الفهرس 
Treatment Planning AlgorithmsOnly 14 pages are availabe for public view
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Abstract
Patients with early stage non-small cell lung cancer NSCLC who are clinically
inoperable or refuse surgery can benefit from stereotactic body radiation therapy
(SBRT). Typically, SBRT is delivered over the course of one to two weeks and consists
of one to five treatment sessions. Multiple beams are used in SBRT to achieve a highly
conformal dose distribution and a rapid falloff at the target’s periphery,
reducing toxicity to the surrounding healthy tissues.
Therefore, calculating the radiation dose deposition for individual patients is a crucial
step in any radiotherapy process. For accurate dose prescription and reporting in
radiation therapy, accurate dose calculation is a prerequisite. The algorithms for
calculating radiation dose can be divided into several categories.
The Collapsed Cone Convolution (CCC) algorithm from Philips Radiation Oncology
Systems in Fitchburg, Wisconsin, and the Anisotropic Analytical Algorithm (AAA)
from Varian Medical Systems in PaloAlto, California, is two examples of superposition
convolution algorithms that are frequently used. The Linear Boltzmann Transport
Equation (LBTE) can now be solved by a brand-new algorithm that Varian recently
unveiled. Using Acuros, this study evaluates the precision of dose calculation.
In this study, a comparison between AAA and Acuros XB calculation algorithm for
lung cases plans with small fields on Computed Tomography (CT) image sets of SBRT
patients. Using the previous calculated plans by AAA and recalculate plans by selecting
Acuros XB, calculating conformity index CI, and homogeneity index HI, gradient index
GI and calculation time.
The CI varies from (1.45±0.55) to (1.58±0.7) (P <0.05), and HI are (0.15±0.07) and
(0.13±0.08) (P<0.05), the GI for AAA was (4.8±2.6) and for AXB reaches to (7.4±3.8)
(P<0.05) and the maximum dose for PTV is differed about 2.3% to 4.5%, and mean
dose is differed about 2.4% to 3.8% and the calculation time 153±43 sec and 185±76
sec for AAA and AXB respectively.
In simple slab geometry, Acuros XB outperforms AAA when compared calculated
plans to measurements. The phantom dimension is 30 × 30 × 30 cm3
and the calculation
points were placed on the central axis, directly under different air gaps depth, at 10 cm
depth. Acuros XB and AAA show differences of -0.7%, 1.6%, 2.2%, 3.4%, 3.6%, 3.6%,
3.3% for AAA and 0.6%, 0.9%, 0.3%, 0.5%, 0.4%, 0.8%, 0.8% respectively for air gaps
1.5, 2.5, 3, 4.5, 5, 6.5, 7cm thicknesses respectively.
Also analyze the effect of calculated grid size on plan calculation for Anisotropic
Analytical Algorithm and Acuros XB Algorithm in lung Stereotactic Body
Radiotherapy and evaluating the difference in each calculation Algorithm.
The dose to PTV predicted when AAA 1-mm CGS plans and AAA 2-mm and 3-mm
CGS plans were compared, and 2.73±1.62 % difference was observed; When AXB 1-
mm CGS plans and AXB 2-mm and 3-mm CGS plans were compared, 1.36±1.21 %
difference was found. No significant difference was found between plans with AAA 1-
mm CGS and plans with AXB 1-mm CGS. On the other hand, there was a significant
difference between plans with AAA 2, 3-mm and plans with AXB 2, 3-mm CGS.
The doses predicted for AXB algorithm are more stable than those of the AAA in
different intensity body regions, specifically in low density tissue as lung cancer AXB
principally predicts lower dose to PTV compared to AAA and the CGS contributes to
the relative dose difference between the two algorithms. For SBRT, 1-mm CGS should
be selected for calculated accuracy