Photoacoustic dose monitoring in clinical high-energy photon beams

Abstract

This work describes all stages of development (setup, optimization, performance, and first experimental measurements) of an acoustic sensor that can be used for range monitoring and dosimetry of clinical radiotherapy beams. The detection device consists of an ultrasonic transducer, a combination of preamplifiers and differential amplifiers with filtered outputs and a digital oscilloscope. Simulations of the experimental setup were carried out to study the optimal measurement geometry and choice of transducer. The dose distributions were calculated with the Monte Carlo code FLUKA, while the acoustic simulations were performed with the analytical wave transport code k-Wave. The temporal profiles of the dose pulses, in the order of μs, were measured with a scintillating crystal coupled to a photomultiplier and used as input for the acoustic simulation. Measurements were performed in a Cyberknife™ radiosurgery beam and a TrueBeam unit. A lead block was submerged in water and placed partially or totally in the irradiation field in order to increase the acoustic signal. Photoacoustic signals were detected with both beams with the expected shape and time-delay, after the frequency response of the detection system was taken into account. The proposed setup can detect photoacoustic signals originating from the penumbra of the treatment fields after being processed with the appropriate image analysis tools.

MRI of radiation chemistry: First images and investigation of potential mechanisms

“…2,3 Other groups are working toward using radiation-induced thermoacoustic effects for in vivo dosimetry and range verification. 4,5 One technique currently being translated into clinical practice is Cherenkov imaging, which uses cameras to monitor for light generated in irradiated areas of the patient's skin by high-energy electrons. 6 These techniques, which have important limitations in energy thresholds, allow for visualization of radiation effects based on the physical deposition of dose through induced radioactivity, thermoacoustic effects, and Cherenkov radiation rather than changes in radiation chemistry.…”

“…For example, researchers have demonstrated that radioactivity induced by proton beams can be imaged with positron emission tomography (PET) or prompt gamma spectroscopy during treatment 2,3 . Other groups are working toward using radiation‐induced thermoacoustic effects for in vivo dosimetry and range verification 4,5 . One technique currently being translated into clinical practice is Cherenkov imaging, which uses cameras to monitor for light generated in irradiated areas of the patient's skin by high‐energy electrons 6 .…”

Risks and Benefits of Fiducial Marker Placement in Tumor Lesions for Robotic Radiosurgery: Technical Outcomes of 357 Implantations

“…Thus, this study again highlighted the need for FM in selected cases and concluded that they did not observe any negative effect of FM on the clinical outcomes of these patients. Another innovative approach to track the tumors in the future could be photoacoustic imaging to detect movements of tumor and organs, which is currently in development [ 46 , 47 ].…”

Dictionary-based protoacoustic dose map imaging for proton range verification

“…This energy deposition results in a small increase in temperature which produces a thermoelastic expansion and a local pressure increase, which in turn induces a measurable ultrasonic pressure wave [ 13 ]. This process is known as the radio-induced thermoacoustic effect, and it is also used for photoacoustic and optoacoustic imaging [ [38] , [39] , [40] , [41] , [42] ]. Under thermal and stress confinement conditions [ 29 , 43 ], the initial pressure distribution can be calculated from the dose distribution as [ 29 , 43 ]: where is the Grüneisen coefficient, a material-specific dimensionless parameter that indicates the conversion efficiency between the absorbed heat energy and the induced pressure ( , where is the speed of sound, is the isobaric volume expansion coefficient and is the specific heat capacity) [ 43 ]; is the dose distribution and is the medium mass density.…”