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RS-VST Stereotaxy
1. ROSE CASE
STEREOTAXY FOR VESTIBULAR SCHWANNOMA
RADIATION ONCOLOGY
SIMULATION TO EXECUTION
DR KANHU CHARAN PATRO
2. HISTORY
• 40 year male
• Diagnosed case of vestibular schwannoma
• Right side
• P/w – Tinnitus – 6 month
• Slight decreasing in hearing loss-3 months
• Dizziness- 3 months
• Facial fasciculation twitching- 3 months
• No facial numbness
14. Imaging conclusion
• RT. CP angle tumor
• Dm-16mm x 21mm x 13mm
• Dm of intracanalicular component 11mm x 9mm
• Indenting RT. middle cerebellar peduncle
• Indenting cisternal part of Vth nerve
• VIIth and VIIIth nerve separately not visualized
• No compression on 4th ventricle
• No internal cystic component
• Hypo on T1 as well as onT2
• Minimal enhancement
• Widened internal meatus
Imaging conclusion
20. Why we have chosen radiation
• Very small tumor
• Not visualized 7th and 8th nerve
• Solid variant
• < 2.5 cm
• Good hearing and facial function
23. Tumor board decision
• After group discussion with neurosurgeon,
radiation oncologist and patient, board
decided to plan for stereotactic radiotherapy
• Patient was explained about complications
and outcome of each procedure
– Hearing preservation
– Facial numbness
24. Patient discussion
• Discussed about RT comparing with surgery
• Discussed about the procedure
• Discussed about hearing preservation
• Discussed about imaging and follow up
• Discussed about tumor response
• Discussed about need of surgery in future
• Discussed about post radiotherapy pain
31. • 1mm slice
• Contrast
• Vertex to neck
• With fraxion
Planning CT
32. MRI protocol
• T1/T2/FLAIR sequence- Usual sequence
• 3D FSPGR sequence- Normal anatomy
• FIESTA sequence- Cochlea and brain stem
• GRE sequence- Cystic changes/Hemorrhage
• 512x 512 matrix
• 1mm slice
• No gap
• No tilt
• Neutral neck
• FOV should include body contour nose, eye and skull
43. SL NO PARAMETER VALUE
1 D MAX 29.83Gy
2 D95% 25.25Gy
3 D100% 24.18Gy
4 V95% 100%
5 V25 Gy[V100%] 97.5%
6 V110% 18.26%
7 V120% 0
8 V130% 0
1. Prescription Isodose level is usually not 100% PD covering 100% PTV
2. Often 95% PD covering 95% PTV or higher
3. Or 100% PD covering 95% PTV or higher.
Michael Torrens,/J Neurosurg (Suppl 2)/2014
PTV coverage index
44. • FORMULA
• VOLUME OF PRESCRIPTION ISODOSE/PTV VOLUME
• 3.214/2.776=1.15
• DESIRABLE=1
[Sonja Petkovska
Proceedings of the Second
Conference on Medical Physics
and Biomedical Engineering]
RTOG conformity index
45. • FORMULA
(VOLUME OF PRESCRIPTION ISODOSE IN AREA OF INTEREST)2
PTV VOLUME X VOLUME OF PRESCRIPTION ISODOSE
• 3.03x3.03/2.776X3.214=1.02
• IDEAL= > 0.85. AND <1
Michael Torrens,/J Neurosurg (Suppl 2)/2014
Paddick conformity index
46. • FORMULA
• MAXIMUM DOSE/PRESCRIPTION DOSE
• 29.83Gy/25Gy=1.19
• DESIRABLE = 1.1-1.3
HOMOGENITY index
47. • Dose fall off observation is very much needed in this
evaluation under headings
• Gradient index
• Difference between various isodose lines
• e.g between 80% and 60%- ideal- <2mm
• Between 80% and 40%- ideal- < 8mm
• For that reason we have to calculate equivalent
radius
Dose fall off
48. • To evaluate dose gradient we have to find out
difference between radius of various isodose line
• But none is iso spherical
• We have to find out equivalent radius from formula
• First find out the specified isodose volume
• Then calculate the radius
• V=4/3 πr3
• r= (3V/4π)1/3
Equivalent radius
50. • FORMULA
– Difference of equivalent radius of prescription
isodose and equivalent radius of 50% isodose
• 1.83mm=0.91mm
• 0.92mm
• It should be between 0.3 to 0.9
Gradient index
51. • BETWEEN 80% AND 60%- IDEAL-<2mm
– HERE- 0.33mm
• BETWEEN 80% AND 40%- IDEAL- <8mm
– HERE- 0.74mm
EORTC-22952-26001
Distance between various isodose lines
53. SL NO ORGAN DESIRABLE ACHIEVED
1 RT. EYE MAX <22.5Gy 1Gy
2 LT. EYE MAX <22.5Gy 1Gy
3 RT. OPTIC NERVE MAX <22.5Gy 1.2Gy
4 LT. OPTIC NERVE MAX <22.5Gy <1Gy
5 OPTIC CHIASM MAX <22.5Gy <2.8Gy
8 BRAIN STEM MAX 23-31Gy 27.19Gy
9 RT. COCHLEA MEAN <25Gy 20.35Gy
10 LT. COCHLEA MEAN <25Gy 1.31Gy
GG HANNA/CLINICAL ONCOLOGY/2016
OAR coverage
54. • MECHANICAL ISOCENTER CHECK
– WINSTON LUTZ TEST
• POINT DOSE VERIFICATION
• TOLERANCE-1MM
Travis R. Denton/JOURNAL OF APPLIED CLINICAL MEDICAL PHYSICS/2015
QA part
58. PREMEDICATION
• TAB. DEXAMETHASONE 8MG THRICE DAILY
STARTING DAY BEFORE
• TAB. ONDANSETRON 8MG THRICE DAILY
STARTING DAY BEFORE
• TAB. PAN 4O ONCE DAILY STARTING DAY
BEFORE
• DIABETES CARE IF
Pre medication-optional
59. • TAPER THE STEROID OVER A WEEK
• ANTI EMETICS
• PPI
Post medication-optional
63. DOCTORS
• DR P S BHATTACHARYA
• DR C R KUNDU
• DR V K REDDY
• DR P MADHURI
• DR SAJAL KAKKAR
PHYSICISTS
• MR A C PRABU
• MR A SRINU
• MR Prasad
• DR ANIL KUMAR
TECHNOLOGIST TEAM
Acknowledgments