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Zhang R.,University of Houston | Taddei P.J.,University of Houston | Fitzek M.M.,Midwest Proton Radiotherapy Institute | Fitzek M.M.,Indiana University | Newhauser W.D.,University of Houston
Physics in Medicine and Biology | Year: 2010

Heavy charged particle beam radiotherapy for cancer is of increasing interest because it delivers a highly conformal radiation dose to the target volume. Accurate knowledge of the range of a heavy charged particle beam after it penetrates a patient's body or other materials in the beam line is very important and is usually stated in terms of the water equivalent thickness (WET). However, methods of calculating WET for heavy charged particle beams are lacking. Our objective was to test several simple analytical formulas previously developed for proton beams for their ability to calculate WET values for materials exposed to beams of protons, helium, carbon and iron ions. Experimentally measured heavy charged particle beam ranges and WET values from an iterative numerical method were compared with the WET values calculated by the analytical formulas. In most cases, the deviations were within 1 mm. We conclude that the analytical formulas originally developed for proton beams can also be used to calculate WET values for helium, carbon and iron ion beams with good accuracy. © 2010 Institute of Physics and Engineering in Medicine.

Perez-Andujar A.,University of Wisconsin - Madison | Perez-Andujar A.,University of California at San Francisco | Deluca P.M.,University of Wisconsin - Madison | Thornton A.F.,Midwest Proton Radiotherapy Institute | And 5 more authors.
Radiation Protection Dosimetry | Year: 2012

This work presents microdosimetric measurements performed at the Midwest Proton Radiotherapy Institute in Bloomington, Indiana, USA. The measurements were done simulating clinical setups with a water phantom and for a variety of stopping targets. The water phantom was irradiated by a proton spread out Bragg peak (SOBP) and by a proton pencil beam. Stopping target measurements were performed only for the pencil beam. The targets used were made of polyethylene, brass and lead. The objective of this work was to determine the neutron-absorbed dose for a passive and active proton therapy delivery, and for the interactions of the proton beam with materials typically in the beam line of a proton therapy treatment nozzle. Neutron doses were found to be higher at 45° and 90° from the beam direction for the SOBP configuration by a factor of 1.1 and 1.3, respectively, compared with the pencil beam. Meanwhile, the pencil beam configuration produced neutron-absorbed doses 2.2 times higher at 0° than the SOBP. For stopping targets, lead was found to dominate the neutron-absorbed dose for most angles due to a large production of low-energy neutrons emitted isotropically. © The Author 2012. Published by Oxford University Press. All rights reserved.

Nichiporov D.F.,Indiana University | Klyachko A.V.,Indiana University | Solberg K.A.,Indiana University | Zhao Q.,Midwest Proton Radiotherapy Institute
Radiation Measurements | Year: 2011

A monitor for a uniformly scanned beam was designed and constructed by the Indiana University Cyclotron Facility for use in a clinical proton gantry at the Midwest Proton Radiotherapy Institute. The beam monitor is a thin-walled, wide-aperture ionization chamber, which provides information about dose, beam size, symmetry, flatness, and position. Several characteristics of the monitor's performance were studied, including linearity in dose rate, reproducibility, recombination correction, and dependence on both radiation field size and gantry angle. Additionally, stability of the detector output was analyzed using daily monitor calibrations performed over a period of 21 months. The beam monitor was found to meet design requirements for linearity (±1%), calibration stability (±2%), and stability of response as a function of gantry angle (±1%). Beam monitor calibration statistics also revealed a sine-like yearly trend with a ±2% maximum deviation from the average. These and other beam monitor test results are presented and discussed in the context of the detector design. Design changes aimed at further improving the detector's performance characteristics are proposed. © 2010 Elsevier Ltd. All rights reserved.

Farr J.B.,Midwest Proton Radiotherapy Institute
Journal of applied clinical medical physics / American College of Medical Physics | Year: 2010

Large area, shallow fields are well suited to proton therapy. However, due to beam production limitations, such volumes typically require multiple matched fields. This is problematic due to the relatively narrow beam penumbra at shallow depths compared to electron and photon beams. Therefore, highly accurate dose planning and delivery is required. As the dose delivery includes shifting the patient for matched fields, accuracy at the 1-2 millimeter level in patient positioning is also required. This study investigates the dosimetric accuracy of such proton field matching by an innovative robotic patient positioner system (RPPS). The dosimetric comparisons were made between treatment planning system calculations, radiographic film and ionization chamber measurements. The results indicated good agreement amongst the methods and suggest that proton field matching by a RPPS is accurate and efficient.

Zhao L.,Midwest Proton Radiotherapy Institute | Zhao L.,Indiana University | Das I.J.,Midwest Proton Radiotherapy Institute | Das I.J.,Indiana University
Physics in Medicine and Biology | Year: 2010

The depth dose verification of active scanning proton beams is extremely time consuming with ion chamber measurements for beam data commissioning and patient specific measurements. With widespread use of Gafchromic EBT films, two-dimensional high-resolution dosimetry is explored in a uniform scanning proton beam. The EBT films were exposed parallel to the beam axis in a solid water phantom in order to obtain the depth-dose curve in a single measurement and compared with the gold standard measurement with a parallel plate ion chamber in water. Our results demonstrate that EBT films perform well in determining the proton beam range, with uncertainty of 0.5 mm. It is also found that EBT film response is a function of energy over the effective energy of 50-160 MeV proton beams with the variations less than 10%. However, an under-dosage of up to 20% was observed at the peak of the Bragg curve. An empirically derived correction factor is proposed to account for the EBT energy dependence. With corrections, EBT films can be a useful tool for the depth dose verification of active scanning proton beams, thus saving valuable proton beam time. © 2010 Institute of Physics and Engineering in Medicine.

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