Diffusion-weighted magnetic resonance imaging in painful bone metastases: Using quantitative apparent diffusion coefficient as an indicator of effectiveness of single fraction versus multiple fraction radiotherapy

Purpose: Bone metastases are a common cause of cancer-related pain. The aim of this study is to determine the optimal radiotherapy schedule for the treatment of painful bone metastases and verify if could cause different biological effects on bone. This has been achieved using functional Magnetic Resonance Imaging (MRI) with diffusion-weighted imaging (DWI). Patients and methods: Fifteen patients received Multiple Fractions Radiation Therapy (MFRT) with a total dose of 30 Gy in 10 daily fractions of 3 Gy given over 2 weeks and 15 patients received a Single Fraction Radiation Therapy (SFRT) with a dose of 8 Gy. Quantitative Apparent Diffusion Coefficient (ADC) values after SFRT or MFRT were compared with response to treatment (pain relief), assessed by Visual Analogue Scale (VAS) before radiotherapy and at 1 and 3 months after the completion of treatment. Results: The two schedules had equal efficacy in terms of pain control, without any difference at 1 and 3 months post radiotherapy. In both treatments, pain reduction was related to an increase in the ADC. However, the median ADC value had an increase of 575 points between the baseline and 3 months (from 1010 to 1585, p = 0.02) in the 30 Gy group, while it was only 178 points (from 1417 to 1595) in the 8 Gy group. Conclusions: The increase in the ADC values after radiotherapy corresponds to increased cell death. Despite an equal pain control, MFRT treatment seems to be more effective to achieve cancer cells kill. Our preliminary data could also explain the higher retreatment rates in SFRT vs MFRT in long survivors.