Quantitative assessment of helical tomotherapy plans complexity

Abstract

Purpose An unnecessary amount of complexity in radiotherapy plans affects the efficiency of the treatments, increasing the uncertainty of dose deposition and its susceptibility to anatomical changes or setup errors. To date, tools for quantitatively assessing the complexity of tomotherapy plans are still limited. In this study, new metrics were developed to characterize different aspects of helical tomotherapy (HT) plans, and their actual effectiveness was investigated. Methods The complexity of 464 HT plans delivered on a Radixact platform was evaluated. A new set of metrics was devised to assess beam geometry, leaf opening time (LOT) variability, and modulation over space and time. Sixty‐five complexity metrics were extracted from the dataset using the newly in‐house developed software library TCoMX: 29 metrics already proposed in the literature and 36 newly developed metrics. Their reciprocal relation is discussed. Their effectiveness was evaluated through correlation analyses with patient‐specific quality assurance (PSQA) results. Results An inverse linear relation was found between the average number of closed leaves and the average number of MLC openings and closures as well as between the choice of the modulation factor and the discontinuity of the field, suggesting some intrinsic link between the LOT distribution and the geometrical complexity of the MLC openings. The newly proposed metrics were at least as correlated as the existing ones to the PSQA results. Metrics describing the geometrical complexity of the MLC openings showed the strongest connection to the PSQA results. Significant correlations were found between at least one of the new metrics and the γ index passing rate for six out of seven groups of plans considered. Conclusion The new metrics proposed were shown to be effective to characterize more comprehensively the complexity of HT plans. A software library for their automatic extraction is described and made available.

Impact of delivery time factor on treatment time and plan quality in tomotherapy

“…In contrast, when the DTF was within the range of 1.2-1.3 and 1.5-1.6 for head and neck and lung cases, respectively, the MF reached 3.0, which is recognized as a much higher value for head and neck plans [34]. A higher MF leads to greater plan complexity in tomotherapy, potentially leading to unacceptable dose delivery [22,23]. Therefore, it is necessary to select a DTF with a good balance between treatment time and plan quality.…”

“…Generally, a pitch of 0.86/n (n is an integer) is used to mitigate the thread effect [21]. The MF is de ned as the maximum leaf opening time divided by the average (non-zero) leaf opening time and is an estimate of plan complexity [22,23]. Increasing the MF enables larger beam modulation resulting in high-quality plans; however, this leads to increased treatment time [4,24].…”

Influence of the Planning Parameters of a New Algorithm on the Dosimetric Quality, Beam-On Time and Delivery Accuracy of Tomotherapy Plans

“…Various local and global absolute gamma index values were recorded, with a threshold of 10%: 3%/3 mm, 2%/2 mm, 1%/1 mm, 3%/2 mm, and 2%/1 mm. For each of these measured plans, we extracted 65 complexity metrics using the MATLAB (version R2023) program TCoMX developed by Cavinato et al [12,13] to study the correlations among the LOT cutoff parameter, the gamma index values, and these metrics.…”

“…Thus, VOLO TM Ultra user using this table should carry out evaluations based on their own patients to confirm th compatibility of their practices with the methods used in this study. We tested the correlations between the gamma index values of the 36 measured plans and 65 complexity metrics [12] (see Appendix F), as well as the correlations between these metrics and the LOT cutoff values (see Appendix G). Our results show that the LOT cutoff value is correlated with certain metrics that are derived based directly on LOT values, such as minLOT, as well as certain CLNS and CFNS scores.…”