2. Clinical Anatomy
The eye is composed of three
layers.
Outer fibrous layer formed by the
sclera posteriorly and the cornea
anteriorly.
Inner layer , sensory retina with
vision concentrated at the fovea
which is lateral to the optic nerve
and directly posterior to the lens.
In between these vascular layer –
the uvea or choroid –which
supplies the retina. The iris is the
outer continuation of the vascular
layer
Lens sits just behind iris,
suspended from the ciliary body.
No lymphatic drainage
3. PATHOLOGY Flexner Wintersteiner
rosettes
-columnar cells around a
central lumen
-also seen in
medulloepithelioma
Homer Wright
-rosettes around a central
neuromuscular core
-neuroblastoma,
medulloepithelioma,
medulloblastomas
Fleurettes
Tumor cells with pear shaped
eosinophilic processes
projecting through
8. Transaxial T2-weighted (TR/TE, 3,460/116 ms) (a) and
T1-weighted (TR/TE, 374/14 ms) precontrast (b) and
postcontrast (c)
MRI of exophytically growing retinoblastoma with secondary retinal
detachment. Retinoblastoma typically has low signal intensity
compared to the vitreous body on T2-weighted images and
intermediate signal intensity on precontrast T1-weighted images,
and it demonstrates marked contrast enhancement
14. RADIOACTIVE PLAQUE APPLICATION
Procedure: 1st USG of eye done: for
tumor dimensions: maximum basal
diameter, max height → surgical
exploration → applicators are applied
over sclera overlying the tumor → 1.5-2
mm margin on either side of basal
diameter → retention sutures → Rx →
Re-exploration for removal of plaques
20. External beam radiotherapy
Indications
Multi-focal retinoblastoma
RB close to macula or optic nerve
Large tumor with vitreous seeding
Positioning
Proper immobilization is important
thermoplastic or Perspex shell
with the patient supine and the
chin in a neutral position
Treatment is done under
anesthesia: Ketamine
Energy: Co-60 or 4-6 MV photons
21. Technique
Lateral field technique
Started in 1930’s
D – shaped lateral field with anterior
border kept at bony orbit
Disadvantage: tumor recurrence at or
near ora serrata
Modified lateral beam technique
Two lateral opposed D-shaped fields
are used
22. Direct Anterior Field [Hungerford et al ]
Whole eye is treated
Disadvantage:
Cataract formation
Dose exits through brain
Lacrimal gland irradiation-impaired tear
production
Advantages:
Simple, easy to setup
Reproducible
Homogenously irradiates entire retina
Anterior lens sparing technique (ALD) [Abramson et al ]
Lateral D-shaped field: Day1-Day 4 by photons
Anterior electron beam field with central circular contact lens as lens
shaped shield: on Day 5
23. Unilateral disease:
one lateral field or
2 oblique portals [superior and
inferior]
Bilateral disease:
parallel opposed lateral fields
The anterior beam edge is
placed at the bony canthus
and the beam is angled 1.5
degrees posteriorly if the
contralateral eye remains in
place.
24. Dose
Ideal: 40-45 Gy, 1.8-2 Gy per fraction, 5 days a week
For large tumor /vitreous seeding: 48-50 Gy
Palliative radiotherapy:
Extra-ocular involvement: 20-25 Gy
Metastatic disease: CNS, bones: 5 Gy/1#, 15 Gy/3#
Unilateral : single lateral field
With anterior extension: anterior field + lateral field tilted 5-15°
posteriorly
Bilateral disease: parallel opposed lateral fields
25. 3D CONFORMAL RADIOTHERAPY TECHNIQUE
Based on 3D CT scan planning
In unilateral RB, 4 non-coplanar fields are used.
fields are anterior oblique: superior, inferior, medial, and lateral.
0.5-cm bolus can be used.
entire retina should be treated, including 5 to 8 mm of the proximal optic
nerve.
Critical structures such as the opposite eye, optic chiasm, pituitary
gland, brainstem, posteriormost upper teeth, and upper cervical spine.
The tumor volume is treated to the 98% or 95% line,with the
aforementioned organs and tissues receiving significantly less dose.
26. bilateral disease, six
noncoplanar fields are used:
two lateral opposing, and
two anterior oblique fields
to each eye following the
same criteria described
previously.
3D CT scan reconstruction image showing beam arrangement for unilateral
RB : anterior medial and lateral fields (A), anterior superior and inferior fields
(B), sagittal view of composite isodose distribution (C), and axial transverse
view of isodose distribution (D)
27. Follow up
1st 6 months: 4-6 week intervals
Upto 3 years: at 4-6 month intervals
Later, yearly
Family history positive: All family members [other
children at birth] should be examined yearly
