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Linear Accelerator Pulse-Synchronized Imaging of Scintillator Emission for Patient Surface Dosimetry

I Tendler1*, P Bruza1 , J Andreozzi1 , B Williams2,3 , L Jarvis2,3 , D Gladstone1,2,3 , B Pogue1,2 , (1) Thayer School of Engineering, Dartmouth College, Hanover NH (2) Department of Medicine, Geisel School of Medicine, Dartmouth College, Hanover NH (3)Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center, Lebanon NH

Presentations

(Saturday, 4/7/2018) 10:30 AM - 12:30 PM

Room: Marquis Ballroom 5-8

Purpose: To develop a novel, scintillator-based, imaging system for surface dosimetry in total skin electron therapy (TSET). Using a camera synchronized to linear accelerator (linac) pulses, simultaneous scintillation and Cherenkov imaging provide quantitative dosimetry measured remotely in real-time.

Methods: During treatment, surface optical images were obtained using an intensified, time-gated, camera synchronized to linac pulses located inside the linac vault. Square (2cm² x 1mm thick) and disc-shaped (1cm Ø x 1mm thick) EJ-212 (Elijen Technology) scintillators were calibrated and then attached to both the patient and TSET patient stand. Patients were positioned according to the modified Stanford technique and received TSET with a Varian Trilogy linac. Thermoluminescent dosimeters (TLDs) were placed adjacent to scintillators on the patient to obtain an absolute dose reference. Patient images were summed over the course of each TSET position, background subtracted, and converted to absolute dose values. Doses read from Cherenkov emission and scintillator signals were related to those reported by TLDs.

Results: The time-gated camera system consistently provided data sufficient to generate intensity maps of scintillator light output and Cherenkov emission. For two patients undergoing TSET, cumulative images and TLD measurements were collected during two therapy sessions. Images show that the Cherenkov emission was not spatially uniform across the skin surface of patients – arms and legs exhibit less light compared to the torso area due primarily to variations in tissue optical properties. Signal from larger surface area square scintillators yielded greater pixel intensities; this signal was proportional to both dose and pixel intensities from the disc-shaped scintillators.

Conclusion: Absolute surface dosimetry can be achieved with an accuracy of <5% of total dose by calibrating a camera system to scintillator targets. Remote imaging of both patient Cherenkov emission and dosimeter scintillation has the potential to provide real-time absolute surface dosimetry for patients undergoing TSET.

Funding Support, Disclosures, and Conflict of Interest: This work has been sponsored by NIH research grants R44 CA199836, R01 EB023909 and used Shared Resources from the Norris Cotton Cancer Center core facilities, sponsored by P30 CA023106. P.Bruza is principal investigator in SBIR subaward B02463 (prime award NCI R44CA199681, DoseOptics LLC). B.Pogue is a president of DoseOptics LLC.

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