Planning and Dosimetric Study of Volumetric Modulated Arc Based Hypofractionated Stereotactic Radiotherapy for Acoustic Schwannoma - 6MV Flattening Filter Free Photon Beam

  • Swamy, Shanmugam Thirumalai (Department of Radiation Oncology, Yashoda Hospital) ;
  • Radha, Chandrasekaran Anu (School of Advanced Sciences, VIT University) ;
  • Arun, Gandhi (Department of Radiation Oncology, Yashoda Hospital) ;
  • Kathirvel, Murugesan (Department of Radiation Oncology, Yashoda Hospital) ;
  • Subramanian, Sai (Department of Radiation Oncology, Yashoda Hospital)
  • Published : 2015.07.13


Background: The purpose of this study was to assess the dosimetric and clinical feasibility of volumetric modulated arc based hypofractionated stereotactic radiotherapy (RapidArc) treatment for large acoustic schwannoma (AS >10cc). Materials and Methods: Ten AS patients were immobilized using BrainLab mask. They were subject to multimodality imaging (magnetic resonance and computed tomography) to contour target and organs at risk (brainstem and cochlea). Volumetric modulated arc therapy (VMAT) based stereotactic plans were optimized in Eclipse (V11) treatment planning system (TPS) using progressive resolution optimizer-III and final dose calculations were performed using analytical anisotropic algorithm with 1.5 mm grid resolution. All AS presented in this study were treated with VMAT based HSRT to a total dose of 25Gy in 5 fractions (5fractions/week). VMAT plan contains 2-4 non-coplanar arcs. Treatment planning was performed to achieve at least 99% of PTV volume (D99) receives 100% of prescription dose (25Gy), while dose to OAR's were kept below the tolerance limits. Dose-volume histograms (DVH) were analyzed to assess plan quality. Treatments were delivered using upgraded 6 MV un-flattened photon beam (FFF) from Clinac-iX machine. Extensive pretreatment quality assurance measurements were carried out to report on quality of delivery. Point dosimetry was performed using three different detectors, which includes CC13 ion-chamber, Exradin A14 ion-chamber and Exradin W1 plastic scintillator detector (PSD) which have measuring volume of $0.13cm^3$, $0.009cm^3$ and $0.002cm^3$ respectively. Results: Average PTV volume of AS was 11.3cc (${\pm}4.8$), and located in eloquent areas. VMAT plans provided complete PTV coverage with average conformity index of 1.06 (${\pm}0.05$). OAR's dose were kept below tolerance limit recommend by American Association of Physicist in Medicine task group-101(brainstem $V_{0.5cc}$ < 23Gy, cochlea maximum < 25Gy and Optic pathway <25Gy). PSD resulted in superior dosimetric accuracy compared with other two detectors (p=0.021 for PSD.


Acoustic schwannoma;VMAT;HSRT;point dosimetry;COMPASS


  1. Wolff HA, Wagner DM, Christiansen H, et al (2010). Single fraction radiosurgery using Rapid Arc for treatment of intracranial targets. Radiation Oncology, 5, 77.
  2. Xin Y, Wang JY, Li L, et al (2012). Dosimetric verification for primary focal hypermetabolism of nasopharyngeal carcinoma patients treated with dynamic intensity-modulated radiation therapy. Asian Pac J Cancer Prev, 13, 985-9.
  3. Minniti G, Clarke E, Lanzetta, et al (2011). Stereotactic radiosurgery for brain metastases, analysis of outcome and risk of brain radionecrosis. Radiation Oncology, 6, 48.
  4. Subramanian S, Srinivas C, Ramalingam K, et al (2012). Volumetric modulated arc-based hypofractionated stereotactic radiotherapy for the treatment of selected intracranial arteriovenous malformations, Dosimetric report and early clinical experience. Int J Radiat Oncol Bio Phys, 82, 1278-84.
  5. Swamy ST, Radha CA, Kathirvel M, et al (2014). Feasibility study of deep inspiration breath-hold based volumetric modulated arc therapy for locally advanced left sided breast cancer patients. Asian Pac J Cancer Prev, 15, 9033-38.
  6. Thirumalai SS, Anuradha C, Kathirvel M, et al (2014). Pretreatment quality assurance of volumetric modulated arc therapy on patient CT scan using indirect 3D dosimetry system. Int J Cancer Ther Onco, 2, 20416.
  7. Visser R, Wauben DJ, de Groot M, et al (2013). Efficient and reliable 3D dose quality assurance for IMRT by combining independent dose calculations with measurements. Med Phys, 40, 021710.
  8. Wang H, Chang RJ, Xiao F (2012). Hypofractionated stereotactic radiotherapy for large arteriovenous malformations. Surg Neurol Int, 3, 105-10.
  9. Kappor S, Batra S, Carson K, et al (2011). Long-term outcomes of vestibular schwannomas treated with fractionated stereotactic radiotherapy, An institutional experience. Int J Radiat Oncol Biol Phys, 81, 647-53.
  10. Li S, Rashid A, He S, Djajaputra A (2004). A new approach in dose measurement and error analysis for narrow photon beams beamlets shaped by different multileaf collimators using a small detector. Med Phys, 31, 2020-32.
  11. Abacioglu V, Ozen Z, Yilmaz Y, et al (2014). Critical appraisal of RapidArc radiosurgery with flattening filter free photon beams for benign brain lesions in comparison to GammaKnife, a treatment planning study. Radiation Oncology, 9, 119.
  12. Benedict SH, Cai J, Libby B, et al (2010). SRT and SBRT, Current practices for QA dosimetry and 3D, Journal of Physics, Conference Series, 250, 012057.
  13. Benedict SH, Yenice KM, Followill D, et al (2010). Stereotactic body radiation therapy, The report of AAPM task group 101. Med Phy, 37, 4078-101.
  14. Boggula R, Lorenz F, Mueller L, et al (2010). Experimental validation of a commercial 3D dose verification system for intensity-modulated arc therapies. PhysMed Biol, 55, 5619-33.
  15. Ekambaram V, Vealyudham R, Swaminathan S, et al (2015). Planning aspects of volumetric modulated arc therapy and intensity modulated radio therapy in carcinoma left breast - A comparative study. Asian Pac J Cancer Prev, 16, 1633-36
  16. Gagnon JC, Riault DT, Guillot M, et al (2012). Dosimetric performance and array assessment of plastic scintillation detectors for stereotactic radiosurgery quality assurance. Med Phys, 39, 429-36
  17. Ingrosso G, Micheli R, Fedele D, et al (2012). Cone-beam computed tomography in hypofractionated stereotactic radiotherapy for brain metastases. Radiation Oncology, 7, 54.

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