Author: Petr Bruza, Megan Clark, David J. Gladstone, Lesley A Jarvis, Allison Matous, Roman Vasyltsiv, Rongxiao Zhang 👨🔬
Affiliation: Dartmouth Health, Dartmouth College, Thayer School of Engineering, Dartmouth College, Dartmouth Cancer Center, University of Missouri 🌍
Purpose: On-patient dosimeters assist in clinical decision-making by measuring surface dose, but single-point measurements cannot monitor area-wide distributions and are misleading in high-gradient regions. This limitation is illustrated in breast radiotherapy with tangent-beam arrangements, where steep dose gradients and complex surface contours can increase contralateral breast dose and, consequently, increase the risk of secondary malignancy. Cherenkov imaging has been used to visualize extraneous dose, but cannot provide quantitative dosimetry. This work introduces a novel 2.5D surface dosimetry technique using a wide-area deformable scintillator array combined with Cherenkov imaging for regional dose monitoring in high-gradient areas.
Methods: A wide-area optical surface dosimetry technique was developed for photon radiotherapy using a deformable scintillator array. Scintillation linearity with dose for 6MV and 10MV photons was verified. Stereovision imaging was used to localize the array and correct for angle-dependent intensity variations, while a gated intensified CMOS camera captured optical emission during irradiation. A tangent field was delivered to an anthropomorphic chest phantom to test feasibility with complex geometry. The dosimetry technique was then translated to a patient receiving post-mastectomy radiotherapy with wide tangents where the cumulative surface dose was compared against 3 TLDs positioned along the central axis of the array.
Results: Scintillator intensity demonstrated linearity with dose (R²>0.999) and maintained minimal response deviation up to 40°. TLD measurements agreed within 5cGy of the scintillator-derived central dose profile. The system resolved dose gradients up to 150cGy/cm at the field edge and captured real-time surface dose distributions during treatment, revealing unexpected dose near the contralateral breast during supraclavicular irradiation.
Conclusion: This work presents a time-resolved 2D photon dosimetry method optimized for irregular surface geometry, enabling spatially-resolved dose measurements across non-uniform treatment regions. The system offers quantitative, high-resolution surface dose measurements as a solution for monitoring dose in high-gradient regions and sensitive structures during complex treatments.