Abstract
Pediatric patients suffering from ependymoma are usually treated with cranial or craniospinal three‐dimensional (3D) conformal radiotherapy (3DCRT). Intensity‐modulated techniques spare dose to the surrounding tissue, but the risk for second malignancies may be increased due to the increase in low‐dose volume. The aim of this study is to investigate if the flattening filter free (FFF) mode allows reducing the risk for second malignancies compared to the mode with flattening filter (FF) for intensity‐modulated techniques and to 3DCRT. A reduction of the risk would be advantageous for treating pediatric ependymoma. 3DCRT was compared to intensity‐modulated radiation therapy (IMRT) and volumetric‐modulated arc therapy (VMAT) with and without flattening filter. Dose–volume histograms (DVHs) were compared to evaluate the plan quality and used to calculate the excess absolute risk (EAR) to develop second cancer in the brain. Dose verification was performed with a two‐dimensional (2D) ionization chamber array and the out‐of‐field dose was measured with an ionization chamber to determine the EAR in peripheral organs. Delivery times were measured. Both VMAT and IMRT achieved similar plan quality in terms of dose sparing in the OAR and higher PTV coverage as compared to 3DCRT. Peripheral dose in low‐dose region, which is proportional to the EAR in organs located in this region, for example, gonads, bladder, or bowel, could be significantly reduced using FFF. The lowest peripheral EAR and lowest delivery times were hereby achieved with VMATFFF. The EAR calculated based on DVH in the brain could not be reduced using FFF mode. VMATFFF improved the target coverage and homogeneity and kept the dose in the OAR similar compared to 3DCRT. In addition, delivery times were significantly reduced using VMATFFF. Therefore, for radiotherapy of ependymoma patients, VMATFFF may be considered advantageous for the combination of Elekta Synergy linac and Oncentra External Beam planning system used in this study.
Highlights
flattening filter free (FFF) modes led to significantly higher conformity index (CI) and homogeneity index (HI) of the target compared to 3DCRT
No significant differences were found between VMATFFF and VMATFF in the planning target volume (PTV)
The comparison of IMRTFFF/VMATFFF with the standard plan 3DCRT led to a significant lower dose for the inner ears, right lens, 3DCRT
Summary
Computed tomography (CT) data of 11 pediatric patients with ependymoma were selected from our treatment database for a retrospective planning study. All patients were completely resected and without metastases. The irradiation approach was used in this planning study in the same way as in the HIT Interim Register for children under 4 yrs[14] (dose per fraction 1.8 Gy, total dose 50.4 Gy). The precursor was the HIT 2000 study, a multicenter therapy optimization study, which provided optimal and risk‐adapted therapy nationwide in Germany and Austria for patients up to the age of 21 with an intracranial localized medulloblastoma, PNET, or ependymoma. Following the completion of the HIT 2000 study, the HIT Interims Register study was launched to bridge the period until the relaunch of the study with the same standard of quality
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