Dosimetric impact and detectability of multi-leaf collimator positioning errors on Varian Halcyon

Skylar S. Gay, Tucker J. Netherton, Carlos E. Cardenas, Rachel B. Ger, Peter A. Balter, Lei Dong, Dimitris Mihailidis, Laurence E. Court

Research output: Contribution to journalArticle

Abstract

The purpose of this study is to investigate the dosimetric impact of multi-leaf collimator (MLC) positioning errors on a Varian Halcyon for both random and systematic errors, and to evaluate the effectiveness of portal dosimetry quality assurance in catching clinically significant changes caused by these errors. Both random and systematic errors were purposely added to 11 physician-approved head and neck volumetric modulated arc therapy (VMAT) treatment plans, yielding a total of 99 unique plans. Plans were then delivered on a preclinical Varian Halcyon linear accelerator and the fluence was captured by an opposed portal dosimeter. When comparing dose–volume histogram (DVH) values of plans with introduced MLC errors to known good plans, clinically significant changes to target structures quickly emerged for plans with systematic errors, while random errors caused less change. For both error types, the magnitude of clinically significant changes increased as error size increased. Portal dosimetry was able to detect all systematic errors, while random errors of ±5 mm or less were unlikely to be detected. Best detection of clinically significant errors, while minimizing false positives, was achieved by following the recommendations of AAPM TG-218. Furthermore, high- to moderate correlation was found between dose DVH metrics for normal tissues surrounding the target and portal dosimetry pass rates. Therefore, it may be concluded that portal dosimetry on the Halcyon is robust enough to detect errors in MLC positioning before they introduce clinically significant changes to VMAT treatment plans.

Original languageEnglish (US)
Pages (from-to)47-55
Number of pages9
JournalJournal of applied clinical medical physics
Volume20
Issue number8
DOIs
StatePublished - Jan 1 2019

Fingerprint

Intensity-Modulated Radiotherapy
collimators
leaves
positioning
Random errors
random errors
Systematic errors
dosimeters
Particle Accelerators
systematic errors
Dosimetry
Neck
Head
Physicians
histograms
Therapeutics
therapy
arcs
Linear accelerators
physicians

Keywords

  • Halcyon
  • MLC
  • VMAT
  • dual-layer
  • head and neck
  • quality assurance

ASJC Scopus subject areas

  • Radiation
  • Instrumentation
  • Radiology Nuclear Medicine and imaging

Cite this

Dosimetric impact and detectability of multi-leaf collimator positioning errors on Varian Halcyon. / Gay, Skylar S.; Netherton, Tucker J.; Cardenas, Carlos E.; Ger, Rachel B.; Balter, Peter A.; Dong, Lei; Mihailidis, Dimitris; Court, Laurence E.

In: Journal of applied clinical medical physics, Vol. 20, No. 8, 01.01.2019, p. 47-55.

Research output: Contribution to journalArticle

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