Program Information
Using CBCT Projections to Triage Head and Neck Patients for Adaptive Radiation Therapy
B Winey*, J Kim , G Sharp , Massachusetts General Hospital and Harvard Medical School, Boston, MA
Presentations
SU-I-GPD-J-55 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To develop a rapid workflow that utilizes CBCT projections to triage head and neck (H&N) patients for adaptive radiation therapy workflow.
Methods: CBCT images require processing to reduce scatter effects to obtain an image useful for dose calculations but the anatomic variations observed in H&N patient populations might be visible in the projections. Raw CBCT projections of H&N patients, sampled on average every week, were acquired during patient positioning scans. The first CBCT was assumed to be the baseline for future comparisons. The images were cropped and renormalized to focus on the neck where the anatomic variation of H&N patients is often visualized. The differences between the projections of the first scan and subsequent scans were analyzed using histograms, raw intensities, localized standard deviation, local difference variation, and entropy.
Results: The sum of the raw intensities in the difference images was found to be most sensitive to the anatomic variations at the edge of the patient volume. Figure 1 displays the histograms, the projection images, and the metric evaluations. Figure 2 displays the sum of the intensity differences versus projection angle for two fractions, one near the beginning of treatment and one near the conclusion of treatment. The effects of the missing tissue can be visualized in the systematic decrease of the signal from fraction 24, circled in figure 1.
Conclusion: CBCT projections potentially capture anatomic variations of head and neck patients and can be used to quickly triage patients for adaptive radiation therapy.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the NCI Federal Share of program income earned by Massachusetts General Hospital on C06 CA059267, Proton Therapy Research and Treatment Center.
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