Intensity Modulated Therapy
External beam radiation treatment is a common approach to treat cancer with radiation. With development in technology especially with computer controlled multileaf collimators (MLC) era of Intensity Modulated Radiation Therapy (IMRT) dawned. IMRT distinguishes itself from the traditional 3D radiation therapy in that the intensity of the beam was modulated over a given aperture/ opening.
The intensity variation as a function of position (beamlets or bixels) in a given beam is in fact accomplished by changing the fluence or number of photons through the bixel. The energy of the beam remains the same. One can argue that the intensity change from bixel to bixel is achieved only by the fluence – the beam energy remains fixed.
To a critical reader it is not the optimization of intensity but optimization of fluence, therefore the term intensity modulation is a misnomer.
By using detailed mathematical modeling and linear optimization formalism, we included the energy of the beam as part of the equation. Notion of simultaneous energy and fluence optimization was invented first time by our group in 2014. Philip McGeachy (graduate student) worked on this investigation towards his doctoral research and coined the term X ray modulated radiation therapy or XMRT.
XMRT uses a simple formalism where two discrete megavoltage clinical photon energies 6 MV and 18 MV are used as part of decision making by the computer algorithm to determine which one is appropriate from a particular location for a custom patient, and tumor and normal tissue geometry. The investigation still continues with application from phantom geometries to real world scenarios.
