Stereotactic radiotherapy (SRT) is an advanced, non-invasive radiation treatment. It focuses high doses of radiation directly on cancerous or abnormal tissues, minimizing damage to surrounding healthy structures. This article explores how SRT works, how its success is measured, factors influencing outcomes, and reported success rates across various cancer types.
What is Stereotactic Radiotherapy
Stereotactic radiotherapy is a specialized external beam radiation therapy that delivers intense, focused doses of radiation to a specific target within the body. Advanced imaging pinpoints the tumor’s exact location, shape, and size. Multiple radiation beams converge at the tumor site, delivering a high dose while rapidly decreasing the dose to nearby healthy tissues. This precision helps reduce potential side effects compared to conventional radiation therapy.
SRT is delivered in a small number of high-dose treatment sessions, unlike traditional radiation therapy which involves many smaller daily doses over several weeks. When applied to the brain or spine, this approach is called Stereotactic Radiosurgery (SRS). For tumors located elsewhere in the body, it is known as Stereotactic Body Radiation Therapy (SBRT). Both SRS and SBRT use precise targeting and high-dose delivery to destroy tumor cells or disrupt their growth.
How Treatment Success is Measured
Evaluating the success of cancer treatments like stereotactic radiotherapy involves several key metrics. Local control refers to the shrinkage or complete disappearance of the tumor at the treated site. This indicates how effectively the radiation has managed the disease in the specific area where it was delivered.
Progression-free survival (PFS) measures the length of time a patient lives with the disease without it worsening or spreading. Overall survival (OS) tracks how long patients live after their treatment. OS is considered a definitive measure of clinical benefit. For advanced cases, success can also include symptom palliation, aiming to relieve pain or other discomfort caused by the tumor.
Factors Affecting Outcomes
The effectiveness of stereotactic radiotherapy is influenced by several factors related to the tumor, the patient, and the treatment itself. Tumor characteristics play a significant role; smaller tumors generally have better local control rates than larger ones. The type of cancer (histology) also matters, as some cancers respond more favorably to radiation than others. A tumor’s location, particularly its proximity to sensitive organs or structures, can impact the maximum dose that can be safely delivered, affecting the outcome.
Patient-specific factors, such as overall health, age, and other medical conditions, can influence treatment tolerance and recovery. A patient’s performance status, which assesses their ability to perform daily activities, is a prognostic factor for overall survival. Prior treatments can also affect how a patient responds to SRT.
The technical aspects of treatment delivery, including the precision of tumor targeting and the total radiation dose delivered, are influential. Higher biologically effective doses (BED) are associated with improved local control. The number of treatment sessions, or fractions, can play a role, with single-fraction treatments sometimes showing superior local control compared to multiple fractions for certain tumor types.
Success Rates for Specific Cancers
Stereotactic radiotherapy demonstrates success rates across various cancer types. For early-stage non-small cell lung cancer (NSCLC), Stereotactic Body Radiation Therapy (SBRT) achieves local control rates consistently above 90%, with some studies reporting 95-98% at one year, 90-96% at two years, and 88-95% at five years. Overall survival rates for medically inoperable early-stage NSCLC patients treated with SBRT range from 74-87% at two years and 31-62% at three years, extending to around 40% at five years.
For brain metastases, Stereotactic Radiosurgery (SRS) shows local control rates around 90% at both one and two years. Overall survival for patients with brain metastases treated with SRS varies, with median survival ranging from 13.6 to 18.7 months, and one-year survival rates around 50.5%.
For localized prostate cancer, SBRT shows high biochemical progression-free survival (bPFS) rates. Studies report overall 5-year bPFS rates of 83.6% to 93%, with rates for low-risk disease reaching 95.7% to 97%. For intermediate-risk prostate cancer, 5-year disease control rates with SBRT are around 96%. For high-risk prostate cancer, SBRT combined with hormone therapy can achieve four-year cure rates of 87%.
SBRT is also used for spinal and liver tumors. For metastatic spine disease, local control rates with SBRT are around 84.7% at six months and 74.7% at one year. Pain relief is a common benefit. For primary liver tumors, SBRT yields local control rates of 93% at one year, 89% at two years, and 86% at three years. For liver metastases, local control rates are slightly lower, at 90% at one year, 79% at two years, and 76% at three years. Overall survival for hepatocellular carcinoma (HCC) patients treated with SBRT is around 77.3% at one year, 39% at three years, and 24.1% at five years.