André Costa

Protection of testes during radiation treatment by irregular and focused fields of 25 MV X-rays: in vivo evaluation of the absorbed dose

During therapeutic irradiation of subdiaphragmatic nodal areas, the gonads are exposed to radiation from the primary beam and scatter. Since young patients have a high probability of cure, limiting exposure to the gonads should be pursued. Primary shielding may be supplemented by additional shields in order to reduce this exposure. Testes dose measurements were performed with thermoluminescent dosimetry (TLD) in 37 patients treated with 25 MV x-rays on subdiaphragmatic nodal areas. Each patient was measured 5 times while under treatment. In 27 cases, an additional shield was placed to protect the testes. For 9 cases, comparative measurements were performed on a phantom with and without additional shielding. The median dose received by gonads was respectively 3% with additional shielding (27 cases) and 5.8% without additional shielding (10 cases, p = 0.001 Mann Whitney test). In the 6 patients for whom the measurements were compared, the differences were also statistically significant (p = 0.028 paired Wilcoxon test). This study confirmed the benefit of additional gonadal shielding during subdiaphragmatic radiation treatment with 25 MV x-rays.

CT measurement of lung density: The role of patient position and value for total body irradiation

To obtain more precise data on pulmonary doses in preparation for total body irradiation, the lung density of patients was systematically analyzed in treatment positions using data obtained by computed tomography (CT). With the patient supine, the lung density was not significantly different for the right and left lungs. In contrast, considerable differences were noted between the two lungs in lateral decubitus positions owing to variations in ventilation and perfusion. The relative electron density of lung was also found to decrease with age, dropping to pe = 0.160 at 71 years.

Étude de cas théoriques de faisceaux avec modulation d’intensité par la technique du step-and-shoot

To initiate Intensity-Modulated Radiation Therapy (IMRT) in our department, theoretical cases were used as a training, to define methods of measurements and to verify the software by comparing results of calculation and measurement on a PMMA phantom. Irradiation was performed with 6 and 25 MV X-rays from a linear accelerator. For measurements, films and ionization chambers have been chosen. The comparison between calculations and measurements shows some discrepancies at the level of junctions and also in areas of low doses especially when many segments were used. These theoretical cases provide a first step on the way towards treatments with intensity modulation.

Development and use of a computer system in a radiotherapy department: SISGRAD.

SISGRAD, the interactive computer system of the Antoine-Lacassagne Cancer Center Radiotherapy Department, has been operational since January 1982. It completes the computerized dosimetry system installed several years earlier and is fully integrated with the institutions central network. SISGRAD is in charge of surveillance of the radiotherapy treatments given by the Centers three radiotherapy units (1400 patients per year); it is also used for administrative purposes in the Department and physically connects all of the Departments operating stations. SISGRAD consists of a series of microcomputers connected to a common mass memory; each microcomputer is used as an intelligent console. SISGRAD was developed to guarantee that the treatments comply with prescriptions, to supply extemporaneous dosimetric data, to improve administrative work, and to supply banks with data for statistical analysis and research. SISGRAD actively intervenes to guarantee treatment quality and helps to improve therapy-related security factors. The present text describes the results of clinical use over a 4-year period. The consequences of integration of the system within the Department are analyzed, with special emphasis being placed on SISGRADs role in the prevention and detection of errors in treatment prescription and delivery.