Speaker
Prof.
Marta Bucciolini
(University of Florence Italy)
Description
Diamond dosimetry has become attractive in radiotherapy, in particular since the introduction of high conformal radiotherapy modalities. With the modern techniques, patients are treated with non-uniform fields, with high dose gradients, variation in space and time of the dose rate and of the beam energy spectrum; the charged particle equilibrium condition is seldom fulfilled, and the perturbation introduced by the detector on the particle fluence strongly affects the measurement. One of the most relevant requirements for a dosimeter is to have small dimensions and high sensitivity. These characteristics should be added to the standard features of a good detector in radiotherapy: short- and long-term stability, linearity versus absorbed dose and dose rate, no energy or LET dependence, as well as no angular dependence of the response. What is more: for treatments characterized by time variation of the fluence, a fast response dynamics is a strong constraint to be met. An ideal dosimeter that fulfills all the above requirements does not exist; diamond, however, thanks to its material properties, seems quite close to satisfying them. Studies about natural diamonds for medical applications are found in the literature since ‘80s. All the existing papers highlight the favorable characteristics of diamond, but its use is limited because of the high cost of the detector. The use of diamond in dosimetry became more appealing when it was proven that synthetic diamonds could be grown in a reproducible way and at a low cost. However, for several years, the clinical use of polycrystalline (p) Chemical Vapour Deposited (CVD) diamond was hampered by its poor response stability. A way to reduce the effect of native defects on response stability is to use single-crystal diamond films. Today, single crystal (s) CVD samples of good quality are available and they can be successfully used also in IMRT applications. In addition to the quality of the material, other factors contribute to determining the performance of a dosimeter: encapsulation, electrical contacts, polarization voltage. Indeed, pCVD detectors used at zero bias, demonstrate an improvement of the dosimetric characteristics, also in IMRT and their performances can be close to those of sCVD diamonds. It is worth of notice that a pCVD diamond with suitable dosimetric characteristics opens up the possibility of developing a bi-dimensional device, useful for dose distribution verification in IMRT treatments.
Primary authors
Dr
Cinzia De Angelis
(Istituto Superiore di Sanità - Rome - Italy)
Dr
Cinzia Talamonti
(University of Florence Italy)
Prof.
Mara Bruzzi
(University of Florence Italy)
Prof.
Marta Bucciolini
(University of Florence Italy)
