Craniospinal Radiotherapy

Indications

• Medulloblastoma 
• PNET (pineoblastoma, ependymoblastomas, unclassified). 
• Germ Cell tumour with CSF and/or MRI positive for malignant cells. 
• Pure germinoma.
• Non Hodgkins Lymphoma with CSF positive for malignant cells. 

Radiotherapy Fields

Patient in prone position with the POCL immobilisation system. 

The cranial volume should be treated by two lateral fields (usually 22?22). The volume should include the whole skull, the cribriform fossa , the temporal fossae, the posterior fossa including the craniotomy and neck scar, and the spinal cord to, or below the C3-C4 interspace where it will junction with the spinal volume. Make sure the lateral skull fields are acquired in the Ximavision and MLC’s drawn The fields are individually shaped by MLCs taking care not to also protect the area of the cribriform plate. The junction between the cranial and spinal fields should be calculated at the anterior border of the spinal cord (usually 0.5cm). Collimate the lateral fields by 8-10 degrees and rotate the couch by 5-6 degrees for making the cranio-spinal field junction non-divergent. Make 2 lines on the sticking plaster (Blue line for cranial field, Red line for the spinal field) for marking the fields.

The spinal volume should be treated with a direct posterior field. In older children more than one spine field may be necessary. The spinal volume should be over the spinal dural sac from the junction with the cranial volume down to the level of S2. The width of the vertebrae should be covered with an allowance for scoliosis and rotation of the vertebral volume, but a spade should not be routinely used to cover the spinal nerve roots.

Posterior fossa to be treated with 3D CRT.

Dose and Fractionation:

PNETs (including medulloblastoma)

(a) The craniospinal axis is to receive 35 Gy, which is given in 1.67 Gy fractions for 21 fractions, 5 times per week, over four weeks. 
(b) The posterior fossa boost should be delivered to 19.8 Gy in 11 fractions of 1.8 Gy, 5 times per week. after the conclusion of CSI.

For Germinoma

CSI-25Gy in 15# in 3 weeks followed by local boost to 15 Gy in 9# in 2 weeks, preferably with 3D CRT 

Patients to be started on Tab Ondansetron 4 mg bd daily on commencement of CSI and weekly blood count check done during CSI. The junctions for cranial and spinal fields and 2 spinal fields are moved 1 cm twice during CSI to spread the hot or cold spot.

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