I: Central Nervous System

The CNS contains a number of malignancies that, on the whole, have a poor prognosis. Radiotherapy plays an important role in the management of these conditions as it allows treatment of malignancy with minimal loss of function.

I have arranged these topics according to the WHO classification of CNS tumours rather than more local definitions.

1: Glioma

This broad category of brain tumours includes glioblastoma (most common in adults), grade III gliomas (anaplastic astrocytoma / anaplastic oligodendroglioma), grade II gliomas (diffuse astrocytoma, oligodendroglioma, oligoastrocytoma) and grade I gliomas (pilocytic astrocytoma). The management of all tumours involves surgical resection.

  • Grade I gliomas are treated with surgery alone, with radiotherapy reserved for cases of incomplete resection (50.4 Gy in 28#)
  • Grade II gliomas are treated with surgery. Immediate therapy with radiation (50.4 Gy) or observation are both options. Immediate therapy is more appropriate for non-oligodendrogliomas in patients over 40, or those who are symptomatic or have had incomplete resection. The role of chemotherapy is controversial
  • Grade III gliomas include anaplastic astrocytoma and anaplastic oligodendroglioma. Anaplastic astrocytoma is treated with adjuvant high dose radiotherapy followed by temozolomide. Dose is 60 Gy in 30 fractions. Anaplastic oligodendroglioma is treated similarly but followed by
  • Grade IV glioma (glioblastoma) is treated with maximal surgical debulking followed by adjuvant chemoradiotherapy (Stupp trial) with 60 Gy in 30 fractions and concurrent temozolomide. The patient then receives 6-12 months of monthly temozolomide cycles.
  • In children, about 10% of CNS tumours are brainstem gliomas which have features of one of the types above. Due to their location most are unresectable except for the less common focal brainstem glioma. The remaining diffuse pontine gliomas are incurable but are treated with radiotherapy to the brainstem (54 Gy in 30#)

2: Meningioma

Meningiomas are the second most common brain tumour in adults and account for about 30% of diagnoses. They are usually benign but a small number may be Grade II (atypical) or Grade III (anaplastic) with associated invasion. Surgery is the treatment of choice for most lesions but may be difficult in the base of skull or when lesions are adjacent to cranial nerves or the sinuses. In these cases radiotherapy is preferred. Radiotherapy is also used adjuvantly after resection of Grade II or III lesions as they have a higher risk of recurrence (eg. 30% for grade II, >80% for grade III).

  • Primary radiotherapy may be either 3D conformal/IMRT or stereotatic
    • 3D conformal radiotherapy prescribes a dose of 54 Gy in 30 fractions to the lesion. The GTV->CTV margin is 0 cm for grade I but should be 0.5 cm for grade II or III. It is important to include the dural tail.
    • Stereotactic radiotherapy delivers 15 Gy in a single fraction to the tumour with no margin. It is most appropriate for grade I lesions as other types may invade brain parenchyma
  • Adjuvant radiotherapy is used for grade II and III lesions. 50.4 Gy is delivered when there has been a complete resection and 54 Gy for residual disease. 60 Gy should be used for grade III lesions.

3: Embryonal Tumours

Includes medulloblastoma and CNS PNET

4: Pineal Tumours

Pineal tumours can include pineocytoma, pineoblastoma, and germ cell tumours.

  • Pineocytoma is a low grade tumour that is treated similarly to grade I glioma. Gross total resection is ideal, followed by observation. If gross total resection is not achievable, radiotherapy is used (54 Gy in 30 #) using a 3D conformal technique. GTV + 0.5 cm = CTV; CTV + 0.5 cm = PTV.
  • Pineoblastoma is a grade IV neoplasm similar to medulloblastoma and primitive neuroectodermal tumours (PNET). Ideal management mirrors medulloblastoma - gross total resection, craniospinal irradiation (36 Gy) with boost to primary tumour bed (GTV + 1 cm) to 54 Gy.
  • Germ cell tumours may occur in the pineal region but are treated differently (see below).

5: Germ Cell Tumours of the CNS

The brain is a potential site of germ cell tumours outside of the gonads. Any of the germ cell tumours can occur here.

  • Germinoma (most common type) is treated with surgical biopsy followed by curative radiotherapy alone. The dose is 24 Gy to the whole ventricular system then a boost to the tumour bed of 21 Gy. Craniospinal irradiation is used for patients with imaging or cytological evidence of CSF involvement.
  • Non-germinomas (except teratoma) are treated in a similar manner with additional systemic chemotherapy (bleomycin, etoposide, cisplatin or BEP). The radiotherapy doses are 30 Gy to whole ventricle/craniospinal axis with a further 24 Gy to the primary tumour.
  • Mature teratomas are benign tumours and are treated with maximal surgical resection. Radiotherapy is used when there is a subtotal resection.

6: Tumours of Cranial/Paraspinal Nerves

Vestibular schwannoma is a benign tumour that arises from the 8th cranial nerve. It is bilateral in patients with neurofibromatosis type II. Patients present with tinnitus on the affected side. Control rates are > 90% for any treatment modality and a major component of treatment is attempting to reduce toxicities of treatment.

  • Primary treatment is either:
    • Surgical resection is possible for any lesion and is more readily available currently. Surgery carries a higher risk of hearing loss and may potentially damage cranial nerves VII and V. It is the treatment of choice when the lesion is large (causing compression of other structures) or the patient is young and may potentially develop late radiotherapy sequalae.
    • Stereotactic radiosurgery is becoming a more popular option. This delivers a dose of 13 Gy to the tumour mass with no expansion. It is best for small lesions.
    • Fractionated stereotactic radiotherapy is a newer technique that delivers dose in a number of separate treatments. It has a higher chance of preserving hearing and causing late toxicities, making it preferred when tumours are large (> 4 cm) which makes single fraction treatment more problematic. Doses vary considerably; 54 Gy in 30# is not unreasonable.
    • Observation is preferred in older patients with preserved contralateral hearing.

7: Tumours of the Sellar Region

Pituitary tumours are classified according to their cell of origin and production of hormones. Treatment is general surgical resection with the exception of prolactinomas which are treated with medical therapy. Radiotherapy is reserved for inoperable patients, for patients with incomplete resection, or with recurrent disease.

  • Non secretory tumours (most common type) are treated with surgery if they are larger than 1 cm. Radiotherapy
  • Prolactinomas are treated with cabergoline or bromocriptine (dopamine agonists) which are effective in > 90% of patients. Surgery is second line therapy. Radiotherapy is used when other approaches have failed.
  • Growth hormone tumours make up 20% of pituitary tumours. They cause acromegaly. Surgery is the initial treatment as radiotherapy works too slowly to reduce growth hormone levels.
  • Other secretory tumours are managed in a similar way to growth hormone tumours. The general rule is that radiotherapy causes a slow reduction in hormone levels (eg. over 10 years) and therefore does not work quickly enough to reverse the hormonal changes caused by the tumours.
  • Radiotherapy dose is typically 45 Gy in 25 # using a 3 field arrangement (two laterals, one anterior/superior beam).
    • Stereotactic radiosurgery delivers doses of 25 Gy (secretory) or 15 Gy (non-secretory) in a single fraction to the pituitary tumour. Dose to optic chiasm must be below 8 Gy.

Microadenomas can be observed if they are non-secretory.

8: Non-Neoplastic CNS Lesions

Arteriovenous malformations are a congenitally acquired nidus of vascular tissue where blood is shunted rapidly from the arterial to venous circulation without an intermediate capillary network. This high flow leads to risks of aneurysm formation and haemorrhage (3% yearly risk).

  • Surgery provides immediate reduction in the risk of haemorrhage and is the preferred treatment
  • Stereotactic radiosurgery is most useful for inoperable small lesions (< 3 cm), where a dose of 20 Gy in a single fraction can provide 90% control at 3 years.

9: Metastatic lesions involving the CNS

Includes secondary brain metastases and spinal cord compression