Monte Carlo Phantom Studies on Radiation Dosimetry Using Flattening-Filter-Free Photon Beam in Nanoparticle-Enhanced Radiotherapy

With advances in biomedical nanotechnology and nanomaterial in cancer therapy and diagnosis, functionalized nanoparticles are designed and synthesized as nano-radiosensitizers in radiotherapy. The nanoparticles transported to the tumor can boost the patient treatment outcome by improving the tumor targeting as well as increasing the cancer cell control. This is because of the particle interaction enhancement between the radiation and nanoparticles. Recently in radiotherapy, the application of a flattening-filter-free photon beam resulted in many advantages in dose delivery, for example, a reduction of head leakage and scatter, and a big increase in dose rate. On the contrary, when the flattening filter is removed from the gantry head of the accelerator, the flattening-filter-free photon beam contains more low-energy photons compared to the flattening-filter beam. The interaction between the flattening-filter-free beam and nanoparticles is therefore changed, leading to a variation in dosimetry, which impacts the dose distribution and the contrast of the medical imaging in radiotherapy. In this chapter, we will discuss the radiation physics and radiobiology of cancer cell control and image contrast enhancement due to the application of heavy-atom nano-radiosensitizers in nanoparticle-enhanced radiotherapy. We will also discuss the photon energy change in the flattening-filter-free beam when the flattening filter is absent in the medical linear accelerator. The applications of flattening-filter-free photon beams and nanoparticles in radiotherapy will be explored with some recent phantom studies based on Monte Carlo simulation.