Assessment And Evaluation OF Photon Beam Dosimetric Accuracy Requirement of Tuning Medical Linear Accelerator

ABSTRACT

In radiotherapy, accuracy and precision are key, and thus, a small deviation in dose delivered by a treatment machine can be detrimental to patients. For this reason, in any radiotherapy department, linacs that have been tuned to match each other dosimetrically require critical assessment and evaluation since patients may be moved between linacs without any adjustments to treatment plans. The main aim of this study was to assess and evaluate the photon beam dosimetric accuracy between two beam-matched Elekta HD linacs (Linac 2 and Linac 3) at St. Olav's Hospital in Norway. The dosimetric photon beam data measured during the commissioning of the test Linac 2 were relatively compared to that of Linac 3, which is the reference Linac. Also, as part of this study, the new quality control data measured for the test Linac 2 has been compared to the annual quality control data of the reference Linac 3 as well as three other linacs (Linac 4, Linac 5 and Linac 6) installed at the department which have also been tuned to match the reference, in order to assess and evaluate the degree of deviations among these beammatched linacs. Comparison was also made in absolute dose terms. The photon beam data (percentage depth doses, beam profiles and output factor) were acquired using an IBA water phantom during the commissioning of the new test Linac 2. Quality control tests were also performed to measure the flatness and symmetry of the beam profiles and the beam quality index (D20/D10). Absolute dose calibration was also performed. These dosimetric beam data measured for the new test linac were compared to that of the department’s reference linac to assess and evaluate the degree of accuracy of the tuning of the test linac and also the consistency among all the linac units.