A quick localization of the tumor site to guide the therapeutic administration is important for an image guided cancer therapy to decrease both mortality and morbidity, especially in prolonged procedures, such as photodynamic and photothermal therapies. Consequently, the images have to be updated quickly enough to capture the patient motion and the movement of therapeutic device, which poses a significant challenge on functional imaging probes. Besides increasing the sensitivity of imaging detectors, advanced image processing methods may play an important role to overcome this challenge. In this work, we investigate the effectiveness of the spatiotemporal processing to shorten the acquisition time of each image frame to be able to capture the object motion with good image quality. The simulation study of beta imaging of a moving tumor phantom at different imaging dose levels demonstrates that the spatiotemporal processing can yield superior image quality compared to either a short acquisition or a prolonged acquisition with only spatial smoothing. The receiver operating characteristic curve analysis also reveals its advantage on the tumor detection, particularly at lower imaging dose or equivalently shorter acquisition time.