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A Study of Using Modulation Complexity Score as a Clinical Decision Aid for VMAT-Based Pancreas SBRT Treatment Planning

Y Zlateva*, X Li, F Yin, Q Wu, C Wang, Duke University Medical Center, Durham, NC


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

To investigate the clinical decision-making impact of using complexity score for pancreas VMAT-based SBRT plan evaluation

Thirty(30) pancreas VMAT SBRT plans generated in Eclipse at our institution were retrospectively studied. Monitor unit (MU)-weighted modulation complexity scores (MCS) were calculated via an in-house script through ESAPI. The MCS metric varies from 0 for high modulation to 1 for minimum modulation. Linear regression was performed on MCS as a function of mean MLC-based equivalent-square field side (EqSq) per plan. Measurement-based patient-specific QA gamma passing rates with 2%/2mm(2/2) and 3%/3mm(3/3) criteria were also examined as a function of MCS, field size, and the combined parameter EqSqMCS, defined as (1 – EqSq/22cm)*MCS.

MCS and field size were strongly correlated (Pearson r=0.85, MCS=0.12-0.45, EqSq=1.4cm-5.1cm). This indicates that modulation, and thus potentially plan quality, could be improved with decreased MLC aperture size. Gamma index was not found to correlate with MCS [r=-0.46(3/3), -0.37(2/2); Gamma test passing rates=91.6%-100.0%(3/3), 78.5-100.0%(2/2)]. This indicates that decreasing the MLC aperture size in these cases would not affect the agreement between calculation and measurement, and thus the dosimetric accuracy [as evidenced by a correspondingly low EqSq r=-0.41(3/3), -0.14(2/2)]. There was also no significant improvement in the correlation with EqSqMCS. The uncertainty effect of plan complexity on dosimetric accuracy is insignificant relative to other factors affecting calculation and delivery.

Based on the strong correlation between MCS and pancreas VMAT SBRT MLC aperture equivalent-square field size, we conclude that MCS can be used to score plan complexity for clinical treatment plan decision making. Given a VMAT plan MLC score, a recommendation of modulation improvement/reduction can be made based on the achieved MCS-MLC aperture size regression with uncertainty range. Such recommendation may reduce time consumption as in the trial-and-error planning manner.


Treatment Planning, Modeling, Radiosurgery


TH- External Beam- Photons: extracranial stereotactic/SBRT

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