Dosimetry study comparing NCS report-5, IAEA TRS-381, AAPM TG-51 and IAEA TRS-398 for high energy electron beams

Several codes of practice based on absorbed dose to water for reference dosimetry in clinical high-energy photon and electron beams have been published recently, to replace the air-kerma based codes of practice. In the present work, comparative dosimetry has been done utilizing absorbed dose based recommendations [AAPM TG-51 and IAEA TRS-398] and four air -kerma based recommendations [NCS report-5 and IAEA TRS-381]. Measurements were performed for five clinical electron beam energies [5MeV. 7MeV, 10MeV, 12MeV, and 14MeV] using three Markus-type plane-parallel chambers. Dosimetry based on direct calibrations of all chambers using [50]Co was investigated. It is shown that the use of [60]Co calibration factors could result in deviations of up to 2.3% in electron beams using different codes of practice. The results show that the obtained absolute dose values at the depth of maximum dose D[max] are not significantly altered by changing from air-kerma based dosimetry to absorbed dose to water based dosimetry when using calibration factors obtained from the Laboratory for Standard Dosimetry. National Institute of Standards, Egypt

quality assurance procedure to monitor mechanical stability on-Linear accelerator-based on stereotactic radiosurgery/sterotatic radio therapy

Stereotactic irradiation, either in the form of stereotactic radiosurgery [SRS] or stereotactic radiotherapy [SRT], of brain lesions requires high precision accuracy in the isocenter, the main determinants were gantry and couch rotations. It is thus necessary to evaluate the isocenter variation due to gantry and couch rotations in the particular setup for SRS/SRT. This paper describes the accuracy of Patients' immobilization and the variation in the isocenter of a Siemens PRIMUS M6/6ST linear accelerator-modified for adapting a couch-mounted radiosurgery system. The accuracy of Patients immobilization was excellent in over twenty patients with 95 setups and 2375 scalp measurements. Ninety two percent of measurements had no displacements from the baseline readings, 7% had 1 mm and one percent had 2 mm displacements. The variations in isocenter position with the table and the gantry rotation were found to be < 0.4 mm with a compounded accuracy of