Confidence limit variation for a single IMRT system following the TG119 protocol

J. D. Gordon, S. P. Krafft, S. Jang, L. Smith-Raymond, M. Y. Stevie, R. J. Hamilton

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Purpose: To evaluate the robustness of TG119-based quality assurance metrics for an IMRT system. Methods: Four planners constructed treatment plans for the five IMRT test cases described in TG119. All plans were delivered to a 30 cm×30 cm×15 cm solid water phantom in one treatment session in order to minimize session-dependent variation from phantom setup, film quality, machine performance, etc. Composite measurements utilized film and an ionization chamber. Per-field measurements were collected using a diode array device at an effective depth of 5 cm. All data collected were analyzed using the TG119 specifications to determine the confidence limit values for each planner separately and then compared. Results: The mean variance of ion chamber measurements for each planner was within 1.7% of the planned dose. The resulting confidence limits were 3.13%, 1.98%, 3.65%, and 4.39%. Confidence limit values determined by composite film analysis were 8.06%, 13.4%, 9.30%, and 16.5%. Confidence limits from per-field measurements were 1.55%, 0.00%, 0.00%, and 2.89%. Conclusions: For a single IMRT system, the accuracy assessment provided by TG119-based quality assurance metrics showed significant variations in the confidence limits between planners across all composite and per-field evaluations. This observed variation is likely due to the different levels of modulation between each planner's set of plans. Performing the TG119 evaluation using plans produced by a single planner may not provide an adequate estimation of IMRT system accuracy.

Original languageEnglish (US)
Pages (from-to)1641-1648
Number of pages8
JournalMedical physics
Issue number3
StatePublished - Mar 2011


  • IMRT
  • commissioning
  • quality assurance

ASJC Scopus subject areas

  • Biophysics
  • Radiology Nuclear Medicine and imaging


Dive into the research topics of 'Confidence limit variation for a single IMRT system following the TG119 protocol'. Together they form a unique fingerprint.

Cite this