Chapter twelve - Evaluation of the risk and benefit of using functionalized nanomaterials as contrast agents in image-guided radiotherapy: a Monte Carlo study on the imaging dose and contrast enhancement

Abstract

Functionalized nanomaterials such as heavy-atom nanoparticles are often used as contrast agents in medical imaging. When nanomaterials are applied to a cancer site in the patient, more nanomaterials would accumulate at the tumor than the surrounding normal tissues. In image-guided radiotherapy using kilovoltage cone-beam computed tomography (kV-CBCT), the tumor with the addition of heavy-atom nanomaterials absorbs more photons than the surrounding tissues with less amount of nanomaterials. This is because of the photoelectric enhancement, with an increase of the compositional atomic number in the tumor due to the addition of nanomaterials. The bigger deviation between the attenuations of the tumor and surrounding tissues leads to an image contrast enhancement. Nanomaterials therefore become an effective contrast agent in kV-CBCT imaging. On the contrary, adding nanomaterials to the patient inevitably results in an increase of imaging dose, as some nanomaterials would accumulate in the normal tissues. This increase of unwanted radiation exposure could lead to some health issues to the patient such as a slightly increased risk of cancer and side effects. Hence, the cost effectiveness of using functionalized nanomaterials as image contrast agent should be studied. We should balance the risk and benefit of using nanomaterials by optimizing the imaging dose and contrast enhancement in image-guided radiotherapy. This chapter will explore using Monte Carlo method to estimate the imaging dose enhancement by applying different functionalized nanomaterials with different variables such as nanoparticle material, concentration, and photon beam energy. We will review and discuss dependences of imaging dose and contrast enhancement with the addition of nanomaterials on these variables using Monte Carlo simulations. Results in this chapter are useful for radiation staff to set up related imaging protocol or safety policy, when using heavy atom–functionalized nanomaterials as contrast agent in kV-CBCT imaging.