Room: AAPM ePoster Library
In radiation therapy, stage 2A Breast Cancer or later involves use of two irradiation fields to accommodating the irradiation of the nodes. These fields meet at the isocenter, forming what is known as the field junction. Even small movements from patient breathing or slight inherent setup uncertainties can manifest as dose-related hot or cold spots at the field junction. Insufficient coverage (cold spots) at the field match can lead to recurrence, and over treating (hot spots) in treatment offer increased risk to healthy tissues if the region of high dose were to migrate out of the PTV.
A controlled study was conducted using identical square fields on an ABS board, and changes in match area were quantified with respect to increased separation/overlap between fields. An anthropomorphic phantom was irradiated using a plan adapted from a patient treated in the clinic, and the techniques developed were then applied to a patient. This patient was imaged using a time-gated intensified CMOS camera (C-Dose Research, DoseOptics LLC, Lebanon, NH) in this IRB-approved, non-clinical trial passive imaging study. All fields were deconvolved using the PSF, 2D Gaussian fit from the LSF.
By applying a threshold to image processed Cherenkov images, the region of field match can be isolated automatically, using an automated bounding feature extraction in MATLAB. The integral from the extracted profiles from these regions were compared over 10 mm of separation to 10 mm of overlap in each of two phantom cases (ABS phantom R² = 0.99, Anthropomorphic phantom R² = 0.86). Profiles from patient imaging sessions were then evaluated similarly and evaluated for consistency.
This technique described provides a method for automated match finding and was shown to be very sensitive to change and could prove instrumental in assessing separation/overlap in the region of field match.
Funding Support, Disclosures, and Conflict of Interest: Authors Prof. Brian Pogue and Dr. Lesley Jarvis M.D. have competing interests with DoseOptics LLC, a company that manufactures Cherenkov cameras used to monitor radiation therapy. This study utilizes cameras on loan from DoseOptics and was not otherwise financially supported by DoseOptics.
Optical Imaging, Treatment Verification, Quality Control
TH- External Beam- Photons: Motion management - interfraction