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


Surface luminescence imaging is a promising technique for real-time visualization of treatment delivery, offering applications in dose verification, treatment monitoring, and retrospective treatment plan comparison. This research aims to explore the feasibility of surface imaging during proton therapy, under conventional and UHDR conditions. 

Approach: Conventional and UHDR PBS proton therapy irradiation of porcine tissue and plastic tissue phantom was imaged using intensified CMOS cameras. The low optical emission was investigated during conventional irradiation using a blue and red-sensitive intensifiers to ensure adequate spectral coverage. Spectral characterization was performed using bandpass filters between the lens and sensor. Conventional imaging (240MeV, 10nA) was performed at 100 Hz while UHDR PBS proton delivery (250MeV, 99nA) was monitored at 1 kHz. Emission yield dependence on proton energy was studied using an optical tissue-mimicking plastic phantom and range shifter. Emission from tissue was investigated under UHDR conditions by imaging a porcine tissue target.

Main results: Under conventional treatment dose rates optical emission was imaged with single spot resolution. Spot profiles were found to agree with the treatment planning system calculation within >90% for all spectral bands and spot intensity was found to vary with spectral filtration. The resultant polychromatic emission presented a maximum intensity at 650 nm and decreasing signal at lower wavelengths, which is consistent with expected attenuation patterns of high-fat and muscle tissue. For UHDR beam imaging, optical yield increased with higher proton energy. Imaging at 1 kHz allowed continuous monitoring of delivery during porcine tissue irradiation, with clear identification of individual dwell positions. The number of dwell positions matched the treatment plan showing adequate temporal capability of iCMOS imaging. 

Significance: For the first time, this study characterizes optical emission from tissue during proton therapy, demonstrating the feasibility of fast optical tracking in both conventional and UHDR settings. &#xD.