A NOVEL TISSUE EQUIVALENT PHANTOM FOR HADRON THERAPY

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A thin silicon sensor will be integrated in a mechanical system for scanning through a tissue equivalent liquid phantom for providing extremely accurate information on the dose deposited by a hadron therapy beam as a function of depth into the phantom and on the position in the plane perpendicular to the beam axis. This will allow a precise knowledge of the dose delivered to the patient (3d dose mapping) with unprecedented spatial resolution and speed. The dose deposited in depth by a hadron therapy beam in the human body follows a typical distribution that terminates with the high energy release called Bragg peak at the end of travel. This high energy deposition is exploited to maximise the effect to the cancer while giving limited amage to the surrounding helthy tissue. The accurate knowledge of the energy deposited by the beam is key to planning the treatment on individual patients. Also, the online monitoring of the Bragg peak position stability during treatment is essential for the success of the treatment.Thanks to the fast response of silicon detectors, the Bragg peak scan will provide real-time information to the operators on the dose to be released by the therapy beam in the target and surrounding tissue. This phantom makes use of a thinned silicon detector to enhance the accuracy of the scan. The precision of the reconstructed profiles can be selected to be as fine as 10 microns (this accuracy comes without cost or hardware complexity penalties). This instrument makes use of a single sensitive element (the silicon detector) moved by a precision motor in axis with the therapy beam. The energy deposition of the beam is continuously measured by the sensor while moved from the entrance point of the phantom to the back end. The beam is stopped within the phantom volume and the scan delivers the energy deposition profile with great accuracy and in real time. This instrument would represent a significant improvement with respect to existing phantoms because of its high spatial resolution and real time response. The precision would prove very valuable at the planning stage of the treatment and the speed for real-time feedback. It could be used at any hadron therapy centre alone or in combination with other existing beam monitoring equipment.