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Delivery Complexity Analysis for Tomotherapy Plans Using a Fluence-Based Complexity Index

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A Xing

A Xing*, S Deshpande , S Arumugam , G Gooze , L Holloway , Liverpool Cancer & Macarthur Cancer Therapy Centre, Sydney, New south Wales


SU-I-GPD-T-213 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Complexity index was used to improve both planning and QA procedure for VMAT and IMRT. The aim of this work is to quantify Tomotherapy plan complexity and investigate its relationship with plan parameters and physics QA results.

Methods: The sinogram of Tomotherapy plan represents a delivery fluence map and divided into a series of angular segments (projections). A new complexity index (CI) was proposed and defined as the summation of the product of the following quantities for each projection divided by the total number of projections: total open time, summation of individual leaf open time; open-area ratio, the ratio of the area defined by open leaves to the total area defined by MLC; leaf eccentricity, the ratio of the shortest distance between central leaf and the opened leaves to the distance between central and first leaf. Variation of CI was calculated for 380 treated patients with different sites and two treatment techniques: SBRT for small brain lesion and whole brain radiotherapy(WBRT). The correlation coefficient and p-value between CI and plan parameters(modulation factor and pitch) and patient-specific QA results (gamma pass rate and measured point dose difference) were calculated.

Results: Complexity index was found to be specific to treatment sites. The mean CI and standard deviation(SD) for majority treatment sites were brain(1.81±1.11), pelvis(4.73±1.65),neck(2.53±0.93), prostate(2.09±1.1.27). The smallest mean CI is SBRT for small brain lesion(0.44±0.55). The largest and smallest SD is 1.65 (pelvis) and 0.11(nose). The p-value between CI and gamma pass rate, point dose difference and modulation factor were larger than 0.01 except for the pitch.

Conclusion: The sinogram-based CI was closely correlated to a specific treatment site and pitch value, but not correlated with modulation factor and physics QA results. It can be potentially used as a clinical tool for treatment-site specific quality control of the new Tomotherapy plan.

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