Using Cherenkov Imaging to Verify Anterior Field Match Lines between Supraclavicular and Tangent Whole Breast Irradiation Fields

Abstract

In radiation therapy, stage 2A Breast Cancer or later (which include the treatment of the axillary nodes) involves use of two irradiation fields: the entirety of the breast (tangent fields) and the supraclavicular (SCLV) fields for the irradiation of the nodes. These fields meet at the isocenter, which is placed at the superior edge of the tangent field and at the inferior edge of the supraclavicular field, 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 field match study was conducted using identical square fields on a white 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, fit from the ESF. By applying a threshold to multiplied Cherenkov images, the region of field match can be isolated automatically, using an automated bounding feature extraction in a computer algorithm. 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 developing technique employs 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.