Comparison of non-coplanar optimization of static beams and arc trajectories for intensity-modulated treatments of meningioma cases

Tiago Ventura,Maria Do Carmo Lopes,Joana Dias,Humberto Rocha,Brigida Da Costa Ferreira

doi:10.1007/s13246-021-01061-8

Abstract

Two methods for non-coplanar beam direction optimization, one for static beams and another for arc trajectories, were proposed for intracranial tumours. The results of the beam angle optimizations were compared with the beam directions used in the clinical plans. Ten meningioma cases already treated were selected for this retrospective planning study. Algorithms for non-coplanar beam angle optimization (BAO) and arc trajectory optimization (ATO) were used to generate the corresponding plans. A plan quality score, calculated by a graphical method for plan assessment and comparison, was used to guide the beam angle optimization process. For each patient, the clinical plans (CLIN), created with the static beam orientations used for treatment, and coplanar VMAT approximated plans (VMAT) were also generated. To make fair plan comparisons, all plan optimizations were performed in an automated multicriteria calculation engine and the dosimetric plan quality was assessed. BAO and ATO plans presented, on average, moderate global plan score improvements over VMAT and CLIN plans. Nevertheless, while BAO and CLIN plans assured a more efficient OARs sparing, the ATO and VMAT plans presented a higher coverage and conformity of the PTV. Globally, all plans presented high-quality dose distributions. No statistically significant quality differences were found, on average, between BAO, ATO and CLIN plans. However, automated plan solution optimizations (BAO or ATO) may improve plan generation efficiency and standardization. In some individual patients, plan quality improvements were achieved with ATO plans, demonstrating the possible benefits of this automated optimized delivery technique.

Highlights

In radiation therapy, non-uniform intensity field techniques are well-established for almost all cancer pathologies since they allow the delivery of highly conformal dose distributions to the target(s) while minimizing the injury to the organs-at-risk (OAR)
We have addressed the static beam angle optimization problem for head-and-neck pathologies [37, 38]
Significant differences in plan quality were only found between the beam angle optimization (BAO) plans and the VMAT plans

Summary

Introduction

Non-uniform intensity field techniques are well-established for almost all cancer pathologies since they allow the delivery of highly conformal dose distributions to the target(s) while minimizing the injury to the organs-at-risk (OAR). The calculation of non-uniform beam intensities is done using inverse planning, where plan objectives are specified by means of physical or biological descriptors in an objective function that guides the fluence map optimization (FMO) process [1]. For conventional C-arm linear accelerators, this type of treatment techniques can be delivered through multiple modulated static or dynamic radiation fields (intensity-modulated radiation therapy—IMRT) or through continuously modulated radiation arcs combining the variation in dose rate,. VMAT treatments are usually more efficient requiring fewer monitor units and shorter delivery times [2]

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Results

Discussion

Conclusion