Ultralow-dose radiation therapy delivers durable pain relief for multiple myeloma bone metastases while preserving bone marrow status and allowing for future treatments, according to prospective clinical trial data presented at the American Society for Radiation Oncology meeting in Boston.
Single and Two-Fraction Doses Provide High Pain Response Rates
Two-thirds of evaluable patients achieved a complete or partial pain response at 4 weeks following either a single 4-Gy radiation therapy dose or two 2-Gy doses. That response rate increased to 86% at 6 months. These regimens sit well below the conventional 30-Gy dose administered across 10 fractions typically prescribed for bone pain.
Treatment-related adverse events emerged in five of the 69 enrolled patients. None of those side effects reached grade 3 or higher severity, and none required treatment interruption or modification.
Bone Marrow Preservation Enables Future Therapies
Leslie Ballas, MD, of Cedars-Sinai Medical Center in Los Angeles, presented the findings at the meeting and emphasized the protective effect on patients’ blood counts. Maintaining bone marrow status allows patients to continue chemotherapy and keeps options open for subsequent treatments like CAR T-cell therapy or transplant.
“The bone marrow is protected, which allows patients to get re-irradiation, maintain their blood counts, continue chemotherapy, and have room for future therapies such as transplant or CAR T-cell therapy,” Ballas said. Only 19% of the study participants required a second course of radiation during the evaluation period.
Chelsea Pinnix, MD, of the University of Texas MD Anderson Cancer Center in Houston, noted that the prospective, single-arm phase II study addresses a frequent complication of the disease. The findings suggest clinicians can safely consider radiotherapy earlier in the course of care for patients experiencing painful bone disease.
Investigators Track Pain Response Rates Across Multiple Time Points
Investigators enrolled 69 patients with multiple myeloma and painful bone lesions defined by a Brief Pain Inventory score of 2 or higher. Eligible participants had no prior radiation therapy or surgery, pathologic fracture in a long bone, spinal cord compression, or skull base or orbital index lesions. Patients were randomized to receive either a single 4-Gy fraction or two 2-Gy fractions.
The primary outcome measured pain response and daily oral morphine equivalent dose at 4 weeks. The 66% response rate observed at 4 weeks dipped slightly to 64% at 8 weeks before surging to 86% at 6 months. Twelve of 63 evaluable patients ultimately required re-irradiation at doses ranging from 8 Gy to 24 Gy, with a median time to re-irradiation of 61 days and a subsequent pain response rate of 69%.
Ballas Deems Phase Two Data Ready for Clinical Practice
Ballas stated that additional clinical trials are likely unnecessary because the phase II data compared favorably to historical controls. She noted that the 2-Gy times two or 4-Gy times one protocols are ready for clinical practice, provided clinicians appropriately counsel patients that a small number may eventually need re-irradiation.
Prior palliative radiation therapy studies in multiple myeloma were predominantly retrospective and observational, with the only prior prospective data coming from a randomized comparison of 30 Gy versus 8 Gy. The changing clinical environment—featuring a 5-year overall survival rate now increased to 64% due to advanced therapeutic agents—makes bone marrow preservation a critical factor when managing patients who receive multiple lines of therapy over their lifetime.
Frequently Asked Questions About Low-Dose Radiation for Myeloma
What radiation doses were tested in the clinical trial?
Patients received either a single 4-Gy dose or two 2-Gy doses of radiation therapy. Both regimens fall significantly below the traditional 30-Gy dose delivered in 10 fractions.
Why is protecting the bone marrow important for multiple myeloma patients?
Patients live longer today and receive multiple lines of therapy over their lifetime. Protecting bone marrow volume allows patients to maintain blood counts, continue chemotherapy, and remain eligible for future treatments like transplant or CAR T-cell therapy.
How many patients required a second course of radiation?
Only 12 out of 63 evaluable patients, or 19%, required re-irradiation at doses ranging from 8 Gy to 24 Gy during the study period.
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