acceptable dose distributions in OAG due to their significantly asymmetric incident fluence profile. This issue was systematically investigated. Materials/Methods: In a randomly selected patient CT image, a total of 9 sphere targets having three different sizes (2, 4, and 6 cm diameter) were placed at three different locations (central axis, 3 cm off-axis, and 6 cm off-axis). Note about 6 or 7 cm off-axis distance is the limit that can be treated using DCAT due to the mechanical limitations of the MLC. For each target, DCAT plans under the same object (95% target volume in prescription dose) were obtained using 4 different beams (6X, 6F, 10X, and 10F, where ‘F’ indicates flattening-filter-free) from a LINAC. For all plans, homogeneity index, HI (max dose to prescription dose) and two conformality indices, CI-100 (prescription isodose volume to target volume) and CI-50 (50% prescription isodose volume to target volume) were investigated. Beam on time (BOT) was also estimated based on obtained MUs and the maximum dose rate available in each beam mode. Results: The 10F showed HI values similar to 10X for 2 cm targets (1.191.25 in 10F vs. 1.17-1.23 in 10X), but noticeably higher values for 4 and 6 cm targets (1.17-1.23 in 10F vs. 1.12-1.14 in 10X). Interestingly, however, 6F showed HI values compatible to or even lower than 6X for all targets (1.10-1.17 in 6F vs. 1.11-1.19 in 6X). Similar values were obtained for both CI-100 (0.99-1.13 in 10F vs. 0.98-1.12 in 10X, and 0.99-1.11 in 6F vs. 0.98-1.11 in 6X) and CI-50 (3.12-4.65 in 10F vs. 3.13-4.73 in 10X, and 3.17-4.30 in 6F vs. 3.11-4.33 in 6X). Note the minimum possible CI-100 value is 0.95 with exact 95% coverage. The ratios of BOT were 0.26-0.32 in 10F/10X and 0.46-0.51 in 6F/6X. Conclusions: It is found 6F beams can be utilized in off-axis geometry without dosimetric compromise. In certain cases, contrary to common perception, it provides even better dose homogeneity than 6X by virtue of dose compensation effect in the medial region. Although 10F can provide more dramatic BOT reduction, in general, it provides less favorable dosimetric indices compared to 6F. Author Disclosure: S. Kim: P. Ownership Other; Shareholder of MT&T, LLC. C. Serago: None. A. Smith: None. S. Ko: None. L. Vallow: None. J. Peterson: None. S. Buskirk: None.