A water calorimeter for on-site absorbed dose to water calibrations in (60)Co and MV-photon beams including MRI incorporated treatment equipment

• Published in: Physics in medicine & biology Vol. 61; no. 13; pp. 5051 - 5076
• Main Authors: de Prez, Leon, de Pooter, Jacco, Jansen, Bartel, Aalbers, Tony
• Format: Journal Article
• Language: English
• Published: England 07.07.2016
• Subjects: Calibration; Calorimetry - instrumentation; Calorimetry - methods; Calorimetry - standards; Magnetic Resonance Imaging - instrumentation; Magnetic Resonance Imaging - methods; Photons - therapeutic use; Radiation Dosage; Radiotherapy - methods
• ISSN: 1361-6560
• DOI: 10.1088/0031-9155/61/13/5051

In reference dosimetry the aim is to establish the absorbed dose to water, D w, under reference conditions. However, existing dosimetry protocols are not always applicable for rapidly emerging new treatment modalities. For primary standard dosimetry laboratories it is generally not feasible to acquire such modalities. Therefore it is strongly desired that D w measurements with primary standards can be performed on-site in clinical beams for the new treatment modalities in order to characterize and calibrate detectors. To serve this need, VSL has developed a new transportable water calorimeter serving as a primary D w standard for (60)Co and MV-photons including MRI incorporated treatment equipment. Special attention was paid to its operation in different beam geometries and beam modalities including the application in magnetic fields. The new calorimeter was validated in the VSL (60)Co beam and on-site in clinical MV-photon beams. Excellent agreement of 0.1% was achieved with previous (60)Co field calibrations, i.e. well within the uncertainty of the previous calorimeter, and with measurements performed in horizontal and vertical MV-photon beams. k Q factors, determined for two PTW 30013 ionization chambers, agreed very well with available literature data. The relative combined standard uncertainty (k  =  1) for D w measurements in (60)Co and MV-photons is 0.37%. Calibrations are carried out with a standard uncertainty of 0.42% and k Q -factors are determined with a relative standard uncertainty of 0.40%.