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Optical Resonator Water Calorimeter

J Abraham

J Abraham*, J DeMarco , D Low , UCLA Department of Radiation Oncology, Los Angeles, CA


SU-F-BRE-12 Sunday 4:00PM - 6:00PM Room: Ballroom E

Purpose:Water calorimetry based on resistance thermometry has matured as a primary standard. Developing an optical technique hold the promise to push the boundaries of what is currently achievable with dosimetry. We will present a feasibility study and the current progress of construction of a Fabry-Perot resonator for dose to water measurement. Additionally, estimations of the theoretical limits resonator sensitivity and potential sources of noise for the system are described.

Methods: A temperature change from the dose to water would be measured by the change in the index of refraction from the water in the cavity. Calculations are presented of the expected signal from the resonator for dose to water. The Fabry-Perot resonator constructed from optical quality narrowband mirrors is described. A water cell will be inserted into the cavity gap to provide the medium swept cavity length technique is explored as a specific implementation of this technique.

Results: Calculations indicate that a dose to water on the order of a Gray is measureable with a reasonably implementable system. A resonator is currently under construction and progress towards a proof of principle measurement will be presented. The primary sources of noise, in order of importance, are expected to be; optical absorption by the medium, mechanical perturbations of the cavity length and thermal expansion of the optical mounts. Estimations of these noise sources and mitigation techniques will be discussed.

Conclusion: A Fabry-Perot resonator is a promising technique for measuring the absorbed dose to water from a radiotherapy beam. This technique has the potential to serve as a check on the current primary standard for dose to water measurements. As well, it may be the foundation for a new class of optical property based dosimetry measurement.

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