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Evaluation of the precision of portal‐image‐guided head‐and‐neck localization: An intra‐ and interobserver study
Author(s) -
Court Laurence E.,
Allen Aaron,
Tishler Roy
Publication year - 2007
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2747050
Subject(s) - isocenter , medicine , head and neck cancer , head and neck , radiation therapy , nuclear medicine , digital radiography , image guided radiation therapy , radiology , radiography , surgery
There is increasing evidence that, for some patients, image‐guided intensity‐modulated radiation therapy (IMRT) for head‐and‐neck cancer patients may maintain target dose coverage and critical organ (e.g., parotids) dose closer to the planned doses than setup using lasers alone. We investigated inter‐ and intraobserver uncertainties in patient setup in head‐and‐neck cancer patients. Twenty‐two sets of orthogonal digital portal images (from five patients) were selected from images used for daily localization of head‐and‐neck patients treated with IMRT. To evaluate interobserver variations, five radiation therapists compared the portal images with the plan digitally reconstructed radiographs and reported shifts for the isocenter ( ∼ C 2 ) and for a supraclavicular reference point. One therapist repeated the procedure a month later to evaluate intraobserver variations. The procedure was then repeated with teams of two therapists. The frequencies for which agreement between the shift reported by the observer and the daily mean shift (average of all observers for a given image set) were less than 1.5 and 2.5 mm were calculated. Standard errors of measurement for the intra‐ and interobserver uncertainty ( SEM intraandSEM inter ) for the individual and teams were calculated. The data showed that there was very little difference between individual therapists and teams. At isocenter, 80%–90% of all reported shifts agreed with the daily average within 1.5 mm , showing consistency in the ways both individuals and teams interpret the images ( SEM inter ∼ 1 mm ) . This dropped to 65% for the supraclavicular point ( SEM inter ∼ 1.5 mm ) . Uncertainties increased for larger setup errors. In conclusion, image‐guided patient positioning allows head‐and‐neck patients to be controlled within 3 – 4 mm . This is similar to the setup uncertainties found for most head‐and‐neck patients, but may provide some improvement for the subset of patients with larger setup uncertainties.