Association of planned-recorded sinogram difference metrics with treatment planning parameters and gamma pass rates in helical tomotherapy.

Abstract

In helical tomotherapy (HT), the beam intensity is modulated by controlling the leaf open time (LOT) of a binary multileaf collimator (MLC), represented as sinograms. Comparing planned and recorded sinograms enables the evaluation of MLC delivery errors. This study proposes a novel sinogram difference metric-the time difference rate (TDR)- and evaluates its association with treatment planning parameters and the Patient-specific quality assurance gamma passing rate (GPR). Treatment plans of 153 patients with head and neck cancer who underwent IMRT with HT were retrospectively analyzed. Planned and recorded sinograms were compared to calculate relative and absolute TDRs, defined as the percentage of active sinogram elements exceeding predefined LOT difference thresholds. Relative TDR thresholds were 2%, 3%, 5%, and 10%, and absolute TDR thresholds were 5, 10, 15, and 20 ms. Associations of TDRs and treatment planning parameters and TDRs were evaluated using Spearman's rank correlation coefficient. Relative and absolute TDRs significantly correlated with modulation factor, beam-on time, and gantry period (p < 0.01), whereas correlations with pitch were weak. Gantry period showed the strongest correlation with relative TDRs. Relative [Formula: see text] and [Formula: see text] showed weak but significant correlations with GPRs, with Spearman's rank correlation coefficients ranging from - 0.241 to - 0.175. Among the absolute metrics, [Formula: see text], [Formula: see text], and [Formula: see text] showed weak but significant negative correlations with GPR 3%/2 mm, with Spearman's rank correlation coefficients of - 0.178, - 0.228, and - 0.154, respectively. Relative [Formula: see text] and [Formula: see text]may complement conventional PSQA by directly evaluating MLC delivery accuracy from recorded sinograms.