Comparative efficiency of the multi-leaf collimator and variable-aperture collimator in intensity-modulated radiotherapy.
The potential of the variable-aperture collimator (VAC) in intensity-modulated radiation therapy (IMRT) has been evaluated by comparing its performance with that of the multi-leaf collimator (MLC). This comparison used a decomposition algorithm to find the series of collimator segments that would treat a given intensity-modulated beam (IMB). Collimator performance was measured using both the number of segments required to complete the IMB and the monitor-unit efficiency of the treatment. The VAC was modelled with aperture sizes from 4 x 4 cm to 20 x 20 cm, and these apertures were allowed to be located anywhere within the IMB. To enable a direct comparison, a similar scanning MLC was modelled at the same range of aperture sizes. Using both collimators, decompositions were run on 10 x 10 and 20 x 20 random IMBs with integer bixel values ranging from 1 to 10. Clinical IMBs from lung, head and neck, and pelvic patients were taken from a Pinnacle treatment-planning system and tested in the same manner. It was found that for all treatment sites, a small, scanning MLC performs as well or better than an equivalent sized VAC in both number of segments and monitor-unit efficiency, and would be an efficient choice for centres looking for a simple collimator for IMRT.
Joint Department of Physics, Institute of Cancer Research and Royal Marsden NHS Foundation Trust, Downs Road, Sutton, Surrey SM2 5PT, UK. james.anderson@icr.ac.uk
J W
JW
Anderson
R
R
Symonds-Tayler
G
G
Hartmann
G
G
Echner
C
C
Lang
W
W
Schlegel
S
S
Webb
D000465:Algorithms; D006801:Humans; D009369:Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000295:instrumentation / Q000379:methods*