Room: AAPM ePoster Library
Purpose: Accounting for the range uncertainty in proton therapy planning has been challenging for decades. The stopping behavior of protons and thus their total range can only be predicted with limited accuracy using current methodologies. This becomes a clinically challenging issue in deep seated tumors of the Central Nervous System (CNS) where organs at risk (OARs) such as the optic nerves, optic chiasm, brainstem, pituitary, and cochlea reside. By measuring the time-of-flight of acoustic waves generated by the thermoacoustic conversion of heat to pressure at the Bragg peak (BP), Protoacoustics is a potential technique for proton range verification.
Methods: Validation of Protoacoustic signals induced by proton pulses from an IBA cyclotron were verified by irradiating a cylindrical (polyethylene) homogeneous solid phantoms; acquiring signals from a five-accelerometer array placed on the distal surface of the phantom. The acoustic signal was processed by a combination of high/low pass filters to obtain the Daubechies4 (db4) wavelet, which was used to obtain the acoustic time-of-arrival (TOF) for each accelerometer. The difference of the TOF between paired accelerators indicates the BP position relative to the accelerometers. Triangulation algorithm for the acoustic array was developed to calculate the BP in homogeneous phantom.
Results: We performed preliminary study of Protoacoustics produced in a hog head. Detectors were positioned on the hog head on the distal side of the proton beam. The detected acoustic signal was overlapped with proton pulse and simulation, in which the acoustic TOF agrees with the distances between BP and detector calculated in TPS. Although sites classically inaccessible to ultrasound imaging, such as the brain and the head and neck, are amenable to protoacoustic range verification.
Conclusion: We have demonstrated, for the first time, the protoacoustic range-verification capability through bone. Providing evidence that it can be used for in-vivo patient monitoring of CNS cases.
Not Applicable / None Entered.