Stereotactic Radiotherapy

Posted on: September 15, 2012

Use Of Stereotactic Radiotherapy

Dr. Rahman By Sophia Rahman, MD Radiation Oncologist Radiosurgery is a non-invasive method of treating benign and ma- lignant tumors that may be otherwise inaccessible or inadequate for open surgery. This type of therapy involves high doses of precisely focused beams of ionizing radiation directed at the lesion. The technique was originally jointly pioneered in 1949 by Swedish neurosurgeon Dr. Lars Leksell and radiobiologist Bjorn Larsson, with an initial application for treatment of lesions in the brain. In 1968, they developed a device exclusively for radiosurgery that uses radioactive Cobalt-60 sources coined the name Gamma Knife. In the 1980s, the use of linear accelerators for radiosurgery was pioneered at the University of Florida, and since then, LINAC-based radiosurgery has become a widespread method of radiosurgery delivery. Some of the common modern techniques include the following: Stereotactic radiosurgery (SRS) is a specialized radiation technique that de- livers a large single dose of focused radiation to one or more intracranial targets with submillimeter precision. This technique is commonly used for brain metastases, either by itself or in conjunction with whole brain radiotherapy. The incidence of brain metastases is rising due to improvements in disease management, as well as improved imaging modalities. SRS may be considered for patients with reasonable performance status, a limited number and size of lesions (typically less than 4 lesions, < 4cm in size), and ideally with controlled extracranial disease. SRS may be preferred over neurosurgery for deep-seated lesions, lesions in eloquent areas of the brain, or for poor surgical candidates. Composite data from 40 nonrandomized trials of radiosurgery involving approximately 2,500 patients with over 4,000 lesions suggests a local tumor control rate of 81%. In addition, there is evidence that the addition of SRS to whole brain radiotherapy improves functional autonomy for patients with up to 3 brain metastases and improves survival for patients with a single unresectable lesion. Fractionated Stereotactic Radiotherapy (FSR) is an extension of SRS that delivers radiation via a fractionated schedule (generally between 2 and 30 fractions) using nonrigid immobilization. It provides the precision of stereotaxy while allowing adjacent normal structures to repair sublethal damage. The choice of technique may depend on the size and location of the lesions. Stereotactic body radiation therapy (SBRT) involves the precise delivery of large doses of radiation delivered over 1 to 5 fractions to an extracranial site, such as lung or liver. This technique may take inherent organ/target motion into ac- count by attempting to limit target motion. Abdominal compression or a vacuum immobilization method may be used to limit diaphragmatic excursion. Approximately 20% of patients with non-small cell lung cancer (NSCLC) present with early, localized disease. Surgery remains the gold-standard treatment for operable patients with a reported 65% 5- year survival rate for stage I patients. Although surgical resection remains the standard treatment for early stage lung cancer, many patients are unable to tolerate surgery due to medical comorbidities, such as chronic obstructive pulmonary disease or heart disease. Stereotactic body radiotherapy (SBRT) is an alter- native highly effective treatment for such patients. Timmerman et al report 3 year local control rates greater than 90% and overall survival rates of 56% with SBRT for early stage peripherally- located non-small cell lung cancer. At Diablo Valley Oncology, we continue to use these advanced stereotactic radiotherapy techniques in the treatment of select patients. As a radiation oncologist at DVO, I provide excellent care to our cancer patients using the latest evidence and technology.