Posture-dependent dose coefficients of mesh-type ICRP reference computational phantoms for photon external exposures

Abstract

Recently, the International Commission on Radiological Protection (ICRP) developed new mesh-type reference computational phantoms (MRCPs) that provide high deformability compared with the current voxel-type reference computational phantoms of ICRP Publication 110. Taking advantage of this deformability, in the present study, the MRCPs were deformed to five non-standing postures (i.e. walking, sitting, bending, kneeling, and squatting) by developing and using a systematic posture-change method based on the as-rigid-as-possible (ARAP) shape-deformation algorithm and motion-capture technology. The non-standing MRCPs were then implemented in the Geant4 Monte Carlo code to calculate a comprehensive dataset of dose coefficients (DCs) for photon external exposures. These include the dose coefficients for 29 individual organs/tissues and the dose coefficients for effective doses from 0.01 MeV to 10 GeV in the antero-posterior (AP), postero-anterior (PA), left-lateral (LLAT), right-lateral (RLAT), rotational (ROT), and isotropic (ISO) geometries. To investigate the dosimetric impact of posture, the DCs of the non-standing MRCPs were compared with those of the original MRCPs (in the standing posture). The results showed that organ/tissue doses are significantly influenced by posture, with arm position mostly influencing dose to organs/tissues in the torso region and leg position influencing dose in the pelvic region. For most cases, the gonads showed notably large differences, ranging from a few tens of percentage points to several orders of magnitude, depending on posture and irradiation geometry. The effective doses showed much smaller differences than the organ/tissue doses, but they were nonetheless significant: for example, the kneeling MRCPs in the AP geometry showed lower values at energies <10 MeV by up to 30% and greater values at higher energies by up to 40%. The presented results indicate that not only different irradiation geometries, but also different postures might be necessary in DC calculations for reliable dose estimates for radiological protection purposes.

Development of a novel program for conversion from tetrahedral‐mesh‐based phantoms to DICOM dataset for radiation treatment planning: TET2DICOM

“…14,19 Helpfully though, tetrahedral mesh (TM)-based computational human phantoms were recently developed for the purposes of precise representation of human anatomy and subsequent evaluation of exposure dose in the radiation protection context. 14,20,21 Indeed, the TM phantoms have been reported to be highly flexible for effective posture deformation, 22 and micronscale radiosensitive tissues, such as the skin layer, 23 eye lens, 24 and Gastrointestinal (GI) tract, 25 can be defined in TM phantom. In addition, the TM phantom has been selected as an international standard phantom and has been used in various studies.…”

Posture-Transformed Monkey Phantoms Developed from a Visible Monkey

“…Consequently, phantoms in various positions are needed for more precise measurements. Although posture-transformed phantoms of whole bodies have been employed in some EMR and SAR studies (the hands of the phantoms were even placed over their ears), these studies did not provide voxel phantoms for other researchers [7,9,10]. Most importantly, not only a monkey phantom but also posture-transformed phantoms with detailed structures were applied.…”

“…Researchers in institutes around the world are developing various human phantoms [1][2][3][4][5][6][7][8][9]. These human phantoms are used to examine the effects of daily electromagnetic radiation dosimetry (EMR) on humans, such as the specific absorption rate (SAR).…”

“…Most phantoms are produced in a supine position from CT or MRI data [1][2][3][4][5][6][7][8]. To accurately simulate the EMR effects on a phantom, the phantoms must be exposed to electromagnetic waves during specific postures because the tissues and organs of living creatures may be influenced differently depending on posture [9,19,20]. In a recent study, a posturetransformed human phantom was produced for EMR simulation.…”

“…In a recent study, a posturetransformed human phantom was produced for EMR simulation. However, the techniques required to create the phantom were so professional that researchers unfamiliar with mathematical algorithms cannot easily repeat the technique [9].…”