PMID- 15152689
OWN - NLM
STAT- MEDLINE
DCOM- 20041119
LR  - 20190726
IS  - 0031-9155 (Print)
IS  - 0031-9155 (Linking)
VI  - 49
IP  - 8
DP  - 2004 Apr 21
TI  - Quantitative measurement of MLC leaf displacements using an electronic portal 
      image device.
PG  - 1521-33
AB  - The success of an IMRT treatment relies on the positioning accuracy of the MLC 
      (multileaf collimator) leaves for both step-and-shoot and dynamic deliveries. In 
      practice, however, there exists no effective and quantitative means for routine 
      MLC QA and this has become one of the bottleneck problems in IMRT implementation. 
      In this work we present an electronic portal image device (EPID) based method for 
      fast and accurate measurement of MLC leaf positions at arbitrary locations within 
      the 40 cm x 40 cm radiation field. The new technique utilizes the fact that the 
      integral signal in a small region of interest (ROI) is a sensitive and reliable 
      indicator of the leaf displacement. In this approach, the integral signal at a 
      ROI was expressed as a weighted sum of the contributions from the displacements 
      of the leaf above the point and the adjacent leaves. The weighting factors or 
      linear coefficients of the system equations were determined by fitting the 
      integral signal data for a group of pre-designed MLC leaf sequences to the known 
      leaf displacements that were intentionally introduced during the creation of the 
      leaf sequences. Once the calibration is done, the system can be used for routine 
      MLC leaf positioning QA to detect possible leaf errors. A series of tests was 
      carried out to examine the functionality and accuracy of the technique. Our 
      results show that the proposed technique is potentially superior to the 
      conventional edge-detecting approach in two aspects: (i) it deals with the 
      problem in a systematic approach and allows us to take into account the influence 
      of the adjacent MLC leaves effectively; and (ii) it may improve the 
      signal-to-noise ratio and is thus capable of quantitatively measuring extremely 
      small leaf positional displacements. Our results indicate that the technique can 
      detect a leaf positional error as small as 0.1 mm at an arbitrary point within 
      the field in the absence of EPID set-up error and 0.3 mm when the uncertainty is 
      considered. Given its simplicity, efficiency and accuracy, we believe that the 
      technique is ideally suitable for routine MLC leaf positioning QA.
FAU - Yang, Yong
AU  - Yang Y
AD  - Department of Radiation Oncology, Stanford University School of Medicine, 
      Stanford, CA 94305-5304, USA.
FAU - Xing, Lei
AU  - Xing L
LA  - eng
PT  - Journal Article
PT  - Research Support, Non-U.S. Gov't
PL  - England
TA  - Phys Med Biol
JT  - Physics in medicine and biology
JID - 0401220
SB  - IM
MH  - Algorithms
MH  - Calibration
MH  - Film Dosimetry
MH  - Humans
MH  - Image Processing, Computer-Assisted
MH  - Particle Accelerators
MH  - Phantoms, Imaging
MH  - Photons
MH  - Radiotherapy Planning, Computer-Assisted
MH  - Radiotherapy, Conformal/*instrumentation/*methods
MH  - Reproducibility of Results
EDAT- 2004/05/22 05:00
MHDA- 2004/12/16 09:00
CRDT- 2004/05/22 05:00
PHST- 2004/05/22 05:00 [pubmed]
PHST- 2004/12/16 09:00 [medline]
PHST- 2004/05/22 05:00 [entrez]
AID - 10.1088/0031-9155/49/8/010 [doi]
PST - ppublish
SO  - Phys Med Biol. 2004 Apr 21;49(8):1521-33. doi: 10.1088/0031-9155/49/8/010.