Abstract：Objective To compare the calculation precision of the collapsed cone convolution (CCC) algorithm and pencil beam convolution (PBC) algorithm in TPS in heterogeneous tissue. Methods We made two virtual lung phantoms, one is single field phantom, In this case the photon beam incident into the phantom,the other is the two fields phantom and a cubic′tumor′ was placed in the centre of the phantom. two opposite photon beams incident into the phantom. We calculated the dose of the′tumor′ and the lung with the CCC and PBC algorithm. We compared the results in both case with if obtained from Monte Carlo (MC) method. Results In the single field phantom, the photon beam incident from the high-density tissue to the low-density lung equivalent tissue, compared with the result of MC algorithm PBC algorithm overestimated the lung equivalent tissue dose (t=3.90,P=0.012) and the result of CCC algorithm is close to it (t=2.25,P=0.087). In the two fields phantom, tumor boundary dose calculated by CCC algorithm and the MC algorithm are lower than that of the PBC algorithm (t=2.43,3.18,P=0.038,0.011), and the difference increase when the field size decrease, the beam energy increase and the density of the inhomogeneity decrease. Conclusions We had better use the CCC algorithm when calculating the dose of the tumor surrounded by low-density tissue or the tumor behind the low-density tissue, such as the lung cancer, esophageal cancer etc.
ZHAO Yan-qun,WANG Pei,LI Jie et al. Compare the calculation precision of collapsed cone convolution and pencil beam convolution algorithm in heterogeneous tissue[J]. Chinese Journal of Radiation Oncology, 2012, 21(1): 72-75.
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