Monte Carlo investigation of the effect of skin tissue optical properties on detected Cherenkov emission

Monte Carlo (MC) study of dose distribution and Cherenkov imaging in total skin electron therapy (TSET) with TOPAS

Malignant tissues can be effectively treated by Total Skin Electron Therapy (TSET) over the entire body surface using 6 MeV electron beams. During the radiation treatment, Cherenkov photons are emitted from the patient's skin, and can potentially be used for in-vivo imaging of the radiation dose distribution. A Monte Carlo (MC) simulation toolkit TOPAS is used to study the generation and propagation of Cherenkov photons that are generated from the interaction of electron radiation with human tissues, and to understand the relationship between the dose distributions and the Cherenkov photon distributions. Validation of MC simulations with experiments are performed at 100 SSD and 500 SSD, and simulations of a patient phantom in realistic clinical treatment setups have been done. These simulations with TOPAS show that the emitted Cherenkov distributions at phantom surfaces closely follow their corresponding dose distributions.

Cherenkov imaging for total skin electron therapy (TSET)

BACKGROUND

Total skin electron therapy (TSET) utilizes high-energy electrons to treat malignancies on the entire body surface. The otherwise invisible radiation beam can be observed via the optical Cherenkov photons emitted from interactions between the high-energy electron beam and tissue.

METHODS AND MATERIALS

With a time-gated intensified camera system, the Cherenkov emission can be used to evaluate the dose uniformity on the surface of the patient in real time. Fifteen patients undergoing TSET in various conditions (whole body and half body) were imaged and analyzed. Each patient was monitored during TSET via in vivo detectors (IVD) in nine locations. For accurate Cherenkov imaging, a comparison between IVD and Cherenkov profiles was conducted using a polyvinyl chloride board to establish the perspective corrections.

RESULTS AND DISCUSSION

With proper corrections developed in this study including the perspective and inverse square corrections, the Cherenkov imaging provided two-dimensional maps proportional to dose and projected on patient skin. The results of ratio between chest and umbilicus points were in good agreement with in vivo point dose measurements, with a standard deviation of 2.4% compared to OSLD measurements.

CONCLUSIONS

Cherenkov imaging is a viable tool for validating patient-specific dose distributions during TSET.