Dosimetric characteristics of VMAT plans with respect to a different increment of gantry angle size for Ca cervix

Aim:We have investigated the influence in volumetric-modulated arc therapy (VMAT) plans by a sequence of increment of gantry angle (IGA) in definitive radiotherapy treatment for cervical cancer. The plans are quantitatively analysed in terms of conformity index (CI), heterogeneity index (HI), dose-gradient index (DGI), target coverage (TC) by prescription dose, monitor unit (MU) usage, control points (CPs) and dose to organs. Materials and Methods:In this retrospective study, we selected 27 patients with cervical cancer having aged between 54 and 69. All the patients enrolled in this study were at T3N1M0 stage of cervical cancer. The prescription dose to planning target volume (PTV) was 50 Gy and was administered in 2 Gy/fraction through VMAT technique. VMAT plans were optimised by varying the parameter 'IGA' as 10, 20, 30 and 40 degrees. Results:Homogenous dose distribution within PTV and TC by prescription dose was significantly enhanced (p < 0 center dot 05) with larger IGA. The difference between volume receiving 15 Gy (V-15Gy) in bowel was up to 10% with larger IGA (30 and 40 degrees) and V-25Gy in femoral head was up to 3% with smaller IGA (10 and 20 degrees). CPs were enhanced and MU usage was reduced with larger IGA (30 and 40 degrees). IGA 40 degrees had reduced the MU usage than IGA 30 degrees but the CI and DGI were compromised due to large MLC field segments. Conclusion:This study recommends that the larger IGA could yield better results when the number of sectors is even, for a cervical cancer patient. However, more data from more patients need to be obtained and analysed to make this an evidence-based hypothesis.