Quality assurance of stereotactic radiotherapy demands the use of equipment with the highest resolution and sensitivity available. This study examines the sensitivity of a commercially available liquid-filled ionization chamber array—the Octavius 1000 SRS (PTW, Frieburg, Germany) for detecting small (sub-millimetre) multi-leaf collimator (MLC) alignment errors in static square fields (side length 16–40 mm). Furthermore, the effectiveness of detecting small MLC errors in clinical stereotactic radiotherapy patient plans using the device was also evaluated. The commonly used gamma pass rate metric (of the measurements compared with treatment planning system generated results) was used. The gamma pass rates were then evaluated as a function of MLC position error (MLC error size 0.1–2.5 mm). The detector array exhibited a drop in pass rate between plans without error and those which had MLC errors induced. For example a drop in pass rate of 4.5 % (gamma criteria 3 %, 1 mm) was observed when a 0.8 mm error was introduced into a 16 mm square field. Furthermore the drop in pass rate increased as the MLC position error increased. This study showed that the Octavius 1000 SRS array could be a useful tool for applications requiring the detection of small geometric delivery uncertainties.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Price includes VAT (USA)
Tax calculation will be finalised during checkout.
Low DA, Moran JM, Dempsey JF, Dong L, Oldham M (2011) Dosimetry tools and techniques for IMRT. Med Phys 38:1313–1338
Alber M, Broggi S, De Wagter C et al (2008) Guidelines for the verfication of IMRT. ESTRO, Brussels
O’Daniel J, Das S, Wu J, Fang-Fang Y (2010) Patient specific quality assurance: transition from IMRT to IMAT. J Phys 250:012050. doi:10.1088/1742-6596/250/1/012050
Gloi AM, Buchanan RE, Zuge CL, Goettler AM (2011) RapidArc quality assurance through MapCHECK. J Appl Clin Med Phys 12:39–47
Li G, Zhang Y, Jiang X, Bai S et al (2013) Evaluation of the ArcCHECK QA system for IMRT and VMAT verification. Phys Med 29:295–303
Oliver M, Gagne I, Bush K, Zavgorodni S et al (2010) Clinical significance of multi-leaf collimator positional errors for volumetric modulated arc therapy. Radiother Oncol 97:554–560
Heilemann G, Poppe B, Laub W (2013) On the sensitivity of common gamma-index evaluation methods to MLC misalignments in rapidarc quality assurance. Med Phys 40:031702
Low DA, Harms WB, Mutic S, Purdy JA (1998) A technique for quantitative evaluation of dose distributions. Med Phys 25:656–661
Markovic M, Stathakis S, Manroidis P, Jurkovic I et al (2014) Characterization of a two-dimensional liquid-filled ion chamber detector array used for verification of the treatments in radiotherapy. Med Phys 41:051704
Poppe B, Stellje TS, Looe HK, Chofor N (2013) Performance parameters of a liquid filled ionization chamber array. Med Phys 40:082106
Shaw E, Kline R, Gillin M, Souhami L et al (1993) Radiation therapy oncology group: radiosurgery quality assurance guidelines. Int J Radiat Oncol Biol Phys 27(5):1231–1239
Kim J, Park S-Y, Hak JK, Kim JH et al (2014) The sensitivity of gamma-index method to the positioning errors of high-definition MLC in patient-specific VMAT QA for SBRT. Radiat Oncol 9:167
Nelms BE, Zhen H, Tome WA (2011) Per-beam, planar IMRT QA passing rates do not predict clinically relevant patient dose errors. Med Phys 38:1037–1044
All PTW equipment used in this study was provided by Nucletron Pty Ltd (Newtown, Australia) on a trial basis to the medical physics department. Measurements taken during the trial period form the basis of this study. The authors would like to extend their gratitude to Nucletron for providing the equipment.
About this article
Cite this article
O’Connor, P., Seshadri, V. & Charles, P. Detecting MLC errors in stereotactic radiotherapy plans with a liquid filled ionization chamber array. Australas Phys Eng Sci Med 39, 247–252 (2016). https://doi.org/10.1007/s13246-016-0421-6
- Octavius 1000 SRS
- Stereotactic QA
- Patient specific QA