Purpose: The purpose of this study is to find out the optimal energy or energy combination in Intensity modulated radiotherapy (IMRT) for oesophagus case.
Methods: Ten oesophagus cases treated in 6MV were replanned with energies 10 MV, 15 MV, 6FFF, 10FFF, energy combinations like (6X+10X), (6X+15X) and (10X+15X) which were selected based on penetration depth and the same planning parameters were applied to all plans. Dosimetry indices like conformity index (CI), homogeneity index (HI), coverage index (COV I), dose gradient index (DGI), dose coverage to planning target volume (PTV), monitor units (MUs), treatment time (TT) and OAR doses were analysed
Results: The significant PTV mean dose value of (6X+10X)is 29.68±0.38Gy compared to 6X (30.14±0.17Gy). The D2% value of (6X+10X) bettered as 30.86±0.38Gy from 31.15±0.11Gy. The D98% value of 27.42±0.67Gy is significant with (6X+10X) with P value 0.006. The D50% value of (6X+10X) gained as 29.84±0.39Gy from 30.2±0.14Gy. The CI95% value of (6X+10X) reduced to 1.103±0.08Gy from 1.257±0.14Gy. Among OARs, the heart mean dose value reduced to 9.95±4.3Gy for (6X+10X) from 10.05±4.7GY and right lung V20, 8.70±6.50Gy reduced to 7.99±6.0Gy with (6X+10X). Left lung V20, 11.98±7.9Gy reduced to 10.59±7.7Gy for (6X+10X) plan and left lung mean dose reduced to 10.00±1.8Gy in (6X+10X) from 10.13±2.4Gy. The spine mean dose of (6X+10X) reduced to 19.99±9.7Gy from 22.76±7.6Gy. The spine D1% reduced to 18.63±9.4Gy in (6X+10X) from 20.04+8.0Gy. The base plan total MU value of 5054.28±2286.1 reduced to 3036.54±1556.2 in (6X+10X) with P value 0.043. For TT the 6X value of 25.12±11.2 reduced to 16.52±11.2 in (6X+10X) plan.
Conclusion: This study suggested to use mixed energy (6X+10X) for optimal plan for better dosimetric indices with PTV coverage, OAR doses, less MUs and TT with negligible photo neutron production when compared to other plans.
Energy Dependence, Flattening Filters, Dose Volume Histograms
TH- External Beam- Photons: treatment planning/virtual clinical studies