TY - JOUR A1 - Alvarez Moret, Judit A1 - Obermeier, Tina A1 - Pohl, Fabian A1 - Löschel, Rainer A1 - Kölbl, Oliver A1 - Dobler, Barbara T1 - Second cancer risk after radiation therapy of ependymoma using the flattening filter free irradiation mode of a linear accelerator JF - Journal of Applied Clinical Medical Physics N2 - 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. KW - Adolescent KW - Child KW - Child, Preschool KW - Ependymoma/radiotherapy KW - Humans KW - Infant KW - Neoplasms, Radiation-Induced KW - Neoplasms, Second Primary KW - Particle Accelerators KW - Radiotherapy Dosage KW - Radiotherapy Planning, Computer-Assisted KW - Radiotherapy, Intensity-Modulated KW - Retrospective Studies Y1 - 2018 U6 - https://doi.org/10.1002/acm2.12438 VL - 19 IS - 5 SP - 632 EP - 639 PB - Wiley ER - TY - JOUR A1 - Haertl, Petra Maria A1 - Löschel, Rainer A1 - Repp, Natalia A1 - Pohl, Fabian A1 - Kölbl, Oliver A1 - Dobler, Barbara T1 - Frameless fractionated stereotactic radiation therapy of intracranial lesions: Impact of cone beam CT based setup correction on dose distribution JF - Radiation Oncology N2 - Background The purpose of this study was to evaluate the impact of Cone Beam CT (CBCT) based setup correction on total dose distributions in fractionated frameless stereotactic radiation therapy of intracranial lesions. Methods Ten patients with intracranial lesions treated with 30 Gy in 6 fractions were included in this study. Treatment planning was performed with Oncentra® for a SynergyS® (Elekta Ltd, Crawley, UK) linear accelerator with XVI® Cone Beam CT, and HexaPOD™ couch top. Patients were immobilized by thermoplastic masks (BrainLab, Reuther). After initial patient setup with respect to lasers, a CBCT study was acquired and registered to the planning CT (PL-CT) study. Patient positioning was corrected according to the correction values (translational, rotational) calculated by the XVI® system. Afterwards a second CBCT study was acquired and registered to the PL-CT to confirm the accuracy of the corrections. An in-house developed software was used for rigid transformation of the PL-CT to the CBCT geometry, and dose calculations for each fraction were performed on the transformed CT. The total dose distribution was achieved by back-transformation and summation of the dose distributions of each fraction. Dose distributions based on PL-CT, CBCT (laser set-up), and final CBCT were compared to assess the influence of setup inaccuracies. Results The mean displacement vector, calculated over all treatments, was reduced from (4.3 ± 1.3) mm for laser based setup to (0.5 ± 0.2) mm if CBCT corrections were applied. The mean rotational errors around the medial-lateral, superior-inferior, anterior-posterior axis were reduced from (−0.1 ± 1.4)°, (0.1 ± 1.2)° and (−0.2 ± 1.0)°, to (0.04 ± 0.4)°, (0.01 ± 0.4)° and (0.02 ± 0.3)°. As a consequence the mean deviation between planned and delivered dose in the planning target volume (PTV) could be reduced from 12.3% to 0.4% for D95 and from 5.9% to 0.1% for Dav. Maximum deviation was reduced from 31.8% to 0.8% for D95, and from 20.4% to 0.1% for Dav. Conclusion Real dose distributions differ substantially from planned dose distributions, if setup is performed according to lasers only. Thermoplasic masks combined with a daily CBCT enabled a sufficient accuracy in dose distribution. KW - CBCT KW - Setup error KW - Reproducibility KW - Daily dose distribution KW - Cumulative dose distribution KW - Actual dose distribution KW - Intracranial lesions Y1 - 2013 U6 - https://doi.org/10.1186/1748-717X-8-153 VL - 8 IS - 1 PB - BioMed Central CY - London ER -