Varian linac 2100cd

As shown in Fig.1A, the light source of CELI is Cherenkov light generated in tissues induced by a linear accelerator (Varian Linac 2100CD, Varian Medical System), at the Norris Cotton Cancer Center, Dartmouth-Hitchcock Medical Center. For radiotherapy, 6MV X-ray radiation delivered from the Linac with a beam size adjusted to cover the entire tumor for treatment purpose. The CELI imaging system was previously reported. In brief, a time-gated intensified CCD camera (ICCD, PI-MAX4 1024i, Princeton Instruments) coupled with a commercial lens (Canon EF 135mmf/2L USM) was used as the detector. To shield the MV X-ray, the camera was put in a homemade lead box about 2 meters away from the imaging field. A band pass filter with center wavelength of 750 nm and spectral bandwidth of 100 nm was used to collect phosphorescence from Oxyphor PtG4. The time-gated ICCD camera was synchronized with the radiation pulse, which was ~3.25 μs long delivered at 360 Hz repetition rate from the Linac. Four CELI images were acquired with the delay times of 5 μs, 10 μs, 20 μs, and 30 μs to fit the lifetime image. To accumulate high enough phosphorescence signals, the intensifier gain was set to the maximum of 100, and 360 repeat cycles were integrated with 200 μs gate width in each cycle. The Linac room was kept dark during the acquisition to minimize stray light.