Introduction

This study was performed to assess the relationship between tumour response and radiation dose in equivalent 2 Gy per fraction (EQD2), and derive the optimal dose to treat patients.

Method

A retrospective cohort analysis of 21 patients with a diagnosis of intracranial hemangiopericytoma between 2000 and 2013 were included in this study. A total of 39 lesions were analysed. The equivalent dose in 2 Gy per fraction was calculated by assigning an alpha-beta ratio of 12 Gy. A paired t-test compared dose (EQD2) and tumour response and as the outcome was binary, a logistic regression analysis was performed.

Results

In total, there were 14 cases of progression and 25 cases of regression. It was estimated that for a one unit increase in EQD2, the odds of regression were increased by a factor of 1.13 (P = 0.026). After adjusting for PTV volume, the estimated effect of EQD2 (min) on tumour response was stronger, with an estimated odds ratio of 1.36 for an increase of one unit and an odds ratio of 21.6 for an increase of ten units (P = 0.015).  The optimum dose range varied with varying PTV volumes. For a median PTV volume of 3.67cm³ the optimal dose range was 30-45Gy.

Conclusion

This study demonstrates that there is a clear relationship between dose (EQD2) and outcome. With increasing dose the likelihood of regression is higher.  When adjusted for PTV volume, the response appeared stronger. The optimum dose varies significantly with changes in the size of the PTV.