UWM, Milwaukee, Wisconsin, USA
ANL, Lemont, Illinois, USA
Lack of online range verification generally limits application of proton therapy to cancers in the brain, spine, and to pediatric patients. Previously, thermoacoustic range verification (TARV) has been demonstrated in weakly scattering media with known sound speed [1]. At ATLAS, we demonstrated the accuracy and robustness of TARV relative to ultrasound (US) images despite acoustic heterogeneity and sound speed errors representing in vivo conditions [2]. 250 ns pulses deposited 0.26 Gy of 16 MeV protons and 2.3 Gy of 60 MeV helium ions into liquid targets. TA signals were detected by an US array that also generated US images. An air gap phantom displaced the Bragg peak by 6.5 mm and the scanner’s propagation speed setting was altered by ±5%. Weak and strong scatterers were placed between the Bragg peak and US array. Estimated Bragg peak locations were translated 6.5 mm by the air gap phantom and agreed with TRIM simulations to within 0.3 mm, even when TA emissions traveled through a strong acoustic scatterer. Soundspeed errors dilated, and acoustic heterogeneities deformed both US images and TA range estimates, confirming that TARV is accurate relative to US images.
[1] Hickling, et al, Med Phys, 45(7), 2018. (review article)
[2] S. Patch, D. Santiago, & B. Mustapha, Med Phys, 46(1), 2019.
