In recent years there has been increased interest throughout the world in the use of proton radiation therapy for treatment of cancer and independent studies project a 20% annual increase in the installed base. The replacement of X-ray therapy with proton therapy will have substantial long term benefit to patients due to greatly reduced long and short term toxicity side effects. Such effects also have substantial costs associated with their treatment that may continue for many years after treatment. Making the cost of delivering proton therapy cost competitive to that of X-ray therapy not only makes a superior treatment mode available, but will also result in substantial long term savings to health care providers. The capital and operating cost of extant systems is a major limiting factor. The procedure referred to as Spot Beam Scanning (SBS), where scanning of a small beam 3D spot (voxel) takes advantage of the physical properties of protons and provides the ultimate in tumor conformality is now rapidly being introduced for use in for dose delivery. SBS eliminates the need for patient-specific devices (collimators and compensators) that are both expensive to manufacture and add considerably to the time needed to deliver each dose to the patient, thereby further reducing operating costs. The SBS approach however is more sensitive to organ motion than traditional procedures. To overcome this fast SBS of the target volume to greatly reduce dose delivery times into the millisecond (ms) time scale is optimal. Phenix believes that fast scanning not only makes the SBS more suitable for treating moving targets but also enables faster dose delivery as needed for new prospective treatment protocols using protons, such as lung tumors. The increasing use of accelerators by vendors that deliver beam in short ms pulses places further challenges on detectors than can rapidly verify the area treated and the magnitude of the dose delivered to the tumor. These dual challenges require detectors that can monitor both the position and dose delivered in real-time and provide rapid feedback to the accelerator to modify further dose to be delivered as required. None of the extant systems now available can satisfy these demands.
The Specific Aims i n this grant application are to perform the research needed to further develop the use of a novel very fast gas scintillation technique to measure the dose delivered and the spot position on a sub-millisecond time scale based on the prototype developed in Phase I.
Technological advances are fueling a new generation of cancer therapy, based on scanning an energetic narrow proton beam, with intensity adjustments at every step, to deliver a radiation dose that conforms to an arbitrary-shaped tumor more precisely than ever before, reducing both the cost and the short- and long-term toxic side effects of the treatment. The need to carry out lateral beam scans in time intervals much shorter than organ motion periods, and to do so possibly with new accelerators that deliver the beam in microsecond-long pulses, demands continuous monitoring of dose delivery with detector capabilities beyond those of existing commercial dosimeters. We aim to develop a new kind of cost-effective dosimeter, in which scintillation of a gas traversed by the beam will simultaneously provide the accuracy, response speed and position resolution matched to the demands of these new treatment protocols.