| The use of external beam proton therapy for treating many types of cancer is being investigated at several centers throughout the world. In such investigations, it is important to be able to compare dose from protons to dose from other radiation beams (e.g. photons and electrons). Additionally, it is important that different proton therapy centers be able to correctly compare results with one another, necessitating a global standard for accurately determining proton dose.;Historically, radiation dosimetry has depended on a quantity w, the average energy required to produce an ion pair. This quantity has been used both in photon and proton radiation dosimetry. The value for photons is fairly well known (∼0.2% uncertainty), but the proton value contributes significantly (∼4%) when used for proton dosimetry.;Dose measurements were made with a combination of ionization chamber and water calorimeter in order to determine the w value in water for proton beams delivered by the Indiana University Cyclotron. A unique calorimeter was developed for this research in which an existing design was modified by eliminating an air jacket in order to reduce the bulkiness of the calorimeter. A novel method was developed and implemented to correct for heat loss which improved the accuracy of the calorimeter in the high intensity proton beam of the cyclotron.;Three separate experiments were performed at 164 MeV, 162 MeV and 133 MeV, with several measurements done at each energy. The values and standard deviations obtained for w and their standard deviations were 33.5 +/- 0.3 eV/ion pair, 33.9 +/- 0.7 eV/ion pair and 34.2 +/- 0.4 eV/ion pair, respectively.;In addition, independent determinations of the proton dose at these three energies were made utilizing an absolute fluence measurement and the Beam Monster software program. The absolute fluence was measured by integrating the current from a secondary electron emission monitor that was cross-calibrated with a Faraday cup. These dose-per-unit charge values compared favorably with the same values measured by the water calorimeter and by the ionization chamber, thereby providing an independent confirmation of the results. |
