[en] Retrospective dosimetry in large cohorts of medically exposed patients is essential to investigate the relationship between the dose delivered and the corresponding risk of cancer incidence over the lifetime. The estimation of doses in such studies is characterised by the poor availability and large diversity of data for the patients geometry, treatment modalities, and anatomical sites of interest. We have developed, at the Institut Gustave Roussy (IGR), two theoretical models (ICTA) and (Dos EG), flexible enough to allow their use in such diverse situations and also robust enough to allow further developments if needed. Both models are well designed to estimate the absorbed doses at numerous sites (151 anatomical points) for every patient in the cohort, and are easily handled. To simulate the patient at the time of treatment, both models use the geometrical parameters of the auxological tables (representing the mean French population). The ICTA model has been adapted to the technical characteristics of the applicators (Ra-226, Sr-90/Y-90, P-32, Y-90) that were used at the IGR for the treatment of skin hemangiomas, and has been used in a European study to evaluate dose-response relationships for radiation induced cancer. The Dos EG model has been adapted to actual treatment techniques used for external radiotherapy in different treatment centres, including various beam qualities from different machines (Cobalt, linear accelerators, betatrons, and orthovoltage tubes). It has been used to study the risk of second cancer following radiotherapy for a solid cancer in a cohort of 4400 children, and following a breast cancer in a cohort of 800 women. (author)

[en] Before 1974 about 5000 children were irradiated at the Institut Gustave-Roussy for a skin hemangioma of whom 20% were treated with radium applicators. To evaluate the absorbed doses to these patients at any site, we have developed a software program which permits simulation of the actual patient and treatment conditions. Part of this software is devoted to constructing an Individual Computerized Tomography Anatomy (ICTA) based on real human transverse slices and auxological tables. From the generated phantom, 160 anatomical sites of epidemiological interest are defined and localized according to a Cartesian co-ordinate system. The gamma doses at all sites from Ra-226 applicators are calculated by an algorithm which permits separation of the radiation paths in air, tissue, and lungs. It includes a correction for attenuation and scatters in infinite and semi-infinite mediums. To evaluate the factor φ(r) for these corrections at any distance or position from the applicator, we have modelled the results from several Monte Carlo simulations. In the range of 1 to 10 cm, the φ(r) values obtained from our model showed good agreement with those obtained by published methods. For several cases, the absorbed doses at points in water and patients from radium applicators estimated by this software, were compared to those measured and estimated at the Karolinska Hospital. The results showed good agreement. (author)

[en] Background and purpose: Before 1974 about 5000 children were treated by radiotherapy at the Institut Gustave-Roussy (IGR) for a skin haemangioma. A human model whose characteristics are as close as possible to those of the patient at the time of the treatment is necessary to effectuate an accurate retrospective estimation of the radiation doses received at distant organs.Methods: We have developed a software package which constructs an individualized phantom based on CT slices and auxological data (ICTA) for this purpose. A set of real CT slices is used to produce a 3-D representation of the human body which is then adjusted to fit the dimensions supplied by published auxological data relative to sex and age for each patient. One hundred sixty-one anatomical landmarks of epidemiological interest have been defined inside the phantom for dose estimation.Results: The transverse, frontal and sagittal views of the phantom displayed permit accurate positioning of radioactive applicators. The software calculates the relevant parameters required for dose estimation based on the patient's probable anatomy. (Copyright (c) 1998 Elsevier Science B.V., Amsterdam. All rights reserved.)

[en] Radium applicators and pure beta emitters have been widely used in the past to treat skin haemangioma in early childhood. A well defined relationship between the low doses received from these applicators and radiation-induced cancers requires accurate dosimetry. A human-based CT scan phantom has been used to simulate every patient and treatment condition and then to calculate the source-target distance when radium and pure beta applicators were used. The effective transmission factor φ_(r) for the gamma spectrum emitted by the radium sources applied on the skin surface was modelled using Monte Carlo simulations. The well-known quantization approach was used to calculate gamma doses delivered from radium applicators to various anatomical points. For ³²P, ⁹⁰Sr/⁹⁰Y applicators and ⁹⁰Y needles we have used the apparent exponential attenuation equation. The dose calculation algorithm was integrated into the ICTA software (standing for a model that constructs an Individualized phantom based on CT slices and Auxological data), which has been developed for epidemiological studies of cohorts of patients who received radium and beta-treatments for skin haemangioma. The φ_(r) values obtained for radium skin applicators are in good agreement with the available values in the first 10 cm but higher at greater distances. Gamma doses can be calculated with this algorithm at 165 anatomical points throughout the body of patients treated with radium applicators. Lung heterogeneity and air crossed by the gamma rays are considered. Comparison of absorbed doses in water from a 10 mg equivalent radium source simulated by ICTA with those measured at the Radiumhemmet, Karolinska Hospital (RAH) showed good agreement, but ICTA estimation of organ doses did not always correspond those estimated at the RAH. Beta doses from ³²P, ⁹⁰Sr/⁹⁰Y applicators and ⁹⁰Y needles are calculated up to the maximum beta range (11 mm). (author)