Radiation Oncology: A Question-Based Review


Boris Hristov and Robert A. Lustig

image Background

What % of all primary intracranial tumors do meningiomas account for in adults?

15%–20% (2nd only to gliomas). Meningioma is the most common benign 1° CNS tumor.

What are the age and gender predilection for meningiomas?

Meningiomas appear late in life (with a peak in the 7th decade). Females are more commonly affected than males (2:1).

What are some risk factors for meningiomas?

Prior RT (RR 10), NF-2, and HRT in women (RR 2)

Which protein is defective in NF-2, and to what else does NF-2 predispose?

Merlin; bilat acoustic neuromas/ependymomas and juvenile subcapsular cataracts

What histologic features can be seen in meningiomas?

Psammoma bodies and calcifications

What % of grade I meningiomas express progesterone receptors?

75% of grade I meningiomas express progesterone receptors.

Name 5 negative prognostic factors for meningiomas.

Negative prognostic factors for meningiomas:

1.     High grade

2.     Young age

3.     Chromosome alterations

4.     Poor performance status

5.     STR

image Workup/Staging

What is the grade classification of meningiomas?

WHO grade I (benign), grade II (atypical), and grade III (anaplastic/malignant)

Of grade I meningiomas, which histologic subtype is most aggressive?

The angioblastic subtype is the most aggressive grade I meningioma.

What is the OS difference between atypical and anaplastic meningiomas?

Atypical 12 yrs vs. anaplastic 3.3 yrs (Yang SY et al., J Neurol Neurosurg Psych 2007)

What are some prognostic factors identified for anaplastic meningiomas?

Brain invasion, adj RT, extent of resection, and p53 overexpression (Yang SY et al., J Neurol Neurosurg Psych 2007)

What is the most common Sx at presentation for meningiomas?

HA is the most common presenting Sx.

What is the appearance of meningiomas on CT/MRI?

Homogeneously and intensely enhancing mass, +/− dural tail

What % of meningiomas exhibit a dural tail? In what other tumors/lesions can dural tails be seen?

60%. Dural tails can also be seen in chloroma, lymphoma, and sarcoidosis.

What proportion of incidentally found meningiomas remain stable on imaging?

The majority remain stable on imaging (two thirds).

For meningiomas, with what are slower growth rates associated?

Slower growth rates are associated with older pts and calcifications.

What surgical grading system is used in meningiomas? For what does it predict?

Simpson grade (I/GTR−IV/STR). The Simpson grade predicts for the likelihood of LR.

GTR is possible in what % of pts?

80% of pts achieve a GTR surgery.

In what anatomic regions is GTR more difficult to achieve for meningioma resection?

Cavernous sinus, petroclival region, post saggital sinus, and optic nerve

What is the prevalence of grade II–III meningiomas?

6% and 4%, respectively. 90% are grade I.

Name the histologies associated with WHO grade II–III meningiomas.

1.     Grade II: atypical, clear cell, chordoid

2.     Grade III: anaplastic, rhabdoid, papillary

How is optic sheath meningioma diagnosed?

Optic sheath meningioma is diagnosed clinically/radiographically by a neuro-ophthalmologist/MRI (no Bx).

image Treatment/Prognosis

What are the Tx paradigms for meningiomas?

Meningioma Tx paradigms:

1.     If incidental/asymptomatic: observation

2.     If grade I and symptomatic/progressive: surgery +/− RT

3.     If grade II or III: surgery + RT

For which types of meningioma is RT the primary Tx modality?

Optic nerve sheath and cavernous sinus (inaccessible regions)

When should observation be considered?

Observation should be considered with incidental/asymptomatic and stable lesions.

When is RT utilized after surgery for meningiomas?

RT should be utilized after surgery if there is recurrent Dz or STR or if there is atypical/anaplastic histology or brain invasion.

What are the 10-yr recurrence rates with surgery alone after either GTR or STR?

10-yr recurrence rates with surgery alone are ~10% after GTR and 40% after STR.

Is there a benefit to upfront RT after STR?

This is controversial (upfront control rates are considered equivalent to salvage rates). Data from an ongoing RCT (EORTC 26-021) is pending.

What are the RT doses employed for meningiomas?

RT doses are 54 Gy for benign and 60 Gy for malignant tumors (PTV = GTV + 1.5 cm).

Is there any RT dose-response data for meningiomas?

Yes. Goldsmith et al. showed improved PFS with doses >52 Gy. (J Neurosurg 1994)

What are typical SRS doses used for meningiomas?

Typical SRS doses range from 12–16 Gy to 50% IDL at the tumor margin (depending on location/size).

What is the 5-yr LC rate for meningiomas after SRS?

The 5-yr LC rate is 98%. It is worse in men and if the RT dose is <12 Gy. (Kullova A et al., J Neurosurg 2007)

What poor prognostic factors have been identified in pts receiving SRS for meningiomas?

Male gender, conformality index <1.4, and size >10 cc (DiBiase SJ et al., IJROBP 2004)

Should the dural tail be covered in the RT field?

Yes (if possible). Some studies have shown improved 5-yr DFS. (DiBiase SJ et al., IJROBP 2004)

image Toxicity

What is the surgical complication rate after resection for meningiomas?

After resection, the surgical complication rate is 2%–30% depending on the location/type; 1%−14% mortality (worse in the elderly).

If observed, pts should get MRIs at what intervals?

At 3 mos, 9 mos, then yearly if stable (q6mos for 5 yrs at Johns Hopkins Hospital)

What is the toxicity rate for SRS if doses >16 Gy are used?

There is temporary toxicity in 10% of pts and permanent toxicity in 6% of pts. Perilesional edema is observed in 15%. (Kullova A et al., J Neurosurg 2007)

What is the RT dose limitation to the chiasm when SRS is used?

The chiasm should be limited to 8 Gy with SRS.

How are optic nerve sheath/cavernous sinus meningioma pts followed?

These pts should be followed with serial MRIs, neuro-ophthalmology exams, and regular endocrinology exams.

What is the latency period of RT-induced meningiomas from the time of RT exposure?

The latency period is ~20 yrs.

What is the avg time to recurrence after surgery for meningiomas?

4 yrs is the avg time to recurrence after surgery.