The development of an optically opaque and non-glossy radiotherapy bolus optimized for surface guided radiotherapy (SGRT)

Abstract

Surface guided radiation therapy (SGRT) is an emerging technology that uses non-ionizing methods for patient positioning and motion tracking during radiotherapy delivery. However, the use of radiotherapy boluses, which are tissue-equivalent materials placed on the skin to increase surface dose, has been shown to interfere with SGRT systems due to reflections from the bolus surface. This thesis presents the development and validation of an opaque and non-glossy radiotherapy bolus called the "Surface Guidance Optimized" (SGO), which is a variation of the previously developed transparent Clearsight bolus.The Surface Guidance Optimized bolus was rendered opaque by adding 0.6% titanium dioxide and given a matte finish using matte release paper. Spectroscopy measurements confirmed optimal opaqueness, while gloss meter readings verified a non-glossy surface. The bolus density was quantified to be 0.853 g/cm3 using water displacement and CT methods. Dosimetric characterization through direct surface dose measurements and Monte Carlo simulations demonstrated the SGO bolus mimics the dose deposition of water-equivalent materials when accounting for density differences. Compatibility testing with the AlignRT SGRT system showed the bolus allowed accurate surface reconstruction and submillimeter tracking (within 0.4 mm) under different lighting conditions. Overall, the SGO bolus mitigates issues of transparency and glossiness that interfered with SGRT systems, while maintaining desirable dosimetric properties for clinical use as a radiotherapy bolus compatible with modern surface guided techniques.