Aim:To assess the local control rate and potential complications of radiotherapy, and the factors influencing response to radiotherapy for primary and locally recurrent giant cell tumor of bone. Materials and Methods: A total of 20 patients diagnosed with either primary or locally recurrent GCTB were included in the study.The inclusion criteria for this study were patients aged 18 years and above, with histologically confirmed primary or locally recurrent giant cell tumor of bone. All patients were scheduled to undergo radiotherapy as part of their treatment and provided written informed consent to participate in the study.The primary outcome measure was the local control rate, defined as the absence of tumor progression or recurrence within the irradiated field. Time to local control was measured from the start of radiotherapy to the date of documented local control. Complications related to radiotherapy were graded according to the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0.Follow-up data included clinical examination findings, imaging studies (X-ray, MRI, CT scan) at regular intervals (3 months, 6 months, 1 year, and annually thereafter), and assessment of functional outcomes using validated scales such as the Musculoskeletal Tumor Society (MSTS) score. Results: Tumor size greater than 5 cm was associated with a higher risk of poor response (Hazard Ratio [HR] = 2.5, p = 0.03), indicating that larger tumors may be more resistant to radiotherapy. Tumor location in the spine also emerged as a significant factor (HR = 3.2, p = 0.01), reflecting the challenges of treating spinal GCTB with radiotherapy. While a total dose greater than 50 Gy showed a trend towards better outcomes (HR = 0.5), it did not reach statistical significance (p = 0.15). Age over 50 years also had a non-significant trend towards worse outcomes (HR = 1.8, p = 0.07). At the 2-year follow-up, 40% of patients had achieved excellent functional outcomes (MSTS score 85-100), while 50% had good outcomes (MSTS score 70-84). Only 10% had fair outcomes (MSTS score 55-69), and no patients had poor outcomes (MSTS score <55). Conclusion: We concluded that the radiotherapy is effective in achieving local control in the majority of GCTB patients, with a relatively high rate of functional recovery. However, the risk of complications, particularly fibrosis and pain, requires careful consideration, especially in patients with larger tumors or those with tumors located in challenging sites such as the spine.