Absorbed dose distributions in 3D imparted by a single Novoste 5F 90Sr/90Y beta particle source of the type formerly used for intravascular brachytherapy were investigated. An innovative dosimetry medium known as BANG3-Pro-1 gel was used as a dosimeter and phantom, while a special high-resolution laser CT scanner with a spatial resolution of 100 mm in all dimensions was used to quantify the data. The results suggest that the radial dose function can be measured very close to the seed with a relative uncertainty of about 1% to 2%. The dose distribution is isotropic only at distances greater than or equal to 2 mm from the seed and is almost symmetric, independent of the depth. We have measured the radial dose function, gL(r), according to the TG 149 protocol, observing that gL(r) increases to a maximum value and then decreases as the distance from the seed increases. This is in good agreement with previous data obtained with Gafchromic film and thermoluminescent dosemeters (TLDs), even if the TLDs underestimate the dose at distances very close to the seed. Contrary to the experimental measurements, gL(r) calculated through Monte Carlo simulations for this seed, and reported previously, steadily decreases without a local maximum as a function of the distance from the seed. Independent of the dosemeter used and the laboratory where the measurements were carried out, at distances less than 1.5 mm, differences of more than 20% are observed between the measurements and the Monte Carlo calculations. This difference could be due to a possible underestimation of the number of electrons absorbed into the seed core and encapsulation in the Monte Carlo simulation, as a consequence of the unknown precise chemical composition of the core and its respective density for this seed. This study indicates that Gafchromic film, as well as BANG3-Pro-1 gel coupled with the special small format laser CT scanner, are valid and accurate methods for measuring the dose distribution at distances close to an intravascular brachytherapy seed.
Citation: Physics in Medicine and Biology
Pub Type: Journals
BANG3-Pro-1gel, beta dosimetry, high-resolution optical CT scanner, intravascular brachytherapy