Kilovoltage energy imaging with a radiotherapy linac with a continuously variable energy range

Journal Article · Thu Mar 15 04:00:00 EDT 2012 · Medical Physics

DOI:https://doi.org/10.1118/1.3681011· OSTI ID:22098772

Roberts, D. A.; Hansen, V. N.; Thompson, M. G.; Poludniowski, G.; Niven, A.; Seco, J.; Evans, P. M. ^[1]

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1. Joint Department of Physics, Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey SM2 5PT (United Kingdom) and Elekta, Crawley, West Sussex RH10 9RR (United Kingdom)

Purpose: In this paper, the effect on image quality of significantly reducing the primary electron energy of a radiotherapy accelerator is investigated using a novel waveguide test piece. The waveguide contains a novel variable coupling device (rotovane), allowing for a wide continuously variable energy range of between 1.4 and 9 MeV suitable for both imaging and therapy.Method: Imaging at linac accelerating potentials close to 1 MV was investigated experimentally and via Monte Carlo simulations. An imaging beam line was designed, and planar and cone beam computed tomography images were obtained to enable qualitative and quantitative comparisons with kilovoltage and megavoltage imaging systems. The imaging beam had an electron energy of 1.4 MeV, which was incident on a water cooled electron window consisting of stainless steel, a 5 mm carbon electron absorber and 2.5 mm aluminium filtration. Images were acquired with an amorphous silicon detector sensitive to diagnostic x-ray energies. Results: The x-ray beam had an average energy of 220 keV and half value layer of 5.9 mm of copper. Cone beam CT images with the same contrast to noise ratio as a gantry mounted kilovoltage imaging system were obtained with doses as low as 2 cGy. This dose is equivalent to a single 6 MV portal image. While 12 times higher than a 100 kVp CBCT system (Elekta XVI), this dose is 140 times lower than a 6 MV cone beam imaging system and 6 times lower than previously published LowZ imaging beams operating at higher (4-5 MeV) energies. Conclusions: The novel coupling device provides for a wide range of electron energies that are suitable for kilovoltage quality imaging and therapy. The imaging system provides high contrast images from the therapy portal at low dose, approaching that of gantry mounted kilovoltage x-ray systems. Additionally, the system provides low dose imaging directly from the therapy portal, potentially allowing for target tracking during radiotherapy treatment. There is the scope with such a tuneable system for further energy reduction and subsequent improvement in image quality.

• OSTI ID: 22098772
• Journal Information: Medical Physics, Journal Name: Medical Physics Journal Issue: 3 Vol. 39; ISSN 0094-2405; ISSN MPHYA6
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
62 RADIOLOGY AND NUCLEAR MEDICINE
CAT SCANNING
COMPUTERIZED SIMULATION
COPPER
DOSIMETRY
FILTRATION
IMAGE PROCESSING
KEV RANGE 100-1000
LAYERS
LINEAR ACCELERATORS
MEV RANGE 01-10
MONTE CARLO METHOD
RADIATION DOSES
RADIOTHERAPY
SI SEMICONDUCTOR DETECTORS
SILICON
STAINLESS STEELS
WATER COOLED REACTORS
WAVEGUIDES
X RADIATION