BACKROUND OF SRS & SBRT
SRS = Single Fraction Radiosurgery (typically to the Brain, Head & Neck)
SBRT = 1 to 5 Fractions of Radiosurgery (typically to the body)
Many cancers cannot be completely eradicated with traditional radiation therapy (RT) techniques. The goal of radiation treatment has always been to maximize the delivery of radiation to tumors while minimizing the amount of radiation to normal tissue. The higher the radiation dose delivered to a tumor, the greater the chance of tumor destruction. Likewise, the lower the radiation dose delivered to surrounding normal tissue, the less destruction. Historically, the available technology was unable to accurately deliver high dose radiation to a tumor without also affecting the surrounding tissue. To minimize collateral damage to the surrounding tissues, radiation oncologists traditionally deliver radiation over many sessions, giving low doses each day over usually several weeks, (25 to 45 days). Following each fraction of radiation the normal tissue cells can recover better than many cancerous cells. Over many sessions, the hope is that more tumor cells die than normal tissue cells. Unfortunately, this strategy is often unsuccessful.
With the development of SRS & SBRT, physicians are now able to deliver lethal (surgical) doses of radiation to a tumor with sub-millimeter accuracy. This methodology maximizes the amount of radiation going directly to the target tissue (and thus maximizing tumor response rate) while minimizing the radiation exposure to surrounding tissue. This is evidenced in the studies that compare the clinical treatment volume (CTV) to the planning treatment volume (PTV). With SRS & SBRT, unlike RT, the CTV and PTV are more closely aligned, which means that SRS & SBRT is able to precisely deliver lethal doses of radiation to the target tissue. By minimizing the impact on healthy tissue, SRS & SBRT shortens patient recovery time and decreases complication rates.
Recent technological advances have enabled physicians to apply SRS & SBRT to lesions in the body, as well as to lesions in the cranium, head, and neck. Procedures were originally performed on cranial tumors because the technology at the time required a frame, which can easily be attached to the skull, as with the Gamma Knife. Attempts to develop body frames were cumbersome and unsuccessful. As a result, initially, no technological solution was available to accurately deliver lethal doses of radiation to tumors below the head without also destroying normal tissue. Current equipment such as CyberKnife, allows for real time tracking of a tumor regardless of where it is in the body. Physicians are now able to achieve submillimeter accuracy in the head, without the frame, by using the anatomical markings of the skull and taking advantage of the stable relationship between the skull and an intracranial tumor. In the same manner, we are now able to use the anatomical markings of the spine to treat spinal lesions. For other tumors in soft tissue throughout the body, we are able to track, in real time, small gold fiducials placed in the tumor to accurately deliver radiosurgical doses.
Over the last several years, SRS & SBRT has proven effective in treating cranial, extracranial/neck, and body tumors. In many cases SRS & SBRT provides a clinically superior alternative to either surgery or traditional RT for head and body lesions. In some cases, SRS & SBRT is the only effective option. The SRS & SBRT approach allows for dose escalation, hypofractionation, heterogeneity of dosage within the tumor volume, and improved conformality and accuracy. As a result, SRS & SBRT delivers unique benefits to the patient, including improved tumor response, higher cure rates, improved pain control, success against tumors that had been radio-resistant or had exceeded tolerance levels, reduction in organ damage, and improved tolerance. These unique benefits apply to tumors regardless of their location in the head/neck or body.