Dosimetric verification of the anisotropic analytical algorithm in lung equivalent heterogeneities with and without bone equivalent heterogeneities

Journal Article · Sun Aug 15 04:00:00 EDT 2010 · Medical Physics

DOI:https://doi.org/10.1118/1.3464748· OSTI ID:22098519

Ono, Kaoru; Endo, Satoru; Tanaka, Kenichi; Hoshi, Masaharu; Hirokawa, Yutaka ^[1]

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1. Department of Radiation Physics, Hiroshima Heiwa Clinic, 1-31 Kawaramachi, Naka-ku, Hiroshima 730-0856 (Japan)

Purpose: In this study, the authors evaluated the accuracy of dose calculations performed by the convolution/superposition based anisotropic analytical algorithm (AAA) in lung equivalent heterogeneities with and without bone equivalent heterogeneities. Methods: Calculations of PDDs using the AAA and Monte Carlo simulations (MCNP4C) were compared to ionization chamber measurements with a heterogeneous phantom consisting of lung equivalent and bone equivalent materials. Both 6 and 10 MV photon beams of 4x4 and 10x10 cm{sup 2} field sizes were used for the simulations. Furthermore, changes of energy spectrum with depth for the heterogeneous phantom using MCNP were calculated. Results: The ionization chamber measurements and MCNP calculations in a lung equivalent phantom were in good agreement, having an average deviation of only 0.64{+-}0.45%. For both 6 and 10 MV beams, the average deviation was less than 2% for the 4x4 and 10x10 cm{sup 2} fields in the water-lung equivalent phantom and the 4x4 cm{sup 2} field in the water-lung-bone equivalent phantom. Maximum deviations for the 10x10 cm{sup 2} field in the lung equivalent phantom before and after the bone slab were 5.0% and 4.1%, respectively. The Monte Carlo simulation demonstrated an increase of the low-energy photon component in these regions, more for the 10x10 cm{sup 2} field compared to the 4x4 cm{sup 2} field. Conclusions: The low-energy photon by Monte Carlo simulation component increases sharply in larger fields when there is a significant presence of bone equivalent heterogeneities. This leads to great changes in the build-up and build-down at the interfaces of different density materials. The AAA calculation modeling of the effect is not deemed to be sufficiently accurate.

• OSTI ID: 22098519
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 8 Vol. 37; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
62 RADIOLOGY AND NUCLEAR MEDICINE
ACCURACY
ALGORITHMS
ANISOTROPY
COMPUTERIZED SIMULATION
CORRECTIONS
DOSIMETRY
ENERGY SPECTRA
IONIZATION CHAMBERS
LUNGS
MONTE CARLO METHOD
PHANTOMS
PHOTON BEAMS
PHOTONS
RADIATION DOSES
RADIOTHERAPY
SKELETON
VERIFICATION