Time of Flight Proton Radiography for Proton Therapy Imaging

Significance Proton therapy uses a precisely defined beam of penetrating charged particles to kill tumor cells while sparing surrounding healthy tissues to a greater extent than is possible with conventional photon based radiation therapy To achieve this precision verification that the treatment dose will be delivered precisely as specified is needed Proton radiography is a promising way to verify correspondence between a modeled proton irradiation plan and observed proton radiation transport through patients With proton radiography precise correspondence between transmitted proton energy predictions and observations can validate treatment plans and enable reduced margins of safety for more precise dose delivery Proton radiography imaging detectors have to date been impractical for use within the proton therapy clinical setting because of their bulk cost and difficulty of rapid electronic readout We propose to use novel ultra high speed imaging detectors manufactured by our company to make a practical proton radiography system Our system will be capable of measuring the time needed for a particle to travel at close to the speed of light over just inches with the required accuracy With our detectors we will measure proton energies using their speed for narrow pulsed pencil beams of protons with known energy Monte Carlo based treatment models will thereby be validated by comparing corresponding Monte Carlo based transmission models with observed time of flight measurements Hypothesis We hypothesize that time of flight and hence residual energy predictions from Monte Carlo models for pencil beam proton bunches which have traversed test phantom objects will correspond with high precision to time of flight measurements performed using our new method Preliminary Data The response of our detector to similar particles has been measured and we have modeled the expected response of our system to the slowed treatment protons that will traverse objects patients and our proton radiography system Specific Aims This project will obtain proof of concept data to guide future radiography system designs In Specific Aim we will construct and test a portable test device for transport to a proton treatment beam In Specific Aim we will test and calibrate our system using protons of known energy both without and then with known amounts of phantom material being traversed by the protons In Specific Aim we will computer model simulate both our Phase I measurements and those expected from a proposed Phase II proton radiography system consistent with our measurements and will predict future systems expected performance for patient specific treatment plan verification within the clinical context To take full advantage of proton therapy s sharply defined dose delivery potential which better targets tumors while sparing nearby healthy tissues precise knowledge of where the beam will stop within a given patient is needed and this can be provided by imaging energy losses for protons that traverse the patient entirely Devices which perform such proton radiography have to date however been bulky expensive slow and impractical for the clinical context We propose a novel device and method that will determine exiting proton energies by measuring proton speeds at near the speed of light thereby providing a practical means for patient specific proton treatment plan verification at treatment time within the clinical proton therapy context