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Objective:To analyze the dosimetric differences of volumetric modulated arc therapy (VMAT) plans for lung cancer caused by different dose calculation algorithms and radiation field settings and thus to provide a reference for designing clinical VMAT plans for lung cancer.Methods:This study randomly selected 20 patients with lung cancer and divided them into four groups of VMAT plans, namely, a group adopting two fields and two arcs based on the AAA algorithm (2F2A_AAA), a group employing two fields and two arcs based on the AXB algorithm (2F2A_AXB), a group using two fields and two arcs based on the MC algorithm (2F2A_MC), and a group adopting one field and two arcs based on the MC algorithm (1F2A_MC). Then, this study evaluated the target coverage, high-dose control, dose homogeneity index (HI), conformity index (CI), and organs at risk (OARs) of the plans using different algorithms and radiation field settings.Results:The planning target volume (PTV) results of two fields combined with two arcs (2F2A) of three groups using different algorithms are as follows. 2F2A_MC achieved better results in both D1% and V 95% (the relative volume of the target volume surrounded by 95% of the prescribed dose) of planning gross target volume (PGTV) than 2F2A_AAA (D1%: t=-2.44, P=0.03; V95%:z=-2.04, P=0.04) and 2F2A_AXB (D1%: t=2.34, P=0.03; z=-3.21, P < 0.01). 2F2A_AXB outperformed 2F2A_AAA ( z=-3.66, P < 0.01) and was comparable to 2F2A_MC in terms of the CI of PGTV. Regarding OARs, 2F2A_AXB and 2F2A_MC decreased the V5 Gy of the whole lung by 0.68% ( z=-2.69, P=0.01) and 3.05% ( z=-3.52, P < 0.01), respectively compared to 2F2A_AAA. 2F2A_AXB achieved a whole-lung Dmean of 1776.44 cGy, which was superior to that of 2F2A_MC ( t=2.67, P=0.02) and 2F2A_AAA ( t=8.62, P < 0.01). Compared to 2F2A_AAA and 2F2A_MC, 2F2A_AXB decreased the V20 Gy of Body_5 mm by 1.45% ( z=-3.88, P < 0.01) and 2.01% ( z=-3.66, P < 0.01), respectively. The results of the two groups with different field settings showed that 1F2A_MC was superior to 2F2A_MC in both the CI of PTV1 and the HI of PTV2 (CI: t=2.61, P=0.02; HI: z=-2.20, P=0.03). Moreover, 1F2A_MC increased the Dmean of the whole lung by 26.29 cGy compared to 2F2A_MC ( t=2.28, P=0.04). Conclusions:Regarding the design of VMAT plans for lung cancer, the MC algorithm is suitable for the target priority and the AXB algorithm is suitable for the OAR priority. When only the MC algorithm is available, it is recommended to choose 1F2A in the case of target priority and select 2F2A in the case of OAR priority.
ABSTRACT
<p><b>BACKGROUND</b>There is no large population-based study of the distribution and changing trend of strabismus surgeries in China. This study aimed to investigate the distribution and the changing trend of strabismus surgery in a tertiary hospital of China.</p><p><b>METHODS</b>A retrospective study of all the strabismus surgeries performed in Beijing Tongren Eye Center from 2003 to 2012 was carried out. Characteristics analyzed included the type of strabismus, age, and gender.</p><p><b>RESULTS</b>Totally 26 524 strabismus surgeries were performed in Tongren Eye Center during the 10-year period. The number of surgeries increased steadily from 1 507 in 2003 to 3 482 in 2008 and slightly decreased to 3 124 in 2009, but there was a sharp drop to 2 569 in 2010 and then kept relatively steady at 2 760 in 2011 and 2 463 in 2012. Intermittent exotropia (30.3%) was the most common among all kinds of strabismus. The number of strabismus surgeries performed on children under 12 years of age (43.60%) was significantly higher than those of the other age groups (P < 0.05). Unilateral superior oblique paralysis was the most common subtype of paralytic strabismus (8.64%).</p><p><b>CONCLUSIONS</b>The type distribution of strabismus surgery has changed during the recent decade. The age and type distribution of different strabismus remained basically constant, among which intermittent exotropia was the most common.</p>