Online Thermoacoustic Range Verification Overlaying Treatment Spot onto Ultrasound Images for Synchrocyclotron Proton Therapy Systems

Particle therapy is a technique for treating solid tumors that is potentially more precise than x ray radiation therapyCharged particles enter the patient at relativistic speedsdepositing increasingly more dose as they come to rest inside the patientX ray photon beams deliver an exponentially decaying dose along the beam pathdosing healthy tissue before and after the tumorWhen patient alignment is accurateproton therapy causes less collateral damage overalldelivering less dose to proximal tissue and sparing distal tissue altogetherTodaypatients are positioned by matching bony structures in daily x ray images to planning CT volumes acquired daysor weekspriorInter fraction changes to soft tissueweight lossedemaare common and intra fraction changesdigestionrespirationetcare unavoidableRange errors incorrectly dose healthy tissue and undertreat the tumorlimiting benefits of proton therapyThereforethe American Society for Therapeutic Radiation Oncology currently supports proton therapy for tumors near the base of the neckspineeye and in pediatric patientsand only in the context of clinical trials for most other tumor sitesThermoacoustic range verification relies upon stress confinement and is suitable for compact synchrocyclotrons recently introduced by two manufacturersMy lab was the first to overlay thermoacoustic range estimates onto ultrasound images of the underlying morphology using a single transducer array to ensure inherent co registrationThe work was performed at national laboratories using low energy beams that generated high frequency thermoacoustic emissions which could be detected by ultrasound imaging arraysThe next step is developing a thermoacoustic range verification prototype for particle therapy systems that pulse delivery of high energyMeV or moreparticlesRange straggle smooths the Bragg curve and bandlimits thermoacoustic emissions below the sensitivity band of ultrasound imaging arraysThereforelow frequency receivers that can detect low frequencyDCkHzthermoacoustic emissions will be added to higher frequencyMHzbiplane ultrasound imaging arraysPhase I will be devoted to developing a prototype that overlays thermoacoustic range estimates into aD visualization of orthogonal biplane ultrasound imagesThermoacoustic range estimates will be updated at a rate ofHzassuming dose is delivered sufficiently quicklyIf successfuldeployment of a clinical prototype for low risk studies to collect thermoacoustic data during the normal course of treatment will follow in Phase II Ion therapy concentrates dose in a small treatmentspotand can minimize collateral damage to nearby healthy tissueif treatment is targeted accuratelyThereforeverifying that dose is delivered to the tumorrather than nearby healthy tissue is criticalbut not yet well addressed by today s range verification techniquesA thermoacoustic range verification prototype that overlays range estimates onto ultrasound images of the patient during treatment will be developed