Abstract
Purpose: The experimental verification of the Acuros XB (AXB) algorithm was conducted in a heterogeneous rectangular slab phantom, and compared to the Anisotropic Analytical Algorithm (AAA). The dosimetric impact of the AXB for stereotactic body radiation therapy (SBRT) and RapidArc planning for 16 non-small-cell lung cancer (NSCLC) patients was assessed due to the dose recalculation from the AAA to the AXB. Methods: The calculated central axis percentage depth doses (PDD) in a heterogeneous slab phantom for an open field size of 3 ×3 cm2 were compared against the PDD measured by an ionization chamber. For 16 NSCLC patients, the dose-volume parameters from the treatment plans calculated by the AXB and the AAA were compared using identical jaw settings, leaf positions, and monitor units (MUs). Results: The results from the heterogeneous slab phantom study showed that the AXB was more accurate than the AAA; however, the dose underestimation by the AXB (up to ?3.9%) and AAA (up to ?13.5%) was observed. For a planning target volume (PTV) in the NSCLC patients, in comparison to the AAA, the AXB predicted lower mean and minimum doses by average 0.3% and 4.3% respectively, but a higher maximum dose by average 2.3%. The averaged maximum doses to the heart and spinal cord predicted by the AXB were lower by 1.3% and 2.6% respectively; whereas the doses to the lungs predicted by the AXB were higher by up to 0.5% compared to the AAA. The percentage of ipsilateral lung volume receiving at least 20 and 5 Gy (V20 and V5 respectively) were higher in the AXB plans than in the AAA plans by average 1.1% and 2.8% respectively. The AXB plans produced higher target heterogeneity by average 4.5% and lower plan conformity by average 5.8% compared to the AAA plans. Using the AXB, the PTV coverage (95% of the PTV covered by the 100% of the prescribed dose) was reduced by average 8.2% than using the AAA. The AXB plans required about 2.3% increment in the number of MUs in order to achieve the same PTV coverage as in the AAA plans. Conclusion: The AXB is more accurate to use for the dose calculations in SBRT lung plans created with a RapidArc technique; however, one should also note the reduced PTV coverage due to the dose recalculation from the AAA to the AXB.
Highlights
Lung cancer is the leading cancer killer in both men and women in the United States, causing more deaths than the three most common cancers combined [1]
Similar to that study [23], the results found in our study indicate that the Acuros XB (AXB) calculations predicted a lower minimum planning target volume (PTV) dose by average 4.3% with a statistical significance (P = 0.00004)
The experimental verification study using a heterogeneous rectangular slab phantom containing two air gaps showed that the AXB is more accurate and provides the better agreement to the measurements than the Analytical Algorithm (AAA)
Summary
Lung cancer is the leading cancer killer in both men and women in the United States, causing more deaths than the three most common cancers combined (colon, breast and prostate) [1]. Surgical resection is considered to be the preferred treatment for the early stage non-small-cell lung cancer (NSCLC). For NSCLC patients who are not candidates for surgical therapy, stereotactic body radiotherapy (SBRT) is an alternative method for the treatment of small lung tumors. SBRT is a highly conformal technique that delivers high radiation dose with few treatment fractions to the tumor while limiting the doses received by the organs at risk (OARs). Previous studies have shown that high probability of tumor control can be achieved with SBRT when compared to the conventional radiation therapy [2,3], with local control rates at 3 years up to 90% [4]. Advanced cancer treatment techniques such as SBRT demand for more accurate dose calculation algorithms
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