 21 of 27 prefer EANM guidelines to national guidelines. The results of this questionnaire justify the need for close co-operation between EANM, EANM member societies, the EANM Task Group on "Quality Assurance and Standardisation" and the Guideline Committee of the SNM. The clinical priorities are considered to be cardiac, renal and brain procedures.

Biodistribution and dosimetry of [123I]iodo-PK 11195: a potential agent for SPET imaging of the peripheral benzodiazepine receptor

The highest concentrations of the peripheral benzodiazepine receptor (PBR) are found in the kidneys and heart. In addition, the PBR has been reported to reflect neuro-inflammatory damage by co-localisation with activated microglia. PK 11195 is a high-affinity ligand for the PBR. The aim of this study was to investigate in humans the biodistribution and dosimetry of [123I]iodoPK 11195, a potential single-photon emission tomography tracer for the PBR. Five healthy volunteers were injected with 112 MBq of [123I]iodo-PK 11195. Sequential whole-body scans were performed up to 72 h post injection. Multiple blood samples were taken, and urine was collected to measure the fraction voided by the renal system. Decay-corrected regions of interest of the whole-body images were analysed, and geometric mean count rates were used to determine organ activity. Organ absorbed doses and effective dose were calculated using the MIRD method. [123I]iodo-PK 11195 was rapidly cleared from the blood, mainly by the hepatobiliary system. Approximately 22% was voided in urine after 48 h. Average organ residence times were 0.74, 0.44 and 0.29 h for the liver, upper large intestine and lower large intestine, respectively. The testes received the highest dose, 109.4 microGy/MBq. All other organs investigated received doses of less than 50 microGy/MBq. The effective dose was 40.3 microSv/MBq. In conclusion, [123I]iodo-PK 11195 is a suitable agent for the visualisation of the PBR and indirectly for the imaging of neuro-inflammatory lesions. Taking into account the radiation burden of 7.46 mSv following an administration of 185 MBq, a [123I]iodo-PK 11195 investigation has to be considered an ICRP risk category IIb investigation.

Correlation of patient skin doses in cardiac interventional radiology with dose-area product

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.

Cytogenetic monitoring of hospital workers occupationally exposed to ionizing radiation using the micronucleus centromere assay

A cytogenetic study was performed in lymphocytes of hospital workers occupationally exposed to X- and gamma-rays using the micronucleus centromere assay. A comparison of the data for the exposed group and an age-matched group of non-exposed hospital workers showed a significant (P < 0.05) increase in centromere-positive micronuclei for the radiation workers, while no effect on centromere-negative micronuclei was present. The observed systematic increase in micronucleus frequency with age was mainly due to increased chromosome loss, reflected in the centromere-positivity of the micronuclei. The micronucleus frequencies were 40% higher in females than in males, which can again be attributed to higher chromosome loss. Two exposed individuals showed exceptionally high micronucleus yields, 90% of which were centromere-positive. In situ hybridization with a centromeric probe for chromosome X shows that X chromosome loss is responsible for these high micronucleus yields. In the studied population, smoking had no significant effect on the micronucleus yields. The results obtained indicate that in contrast to the predominantly clastogenic action of acute exposure to ionizing radiation, the aneugenic properties of radiation may be important after long-term chronic low dose exposure.

57Co-EDTA renal imaging in rats

We studied the synthesis of 57Co-EDTA (Ey = 122 keV), its biodistribution in Wistar rats and its blood and urinary elimination compared with that of 51Cr-EDTA. We added 6 mumol EDTA diluted in 3-5 ml isotonic phosphate buffer (Na2HPO4) to a commercial 57CoCl2 radioactive 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 (n = 3) 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 (Kstab = 10E36). No free or protein-bound 57Co was found. The ratio of 51Cr-EDTA to 57Co-EDTA remained constant (P = 0.133, n = 4). 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.

Apoptosis induced by gamma irradiation in peripheral blood mononuclear cells is not mediated by cytochrome-c release and only partially involves caspase-3-like proteases

Caspase 3 has been shown to be actively involved in the apoptotic process in thymocytes after gamma-irradiation. We examined caspase 3 activation in mature peripheral blood lymphocytes (PBL) after gamma irradiation. Since the activation of caspase 3 is generally prceded by a decrease in mitochondrial membrane potential (delta psi m) and cytochrome c release, these two parameters were also examined. Apoptosis in PBL after a 5-Gy gamma irradiation, is characterized by a decrease in delta psi m, 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 delta psi m with cytochrome-c release and a clear caspase 3 activation. We were unable to block the decrease in delta psi m with the caspase-inhibitors zVAD-fmk or zDEVD-fmk after gamma irradiation, but DNA fragmentation as measured by the TUNEL assay was partially inhibited. Therefore, in gamma irradiated mature PBL, caspase-dependent and -independent pathways, but not cytochrome c, seem to be involved in the apoptotic process.

Analysis of chromosome loss and chromosome segregation in cytokinesis-blocked human lymphocytes: non-disjunction is the prevalent mistake in chromosome segregation produced by low dose exposure to ionizing radiation

The aim of the present work was to examine in human lymphocytes, firstly, whether in vitro gamma-rays as compared with X-rays also induce chromatid malsegregation and at higher frequencies than chromosome loss and, secondly, whether the cytokinesis-blocked micronucleus assay combined with fluorescence in situ hybridization might be useful for the biomonitoring of individuals exposed to ionizing radiation. After irradiation, the relative frequencies of centromere-positive micronuclei decreased from 39.2% at 0.1 Gy to 21. 63% at higher doses. There was no statistically significant increase in MNCen+ frequencies at doses below 1 Gy (0.1, 0.25 and 0.5 Gy), but a statistically significant increase at 1 (P < 0.05) and 2 Gy (P < 0.001) was observed for all the donors. No significant differences in baseline and gamma-ray-induced non-disjunction frequencies for chromosomes 1 (P = 0.9) and 17 (P = 0.8) between individuals were detected. For radiation-induced non-disjunction, lower doses (0.1, 0. 25 and 0.5 Gy) of gamma-rays did not induce a statistically significant increase in non-disjunction frequencies whereas 1 Gy and above clearly induced a statistically significant increase in the total non-disjunction frequencies for all the donors (P < 0.05 at 1 Gy and P < 0.0001 at 2 Gy). The aneugenic effect of radiation is less clearly dose dependent at the lower doses, suggesting an apparent threshold below which no change could be demonstrated. At high radiation doses the major mechanism for gamma-ray-induced aneuploidy is related to chromosome loss through non-disjunction, as has been demonstrated using X-rays, and not through the formation of micronuclei.

Biodistribution and dosimetry of (iodine-123)-iodomethyl-N, N-diethyltamoxifen, an (anti)oestrogen receptor radioligand

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.

A cytogenetic study of nuclear power plant workers using the micronucleus-centromere assay

A cytogenetic study was performed in 215 nuclear power plant workers occupationally exposed to radiation using the micronucleus-centromere assay for peripheral blood lymphocytes. As control population served administrative staff with yearly doses below 1 mSv. The increase of the micronucleus frequency with age, observed in the non-smoking control population, is mainly due to an enhanced number of centromere-positive micronuclei, pointing to an increased chromosome loss. No differences in the number of micronuclei, centromere-positive and centromere-negative micronuclei between smokers and non-smokers are observed. An analysis of the micronucleus data vs. the dose accumulated over the 10 years preceding the venepuncture shows no significant clastogenic or aneuploidogenic effects of the exposure in the studied population which is representative for workers in the nuclear industry at present. According to the linear fits to our data an increase of the micronucleus frequency pro rata 0.5 per 1000 binucleated cells per year, related to the centromere-negative micronuclei, may be expected for workers with the maximal tolerable dose of 20 mSv/year.

Dose measurements compared with Monte Carlo simulations of narrow 6 MV multileaf collimator shaped photon beams

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/EGS4 to 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 10x2 cm2 field, 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.