Radiotherapy Medulloblastoma , Radiation oncology guidelines for radiotherapy

1. Medulloblastoma
Management
Dr Savio James
DNB Resident
Department of radiotherapy
MCS

2. • Medulloblastoma is the most common malignant (WHO grade IV)
brain tumor of childhood
• It is an embryonal lesion arising from progenitor cell populations
present during early brain development.
• Medulloblastoma is currently treated with maximal safe resection,
chemotherapy, and craniospinal radiation.
• Despite such aggressive therapy, 30% of patients eventually succumb
to this disease
• Survivors cope with the long-term side effects of treatment that have
significant impacts on their quality of life.

3. Paterson E et al

7. Came on the basis of COG trails

8. Risk adaptive management
• Average risk –
• Conventional dose: 30–36 Gy CSI and boosting the primary brain site to
54–55.8 Gy with or without adjuvant chemotherapy ( usually not given)
Or
• Reduced dose: May consider reduced dose radiation
• 23.4 Gy/14# CSI with concurrent weekly Vincristine (1.5mg/m2) and
boosting the primary brain site to 54–55.8 Gy
• f/b Adj chemotherapy 6 cycles of ( Vincristine (1.5mg/m2) ,Cisplatin
(75mg/m2) , Lomustine ( 75mg/m2) or Cyclophosphomide (75mg/m2)

9. Risk adaptive management
• High risk –
• 35-36GY/21# with weekly vincristine or carboplatin(35mg/m2 for 15
days) and boosting primary brain site to 54–55.8 Gy
• f/b Adj chemotherapy 8 cycles of ( Vincristine (1.5mg/m2) ,Cisplatin
(75mg/m2) , Lomustine ( 75mg/m2 )
• Omission of vincristine during radiotherapy phase of therapy or dose
modification may be required for adults because they do not tolerate
this regimen as well.

10. Medulloblastoma in infants
• Risks of neurocognitive decline associated with the use of
radiotherapy in infants and very young children
• Localized medulloblastoma : 5 cycles of cisplatin, vincristine,
etoposide, and cyclophosphamide - followed by a single high-dose
myeloablative chemotherapy regimen of thiotepa, carboplatin, and
etoposide
• Disseminated disease- intraventricular/thecal methotrexate is also
added

11. Craniospinal
Irradiation
Indications
• Medulloblastoma
• Pineoblastoma
• Supratentorial PNET
• Germinoma
• Anaplastic ependymoma

12. Radiation Planning
• Positioning
• Immobilization
• Simulation
• Target Volume delineation
• Treatment planning

13. Patient positioning
Prone Position :
• Advantage :
• Direct visualisation of the field junctions
• Good alignment of spine
• Disadvantage
• Uncomfortable, and large scope for patient
movement
• Difficult for anaesthetic procedures
Prone Position :
• Advantage :
• More comfortable
• Better reproducibility
• Safer for general anaesthesia
• Disadvantage
• Direct visualisation of spinal field not
possible
Head position
Extended : most commonly used – allows the mandible to move out of the spinal field
Flexed : probably straighten he cervical spine – more homogenous dose distribution

15. Simulation
• Concern 1
• Divergence of upper border of spinal field in case of single spinal field (and inter divergence of
spinal fields in case of 2 spinal filed )
• Concern 2
• Divergence of both cranial fields
• Solution
• Spinal field simulated first
• 2 spinal fields if the length is >36 cm
• Upper border at low neck
• Lower border at termination of thecal sac or S2 which ever is lower
• In case of 2 spinal; fields , junction at L2/L3

16. Spinal field simulation
• Patient is aligned with alignment laser system
• Thoracic spine field is simulated first
• The upper border is above the shoulder but without exiting through the mouth .
• The upper border of thoracic field is marked on the lateral aspect of neck also to show the divergence ( to
match with brain field )
• The superior beam should reach to the L1-L2 space to avoid junctions over the inferior part of the spinal cord
• Lumbar spine also simulated , enough to include sacral nerve and roots .
• Inferior border at S3 because the dural sac ends at S2
• Posterior field ( PA )radiographs are taken for both fields
• A lateral radiograph is also obtained with lead wire marking the sagittal dorsal contour of the patient to see
depth of spinal cord . ( reference point is kept at anterior border of body )( thecal sac border )
• Field width should be adjusted so that the lateral field borders are at least 1 cm lateral to the lateral edge of
each ipsilateral pedicle
• Caudal end of the craniospinal field needs to be widened by 1.2 to 1.8 cm to encompass the increase in
distance between nerve root exits as

17. Carinal + cervical spinal field simulation
• The patient is fixed in a prone position with the head ideally
aligned and the neck as straight as possible.
• Eyelid markers are necessary
• Parallel-opposed large lateral fields are simulated with the central
ray in the pineal region
• The collimator should be angled to accommodate the superior
diverging spine field
• Blocks are drawn on the radiograph so that the irradiated volume
includes
• the olfactory groove (cribriform plate),
• the orbits 3 cm posterior to the eyelid markers (2 cm if gantry is angled),
• the middle cranial fossa plus a >1-cm margin, and
• the posterior halves of the odontoid process and the included cervical
vertebral bodies
Anterior block border is approximately
 0.5 cm inferior to the projection of the cribriform plate,
 3 cm posterior to the ipsilateral eyelid surface and
 0.5 cm inferior to the middle cranial fossa floor, and
 approximately bisects the cervical vertebral bodies

18. Field selection
• Cranial fields : two parallel opposing lateral fields
• Spinal fields :
• Conventional SSD : Two fields
• Extended SSD : One field may be enough

19. Problem in field matching
• Cranial and spinal field divergence
• Using half beam block technique
• Using collimator couch rotation
technique
• Using planned gaps
• Spinal field divergence
• Gap is given as per calculated formula
• Abutting fields treated with double
junction technique (spinal shift
technique )
• Gap feathering technique

20. Solution for Cranial and spinal field divergence
• Divergence of spinal field into the cranial field is overcome with
collimator rotation
• Divergence of carinal field into spinal field is overcome with couch
rotation( foot end move towards gantry )
• Both this rotations are performed during cranial field treatment

24. Spinal field divergence
1. Abutting fields treated double junction technique ( spinal shift
technique )
2. Filed gap technique : will result in cold spots above and hot spots in
the deeper tissue ( Gap given as per formula )
3. Feathering of gap can smoothen out dose gradient

25. Double junction technique
• Method to ensure dose homogeneity without need for gaps
• Described by Johnson and Kepka ( 1982)
• Principle: an overlapping segment is treated with two different fields
on alternate days
• The junction is therefore automatically feathered on alternate days
• Receives homogenous dose 50% of time and receives junctional dose
in remaining 50% of time ( from the other 2nd field ) .
• No cold spots are generated , actually no overlap is taking place

27. Field Gap technique
• Gap is calculated by

28. Gap feathering
• Feathering refers to movement of the junctions of the two fields
• Purpose : reduce overdose ( due to overlap )
• Reduce underdose ( due to gap)
Allows a longer segment of cord to be exposed to more homogenous
dose
• Feathering also reduces impact of setup errors
• As the treatment progress the under and over dose gets spread over
a greater area of the spinal cord allowing more homogenous dose
distribution

29. • Usually shifted by 1 to2 cm at
each shift
• Done every few fractions (5 or
7)
• Either in cranially or caudal
direction ( so set up easy )
• If to be shifted cranially all
borders are shifted cranially .
• Lower border of lower field is a
constant

31. Conformal techniques of CSI

32. • CT simulation is necessary to ensure
adequate coverage of the CTV in the
subfrontal region at the cribriform plate
• CT simulation is also helpful in identifying the
lateral aspect of CTV for the spine field that
includes the extensions of the meninges
along the nerve roots to the lateral aspects
of the spinal ganglia

33. Imaging techniques
• A planning CT scan is obtained using 1–2.5 mm slice thickness from
the vertex to the lower border of C3 vertebrae
• 2–5 mm slice thickness from the lower border of C3 vertebrae to the
upper part of the femur (2–2.5 mm for younger children).

34. CTV cranial
• Cranial CTV: includes brain with entire frontal lobe and cribriform plate.
The geometric edge of the shielding should extend at least 0.5 cm inferiorly
below the cribriform plate and at least 1 cm elsewhere below the base of
the skull
• Firstly, the inner table of the skull is outlined using bony window settings
(suggested CT Window/level: 1500–2000/300–350).
• Secondly, ensure that the cribriform plate, the most inferior parts of the
temporal lobes, and the whole pituitary fossa, which contains CSF are
included in the CTVcranial.
• Thirdly, the CTVcranial is modified to include the extension of CSF within
the dural sheath of cranial nerves

35. CTV Spinal
• The CTVspinal should include the entire subarachnoid
space to encompass the extensions along the nerve
roots laterally
• Inferior border of Spinal CTV must be determined by
imaging the lower limit of the thecal sac on a spinal
MRI; inferior treatment field border should be set 1 cm
below this
• The lower border of the spinal CTV should include the
lower border of the thecal sac, which can be as high as
L5 or as low as S3

37. Planning target volume (PTV)
• The PTV margin should be based on departmental data.
• Most institutions add a 3–5 mm margin to CTVcranial and a 5–8 mm
margin to CTVspinal

38. Treatment Planning and Delivery
• Using modern tools for treatment planning and delivery, it is possible to
greatly simplify the technique and substantially reduce planning and
delivery times
• In general, photons in the 6- to 10-MV range provide satisfactory coverage
of the PTV
• Electrons are used in some centres to treat the spinal axis because of
improved dose calculation algorithms and even electron dose modulation
techniques
• Treatment planning and delivery methods such as intensity modulated
radiation therapy (IMRT) together with daily image verification allow for
improved dosimetry with photons with clinically relevant dose reductions

39. New Treatment Modalities for CSI
• Protons provide a dose distribution for CSI that cannot be achieved by
even the most sophisticated photon beam treatment planning
• With significant reduction in low dose exposure outside the target
volume
• There may be significant benefits from reduced irradiation of the
heart and organs anterior to the spine
• Currently, an increasing number of children requiring craniospinal
radiotherapy are treated by proton therapy

45. • Thank you