Journal of Medical Physics
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Year : 2010  |  Volume : 35  |  Issue : 3  |  Page : 144-150

Optimized point dose measurement for monitor unit verification in intensity modulated radiation therapy using 6 MV photons by three different methodologies with different detector-phantom combinations: A comparative study

1 Department of Radiation Oncology and Medical Physics, Advanced Medicare and Research Institute (AMRI) Cancer Centre, Advanced Medicare and Research Institute (AMRI) Hospitals, Kolkata, India
2 Centre of Applied Mathematics and Computational Sciences, Saha Institute of Nuclear Physics, Kolkata, India

Correspondence Address:
Biplab Sarkar
Department of Medical Physics, AMRI Hospitals, 15 Panchanantala Road, Kolkata- 700 029
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-6203.62129

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The study was aimed to compare accuracy of monitor unit verification in intensity modulated radiation therapy (IMRT) using 6 MV photons by three different methodologies with different detector phantom combinations. Sixty patients were randomly chosen. Zero degree couch and gantry angle plans were generated in a plastic universal IMRT verification phantom and 30Χ30Χ30 cc water phantom and measured using 0.125 cc and 0.6 cc chambers, respectively. Actual gantry and couch angle plans were also measured in water phantom using 0.6 cc chamber. A suitable point of measurement was chosen from the beam profile for each field. When the zero-degree gantry, couch angle plans and actual gantry, couch angle plans were measured by 0.6 cc chamber in water phantom, the percentage mean difference (MD) was 1.35%, 2.94 % and Standard Deviation (SD) was 2.99%, 5.22%, respectively. The plastic phantom measurements with 0.125 cc chamber Semiflex ionisation chamber (SIC) showed an MD=4.21% and SD=2.73 %, but when corrected for chamber-medium response, they showed an improvement, with MD=3.38 % and SD=2.59 %. It was found that measurements with water phantom and 0.6cc chamber at gantry angle zero degree showed better conformity than other measurements of medium-detector combinations. Correction in plastic phantom measurement improved the result only marginally, and actual gantry angle measurement in a flat- water phantom showed higher deviation.

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