a study of the impact of trs-483 recommended correction factors for dosimetry of small fields in flattening filter free beams used in truebeam linear accelerators

Introduction: to study the effect of the international atomic energy agency (iaea) trs-483 recommended beam quality correction factor in reference dosimetry and to examine the recommended field output correction factor for relative dosimetry of 6-mv flattening filter free (fff) small fields, used in a varian truebeam linear accelerator (linac). material and methods: the beam quality and field output correction for 6-mv fff beams were adopted from the trs-483 protocol. monte carlo (mc) simulation of the output factor was performed using the penelope-based primo software and compared with the trs-483 corrected output factors. two analytical anisotropic algorithm (aaa) models in the eclipsetm treatment planning system (tps) were created; one with an output factor taken as the ratio of meter readings and one with an output factor obtained by multiplying the trs-483 correction factor by the ratio of meter readings. besides, box field and dynamic conformal arc (dca) plans were created for both aaa models for verification and validation. the patient-specific quality assurances (qa) for ten different targets were performed, and deviations between the measured and tps-calculated point doses in both models were examined. results: separate beam quality correction factors for fff beams in the trs-483 protocol only resulted in an improvement of 0.1% in reference dosimetry. the trs-483 corrected output factor was in a better agreement with the mc-calculated output factor. for a patient-specific qa of dca plans, the output factor-corrected aaa dose calculation algorithm showed a better agreement between the measured and simulated doses. also, there was a smaller deviation (1.2%) for the smallest target of 0.23 cc (8 mm equivalent sphere diameter) used in this study. conclusion: the field output factors for the linac small beams can be improved by incorporating the trs-483 correction factors. however, the extent of improvement that can be expected depends on the source model of the calculation algorithm and how these well-generalized corrections are suitable for user beams and detectors.