(Sunday, 7/29/2018) 2:05 PM - 3:00 PM
Room: Karl Dean Ballroom B1
Purpose: Cherenkov light emission has been shown to correlate with ionizing radiation (IR) dose delivery. To test the feasibility of treatment verification, we acquired Cherenkov light images during radiation beam delivery to phantom material. Specifically, the treatment modality of matched photon and electron fields was tested, and an analysis method was developed to quickly quantify field spacing. This novel application can be used to detect field matching errors during treatment delivery.
Methods: Cherenkov light emission was captured using a PI-MAX4 intensified charge coupled device (ICCD) system (Princeton Instruments). A Varian Trilogy linear accelerator was operated at 6 / 18 MV photon and 6 / 16 MeV electron energies a rate of 600 MU/min to deliver an Anterior-Posterior beam to a 5 cm thick block phantom positioned at 100 cm SSD. Matched fields with known overlap/gap distances of 0, 2, 5, and 10 mm were delivered and then evaluated after Cherenkov image acquisition. A total of 100 MU was delivered to acquire 200 frames for each field. Composite images were created through median summation of frames and background subtraction. Image post-processing was performed with ImageJ. Field edges of interest were modeled by hyperbolic tangents and polynomial background functions. The point of highest slope of the hyperbolic tangent was used to identify the field boundary. The position of each field edge of interest was used to quantify the spacing between the two fields.
Results: Gap and overlap widths of 2 mm were readily detected, indicating the feasibility of real time detection of these errors in a clinical situation involving matched fields. Image analysis indicated an average discrepancy of < 0.5 mm for all matched fields.
Conclusion: Our study indicates that Cherenkov imaging can improve our ability to immediately recognize and account for millimeter-scale delivery and positioning errors.
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