Use of alanine for dosimetry intercomparisons among Italian radiotherapy centers.

A pilot program of postal dosimetry intercomparison among 16 Italian Radiotherapy Centers was performed using the ISS Alanine/EPR dosimetry as a transfer system. Dosimeters were irradiated at 10 Gy with high-energy photon beams, both in reference condition in a water phantom and in an anthropomorphic phantom during the simulated treatment of rectum cancer. Intercomparison design along with alanine performances analyzing the different contributions to the combined uncertainty in dose assessment are reported. Main results of the pilot intercomparison, terminated in 2002, are also presented.

Radiochromic film dosimetry of a low energy proton beam.

In this work some dosimetric characteristics of MD-55-2 GafChromic films were studied in a low energy proton beam (21.5 MeV) directly in a water phantom. The nonlinearity of the optical density was quantified by a factor P(lin). A correction factor P(en), that accounts for optical density dependence on the energy, was empirically determined. The effects of detector thickness in depth dose measurements and of the film orientation with respect to beam direction were investigated. The results show that the MD-55-2 films provide dose measurements with the films positioned perpendicularly to the proton beam. A dosimetric formalizm is proposed to determine the dose to water at depth d, with films oriented perpendicularly to the beam axis. This formalism uses a calibration factor of the radiochromic film determined directly on the proton beam at a reference depth in water, and the P(lin) factor, that takes into account the nonlinearity of the calibration curve and the P(en) factor that, in turn takes into account the change of proton beam energy in water. The MD-55-2 films with their high spatial resolution and the quasiwater equivalent material are attractive, positioned perpendicularly along the beam axis, for the absolute dose determination of very small beam sizes and modulated proton beams.

Alanine/EPR dosimetry in brachytherapy.

The paper reports the experimental procedure adopted to determine the absorbed dose rate in water per reference air kerma rate, D(Kr), (d, theta), along the transverse bisector axis of a 137Cs brachytherapy source. The dose rate measurements have been carried out at difference distances, d, from the source using alanine dosemeters in a water phantom. The reference air kerma rate, Kr, was determined adopting a 'direct procedure' that uses a spherical ionization chamber in air. The dose rate constant of the source examined was D(Kr) (1, pi/2) = 0.99 +/- 0.03 cGy h(-1) (microGy h(-1))(-1). The values of the radial dose function along the transverse axis, g(d), determined with an uncertainty of 3.4% (1sigma), were found to be in good agreement with the results reported in the literature. The uncertainty in dose rate value has been estimated as 2.8% (1sigma) for distances from the source up to 7 cm. Kr has been determined with 1.2% (1sigma) uncertainty. So D(r) (d, pi/2) values were determined with 3% (1sigma) uncertainty.

Dosimetric characterization of silicon and diamond detectors in low-energy proton beams.

The dosimetric behaviour of a Scanditronix p-type silicon diode and a PTW natural diamond detector was studied in low-energy proton beams in the 8.3-21.5 MeV range. The properties investigated were linearity, reproducibility, dose rate dependence, energy and linear energy transfer (LET) dependence. The influence of detector thickness on the results of depth dose measurements was also demonstrated. A Markus parallel plate ionization chamber was used for reference dosimetry. Silicon diode and diamond detectors showed linearity at therapeutic dose level, reproducibility better than 1% (1sigma) and sensitivity variation with dose rate and proton energy.

Monte Carlo as a tool to evaluate the effect of different lung densities on radiotherapy dose distribution.

This study aims at evaluating the effects of different lung densities on dose distribution after irradiation at different field sizes, by comparing experimental measurements, GEANT4 Monte Carlo (MC) simulations and two TPS calculation algorithms on ad hoc phantoms. Irradiations were performed with a Varian Clinac 2100 C/D with a nominal energy of 6 MV. Dosimetric experimental measurements were obtained with radiochromic films. A model based on GEANT4 MC code was developed to simulate both the accelerator and the phantoms. Results of dose distribution show an acceptable agreement between MC simulations and experimental measurements, both in the tumour-equivalent region and in the normal tissue-equivalent ones. On the opposite, results vary among the TPS algorithms, especially in regions of lung-equivalent material at low density, but also at the interface between lung- and tumour-equivalent materials.

Transferability of ASTM/NIST alanine-polyethylene recipe at ISS. American Society for Testing and Materials/National Institute for Standards and Technology. Istituto Superiore de Sanita

Alanine-polyethylene solid state dosimeters were prepared at Istituto Superiore di Sanita (ISS) following the recipe proposed by National Institute of Standards and Technology (NIST) with the goal of testing its transferability. Dosimeters were prepared using 95% alanine and 5% polyethylene, by weight. They are rugged and of increased sensitivity, repeatability and reproducibility as respect to the ISS alanine-paraffin pellets. Reproducibility of about 1% was obtained at 10 Gy and at 3 Gy if one single pellet or a stack of five dosimeters were used, respectively.