ABSTRACT
Proton radiation therapy beams deposit a large fraction of their dose at the end of their range. Although dosimetrically advantageous, treatment is complicated by range uncertainty. One possible method for in vivo measurement of the proton range is to measure the thermoacoustic pressure waves that are emitted when proton dose is converted to heat. Here, this acoustic-based technique – also called ionoacoustics, Radiation-Induced Acoustic Computed Tomography, or protoacoustics – is reviewed. The underlying physics is discussed and current research in the field is summarized. The largest challenges to future adoption of protoacoustic proton range verification are low signal levels, error-inducing tissue heterogeneity, and limited anatomical sites of application due to poor transmission through air and bone. Based on water tank measurements, several groups have demonstrated submillimeter range verification accuracy at high (>3 Gy) dose levels. Heterogeneity is expected to degrade protoacoustic accuracy due to variable sound speeds, but ultrasound imaging may provide self-corrected anatomical registration. Protoacoustic results are promising, and the method may provide a simple, low-cost, and real-time proton range verification in the future.
