Circular collimator arc versus dynamic conformal arc treatment planning for linac-based stereotactic radiosurgery of an intracranial small single lesion: a perspective of lesion asymmetry

Yongsook C Lee,Yongbok Kim

doi:10.1186/s13014-019-1307-z

Abstract

BackgroundAlthough circular collimator arcs (CCA) and dynamic conformal arcs (DCA) are commonly used linear accelerator-based treatment planning techniques for intracranial stereotactic radiosurgery (SRS) of a small single lesion, these two techniques have not been rigorously compared in terms of tumor shape. Therefore, this study compared clinical CCA plans with re-planned DCA plans using conformity index (CI) and V12Gy (volume of normal brain tissue receiving 12 Gy or higher) from a perspective of asymmetry (Asym) of planning target volume (PTV).MethodsNinety-five clinical CCA plans delivered for a small single lesion with PTV size < 1.4 cm3 were selected and re-planned using DCA. PTV Asym (%) was defined and calculated from three dimensions of PTV. A pair of the 95 plans was first considered as one group without grouping and then categorized into two groups with respective to either PTV size or PTV Asym, and four groups with respect to PTV size and PTV Asym. For grouping, median values of PTV size and PTV Asym were used. A non-parametric paired test was performed for CI and V12Gy to compare CCA and DCA plans in each group.ResultsMedian values of PTV size and PTV Asym were 0.415 cm3 (range: 0.076 cm3–1.369 cm3) and 6.12% (range: 0.52–25.74%), respectively. DCA plans had a lower average CI value than CCA plans for all groups. CCA plans had a smaller average V12Gy value than DCA plans for lesions with PTV Asym ≤6.12%, while CCA and DCA plans had similar average V12Gy values for lesions with PTV Asym > 6.12%.ConclusionsThe DCA technique is recommended when a lesion has PTV Asym > 6.12% regardless of PTV size. For lesions with PTV Asym ≤6.12%, a technique choice would depend on the preference of CI or V12Gy.

Highlights

Circular collimator arcs (CCA) and dynamic conformal arcs (DCA) are commonly used linear accelerator-based treatment planning techniques for intracranial stereotactic radiosurgery (SRS) of a small single lesion, these two techniques have not been rigorously compared in terms of tumor shape
Linac-based systems are capable of multiple delivery techniques such as circular collimator arcs (CCA), dynamic conformal arcs (DCA), intensity modulated radiation therapy and volumetric modulated arc therapy (VMAT) [5]
Clinical circular collimator arc treatment planning For each patient, CCA treatment planning was performed in the iPlan RT treatment planning system (TPS) which supports a pencil beam algorithm with tissue inhomogeneity corrections

Summary

Introduction

Circular collimator arcs (CCA) and dynamic conformal arcs (DCA) are commonly used linear accelerator-based treatment planning techniques for intracranial stereotactic radiosurgery (SRS) of a small single lesion, these two techniques have not been rigorously compared in terms of tumor shape. Methods: Ninety-five clinical CCA plans delivered for a small single lesion with PTV size < 1.4 cm were selected and re-planned using DCA. Median values of PTV size and PTV Asym were used. Results: Median values of PTV size and PTV Asym were 0.415 cm (range: 0.076 cm3–1.369 cm3) and 6.12% (range: 0.52–25.74%), respectively. Linac-based systems are capable of multiple delivery techniques such as circular collimator arcs (CCA), dynamic conformal arcs (DCA), intensity modulated radiation therapy and volumetric modulated arc therapy (VMAT) [5]. Treatment of multiple lesions with a single isocenter approach has been employed since VMAT was introduced and its delivery has become highly efficient [7, 8]

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