Daniel E. Spratt, Marsha Reyngold, and Yoshiya (Josh) Yamada
• SRS: Stereotactic radiosurgery; a single high-precision RT treatment for brain lesions
• SBRT: Stereotactic body radiotherapy; extracranial high-precision Rx consisting of 1–5 treatments, also referred to as SABR (stereotactic ablative body radiotherapy)
• Uses high dose per fraction. Conventional RT = ∼2 Gy/fx. Stereotactic RT = ∼5–24 Gy/fx
• Only a small target volume is treated.
• More ablative. Relies on poorly understood mechanisms involving sphingomyelin/ceramide-activated apoptosis of tumor vasculature. Standard radiobiology models do not apply. (Cancer Cell 2005:89–91)
• LINAC: most common device, generates photons by a mechanism similar to an x-ray tube; typical treatment consists of ∼5–12 beams from different angles to converge on target.
• CyberKnife: Specialized robotic LINAC that continuously tracks & adjusts to tumor motion.
• GammaKnife: A helmet device containing 201 Cobalt-60 sources in a semicircular array that generates convergent photon beams by radioactive decay.
• Tomotherapy: A helical slice-by-slice CT-guided system to deliver conformal IMRT.
• Most centers use a stereotactic rigid frame for SRS, & additional immobilization for SBRT to improve accuracy & spare nl tissue.
• Often use image guidance to aid in treatment accuracy.
SRS/SBRT: Advantages & Disadvantages