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Dynamic splitting of large intensity-modulated fields.

Publication ,  Journal Article
Wu, Q; Arnfield, M; Tong, S; Wu, Y; Mohan, R
Published in: Phys Med Biol
July 2000

The aims of this paper are to describe a method of splitting large intensity-modulated fields that cannot be delivered as a single field and to verify the accuracy of our method. Some multi-leaf collimators may be operated in the dynamic mode to deliver intensity-modulated radiation treatments (IMRT) using the 'sliding window' technique. In this technique each pair of leaves sweeps over the treatment field while the beam is on. However, there are limitations on the width of the field that can be treated due to the limited length of the leaves. For instance, the leaf length of the Varian MLC is 14.5 cm. Since each leaf pair must travel from the left boundary to the right boundary of the beam aperture, the maximum width of the field aperture that can be accommodated in one sweep of leaves is also limited to 14.5 cm, in fact to a slightly smaller value. It has been shown that IMRT is more efficient when used to plan and deliver the large and boost fields simultaneously. In such situations, the fields must be large enough to cover simultaneously the volumes of the gross tumour, microscopic disease and electively treated regions. Such field sizes are often larger than 14.5 cm wide. In this paper, we present a dynamic 'feathering' technique to split the large intensity-modulated fields into smaller fields. In this technique, the component beams overlap each other by a small amount, and the intensity in the overlap region gradually decreases for one field component and increases for the other. The sum of intensities remains the same as for the original field. This method eliminates the field matching problems associated with the conventional step 'break' for static fields. The splitting process is integrated into the IMRT treatment procedure and the entire planning process is automated. Comparison of dose distributions calculated and measured in a phantom showed good agreement. Such a method can be applied to the 'step and shoot' technique as well. IMRT fields of widths up to 25 cm can be delivered by splitting only once, which is adequate for most treatments.

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Published In

Phys Med Biol

DOI

ISSN

0031-9155

Publication Date

July 2000

Volume

45

Issue

7

Start / End Page

1731 / 1740

Location

England

Related Subject Headings

  • Radiotherapy, Conformal
  • Radiotherapy Planning, Computer-Assisted
  • Physics
  • Physical Phenomena
  • Phantoms, Imaging
  • Nuclear Medicine & Medical Imaging
  • Models, Statistical
  • Algorithms
  • 5105 Medical and biological physics
  • 1103 Clinical Sciences
 

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Wu, Q., Arnfield, M., Tong, S., Wu, Y., & Mohan, R. (2000). Dynamic splitting of large intensity-modulated fields. Phys Med Biol, 45(7), 1731–1740. https://doi.org/10.1088/0031-9155/45/7/302
Wu, Q., M. Arnfield, S. Tong, Y. Wu, and R. Mohan. “Dynamic splitting of large intensity-modulated fields.Phys Med Biol 45, no. 7 (July 2000): 1731–40. https://doi.org/10.1088/0031-9155/45/7/302.
Wu Q, Arnfield M, Tong S, Wu Y, Mohan R. Dynamic splitting of large intensity-modulated fields. Phys Med Biol. 2000 Jul;45(7):1731–40.
Wu, Q., et al. “Dynamic splitting of large intensity-modulated fields.Phys Med Biol, vol. 45, no. 7, July 2000, pp. 1731–40. Pubmed, doi:10.1088/0031-9155/45/7/302.
Wu Q, Arnfield M, Tong S, Wu Y, Mohan R. Dynamic splitting of large intensity-modulated fields. Phys Med Biol. 2000 Jul;45(7):1731–1740.
Journal cover image

Published In

Phys Med Biol

DOI

ISSN

0031-9155

Publication Date

July 2000

Volume

45

Issue

7

Start / End Page

1731 / 1740

Location

England

Related Subject Headings

  • Radiotherapy, Conformal
  • Radiotherapy Planning, Computer-Assisted
  • Physics
  • Physical Phenomena
  • Phantoms, Imaging
  • Nuclear Medicine & Medical Imaging
  • Models, Statistical
  • Algorithms
  • 5105 Medical and biological physics
  • 1103 Clinical Sciences