Treatment planning evaluation of sliding window and multiple static segments technique in intensity modulated radiotherapy

Abstract

Background

The demand of improved dose conformity of the tumor has been increased in radiation therapy with the advent of recent imaging facilities and efficient computer technologies.

Aim

We compared the intensity modulated radiotherapy (IMRT) plans delivered with the sliding window (SW IMRT) and step and shoot (SS IMRT) techniques.

Materials and methods

Thirteen patients were planned on 15 MV X-ray for five, seven, nine and thirteen beams direction making the dose constraints analogous. Eclipse treatment planning system with Helios inverse planning software, and Linear Accelerator Varian 2100[[ce:hsp sp="0.25"/]]C/D with 120 multileaf collimators (MLCs) were used. Gamma analysis was applied to the data acquired with the MapCheck 2™ for different beam directions plan in the sliding window and step and shoot technique to meet the 95% pass criteria at 3%/3[[ce:hsp sp="0.25"/]]mm. The plans were scrutinized using D_mean, D_max, D1%, D95%, dose uniformity index (UI), dose conformity index (CI), dose homogeneity index (HI) and monitor units (MUs).

Results

Our data show comparable coverage of the planning target volume (PTV) for both the sliding window and step and shoot techniques. The volume of PTV receiving the prescription dose was 99.8[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.05% and the volume of PTV receiving the maximum dose was 107.6[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]2.5% in both techniques. Bladder and rectum maximum mean doses for the sliding window and step and shoot plans were 38.1[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]2.6% and 42.9[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]10.7%. Homogeneity index (HI) for both techniques was 0.12[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.02 and 0.13[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.02, uniformity index (UI) was 1.07[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.02 and 108[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.01 and conformity index at 98% isodose (CI 98%) was 0.96[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.005 and 0.96[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]0.005 for the sliding window and step and shoot techniques, respectively, and MUs were 10[[ce:hsp sp="0.25"/]]±[[ce:hsp sp="0.25"/]]12% lower in the step and shoot compared to the sliding window technique.

Conclusion

All these factors indicate that coverage for PTV was nearly identical but dose to organs-at-risk (OARs) was lower in the step and shoot technique.