The effects of intra-fraction organ motion on the delivery of dynamic intensity modulation

Cedric X. Yu, David A. Jaffray, John Wong

Research output: Contribution to journalArticle

Abstract

Computer optimized treatment plans, aimed to enhance tumour control and reduce normal tissue complication, generally require non-uniform beam intensities. One of the techniques for delivering intensity modulated beam is the use of dynamic multileaf collimation, where the beam aperture moves and the field shape changes during irradiation. When intensity modulated beams are delivered with dynamic collimation, the problem of intra-fraction organ motion can cause distortions to the desired beam intensities. Unlike static field treatments, where intra fraction organ motion only affects the boundaries creating broad dose penumbra, the interplay of the movement of the beam aperture and the movement of the patient anatomy can create 'hot' and 'cold' spots throughout the field. The mechanism for creating these effects is not well understood. This paper provides a simple analytical model which illustrates the fundamental mechanism for creating the dosimetric variations in the target when both the beam aperture and the target move during irradiation. Numerical analysis was carried out which calculates the cumulative primary photon fluence, or beam intensity received by each point in the target, for a given pattern of motion. The results show that for clinically realistic parameters, the magnitude of intensity variations in the target can be greater than 100% of the desired beam intensity. The magnitude of the photon intensity variations is strongly dependent on the speed of the beam aperture relative to the speed of the target motion and the width of the scanning beam relative to the amplitude of target motion. The effects of fractionation as well as methods of minimizing and eliminating the dosimetric effects of intra fraction organ motion are discussed.

Original languageEnglish (US)
Pages (from-to)91-104
Number of pages14
JournalPhysics in Medicine and Biology
Volume43
Issue number1
DOIs
StatePublished - 1998
Externally publishedYes

Fingerprint

organs
delivery
Photons
Modulation
Irradiation
modulation
Fractionation
Numerical analysis
Tumors
Analytical models
Tissue
Scanning
apertures
collimation
Anatomy
penumbras
irradiation
anatomy
photons
Therapeutics

ASJC Scopus subject areas

  • Biomedical Engineering
  • Physics and Astronomy (miscellaneous)
  • Radiology Nuclear Medicine and imaging
  • Radiological and Ultrasound Technology

Cite this

The effects of intra-fraction organ motion on the delivery of dynamic intensity modulation. / Yu, Cedric X.; Jaffray, David A.; Wong, John.

In: Physics in Medicine and Biology, Vol. 43, No. 1, 1998, p. 91-104.

Research output: Contribution to journalArticle

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