Accounting for beta-particle energy loss to cortical bone via paired-image radiation transport (PIRT)

• Published in: Medical physics (Lancaster) 2005-05, Vol.32 (5), p.1354-1366
• Main Authors: Shah, Amish P., Rajon, Didier A., Patton, Phillip W., Jokisch, Derek W., Bolch, Wesley E.
• Format: Article
• Language: English
• Subjects: absorbed fraction; Aged; Algorithms; Beta Particles; Biomedical modeling; biomedical MRI; Body Burden; bone; Bone and Bones - diagnostic imaging; Bone and Bones - physiology; Bone and Bones - radiation effects; Bone Density - physiology; Bone Density - radiation effects; BONE MARROW; BONE TISSUES; Cadaver; Clinical applications; Computed radiography; Computed tomography; Computer Simulation; computerised tomography; COMPUTERIZED TOMOGRAPHY; dosimetry; Dosimetry/exposure assessment; Electron sources; Electronic transport; energy loss of particles; ENERGY LOSSES; ERBIUM 169; Humans; IMAGE PROCESSING; image segmentation; Linear Energy Transfer - physiology; LUTETIUM 177; Male; marrow dose; medical image processing; Medical image segmentation; Medical imaging; Models, Biological; NMR IMAGING; NMR microscopy; Nuclear magnetic resonance; Nuclear magnetic resonance imaging; Organ Specificity; PHOSPHORUS 32; PHOSPHORUS 33; Radiation Dosage; RADIATION DOSES; radiation therapy; RADIATION TRANSPORT; Radiography; RADIOLOGY AND NUCLEAR MEDICINE; Radiometry - methods; radionuclide; radionuclide S value; RADIOTHERAPY; Radiotherapy Planning, Computer-Assisted - methods; Relative Biological Effectiveness; RHENIUM 186; RHENIUM 188; SAMARIUM 153; skeletal dosimetry; SKELETON; STRONTIUM 89; value; YTTRIUM 90
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.1898463

Current methods of skeletal dose assessment in both medical physics (radionuclide therapy) and health physics (dose reconstruction and risk assessment) rely heavily on a single set of bone and marrow cavity chord-length distributions in which particle energy deposition is tracked within an infinite extent of trabecular spongiosa, with no allowance for particle escape to cortical bone. In the present study, we introduce a paired-image radiation transport (PIRT) model which provides a more realistic three-dimensional (3D) geometry for particle transport in the skeletal site at both microscopic and macroscopic levels of its histology. Ex vivo CT scans were acquired of the pelvis, cranial cap, and individual ribs excised from a 66 - year male cadaver (BMI of 22.7 kg m − 2 ). For the three skeletal sites, regions of trabecular spongiosa and cortical bone were identified and segmented. Physical sections of interior spongiosa were taken and subjected to microCT imaging. Voxels within the resulting microCT images were then segmented and labeled as regions of bone trabeculae, endosteum, active marrow, and inactive marrow through application of image processing algorithms. The PIRT methodology was then implemented within the EGSNRC radiation transport code whereby electrons of various initial energies are simultaneously tracked within both the ex vivo CT macroimage and the CT microimage of the skeletal site. At initial electron energies greater than 50 – 200 keV , a divergence in absorbed fractions to active marrow are noted between PIRT model simulations and those estimated under existing techniques of infinite spongiosa transport. Calculations of radionuclide S values under both methodologies imply that current chord-based models may overestimate the absorbed dose to active bone marrow in these skeletal sites by 0% to 27% for low-energy beta emitters ( P 33 , Er 169 , and Lu 177 ), by ∼ 4 % to 49% for intermediate-energy beta emitters ( Sm 153 , Re 186 , and Sr 89 ), and by ∼ 14 % to 76% for high-energy beta emitters ( P 32 , Re 188 , and Y 90 ). The PIRT methodology allows for detailed modeling of the 3D macrostructure of individual marrow-containing bones within the skeleton thus permitting improved estimates of absorbed fractions and radionuclide S values for intermediate-to-high energy beta emitters.