SU-F-T-353: Effect of Planning Parameters On Tomotherapy Plan Quality and Treatment Time

Abstract

Purpose: Aim of this study is to evaluate the effect of planning parameters such as pitch & field width on tomotherapy treatment plan quality and treatment time. Methods: We chose three treatment plans from different sites for this study. Combination of three different field widths (1 cm, 2.5 cm & 5 cm) and three different pitch values (0.215, 0.287 & 0.430) are used to generate plans. For a given patient all plans were optimized with same objectives, constrains, number of iterations and modulation factor. Plan quality was compared using clinically significant Dose Volume Histogram (DVH) indices (D98%, D95%, D50%, Dmean, D2, Dmax) and Homogeniety Index (HI). Also treatment times for all plans were compared to evaluate the delivery efficiency Results: DVH indices of target (D98%, D95%, D50%, Dmean, D2) showed increasing trend with the increase in the pitch as well as field width. The difference in DVH indices was less than 1.5%. Similarly critical structure DVH indices (Dmax, Dmean) also had increasing trend with the pitch value field width. The difference in DVH indices is upto 10% for the pitch and upto 50% increase in dose for 5cm collimator. The variation in homogeneity index with reference to 1 cm field width was 1–4% and 2.2 – 5% for 2.5cm and 5cm field widths respectively. For a given field width increase in pitch reduces the treatment time upto 30%. Increase in field width from 1cm to 5 cm reduces the treatment time upto 75%. Conclusion: Effects of planning parameters on tomotherapy plan quality & treatment time were studied. The effect of pitch is found to be less than the field width on the target, critical structures dose as well as treatment time. Optimal selection of planning parameter will improve the treatment delivery efficiency with appropriate dose to target and critical structure.