Understanding Response to Precision Radiation Therapy for Bone Metastases

Table of Contents

• Background: Why This Research Matters
• Study Methods: How the Research Was Conducted
• Key Findings: Detailed Results with All Numbers
• Clinical Implications: What This Means for Patients
• Limitations: What the Study Couldn't Prove
• Recommendations: Actionable Advice for Patients
• Source Information

Background: Why This Research Matters

Many patients with advanced cancer develop bone metastases, which are tumors that have spread to bones from other parts of the body. These metastases occur in up to 70% of patients with prostate and breast cancer, making them a major cause of pain and disability. The spine is particularly vulnerable, with over 10% of cancer patients developing symptoms in this area.

Radiotherapy has long been used to relieve pain from bone metastases. However, as cancer treatments improve and patients live longer, there's growing need for more precise, effective local treatments. Stereotactic body radiation therapy (SBRT) represents an advanced approach that delivers high, targeted radiation doses to tumors while sparing surrounding healthy tissue.

While SBRT shows promise for treating bone metastases, assessing how well it works can be challenging. Unlike some cancers where blood tests can monitor progress, bone metastases require imaging scans to evaluate treatment response. This study specifically examines how different imaging techniques help doctors understand whether SBRT is effectively controlling bone metastases.

Study Methods: How the Research Was Conducted

Researchers conducted a retrospective analysis of 74 adult patients treated at Bern University Hospital in Switzerland between December 2008 and October 2018. After applying strict exclusion criteria, 35 patients with 43 bone metastases remained for analysis. The team included only patients without previous radiation to the same area and those with adequate follow-up imaging.

The patient group was predominantly male (77.1%, n=27) with a median age of 66 years (range 38-84). Prostate cancer accounted for 51.4% (n=18) of cases, followed by breast cancer at 14.3% (n=5). The bone metastases were nearly evenly split between spinal (51.2%, n=22) and non-spinal locations (48.8%, n=21), with pelvic/hip bones being the most common non-spinal site.

Treatment involved delivering precisely targeted radiation using advanced systems like CyberKnife® for spine metastases and NovalisTX for other bone locations. Patients received a median total radiation dose of 24 Gy (range 24-42 Gy) in typically 3 fractions (range 2-7), meaning they received treatment over several days. The radiation was prescribed to cover the tumor completely while minimizing exposure to nearby organs.

Two independent radiologists who didn't know when treatment occurred analyzed all imaging studies. They used multiple assessment criteria including the University of Texas MD Anderson Cancer Center classification system to evaluate treatment response. The team also tracked pain levels using standardized scales and recorded medication use before and at least six months after SBRT.

Key Findings: Detailed Results with All Numbers

After a median follow-up of 1.8 years (range less than 1 to 8.2 years), the researchers found compelling results about SBRT's effectiveness for bone metastases:

• Local control achieved in 80% of patients - 68.6% (n=24) showed stable disease while 11.4% (n=4) demonstrated partial response
• Disease progression occurred in 20% (n=7) of patients despite SBRT treatment
• No patients achieved complete response where all evidence of cancer disappeared
• 57.1% (n=20) of patients died during follow-up, all from disease progression elsewhere in their bodies
• Notably, 70% (n=14) of those who died maintained local control at the treated bone site

The pain response results were particularly encouraging for patients experiencing discomfort from their metastases:

• 62.9% (n=22) of patients remained asymptomatic (without pain) at the treated site
• 44.4% of symptomatic patients available for follow-up reported pain reduction after SBRT
• Only 5.7% (n=2) experienced increased pain after treatment
• 8.6% (n=3) reported stable pain levels
• No patients developed neurological deficits related to their treatment

The imaging analysis revealed fascinating patterns about how different scan types show treatment response:

Computed tomography (CT) scans with contrast showed increases in tumor measurements after SBRT - width increased by 11.82 units (p<0.001), depth by 5.73 units (p=0.017), and height by 7.27 units (p=0.012). Meanwhile, positron emission tomography/computed tomography (PET/CT) scans showed decreases in these same measurements. Magnetic resonance imaging (MRI) results generally fell between these two patterns, showing relative stability.

Treatment complications were minimal, with only one vertebral compression fracture (4.6%) in spine metastases and one new/progressive fracture (4.8%) in non-spine metastases among the 43 treated sites.

Clinical Implications: What This Means for Patients

This research provides valuable insights for patients considering SBRT for bone metastases. The high local control rate of 80% suggests that this precision radiation approach effectively manages tumors in bone, potentially preventing fractures and other complications. Even when cancer progresses elsewhere in the body, the treated bone sites often remain stable.

The pain reduction findings are particularly significant. Nearly half of symptomatic patients experienced meaningful pain relief, which can dramatically improve quality of life. This reinforces SBRT's role not just as an anti-cancer treatment but as an important palliative approach for managing cancer-related pain.

The imaging findings help explain why different scans might tell seemingly different stories after radiation treatment. The fact that CT scans might show size increases while PET scans show metabolic decreases highlights the complex nature of assessing radiation response. Patients should understand that their doctors need to interpret different scan types in context rather than relying on any single measurement.

For patients with prostate and breast cancer metastases (which comprised 65.7% of this study group), these results are especially relevant. The treatment approach proved effective across these common cancer types that frequently spread to bone.

Limitations: What the Study Couldn't Prove

While this research provides valuable insights, patients should understand its limitations. The retrospective nature means researchers analyzed existing records rather than following a predetermined study plan. This can introduce biases that prospective studies avoid.

The relatively small sample size of 35 patients limits how broadly we can apply these findings. Larger studies would provide more definitive evidence about SBRT's effectiveness for bone metastases.

The imaging follow-up was inconsistent between patients, with different scan types performed at different time intervals. This heterogeneity makes direct comparisons challenging and highlights the need for standardized imaging protocols in future research.

The study couldn't account for all variables that might influence outcomes, such as specific cancer genetics, previous treatments, or individual patient factors. Additionally, the lack of a control group (patients not receiving SBRT) means we can't directly compare outcomes against alternative approaches.

Finally, the single-institution design means all treatments occurred at one hospital with specific techniques and expertise. Results might differ at other centers with different equipment and experience levels.

Recommendations: Actionable Advice for Patients

Based on this research, patients with bone metastases should consider these recommendations when discussing treatment options with their healthcare team:

1. Discuss SBRT as an option - If you have limited bone metastases, especially from prostate or breast cancer, ask your radiation oncologist whether SBRT might be appropriate for your situation
2. Set realistic expectations - Understand that while SBRT provides excellent local control (80% in this study), it may not eliminate all evidence of cancer on scans
3. Consider pain management benefits - If you're experiencing pain from bone metastases, SBRT may provide significant relief, with nearly half of symptomatic patients in this study reporting improvement
4. Prepare for multiple scans - Recognize that your doctors may need different types of imaging (CT, MRI, PET) to fully assess how your treatment is working, as each provides complementary information
5. Ask about experience - Since this was a single-institution study, inquire about your treatment center's experience with SBRT for bone metastases to ensure they have appropriate expertise
6. Discuss timing - The optimal timing for SBRT may depend on your specific cancer type and overall disease burden - have this conversation with your oncology team

Remember that treatment decisions should always be made in consultation with your medical team, considering your specific diagnosis, overall health, and personal preferences.

Source Information

Original Article Title: Response assessment after stereotactic body radiation therapy for spine and non-spine bone metastases: results from a single institutional study

Authors: Dora Correia, Barbara Moullet, Jennifer Cullmann, Rafael Heiss, Ekin Ermiş, Daniel M. Aebersold, Hossein Hemmatazad

Publication: Radiation Oncology (2022) 17:37

Note: This patient-friendly article is based on peer-reviewed research originally published under a Creative Commons Attribution 4.0 International License.