title: Dosimetric accuracy of a dual photon energy linac at low monitor setting for various pulse repetition frequencies.
abstract: Accuracy of dose delivery at low monitor unit setting is studied for a dual photon energy linear accelerator. Dose delivered per MU is found to be constant for both the photon beams for MU settings above 30. For lower MUs there is definite deviation from the calibrated value and the error is found to be increasing as fewer MUs are set for dose delivery. This dose/MU ratio at low MU setting is found to be dose-rate dependent, showing an increasing trend with pulse repetition frequency (PRF). Also, the dosimetric ratio is observed to be mode dependent; its value for an 18 MV beam is almost double that observed in the case of a 6 MV beam at very low MU setting. The magnitude of this error should be determined for each energy so that appropriate corrections can be applied if very low MUs are to be used.
authors.affiliation: Department of Radiation Physics, Kidwai Memorial Institute of Oncology, Bangalore, India.
authors.forename: A K
authors.initials: AK
authors.lastname: Sharma
authors.forename: S S
authors.initials: SS
authors.lastname: Supe
authors.forename: N
authors.initials: N
authors.lastname: Anantha
authors.forename: K
authors.initials: K
authors.lastname: Subbarangaiah
mesh_terms: D010315:Particle Accelerators; D017785:Photons; D011834:Radiation Monitoring; D011874:Radiometry / Q000592:standards*