Determination of zero-field size percent depth doses and tissue maximum ratios for stereotactic radiosurgery and IMRT dosimetry: Comparison between experimental measurements and Monte Carlo simulation
- Department of Radiation Oncology, Morristown Memorial Hospital, Morristown, New Jersey 07962 (United States)
In this study, zero-field percent depth dose (PDD) and tissue maximum ratio (TMR) for 6 MV x rays have been determined by extrapolation from dosimetric measurements over the field size range 1x1-10x10 cm{sup 2}. The key to small field dosimetry is the selection of a proper dosimeter for the measurements, as well as the alignment of the detector with the central axis (CAX) of beam. The measured PDD results are compared with those obtained from Monte Carlo (MC) simulation to examine the consistency and integrity of the measured data from which the zero-field PDD is extrapolated. Of the six most commonly used dosimeters in the clinic, the stereotactic diode field detector (SFD), the PTW Pinpoint, and the Exradin A14 are the most consistent and produce results within 2% of each other over the entire field size range 1x1-40x40 cm{sup 2}. Although the diamond detector has the smallest sensitive volume, it is the least stable and tends to disagree with all other dosimeters by more than 10%. The zero-field PDD data extrapolated from larger field measurements obtained with the SFD are in good agreement with the MC results. The extrapolated and MC data agree within 2.5% over the clinical depth range (d{sub max}-30 cm), when the MC data for the zero field are derived from a 1x1 cm{sup 2} field simulation using a miniphantom (1x1x48 cm{sup 3}). The agreement between the measured PDD and the MC data based on a full phantom (48x48x48 cm{sup 3}) simulation is fairly good within 1% at shallow depths to approximately 5% at 30 cm. Our results seem to indicate that zero-field TMR can be accurately calculated from PDD measurements with a proper choice of detector and a careful alignment of detector axis with the CAX.
- OSTI ID:
- 20953491
- Journal Information:
- Medical Physics, Vol. 34, Issue 8; Other Information: DOI: 10.1118/1.2750968; (c) 2007 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-2405
- Country of Publication:
- United States
- Language:
- English
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