Shielding in Posterior III Shielding in Posterior III ventricular lesionsventricular lesions

Techniques & pitfallsTechniques & pitfalls

Deepak AgrawalDeepak AgrawalDepartment of Neurosurgery & Gamma KnifeDepartment of Neurosurgery & Gamma Knife

All India Institute of Medical Sciences, New Delhi &All India Institute of Medical Sciences, New Delhi &

Shielding (Plugging)Shielding (Plugging)

►beam channel blocking beam channel blocking

►The main effect of the source blocking is the The main effect of the source blocking is the faster dose falloff in the junction area faster dose falloff in the junction area between the target and the critical between the target and the critical structure. structure.

TechniqueTechnique►Appropriate sized plug Appropriate sized plug

is placed in the critical is placed in the critical areaarea

►Helmets to be plugged Helmets to be plugged chosenchosen

►Maximum number of Maximum number of plugs chosenplugs chosen

►Data merged with the Data merged with the gamma-plan to gamma-plan to generate plug patterngenerate plug pattern

AIMS & OBJECTIVESAIMS & OBJECTIVES

To evaluate the effect of shielding To evaluate the effect of shielding (plugging) in optimizing conformity and (plugging) in optimizing conformity and dosing for posterior third ventricular lesionsdosing for posterior third ventricular lesions

Materials & MethodsMaterials & Methods

►Prospective study over 12 month periodProspective study over 12 month period

►Included pts with post 3Included pts with post 3rdrd ventr lesions who ventr lesions who underwent GK by one author (DA)underwent GK by one author (DA)

►Shielding was used judiciously to optimize Shielding was used judiciously to optimize marginal dose & decrease brainstem dosemarginal dose & decrease brainstem dose

ResultsResults

►14 patients14 patients Vascular-Vascular- 88 Tumor-Tumor- 66

►Shielding used in 12 (85.7%)Shielding used in 12 (85.7%)

ResultsResults

SHIELDINGSHIELDING►Increased marginal dose Increased marginal dose

Mean increase- 6.2 Gy (2.5- 9 Gy)Mean increase- 6.2 Gy (2.5- 9 Gy)

►Decreased brainstem doseDecreased brainstem dose Mean decrease- 2.3 Gy (0.8-4.3 Gy)Mean decrease- 2.3 Gy (0.8-4.3 Gy)

►In 1 pt shielding paradoxically increased the In 1 pt shielding paradoxically increased the brainstem dose necessitating its removalbrainstem dose necessitating its removal

REPRESENTATIVE CASE 1

•16 yr old female

•Post 3rd ventricular PNET

•Surgery

•WBRT

•Chemotherapy

•Recurrence at 1 yr

•No S/M deficits (Karnofsky is 100%)

FU PET at 1 year showed recurrence with increase in size of the tumor

O/E alert, No sensory/motor deficits

REPRESENTATIVE CASE 2

•40 yr old female

•FUC of Tentorial DAVF

•Embolised twice

•Subsequently bled

•Now planned for GK

•No S/M deficits

REPRESENTATIVE CASE 3

►45 yr old female45 yr old female►CAD/HT/DMCAD/HT/DM►headache & vomitingheadache & vomiting►Refused for surgeryRefused for surgery

REPRESENTATIVE CASE 4

►22 yr old male22 yr old male►Sudden onset headache & vomitingSudden onset headache & vomiting►CT- Rt thalamic bleedCT- Rt thalamic bleed►Angio- Rt Thalamic AVMAngio- Rt Thalamic AVM►Not suitable for embolisationNot suitable for embolisation►Present status: Lt hemiperesis 4-/5Present status: Lt hemiperesis 4-/5

CONCLUSIONSCONCLUSIONS

►Shielding in GK radiosurgery is particularly Shielding in GK radiosurgery is particularly valuable in post 3valuable in post 3rdrd ventricular lesions. ventricular lesions.

►Requires skill & experienceRequires skill & experience

►Overall planning is very important prior to Overall planning is very important prior to use of shieldinguse of shielding

THANK YOUTHANK YOU