Use of metrics to quantify IMRT and VMAT treatment plan complexity: A systematic review and perspectives

Purpose: A recently introduced commercial tool is tested to assess whether it is able to reduce the complexity of a treatment plan and improve deliverability without compromising overall quality. Methods: Ten prostate and ten oropharynx plans of previously treated patients were reoptimized using the aperture shape controller (ASC) tool recently introduced in Eclipse TPS (Varian Medical Systems, Palo Alto, CA). The performance of ASC was assessed in terms of the overall plan quality using a plan quality metric, the reduction in plan complexity through the analysis of 14 of the most common plan complexity metrics, and the change in plan deliverability through 3D dosimetric measurements. Similarly, plans optimized limiting the total number of delivered monitor units was assessed and compared. The two strategies were also combined to assess their potential combination. Results: The plans optimized by exploiting the ASC generally show a reduced number of total Monitor Units, a more constant gantry rotation and a MLC modulation characterized by larger and less complicated shapes with leaves traveling shorter overall lengths. Conclusions: This first experience suggests that the ASC is an effective tool to reduce the unnecessary complexity of a plan. This turns into an increased plan deliverability with no loss of plan quality. K E Y W O R D S aperture shape controller, complexity metrics, MLC, plan complexity, plan quality metric, treatment planning 1 | INTRODUCTION Volumetric modulated arc therapy (VMAT) is nowadays the standard treatment technique in high-quality radiation therapy delivered with clinical LINACs. The rapid dose fall-off outside target boundaries grants highly conformed dose distributions and near-optimal sparing of surrounding critical structures. Volumetric modulated arc therapy has generally replaced intensity-modulated radiation therapy (IMRT) because of the shorter treatment time obtained through the simultaneous variation of gantry speed, dose rate and MLC position. 1,2 Moreover, VMAT tends to use fewer monitor units (MU) per fraction than IMRT and thus reduces the burden of second malignancies. 3-5

Section: D | Metrics Of Complexitymentioning

confidence: 99%

Limiting treatment plan complexity by applying a novel commercial tool

Scaggion

Fusella

Agnello

et al. 2020

“…Previous reviews of complexity metric correlations generally report weak to moderate correlations to quality assurance results, 3,10 as is the case in this work. The complexity metrics selected for this study were primarily used to describe the general MLC movement and aperture shape of treatments.…”

Section: Discussionmentioning

confidence: 50%

“…Quality assurance results are affected by the characteristics of the detector and phantom used for measurement, as well as the linac used for delivery, and the TPS used to generate treatment plans, particularly the accuracy of beam modeling. Analysis is further affected by the correlation method used, the criteria used for PSQA, as well as the number of treatment plans investigated and the corresponding treatment volume 3,10 . While specific results may not be applied to other institutions, the methodology can be used to develop institute specific PTQA tools to aid in the treatment planning process.…”

Section: Discussionmentioning

confidence: 99%

“…The degree of complexity of VMAT treatment plans was evaluated using previously established complexity metrics 3–6,8–12 . Metrics were selected from those reported to have statistically significant correlations to quality assurance results in previous works, with an emphasis on those describing MLC behavior of the treatment.…”

Section: Methodsmentioning

confidence: 99%

“…An increased modulation often leads to increased uncertainty in dose because of the limitations of accurately modeling linac components such as MLC tongue and groove which affects the interleaf leakage, and leaf offset between the calculated rounded leaf tip value and the measured one. Generally, higher degrees of modulation suggest more complex treatments, and consequently increased uncertainty in delivery 3–12 …”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Quantified VMAT plan complexity in relation to measurement‐based quality assurance results

Nguyen

Chan

2020

Volumetric‐modulated arc therapy (VMAT) treatment plans that are highly modulated or complex may result in disagreements between the planned dose distribution and the measured dose distribution. This study investigated established VMAT complexity metrics as a means of predicting phantom‐based measurement results for 93 treatments delivered on a TrueBeam linac, and 91 treatments delivered on two TrueBeam STx linacs. Complexity metrics investigated showed weak correlations to gamma passing rate, with the exception of the Modulation Complexity Score for VMAT, yielding moderate correlations. The Spearman’s rho values for this metric were 0.502 (P < 0.001) and 0.528 (P < 0.001) for the TrueBeam and TrueBeam STx, respectively. Receiver operating characteristic analysis was also performed. The aperture irregularity on the TrueBeam achieved a 53% true positive rate and a 9% false‐positive rate to correctly identify complex plans. Similarly, the average field width on the TrueBeam STx achieved a 60% true‐positive rate and an 8% false‐positive rate. If incorporated into clinical workflow, these thresholds can identify highly modulated plans and reduce the number of dose verification measurements required.

Quantitative assessment of helical tomotherapy plans complexity

Cavinato

Fusella

Paiusco

et al. 2022

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.