OC-0269: Comparison of dosimetric parameters of two techniques with VMAT for head and neck cancers

Results: With automated planning, high quality CK and VMAT plans could be generated without user dependency and trialand-error approach. PTV coverage was similar for the 3 approaches, with on average a V100% of 95.2, 95.4%, and 94.1% for CK, VMAT-3mm and VMAT-5mm. However, for some VMAT plans with 5mm margin, coverage > 95% was not feasible. Mean values for rectum D1cc were 26.1, 28.5, and 34.3 Gy, for rectum Dmean 6.3, 7.1, and 10.8 Gy, for bladder D1cc 37.7, 37.3, and 39.4 Gy, and for bladder Dmean 8.7, 7.5, and 9.2 Gy, for CK, VMAT-3mm and VMAT-5mm, respectively. Rectum doses were lower with CK compared to VMAT-3mm (p = 0.015 and p = 0.08 for rectum D1cc and Dmean) and highly decreased compared to VMAT-5mm (p = 0.007 and 0.008). Bladder sparing worsened slightly with CK compared to VMAT-3mm, but this was not statistically significant. No relevant differences were found for other OARs. With CK, the low-medium dose bath was reduced compared to VMAT: V10Gy = 1157.5, 1525.6, 1741.8 cc, V20Gy = 286.3, 325.5, 382.0 cc, for CK, VMAT-3mm and VMAT-5mm, respectively, with p = 0.007 and p=0.008 for CK comparing to VMAT 3 and 5 mm.