Dosimetric evaluation of field-in-field and slidingwindowIMRT in endometrium cancer patients with anew approach for the conformity index

Background: purpose of the study is to evaluate field-in-field (fif) and slidingwindowintensity modulated radiation therapy (sw-imrt) treatment plans interms of homogeneity index (hi), conformity index (ci) and normal tissuedoses for organs at risk (oar) in patients with endometrial carcinoma alongwith deriving a new expression for ci. materials and methods: four differentfif plans with different mlc (multi-leaf collimator) margins and sw-imrt planwere compared in 20 endometrial cancer patients who underwent adjuvantpelvic radiotherapy with 50.4 gy in 28 fractions. normal tissue doses wereassessed for oar from dose volume histograms (dvhs). hi and ci values werecalculated according to the reports of international commission on radiationunits and measurements (icru)-83, radiation therapy oncology group(rtog) 1993 and icru-62. a new ci was developed and named cioptstanding for optimized conformity index. results: sw-imrt provided asignificantly better ci in comparison to other fif plans (p< 0.001).conventional-fif (c-fif) was the most homogeneous plan compared to allother fif plans and sw-imrt (p≤0.001). the absolute volume of smallintestine that received ≥45 gy (v45) and doses received by a 30% volume ofrectum (d30) were dramatically reduced in sw-imrt (p < 0.001). conclusion:mlc margins had a substantial influence on oar doses, hi and ci. a closeproximity of ciopt to 1 indicated that this formulation of ci was a useful planevaluation tool, which was also compatible with the rtog 1993 and icru-62reports.