Photon Specific Absorbed Fractions Calculated in the Trunk of an Adult Male Voxel-Based Phantom

Abstract

A new approach for calculating internal dose estimates was developed through the use of a more realistic computational model of the human body. The study demonstrates the capability of building a patient-specific phantom with voxel-based data for the simulation of radiation transport and energy deposition using Monte Carlo methods such as the MCNP-4B code. MCNP-4B was used to calculate absorbed fractions for photons in a voxel-based phantom, and values were compared to reference values from traditional phantoms used for many years. Results obtained in general agreed well with previous values, but considerable differences were found in some cases due to two major causes; differences in the organ masses between the phantoms and the occurrence of organ overlap in the voxel-based phantom (which is not well modeled in the mathematical phantoms). These new techniques offer promise of developing a new generation of more realistic phantoms for internal, as well as external, dose assessment. The principal area of implementation in internal dose assessment should be the development of patient-specific dose estimates in nuclear medicine therapy, such as radioimmunotherapy (RIT). However, as new voxel-based phantoms for different individuals can be developed, they may also be used with the techniques developed here to derive new absorbed fractions and replace the traditional values usedfor other applications in internal and external dose assessment, which have been based on mathematical constructs that are not always very representative of real human organs.

RADAR Reference Adult, Pediatric, and Pregnant Female Phantom Series for Internal and External Dosimetry

“…Realistic, voxel-based models derived from real human images have notable differences in organ proximity, compared with the traditional, stylized models, as was illustrated by Stabin and Yoriyaz (24). Organs are closer together, and many are in direct contact with each other (kidneys/adrenals, lungs/heart), whereas in stylized models, separation of organ spaces occurs because of the simplicity of the shapes used to model them.…”

A review of the use and potential of the GATE Monte Carlo simulation code for radiation therapy and dosimetry applications

“…GATE calculations (S values and SAFs) performed on the Zubal phantom (4 × 4 × 4 mm sampling) have been compared with MCNP-4B and MCNPX published data. [64][65][66] Although fairly good agreement between the various datasets was reported, some discrepancies were observed, especially for very low S values where the associated statistical uncertainty was high. In a further study, the relevance of processing paired organs as a single entity for absorbed dose calculation was investigated.…”

Specific Absorbed Fractions for Internal Photon Emitters Calculated for a Tomographic Model of a Pregnant Woman

“…Although the numerical difference between the results is large, however, the impact on overall dose calculations is likely to be small for most emitters, as contributions from low energy photons are not often important to the overall organ doses. Stabin and Yoriyaz (2002) found similar differences while comparing cross irradiation between liver and kidneys using the Zubal et al (1994) and MIRD models (Cristy and Eckerman 1987).…”

“…Because the images of this subject cover only a portion of the whole body, some organs and tissues are only partial organs, as with the study by Stabin and Yoriyaz (2002). Those organs and tissues are: bone, body tissues, oesophagus, heart, lungs, muscle, and skin.…”

“…Xu and Chao (2003) also published SAFs for the GI-tract for both electrons and photons. Stabin and Yoriyaz (2002) used a partial male model developed from CT images by Zubal et al (1994) to calculate photon SAFs. The results showed differences from the MIRD models; the authors explained the differences could be attributed to the differences in organ masses and geometries between the models.…”