Equivalent Whole-body Dose Research Articles

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 γ-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.

Risk assessment of radiation-induced malignancies based on whole-body equivalent dose estimates for IMRT treatment in the head and neck region

Background and purpose: Intensity modulated radiation therapy (IMRT) has been introduced in our department for treatment of the head and neck region with the intention of reducing complications without compromising treatment outcome. However, these new treatment modalities inevitably require a substantial increase in monitor units per target dose yielding an increased risk of secondary malignancies induced by the treatment. This study aims at assessing the increased risk by means of in vivo measurements of the whole-body equivalent dose of both the conventional and the IMRT treatment techniques for head and neck lesions.Material and methods: A conventional technique using parallel opposed, wedged treatment fields has been compared with a slice-by-slice arc rotation technique for IMRT. Both techniques were used to treat head and neck lesions with a 6-MV photon beam. Thermoluminescent badges and neutron bubble detectors designed for personnel monitoring have been applied to obtain the estimated whole-body equivalent dose on three patients for each treatment technique. The nominal probability coefficient for a lifetime risk of excess fatal cancer, recommended by the ICRP 60 has been used for risk estimates based on the estimated dose values.Results: An estimated whole-body equivalent dose per monitor unit equal to 1.2×10−2 mSv/MU and 1.6×10−2 mSv/MU have been obtained with the conventional and IMRT technique, respectively. Applying the average amount of MU necessary to realize a 70 Gy target dose the estimated whole-body equivalent dose for both treatment techniques becomes 242 mSv (conventional) and 1969 mSv (IMRT), yielding an increase in the risk for secondary malignancies with a factor 8.Conclusions: Historically the risk of secondary malignancies has been accepted to take advantage of the possible benefits of improved local control and treatment outcome. However, the introduction of new and sophisticated treatment techniques will also increase the risk of radiation induced malignancies. Therefore, these risk estimates become important to assess whether the benefits of the treatment technique outweigh the possible risks.

Estimation of dose in cancer patients treated with fractionated radiotherapy using translocation, dicentrics and micronuclei frequency in peripheral blood lymphocytes

The frequency of translocation, dicentrics (DC) and micronuclei (MN) was studied in blood samples exposed in vitro to 60 Co gamma radiation and cervical cancer patients undergoing fractionated radiotherapy. The samples exposed under in vitro condition showed that the frequency of translocation and dicentric followed Poisson distribution (` u' varied between −0.04 and +1.41 for translocation and between −0.09 and +1.81 for DC) and that obtained with MN follow over dispersion (` u' varied between +2.04 and +9.28). However, the cervical cancer patients undergoing radiotherapy showed over dispersion for all these three aberrations (DC, MN and translocation). The frequencies of aberrations obtained in cancer patients were found to be lower than those obtained for in vitro exposure for doses more than 2 Gy equivalent whole body dose (EWBD). The dose–response curves were constructed using the frequencies of DC, MN and translocation as a function of EWBD. Doses as measured from the dose response curves were compared with the estimated dose in order to check whether the measured and estimated doses agree. The percent variation between the doses measured from aberration frequencies and that of the estimated dose was lower with translocation (10.8±7.41%) compared to those obtained with DC (38.08±31.85%) and MN (47.19±31.80%).

Measurements of the equivalent whole-body dose duringradiation therapy by cytogenetic methods

Estimates of equivalent whole-body dose following partial body exposure can be performed using different biophysical models. Calculations should be compared with biodosimetry data, but measurements are complicated by mitotic selection induced in target cells after localized irradiation. In this paper we measured chromosomal aberrations in peripheral blood lymphocytes during radiotherapy, and estimated the equivalent whole-body dose absorbed, by using the novel technique of interphase chromosome painting. Premature chromosome condensation was induced in stimulated lymphocytes by incubation in calyculin A, and slides were hybridized in situ with whole-chromosome DNA probes specific for human chromosomes 2 and 4. Reciprocal exchanges were used to estimate the equivalent whole-body dose, based on individual pre-treatment in vitro calibration curves. Equivalent whole-body dose increased as a function of the number of fractions, and reached a plateau at high fraction numbers. Chromosomal aberration yields were dependent on field size, tumour position and concurrent chemotherapy. Results suggest that interphase chromosome painting is a simple technique able to give a reliable estimate of the equivalent whole-body dose absorbed during therapeutic partial-body irradiation.

Estimates of whole-body dose equivalent produced by beam intensity modulated conformal therapy

To estimate the dose delivered to patients by photons and neutrons outside the radiation fields when beam intensity modulation conformal radiotherapy is given. These estimates are then used to compute the risk of secondary cancers as a sequela of the radiation therapy. The x-ray and neutron leakage accompanying two beam-intensity modulation techniques delivered by currently available linear accelerators were estimated for 6-MV, 18-MV, and 25-MV x-ray energies. Estimates of whole-body dose equivalents were determined using leakage measurements reported in the literature and treatment parameters derived for two modulated beam-intensity conformal therapy techniques. Risk values recommended by the National Council on Radiation Protection and Measurements (NCRP) were used to estimate the resulting risk of fatal radiation-induced cancer for 70.00 Gy prescribed tumor doses. The computed worst-case risks of secondary cancers increased in the range from 1.00% for 6-MV x-rays to 24.4% for 25-MV x-rays. Careful consideration should be made of the risks associated with secondary whole-body radiation before implementation of beam intensity modulated conformal therapy at x-ray energies greater than 10 MV.

Micronuclei in cytokinesis-blocked lymphocytes may predict patient response to radiotherapy.

We have applied the cytokinesis-block micronucleus assay to peripheral blood lymphocytes of patients undergoing radiotherapy in pelvic and pulmonary sites, in order to evaluate the individual cytogenetic response. Our cytogenetic data correlated with the equivalent whole-body dose are homogeneous and compare well with the data presented by other authors. We have used an exponential mathematical formula to calculate the attenuation of the cytogenetic effect with time. The k coefficient (cytogenetic recovery factor) in the formula expresses the degree of attenuation. In lymphocytes from patients after radiotherapy, the trend of the micronucleus frequency observed after 2 Gy of in vitro X-irradiation demonstrates that the cytogenetic effect obtained in vitro is added to that obtained in vivo. The k coefficient is inversely proportional to the micronucleus frequency observed after 2 Gy in vitro. The micronucleus assay and the cytogenetic recovery factor are proposed as suitable diagnostic tools for application in the field of radiotherapy.

Micronucleus induction in peripheral blood lymphocytes of patients under radiotherapy treatment for cervical cancer or Hodgkin's disease.

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.

Effective dose values in bone mineral measurements by photon absorptiometry and computed tomography.

A high degree of uncertainty and irritation predominates in the assessment and comparison of radiation dose values resulting from measurements of bone mineral density of the lumbar spine by photon absorptiometry and X-ray computed tomography. The skin dose values which are usually given in the literature are of limited relevance because the size of the irradiated volumes, the relative sensitivity of the affected organs and the radiation energies are not taken into account. The concept of effective dose, sometimes called whole-body equivalent dose, has to be applied. A detailed analysis results in an effective dose value of about 1 microSv for absorptiometry and about 30 microSv for computed tomography when low kV and mAs values are used. Lateral localizer radiographs, which are necessary for slice selection in CT, mean an additional dose of 30 microSv. Lateral X-ray films of the spine which are frequently taken in combination with absorptiometry result in a dose of 700 microSv or more. The concept of effective dose, the basic data and assumptions used in its assessment and a comparison with other dose burdens (for example the natural background radiation, of typically 2400 microSv per year) are discussed in detail.

Micronuclei in Cytokinesis-blocked Lymphocytes of Cancer Patients Following Fractionated Partial-body Radiotherapy

We applied the cytokinesis-block micronucleus assay to measure chromosome damage in lymphocytes of 11 cancer patients undergoing fractionated partial-body irradiation. Measurements performed before, during and after cessation of radiotherapy showed a dose-related increase in micronucleus frequency in each of the patients studied. When the results for micronucleus frequency (Y) were plotted against the estimated equivalent whole-body dose (X) the dose-response relationship obtained was Y = 75.8X + 49.5 (r = 0.783, P less than 0.0001). A general decline in MN frequency was observed during the post-treatment period down to 57 per cent (+/- 10) after 12 months but there was considerable variation between individuals. The advantages and disadvantages of the application of the cytokinesis-block micronucleus assay as a biological dosimeter for lymphocytes irradiated in vivo are discussed.

Dose Estimation by Cytogenetic Analysis in a Radiation Accident with 137Cs in Goiania (Brazil): Evaluation of Probable Exposure Doses Range

An in vitro dose response curve for 137 Cs at a dose rate of 3 Gy.h -1 was generated in order to estimate equivalent whole-body doses after accidental exposures. Twenty two blood samples from persons involved in the radiation accident with 137 Cs in Goiania, Brazil, were analysed, taking into consideration the dose rate effect, and post-irradiation blood sampling delay using correction factors of 1.39 to t=30 days and 1.63 to t=60 days after the initial exposure

Results of 10 y of radiation protection dosimetry at the neutrontherapy facility in Louvain-la-Neuve.

After 10 y of routine operation, radiation hazards to the neutron therapy staff at Louvain-la-Neuve were evaluated. These hazards to the staff in neutron therapy are a matter of concern, not only because of the dose levels due to induced activation after treatment but also because of the difficulty of evaluating adequately the dose equivalent rates (including the quality factor, QF) during the irradiation. Build-up of radioactivity near the collimator and in the therapy room is reported. In the beam axis, dose rates due to activation can amount up to 5 mGy h-1. However, these rates are efficiently reduced to 0.3 mGy h-1 by automatically withdrawing the target after irradiation. Other problems of radioactive contamination (for instance, the choice of the Fe composition of the collimator) are discussed. Dose equivalent rates were determined during treatment at different positions inside and outside the treatment room. At these locations, neutrons of widely varying energies are present, accompanied by a significant proportion of gamma rays. The measurements of neutron-dose equivalent rates were performed with three commercial neutron detectors: a BF3 and a He3 remcounter (Nuclear Enterprises and Nardeux) and the Dineutron multisphere remcounter (Nardeux). The Dineutron also allowed the evaluation of QF. The results of these detectors were compared with the results of the integration of microdosimetry spectra obtained in free air with a TE proportional counter (Far West Technology). For the p(65) + Be neutrons, the dose equivalent rate was equal to 0.4 Sv h-1 in the treatment room (at 2.5 m from the collimator) and was reduced to 2-3 microSv h-1 at the room entrance. The gamma component increased from 55% to 95% at the same positions, respectively. Ratios of the responses of all detectors and QF values are compared and discussed at the different positions. The whole-body dose equivalents to the neutron therapy staff over the 10 y considered are presented; although they are higher than for conventional radiotherapy, they remain far below the ICRP recommended dose limits.

Patient risk from intraoral dental radiography.

The age- and sex-specific risk for female patients from a full-mouth dental radiographic examination has been estimated, using a modification of the ICRP effective dose equivalent and organ doses from a Monte Carlo program simulating radiation transport in human anatomy. Risk is expressed as an equivalent whole-body radiation dose of 31 to 446 μSv, or the probability of fatal cancer or of mutation expressed in the first two postirradiation generations of 0.2 to 7 effects per million examinations, depending on the age of the patient and radiographic technique.

Patient risk from rotational panoramic radiography.

Age- and sex-specific risks for adult female patients from rotational panoramic radiography have been estimated by means of a modification of the ICRP effective dose equivalent and computer simulation of radiation transport in human anatomy using Monte Carlo techniques. Risks are expressed as the equivalent whole-body radiation doses of 6.6 to 28 μSv, and the probability of stochastic effect (fatal cancer or mutation expressed in the first two postirradiation generations) of 0.07 to 0.4 per million examinations.

Chromosome aberrations in the peripheral lymphocytes induced by brachytherapy and external cobalt teletherapy

In the present study, the induction efficiencies of chromosome aberrations were analyzed in patients receiving various modalities of interstitial radiotherapy with small radiation sources in the oral cavity area and compared with those in patients treated with external telecobalt irradiation in the thoracic region. Further, as a local nonstochastic effect, the acute mucosal reaction was investigated. The mucosal reaction in the area treated by brachytherapy reached a maximum at two to three weeks after the implantation. The frequencies of dicentrics plus rings of peripheral lymphocytes, on the other hand, revealed rapid increases and approached plateau levels as early as two days after the implantation. The whole-body effects, evaluated on the basis of the chromosome aberration frequencies of peripheral lymphocytes in the patients who underwent brachytherapy, were compared with the effects observed in those patients treated with external radiotherapy or bleomycin injection and discussed with regard to their effectiveness in control of the tumor and side effects. The radiation doses used in the patients who received brachytherapy or a single external irradiation were found to exert the same effects on the chromosome aberration induction. However, even in the case of brachytherapy in which whole-body side effects were believed to be trivial, the peripheral lymphocyte count was temporarily reduced to one half or less of the preirradiation level. An equivalent whole-body dose of 50 cGy was obtained from the frequencies of dicentrics and rings.

Fast neutron therapy at Edinburgh: staff protection.

The major hazards encountered by staff using neutrons for radiotherapy are discussed. Specific reference is made to the experience gained at the MRC Cyclotron Unit at the Western General Hospital, Edinburgh, using neutrons generated by the d(15 MeV) + Be reaction. The neutron therapy facility consists of a cyclotron and both a fixed horizontal and an isocentric therapy beam, and staff protection during five years' operation is reviewed. Levels of induced activity in the cyclotron and therapy equipment are reported and problems of radioactive contamination discussed. Summaries of whole-body and finger dose equivalents received by engineering staff, and of whole-body dose equivalents received by physics and radiography staff, are presented and analysed. It is shown that, although doses received by staff are higher than for staff in an X-ray facility, they are all well below the maximum permissible levels, and it is also concluded that radioactive contamination of staff is minimal.

The chromosomal changes in the patients suffering from malignant diseases during radio and chemotherapy

Angiocardiography is an X-ray examination of the blood vessels or chambers of the heart for evaluation of the number and severity of blockages in arteries that supply blood to the heart. Cardiologists and staff members applying these procedures are exposed to high levels of scattered radiation. In the present study we analyzed and followed-up on the cytogenetic effects of X-ray angiography in personnel of laboratories for treatment of cardiovascular disease. According to film dosimeter analysis, personnel received 0.25–15 mSv during the previous year (average of 3 mSv/y), which indicated an exposure below the limit established by the International Commission on Radiological Protection (ICRP). Samples of peripheral blood were collected from cardiologists, nurses and technicians and from a matched control group. The incidence of unstable chromosomal aberrations (dicentrics, acentric fragments, ring chromosomes) and cytokinesis-blocked micronuclei were analyzed. Results show a high frequency of acentric fragments in cardiologists, nurses and technicians compared to controls (P < 0.001). When the exposed groups were compared, a higher percentage of acentric fragments was observed in the nurses and technicians compared to cardiologists (P = 0.004). Six individuals presented with dicentric chromosomes and their equivalent whole-body doses ranged from 0.05 to 0.10 Gy. No correlation was observed between chromosome aberrations and annual effective dose or age of the exposed groups. Although the mean frequency of chromosome aberrations in the male workers was slightly higher than in the females, no significant difference was observed between male and female workers in each group (P = 0.86). The mean number of micronuclei per 1000 binucleated cells was significantly higher in the exposed groups compared with the matched control group (P < 0.001). In a follow-up study, chromosome aberrations in lymphocytes of 23 exposed personnel were analyzed five times during 3 years. Results show that the mean number of acentric fragments decreased gradually during 36 months in those workers who followed the radiation protection guides. The results of this study emphasize the importance of individual biomonitoring, limiting exposure and radiation safety programs.

Chromosome Aberrations in the Leukocytes of Partial-Body- and Whole-Body-Irradiated Swine

Mature Yorkshire sows were given 400-R exposures to60 Co gamma radiation delivered either to the total body or to the anterior or posterior body half only. At 20 min and at 24 hr after the exposure, blood samples were taken for the determination of chromosome aberrations as well as for hematological evaluation. White blood cells were subsequently monitored through the 14th wk postexposure. The recovery from depressed leukocyte numbers in the peripheral system tended to be slower and less complete after whole-body irradiation. Both one-event and two-event chromosome aberrations were induced in the leukocytes of whole-body irradiated sows at approximately three times the level seen with half-body exposures. The results indicate that the calculation of whole-body equivalencies from chromosome aberrations scored after partial-body exposures may lead to an underestimate of the equivalent whole-body dose.