3545 - Changes in Apparent Diffusion Coefficient After Radiation Therapy for Bone Metastases: A Comparative Study of SBRT and Conventional RT
Presenter(s)
O. Tanaka1, T. Taniguchi1, K. Ono2, S. Nakaya1, T. Kiryu3, C. Makita4, and M. Matsuo5; 1Department of Radiation Oncology, Asahi University Hospital, Gifu, Japan, 2Asahi University Hospital, Department of Radiation Oncology, Gifu, Japan, 3Asahi University Hospital, Hashimoto-Cho, Gifu city, Gifu, Japan, 4Gifu University School of Medicine, Department of Radiology, Gifu, Japan, 5Innovation Research Center for Quantum Medicine, Graduate School of Medicine, Gifu University, Gifu, Japan
Purpose/Objective(s): Palliative radiation therapy (RT) aims to relieve pain, stabilize the affected bones, and enhance patient quality of life. However, the duration of treatment efficacy varies among patients, and there is a growing need for predictive biomarkers to assess therapeutic response. The apparent diffusion coefficient (ADC), derived from diffusion-weighted MRI (DW-MRI), has been suggested as a potential imaging biomarker for evaluating tumor response to treatment. Changes in ADC values may reflect cellular alterations post-RT and provide insights into treatment effectiveness.
This study aims to investigate changes in ADC values before and after RT for bone metastases and their correlation with clinical treatment response. Specifically, it compares the effects of stereotactic body radiation therapy (SBRT) and conventional RT to determine whether ADC changes can serve as a reliable indicator of treatment efficacy.Materials/Methods: A prospective study was conducted, including 13 patients diagnosed with bone metastases who underwent either SBRT (30 Gy in 3 fractions) or conventional RT (8 Gy in a single fraction). MRI scans, including DW-MRI, were performed before and after treatment. ADC values were measured in predefined regions of interest (ROI) by experienced radiologists. Clinical response was evaluated using the Numeric Rating Scale (NRS) for pain assessment, and treatment outcomes, including recurrence and need for re-irradiation, were monitored over time.
Results: A significant increase in ADC values was observed after RT in both treatment groups, indicating reduced tumor cell density and increased water diffusivity within metastatic lesions. However, the SBRT group demonstrated a greater and more sustained ADC elevation compared to the conventional RT group (p<0.01). In terms of pain relief, both groups showed a significant reduction in NRS scores, confirming treatment efficacy (p<0.01 for SBRT, p=0.02 for conventional RT). Notably, patients in the SBRT group reported longer-lasting pain relief and better local tumor control. Two patients in the SBRT cohort remained recurrence-free for 12–18 months without requiring additional treatment. Conversely, five patients required re-irradiation within 3–8 months, and in these cases, a secondary increase in ADC values was observed following additional RT, suggesting a correlation between ADC changes and treatment response.
Conclusion: This study highlights the potential role of ADC values as a biomarker for assessing RT response in bone metastases. The findings indicate that SBRT results in a more pronounced and sustained increase in ADC values compared to conventional RT, suggesting superior tumor control. Given the correlation between ADC elevation and clinical response, ADC measurements could be integrated into routine imaging protocols to aid in personalized RT planning.