Volume 17 (2011): Issue 3 (September 2011)

A number of experiments was performed using standard protocols, in order to evaluate the dosimetric accuracy of Leksell Gamma Knife 4C unit. Verification of the beam alignment has been performed for all collimators using solid plastic head phantom and Gafchromic™ type MD-55 films. The study showed a good agreement of Leksell Gammaplan calculated dose profiles with experimentally determined profiles in all three axes. Isocentric accuracy is verified using a specially machined cylindrical aluminium film holder tool made with very narrow geometric tolerances aligned between trunnions of 4 mm collimator. Considering all uncertainties in all three dimensions, the estimated accuracy of the unit was 0.1 mm. Dose rate at the centre point of the unit has been determined according to the IAEA, TRS-398 protocol, using Unidose-E (PTW-Freiburg, Germany) with a 0.125 cc ion chamber, over a period of 6 years. The study showed that the Leksell Gamma Knife 4C unit is excellent radiosurgical equipment with high accuracy and precision, which makes it possible to deliver larger doses of radiation, within the limits defined by national and international guidelines, applicable for stereotactic radiosurgery procedures.

The novel type of detector for X-ray energy evaluation has been developed. Thanks to a simultaneous analysis of the attenuation of X-rays by different thicknesses of well known material, the maximum energy of electrons on the conversion target can be deducted. Fast operation allows for pulse-to-pulse measurement, which is a must for modern, interlaced-energy cargo inspection systems. In this article the construction of the detector and software description are presented.

With increased demand for low ¹⁰³Pd (palladium) seed sources, to treat prostate and eye cancers, new sources have been designed and introduced. This article presents the two new palladium brachytherapy sources, IR03-¹⁰³Pd and IR04-¹⁰³Pd that have been developed at Nuclear Science and Technology Research Institute. The dosimetry parameters such as the dose rate constant Λ, the radial dose function g(r), and the anisotropy function F(r,θ), around the sources have been characterized using Version 5 Monte Carlo radiation transport code in accordance with the update AAPM Task Group No. 43 report (TG-43U1). The results indicated the dose rate constant of 0.689±0.02 and 0.667±0.02 cGy h^-1 U^-1 for the IR03-¹⁰³Pd and IR04-¹⁰³Pd sources respectively, which are in acceptable agreement with other commercial seeds. The calculated results were compared with published results for those of other source manufacturers. However, they show an acceptable dose distribution, using for clinical applications is pending experimental dosimetry.

Commissioning beam data are treated as a reference and ultimately used by treatment planning systems, therefore, it is vitally important that the collected data are of the highest quality, in order to avoid dosimetric and patient treatment errors that may subsequently lead to a poor radiation outcome. High-energy photon and electron beams from different accelerators of the same nominal energy may have different dosimetric characteristics due to differences in target and flattening filter materials, accelerator guide and collimator designs. In the present study, clinically pertinent data for the available photon energy were investigated. For making measurements in water, first time in India, a three dimensional radiation field analyzer RFA (CRS- Scan -O-Plan) was used. For absolute dosimetry and other measurements like relative output factors, wedge factors etc., a DOSE1 electrometer (Scanditronix Wellhofer) in a white polystyrene was employed. All the measured data were utilized as an input to the ECLIPSE treatment planning system for further clinical use.

Recombination chambers and 2202D Studsvik-Alnor reference remmeter were used for determination of ambient dose equivalent, H^*(10) and its neutron and gamma components at the door to the maze of 15 MV medical accelerator. The measurements were performed at opened and partly closed door. The results showed that the ambient dose equivalent rate was 76.2 μSv h^-1 at the opened door and only 2.7 μSv h^-1 at slightly opened door, 2.5 m from the entrance to the maze.