Author: Petr Bruza, David J. Gladstone, Lesley A Jarvis, Natasha Mulenga, Kevin J. Willy 👨🔬
Affiliation: Thayer School of Engineering, Dartmouth College, Dartmouth Cancer Center 🌍
Purpose: The goal of this work was to use Cherenkov emission imaging to verify patient position, accessory block positioning and dose delivery in Total Skin Electron Therapy (TSET).
Methods: A gated, intensified CMOS camera was used to image Cherenkov emission from 3 patients receiving either 12 or 16 fractions of TSET using the Stanford 6-field technique with 6MeV electron beams. Dose measurements were obtained using a diode positioned at each patient's umbilicus or thermoluminescent dosimeters (TLDs) placed on various locations on patients: forearm, chest, umbilicus, and thigh. Cumulative Cherenkov intensity was measured in consistent regions of interest near the dosimeter placements, with measurements collected for left anterior oblique (LAO), right anterior oblique (RAO), and anterior-posterior (AP) positions. The correlation between Cherenkov intensity and dose was analyzed for each patient position.
Results: Cherenkov imaging identified non-ideal block positioning in one patient during 2 of their 12 treatment days (16.7%), leading to inadequate facial shielding that was subsequently corrected. Dose measurements at the umbilicus for each position varied by approximately 50-55% between patients with ranges from 27-42 cGy for oblique positions and 40-60 cGy for the anterior position, primarily due to variations in patient positioning within the beam. Dose variations were observed across different body areas (e.g., 40 cGy for arm vs. 60 cGy for chest), attributable to the inherent lack of field homogeneity and patient positioning variations. The relationship between Cherenkov intensity and measured dose showed variation between patients and across different body locations, with anatomical location appearing to be the more dominant factor. Arms consistently showed lower doses than thighs, but similar intensity, likely due to differences in optical properties between anatomical locations.
Conclusion: Cherenkov intensity correlated with variation in dose delivered to individual patients. Treatment consistency may therefore be verified through routine monitoring of Cherenkov image intensity.