Dosimetry Intercomparison Research Articles

Quality audit of megavoltage radiotherapy units: intercomparison of dose at a reference point using a mailed TL-dosimetry system

A dosimetry intercomparison based on mailed TL-dosimeters and the well proven IAEA/EORTC phantom is described. Its aim is to identify discrepancies in dosimetry larger than +/- 3%. Dosimeters were mailed to all radiotherapy centres in Switzerland for irradiation with 2 Gy at a reference point in a water container, using photons and electrons. Thirty-six beams were monitored. The results show an agreement of within 2% for the majority of the beams monitored. Two electron beams were at 6% of the reference value.

The Status of the US Department of Energy's Environmental Dosimetry Intercomparison Programme

The Status of the US Department of Energy's Environmental Dosimetry Intercomparison Programme

Dose intercomparison at the radiotherapy centers in The Netherlands. 3. Characteristics of electron beams

Dosimetric characteristics of a number of clinically applied electron beams were analyzed as part of a dosimetry intercomparison program performed at the radiotherapy centers in The Netherlands. Absorbed dose values, determined under reference conditions, were compared during site visits with stated dose values. The mean deviation was 0.2% with a standard deviation (SD) of 2.5%. The maximum deviation was 5.7%. The largest differences were due to differences in the calibration procedures and differences in the numerical values of conversion factors adopted from different dosimetry protocols. In addition, a number of clinically relevant parameters of the dose distribution on the central beam axis were analyzed including the depth of the 85% and 50% relative dose, the dose reduction at the depth of the 50% relative dose and the surface dose. The average difference between the stated and measured therapeutic depth (85% dose level) was -0.4 mm with an SD = 1.2 mm. Due to this dosimetric uncertainty observed a safety margin of about 3 mm at the therapeutic depth is recommended. The maximum difference between stated and observed mean energy of the electron beams had only a small influence, < 1%, on the absorbed dose determination. The normalized dose gradient is not an adequate parameter to describe the dose reduction beyond the therapeutic depth. The depth of a low dose level is a better parameter. The relative dose at the surface showed differences up to 10% between scanning electron beams and beams from accelerators with a single scattering foil and closed wall collimating system.

The Status of the US Department of Energy's Environmental Dosimetry Intercomparison Programme

The Status of the US Department of Energy's Environmental Dosimetry Intercomparison Programme

Dose intercomparison at the radiotherapy centers in the Netherlands. 3. Characteristics of electron beams

Dosimetric characteristics of a number of clinically applied electron beams were analyzed as part of a dosimetry intercomparison program performed at the radiotherapy centers in The Netherlands. Absorbed dose values, determined under reference conditions, were compared during site visits with stated dose values. The mean deviation was 0.2% with a standard deviation (SD) of 2.5%. The maximum deviation was 5.7%. The largest differences were due to differences in the calibration procedures and differences in the numerical values of conversion factors adopted from different dosimetry protocols. In addition, a number of clinically relevant parameters of the dose distribution on the central beam axis were analyzed including the depth of the 85% and 50% relative dose, the dose reduction at the depth of the 50% relative dose and the surface dose. The average difference between the stated and measured therapeutic depth (85% dose level) was -0.4 mm with an SD = 1.2 mm. Due to this dosimetric uncertainty observed a safety margin of about 3 mm at the therapeutic depth is recommended. The maximum difference between stated and observed mean energy of the electron beams had only a small influence, < 1%, on the absorbed dose determination. The normalized dose gradient is not an adequate parameter to describe the dose reduction beyond the therapeutic depth. The depth of a low dose level is a better parameter. The relative dose at the surface showed differences up to 10% between scanning electron beams and beams from accelerators with a single scattering foil and closed wall collimating system.

A dosimetric intercomparison of megavoltage photon beams in UK radiotherapy centres

A dosimetry intercomparison has been carried out for all 64 radiotherapy centres in the UK. Doses were measured with an ionization chamber in an epoxy resin water-substitute phantom of relatively simple geometry. Reference-point measurements were made for all MV photon beams. For 61 Co-60 beams, a mean ratio of measured-to-stated dose of 1.002 was observed with a standard deviation of 0.014, whilst for 100 MV X-ray beams, the corresponding figures were 1.003 and 0.015, 97% of beams lay within a +or- 3% deviation. One measurement was instrumental in discovering a large discrepancy. Doses were also investigated in two planned three-field distributions at one beam quality in each centre. One of these was in a homogeneous phantom, whilst the second included a lung-equivalent insert. Doses were measured at the central point and at four other points in the high dose volume. In both situations, the mean ratio of measured-to-calculated doses for all points was 1.008, with standard deviations of 0.027 and 0.035 for the uniform and non-uniform phantoms, respectively.

Three-dimensional dose distribution of tangential breast treatment: a national dosimetry intercomparison

From August 1990 to February 1991, a dosimetry intercomparison of breast treatment was performed at all 21 radiotherapy centres in The Netherlands. The absorbed dose was measured in three planes in a breast phantom during tangential breast irradiation, according to a prescribed technique. The beam energy could be chosen by the radiotherapy centre as normally applied for this type of "patient", and varied between 60Co and 8 MV X rays. The dose measured by the visiting team in 22 points inside the phantom was compared with the dose calculated by the institution using their local treatment planning system. In the institutions the mean ratio (the mean value of the ratios of the absolute calculated dose and the measured absolute dose in the 22 points) varied between 0.92 and 1.08 with an overall mean ratio of 1.04. There was no significant difference in this ratio between the three planes in a particular institution. In the isocentre the mean ratio of calculated and measured dose was 1.021 with a SD of 0.028, i.e. the algorithms in the six different commercial treatment planning systems calculate the dose generally somewhat too high. In order to explain the results, a measurement of the output under reference conditions was performed at each treatment unit. The mean ratio of the dose stated by the institution and the dose measured by the visiting team was 1.011 with a SD of 0.015 with a maximum deviation of 0.040. This small deviation explains therefore only part of the variation in the ratio of calculated and measured dose for tangential breast irradiation.(ABSTRACT TRUNCATED AT 250 WORDS)

A high-dose intercomparison study involving red 4034 perspex and FWT-60-00 radiochromic dye films

Abstract The results of a dosimetry intercomparison exercise involving red 4034 Perspex and FWT-60-00 dye film, used in commercial radiation processing, are reported. Spectrophotometric measurements, irradiations, and thickness measurements were compared by the participating laboratories. Good agreement was obtained for all the measurements undertaken.

Nuclear Accident Dosimetry Intercomparison Studies

Twenty-two nuclear accident dosimetry intercomparison studies utilizing the fast-pulse Health Physics Research Reactor at the Oak Ridge National Laboratory have been conducted since 1965. These studies have provided a total of 62 different organizations a forum for discussion of criticality accident dosimetry, an opportunity to test their neutron and gamma-ray dosimetry systems under a variety of simulated criticality accident conditions, and the experience of comparing results with reference dose values as well as with the measured results obtained by others making measurements under identical conditions. Sixty-nine nuclear accidents (27 with unmoderated neutron energy spectra and 42 with eight different shielded spectra) have been simulated in the studies. Neutron doses were in the 0.2-8.5 Gy range and gamma doses in the 0.1-2.0 Gy range. A total of 2,289 dose measurements (1,311 neutron, 978 gamma) were made during the intercomparisons. The primary methods of neutron dosimetry were activation foils, thermoluminescent dosimeters, and blood sodium activation. The main methods of gamma dose measurement were thermoluminescent dosimeters, radiophotoluminescent glass, and film. About 68% of the neutron measurements met the accuracy guidelines (+/- 25%) and about 52% of the gamma measurements met the accuracy criterion (+/- 20%) for accident dosimetry.

The Clatterbridge high-energy neutron facility: dosimetry intercomparisons

Dosimetry intercomparisons have been performed between the Clatterbridge high-energy neutron facility and the following institutions, all employing beams with similar neutron energies: Université Catholique de Louvain, Belgium; University of Washington, Seattle, USA; MD Anderson Hospital, Houston, USA; and Fermi National Accelerator Laboratory, Batavia, USA. The purpose of the intercomparison was to provide a basis for the exchange of dose-response data and to facilitate the involvement of Clatterbridge in collaborative clinical trials. Tissue-equivalent ionization chambers were used by the participants in each intercomparison to compare measurements of total (neutron plus gamma) absorbed dose in the host institution's neutron beam, following calibration of the chambers in a reference photon beam. The effects of differences in exposure standards, chamber responses in the neutron beams and protocol-dependent dosimetry factors were all investigated. It was concluded that the overall difference in the measurement of absorbed dose relative to that determined by the Clatterbridge group was less than 2%.

Performance Characteristics of Neutron Personnel Dosemeters used in the Oak Ridge Intercomparison Studies

Abstract To provide an opportunity for dosimetrists to test and calibrate their neutron personnel monitoring systems, the staff of the Dosimetry Applications Research Facility at the Oak Ridge National Laboratory (ORNL) has conducted personnel dosimetry intercomparison studies (PDIS) periodically since 1974. During these studies, neutron dosemeters are mailed to ORNL, exposed to low level (less than 15 mSv) dose equivalents in a variety of mixed radiation fields produced using the Health Physics Research Reactor (HPRR), and then returned to the participants for evaluation. Beginning with the Seventh PDIS in 1981, interest and participation in the Oak Ridge intercomparisons increased significantly and consistent and documented methods for determining reference neutron dose equivalents for the HPRR were introduced. This paper presents a summary and analysis of about 3450 neutron dose equivalent measurements reported for PDIS 7 through 12 (1981-1986) with particular emphasis on low dose equivalent sensitivity, accuracy and precision, and performance relative to accreditation standards for the basic types of personnel dosimetry systems.

Clinical Dosimetry of High Energy Neutron Beams: Future Developments

Abstract Accuracy requirements for the assessment of absorbed dose in a patient irradiated by high energy neutron beams will be formulated by analysing dose-effect curves for local tumour control and for normal tissue complications. Uncertainties in the various steps in the delivery of the prescribed absorbed dose in a patient will then be estimated for both fast neutron and megavoltage X ray beams. At present, even for simple treatment conditions, the proposed accuracy in absorbed dose delivery cannot be fully achieved in photon therapy while fast neutron therapy is even less accurate. Reduction of type A uncertainties can be obtained by an extensive quality control programme, including dosimetry intercomparisons under actual treatment conditions applying dose calculations using the computer planning system. Reduction of type B uncertainties can be obtained by performing dosemeter calibrations directly in neutron beams and by better knowledge of the physical parameters employed in ionisation chamber dosimetry. Recommendations given in the new ICRU Report on Clinical Neutron Dosimetry, and accepted by both US and European groups, will be discussed. With the increasing clinical interest in three dimensional dose distributions, methods for dose calculations have to be refined. Some recent developments for photon beams will be discussed and possible application of these procedures in neutron dosimetry will be indicated.

Dose intercomparison at the radiotherapy centres in The Netherlands. 1. Photon beams under reference conditions and for prostatic cancer treatment

In 1985, a dosimetry intercomparison was performed at all 20 radiotherapy centres in The Netherlands. Absorbed dose was determined with an ionization chamber under reference conditions in a water phantom for cobalt-60 gamma-ray and megavoltage X-ray beams. The mean difference between measured and stated dose values was 0.5% with a standard deviation of 1.9%, but up to 6% at maximum. As soon as all institutes apply a common dosimetry protocol, this maximum difference will reduce to about 2%. In addition, an anthropomorphic phantom was irradiated to simulate the treatment of a prostatic cancer. The dose, determined with an ionization chamber at the isocentre and thermoluminescent dosimeters (TLD) powder at several points situated in the target volume, the bladder and the rectum, was compared with the stated dose calculated with the local planning system. Only small differences were found between the measured and stated dose at the isocentre: on the average 1.5%, with a standard deviation of 1.5%. The difference between stated and measured dose at several points situated in the target volume was on the average 0.4%, with a standard deviation of 5.2%. Almost the same result was found for a point situated in the bladder. In the rectum, the average difference was about 4%, however, with a large standard deviation, 18%, due to the relatively steep dose gradient at these points.

The amsterdam fast neutron therapy project: A final report

In the period from February 1975 through September 1981 a total of 435 patients received radiotherapy with the 14 MeV d + T neutron generator, hospital based in the Netherlands Cancer Institute (the Antoni van Leeuwenhoek Hospital). Preliminary data on clinical results were published during the past few years. In this paper a final report is given of the program. The results can be summarized as follows: The neutron generator fulfilled the criteria for clinical use, that is it was reliable and had the required minimal output of 10(12) neutrons s-1. However, the dose distribution was more comparable with a 250 kV X-ray machine than with a modern accelerator. A number of physical parameters of importance for clinical neutron dosimetry have been determined for our therapy unit. These data, as well as the results of dosimetry intercomparisons in which our institute participated, contributed in the drafting of a European protocol for clinical neutron dosimetry. Pilot studies were carried out on different tumor sites, including head and neck, brain, pelvis, soft tissue and pulmonary metastases. In many patients local tumor control was seen, however, often concomitant with severe complications, especially in deep seated tumors. Randomized clinical trials were carried out for head and neck tumors (in collaboration with some other European centers) and for inoperable bladder and rectal tumors. No significant difference was observed in local tumor control or late morbidity between photon and neutron irradiation for the head and neck tumors. Also the results for pelvic tumors failed to demonstrate an advantage for neutron therapy. In this study two neutron arms were used with different dose schedules. As could be expected a higher local control rate was noticed for the higher neutron dose group, but concomitant with a higher complication rate. From our experience we have to conclude that treatment with our fast neutron treatment facility did not result in a benefit over photon irradiation. It seemed that the differential effect between tumor and normal tissues is smaller with fast neutrons than with photons.

TLD-700 Gamma Measurements in Mixed Neutron-Gamma Radiation Fields

Neutron and gamma ray personnel dosimetry intercomparison studies have been conducted at the Oak Ridge National Laboratory using the Health Physics Research Reactor for more than a decade. The TLD-700 dosemeter is the most used gamma dosemeter in these mixed field studies. Performance data for the TLD-700 dosemeters under a wide variety of irradiation conditions are presented and analysed. Conclusions about the performance of the TLD-700 dosemeters are presented.

Performance comparison of thorium track, polycarbonate, and CR-39 neutron dosimeters

Abstract Personnel dosimetry intercomparison studies have been ongoing at the Oak Ridge National Laboratory since 1974. Track neutron dosimeters have been used by various participants in each of these studies to date. Specific types of track dosimeters used include thorium track, polycarbonate, CR-39, and combination (CR-39 and polycarbonate). The results of 313 track dosimeter measurements made by participants during 61 operations of the Health Physics Research Reactor in 6 different shielding conditions over a 10-yr period are presented, compared, and analyzed.

Neutron Dosimetry Intercomparison Studies

Twenty nuclear accident dosimetry intercomparison studies and nine personnel neutron dosimetry intercomparison studies have been conducted at the Oak Ridge National Laboratory. More than 100 organisations have participated in these annual studies. The studies are described, the participation is analysed, the dosemeters tested are discussed, detailed references are cited, and study results and conclusions are presented. The results and conclusions are a summary of the status of neutron dosimetry.

Intercomparison of personnel dosimetry for thermal neutron dose equivalent in neutron and gamma ray mixed fields.

In order to consider the problems concerned with personnel dosimetry, an Intercomparison of personnel dosimetry, especially dose equivalent responses of personnel dosimeters to thermal neutron, was carried out in neutron and gamma ray mixed fields.The dose equivalent responses and their standard deviations of individual dosimeter were almost independent on cadmium ratio and gamma ray contamination in the radiation fields. However, a difference of about 4 times was observed among the relative thermal neutron dose equivalents of individual dosimeter normalized to the ICRP recommended value.It is suggested that the standardization of dose evaluation method is required from the practical point of radiation protection and safety.

Summary and Analysis of Neutron Measurements Conducted During the 1982 US-CEC Personnel Dosimetry Intercomparison Study

Summary and Analysis of Neutron Measurements Conducted During the 1982 US-CEC Personnel Dosimetry Intercomparison Study

Medical radiation dosimetry

Current dose measuring practices in the diagnostic and therapeutic use of radiation are reviewed. Radiation doses typically received by patients from diagnostic X-ray studies, including mammography and computerized axial tomography, are presented. Modern-day radiation therapy, both with conventional photons and with electrons and high-LET particles, emphasizes the need for accurate dosimetry. The different methods of beam calibration and dosimetry intercomparisons for the variety of radiation beams are discussed. Results of several important dosimetry intercomparisons are also presented.