Craniospinal irradiation is RT technique employed for treating medulloblastoma patients post-operative.

1. FIELD MATCHING IN
MEDULLOBLASTOMA
Name : Rohit
Diagnosis : Medulloblastoma
Dose : 36Gy/18# f/b 18/10# Gy posterior fossa boost
Machine : NDBX

2. INTRODUCTION
 Cerebellum
 Median age of diagnosis is 6 years.
 Craniospinal Irradiation (CSI)
 laterally opposed cranial fields, are matched to a posterior
spine

3. RATIONALE FOR CRANIOSPINAL
IRRADIATION(CSI) IN MEDULLOBLASTOMA
CSF dissemination is known in 16-46% of cases
Posterior fossa, spinal cord, ventricular walls & supratentorial region
including the cribriform plate form the main sites of relapse.
Being radiosensitive, RT is curative in up to 70% of standard risk
patients.

4. CHALLENGES
Large treatment fields
Multiple treatment fields
Problems with matching the multiple fields
Inhomogeneity at the junctions between the
brain and spinal fields

5. PLANNING
 Symmetrical bilateral cranial field and posterior spine field are
planned to cover entire length of Planning Target Volume
(PTV).
Techniques for matching craniospinal fields.
Collimator/couch rotation
Half beam block
Asymmetric jaws
Penumbra generators
Wedge
Tissue compensator
 The both fields are matched either by
 GAP JUNCTION METHOD or by
 ROTATING COUCH AND COLLIMATOR.
Gap junction method can be done when planning manually

6. PLANNING CONT….

7. MATCHING CRANIAL AND SPINAL FIELD
Because radiation beams are
divergent, adjacent fields can overlap
at depth and give rise to regions of
excessive dose or hot spots.
Overlaps can be avoided by
separating the fields, but this in turn
can give rise to areas of reduced
dose or "cold spots.“ if done
incorrectly .

8. COLLIMATING THE CRANIAL
FIELD

9. WHAT IF 2 POSTERIOR
FIELDS ARE TO BE GIVEN ?

10. CAN WE SOLVE THIS AGAIN
WITH HALF BEAM BLOCK AND
COLLIMATING ONE FIELD AS
DONE WITH CRANIOSPINAL
FIELD MATCHING
NO
How to solve
This ?

11. ROTATING THE COUCH BY 90’
AND GIVING SOME ANGLE TO
GANTRY

12. POSTERIOR FOSSA BOOST
Borders
Anterior: Posterior clinoid process.
Posterior: Internal occipital protuberance.
Inferior: C2-C3 interspace.
Superior: Midpoint of foramen magnum & vertex
or 1 cm above the tentorium (as seen on MRI).
Field arrangement
Two lateral opposing fields.

13. SUPINE CSI BY
CONVENTIONAL
SIMULATION
Positioning:
Supine with arms by the side of body.
Neck should be slightly extended

19. THANK YOU
Gap junction
 ???? Missing

26. MEDULLOBLASTOMA
I. Craniospinal Fields Are Given .
II. Both The Fields Are Orthogonal To Each Other .
III. BiLaterals
IV. Posterior
NOTE :
There is a possibility of a large DOSAGE ERROR across the JUNCTION .
Consequently, this region is at risk for TUMOR RECURRENCE if
UNDERDOSED
SEVERE COMPLICATIONS if OVERDOSED

27. PLANNING
Having field size limitation to covert entire PTV (40*40 CM2).
TWO FILEDS ARE GIVEN
BILATERALS FOR CNI (CRANIOSPINAL IRRADIATION )
POSTERIOR FOR SPINE IRRADIATION
FIELDS
CRANIAL
(BILATERAL
S)
CERVICOTHORACIC
SPINE FIELD
LUMBOSACRAL
SYMMETRICAL
SPINE FIELD
SPINAL
(POSTERIO
R)

28. STEP-1
1. Firstly , BILATERALS are given for CNI .
2. Secondly, POSTERIOR SPINE FIELD is given through the couch
,gantry @ 180
3. In the given patient one field is enough to cover the spine
4. the field is given such that the PTV is covered adequately
5. After calculating dose for the same the result will be :
HOTSPOTS will be there and the dose to OARS
COLDSPOTS will be there too .

29. STEP-2
The need of FIELD MATCHING as the hotspots are there due to
overlapping of fields
The divergence matching is required
1. The HALF BEAM BLOCK is done in bilaterals
2. The isocenter is set at the border
3. Spine field is given to cover the entire PTV
4. Then with the help of collimation in bilaterals the divergence is
matched
5. At one collimation divergence will be matched exactly and no risk
of dose inhomogeneity
6. Ideally mandible is an oar and should not come in the field but due
to patient positioning or due to the head size this was not achieved

30. STEP-3 (SPINE IS LARGER)
1. Here , two fields are given to cover the spine
2. The half beam blocking is done of the second field
3. Isocenter ??
4. Keeping both the field at 180 ,divergence matching is not
achievable at any collimator angle
5. Therefore here couch is at 90 and the field is given
6. Here we give the second field with gantry at an some angle to
match the divergence which depends on the patient anatomy
7. Once the junction matching is done the dose is calculated .
8. This is how medulloblastoma patient is treated

31. GAP JUNCTION METHOD
From khan