Quality assurance| Volume 89, ISSUE 3, P330-337, December 2008

Download started.


Moving from IMRT QA measurements toward independent computer calculations using control charts


      Background and purpose

      In this study, we investigated IMRT QA using Statistical Process Control for the purpose of comparing the processes of patient-specific measurements and the corresponding independent computer calculations.

      Materials and methods

      Point dose data from the treatment planning system (TPS), independent computer calculations, and physical measurements for prostate and head and neck cases were studied. Control charts were used to analyze the IMRT QA processes from several institutions in the academic and community setting. Control charts are a method to describe the performance of a process. The width of the control chart limits (or action limits) describes the process’ ability to meet clinical specifications of ±5%. In all, 24 process comparisons were made (12 measurement QA and 12 independent computer calculation QA).


      For head and neck IMRT QA, the average process ability for the measurement QA was ±6.9% compared to ±7.2% for the independent computer calculation QA. For prostate IMRT QA, the average process ability was 4.4% for both measurement QA and independent computer calculation QA. It was found that 11 of the 24 processes were in control. At none of the institutions were the processes of measurements and independent computer calculations both in control and performing within clinical specifications.


      There is room to improve the processes of IMRT QA measurements and independent computer calculations. In situations where the improvement of the processes is such that each is in control and well within clinical specifications, it may be appropriate to suspend patient-specific IMRT QA measurements for every patient in the place of independent computer calculations.


      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to Radiotherapy and Oncology
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Basran P.S.
        • Woo M.K.
        An analysis of tolerance levels in IMRT quality assurance procedures.
        Med Phys. 2008; 35: 2300-2307
        • Boehmer D.
        • Bohsung J.
        • Eichwurzel I.
        • Moys A.
        • Budach V.
        Clinical and physical quality assurance for intensity modulated radiotherapy of prostate cancer.
        Radiother Oncol. 2004; 71: 319-325
      1. Breen S, Moseley D, Sharpe M. Process control for IMRT dosimetry. In: XVth international conference on the use of computers in radiation therapy. Toronto, Canada: Novel Digital Publishing, Oakville, Ontario; 2007. p. 318–22.

        • Georg D.
        • Nyholm T.
        • Olofsson J.
        • et al.
        Clinical evaluation of monitor unit software and the application of action levels.
        Radiother Oncol. 2007; 85: 306-315
        • Linthout N.
        • Verellen D.
        • Van Acker S.
        • Storme G.
        A simple theoretical verification of monitor unit calculation for intensity modulated beams using dynamic mini-multileaf collimation.
        Radiother Oncol. 2004; 71: 235-241
        • Liu G.
        • Fernando W.
        • Grace M.
        • Rykers K.
        An IMRT dose distribution study using commercial verification software.
        Australas Phys Eng Sci Med. 2004; 27: 129-135
        • Miles E.A.
        • Clark C.H.
        • Bidmead M.
        • et al.
        The impact of introducing intensity modulated radiotherapy into routine clinical practice.
        Radiother Oncol. 2005; 77: 241-246
        • Pawlicki T.
        • Whitaker M.
        • Boyer A.L.
        Statistical process control for radiotherapy quality assurance.
        Med Phys. 2005; 32: 2777-2786
        • Wheeler D.J.
        • Chambers D.S.
        Understanding statistical process control.
        SPC Press, Knoxville1992
        • Xing L.
        • Li J.G.
        Computer verification of fluence map for intensity modulated radiation therapy.
        Med Phys. 2000; 27: 2084-2092
        • Yang Y.
        • Xing L.
        • Li J.G.
        • et al.
        Independent dosimetric calculation with inclusion of head scatter and MLC transmission for IMRT.
        Med Phys. 2003; 30: 2937-2947
        • Zhu J.
        • Yin F.F.
        • Kim J.H.
        Point dose verification for intensity modulated radiosurgery using Clarkson’s method.
        Med Phys. 2003; 30: 2218-2221