Residency · Residency · Radiation Oncology
Palliative Bone Radiation: Single Fraction vs. Multi-Fraction Regimens
Introduction
Bone metastases occur in up to 70% of patients with advanced breast and prostate cancer and represent a significant source of morbidity. Palliative radiation therapy stands as the most effective non-pharmacologic treatment for painful bone metastases, providing pain relief in 60-80% of patients. Despite level I evidence supporting the use of single-fraction radiation, multi-fraction regimens continue to be overutilized in clinical practice. This lecture aims to review the evidence behind these approaches, guide appropriate fractionation selection, and discuss considerations for retreatment.
Epidemiology and Clinical Impact
Bone metastases most commonly affect the spine, pelvis, ribs, long bones, and skull. These lesions can lead to skeletal-related events (SREs), which include pain, pathologic fractures, spinal cord compression, and hypercalcemia. Managing pain from bone metastases follows a hierarchy that begins with analgesics, followed by bone-modifying agents such as bisphosphonates or denosumab, then radiation therapy, and finally surgery if needed. Although bone-modifying agents like zoledronic acid and denosumab reduce the incidence of SREs, they do not replace radiation therapy for effective pain control.
Common Fractionation Regimens
Single Fraction
The most studied and widely recommended single-fraction regimen is 8 Gy delivered in one session. This approach has demonstrated equivalent pain response rates compared to multi-fraction regimens, supported by level I evidence. However, the retreatment rate after single-fraction radiation is higher, approximately 20-25%. Single-fraction treatment is ideal for patients with limited life expectancy, those facing transportation or logistical barriers, or individuals with multiple painful sites requiring sequential treatment.
Multi-Fraction Regimens
Multi-fraction regimens commonly include 30 Gy delivered in 10 fractions, which is the most frequently used schedule. Other regimens such as 20 Gy in 5 fractions and 24 Gy in 6 fractions are also employed in some institutions. These regimens have a lower retreatment rate, around 8-10%, compared to single-fraction therapy. Multi-fraction radiation is preferred when durable local control is desired, such as in patients with longer life expectancy or when treating weight-bearing bones at risk of fracture.
| Regimen | Total Dose / Fractions | Pain Response | Complete Response | Retreatment Rate | Best Suited For |
|---|---|---|---|---|---|
| Single fraction | 8 Gy / 1 fx | 60–70% | ~25% | 20–25% | Limited life expectancy, logistical barriers, multiple sites |
| Short course | 20 Gy / 5 fx | 60–70% | ~25% | 8–10% | Intermediate prognosis |
| Standard multi-fraction | 30 Gy / 10 fx | 60–70% | ~25% | 8–10% | Longer life expectancy, weight-bearing bones, post-op |
Evidence for Equivalence
The American Society for Radiation Oncology (ASTRO) guideline, initially published in 2011 and updated in 2017, strongly recommends single-fraction 8 Gy as an option for uncomplicated bone metastases. A meta-analysis of 25 randomized trials involving over 5,000 patients demonstrated that overall pain response rates are equivalent between single- and multi-fraction regimens, with both achieving 60-70% pain relief. Complete response rates are also similar, approximately 25% for both approaches. Key studies such as the Dutch Bone Metastasis Study, RTOG 97-14, and NCIC SC.20 all support this equivalence.
Factors Guiding Fractionation Choice
Favoring Single Fraction (8 Gy x 1)
Single-fraction radiation is favored in patients with limited life expectancy, generally less than 3 to 6 months, as well as those facing transportation or logistical challenges. It is also preferred when multiple painful sites require treatment sequentially, in cases of uncomplicated bone metastases without fracture risk, and when patients express a preference for convenience. Importantly, retreatment can be offered if pain recurs after initial single-fraction therapy.
Favoring Multi-Fraction (20-30 Gy)
Multi-fraction regimens are preferred for patients with longer life expectancy, typically greater than 6 months, especially when treating weight-bearing bones at risk of impending fracture. They are also indicated when a neuropathic pain component is present, such as spinal metastases causing radiculopathy, or when a durable response with a lower probability of retreatment is desired. Post-operative radiation following surgical stabilization and cases involving a soft tissue mass requiring volume reduction also favor multi-fraction schedules.
Retreatment
Indications
Retreatment is considered when there is pain recurrence or progression after an initial response to radiation therapy. Typically, retreatment is performed at least 4 to 6 weeks after the initial treatment. The standard retreatment dose for single-fraction therapy is again 8 Gy in one fraction. Retreatment response rates are comparable to initial treatment, ranging from 60-70%.
NCIC SC.20 Trial
The NCIC SC.20 trial evaluated retreatment of previously irradiated painful bone metastases, comparing 8 Gy in one fraction to 20 Gy in five fractions. The study found equivalent pain response rates, with 28% versus 32% overall response, respectively. This supports the use of single-fraction radiation for retreatment as well.
Cumulative Dose Considerations
When retreating spinal metastases, cumulative spinal cord dose must be carefully assessed to avoid toxicity. Peripheral bone metastases generally tolerate retreatment well. For select patients, spine stereotactic body radiation therapy (SBRT) may be considered as a reirradiation option, as discussed in Lecture 68.
Treatment Technique
Field Design
For most sites, treatment involves a simple anterior-posterior/posterior-anterior (AP/PA) or single direct field. The entire involved bone segment should be included with 2-3 cm margins. In spinal metastases, the field should encompass one vertebral body above and below the affected level. CT simulation is preferred for spinal and pelvic metastases to ensure precise targeting, while clinical setup is acceptable for extremity lesions.
Special Situations
For rib metastases, a single direct field with adequate depth is used. Femoral metastases require inclusion of the full length of the involved femur or the affected segment. Pelvic metastases may be treated with AP/PA or hemi-pelvis fields depending on the extent of disease. Humeral metastases are treated with a direct field, sometimes using a skin bolus if necessary.
Pathologic Fracture Risk Assessment
Mirels Scoring System
The Mirels scoring system predicts fracture risk for long bone metastases by evaluating four variables: site, pain, lesion type (lytic, blastic, or mixed), and size based on the percentage of cortical involvement. A score greater than 8 indicates a high risk of fracture and warrants prophylactic surgical fixation before radiation. Scores less than 7 suggest that radiation alone is appropriate. Orthopedic surgery consultation is advised for impending fractures.
Post-Operative Radiation
Post-operative radiation is delivered after internal fixation or arthroplasty to prevent tumor progression and further bone destruction. The standard post-operative dose is 30 Gy in 10 fractions. Radiation typically begins 2 to 4 weeks after surgery, once wound healing permits.
Bone-Modifying Agents
Bisphosphonates such as zoledronic acid, administered intravenously every 3 to 4 weeks, and denosumab, given subcutaneously every 4 weeks, reduce skeletal-related events by 30-40%. These agents complement radiation therapy but do not replace it for pain control. Some trials have shown denosumab to be superior to zoledronic acid in reducing SREs. Monitoring for adverse effects such as osteonecrosis of the jaw and hypocalcemia is essential during treatment.
Emerging Approaches
Radionuclide Therapy
Radium-223 (Xofigo), an alpha emitter, is approved for bone-predominant metastatic castration-resistant prostate cancer and has demonstrated improved overall survival in the ALSYMPCA trial. Beta emitters like strontium-89 and samarium-153 are less commonly used today. Radionuclide therapy is particularly useful for patients with diffuse painful bone metastases that are not amenable to focal radiation therapy.
SBRT for Bone Metastases
Stereotactic body radiation therapy (SBRT) offers higher local control rates compared to conventional palliative radiation and is considered for oligometastatic disease or radioresistant histologies. However, SBRT is not standard for routine palliative management of bone pain.
Key Clinical Pearls
Eight Gray delivered in a single fraction provides pain relief equivalent to multi-fraction regimens for uncomplicated bone metastases, as supported by level I evidence from multiple randomized trials. Despite strong guideline recommendations, single-fraction radiation remains underutilized and should be considered the default treatment for most patients with painful bone metastases. Multi-fraction regimens are preferred when treating weight-bearing bones, patients with longer life expectancy, post-operative settings, or when a lower probability of retreatment is desired. A Mirels score greater than 8 indicates a high risk of pathologic fracture, and prophylactic surgical fixation should precede radiation in these cases. Retreatment with 8 Gy in a single fraction is effective for recurrent pain following initial palliative radiation therapy.
References
- Chow E, Harris K, Fan G, et al. Palliative radiotherapy trials for bone metastases: a systematic review. J Clin Oncol. 2007;25(11):1423-1436.
- Hartsell WF, Scott CB, Bruner DW, et al. Randomized trial of short- versus long-course radiotherapy for palliation of painful bone metastases. J Natl Cancer Inst. 2005;97(11):798-804.
- Chow E, van der Linden YM, Roos D, et al. Single versus multiple fractions of repeat radiation for painful bone metastases: a randomised, controlled, non-inferiority trial. Lancet Oncol. 2014;15(2):164-171.
- Lutz S, Balboni T, Jones J, et al. Palliative radiation therapy for bone metastases: update of an ASTRO Evidence-Based Guideline. Pract Radiat Oncol. 2017;7(1):4-12.