Pocket Oncology (Pocket Notebook Series), 1st Ed.

STEREOTACTIC RADIOTHERAPY

Daniel E. Spratt, Marsha Reyngold, and Yoshiya (Josh) Yamada

Definitions

• 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)

Mechanism

• 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)

Delivery Machines

• 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

Primary Uses