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Title: Statistical process control for IMRT dosimetric verification

Abstract

Patient-specific measurements are typically used to validate the dosimetry of intensity-modulated radiotherapy (IMRT). To evaluate the dosimetric performance over time of our IMRT process, we have used statistical process control (SPC) concepts to analyze the measurements from 330 head and neck (H and N) treatment plans. The objectives of the present work are to: (i) Review the dosimetric measurements of a large series of consecutive head and neck treatment plans to better understand appropriate dosimetric tolerances; (ii) analyze the results with SPC to develop action levels for measured discrepancies; (iii) develop estimates for the number of measurements that are required to describe IMRT dosimetry in the clinical setting; and (iv) evaluate with SPC a new beam model in our planning system. H and N IMRT cases were planned with the PINNACLE{sup 3} treatment planning system versions 6.2b or 7.6c (Philips Medical Systems, Madison, WI) and treated on Varian (Palo Alto, CA) or Elekta (Crawley, UK) linacs. As part of regular quality assurance, plans were recalculated on a 20-cm-diam cylindrical phantom, and ion chamber measurements were made in high-dose volumes (the PTV with highest dose) and in low-dose volumes (spinal cord organ-at-risk, OR). Differences between the planned and measured doses weremore » recorded as a percentage of the planned dose. Differences were stable over time. Measurements with PINNACLE{sup 3} 6.2b and Varian linacs showed a mean difference of 0.6% for PTVs (n=149, range, -4.3% to 6.6%), while OR measurements showed a larger systematic discrepancy (mean 4.5%, range -4.5% to 16.3%) that was due to well-known limitations of the MLC model in the earlier version of the planning system. Measurements with PINNACLE{sup 3} 7.6c and Varian linacs demonstrated a mean difference of 0.2% for PTVs (n=160, range, -3.0%, to 5.0%) and -1.0% for ORs (range -5.8% to 4.4%). The capability index (ratio of specification range to range of the data) was 1.3 for the PTV data, indicating that almost all measurements were within {+-}5%. We have used SPC tools to evaluate a new beam model in our planning system to produce a systematic difference of -0.6% for PTVs and 0.4% for ORs, although the number of measurements is smaller (n=25). Analysis of this large series of H and N IMRT measurements demonstrated that our IMRT dosimetry was stable over time and within accepted tolerances. These data provide useful information for assessing alterations to beam models in the planning system. IMRT is enhanced by the addition of statistical process control to traditional quality control procedures.« less

Authors:
; ; ;  [1]
  1. Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9 (Canada) and Department of Radiation Oncology, Faculty of Medicine, University of Toronto, FitzGerald Building, 150 College Street, Toronto, Ontario M5S 3E2 (Canada)
Publication Date:
OSTI Identifier:
22095214
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 35; Journal Issue: 10; Other Information: (c) 2008 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; 61 RADIATION PROTECTION AND DOSIMETRY; DOSIMETRY; HEAD; IONIZATION CHAMBERS; LINEAR ACCELERATORS; NECK; PHANTOMS; PROCESS CONTROL; QUALITY ASSURANCE; QUALITY CONTROL; RADIATION DOSES; RADIOTHERAPY; SPINAL CORD; VERIFICATION; EXTERNAL BEAM RADIATION THERAPY

Citation Formats

Breen, Stephen L., Moseley, Douglas J., Zhang, Beibei, Sharpe, Michael B., Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, and Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9. Statistical process control for IMRT dosimetric verification. United States: N. p., 2008. Web. doi:10.1118/1.2975144.
Breen, Stephen L., Moseley, Douglas J., Zhang, Beibei, Sharpe, Michael B., Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, & Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9. Statistical process control for IMRT dosimetric verification. United States. https://doi.org/10.1118/1.2975144
Breen, Stephen L., Moseley, Douglas J., Zhang, Beibei, Sharpe, Michael B., Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9, and Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9. 2008. "Statistical process control for IMRT dosimetric verification". United States. https://doi.org/10.1118/1.2975144.
@article{osti_22095214,
title = {Statistical process control for IMRT dosimetric verification},
author = {Breen, Stephen L. and Moseley, Douglas J. and Zhang, Beibei and Sharpe, Michael B. and Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9 and Radiation Physics Department, Princess Margaret Hospital, 610 University Avenue, Toronto, Ontario M5G 2M9},
abstractNote = {Patient-specific measurements are typically used to validate the dosimetry of intensity-modulated radiotherapy (IMRT). To evaluate the dosimetric performance over time of our IMRT process, we have used statistical process control (SPC) concepts to analyze the measurements from 330 head and neck (H and N) treatment plans. The objectives of the present work are to: (i) Review the dosimetric measurements of a large series of consecutive head and neck treatment plans to better understand appropriate dosimetric tolerances; (ii) analyze the results with SPC to develop action levels for measured discrepancies; (iii) develop estimates for the number of measurements that are required to describe IMRT dosimetry in the clinical setting; and (iv) evaluate with SPC a new beam model in our planning system. H and N IMRT cases were planned with the PINNACLE{sup 3} treatment planning system versions 6.2b or 7.6c (Philips Medical Systems, Madison, WI) and treated on Varian (Palo Alto, CA) or Elekta (Crawley, UK) linacs. As part of regular quality assurance, plans were recalculated on a 20-cm-diam cylindrical phantom, and ion chamber measurements were made in high-dose volumes (the PTV with highest dose) and in low-dose volumes (spinal cord organ-at-risk, OR). Differences between the planned and measured doses were recorded as a percentage of the planned dose. Differences were stable over time. Measurements with PINNACLE{sup 3} 6.2b and Varian linacs showed a mean difference of 0.6% for PTVs (n=149, range, -4.3% to 6.6%), while OR measurements showed a larger systematic discrepancy (mean 4.5%, range -4.5% to 16.3%) that was due to well-known limitations of the MLC model in the earlier version of the planning system. Measurements with PINNACLE{sup 3} 7.6c and Varian linacs demonstrated a mean difference of 0.2% for PTVs (n=160, range, -3.0%, to 5.0%) and -1.0% for ORs (range -5.8% to 4.4%). The capability index (ratio of specification range to range of the data) was 1.3 for the PTV data, indicating that almost all measurements were within {+-}5%. We have used SPC tools to evaluate a new beam model in our planning system to produce a systematic difference of -0.6% for PTVs and 0.4% for ORs, although the number of measurements is smaller (n=25). Analysis of this large series of H and N IMRT measurements demonstrated that our IMRT dosimetry was stable over time and within accepted tolerances. These data provide useful information for assessing alterations to beam models in the planning system. IMRT is enhanced by the addition of statistical process control to traditional quality control procedures.},
doi = {10.1118/1.2975144},
url = {https://www.osti.gov/biblio/22095214}, journal = {Medical Physics},
issn = {0094-2405},
number = 10,
volume = 35,
place = {United States},
year = {Wed Oct 15 00:00:00 EDT 2008},
month = {Wed Oct 15 00:00:00 EDT 2008}
}