The calibration chain for medical radiotherapy beams requires a primary reference standard that defines the quantity of absorbed dose to water. Water calorimetry is the most direct technique for such measurements; however, its susceptibility to systematic errors due to conduction and convection effects within the water has slowed its adoption by the international metrology community. The usual practice for correcting such errors involves finite-element simulations to estimate the step response of a given calorimeter to sequences of radiation exposure; as such, these corrections depend upon the exposure timing and must be recalculated when conditions change. We have developed an alternative approach in which calorimeter response is characterized in the frequency domain as a transfer function containing thermal properties as parameters. This approach offers useful insights for optimizing the signal-to-noise ratio and eliminating systematic errors, and, when applied to simulated data, produces a transfer function that characterizes the experimental data.
Proceedings Title: Proceedings of ITCC29/ITES17 Conference
Conference Dates: June 1, 2007
Conference Title: ITCC
Pub Type: Conferences
effects of conduction and convection, frequency domain analysis, transfer function, water calorimetry