Characterization of megavoltage electron beams delivered through a photon multi-leaf collimator (pMLC)

F. C P Du Plessis, A. Leal, Sotirios Stathakis, W. Xiong, C. M. Ma

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

A study is presented that characterizes megavoltage electron beams delivered through an existing double-focused photon multi-leaf collimator (pMLC) using film measurements in a solid water phantom. Machine output stability and linearity were evaluated as well as the effect of source-to-surface distance (SSD) and field size on the penumbra for electron energies between 6 and 18 MeV over an SSD range of 60-100 cm. Penumbra variations as a function of field size, depth of measurement and the influence of the jaws were also studied. Field abutment, field flatness and target coverage for segmented beams were also addressed. The measured field size for electrons transported through the pMLC was the same as that for an x-ray beam up to SSDs of 70 cm. At larger SSD, the lower energy electron fields deviated from the projected field. Penumbra data indicated that 60 cm SSD was the most favourable treatment distance. Backprojection of P20-80 penumbra data yielded a virtual source position located at 98.9 cm from the surface for 18 MeV electrons. For 6 MeV electrons, the virtual source position was at a distance of 82.6 cm. Penumbra values were smaller for small beam slits and reached a near-constant value for field widths larger than 5 cm. The influence of the jaws had a small effect on the penumbra. The R90 values ranged from 1.4 to 4.8 cm between 6 and 21 MeV as measured at 60 cm SSD for a 9 × 9 cm2 field. Uniformity and penumbra improvement could be demonstrated using weighted abutted fields especially useful for small segments. No detectable electron leakage through the pMLC was observed. Bremsstrahlung measurements taken at 60 cm SSD for a 9 × 9 cm2 field as shaped by the pMLC compared within 1% to bremsstrahlung measurements taken at 100 cm SSD for a 10 × 10 cm 2 electron applicator field at 100 cm SSD.

Original languageEnglish (US)
Pages (from-to)2113-2129
Number of pages17
JournalPhysics in Medicine and Biology
Volume51
Issue number8
DOIs
StatePublished - Apr 21 2006
Externally publishedYes

Fingerprint

collimators
Photons
leaves
penumbras
Electron beams
electron beams
Electrons
photons
Jaw
electrons
bremsstrahlung
Silver Sulfadiazine
electron energy
Applicators
flatness
X-Rays
linearity
slits
leakage
Water

ASJC Scopus subject areas

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

Cite this

Characterization of megavoltage electron beams delivered through a photon multi-leaf collimator (pMLC). / Du Plessis, F. C P; Leal, A.; Stathakis, Sotirios; Xiong, W.; Ma, C. M.

In: Physics in Medicine and Biology, Vol. 51, No. 8, 21.04.2006, p. 2113-2129.

Research output: Contribution to journalArticle

Du Plessis, F. C P ; Leal, A. ; Stathakis, Sotirios ; Xiong, W. ; Ma, C. M. / Characterization of megavoltage electron beams delivered through a photon multi-leaf collimator (pMLC). In: Physics in Medicine and Biology. 2006 ; Vol. 51, No. 8. pp. 2113-2129.
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