Ion Stopping Powers and Dual Energy CT Numbers of Animal Tissues for Monte Carlo Dose Calculations
PO-1356
Abstract
Ion Stopping Powers and Dual Energy CT Numbers of Animal Tissues for Monte Carlo Dose Calculations
Authors: ZENG|, Lingpeng(1)*[Alex_Zeng2019@foxmail.com];Michael|, F.Moyers(1);
(1)Shanghai Proton and Heavy Ion Center, Department of Medical Physics, Shanghai, China;
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Purpose or Objective
For ion beam treatment, most treatment planning systems(TPSs) use a pencil beam algorithm that calculates dose distributions using depth dose data measured in water and an algorithm that converts the X-ray computed tomography number of a given material to its linear stopping power relative to water(RLSP). Recently some TPSs have started using Monte Carlo type dose calculations. These calculations typically need the physical density and elemental composition of the tissues to determine penetration and calculate dose.
Material and Methods
Samples of 10 different animal tissues were obtained and packed in regularity-shaped containers including brain. heart. fat. cartilage. hard bone. muscle. liver. kidney and lung. The physical density of each sample was measured. The samples were then scanned with a dual energy CT scanner. Additionally, The samples were placed between the exit of a beaming and a Peak Finder to measure single-spot integrated depth dose distributions. Beams of protons accelerated to energies of 118.0,167.3,and222.1Mev and carbon ions accelerated to 216.7, 322.8 and 430 MeV/u were used.
Figure1: PTW Peak Finder and measurement setup
Results
For each tissue a dual-energy CT index was derived. This index may be used for determining the elemental composition classification for each tissue used in the Monte Carlo calculations. RLSPs were derived for each tissue for verification of the correct conversion function. In addition. two pairs of data. the Bragg peak width and the distal gradient. relative electron density and effective atomic number for each tissue as the specific material indicators were obtained respectively.
Figure 2:Measured single spot integrate depth dose distribution for 167.3 MeV proton for each sample. empty box. air and water placed between the radiation head and the Peak Finder.
Conclusion
Data for converting dual energy CT number for Monte Carlo dose calculation were obtained as well as data for verifying the correct conversion. A software workflow for the use of Siemens DEXCT images for Monte Carlo in the SPHIC in the future was suggested