Ultrasonic Thermometers for Medical Dosimetry

PML researchers are exploring whether ultrasound can be used as a faster, more efficient way to take three-dimensional images of radiation dose profiles in water.

Medical clinics that treat cancer patients with beams of ionizing radiation need to make regular quality-assurance measurements using instruments such as ionization chambers. These chambers are themselves calibrated based on a primary standard that measures the heat created by therapeutic beams in water.

The Dosimetry Group of PML's Radiation Physics Division has been developing a new thermometry technique that employs ultrasonic transducers to measure changes to the speed at which sound travels through a water phantom.*

In a recent sequence of experiments, researchers used a pair of ultrasonic transducers to measure how the radiation-induced temperature rise, which corresponds with absorbed radiation dose, varies with depth in a water phantom exposed to radiotherapy beams of high-energy electrons.

Their results were in agreement with the results of conventional methods, obtained by mechanically scanning an ionization chamber throughout the water phantom. An imaging array based on the ultrasound technique might eventually enable high-speed visualization of dose distributions within matter, including solids.

The work may lead to improved quality-assurance procedures and could potentially spur commercial development of new types of clinical dosimetry instruments.

-- Reported and written by Jennifer Lauren Lee

*The speed of sound through a medium varies with temperature.

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