Over recent years radiotherapy for glioblastoma has been shifting from traditional 3D conformal techniques to using intensity modulation being Volumetric Arc Therapy (VMAT) with coplanar full arcs a broadly accepted approach. This improvement in technical delivery of radiotherapy enables us to obtain optimum dose distribution to the PTV whilst reducing doses to the organs at risk. This is particularly important in glioblastoma radiotherapy where the proximity of the OARs to the PTV makes it difficult to create optimised VMAT plans.
Non-Coplanar VMAT Technique
In 2015 at Aberdeen Royal Infirmary we developed a VMAT technique utilising non coplanar partial arcs, the objective being to optimise PTV coverage and dose conformity, whilst sparing surrounding OARs and reducing dose to normal brain. This was investigated with a retrospective treatment planning study which found, in particular for lateralised tumours, the use of half arcs gave a significant reduction in whole brain dose. The addition of a non-coplanar arc improved conformity.
Treatment is delivered through VMAT technique with two coplanar half arcs and one or two non-coplanar half arcs delivered with the couch at 90°. This current study looks at the outcomes of all Glioblastoma patients that went on to be treated between January 2015 – January 2017 using this technique, with 60Gy in 30# and concurrent temozolamide. Progression free survival and overall survival was analysed using Kaplan Meier survival analysis and compared to outcomes in the literature.
21 patients were in this time period. Eight (38.1%) were female and thirteen (61.9%) male. Median age was 50.3 years with a range from 26 - 73. 10 (47.6%) of these patients were MGMT mutated. 9 had >90% surgical resection (reported on post op MRI), 3 had 50-89%, 4 had <50% resection, 3 had biopsies and in 2 cases resection was not reported. Median progression free survival in this population was 11 months with median overall survival of 16 months.
On review of this cohort of patients, the outcomes in terms of overall and progression free survival are similar to those seen in the literature. The median overall survival of 16 months and PFS of 11 months seen in this group is non inferior to those reported by Stupp et al in 2005, that demonstrated a median overall survival of 14.6 months and PFS of 6.9 months for patients treated with radiotherapy plus temozolamide.
Some patients received re-irradiation or palliative chemotherapy at the time of progression which may have impacted the figures above.
The aim is to continue prospective data collection and analysis of toxicity and survival and its correlation with other molecular prognostic markers.
This planning technique has now been extended to all Glioblastoma patients including those treated with hypofractionated radiotherapy (40Gy in 15#).