P&P of Rad_CH 30_Central Nervous System Tumors

4. What is the most common CNS tumor in children? a. Medulloblastoma b. Metastatic lesion c. Astrocytoma d. Craniopharyngioma

ANS: A Medulloblastomas are the most common malignant nervous system tumors of childhood.

2. From which cells to medulloblastomas arise? a. Primitive neuroectodermal tumor (PNET) b. Primitive neuroectodermal cells c. Astrocytes d. Lymphocytes

ANS: A Medulloblastomas arise from the primitive neuroectodermal cell. These cells comprise a family of the small, blue, round cell mass. These cells do not usually remain in the body after birth.

Patients treated to the cranium should be advised to protect their heads from direct sunlight because the sun _____________________________. a. enhances radiation-induced side effects b. causes lower white cell blood counts c. enhances feelings of nausea d. lowers tolerance to anti-inflammatory medications

ANS: A Patients should be cautioned against exposing to direct sunlight areas of the body being treated. The radiation from the sun in combination with the radiation from treatment enhances the adverse side effects.

Which of the following is the dose at which radiation necrosis of brain tissue is most likely to occur? a. 6000 cGy b. 4500 cGy c. 4000 cGy d. 2000 cGy

ANS: A Radiation tolerance for normal tissues within the CNS include 5000 cGy for whole brain, 6000 cGy for partial brain, and 4500 to 5000 cGy for the spinal cord. These tolerances are based on TD5/5, which assumes a 5% incidence of complications at a 5-year period.

The 5-year survival of patients with glioblastoma multiforme (GBM) is: a. 35% b. 55% c. 75% d. 95%

ANS: A The 5-year survival rates for patients with primary central nervous system (CNS) tumors have risen over the past two decades to 35% overall.

9. Which portion of the brain is the site of intelligence and judgment? a. Cerebrum b. Cerebellum c. Brain stem d. Thalamus

ANS: A The function of the cerebrum includes interpretation of sensory impulses and voluntary muscular activities; it is the center for memory, learning, reasoning, judgment, intelligence, and emotions.

Which of the following beam arrangements is most typical for treatment of a malignant primary brain tumor? a. Parallel opposed whole brain fields b. Small fields with 1 to 3 cm margins c. Oblique fields to include the supraorbital ridge d. Large fields with 5 to 10 cm margins

ANS: B In the past, whole-brain irradiation has been used via lateral portals with a boost to the tumor bed after initial treatment. With the advent of computed tomography (CT) and magnetic resonance imaging (MRI), more accurate tumor localization allows smaller fields to be simulated and treated. Smaller field designs and unique configurations through the use of specialized blocking make simulation and daily reproducibility of the setup an even more important part of the treatment process.

Which of the following is a late effect of brain irradiation in children? a. Leukemia b. Decreased IQ c. Gigantism d. Chronic fatigue

ANS: B Late effects after CNS treatment in children include decreased mean intelligent quotient (IQ) scores and the regrowth of hair.

7. Which of the following cells is responsible for myelin production? a. Neurons b. Schwann cells c. Astrocytes d. Ependymal cells

ANS: B Schwann cells, in addition to oligodendrocytes, produce a fatty insulating substance called myelin, which insulates and protects nerves outside the CNS.

What is the 5-year survival rate for all CNS tumors combined? a. 20% b. 35% c. 50% d. 75%

ANS: B The 5-year survival rates for patients with primary CNS tumors during the past four decades has ranged from 19% from 1960 to 1985 and has risen to an overall survival of 35% during the past two decades.

5. What is the most common source of brain metastases among the following? a. Colon b. Lung c. Breast d. Melanoma

ANS: B The most common primary site of disease responsible for producing brain metastases is the lung.

6. Which tumors spread through the cerebral spinal fluid? a. Astrocytoma b. Oligodendroglioma c. Medulloblastoma d. Schwannoma

ANS: C The common route of spread for medulloblastomas and PNETs is via cerebrospinal fluid to points in the CNS.

Which class of chemotherapy drugs has the ability to cross the blood-brain barrier? a. Antimetabolites b. Plant alkaloids c. Nitrosoureas d. Hormonal agents

ANS: C The nitrosourea drugs are lipid soluble, allowing them to cross the blood-brain barrier.

Chemicals that enhance the lethal effects of radiation are known as ____________. a. cytotoxins b. corticosteroids c. radioprotectors d. radiosensitizers

ANS: D Chemicals that enhance the lethal effects of radiation are known as radiosensitizers. Hypoxic cell sensitizers and halogenated pyrimidines are under investigation.

What is the most common type of brain tumor? a. GBM b. Astrocytoma c. Meningioma d. Metastatic brain lesions

ANS: D Primary brain tumors are relatively uncommon. However, cerebral metastases occur in approximately 30% of patients with cancer and are the most common brain lesions.

8. Which of the following factors can limit the usefulness of surgery for CNS neoplasms? a. Tumor location and extent b. Patient status c. Risk of causing neurologic damage d. All of the above

ANS: D Surgery can be limited by the tumor location and extent, patient status, and risk of causing debilitating neurologic deficits.

What defines the inferior radiation field border for the treatment of the whole brain for palliation? a. 1-cm flash b. Superior orbital ridge c. External auditory meatus d. Both b and c

ANS: D The inferior margin of the field intersects the superior orbital ridge and external auditory meatus.

Which of the following conditions is a contraindication for stereotactic radiosurgery (SRS)? a. Spherical tumor b. 2-cm tumor c. Brain metastases d. Five lesions

ANS: D To be a candidate for SRS, the target volume should be spherical and as large as 3 cm only at its maximum dimension.

Which of the following is most significant to the prognosis of brain tumors? a. Tumor size b. Lymph node involvement c. Metastases d. Grade

ANS: D Tumor grade rather than size is the primary factor involved with prognosis.

Epilation may be permanent when the cranium is treated beyond the threshold dose of ______ cGy. a. 1000 b. 2000 c. 3000 d. 4000

ANS: D With doses of greater than 4000 cGy, hair loss may be permanent.