Patient reported fatigue after proton therapy for malignant brain tumours - Is there a relation between radiation dose and brain structures?

Background: Fatigue may significantly effect everyday- and working life for radiotherapy patients. Some studies indicate a correlation between radiation dose and irradiated volume of the brain and the presence of fatigue. Our hypothesis was that patient reported outcome measures (PROMs) can improve our understanding of the patients' symptoms following proton beam therapy (PBT) and optimize PBT for future patients. Methods: This study included 167 adult patients (>18 years) who received PBT for malignant brain tumours. Data on dose metrics to intra-cranial structures was obtained from PBT treatment plans. To explore fatigue and health related quality of life (HRQoL); Multidimensional Fatigue Inventory (MFI-20) and EORTC QLQ-C30 was used at 6-, 12-, 24- and 36 months post PBT. The correlation between fatigue and dosimetry was explored using Spearman's signed rank test. Results: No severe fatigue was recorded during the 36 months follow-up. Correlations between higher radiation dose and worsened fatigue scores were generally weak (rho < 0.3). At 12 months post PBT, higher mean dose to the brain, brainstem, hippocampi and pituitary was correlated to worsened MFI Physical Fatigue. Further, Reduced Motivation according to MFI was correlated to higher radiation dose to the brainstem and the pituitary gland. At 36 months follow-up post-PBT, both Reduced Activity and Reduced motivation according to MFI were correlated to higher radiation dose to the brain, brainstem and hippocampi. Conclusion: Proton beam therapy are well tolerated, with similar degree of fatigue pre- and post PBT. Achieving further reduction in mean brain dose appears beneficial.