Sperduto_Khan's Treatment Planning in Radiation Oncology, 5e

448 SECTION III Treatment Planning: Physics and Dosimetric Principles

Also displayed is the resulting dose distribution performed using the Attila dose calculation engine. The black areas on each image are regions where the difference between the MC and BTE calculations exceeded 5% of the maxi mum dose. A more quantitative comparison can be seen by looking at a dose profile through the center of the PTV (Line “L1” on Fig. 20.8) and off-axis (Line “L2”). The dose profiles for both the Attila and EGSnrc codes for these lines are displayed in Figure 20.9. The overall agreement between these two methods was good, with over 98% of the calculation points within a ±3%/±3 mm criterion.

Since the release of Acuros XB, there have been a num ber of planning studies investigating the efficiency and accuracy of the discrete ordinates method. Comparisons are made either with other planning algorithms or with measured results for a variety of treatment sites includ ing lung, 49,50 breast, 51 and nasopharynx. 52 Evaluations of Acuros for calculations within heterogeneous media 53 or for radiosurgery treatments 54 have also been reported. The interested reader is referred to these works for addi tional information.

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FIGURE 20.9. Dose line plot comparisons between EGSnrc ( red ) and Attila ( blue ) along line L1 A and L2 B in Figure 20.8. Sharp peaks and dips in the Attila solution correspond to material heterogeneities, which are revolved at the CT image pixel level by Attila. (Reprinted from Vassiliev, Wareing TA, Davis IM, et al. Feasibility of a multigroup deterministic solution method for three-dimensional radiotherapy dose calculations. Int J Rad Onc Biol Phys. 2008;72:220–227, with permission.)