Abstract
AimIn patients with isocitrate dehydrogenase (IDH) mutated anaplastic glioma determine the dosimetric benefits of delivering radiation therapy using a PET guided integrated boost IMRT technique (ib-IMRT) compared with standard IMRT (s-IMRT) in reducing dose to normal brain.MethodsTen patients with anaplastic glioma, identified as a favourable molecular subgroup through presence of IDH mutation, and managed with radiation therapy using an ib-IMRT were enrolled into a dosimetric study comparing two RT techniques: s-IMRT to 59.4Gy or ib-IMRT with 59.4/54Gy regions. Gross Tumour volume (GTV) and Clinical Target Volumes (CTV) were determined by MRI, 18F-Fluoroethyltyrosine (FET) and 18F-Fluorodeoxyglucose (FDG) PET imaging. A standard risk Planning Target Volume (PTVsr) receiving 59.4Gy (PTV59.4) in the s-IMRT technique was determined by MRI T2Flair and FET PET. For the ib-IMRT technique this PTVsr volume was treated to 54Gy, and the high-risk PTV (PTVhr) receiving 59.4Gy was determined as a higher risk region by FDG PET and MRI gadolinium enhancement. Standard dosimetric criteria and normal tissue constraints based on recent clinical trials were used in target delineation and planning. Normal Brain was defined as Brain minus CTV. Endpoints for dosimetric evaluation related to mean Brain dose (mBrainDose), brain volume receiving 40Gy (Brainv40) and 20Gy (Brainv20). The variation between the dosimetric endpoints for both techniques was examined using Wilcoxon analysis.ResultsThe 10 patients had tumours located in temporal (1), parietal (3), occipital (2) and bifrontal (4) regions. In ib-IMRT technique the median volume of PTVhr was 25.5 cm3 compared with PTVsr of 300.0 cm3. For dose to PTVhr the two treatments were equivalent (p = 0.33), and although the ibIMRT had a prescribed 10% dose reduction from 59.4Gy to 54Gy the median reduction was only 5.9%. The ib-IMRT dosimetry was significantly improved in normal brain endpoints specifically mBrainDose (p = 0.007), Brainv40 (p = 0.005) and Brainv20 (p = 0.001), with a median reduction of 9.3%, 19.0 and 10.8% respectively. After a median follow-up of 38 months two patients have progressed, with no isolated relapse in the dose reduction region.ConclusionAn approach using ib-IMRT for anaplastic glioma produces significant dosimetric advantages in relation to normal brain dose compared with s-IMRT plan. This is achieved without a significant reduction to the target volume dose despite the reduction in prescribed dose. This technique has advantages to minimise potential late neurocognitive effects from high dose radiation in patients with favorable subtype anaplastic glioma with predicted median survival beyond ten years.
Highlights
Anaplastic oligodendroglial tumours are a favourable subsite of high grade glioma that have recently been shown to be associated with median survival beyond 10–15 years with management by combined modality therapy with limited surgery, radiation therapy and chemotherapy [1, 2]
This study aims to evaluate the dosimetric benefits of a novel radiation approach for favourable anaplastic glioma (AG) utilizing improved targeting of radiation therapy to areas within the tumour at different dose levels defined by MRI and nuclear medicine techniques
Consecutive adult patients diagnosed with AG and referred to The Department of Radiation Oncology at the Northern Sydney Cancer Centre were entered into a prospective database, approved by Institutional Ethics Review Board. 10 patients with favourable molecular subgroup as defined by presence of isocitrate dehydrogenase (IDH) mutation were included in this dosimetric study
Summary
Anaplastic oligodendroglial tumours are a favourable subsite of high grade glioma that have recently been shown to be associated with median survival beyond 10–15 years with management by combined modality therapy with limited surgery, radiation therapy and chemotherapy [1, 2]. In recent years these and other patients whose tumours are harbouring an isocitrate dehydrogenase (IDH) mutation are being classified into a more favourable subgroups of patients with prolonged survival [3,4,5]. Radiation therapy is the key component of management but high dose therapy and large volume standard treatment has been associated with late neurocognitive effects that will reach clinical significance in patients with durable survival [8, 9]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
