[Optimization of a dosimetric procedure in total body irradiation]. / Ottimizzazione di una procedura dosimetrica per la irradiazione totale corporea.

The experimental dosimetry of 2 radiotherapy beams produced by a 60Co Picker unit and by a Siemens 4 MV unit, respectively, was analyzed to verify the use of tissue air ratio (TAR) and tissue maximum ratio (TMR) in the computerized planning of total body irradiation (TBI). The use of a small ionization chamber PRO5P Capintec in anthropometric phantoms allowed us to test a computed calculation procedure adopted to reduce both experimental uncertainties and time consumption. The experimental test on the computed procedure was also useful to identify the equivalent fields the patient's body had to be divided into for dosimetric planning. Such dosimetric specifications as average dose to the patient and degree of dose inhomogeneity are calculated when the thickness of compensator filters in perspex is optimized. Following the guidelines reported in ICRU 29, a dosimetric record is presented. In page 1 the target volume is described, in page 2 the provisional treatment planning, and in page 3 the actual treatment planning, checked with in vivo TLD measurements, and the dose specifications for TBI.

A study of quality of bremsstrahlung spectra reconstructed from transmission measurements.

A numerical method for the reconstruction of bremsstrahlung spectra has been applied to the analysis of simulated data. The method is found to be reliable in reconstructing x-ray spectra of maximum energy up to 10 MeV. Measurements of aluminum transmission data carried out for five linear accelerators have also been analyzed by this method to determine the fractional energy fluence. The values of the Spencer-Attix water/air stopping power ratio, SS.A. w,air, reported as a function of the ratios TPR20 10, are in good agreement with computed results. Quality index values were correlated to mean incident energies of x-ray beams used in radiotherapy. The experimental setup has also provided information regarding the softening effect on the off-axis beam, which can be used in clinical computer dosimetry to correct conventional zero field size tissue maximum ratio.