Author: Petr Bruza, Megan Clark, David J. Gladstone, Lesley A Jarvis, Allison Matous 👨🔬
Affiliation: Thayer School of Engineering, Dartmouth College, Dartmouth Cancer Center, Dartmouth Health 🌍
Purpose: In vivo dosimetry (IVD) is underutilized, in part, because measured point doses cannot be accurately localized to the patient or treatment planning system (TPS), complicating the clinical and root-cause interpretation of unexpected doses—whether from the treatment plan, improper setup, or choice of measurement point. While clinical Cherenkov imaging provides relative visualization of dose deposition, IVD can be achieved through imaging a scintillator placed in the treatment field. This work demonstrates the first optical correlation of IVD measurements with the treatment plan and implements this technique in an ongoing clinical trial to quantify contralateral breast dose (CBD).
Methods: The intrinsic and extrinsic characteristics of a Cherenkov imaging system (DoseOptics, LLC) were harnessed to correlate the 2D images with 3D world coordinates. Treatment plan dose predictions were exported from Eclipse, sampled from 0-5 mm at the surface, and transformed into camera point-of-view 2D image coordinates. Surface doses from thermoluminescent dosimeters (TLDs) and scintillation imaging were validated against the 2D projected treatment plan using phantom measurements. This technique was tested for patients with CBD identified via Cherenkov imaging, where a scintillator and TLD were placed on the contralateral breast during subsequent treatment factions for dose measurement.
Results: In phantoms, scintillation imaging agreed within 4±2 cGy of TLDs and 2±1 cGy of the TPS. The rate of unintended CBD in patients receiving breast radiation was identified to be ~25%. In an example patient case, CBD was predicted to be 50±15 cGy in the TPS but measured as high as 140±5 cGy with TLDs and 96±5 cGy with scintillation imaging.
Conclusion: The ability to directly compare measured with planned doses has the potential to change the field of IVD. We show that spatially-calibrated Cherenkov imaging can be combined with scintillator placement for incident detection, dosimetry, and direct comparison to planned dose estimates.