Circumferential or sectored beam arrangements for stereotactic body radiation therapy (SBRT) of primary lung tumors: Effect on target and normal-,structure dose-volume metrics

To compare 2 beam arrangements, sectored (beam entry over ipsilateral hemithorax) vs circumferential (beam entry over both ipsilateral and contralateral lungs), for static-gantry intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) delivery techniques with respect to target and organs-at-risk (OAR) dose-volume metrics, as well as treatment delivery efficiency. Data from 60 consecutive patients treated using stereotactic body radiation therapy (SBRT) for primary non-small-cell lung cancer (NSCLC) formed the basis of this study. Four treatment plans were generated per data set: 1MRT/VMAT plans using sectored (-s) and circumferential (-c) configurations. The prescribed dose (PD) was 60 Gy in 5 fractions to 95% of the planning target volume (PTV) (maximum PTV dose 150% PD) for a 6-MV photon beam. Plan conformality, Rso (ratio of volume circumscribed by the 50% isodose line and the PTV), and D-2 CM (Dmax at a distance >2 cm beyond the PTV) were evaluated. For lungs, mean doses (mean lung dose [MLD1) and percent V-30/V-20/V(1)o/V-5 Gy were assessed. Spinal cord and esophagus D. and D5/D50 were computed. Chest wall (CW) Dmax and absolute V30/V20/V10/V5 Gy were reported. Sectored SBRT planning resulted in significant decrease in contralateral MLD and Vio/ Vs Gy, as well as contralateral CW Dn,a. and V(1)o/V-5 Gy (all p < 0.001). Nominal reductions of D. and Ds/ Dso for the spinal cord with sectored planning did not reach statistical significance for static-gantry IMRT, although VMAT metrics did show a statistically significant decrease (all p < 0.001). The respective measures for esophageal doses were significantly lower with sectored planning (p < 0.001). Despite comparable dose conformality, irrespective of planning configuration, Rso significantly improved with 1MRT-s/VMAT-c (p < 0.001/p = 0.008), whereas D2 cm significantly improved with VMAT-c (p < 0.001). Plan delivery efficiency improved with sectored technique (p < 0.001); mean monitor unit (MU)/cGy of PD decreased from 5.8 1.9 vs 5.3 - 1.7 (IMRT) and 2.7 0.4 vs 2.4 - 0.3 (VMAT). The sectored configuration achieves unambiguous dosimetric advantages over circumferential arrangement in terms of esophageal, contralateral CW, and contralateral lung sparing, in addition to being more efficient at delivery. (C) 2013 American Association of Medical Dosimetrists.