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Sheilding in posterior third ventricular tumors


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Sheilding in posterior third ventricular tumors

  1. 1. Shielding in Posterior III ventricular lesions Techniques & pitfalls Deepak Agrawal Department of Neurosurgery & Gamma Knife All India Institute of Medical Sciences, New Delhi &
  2. 2. Shielding (Plugging) <ul><li>beam channel blocking </li></ul><ul><li>The main effect of the source blocking is the faster dose falloff in the junction area between the target and the critical structure. </li></ul>
  3. 3. Technique <ul><li>Appropriate sized plug is placed in the critical area </li></ul><ul><li>Helmets to be plugged chosen </li></ul><ul><li>Maximum number of plugs chosen </li></ul><ul><li>Data merged with the gamma-plan to generate plug pattern </li></ul>
  4. 4. AIMS & OBJECTIVES <ul><li>To evaluate the effect of shielding (plugging) in optimizing conformity and dosing for posterior third ventricular lesions </li></ul>
  5. 5. Materials & Methods <ul><li>Prospective study over 12 month period </li></ul><ul><li>Included pts with post 3 rd ventr lesions who underwent GK by one author (DA) </li></ul><ul><li>Shielding was used judiciously to optimize marginal dose & decrease brainstem dose </li></ul>
  6. 6. Results <ul><li>14 patients </li></ul><ul><ul><li>Vascular- 8 </li></ul></ul><ul><ul><li>Tumor- 6 </li></ul></ul><ul><li>Shielding used in 12 (85.7%) </li></ul>
  7. 7. Results <ul><li>SHIELDING </li></ul><ul><li>Increased marginal dose </li></ul><ul><ul><li>Mean increase- 6.2 Gy (2.5- 9 Gy) </li></ul></ul><ul><li>Decreased brainstem dose </li></ul><ul><ul><li>Mean decrease- 2.3 Gy (0.8-4.3 Gy) </li></ul></ul><ul><li>In 1 pt shielding paradoxically increased the brainstem dose necessitating its removal </li></ul>
  8. 8. REPRESENTATIVE CASE 1 <ul><li>16 yr old female </li></ul><ul><li>Post 3 rd ventricular PNET </li></ul><ul><li>Surgery </li></ul><ul><ul><li>WBRT </li></ul></ul><ul><ul><ul><li>Chemotherapy </li></ul></ul></ul><ul><li>Recurrence at 1 yr </li></ul><ul><ul><ul><li>No S/M deficits (Karnofsky is 100%) </li></ul></ul></ul>
  9. 12. FU PET at 1 year showed recurrence with increase in size of the tumor O/E alert, No sensory/motor deficits
  10. 17. REPRESENTATIVE CASE 2 <ul><li>40 yr old female </li></ul><ul><li>FUC of Tentorial DAVF </li></ul><ul><li>Embolised twice </li></ul><ul><ul><li>Subsequently bled </li></ul></ul><ul><li>Now planned for GK </li></ul><ul><ul><ul><li>No S/M deficits </li></ul></ul></ul>
  11. 21. REPRESENTATIVE CASE 3 <ul><li>45 yr old female </li></ul><ul><li>CAD/HT/DM </li></ul><ul><li>headache & vomiting </li></ul><ul><li>Refused for surgery </li></ul>
  12. 25. REPRESENTATIVE CASE 4 <ul><li>22 yr old male </li></ul><ul><li>Sudden onset headache & vomiting </li></ul><ul><li>CT- Rt thalamic bleed </li></ul><ul><li>Angio- Rt Thalamic AVM </li></ul><ul><li>Not suitable for embolisation </li></ul><ul><li>Present status: Lt hemiperesis 4-/5 </li></ul>
  13. 31. CONCLUSIONS <ul><li>Shielding in GK radiosurgery is particularly valuable in post 3 rd ventricular lesions. </li></ul><ul><li>Requires skill & experience </li></ul><ul><li>Overall planning is very important prior to use of shielding </li></ul>
  14. 32. THANK YOU