Comparison of RTPS and Monte Carlo Dose Distributions in Heterogeneous Phantoms for Photon Beams

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  • Nakaguchi Yuji
    Department of Radiological Technology, Kumamoto University Hospital Graduate School of Health Sciences, Kumamoto University
  • Araki Fujio
    School of Health Sciences, Kumamoto University
  • Maruyama Masato
    Department of Radiological Technology, Kumamoto University Hospital
  • Fukuda Shogo
    Graduate School of Health Sciences, Kumamoto University

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Other Title
  • 放射線治療計画装置における不均質領域の線量計算精度の評価－Ｍｏｎｔｅ　Ｃａｒｌｏ計算との比較－
  • 放射線治療計画装置における不均質領域の線量計算精度の評価--Monte Corlo計算との比較
  • ホウシャセン チリョウ ケイカク ソウチ ニ オケル フキンシツ リョウイキ ノ センリョウ ケイサン セイド ノ ヒョウカ Monte Corlo ケイサン ト ノ ヒカク

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The purpose of this study was to compare dose distributions from three different RTPS with those from Monte Carlo (MC) calculations and measurements, in heterogeneous phantoms for photon beams. This study used four algorithms for RTPS: AAA (analytical anisotropic algorithm) implemented in the Eclipse (Varian Medical Systems) treatment planning system, CC (collapsed cone) superposition from the Pinnacle (Philips), and MGS (multigrid superposition) and FFT (fast Fourier transform) convolution from XiO (CMS). The dose distributions from these algorithms were compared with those from MC and measurements in a set of heterogeneous phantoms. Eclipse/AAA underestimated the dose inside the lung region for low energies of 4 and 6 MV. This is because Eclipse/AAA do not adequately account for a scaling of the spread of the pencil (lateral electron transport) based on changes in the electron density at low photon energies. The dose distributions from Pinnacle/CC and XiO/MGS almost agree with those of MC and measurements at low photon energies, but increase errors at high energy of 15 MV, especially for a small field of 3×3 cm2. The FFT convolution extremely overestimated the dose inside the lung slab compared to MC. The dose distributions from the superposition algorithms almost agree with those from MC as well as measured values at 4 and 6 MV. The dose errors for Eclipse/AAA are lager in lung model phantoms for 4 and 6 MV. It is necessary to use the algorithms comparable to superposition for accuracy of dose calculations in heterogeneous regions.

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