Abstract

Range verification limits clinical utility of particle therapy, which concentrates dose in space compared to x-ray radiation therapy. Treatment plans can be computed with sub-millimeter precision, but treatment is delivered without a feedback loop to verify dose accuracy in vivo. Therefore, margins of several millimeters are added and robust planning selects beam angles that are robust to range errors. Large margins and robust planning tend to increase collateral damage, reducing clinical benefit.   Adding clinical benefit requires estimating range with millimeter accuracy. But thermoacoustic emissions are bandlimited below 100 kHz, which implies a diffraction limit of 7.5 mm. Incorporating a priori information from the patient images and treatment plan can be used to estimate range shifts with submillimeter accuracy.   As we retire technical risks, the greatest impediments to transitioning thermoacoustic range verification into the clinic become clinical. Mathematicians may be happy with a table of range shifts reported in millimeters, but clinicians may prefer plots of dose volume histogram, or image volumes of dose error.   Time permitting, we will also discuss sampling requirements and contrast with other range verification techniques. Because thermoacoustic emissions are weak, vertical resolution is a challenge. Thermoacoustic and nuclear (PET, prompt gamma) emissions are generated during treatment. Range verification based upon these emissions are inverse source problems. These techniques can be implemented passively, without requiring additional radiation or contrast agents.