Post-operative stereotactic radiotherapy for the treatment of intracranial haemangiopericytoma: 'A Study of Dose and Outcome'.

INTRODUCTION: This study was performed to assess the relationship between tumour response and radiation dose in equivalent 2 Gy per fraction (EQD2).

METHOD: A retrospective cohort analysis of 21 patients with a diagnosis of intracranial haemangiopericytoma between 2000 and 2013 was 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 non-progression. It was estimated that for a one unit increase in EQD2, the odds of non-progression 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 10 units (P = 0.015). The dose range varied with varying PTV volumes. Based on the logistic model, the probability of having non-progression is larger than 50% for EQ2Dmin doses larger than 30-40 Gy, in particular for volumes larger than 3.67 cm3 .

CONCLUSION: This study demonstrates that there is a 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 dose varied significantly with changes in the size of the PTV.