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Louise Lambert Radiation Oncology Department Montreal University ASTRO 2006

STEREOTACTIC RADIOTHERAPY FOR INTRACRANIAL MENINGIOMAS: ROLE OF INTRA-OBSERVER AND INTER-OBSERVER VARIABILITY IN CHOICE OF MARGINS. Louise Lambert Radiation Oncology Department Montreal University ASTRO 2006. Intracranial Meningiomas. 20% primary tumors 90% benign tumors

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Louise Lambert Radiation Oncology Department Montreal University ASTRO 2006

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  1. STEREOTACTIC RADIOTHERAPY FOR INTRACRANIAL MENINGIOMAS: ROLE OF INTRA-OBSERVER AND INTER-OBSERVER VARIABILITY IN CHOICE OF MARGINS Louise Lambert Radiation Oncology Department Montreal University ASTRO 2006

  2. Intracranial Meningiomas • 20% primary tumors • 90% benign tumors • Standard treatment:Surgery • Radiotherapy possibly beneficial when: • Incomplete excision • Relapse • Patients who are not surgical candidates

  3. Radiotherapy • Better localization of tumor and immobilization techniques: prognostic factors Goldsmith BJ et al. J Neurosurgery 1994; 80:195 • Fractionated Stereotactic Radiotherapy (FSRT): • Precision of position • Radiobiologic effect of fractions Alheit H. Radiother Oncol 1999;50:145-50

  4. Goal • Literature Review: • No consensus for margins with FSRT • Between 1 mm and 10 mm Alheit H. Radiother Oncol 1999; 50:145-50 Selch MT. IJROBP 2004; 59:101-11 • Measure intra-observer and inter-observer variability in order to select an appropriate margin

  5. Volumes • GTV = CTV • PTV = CTV + margin

  6. Methods and Material • 12 consecutive patients, treated for benign intracranial meningiomas • 2 radiation oncologists and 1 neuroradiologist • Contouring on merged images of CT-MRI with Brainscan • Contouring target volumes: • 2 separate drawing sessions • 1 week interval • blinded

  7. Methods and Material (2) • Intra-observer variability: Mean differences between the two volumes • Inter-observer variability: • Mean absolute difference between volumes • Absolute positional shift in 3D

  8. Results: Intra-observer • Mean 0.56cc (5.2%) • Maximum 0.59cc (12.97%)

  9. Results: inter-observer (1) • Mean maximal difference: 2.13cc (± 0.84cc) • Maximal difference: 7.14cc On a mean volume of 20cc

  10. Results:inter-observer (2) • Vectorial center of mass variation: R= (x2+y2+z2) • Mean center of mass variation: 1.03mm  0.44mm • Maximal variation: 2.79mm

  11. Results:inter-observer (3) V = 4∏r3/3 dV = 4∏r2dr Maximal volume difference 7.14cc is within a 2mm variation in radius.

  12. Conclusion (1) • Important aspects of planning: • Accurate delimitation of tumor volumes • Choice of margins • Intra-observer variability: not significant

  13. Conclusion (2) • Inter-observer variability: • Center of mass variation R = 2mm for 95% • Includes intra- and inter-observer volume variation

  14. Limitations and Future Work • Only 12 patients • Exclusion volumes • DVH

  15. Acknowledgements • Marie-Andrée Fortin, M.D. • Carole Lambert, M.D. • Jean-Paul Bahary, M.D. • Christian Berthelot, M.D. • Robert Doucet, M.Sc • Martin Hinse,M.Sc

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