Design of a 2D Calorimeter Array for Measurement of Radiation Therapy Treatment Beams

University of Wisconsin – Madison/UWMRRC, Madison, WI, United States

^* Corresponding author: jlambeck.medphys@gmail.com

Published online: 7 March 2025

Abstract

In the field of Medical Physics, calorimeters are often used as an absolute dose measurement in standards labs as part of the chain of calibrations for radiation therapy treatment machines in hospitals and cancer centers. Currently, every calorimeter designed for this purpose is either position-insensitive or 1-dimensional, despite the radiation dose deposited not always being homogeneous across the entire irradiated area. Therefore, a 2-dimensional, position-sensitive, calorimeter array is being designed to provide information on the dose both on the central axis of the radiation beam as well as the dose fall off away from center. The device is composed of 9 voxels in a 3x3 configuration. Each voxel contains a cylindrical core made of high-purity aluminum which is the volume of interest for heating measurements and therefore dose determination. Each core is surrounded by alternating shells of solid Aerogel insulation and additional high-purity aluminum. The outer aluminum shell is operated isothermally with a set temperature above what the ambient air could reach. This provides a buffer for each core from both air temperature fluctuations and heat flow between voxels during measurements. The inner aluminum shell and the core maintain a quasiadiabatic state to prevent heat flow into or out of the core except from the energy deposited from the radiation. Both temperature measurements and necessary heating for the quasi-adiabatic or isothermal conditions are accomplished using embedded thermistors connected to a LabJack T7 data acquisition (DAQ) device operated by a purpose-built Python control code. The calorimeter array is currently being constructed for testing later this year.