Prog Med Phys.  2016 Sep;27(3):111-116. 10.14316/pmp.2016.27.3.111.

Clinical Implications of High Definition Multileaf Collimator (HDMLC) Dosimetric Leaf Gap (DLG) Variations

Affiliations
  • 1Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea. jwkwak0301@gmail.com

Abstract

This study is to evaluate the dosimetric impact of dosimetric leaf gap (DLG) and transmission factor (TF) at different measurement depths and field sizes for high definition multileaf collimator (HD MLC). Consequently, its clinical implication on dose calculation of treatment planning system was also investigated for pancreas stereotactic body radiation therapy (SBRT). The TF and DLG were measured at various depths (5, 8, 10, 12, and 15 cm) and field sizes (6×6, 8×8, and 10×10 cm²) for various energies (6 MV, 6 MV FFF, 10 MV, 10 MV flattening filter free [FFF], and 15 MV). Fifteen pancreatic SBRT cases were enrolled in the study. For each case, the dose distribution was recomputed using a reconfigured beam model of which TF and DLG was the closest to the patient geometry, and then compared to the original plan using the results of dose-volume histograms (DVH). For 10 MV FFF photon beam, its maximum difference between 2 cm and 15 cm was within 0.9% and it is increased by 0.05% from 6×6 cm² to 10×10 cm² for depth of 15 cm. For 10 MV FFF photon beam, the difference in DLG between the depth of 5 cm and 15 cm is within 0.005 cm for all field sizes and its maximum difference between field size of 6×6 cm² and 10×10 cm² is 0.0025 cm at depth of 8 cm. TF and DLG values were dependent on the depth and field size. However, the dosimetric difference between the original and recomputed doses were found to be within an acceptable range (<0.5%). In conclusion, current beam modeling using single TF and DLG values is enough for accurate dose calculation.

Keyword

HDMLC; Dosimetric leaf gap (DLG); MLC transmission factor; Stereotactic body radiation therapy (SBRT); Pancreas

MeSH Terms

Humans
Pancreas

Figure

  • Fig. 1 Measurement of tumor size and depth.

  • Fig. 2 Measured transmission factor (a) and dosimetric leaf gap (b) at a field size of 10×10 cm2 at different depths (2, 5, 10, and 15 cm) and with a photon beam energy of 6 MV, 6 MV FFF, 10 MV, 10 MV FFF, and 15 MV.

  • Fig. 3 Measured transmission factor (a) and dosimetric leaf gap (b) with a 10 MV FFF photon beam at different field sizes (6×6, 8×8, and 10×10 cm2) and different depths (5, 10, and 15 cm).

  • Fig. 4 Dose volume histogram (DVH) of original plan (▲) and modified plans (■) for depths 5 cm (a), 8 cm (b), and 10 cm (c).


Reference

1.Otto K. Volumetric modulated arc therapy: IMRT in a single gantry arc. Med Phys. 35:310–317. 2008.
Article
2.Xing L., Thorndyke B., Schreibmann E, et al. Overview of image-guided radiation therapy. Med Dosim. 31:91–112. 2006.
Article
3.Yoon SM., Lim YS., Park MJ, et al. Stereotactic body radiation therapy as an alternative treatment for small hepatocellular carcinoma. PLoS One 8: e79854, 1-10. 2013.
Article
4.Kantz S., Söhn M., Troeller A, et al. Impact of MLC properties and IMRT technique in meningioma and head-and-neck treatments. Radiat Oncol 10: 184. 2015.
Article
5.Yu CX., Li XA., Ma L, et al. Clinical implementation of intensity-modulated arc therapy. Int J Radiat Oncol Biol Phys. 53:453–63. 2002.
6.Huq MS., Das IJ., Steinberg T., Galvin JM. A dosimetric comparison of various multileaf collimators. Phys Med Biol. 47:N159–70. 2002.
Article
7.Hong CS., Ju SG., Kim M, et al. Dosimetric effects of multileaf collimator leaf width on intensity-modulated radiotherapy for head and neck cancer. Med Phys 41: 021712. 2014.
Article
8.Sharma DS., Dongre PM., Mhatre V., Heigrujam M. Physical and dosimetric characteristic of high-definition multileaf collimator (HDMLC) for SRS and IMRT. J Appl Clin Med Phys. 12:3475. 2011.
Article
9.LoSasso T., Chui CS., Ling CC. Physical and dosimetric aspects of a multileaf collimation system used in the dynamic mode for implementing intensity modulated radiotherapy. Med Phys. 25:1919–27. 1999.
Article
10.Kumaraswamy LK., Schmitt JD., Bailey DW, et al. Spatial variation of dosimetric leaf gap and its impact on dose delivery. Med Phys 41: 111711. 2014.
Article
11.Kielar KN., Mok E., Hsu A., Wang L., Luxton G. Verification of dosimetric accuracy on the TrueBeamSTx: rounded leaf effect of the high definition MLC. Med Phys. 39:6360–71. 2012.
12.Yao W., Farr JB. Determining the optimal dosimetric leaf gap setting for rounded leaf-end multileaf collimator systems by simple test fields. J Appl Clin Med Phys. 16(4):5321. 2015.
Article
13.Szpala S., Cao F., Kohli K. On using the dosimetric leaf gap to model the rounded leaf ends in VMAT/RapidArc plans. J Appl Clin Med Phys. 15:4484. 2014.
Article
14.Chang KH., Kwak J., Cho B, et al. Evaluation of dosimetric leaf gap (DLG) at different depths for dynamic IMRT. Prog Med Phys. 26:153–159. 2015.
Article
15.Wasbø E., Valen H. Dosimetric discrepancies caused by differing MLC parameters for dynamic IMRT. Phys Med Biol. 53:405–15. 2008.
Article
Full Text Links
  • PMP
Actions
Cited
CITED
export Copy
Close
Share
  • Twitter
  • Facebook
Similar articles
Copyright © 2024 by Korean Association of Medical Journal Editors. All rights reserved.     E-mail: koreamed@kamje.or.kr