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SU‐E‐T‐146: Uncertainty of Stopping Powers of Tissue Equivalent Materials in Uniformly Scanned Proton Beam
Author(s) -
Butuceanu C,
Athar B,
Baillie N,
Duvvuri S,
Keppel C,
Lee T,
Nazaryan V,
Shahnazi K
Publication year - 2011
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3612097
Subject(s) - stopping power , proton , proton therapy , bragg peak , beam (structure) , dosimetry , range (aeronautics) , imaging phantom , materials science , ionization chamber , scanner , ionization , physics , nuclear physics , nuclear medicine , optics , ion , medicine , quantum mechanics , detector , composite material
Purpose: To quantify uncertainties associated with the extraction of CT HU to stopping power conversion curve for tissue equivalent materials in uniformly scanned (US) proton beams. Methods and Materials: The Philips Gemini TF Big Bore PET/CT scanner at the Hampton University Proton Therapy Institute (HUPTI), was used to extract the HU numbers for several tissue equivalent materials in the CIRS M062 phantom. Proton stopping power for each material was extracted by measuring the range change with and without the material, in a US proton beam pristine Bragg peak, and comparing to its physical thickness. The in‐beam measurements were performed using a Multilayer Ionization Chamber device (IBA Dosimetry, Zebra). Data were analyzed using both IBA OmniPro Incline and an in‐house software analysis package. Several proton beam energies were used: 143 MeV, 175 MeV, and 210 MeV. For each material and energy the difference between measured and predicted value of the stopping power was quantified. Results: The difference between measured and calculated stopping power with proton energy was found to be within 1–2.5 percent. The upper value of this variation was added to the machine specific systematic error of the CT HU number and quantified as the uncertainty of the CT HU to proton stopping power conversion curve. It was added to the total uncertainties (proton range and lateral profile), when PTV margins were implemented in the TPS. Conclusions: The relative linear stopping powers of 9 different tissue equivalent materials were measured using a range of uniformly scanned proton beam energies. These values were compared with predicted stopping powers calculated using current prescriptions and quantified as uncertainties of the CT HU to proton stopping power calibration curve. This work supports the accuracy of the proton stopping power implementation in the TPS and implicit the accuracy of patient treatment at HUPTI.