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Advanced methods for delivering conformal therapy and dose planning techniques

Publication ,  Journal Article
Webb, S; Oldham, M
Published in: Physica Medica
January 1, 1997

Highly-conformal dose-distributions can be created by the superposition of many radiation fields from different directions, each with its intensity spatially modulated. One class of treatment technique, sometimes referred to as tomotherapy, involves creating a narrow slit of radiation and modulating the intensity of the radiation along the slit with a series of small stubby vanes moving at right angles to the long axis of the slit aperture. At the planning stage, the intensity of radiation of each beam-element (or bixel) is determined by working out the effect of superposing the radiation through all bixels using an elemental dose-distribution specified as that for a single bixel with all its neighbours closed. However, at the treatment delivery stage neighbouring bixels may not necessarily be closed. Instead the slit beam is delivered with the vanes closed for different periods of time to create the intensity-modulation. As a result, the three-dimensional dose- distribution actually delivered will be different from that determined at the planning stage. This paper explores these differences. At the planning stage an elemental dose contribution was assumed that corresponded to that for a single open bixel of a NOMOS MIMIC prototype collimator either: i) as directly measured or ii) as fitted to a 'stretched function' with the property that combinations of adjacent open bixels create a flat field. Delivery was simulated in two modes. The 3D dose-distribution has been computed in 'independent vane (IV)' mode, corresponding to delivery of each bixel component independently in time and in 'component delivery (CD)' mode which models the actual treatment geometry in which the 'walls' of a bixel have different configurations for different fractions of the total irradiation time per bixel. CD-mode delivery has been coded and the resulting 3D dose distributions compared with the planned (IV) dose-distributions. The CD-mode dose-distributions are better matched to the IV-mode dose distributions when the latter are calculated using the stretched fit to the elemental dose-distribution. However there are still differences which the inverse-planning calculation does not take into account. The CD-mode dose distributions compared favourably with experimental delivery with a prototype NOMOS MIMIC collimator attached to a Philips SL75/5 accelerator.

Duke Scholars

Published In

Physica Medica

ISSN

1120-1797

Publication Date

January 1, 1997

Volume

13

Issue

SUPPL. 1

Start / End Page

39 / 44

Related Subject Headings

  • Nuclear Medicine & Medical Imaging
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
  • 3202 Clinical sciences
  • 11 Medical and Health Sciences
  • 06 Biological Sciences
  • 02 Physical Sciences
 

Citation

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Webb, S., & Oldham, M. (1997). Advanced methods for delivering conformal therapy and dose planning techniques. Physica Medica, 13(SUPPL. 1), 39–44.
Webb, S., and M. Oldham. “Advanced methods for delivering conformal therapy and dose planning techniques.” Physica Medica 13, no. SUPPL. 1 (January 1, 1997): 39–44.
Webb S, Oldham M. Advanced methods for delivering conformal therapy and dose planning techniques. Physica Medica. 1997 Jan 1;13(SUPPL. 1):39–44.
Webb, S., and M. Oldham. “Advanced methods for delivering conformal therapy and dose planning techniques.” Physica Medica, vol. 13, no. SUPPL. 1, Jan. 1997, pp. 39–44.
Webb S, Oldham M. Advanced methods for delivering conformal therapy and dose planning techniques. Physica Medica. 1997 Jan 1;13(SUPPL. 1):39–44.
Journal cover image

Published In

Physica Medica

ISSN

1120-1797

Publication Date

January 1, 1997

Volume

13

Issue

SUPPL. 1

Start / End Page

39 / 44

Related Subject Headings

  • Nuclear Medicine & Medical Imaging
  • 5105 Medical and biological physics
  • 4003 Biomedical engineering
  • 3202 Clinical sciences
  • 11 Medical and Health Sciences
  • 06 Biological Sciences
  • 02 Physical Sciences