Success Rate and Survival After Stereotactic Radiotherapy

Stereotactic Radiotherapy, also known as stereotactic ablative radiotherapy (SABR), is a specialized form of radiation treatment. It involves delivering a very high, focused dose of radiation directly to a tumor while carefully minimizing the amount of radiation reaching nearby healthy tissues and organs. This approach allows for a greater overall radiation dose to be given over a significantly shorter period, often just a few treatment sessions, compared to traditional radiation therapy. It’s frequently chosen as a treatment option for patients with limited volume tumors, especially when surgery is not considered the most suitable approach.

What is Stereotactic Radiotherapy (SRT)?

Stereotactic Body Radiation Therapy (SBRT), also referred to as stereotactic ablative radiotherapy (SABR), is a specialized type of radiation treatment characterized by its highly focused delivery. It concentrates an intense dose of radiation directly onto a tumor. This method applies principles similar to the precise radiation techniques used for treating tumors and metastases in the brain.

SBRT differs significantly from conventional radiation therapy in several ways. While conventional therapy delivers relatively small radiation doses over many weeks with daily sessions, SBRT allows for a much greater total dose of radiation to be delivered in considerably fewer treatments, typically completed within a week or about 10 days. This difference in delivery leads to substantially better outcomes, with two-year success rates for SBRT ranging from 80% to 90%, comparable to surgery, versus 30% to 40% for conventional treatment, according to the texts. Despite delivering higher doses to the tumor, patients often experience fewer side effects compared to conventional treatment. The shorter treatment course is also more convenient, usually involving short outpatient visits with little disruption to other therapies.

The precision targeting in SBRT is a key benefit. It requires highly accurate localization of the tumor, utilizing advanced imaging like 4D scanning and sometimes involving the placement of small gold seeds (fiducials) in the tumor to track its exact position, even as it moves with breathing. This enables physicians to deliver the high radiation dose accurately to the tumor while precisely limiting the dose to nearby healthy tissues and critical structures. This ability to spare healthy tissue while intensifying the dose is highlighted as a primary advantage, particularly important when tumors are located close to vital organs.

source: www.cancercouncil.com

How Effective is Stereotactic Radiotherapy?

Stereotactic Body Radiation Therapy (SBRT) has shown notably improved results compared to traditional radiation methods, with high local tumor control rates and two-year success rates reaching 80% to 90% for many indications. It is considered to be comparable in effectiveness to surgery but with fewer risks and side effects.

Effectiveness in Brain Metastases

A 2011 study by Minniti et al., published in BMC Radiation Oncology, investigated Stereotactic Radiosurgery (SRS) as primary treatment for brain metastases in 206 patients. Key results showed median overall survival of 14.1 months and brain control of 10 months, with 1 and 2-year local control rates of 92% and 84%. Neurological complications were observed in 13% of patients (5.8% severe). Brain radionecrosis occurred in 24% of treated lesions (10% symptomatic). The study identified volumes receiving 10 to 16 Gy (V10-V16 Gy), particularly V10 and V12, as independent risk factors for radionecrosis, noting lesions with V12 > 8.5 cm³ had a radionecrosis risk over 10%

A 2014 review by Lippits et al., published in Cancer Treatment Reviews, summarized literature on single-session Stereotactic Radiosurgery (SRS) for brain metastases. The review found SRS effectively overcomes limitations of WBRT, showing reproducible local tumor control with high rates: 90–94% for breast cancer, 81–98% for lung cancer, 73–90% for melanoma, and 83–96% for renal cell cancer metastases, ideally using ≥18 Gy doses. High local control was documented even for multiple metastases. While distant recurrence rates were comparable to WBRT, SRS can be repeated. For smaller lesions, Gamma Knife SRS was equally effective as surgery (Level I evidence) and avoided cognitive issues seen with WBRT (Level I evidence), favoring its high local efficacy and brain function preservation.

Effectiveness in Other Tumors

A 2020 meta-analysis by Lehrer et al., published in JAMA Oncology, evaluated Stereotactic Ablative Radiotherapy (SABR) in patients with oligometastatic cancer (up to 5 extracranial sites). Based on 21 trials (943 patients, 1290 metastases), primarily from prostate, colorectal, breast, and lung cancers, results showed estimated rates of acute and late severe toxic effects (grade 3-5) were low at 1.2% and 1.7%. Estimated 1-year outcomes included a high local control rate of 94.7%, overall survival of 85.4%, and progression-free survival of 51.4%. The authors concluded that SABR appears relatively safe and provides clinically acceptable control and survival rates.

In a 2024 study published in Clinical Oncology, researchers reported on the UK’s first experience with stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) for locally advanced pancreatic cancer (LAPC). Treating 55 patients with 40 Gy in 5 fractions, they observed acceptable toxicity rates, with 71% experiencing only grade 0-1 acute toxicity and no grade >3 acute toxicity. Median overall survival post-diagnosis was 19 months, and one-year local control post-SMART was 65%, demonstrating SMART’s potential to safely deliver ablative doses.

Wolf et al. (2024), published in Seminars in Thoracic and Cardiovascular Surgery, reviewed SABR (SBRT/SRS) for high-risk stage I NSCLC patients. Analyzing 16 prospective and 14 retrospective studies involving 54,697 patients, they found SABR primarily used for medically inoperable cases (93-95%). Common dosing regimens were 48-66 Gy in 3-5 fractions, with a median 30-month follow-up. The review summarized complications, oncological results, and quality of life after SABR, highlighting the need for ongoing randomized trials comparing SABR to sublobar resection.

Who is Not a Good Candidate for SBRT?

Patients with tumors located centrally or in close proximity to airways or the heart have sometimes been considered less suitable due to a potentially higher risk of complications, although modified approaches have been used in these cases.

For brain metastases specifically, larger lesions, described as greater than 8 to 10 cubic centimeters, are indicated as situations where surgical removal should be considered as an alternative to stereotactic radiosurgery. Additionally, certain characteristics of brain lesions related to the volume receiving a specific radiation dose (for example, V12 greater than 8.5 cm³) are linked to an increased risk of radionecrosis, suggesting that single-session stereotactic radiosurgery might be less preferable in these instances, especially if the lesion is near a critical brain area, and hypofractionated treatment may be considered.

While the therapy is typically used for localized tumors up to about 6-7 cm or a limited number of tumors (often 3 to 5), and a study on oligometastatic disease focused on patients with 5 or fewer extracranial sites, the material primarily highlights risk factors and alternative treatment considerations rather than strict contraindications for SBRT in general.

Potential Side Effects and Management

Potential side effects of Stereotactic Body Radiation Therapy and Stereotactic Radiosurgery,  include several types, though overall fewer are reported compared to conventional radiation therapy, such as reduced instances of radiation pneumonia. A commonly noted acute side effect for SBRT is slight fatigue, typically lasting for about one week after treatment. Immediate post-treatment sessions are generally free of significant pain or side effects.

Short-Term Side Effects

After undergoing SBRT, a commonly encountered short-term effect is mild fatigue, which typically subsides within about one week following the treatment course. Patients are also noted to generally be free from significant pain or immediate adverse reactions upon completing each individual treatment session.

A 2021 study by Jorgo et al., published in Radiation Oncology, evaluated acute side effects of extremely hypofractionated SBRT (37.5-40 Gy in 5 fractions over ~1 week) for prostate cancer in 205 patients. 1 Treatment was well tolerated, with no acute Grade ≥ 4 toxicity. Acute genitourinary side effects were primarily Grade I (30.7%) and II (50.7%), with 1.5% Grade III. Acute gastrointestinal side effects were mostly Grade 0 (62.4%) and I (31.7%), with 5.9% Grade II. The study concluded SBRT is safe with slight or moderate early side effects for prostate cancer.

Long-Term Risks and Complications

Concerning potential long-term risks and complications, several issues are pointed to. For brain stereotactic radiosurgery, brain radionecrosis is noted as a potential outcome, affecting a portion of treated lesions, with certain dose volumes identified as risk factors. For body SABR applied to oligometastatic disease, a study reported a low estimated rate of severe late toxic effects (Grade 3 to 5), considered clinically acceptable, although the specific types of these long-term issues are not detailed.

A potential for increased complication rates exists when tumors are located centrally or near vital structures like airways or the heart, and modified treatment approaches are used to address this risk, which could involve long-term complications. Additionally, neurological complications were reported in brain SRS, though the timing of these is not exclusively defined as late.

A 2024 randomized controlled trial (PACE-A) by Van As et al., published in European Urology, compared patient-reported outcomes for SBRT versus prostatectomy in men with localized intermediate-risk prostate cancer. 1 At 2 years, significantly fewer SBRT patients (6.5%) reported using one or more urinary pads daily compared to prostatectomy patients (50%). SBRT was also associated with better patient-reported sexual scores. Conversely, prostatectomy was linked to better bowel scores, indicating slightly more bowel issues with SBRT. The study concluded SBRT resulted in less urinary incontinence and sexual dysfunction but slightly more bowel bother than prostatectomy.

Read OncoDaily’s Special Article About Stereotactic Ablative Radiotherapy

Can Stereotactic Radiotherapy Replace Surgery?

Stereotactic Radiotherapy, including SBRT and SRS, can serve as an alternative to surgery in certain situations. For patients with limited volume tumors, particularly when surgery may not be the most suitable option due to factors like the risk of functional deficit or other patient considerations, SBRT is presented as a treatment choice.

When is SBRT a Better Choice Than Surgery?

A 2022 meta-analysis by Viani et al., published in Jornal Brasileiro de Pneumologia, compared SBRT versus surgery for early-stage non-small cell lung cancer across 30 studies (29,511 patients). Results indicated surgery generally yielded better 3-year overall survival (HR = 1.35) and cancer-specific survival (HR = 1.23) compared to SBRT. 1 However, 3-year local control was found to be similar between the two treatments (HR = 0.97). Subgroup analysis showed no significant difference in 3-year overall survival for T1N0M0 tumors (HR = 1.26), nor in 3-year cancer-specific survival when comparing SBRT to sublobar resection (HR = 1.21). The study concluded SBRT provides local control comparable to surgery and has important implications for patients unable to undergo surgery.

A 2019 systematic review and meta-analysis by Jackson et al., published in International Journal of Radiation Oncology Biology Physics, analyzed 38 prospective series (6116 patients) on curative-intent prostate SBRT. Results showed strong biochemical recurrence-free survival rates at 5 years (95.3%) and 7 years (93.7%). Estimated rates for severe late genitourinary and gastrointestinal toxicity (Grade ≥3) were low, at 2.0% and 1.1% respectively.

Patient-reported urinary and bowel function scores were found to return to baseline by 2 years post-treatment. The study also noted that while increasing SBRT dose improved biochemical control, it was associated with worse late severe GU toxicity. The authors concluded that prostate SBRT is supported by substantial evidence as a standard treatment option for localized prostate cancer, demonstrating favorable tumor control, patient-reported outcomes, and toxicity levels.

How to Prepare for Stereotactic Radiotherapy Treatment?

Preparation for Stereotactic Radiotherapy Treatment centers on precisely locating the tumor and planning the radiation delivery.  This starts with diagnostic imaging to find the tumor and define the treatment area, including using four-dimensional imaging to map the target’s movement, for instance, during breathing.  Sometimes, small gold seeds, known as fiducials, are placed within the tumor before imaging; this is noted as the sole invasive component of the planning process. Fiducials aid in accurate tumor localization and tracking and are implanted minimally invasively, guided by imaging, often with the assistance of radiologists or surgeons.

Precise tumor localization during a radiation simulation is also a necessary step. Furthermore, creating an accurate, custom map of each patient’s anatomy and organ motion is part of the preparation, using various imaging technologies like PET, MRI, CT, and 4D imaging.

Is SBRT Safe for Older Patients?

A 2020 study by Rades et al., published in In Vivo, evaluated factors impacting survival in 104 elderly patients with 1-3 cerebral metastases treated with SRS or FSRT. Multivariate analysis identified KPS 90-100, single lesion, maximum cumulative diameter <16 mm, and supratentorial involvement only as significantly associated with better survival. A newly created score predicted 12-month survival rates of 7%, 34%, and 58% for distinct score groups. The score showed very high accuracy (95% positive predictive value) in predicting death within 12 months but lower accuracy (54% positive predictive value) for predicting survival lasting 12 months or longer.

Written By Aren Karapetyan, MD