An Off-Line QA Tool for Evaluating Reproducibility of Deep Inhalation Breath-Hold Treatment for Breast Radiotherapy
W Yang*, Y Yue, A Mirhadi, B Hakimian, M Burnison, R Tuli, H Sandler, B Fraass, Cedars-Sinai Medical Center, Los Angeles, CASU-E-J-151 Sunday 3:00PM - 6:00PM Room: Exhibit Hall
Purpose: To develop an off-line QA tool for evaluating reproducibility of deep inhalation breath hold (DIBH) breast treatment using a spirometer-based breathing control system with video guidance.
Methods:Tangential beam plans (open medial field; lateral IMRT field) used for whole breast radiation with DIBH-guided by a spirometer-based breathing control system have been studied. An imaging sequence was set-up at the treatment machine to acquire multiple (>15) EPID image frames during beam-on with source-to-imager distance 150cm. Images were exported from the EPID and imported into an off-line QA tool developed in-house for evaluation of intra- and inter-fractional uncertainties for DIBH treatments. The user defines a region of interest (ROI) (e.g., expander, clip(s), chestwall) on the first (reference) image. A rectangular imaging template is created from the ROI with a defined expansion (e.g., 1cm). The template is then matched to each of the following image frames using cross-correlation. Template movement is used to estimate breast motion during one or multiple breath-hold sessions. The breath-hold lung volume information is extracted from the spirometer and compared to the corresponding motion curve estimated from the EPID images.
Results:Motions of different regions of the breast can be visualized and shown to be constant within 1mm at the imager (~.7mm in the breast) for some patients. Both drifting and random motions can be identified on individual patients on specific days. Off-line analysis of these data may provide a useful tool to assure that individual patients are adequately performing the DIBH technique, and to identify patients who require new margins or planning strategies.
Conclusion:An off-line QA motion evaluation tool has been designed for DIBH breast treatment, and is an effective method for evaluation of DIBH reproducibility both intra- and inter-fraction.