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Title: Analysis of CT Numbers and Relative Proton Stopping Powers for Real Tissue Samples

Abstract

The accuracy of computer planning of clinical proton dose distribution is partly determined by the precision of the conversion of CT Hounsfield Units to relative proton stopping powers. The calibration curves from three different sources were compared. We have found about 5% differences between proton stopping power values in the range from -700 HU to 0 HU. Calibration data for several soft tissues and phantom materials were also experimentally measured. The data for the tissues are in a good agreement with the calibration curves however data for phantom materials have significant deviations.

Authors:
; ;  [1];  [2];  [3]
  1. Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25, 117259 Moscow (Russian Federation)
  2. M. V. Lomonosov Moscow State University Physics Faculty, Leninskie Gory, 1-2, GSP-1, 11991, Moscow (Russian Federation)
  3. (Russian Federation)
Publication Date:
OSTI Identifier:
21366915
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 1204; Journal Issue: 1; Conference: 5. international summer school on nuclear physics methods and accelerators in biology and medicine, Bratislava (Slovakia), 6-15 Jul 2009; Other Information: DOI: 10.1063/1.3295651; (c) 2009 American Institute of Physics
Country of Publication:
United States
Language:
English
Subject:
07 ISOTOPES AND RADIATION SOURCES; CALIBRATION; PHANTOMS; PROTON BEAMS; PROTONS; RADIATION DOSE DISTRIBUTIONS; STOPPING POWER; TOMOGRAPHY; X-RAY SPECTROSCOPY; BARYONS; BEAMS; DIAGNOSTIC TECHNIQUES; ELEMENTARY PARTICLES; FERMIONS; HADRONS; MOCKUP; NUCLEON BEAMS; NUCLEONS; PARTICLE BEAMS; SPECTROSCOPY; STRUCTURAL MODELS

Citation Formats

Ryazantsev, Oleg, Karpunin, Vladimir, Haibullin, Vadim, Matusova, Tatiana, and Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25, 117259 Moscow. Analysis of CT Numbers and Relative Proton Stopping Powers for Real Tissue Samples. United States: N. p., 2010. Web. doi:10.1063/1.3295651.
Ryazantsev, Oleg, Karpunin, Vladimir, Haibullin, Vadim, Matusova, Tatiana, & Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25, 117259 Moscow. Analysis of CT Numbers and Relative Proton Stopping Powers for Real Tissue Samples. United States. doi:10.1063/1.3295651.
Ryazantsev, Oleg, Karpunin, Vladimir, Haibullin, Vadim, Matusova, Tatiana, and Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25, 117259 Moscow. 2010. "Analysis of CT Numbers and Relative Proton Stopping Powers for Real Tissue Samples". United States. doi:10.1063/1.3295651.
@article{osti_21366915,
title = {Analysis of CT Numbers and Relative Proton Stopping Powers for Real Tissue Samples},
author = {Ryazantsev, Oleg and Karpunin, Vladimir and Haibullin, Vadim and Matusova, Tatiana and Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya, 25, 117259 Moscow},
abstractNote = {The accuracy of computer planning of clinical proton dose distribution is partly determined by the precision of the conversion of CT Hounsfield Units to relative proton stopping powers. The calibration curves from three different sources were compared. We have found about 5% differences between proton stopping power values in the range from -700 HU to 0 HU. Calibration data for several soft tissues and phantom materials were also experimentally measured. The data for the tissues are in a good agreement with the calibration curves however data for phantom materials have significant deviations.},
doi = {10.1063/1.3295651},
journal = {AIP Conference Proceedings},
number = 1,
volume = 1204,
place = {United States},
year = 2010,
month = 1
}
  • Purpose: For proton therapy, an accurate model of CT HU to relative stopping power (RSP) conversion is essential. In current practice, validation of these models relies solely on measurements of tissue substitutes with standard compositions. Validation based on real tissue samples would be much more direct and can address variations between patients. This study intends to develop an efficient and accurate system based on the concept of dose extinction to measure WEPL and retrieve RSP in biological tissue in large number of types. Methods: A broad AP proton beam delivering a spread out Bragg peak (SOBP) is used to irradiatemore » the samples with a Matrixx detector positioned immediately below. A water tank was placed on top of the samples, with the water level controllable in sub-millimeter by a remotely controlled dosing pump. While gradually lowering the water level with beam on, the transmission dose was recorded at 1 frame/sec. The WEPL were determined as the difference between the known beam range of the delivered SOBP (80%) and the water level corresponding to 80% of measured dose profiles in time. A Gammex 467 phantom was used to test the system and various types of biological tissue was measured. Results: RSP for all Gammex inserts, expect the one made with lung-450 material (<2% error), were determined within ┬▒0.5% error. Depends on the WEPL of investigated phantom, a measurement takes around 10 min, which can be accelerated by a faster pump. Conclusion: Based on the concept of dose extinction, a system was explored to measure WEPL efficiently and accurately for a large number of samples. This allows the validation of CT HU to stopping power conversions based on large number of samples and real tissues. It also allows the assessment of beam uncertainties due to variations over patients, which issue has never been sufficiently studied before.« less
  • One of the advantages of ion beam therapy is the steep dose gradient produced near the ion's range. Use of this advantage makes knowledge of the stopping powers for all materials through which the beam passes critical. Most treatment planning systems calculate dose distributions using depth dose data measured in water and an algorithm that converts the kilovoltage X-ray computed tomography (CT) number of a given material to its linear stopping power relative to water. Some materials present in kilovoltage scans of patients and simulation phantoms do not lie on the standard tissue conversion curve. The relative linear stopping powersmore » (RLSPs) of 21 different tissue substitutes and positioning, registration, immobilization, and beamline materials were measured in beams of protons accelerated to energies of 155, 200, and 250 MeV; carbon ions accelerated to 290 MeV/n; and iron ions accelerated to 970 MeV/n. These same materials were scanned with both kilovoltage and megavoltage CT scanners to obtain their CT numbers. Measured RLSPs and CT numbers were compared with calculated and/or literature values. Relationships of RLSPs to physical densities, electronic densities, kilovoltage CT numbers, megavoltage CT numbers, and water equivalence values converted by a treatment planning system are given. Usage of CT numbers and substitution of measured values into treatment plans to provide accurate patient and phantom simulations are discussed.« less
  • A comparison between theoretical and experimental values of the relative stopping powers of pure gases for electrons has been presented. The experimental data were obtained by using the beta -ray spectrum from thick sources of S/sup 35/, P/sup 32/, and Y/sup 90/. The gases studied were: hydrogen, helium, nitrogen, oxygen, air, neon, argon, krypton, and xenon. Values of the relative stopping powers for bone and muscle have been computed from the experimental data. (auth)