Radiation can be delivered to the pituitary adenoma with higher precision using stereotactic techniques. These require firm immobilization usually using a relocatable stereotactic frame, high-precision localization of the lesion on CT/ MRI using a fiducial coordinate system such as that employed in stereotactic neurosurgery, and a more focused delivery of radiation to a smaller PTV (using
a smaller margin). More localized irradiation is achieved using multiple fixed individually shaped radiation beams (usually 4-6) distributed in space (12,13), and this is called stereotactic conformal radiotherapy (see Figs. 1 and 2). Previously, multiple arc techniques to treat single or multiple isocenters result in nonhomogeneous-dose distribution, and these techniques are not appropriate, particularly in proximity to critical structures. Their use in the treatment of pituitary adenoma is questionable.
High-precision focal irradiation given in multiple doses is described as fractionated stereotactic conformal radiotherapy (SCRT). The dose fractionation schemes for SCRT are usually identical to those described for conventional radiotherapy. High-precision radiation given in a single large dose is described as radiosurgery, regardless of the machine used to deliver it.
A new potentially useful technique of conformation is intensity-modulated radiotherapy (IMRT), which also delivers defined doses to specific regions within and outside the tumor. Although the overall role of IMRT in pituitary radiotherapy is not yet defined, studies using the Peacock system demonstrate inferior dose distribution compared with SCRT (14).
High-energy proton beams deposit energy at the end of their paths within a Bragg peak. Proton irradiation is theoretically considered a superior method of conformal radiotherapy, sparing more normal tissue than could be achieved with conventional photon radiotherapy. There are only a few proton facilities worldwide, and the costs of such installations are not matched by a sufficient magnitude of measurable or even potential benefit. The biologic principles of the damaging effect of protons are identical to photon irradiation.
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