Stereotactic Radiosurgery (SRS) is one of the most precise and effective forms of radiation therapy. It combines the principles of 3 dimensional target localization (stereotaxy) with multiple intersecting radiation beams to precisely treat tumors in difficult or hard to reach areas with common techniques. This technique, offered at UPMC Shadyside, is minimal or non-invasive. However, it allows for therapeutic doses necessary to destroy tumors with minimal risk to surrounding sensitive or critical structures compared to other more conventional techniques.
SRS may be delivered using cones, or similarly using circular collimators (tubes with lenses that shape the beam of radiation). Alternatively, SRS can be delivered using a computer drive leaf system called a multi-leaf collimator (MLC). SRS delivered by MLC enables more precise beam shaping for complex, non-circular tumors and is chiefly achieved by intensity-modulated radiosurgery (IMRS).
A Trilogy™ machine performing IMRS
Intensity-modulated radiosurgery, or IMRS, is an advanced form of radiotherapy that gives radiation oncologists the ability to completely treat certain types of tumors that even IMRT would not be able to fully treat. IMRS is more flexible than IMRT, which can be very important in treating certain types of cancer.
IMRS differs from IMRT in the shape of the radiation that is delivered to the tumor. IMRT puts out beams that are generally larger but may also give radiation to nearby normal tissues. As mentioned above, radiosurgery can be delivered using cones or circular collimators; however, for certain tumors, using a circular beam would either injure healthy tissue near the tumor, or else miss areas of the tumor that fall between the circles. IMRS instead delivers radiation as shapable 'leaves', which don't have the same size and shape restrictions as do the cones. This means that tumors which could previously only be treated with lower does of radiation can be given the highest level appropriate, without fear of damage to nearby tissue.
IMRS is a very new form of radiosurgical treatment, and UPMC is the only medical center in the region to offer IMRS.
See also: Trilogy, IMRT, CyberKnife
Images on this page were provided by Varian Medical Systems