Medulloblastoma

MEDULLOBLASTOMA
By
Dr. Ayush Garg
“© Mayo Foundation for Medical Education and Research. All Rights Reserved. Used with permission.”

• Learning Objectives for JRs
• New molecular classification system
• CSF Pathway
• Risk groups
• Learning Objectives for SRs
• Line of management in recurrence

• Introduction
• Epidemiology
• Anatomy- CSF Pathway
• Clinical Features
• Classification
• Diagnostic Work Up
• Treatment

Introduction
• Most common childhood malignant tumors.
• Accounts for 15% to 20% of all CNS tumors in children.
• Median age of presentation is 6 years.
• The tumor arises in the cerebellar vermis and projects into the fourth
ventricle.
• It is a malignant invasive embryonal tumor of the cerebellum with
predominantly neuronal differentiation and an inherent tendency to
metastasize via CSF pathways.
• Rare tumor in adults with an incidence of 0.5 per 100,000.
• In adults the 20 to 40 years age group

• Leptomeningeal seeding at diagnosis is 30% to 35%
• Systemic spread is seen in 5% of patients, mostly to bone and
bone marrow.
• Overall 5-year OS & DFS is approx 70% to 85%.

Epidemiology
• There is a 1.5:1 male-to-female ratio, and 70% of
medulloblastomas are diagnosed by age 20 years.
• Rarely cases found in those older than 50 years.
• Gorlin and Turcot syndromes have increased rates of
medulloblastoma but account for only 1% to 2% of cases
• Location – Cerebellum –
• Vermis (>75%)
• Hemispheric – more in adults

• Turcot syndrome is a condition characterized by
multiple adenomatous colon polyps
• Gorlin Syndrome A genetic condition that causes
unusual facial features and disorders of the skin, bones,
nervous system, eyes, and endocrine glands.

EMBRYONAL TUMORS OF CNS
• WHO classification (2007) – Grade IV
Medulloblastomas (MB)
CNS primitive neuroectodermal tumors (CNS PNET)
Supratentorial PNET
Medulloepithelioma
Ependymoblastoma
Atypical teratoid / rhabdoid tumors (AT/RT)
• Earlier - all tumors under the generic term PNET
• Recent data support separation - Each tumor distinctive profile (morphology,
immunohisto-chemical, molecular genetic & clinical)

Classification of Medulloblastoma
(WHO 2007)
Medulloblastomas (histologically defined)
 Classic
 4 histological variants
 Desmoplastic/nodular
 MB with extensive nodularity (MBEN)
 Large cell MB
 Anaplastic MB

Medulloblastoma is a densely cellular tumor with small, darkly staining ovoid cells with
hyperchromatic nuclei and frequent mitoses. Homer Wright rosettes (clustered cells surrounding a
central eosinophilic core) are characteristic.
• Indicative of Neuronal diff.
– Nuclei around a round solid central eosinophilic fibrillary zone containing cellular processes
(neurofibrils)
– No lumen
– IHC positive for synaptophysin & neurofilament
Medulloblastoma: small blue round cell tumor

Medulloblastoma (genetically defined)
1. Medulloblastoma WNT activated
2. Medulloblastoma, SHH activated and TP53 mutant
 Medulloblastoma, SHH activated and TP53 mutant
 Medulloblastoma, SHH activated and TP53 wild type
3. Medulloblastoma, group 3
4. Medulloblastoma, group 4
Medulloblastoma, non-WNT/non-SHH

WNT (Wingless)
• Least common in Medulloblastoma, found in
approximately 10% of cases
• WNT tumors most frequently occur in late childhood
and adolescence but can arise in all ages
• M:F ratio is 1:1.
• Rarely metastatic
• Most favorable prognosis
• 5year survival>95%

• Tumors arise from the developing lower rhombic lip and
embryonic dorsal brain stem
• Prognosis- worse in adults, relative to pediatric
patients
• Most WNT tumors display classic medulloblastoma
histology and nuclear localization of beta-catenin
nucleopositivity, CTNNB1 gene mutations, and
monosomy-6.
• Associated with Turcot Syndrome

SHH (Sonic Hedgehog)
• They are named after the sonic hedgehog signaling
pathway, which is considered to drive tumor initiation in
the majority of cases.
• Incidence bimodal- infants aged <3 years and adults
• M:F ratio is 1:1
• Intermediate prognosis between Group 3 and WNT
• 5-year survival of approximately 70%
• Associated with Gorlin Syndrome

• Tumors arise from neuron precursors found in the
external granule layer of the developing cerebellum
• The SHH MB subgroups include TP53 mutant and
TP53 wild-type subgroups.
• All nodular desmoplastic medulloblastomas can be
characterized as SHH subgroup.

Group 3
• Group 3 tumors affect mostly infants and children, are
rare in adults
• Characterized by amplification of the MYC proto-
oncogene, and almost all cases exhibit aberrant MYC
expression.
• M> F
• Prognosis- worst (50% overall survival rate), often
metastatic at the time of presentation
• The majority of MBs in group 3 are classical MB and
include the majority of large cell/anaplastic tumors.

Group 4
• Affect patients of all ages, seen in 30-40% of cases
• Most common subgroup, found in 40% of all patients
and associated with intermediate prognosis
• They include classical and large cell/anaplastic
histologies
• M:F ratio is 3:1.
• Association is seen with Isochromosome 17q in few
cases.

Age distribution shown for males (solid lines) and females (dotted lines)
Characteri
stic
WNT SHH Group 3 Group 4
Frequency ~10% ~30% ~25% ~35%
Age (Yrs ) Distributed across
ages median (9-10
yrs) – never in infancy
Primarily in infants
<3 & adults >16.
Uncommon in 3-16
yrs group.
Children – Peak
3 – 10 yrs. Rare
in adults
Distributed across
ages – median: 9-10
yrs. More in
adolescents

Diagnostic Work up
• H&P
• MRI of the brain (preop and postop within 24–48 h after
surgery)
• MRI of the spine to rule out leptomeningeal spread
• CSF cytology
• Baseline audiometry, IQ, TSH, CBC, and growth
measurements
• Eighty percent of systemic metastases are osseous. A
bone scan, chest x-ray, and bilateral marrow biopsies
should be routinely performed for M2 and M3 stages.

Radiographic Features
• MRI is the gold standard.
• Medulloblastomas are typically iso- to hypointense on T1-
weighted images and of variable signal intensity on T2-weighted
images and enhance heterogeneously.
• MRI provides improved evaluation of
• Foraminal extent beyond the fourth ventricle,
• Invasion of the brain stem, and subarachnoid metastases.
• On CT, medulloblastomas are classically discrete vermian masses
that are hyperattenuated compared with the adjacent brain and
enhance avidly.

Postoperative axial T2-weighted magnetic resonance imaging for a patient
receiving craniospinal irradiation (CSI) for medulloblastoma showing
extension of cerebrospinal fluid along the optic nerves to the lamina cribrosa
(A) and into the internal auditory canals (B).

T1 (A) and T1 contrast (B) MRI in an 11-year-old boy.
The typical midline location of the tumor that is causing ventricular outlet
obstruction with dilatation of the third and lateral ventricles.

Extension of cerebrospinal fluid along the optic nerves to the lamina cribrosa
(A) and into the internal auditory canals (B)

Cerebrospinal Fluid Cytology
• Sampling of the CSF in the immediate postoperative
period may lead to false-positive results
• Best done before surgery or more than 3 weeks after
surgery, as long as intracranial pressure is not elevated.
• CSF findings:
• CSF pressure above 150 mm H2O at the lumbar level in a
laterally positioned patient,
• elevated protein level (>40 mg/dL in the lumbar cistern),
• a reduced glucose level (below 50 mg/mL), tumor cells by
cytologic examination.
• Tumor markers in the CSF may help in making the diagnosis.

• On MRI CSF dissemination is seen as diffuse
enhancement of the thecal sac, nodular enhancement
of the spinal cord or nerve roots, or nerve root
clumping, predominantly seen along the posterior
aspect of the spinal cord based on CSF circulatory
patterns.
• Spine MRI- Ideal time prior to surgery; otherwise, 10 to
14 days post surgery to avoid a potential false-positive
interpretation from surgical cellular debris and
blood products.

Pediatric MB
Chang Criteria
 primary staging system
since their inception 1969
 2-tier stratification system
Staging
Packer RJ, Goldwein J, Nicholson HS, Vezina LG, Allen JC, Ris MD, et al. Treatment of children with medulloblastomas with reduced-dose craniospinal radiation therapy
and adjuvant chemotherapy: a Children’s Cancer Group Study. J Clin Oncol.1999;17:2127–36.
A modified version of the
Chang staging system is
currently used.

M Staging
 M0 represents no tumor dissemination,
 M1 represents tumor cells in the CSF
 M2 represents presence of gross tumor nodules in the
intracranial, subarachnoid, or ventricular space
 M3 represents gross tumor nodules in the spinal
subarachnoid space
 M4 represents systemic metastasis.

Current clinical risk-stratification for medulloblastoma
Average-risk High-risk
Age ≥3 yrs <3 yrs
Residual Tumor ≤1.5 x 1.5 cm2 >1.5 cm2
Metastases No metastases (M0) Metastases
(M1 – M4)
Pathology Desmoplastic Anaplastic
Brain Stem invasion None Present
Mitotic index Low High
Tumor DNA Content Diploid Aneuploid
Apoptotic Index High Low
DFS 60–90% 20–40%, increased to 50–85%
with adjuvant chemo

Risk Groups
• The presence of metastatic disease is prognostically
significant, with 5-year PFS rates according to CCG-921:
• 70% for M0 disease
• 57% for M1
• 40% for M2 or higher
• The disease-free survival of high-risk patients treated
with CSI with or without chemotherapy is 25% to 30%

Management of Medulloblastoma
• Previously standard of care for patients>3 years with
standard-risk disease-> PORT to the craniospinal axis
to a dose of 35 to 36 Gy followed by a boost to the
whole posterior fossa to a total dose of 54 to 55.8 Gy
• Long term results were EFS in 60% to 65% of patients
• Sequelae of treatment include hormonal deficits,
decreased bone growth, and neurocognitive deficits that
correlate with the age of the child and the radiation
dose.

Management of Standard-Risk
Medulloblastoma
• Currently, the standard of care for children with
standard-risk MB is with CSRT 23.4 Gy with a boost to
the tumor bed to a total dose of 54.0 Gy, followed by
eight cycles of chemotherapy with vincristine, CCNU,
and cisplatin.

Management of High-Risk
Medulloblastoma
According to COG study hyperfractionated accelerated
radiotherapy (HART) regimen given in combination with
pre- and postradiotherapy chemotherapy is being tried
for high risk cases

Is there a role for modified fractionation?
HFRT & HART
Strong radio-biologic rationale
SFOP pilot study- tested HFRT to a CSI dose of 36 Gy without chemotherapy,
early toxicity was reduced and progression-free survival at 3 years was 81%.

HFRT in Medullblastoma: TMH Study
• Median age: 8 years (range 5-14 years)
• Risk-stratification: Average-risk disease (all patients)
• CSI dose: 36 Gy/36 fx, 1 Gy BID, 6 hrs apart over 3.5 wks
• Tumor bed boost: 32 Gy/32 fx, 1 Gy BID, 6 hrs apart over 3
wks
• Total tumor bed dose: 68 Gy /68 fx, 1 Gy BID, 6 hrs apart over
6.5 wks
• Adjuvant chemotherapy: Given only at progression
• Median follow-up: 27 months (range 13-54 months)
HFRT without upfront chemotherapy has an acceptable acute toxicity
profile, without an unduly increased risk of relapse, with preserved
cognitive functioning in children with average-risk medulloblastoma.
Gupta T,IJROBP 2012

Is Hyperfractionated RT better than Standard fractionation in Avg risk
Medulloblastoma..... SIOP PNET 4 Randomised trial
Lannering, JCO 2012
• 322 Children with avg risk medulloblastoma across 122 european centres.
• Standard fraction:23.4 Gy to the CS axis and 54 Gy to whole posterior fossa
• HFRT: 36Gy CS and 60 Gy to Posterior fossa in 68Fractions,1Gy/# twice daily
• Chemotherapy regimen consisting of eight cycles of cisplatin, lomustine, and vincristine
• EFS and OS for HFRT was not superior to STRT

Medical Therapy
Medical decompressive therapy is recommended in the
pre-operative Period
• The steroid of choice is dexamethasone administered in a
loading dose of 0.5-1 mg/kg intravenously (with the
maximum dose being 10 mg).
• Subsequently, dexamethasone (0.25-0.5 mg/kg/day) iv or
PO in divided doses 6-8 hourly, + antacids for GI protection.
• Severe hydrocephalus may require Mannitol or frusemide
• Elevation of the head-end of the bed
(by 30 degrees) can help children with
symptomatic hydrocephalus

Surgery
• Complete surgical resection is ideal, but this may
not always be safe or feasible.
• In such cases, it is recommended to attempt maximal
safe resection to avoid aggressive surgical resection
that can cause significant morbidity

• Generally a radiosensitive &
chemosensitive tumour
• Historical controls: No long-term
survivors without RT
• High recurrence rates with focal
posterior fossa (PF) RT
• High recurrence rates for reduced
dose craniospinal irradiation (CSI)
without chemotherapy (CT)
Landberg, 1953
RADIATION
ALONE
PF- 5%
PF+SC- 25%
PF+CSI- 53%
Rationale of radiotherapy in medulloblastoma
Radiotherapy

Radiotherapy
• PORT should begin within 28 to 31 days following
surgical resection whenever possible.
• Radiotherapy is delivered to the entire craniospinal
axis followed by a boost to the tumor bed for
average-risk patients and to the posterior fossa and
gross metastatic disease for high-risk patients.
• Adults treated for medulloblastoma with a mean dose
to the whole brain of 35 Gy

• Young adults with average-risk disease- reduced-dose
CSI (23.4 Gy)
• High-risk disease- Full-dose CSI (36 Gy)
• This is then followed by a boost to the posterior fossa.
• Intracranial and spinal metastases should be boosted as
well to total doses on the order of 45 to 50 Gy for spinal
metastases and 50 to 54 Gy for intracranial metastases.
Treatment is usually delivered at 1.8 Gy/day

ALTERNATIVE DELIVERY METHODS
• Protons may be employed to reduce exit dose and
toxicity, particularly the risk for secondary malignancy
• The use of proton therapy has been associated with a
meaningful reduction in hematologic and GI toxicity
• Tomotherapy may avoid the need to match fields, but
greater whole body dose exposure
• VMAT may be used to increase conformality and reduce
toxicity

Chemotherapy
• CNS tumors in which combination regimens are
standard of care include CCNU, cisplatin, and vincristine
or cisplatin, cyclophosphamide and vincristine
• The role of adjuvant chemotherapy in children with
medulloblastoma is well established but remains
unclear in adults.

Chemotherapy Recommendations:
• Adjuvant chemotherapy following RT
• Adjuvant chemotherapy following surgery in infant
medulloblastoma (<3-years)
• Pre-irradiation chemotherapy in infant medulloblastoma
to defer RT (till 3-years)
• High-dose chemotherapy with autologous stem-cell
rescue
• Concurrent chemotherapy with RT
• Salvage therapy in relapsed/recurrent
medulloblastoma.

• A series of 32 adults with medulloblastoma from
Germany has shown a nonsignificant trend to prolonged
survival with adjuvant chemotherapy.
• NOA-07 trial of chemoradiotherapy for adult
medulloblastoma demonstrated favorable EFS-67%.

Concurrent chemotherapy with RT
• Concurrent weekly vincristine (1.5mg/m2) given as iv
bolus throughout the course of RT is recommended for
children with standard risk disease being treated with
reduced dose CSI.
• Daily concurrent carboplatin (35mg/m2) as a short
intravenous infusion throughout the course of RT For
children with high risk medulloblastoma is
recommended

For standard-risk patients
• A phase II trial of lomustine, vincristine, and cisplatin
for eight cycles following the reduced CSI prescription
of 23.4 Gy demonstrated PFS rates of 86% and 79% at
3 and 5 years, respectively.
• Hence CSI to 23.4 Gy with chemotherapy is the
standard of care

• High-risk Medulloblastoma- chemotherapy dose
intensification.
• Vincristine, lomustine, and prednisone resulted in a
63% 5-year PFS rate, which was better than an eight-
in-one chemotherapy regimen.
• Eight drugs (vincristine, hydroxyurea, procarbazine,
CCNU, cisplatin, cytosine arabinoside, high-dose
methylprednisolone, and either cyclophosphamide or
dacarbazine) were administered within 12 hours
in an attempt to minimize myelosuppression

Chemotherapy for medulloblastoma
(>3-years of age)
Recommendations for adjuvant chemotherapy (>3-years):
• It should start at least 3 weeks after completion of RT to
allow for myelo-recovery
• Neuraxial imaging should be done for re-assessment of the
disease status prior to initiation of adjuvant chemotherapy
• RFT, LFT, S. Electrolytes- Normal
• Baseline hearing assessment with pure-tone audiometry
prior to starting adjuvant chemotherapy and repeat after
every two cycles of platinum-containing regimen
• A total of 6-8 cycles of adjuvant chemotherapy should be
administered generally cycled at 3-6 weekly interval

Chemotherapy for Infant
Medulloblastoma (<3-years of age)
• Multi-agent chemotherapy including carboplatin/
cisplatin, etoposide, cyclophosphamide, vincristine with
or without the use of systemic high dose methotrexate
and/or intrathecal methotrexate.

Craniospinal Axis Irradiation
• Craniospinal axis irradiation is required in most
medulloblastomas and occasionally in other brain
tumors, such as
• Advanced or metastatic germ cell tumors
• Primitive neuroectodermal tumors
• Pinealoblastoma
• Ependymomas
• Neuroblastoma with leptomeningeal spread
• Leukemia/lymphoma (with CNS axis mets)

• CSI is a very complex technique
• Goal is to achieve uniform dosage
Throughout the subarachnoid space,
Encompassing the entire intracranial vault and spinal canal
• Fundamental is
The use of opposed lateral fields including the cranium and
upper cervical spinal canal,
Matching a posterior spinal field including the full spinal
subarachnoid space with cranial field
In larger children, the upper posterior spinal field matching
with a separate lower posterior spinal field

Radiotherapy Techniques
• EBRT using Conventional RT, 3D-CRT or IMRT (WBRT or
Partial Brain Irradiation)
• Stereotactic radiosurgery (SRS)
• Fractionated Stereotactic RT (FSRT)
• Craniospinal Irradiation (CSI)
• Interstitial brachytherapy may have a role in selected
patients.

Target Volume:
• Entire brain and its meningeal coverings with the CSF
• Spinal cord and the leptomeninges with CSF
• Posterior fossa – boost

Target Volume Definition
• CT simulation is necessary to ensure adequate coverage
of the CTV in the subfrontal region at the cribriform
plate.
• Traditionally, blocks have been used in the lateral fields
to shield not only the facial structures but also the
lenses.

• The lower border of the spinal CTV
(using MRI) should include the lower
border of the thecal sac, which can be
at L5 or S3.
• The use of CT simulation with
contouring of the cord and overlying
meninges that extend laterally to the
lateral aspect of the spinal ganglia
results in a field width that is
narrower than one based on bony
anatomy.
• The addition of shielding further
reduces the volume of normal tissues
included in the treated volume.

GTV- Tumor bed on MRI
CTV = GTV + 15 mm.
PTV = CTV + 3-5 mm, modified only at sella.
Immobilization accuracy +/- 3-5 mm.
95% of isodose covers 100% of CTV & 95% of PTV.
Constraints:
< 70% Supratentorial brain to receive > 50% boost dose.
< 80% Left & right cochlea to receive > 80% of boost
dose.
< 50% Pituitary to receive > 30% of boost dose.
< 10% Left & right optic nerve & chiasma to receive >50.4
Gy each.

• Energy
• 4-6 MV linac or Co60
• Portals
• Whole Brain: Two parallel opposed lateral field.
• Spine: Direct Posterior field
• Scheduling of radiotherapy:
• Starting time : within 28 - 40 days following surgery
• Duration of treatment : 45 to 47 days

WBRT
• Superior: Skin fall off
• Anterior: Skin fall off
• Posterior: Skin fall off
• Inferior: Skull base

Radiation Dose and Dose Fractionation
Regimens
• The total dose is generally 54 to 55.8 Gy @ 1.8Gy/#.
• Lower doses for children <3 years to reduce the risk of
neurocognitive deficits
• When the target contains only a small volume of normal
brain tissue, dose escalation may be possible using
HFRT.

Dose (Conventional)
• CSI (Phase I)
• 30- 36 Gy in 18 - 21 # over 4 weeks to the cranium @ 1.5-
1.8 Gy per #
• 30-36 Gy in 18-21 # over 4 weeks to the spine @ 1.5-1.8 Gy
per #
• Posterior fossa boost (Phase II)
• 18-20 Gy in 10-11# over 2 weeks to the posterior fossa

Doses & volumes as per risk-stratification
CSI for average-risk disease
Standard dose CSI: 35-36 Gy/21-20#/4 weeks @ 1.67-1.8 Gy/#
Reduced dose CSI: 23.4 Gy/13#/2.5 weeks @1.8 Gy/# (+ adj CT)
Boost
If Standard dose CSI : PF or TB boost: 19.8 Gy/11#/2 weeks
If reduced dose CSI: Tumour bed boost: 32.4 Gy/18#/3.5 weeks
CSI for high-risk disease
Standard dose CSI: 35-36 Gy/21-20#/4 weeks @ 1.67-1.8 Gy/#
Higher dose spinal RT: 39.6 Gy/22#/4.5 weeks @1.8 Gy/#
Boost
Whole posterior fossa boost: 19.8 Gy/11#/2 weeks
Boost for gross focal spinal deposit: 5.4-9 Gy/3-5#/1 week
Total tumor bed dose: 54-56 Gy/30-33#/ 6.5 weeks (conventional #)

Treatment Planning and Delivery
• Newer treatment planning and delivery methods such
as IMRT together with daily image verification allow for
improved dosimetry
• Clinically relevant dose reductions to structures anterior
to the target volume such as the heart, gastrointestinal
(GI) tract, and gonads.

PLANNING STEPS
• Positioning
• Immobilization
• Simulation
• Field arrangement
• Matching of CSI
• Aligning of spinal field
• Implementation of plan

• Prone (preferred)
• Supine:
• More patient comfort.
• In-anaesthetic patient for airway
• Head position
• Slightly extended and the shoulders pulled
down to avoid beam divergence into the
mandible & dentition.
• Facilitates the use of a moving junction
between the cephalad border of post.
Spine field and the lower borders of cranial
fields.
• Lumbar and Thoracic spine parellel to couch
• Immobilization is essential and involves the
use of a head shell or full-body
immobilization.
Patient Positioning and Immobilization

Different RT techniques for CSI
• Initially entire CNS is irradiated at one stretch
with a single field. Pt. is prone below a shielded
screen on top of RT table. It is known as
Patterson FARR technique. Co60 source
exposes the entire craniospinal axis at a focus
distance of 125 c.m.
• Moving Field technique: Table and pt. moves
longitudinally in relation to a perpendicular Co60
beam which is stationary at 50 cm focal skin
distance.
• Hockey Stick technique: Pt. prone with head
turned to one side.
• Field at base of brain is defined by cribriform
plate and is above both orbital cavities.
• Include middle cranial fossa and to exclude
orbit and lens.
• Each side of head is treated on alternate
days.

German Helmet Technique
German Helmet Technique:
• Field set so that beam flashes over entire head in ant , post, & sup directions and only the
caudal margin is defined by collimator by RT machine .
• Caudal margin is set up so that it follows a line drawn from Lateral canthus through the
ext. auditory canal to the post aspect of the skull At C2-C3 jt.
• Here we shield extra-Cranial structure in the subfrontal region,facial structures, teeth and
lens.

Field Arrangements
• Whole brain
o In the simulator, opposing lateral fields
are applied to the whole brain with a
collimator rotation of 7-11o to match the
divergence of the direct posterior spinal
field.
• SFOP guidelines- The recommended
placement of block is:
o 0.5 cm below the orbital roof .
o 1 cm below and 1 cm in front of the lower
most portion of the temporal fossa .
o 1 cm away from the extreme edges of the
calvaria.
In Medulloblastoma nearly 15-20% of recurrences occur at cribriform plate site which is attributed to
overzealous shielding ,because of its proximity to ocular structure it often get shielded.

Spinal Field
 Laterally - 1 cm margin
beyond the pedicles, to cover
the spinal cord and meninges
along the nerve roots upto the
spinal ganglia
 Caudal- 1cm below the
termination of the thecal sac
i.e. L5 –S3.
 2 spinal fields are used if the
length is > 36 cm.
 In Dorsal Region, block lat.
Field to cover heart and lungs.
 In Lumber Region, reduce
field to spare BM and Gonads.
SSD technique
Gantry Angle = 0 degree
IMP point is length and depth of spinal fields.
Field of approx.4–6 cm wide box over the spinal
cord/vertebral bodies extends from C2 –S2

Post fossa boost
• Volume includes entire Infratentorial
compartment.
• Field arrangement :
 Two lat opposing fields .
SFOP Guidelines :
 Ant -0.5 cm in front of clivus
 Upper -1 cm above midpoint b/w line
joining foramen magnum and the skull.
 Post- ll to ant margin in air .
 Lower – 1 cm below occipital foramen.

TECHNIQUES OF MATCHING CS FIELDS
Collimator/Couch rotation
Half beam block
Asymetric jaws
Moving Junction technique

Collimator Couch rotation
 Classically described
technique.
 Divergence of the spinal field
into the cranial field is
overcome with collimator
rotation
 Divergence of the cranial
fields into the spinal fields is
overcome with couch rotation
(rotated so that the foot end
moves towards the gantry).

Collimator rotation allows
cranial field to match
spinal field divergence
Coll θ = arc tan (L1 /2 x SSD)
For Co60 SSD = 80
Zone of overlap of spinal field if collimator rotation is
not applied in cranial field
SSD
L1
Collimator rotation : While treating cranial field rotate Collimator of lateral field so that
its inferior border is parallel to divergence of sup. Aspect of spinal field .
θ

In order to avoid the overlap
resulting from inf. Divergence
of cranial field, rotate the
couch towards the collimator
so that fields margins of two
fields become parallel.
Degree of couch rotation
depends upon the length of
lateral cranial fields and SAD
Θ couch = arc tan
(1/2 x L2 /SAD)
L2 = Cranial field length
COUCH ROTATION
Fig: Rotation of the couch toward the gantry is necessary to
match the caudal margin of the lateral cranial fields with the
cephalad margin of the posterior spinal field.

Couch θ = arc tan (L2/2 x SAD)
For Co60 SAD = 80
L2 ( Length of
cranial field)
Cranial field
SAD
Zone of
overlap
Spinal field
Couch rotation
during
treatment of
cranial field
θ
COUCH ROTATION

Half Beam Blocking
Actual Field Length
Spinal field

Moving junction in CSI
• Feathering after every 5-7 fraction
smoothes out any over or underdose
over a longer segment of cord .
• Usually shifted by 1-2cm at each shift .
• Either in cranial or caudal direction.
• Lower border of sup. Spinal field & sup.
Border of inf. Spinal field are also
shifted superiorly , maintaining the
calculated gap b/w them.
“Feathering” refers to movement of the junction of the two fields across the treatment length.

Aligning Spinal field
 Abutting fields : will result in heterogenous dose to
the spinal cord .
 To overcome this various techniques are available
o Gap technique
o Double junction technique
o Moving junction technique

Fixed or calculated gap spinal fields
Gap calculation formula
S= [½ x L1(d/SSD1)] + [½ x L2(d/SSD2)]
Cold Spot Hot Spot
SSD 2 SSD 1
L2 S L1

Double junction techniques
 The post field divided
into two halves.
 An overlapping segment
is treated with two diff.
fields on alternate days.
 The junction is therefore
automatically feathered
on
alternate days
Upper Spine Lower Spine
Day of Planning
Day 1: The upper spinal
field is shortened
Day 2: The lower spinal field is
shortened
Junction on D 1 Junction on D 2

Metastatic Medulloblastoma?
M2-M3 Medulloblastoma
SIOP-PNET3 study
1 in 2 children likely to survive for 5 years even with metastatic disease
SIOP PNET 3 STUDY

TECHNICAL CONSIDERATIONS FOR CRANIOSPINAL IRRADIATION
Target volume definition may be
difficult using conventional simulation
Use CT simulation with CT-MRI co-
registration
Prone position- Uncomfortable, Difficult
to monitor airway
Supine position preferred
Field matching over cervical spine/risk
of over- or Underdosage
Angle brain fields
Use half-beam block for brain fields
Use couch rotation or match line wedge
Choice of extended SSD or second field
for treatment of spinal axis
Two fields preferred
Inhomogeneity along spinal axis Use compensator, MLC
Irradiation of normal tissues-
Mandible/teeth, Thyroid, Heart, GI
tract, Gonads
Neck extension, Care with level of
junction, Use lower junction, Care with
width of spine field, Use protons, IMRT,
electrons, Use protons, IMRT,
electrons, Care with lower limit and
width of spine field

RADIATION TOXICITY
ACUTE TOXICITY
• Nausea, vomiting
• Neutropenia,
thrombocytopenia
• Fatigue, headache,
drowsiness
• Alopecia, mild dermitis
• Serous otitis media
• Mucositis, oesophagitis
(exit dose from spinal
cord)
Spinal cord Chronic progressive myelitis
Brain Radiation necrosis, Intellectual
deficit
Lens of eye Cataract formation
Retina Radiation retinopathy
Optic nerve Optic neuritis
Inner ear Sensorineural hearing loss
Hypothalamic
-pituitary axis
Endocrinopathies (
hypothyroidism and decreased
growth hormone secretion)
Gonads Reduced Fertility
Secondary
Malignancy
LATE TOXICITY

Radiotherapy Toxicity: Dose-Volume Related
Mulhern et al: Lancet Oncol 2004

Strategies that have been used to avoid or
minimize the long-term effects of treatment for
pediatric brain tumors include the following:
• Use of new radiation modalities- Proton
• Reduced target volumes: e.g., tumor bed rather than
whole posterior fossa for the boost in standard-risk
• Reduction of radiotherapy dose (e.g., in young patients
with standard-risk dose for CSI has been reduced
progressively from 35 to 36 Gy to 23.4 Gy and to 18 Gy
for children younger than 8
• Use of HFRT in standard-risk medulloblastoma

Follow-Up During and After Radiotherapy
• Nausea and vomiting can be prevented by using 5HT-3
antagonists.
• Headache is not an expected side effect and should be
investigated by physical examination for signs of raised ICP
and imaging.
• Steroids, usually are tapered by the second or third week of
treatment.
• Fatigue is a rather common symptom and is cumulative.
• Children usually recover relatively quickly and often can get
back to their usual routine quite soon after completion of
treatment.

• Hormonal deficits, especially primary hypothyroidism and growth
hormone deficit secondary to inclusion of the hypothalamic–
pituitary axis.
• Patients should be monitored closely in follow-up
• Regular follow-up in ophthalmology and audiology.
• Extra pedagogic support may be necessary.
• Patients should have ready access to a neuropsychologist for
evaluation of any special needs and in the longer term to
vocational assessment and counseling.

Recurrence
• There are no curative treatments, and most patients
succumb from the disease in less than 2 years
• Nonsurgical treatment options for this group consist of
second-line chemotherapy
• Stem cell harvest with high-dose chemotherapy
• Reirradiation

Recurrence
• Recurrent medulloblastoma is responsive to a variety of
neoplastic agents, including vincristine, nitrosoureas,
procarbazine, cyclophosphamide,etoposide, and cisplatin
• A CCG trial to evaluate carboplatin, thiotepa, and
etoposide with peripheral stem cell rescue showed 3-year
EFS and OS rates of 34% and 46%, respectively.

Follow up
• MRI should be repeated every 3 months the first year;
every 4-6 months the second year; and yearly
thereafter.
• Lower cranial nerve or cerebellar signs also may signal
recurrence.

Clinical Evidences
• Huang et al. n=15, treated with conventional
craniospinal radiotherapy followed by a boost to the
posterior fossa using IMRT.
• IMRT delivered lower doses of radiation to the auditory
apparatus while maintaining full doses to the desired
target volume.
• Conclusion- Despite receiving higher doses of cisplatin
and despite receiving radiotherapy before cisplatin
therapy, IMRT can significantly decrease the rate of
hearing loss in children treated for medulloblastoma.

• Eaton et al, n=88, chemotherapy + RT (either photon
or proton) for standard-risk found no significant
difference in disease control, survival, or patterns of
failure between proton and photon radiation, suggesting
equivalent efficacy.

• Barney et al., n=50 treated with proton CSI, documented
extremely low median radiation doses to the thyroid of
0.003 Gy (RBE); the lung 1.1 Gy (RBE), heart 0.002 Gy
(RBE), kidney 0.04 Gy (RBE), bowel 0.02 Gy (RBE),
testicles 0.003 Gy (RBE), and ovaries 0.003 Gy (RBE).
• Treatment-related morbidity included grade 3 leukopenia in
9%, thrombocytopenia in 2%, and median weight loss of
1.1 kg or 1.6% loss from baseline.
• PFS at 2 and 5 years were 82% and 68%, with 80% of
treatment failures involving a local recurrence.
These data suggest that craniospinal irradiation with
proton therapy is effective but potentially much less
toxic acutely and much less likely to result in late
effects.

Summary
• Common & radiosensitive childhood brain tumor
• Molecular classification has identified four distinct subtypes:
WNT, SHH, group 3 and group 4.
• Maximal surgical resection should be performed, where
feasible.
• Standard treatment consists of postoperative radiotherapy
to the craniospinal axis followed by a boost to the tumor
bed for average-risk disease and to the posterior fossa and
any intracranial/spinal metastases for high-risk disease.
• The use of chemotherapy generally follows the pediatric
indications and guidelines.

• Patients typically present with symptoms and signs of raised
intracranial pressure (i.e., headache and morning vomiting).
• On MRI, medulloblastomas appear as solid masses that
enhance usually fairly homogeneously with contrast
material.
• Investigation at diagnosis must include a gadolinium-
enhanced MRI of the spinal axis and CSF cytology. The
former should be obtained whenever possible preoperatively
or else at least 2 weeks postoperatively
• Radiotherapy: An integral component of multi-modality
management

TMH Protocol for Medulloblastomas /PNET
https://tmc.gov.in/SBF/Nouro/flowcharts_final.pdf

Medulloblastoma

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