PP66. OUTCOMES OF HIGH GRADE GLIOMA PATIENTS TREATED WITH TWO DIFFERENT RADIOTHERAPY REGIMES: THE EFFECT OF PRIORITISING TUMOUR DOSE VERSUS LIMITING DOSE TO ORGANS AT RISK

Abstract

INTRODUCTION: High grade gliomas, grade III and IV, have poor survival rates. Glioblastomas are the commonest, but also, the most aggressive type of glioma. It is associated with a poor prognosis. Median survival of patients after treatment with debulking surgery followed by concurrent chemoradiotherapy and adjuvant chemotherapy is 14.8 months. Currently, post-operative fractionated radiotherapy is prescribed to a range of 54 to 60 Gy in fractions of 2 Gy. Organs at risk (OAR) including optic chiasm, optic nerves and the brain stem, may lie within, or in close proximity to the PTV. Neuropathy and/or necrosis has been shown to occur when the maximum dose exceeds 55Gy in the optic chiasm and 54Gy to the whole brainstem. The previous standard practice at the Rosemere Cancer Centre was to prioritise the OAR at the expense of the total dose, therefore prescribing to a dose of 54Gy whenever the OAR is included in the PTV. This may have repercussions on tumour control and ultimately, overall survival. AIMS: This retrospective analysis aims to compare patient outcomes between the 54Gy/57Gy and 59.4Gy/60Gy regimes, to determine if compromising the dose to spare OARs is detrimental to tumour control and survival. METHODS: The data of all glioma patients treated with radiotherapy between December 2012 and December 2014 at Rosemere Cancer Centre, were collected from our electronic databases. A total of 167 patients were identified. Patients with low grade glioma and those treated with a palliative intent were excluded. Fifty eight patients were included in the analysis. RESULTS: 21 patients were on a lower dose radiotherapy regime of 54Gy or 57Gy. The remaining 37 were on a higher dose regime of 59.4Gy or 60Gy. The two groups appeared to be similar in terms of age at diagnosis, gender, the percentage receiving concurrent and adjutant Temozolomide, median time on treatment and median time from diagnosis to treatment. A higher proportion of patients in the radiotherapy regime 59.4gy/60gy had a frontal or parietal tumour whereas a higher proportion of patients in the radiotherapy regime 54gy/57gy had a temporal tumour. A higher proportion of patients receiving the higher dose had a grade 4 glioma, 47.6% versus 75% (p=0.063). A higher proportion of patients had debulking in the radiotherapy regime group 59.4Gy/60Gy compared with the radiotherapy regime group 54gy/57gy (p=0.069). There was a statistically significant difference (p=0.05) in patients treated with the higher dose regime comparatively, of an additional 7.2 months median overall survival (mOS) benefit. The mortality hazard for the higher dose regime is 37% lower than the lower dose regime. CONCLUSION: The outcome of patients treated with the higher dose regime has shown to be statistically significant with a mOS benefit and lower mortality hazard. It is therefore clear that maintenance of the higher dose (59.4/60Gy) should be a priority, either at the expense of the OAR or to as much of the tumour volume as possible, whilst still observing the OAR constraints. Different approaches are valid and justifiable.