The impact of leaf width and plan complexity on DMLC tracking of prostate intensity modulated arc therapy

Abstract

Purpose: Intensity modulated arc therapy (IMAT) is commonly used to treat prostate cancer. The purpose of this study was to evaluate the impact of leaf width and plan complexity on dynamic multileaf collimator (DMLC) tracking for prostate motion management during IMAT treatments. Methods: Prostate IMAT plans were delivered with either a high-definition MLC (HDMLC) or a Millennium MLC (M-MLC) (0.25 and 0.50 cm central leaf width, respectively), with and without DMLC tracking, to a dosimetric phantom that reproduced four prostate motion traces. The plan complexity was varied by applying leaf position constraints during plan optimization. A subset of the M-MLC plans was converted for delivery with the HDMLC, isolating the effect of the different leaf widths. The gamma index was used for evaluation. Tracking errors caused by target localization, leaf fitting, and leaf adjustment were analyzed. Results: The gamma pass rate was significantly improved with DMLC tracking compared to no tracking (p < 0.001). With DMLC tracking, the average gamma index pass rate was 98.6% (range 94.8%-100%) with the HDMLC and 98.1% (range 95.4%-99.7%) with the M-MLC, using 3%, 3 mm criteria and the planned dose as reference. The corresponding pass rates without tracking were 87.6% (range 76.2%-94.7%) and 91.1% (range 81.4%-97.6%), respectively. Decreased plan complexity improved the pass rate when static target measurements were used as reference, but not with the planned dose as reference. The main cause of tracking errors was leaf fitting errors, which were decreased by 42% by halving the leaf width. Conclusions: DMLC tracking successfully compensated for the prostate motion. The finer leaf width of the HDMLC improved the tracking accuracy compared to the M-MLC. The tracking improvement with limited plan complexity was small and not discernible when using the planned dose as reference.

• author: Pommer, Tobias ; Falk, Marianne ; Poulsen, Per Rugaard ; Keall, Paul J. ; O'Brien, Ricky T. and Munck Af Rosenschöld, Per
• publishing date: 2013-11
• type: Contribution to journal
• publication status: published
• subject: Radiology and Medical Imaging
• keywords: intrafraction motion, motion management
• in: Medical Physics
• volume: 40
• issue: 11
• article number: 111717
• publisher: John Wiley & Sons Inc.
• external identifiers: scopus:84889668097; pmid:24320425
• ISSN: 0094-2405
• DOI: 10.1118/1.4824434
• language: English
• LU publication?: no
• additional info: Funding Information: The authors wish to thank Katja Langen and Patrick Kupelian (MD Anderson Orlando) for use of the prostate motion traces; Pekka Uusitalo, Janne Nord, and Jarkko Peltola (Varian Medical Systems, Helsinki, Finland) for supplying the research treatment planning system; Stephan Erbel, Cornel Schlossbauer, and Kristian Seiron (Brainlab, Germany) for support in using ExacTrac for position monitoring; Amit Sawant (University of Texas Southwestern, Dallas), Dan Ruan (University of California, Los Angeles), and Byung Chul Cho (University of Ulsan College of Medicine, Korea) for development of the DMLC tracking software; and Herbert Cattell (Varian Medical Systems, Palo Alto) for contributions to the DMLC tracking program. Tobias Pommer acknowledges grant support from the Niels Bohr Institute, Copenhagen University. Marianne Falk has research grants from Varian Medical Systems, Palo Alto, CA and Niels Bohr Institute, Copenhagen University. Per Rugaard Poulsen has a research agreement with Varian Medical Systems, Palo Alto, CA. Paul J Keall acknowledges grant support of US NIH/NCI R01-93626 and a NHMRC Australia Fellowship. Per Munck af Rosenschöld has research and educational collaboration agreements with Varian Medical Systems, Palo Alto, CA.
• id: 178555f2-c8ba-4fa7-9a6a-b5d744ec7cd2
• date added to LUP: 2023-07-19 09:41:05
• date last changed: 2025-04-04 14:26:27