Performance comparison of quantitative metrics for analysis of in vivo Cherenkov imaging incident detection during radiotherapy

Abstract

Objectives: Examine the responses of multiple image similarity metrics to detect patient positioning errors in radiotherapy observed through Cherenkov imaging, which may be used to optimize automated incident detection. Methods: An anthropomorphic phantom mimicking patient vasculature, a biological marker seen in Cherenkov images, was simulated for a breast radiotherapy treatment. The phantom was systematically shifted in each translational direction, and Cherenkov images were captured during treatment delivery at each step. The responses of mutual information (MI) and the γ passing rate (%GP) were compared to that of existing field shape matching image metrics, the Dice coefficient and mean distance to conformity (MDC). Patient images containing other incidents were analyzed to verify the best detection algorithm for different incident types. Results: Positional shifts in all directions were registered by both MI and %GP, degrading monotonically as the shifts increased. Shifts in intensity, which may result from bolus-tissue air gaps, were detected most by %GP. However, neither metric detected beam shape misalignment, such as that caused by dose to unintended areas, as well as currently employed metrics (Dice and MDC). Conclusions: This study indicates that different radiotherapy incidents may be detected by comparing both inter- and intrafractional Cherenkov images with a corresponding image similarity metric, varying with the type of incident. Future work will involve determining appropriate thresholds per metric for automatic flagging. Advances in knowledge: Classifying different algorithms for the detection of various radiotherapy incidents allows for the development of an automatic flagging system, eliminating the burden of manual review of Cherenkov images.

Color-resolved Cherenkov imaging allows for differential signal detection in blood and melanin content

“…Melanin concentrations were selected to match the expected range of human skin color based on several factors 13 , 14 . Primarily, we employed the Fitzpatrick scale, 15 which assessed skin color based on reaction to ultraviolet radiation.…”

“…Melanin concentrations were selected to match the expected range of human skin color based on several factors. 13,14 Primarily, we employed the Fitzpatrick scale, 15 which assessed skin color based on reaction to ultraviolet radiation. Pigmented phantoms representing the following Fitzpatrick scale types were fabricated: Fitzpatrick type 1 (score 0 through 6), type II (score 7 through 13), type III (score 14 through 20), type IV (score 21 through 27), type V (score 29 through 34), and type VI (score 35+).…”

Imaging and characterization of optical emission from ex vivo tissue during conventional and UHDR PBS proton therapy

“…While previous studies have characterized the feasibility of intensified imaging of Cherenkov signal to monitor incidents during electron and photon radiotherapy (Decker et al 2022), the work in this study presents the first demonstration of tissue luminescence imaging during PBS proton treatment under conventional and UHDR irradiation. The nature of emission under proton irradiation is expected to differ from photon and electron irradiation.…”

Non-contact scintillator imaging dosimetry for total body irradiation in radiotherapy

“…Two phantoms were used in this study. A 2.5 cm thick, flat anthropomorphic tissue phantom made of a silicone rubber compound (Dragon Skin, Smooth-On Inc., PA) which was then colored with SilcPig optical scatter and absorption pigments (Smooth-On Inc., PA) to provide visible tissue-like Cherenkov emission and attenuation properties that match soft mammalian tissues (Decker et al 2022). This was simulated tissue used to measure the effects of barriers such as bolus and the plexiglass spoiler.…”