Dartmouth Events

Abstract: While Cherenkov emission was discovered more than eighty years ago, the potential applications of imaging this during radiation therapy have just recently been explored. With approximately half of all cancer patients being treated by radiation at some point during their cancer management, there is a constant challenge to ensure optimal treatment efficiency is achieved with maximal tumor to normal tissue therapeutic ratio.  To achieve this, the treatment process as well as biological information affecting the treatment should ideally be effective and maximally informative. The value of Cherenkov emission imaging was examined here, primarily for visualization of treatment monitoring and then secondarily for Cherenkov-excited luminescence for tissue biochemical sensing within tissue.
        Through synchronized gating to the short radiation pulses of a linear accelerator (200Hz & 3 µs pulses), and applying a gated intensified camera for imaging, the Cherenkov radiation can be captured near video frame rates (30 frame per sec) with dim ambient room lighting.  This procedure, sometimes termed Cherenkoscopy, is readily visualized without affecting the normal process of external beam radiation therapy. With simulation, phantoms and clinical trial data, each application of Cherenkoscopy was examined: i) for treatment monitoring, ii) for patient position monitoring and motion tracking, and iii) for superficial dose imaging. The temporal dynamics of delivered radiation fields can easily be directly imaged on the patient’s surface. Image registration and edge detection of Cherenkov images were used to verify patient positioning during treatment. Inter-fraction setup accuracy and intra-fraction patient motion was detectable to better than 1 mm accuracy.
        Cherenkov emission in tissue opens up a new field of biochemical sensing within the tissue environment, using luminescent agents which can be activated by this light. In the first study of its kind with external beam irradiation, a dendritic platinum-based phosphor (PtG4) was used at micromolar concentrations (~5 µM) to generate Cherenkov-induced luminescent signals, which are sensitive to the partial pressure of oxygen. Both tomographic reconstruction methods and linear scanned imaging were investigated here to examine the limits of detection. Recovery of optical molecular distributions was shown in tissue phantoms and small animals, with high accuracy (~1 µM), high spatial resolution (~0.2 mm) and deep-tissue detectability (~2 cm for CELSI), indicating potentials for in vivo and clinical use. In summary, many of the physical and technological details of Cherenkov imaging and Cherenkov-excited emission imaging were specified in this study.