Consistency analysis for the performance of planar detector systems used in advanced radiotherapy
Purpose: To evaluate the performance linked to the consistency of a-Si EPID and ion-chamber array detectors for dose verification in advanced radiotherapy.
Methods: Planar measurements were made for 250 patients using an array of ion chamber and a-Si EPID. For pre-treatment verification, the plans were generated on the phantom for re-calculation of doses. The γ-evaluation method with the criteria: dose-difference (DD) ≤ 3% and distance-to-agreement (DTA) ≤ 3 mm was used for the comparison of measurements. Also, the central axis (CAX) doses were measured using 0.125cc ion chamber and were compared with the central chamber of array and central pixel correlated dose value from EPID image. Two types of statistical approaches were applied for the analysis. Conventional statistics used analysis of variance (ANOVA) and unpaired t-test to evaluate the performance of the detectors. And statistical process control (SPC) was utilized to study the statistical variation for the measured data. Control charts (CC) based on an average , standard deviation ( ) and exponentially weighted moving averages (EWMA) were prepared. The capability index (Cpm) was determined as an indicator for the performance consistency of the two systems.
Results: Array and EPID measurements had the average gamma pass rates as 99.9% ± 0.15% and 98.9% ± 1.06% respectively. For the point doses, the 0.125cc chamber results were within 2.1% ± 0.5% of the central chamber of the array. Similarly, CAX doses from EPID and chamber matched within 1.5% ± 0.3%. The control charts showed that both the detectors were performing optimally and all the data points were within ± 5%. EWMA charts revealed that both the detectors had a slow drift along the mean of the processes but was found well within ± 3%. Further, higher Cpm values for EPID demonstrate its higher efficiency for radiotherapy techniques.
Conclusion: The performances of both the detectors were seen to be of high quality irrespective of the radiotherapy technique. Higher Cpm values for EPID indicate its higher efficiency than array.
Li XA, Wang JZ, Jursinic PA, et al. Dosimetric advantages of IMRT simultaneous integrated boost for high-risk prostate cancer. Int J Radiat Oncol Biol Phys 2005; 61:1251-7.
Cilla S, Macchia G, Digesù C, et al. 3D-Conformal versus intensity-modulated postoperative radiotherapy of vaginal vault: A dosimetric comparison. Med Dosim 2010; 35:135-42.
Bucci MK, Bevan A, Roach M 3rd. Advances in radiation therapy: conventional to 3D, to IMRT, to 4D, and beyond. CA Cancer J Clin 2005; 55:117-34.
Alvarez-Moret J, pohl F, Koeibl O, et al. Evaluation of Volumetric modulated arc therapy (VMAT) with Oncentra MasterPlan® for the treatment of head and neck cancer. Radiat Oncol 2010; 5:110.
Chao KS, Majhail N, Huang CJ, et al. Intensity-modulated radiation therapy reduces late salivary toxicity without compromising tumor control in patients with oropharyngeal carcinoma: a comparison with conventional techniques. Radiother Oncol 2010; 61:275-80.
Webb S. Intensity-modulated Radiation Therapy. IOP publication, 2002
Otto K. Volumetric modulated arc therapy: IMRT in a single gantry arc. Med Phys 2008; 35: 310-7.
Teoh M, Clark CH, Wood K, et al. Volumetric modulated arc therapy: a review of current literature and clinical use in practice. Br J Radiol 2011; 84: 967-96.
Galvin JM, Ezzell G, Eisbrauch A, et al. Implementing IMRT in clinical practice: a joint document of the American Society for Therapeutic Radiology and Oncology and the American Association of Physicists in Medicine. Int J Radiat Oncol Biol Phys 2004; 58:1616-34.
Van Dyk J, Purdy J. Clinical implementation of technology and the quality assurance process; in The Modern Technology of Radiation Oncology. Medical Physics, Madison WI, 1999.
Low DA, Moran JM, Dempsey JF, et al. Dosimetry tools and techniques for IMRT. Med Phys 2011; 38:1313-37.
Low DA, Harms WB, Sasa M, Purdy JA. A technique for the quantitative evaluation of dose distributions. Med Phys 1998; 25:1919-27.
Depuydt T, Van Esch A, Huyskens DP. A quantative evaluation of IMRT dose distributions: refinement and clinical assessment of the gamma evaluation. Radiother Oncol 2002; 62:309-19.
Pawlicki T, Whitaker M, Boyer AL. Statistical process control for radiotherapy quality assurances. Med Phys 2005; 32:2777-86.
Pawlicki T, Yoo S, Court LE, et al. Moving from IMRT QA measurements toward independent computer calculations using control charts. Radiother Oncol 2008; 89:330-7.
Gerad K, Grandhaye JP, Marchesi V, et al. A comprehensive analysis of the IMRT dose delivery process control (SPC). Med Phys 2009; 36:1275-85.
Breen Sl, Moseley DJ, Zhang B, et al. Statistical process control for IMRT dosimetric verification. Med Phys 2008; 35:4417-25.
Thomadsen BR, Dunscombe P, Ford E, et al. Quality and Safety in Radiotherapy: Learning the New Approaches in Task Group 100 and Beyond, AAPM Monograph #36, Medical Physics Publication, 2013.
Gagneur JD, Ezzell GA. An improvement in IMRT QA results and beam matching in linacs using statistical process control. J Appl Clin Med Phys 2014; 15:4927.
Acquah GF, Gustavsson M, Doudoo CO, et al. Clinical use of electronic portal imaging to analyze tumor motion variation during a 3D-conformal prostate cancer radiotherapy using online target verification and implanted markers. Int J Cancer Ther Oncol 2014; 2:02044.
Stanley DN, Papanikolaou N, Gutierrez AN. An evaluation of the stability of image quality parameters of Varian on-board imaging (OBI) and EPID imaging systems. Int J Cancer Ther Oncol 2014; 2:020236.
Howell RM, Smith IP, Jarrio CS. Establishing action levels for EPID-based QA for IMRT. J Appl Clin Med Phys 2008; 9:2721.
Rout BK, Shekar MC, Kumar A, Ramesh KKD. Quality control test for electronic portal imaging device using QC-3 phantom with PIPSpro. Int J Cancer Ther Oncol 2014; 2:02049.
Jassal K, Munshi A, Sarkar B, et al. Validation of an integrated patient positioning system: Exactrac and iViewGT on Synergy Platform. Int J Cancer Ther Oncol 2014; 2:020212.
Kawrakow I, Fippel M, Friedrich K. 3D electron dose calculation using a Voxel based Monte Carlo algorithm (VMC). Med Phys 1996; 23:445-57.
Fippel M, Laub W, Huber B, Nüsslin F. Experimental investigation of a fast Monte Carlo photon beam dose calculation algorithm. Phys Med Biol 1999; 44:3039-54.
Jarque CM, Bera AK. A Test for Normality of Observations and Regression Residuals. International Statistical Review 1987; 55: 163-72.
Kothari CR, Research Methodology: Methods and Techniques; Wiley Eastern Limited, New Delhi, 2006.
Wheeler DJ, Chambers D S, Understanding Statistical Process Control, 2nd edition; Knoxville SPC press, 1992.
Montgomery DC. Introduction to Statistical Quality Control; Wiley, New York, 2004
Lucas JM, Saccucci MS. Exponentially weighted moving averages control schemes: Properties and enhancements. Technometrics 1990; 32:1-29.
Chan LK, Cheng SW, Spiring FA. A new measure of process capability: Cpm. Journal of Quality Technology 1988; 20:162-75.
Pillet M, Rochon S, Duclos E. SPC- Generalization of capability index Cpm: Case of unilateral tolerances. Quality Engineering 1997; 10: 171-6.
Taguchi G, Elsayed A. E and Hsiang T. Quality Engineering in production systems, McGraw Hill, New York, 1989.
Van Esch A, Depuydt T, Huyskens DP. The use of an aSi-based EPID for routine absolute dosimetric pre-treatment verification of dynamic IMRT fields. Radiother Oncol 2004; 71:223-34.
McDermott LN, Wendling M, van Asselen B, et al. Clinical experience with EPID dosimetry for prostate IMRT pre-treatment dose verification. Med Phys 2006; 33:3921-30.
van Zijtveld M, Dirkx MLP, de Boer HC, Heijmen BJ. Dosimetric pre-treatment verification of IMRT using an EPID; clinical experience. Radiother Oncol 2006; 81:168-75.
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