Evidence for a significant timer error on a linear accelerator: consequences for a special therapy application.
A significant timer error has been found on a linear accelerator used for intraoperative radiation therapy. Since typical treatment doses range up to 20 Gy, calibrations that do not account for this effect can incur a large dosimetry error. The effect is dose rate dependent, but energy independent. For a dose rate of 900 cGy min(-1), the error in dose calibration varies between 2 and 3% for an average of 2.5%. At dose rates of 600 and 300 cGy min(-1), the error was 1.7% and 0.8% respectively. The average timer error at 900 cGy min(-1) was found to be 1.2 +/- 0.1 monitor units. It is argued that even a small timer error has serious dosimetry consequences for the implementation of intensity modulated radiation therapy.
Biggs
P J
PJ
Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston 02114, USA.
D002138:Calibration; D007431:Intraoperative Complications; D010315:Particle Accelerators; D011874:Radiometry; D011878:Radiotherapy / Q000009:adverse effects*; D013997:Time Factors