pmp Progress in Medical Physics Progress in Medical Physics 2508-4445 2508-4453 Korean Society of Medical Physics 10.14316/pmp.2016.27.2.86 pmp-27-86 Original Article Image-based Absorbed Dosimetry of Radioisotope ParkYong Sung ∗ LeeYong Jin ∗ YoungWook Kim ∗ JiHoon † KimKum Bae † KangJoo Hyun ∗ LimSang Moo ∗ WooSang-Keun ∗ Division of RI-Convergence Research, Seoul, Korea Department of Radiation Oncology, Korea Institute of Radiological and Medical Sciences, Seoul, Korea Correspondence: Sang-Keun Woo (skwoo@kirams.re.kr) Tel: 82-2-970-1659, Fax: 82-2-970-1341 06 2016 20 06 2016 27 2 86 92 Copyright © 2016 Korean Society of Medical Physics 2016 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract

An absorbed dose calculation method using a digital phantom is implemented in normal organs. This method cannot be employed for calculating the absorbed dose of tumor. In this study, we measure the S-value for calculating the absorbed dose of each organ and tumor. We inject a radioisotope into a torso phantom and perform Monte Carlo simulation based on the CT data. The torso phantom has lung, liver, spinal, cylinder, and tumor simulated using a spherical phantom. The radioactivity of the actual absorbed dose is measured using the injected dose of the radioisotope, which is Cu-64 73.85 MBq, and detected using a glass dosimeter in the torso phantom. To perform the Monte Carlo simulation, the information on each organ and tumor acquired using the PET/CT and CT data provides anatomical information. The anatomical information is offered above mean value and manually segmented for each organ and tumor. The residence time of the radioisotope in each organ and tumor is calculated using the time activity curve of Cu-64 radioactivity. The S-values of each organ and tumor are calculated based on the Monte Carlo simulation data using the spatial coordinate, voxel size, and density information. The absorbed dose is evaluated using that obtained through the Monte Carlo simulation and the S-value and the residence time in each organ and tumor. The absorbed dose in liver, tumor1, and tumor2 is 4.52E–02, 4.61E–02, and 5.98E–02 mGy/MBq, respectively. The difference in the absorbed dose measured using the glass dosimeter and that obtained through the Monte Carlo simulation data is within 12.3%. The result of this study is that the absorbed dose obtained using an image can evaluate each difference region and size of a region of interest.

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Acquired PET data using torso phantom. (a) The shape of torso phantom. Torso phantom made of a cylinder and mimic the human organ which is lung, liver, spine insert. The glass dosi-meter (circle line) was located in lung, liver, background, tumor1, and tumor2. (b) Positioning of torso phantom when acquired PET data.

The scheme of Monte Carlo simulation. This process was used a MCNP code and CT density information and acquired radioactivity using PET data.

Acquired image data using the PET/CT scanner. (a) Acquired CT image using torso phantom. (b) Acquired Cu-64 radioisotope and PET data using torso phantom. (c) PET/CT fusion data.

Measured residence time. (a) Segmentation method using a mean-based region growing method and performer manually. (b) Residence time in Liver, tumor1, and tumor2. Residence time (MBq-hr/MBq) was calculated by area under the curve of time-activity curves expressed as percentage of injected radioactivity (data not shown).

Calculated absorbed dose in torso phantom. (a) Indicate absorbed dose map of voxel unit was obtained density information using Monte Carlo simulation. (b) Compared the absorbed dose of MC dose and Glass dosimeter dose in liver, tumor1, and tumor2.

Monte Carlo simulated S-value of organs and tumors in torso phantom.

S-value (mGy/MBq) ) Liver Lung Tumor1 Tumor2
Liver 7.79E+01 6.84E–01 9.25E+00 9.09E+00
Lung 7.16E–01 7.48E+01 6.98E–01 5.90E–01
Tumor1 8.40E–02 6.51E–03 7.43E+01 4.56E–01
Tumor2 6.49E–02 5.05E–03 3.75E–01 7.39E+01