Dosimetric characterization of large photon fields (Varian, Clinac 2100c, X-6mv) by using standard measurement approach

Abstract

The most optimal dosimetry model for the application of large photon fields (dimensions larger than 40x40 cm) at extended focus-phantom/patient distances has not been adopted yet. A method based on a "classical" approach, that helps establishing a database (PDD, output and OF, PSF, Sc and TMR parameters) is discussed. Large photon fields produced by a CLINAC 2100C, Varian, in the low energy mode (6 MV) were analyzed by application of absolute and relative radiation dosimetry, as well as, by comparison with calculated data. A good agreement between measured and calculated values of radiation parameters examined, at FFD=180 and 300 cm, was observed Slight increase in discrepancy (about 10 percent) of the TMR at FFD=300 cm for fields larger than 50x50 cm and at larger depths was observed by comparison of calculated and measured values. Discrepancies of outputs between measured and calculated values (calculated by the inverse square law) were less than 2 percent. Most of the dosimetric data obtained points out the possibility of application of radiotherapy unit CLINAC 2100C (Varian) for therapies with large fields in given conditions.

Keywords

• Whole-body irradiation
• radiotherapy dosage
• radiotherapy
• radiometry