Our aim is to optically monitor the delivery of the chemotherapy drugs for brain tumours, particularly used in the central nervous system (CNS) lymphoma therapy. In vivo monitoring would help to optimize the treatment and avoiding unnecessary medications. Moreover, it would be beneficial to be able to measure which of the multi-regimen drugs actually do penetrate and how well into the brain tissue. There exist several potential optical measurement techniques to be utilised for the purpose. The most desired method would allow the detection of the drugs without using optical biomarkers as a contrast agent. In this case, for non-invasive sensing of the drug in the brain cortex, the drug should have a reasonably strong optical absorption band somewhere in the range between 600 nm and 1700 nm, and not directly coincident with the strong bands of haemoglobin or water. Alternatively, mid-infrared (MIR) range has the potential for invasive drug monitoring techniques. In this paper, we report the optical properties of several chemotherapy drugs used in CNS lymphoma therapy, such as rituximabi, cyclophosphamide and etoposide. We measured their transmittance and reflectance spectra in near-infrared (NIR) range, particularly 900 nm-2500 nm, to be considered when choosing the in vivo monitoring method to be developed. The absorption and scattering coefficients were retrieved from the measurements and applying Beer's law. For the measurement of the sum of total transmission and reflection in NIR range we used integrating sphere with spektralo to enable calculation of the scattering coefficient.