Radiotherapy and Stereotactic Radiosurgery Flashcards
Which one of the following statements about stereotactic radiosurgery is most accurate a. A high dose of radiation is delivered in a single sitting often to a volume limited target, typically one lesion is treated how- ever more than one can be
b. Itisusedtodeliverprophylacticcraniosp- inal irradiation
c. Radiation is delivered in multiple sessions to a single target
d. Requires a cobalt source for generating ionizing radiation
e. Requires a copper source for generating non-ionizing radiation
a. A high dose of radiation is delivered in a single sitting often to a volume limited target, typically one lesion is treated how- ever more than one can be
single sitting only to a single target
Radiosurgery usually implies a single outpatient treatment with high dose delivered to a small tar- get, with multiple beams creating a high dose gra- dient. As no single beam contributes significantly to the cumulative dose the amount of radiation delivered to normal tissues in the beams’ paths is minimized while targets less than 4 cm large receive a high dose. Effective radiosurgical treat- ment of targets larger than 4 cm with would require an unacceptable increase in dose to adja- cent normal brain tissue. It can be performed using various devices including linear accelera- tors, Gamma Knife (GK), and particle beam devices.
Which one of the following utilizes a cobalt- 60 source for photon production?
a. 3D conformal radiotherapy
b. Carbon-ion therapy
c. Gamma Knife surgery
d. Linac-based radiosurgery
e. Proton beam therapy
c. Gamma Knife surgery
In radiotherapy planning, which one of the following terms best describes the volume that should be treated to account for the tumor, microscopic spread, and setup errors (systematic and random)?
a. Clinical target volume
b. Gross tumor volume
c. Planning organ at risk volume
d. Planning target volume
e. Systematic target volume
d. Planning target volume
Which one of the following descriptions does not describe the radiobiological response of common intracranial targets for radiosurgery?
a. Target volume contains no abnormal tissue and normal tissue shows early radiobiologic effect
b. Target volume contains no normal tissue and abnormal tissue shows early radiobio- logic effect
c. Target volume is late responding as con- tains normal and abnormal tissue
d. Target volume is late responding but only in abnormal tissue and with marked radio- biologic effect
e. Target volume shows small, early effect on abnormal tissue but bigger, late effect on normal tissue
a. Target volume contains no abnormal tissue and normal tissue shows early radiobiologic effect
In which one of the following forms of radi- ation therapy is the Bragg peak utilised to focus treatment and minimise collateral dam- age to non-targeted structures?
a. Brachytherapy
b. CyberKnife radiosurgery
c. Gamma Knife surgery
d. Linac-based radiosurgery
e. Proton beam therapy
e—Proton beam therapy
As a photon beam passes through material and is absorbed, the overall intensity of the beam is reduced. In contrast, particles such as protons and ions travel a finite distance, which is termed the range. They deposit a disproportionate amount of energy in the last few millimeters of their path. This large transfer of energy is known as the Bragg peak. The physical depth penetrated by the particles depends on tissue density and the beam’s energy.
Which one of the following is not an impor- tant biological factor explaining the efficacy of fractionation?
a. Radiosensitivity
b. Reassortment (redistribution)
c. Reduction
d. Reoxygenation
e. Repair
f. Repopulation
c. Reduction
Stereotactic radiotherapy for brain metastasis is LEAST likely to be appropriate in which one of the following situations?
a. CNS and systemic progression of disease, with few systemic treatment options and poor performance status
b. Local relapse after surgical resection of a single brain metastasis
c. Oligometastases (1-3) metastases espe- cially if primary tumor is known to be radiotherapy resistant
d. Postsurgical resection of a single BM, especially if 3 cm or smaller and in the posterior fossa
e. Salvage therapy for recurrent oligometas- tases (1-3) after WBRT
a. CNS and systemic progression of disease, with few systemic treatment options and poor performance status
Both surgery and SRS have a proven survival ben- efit in the management of a single brain metasta- sis. Typically, surgery is preferred in patients with good performance status, large lesions (>3 cm), or symptomatic tumors with substantial vaso- genic edema. In patients who are good candidates for either surgery or SRS, there are no random- ized data currently available to indicate which is the preferred treatment modality. In general, the current debate regarding patients with multi- ple metastases surrounds whether to use WBRT, SRS, or both. Survival, recurrence, focal neuro- logical deficit and neurocognitive outcome are key considerations. Proponents of SRS suggest that highly targeted therapy spares normal brain tissue and preserves neurocognitive function, while WBRT supporters argue that SRS will not treat the invisible micrometastatic foci which will grow to cause neurological deterioration later on. Current practices may be summarized as:
Consider SRS when:
* Oligometastases (1-3) or multiple (4-10)
metastases especially if primary tumor is
known to be radiotherapy resistant
* PostsurgicalresectionofasingleBM,espe- cially if 3cm or bigger and in the
posterior fossa
* Local relapse after surgical resection of a
single brain metastasis
* Salvage therapy for recurrent oligometas-
tases (1-3) after WBRT
Consider WBRT in brain metastasis when:
* CNS and systemic progression of disease, with few systemic treatment options and
poor performance status
* Multiple(4-10)brainmetastasisespeciallyif
primary tumor known to be radiotherapy sensitive (NB current data support SRS use in up to 3 metastasis but there is a grow- ing trend to use it in up to 10)
Large(>4cm)brainmetastasisnotamena- ble to SRS
* Postsurgicalresectionofadominanthemi- sphere brain metastasis with multiple (4-10) remaining BMs
* SalvagetherapyforrecurrentBMafterSRS or WBRT failure
Which one of the following statements regarding radiotherapy for low-grade glioma is most accurate?
a. Early postoperative radiotherapy increa- ses survival
b. Early postoperative radiotherapy is asso- ciated with better seizure control
c. Early postoperative radiotherapy is asso- ciated with reduced side-effects
d. Early postoperative radiotherapy results in increased malignant transformation of residual tumor
e. Early postoperative radiotherapy shows no advantage in time to tumor progression
b. Early postoperative radiotherapy is asso- ciated with better seizure control
In a single prospective RCT (n 1⁄4 311) People with LGG who undergo early postoperative radiother- apy showed an increase in time to progression compared with people who were observed and had radiotherapy at the time of progression (mean 5.3 vs. 3.4 years). There was no significant differ- ence in overall survival between people who had early versus delayed radiotherapy; however, this finding may be due to the effectiveness of rescue radiotherapy in the delayed arm (required in 65% of this group). People who underwent early radiation had better seizure control at 1 year than people who underwent delayed radiation. Early radiation therapy was associated with skin reac- tions, otitis media, mild headache, nausea, and vomiting. There were no cases of radiation- induced malignant transformation of LGG. How- ever, it remains unclear whether there are differ- ences in memory, executive function, cognitive function, or quality of life between the two groups since these measures were not evaluated.
What is the target for stereotactic radiosur- gery treatment for trigeminal neuralgia?
a. Cisternal portion of the trigeminal nerve adjacent to the brainstem
b. Sensory trigeminal nucleus in pons
c. Superficial cerebellar artery
d. Trigeminal ganglion in Meckel’s cave
e. Trigeminal nerve in foramen ovale
a. Cisternal portion of the trigeminal nerve adjacent to the brainstem
For patients refractory to medications SRS is the least invasive procedure, though microvascular decompression remains superior in candidates fit for surgery. Typical doses are 70-90 Gy in a single fraction directed at the dorsal root entry zone of cranial nerve V near the pons. Initial SRS direc- ted at the gasserian ganglion produced inferior results. Pain relief is experienced with a latency of approximately 1 month. Paresthesia is the most common side effect. Some pain relief (partial or complete) is seen in 60-70% of patients treated.
Which one of the following scenarios describes the most appropriate action taken?
a. 1 cm Spetzler-Martin grade 3 AVM in the left thalamus treated with embolization
followed by stereotactic radiosurgery
b. 1.5 cm Spetzler-Martin grade 2 AVM in left
parietal cortex treated with embolization
c. 1.5 cm Spetzler-Martin grade 3 AVM in right thalamus treated with stereotactic radiosurgery
d. 4 cm Spetzler-Martin grade 3 AVM in right frontal lobe treated with stereotactic radiosurgery
e. 5 cm Spetzler-Martin grade 3 AVM in left
temporal lobe treated with surgical excision
c. 1.5 cm Spetzler-Martin grade 3 AVM in right thalamus treated with stereotactic radiosurgery
Arteriovenous malformations (AVMs) harbor a risk of hemorrhage of about 2-4% per year, mor- tality of 10-15% and morbidity of 50% and given the cumulative lifetime risk treatment is often considered in an asymptomatic patient. Treat- ment options include observation, embolization, surgery, or stereotactic radiosurgery. Surgery is the treatment of choice, when feasible, as it immediately removes the risk of hemorrhage (compared to the persisting risk of hemorrhage during the latency period between SRS and even- tual AVM obliteration). As such, SRS is an approved treatment option for intracranial AVMs that are not treatable via microsurgery. For low- grade deep AVMs smaller than 3 cm, SRS alone can be performed when microsurgery is not pos- sible. Smaller AVMs allow large doses of radia- tion to be applied safely and thus have a higher obliteration rate. The high dose of radiation pre- sumably unleashes a cytokine cascade that induces fibrointimal reaction, thrombosis, and eventual obliteration of the AVM nidus over 1-3 years (latency period). Given the concomitant increased risks of adverse radiation effects, high doses of radiation cannot be safely used in large AVMs, thereby resulting in a worse obliteration rate. Thus, a multimodal approach consisting of a combination of embolization and SRS has been widely used. Embolization may reduce the size of larger AVMs, making them more amenable to radiosurgery. In addition, intranidal aneurysms and arteriovenous fistulas associated with AVMs not only have a high risk of hemorrhage but are also less sensitive to radiosurgery and can be trea- ted using embolization followed by radiosurgery.
Which one of the following has not been shown to increase the risk of developing edema after stereotactic radiosurgery for the treatment of meningiomas is most accurate?
a. Brain-tumor interface >1 cm2
b. Clinical treatment volume of >5 cm3
c. Location in cavernous sinus
d. Presence of edema on pretreatment scan
e. Radiation dose greater than 16 Gy
c. Location in cavernous sinus
Radiosurgery plays an important role in the treat- ment of small lesions (<3 to 4 cm) that are surgi- cally inaccessible, such as those in cavernous sinus or posterior parasagittal locations, or those that have been subtotally resected but consistently have been shown to result in high recurrence rates. Two of the largest series that have examined results of SRS are from the Mayo Clinic and the University of Pittsburgh, both of which have shown local control in more than 90% for benign meningiomas at 5 years; doses 12-16 Gy, due to increased risk of edema above this dose.
The most common toxicities include cranial nerve deficits for basal tumors and peritumoral edema for non-basal tumors. The risk of optic neuropathy is very low, with maximum dose con- straints to the optic nerves and chiasm of between 8 and 10Gy. Risk of peritumoral edema is increased by: high dose, a treatment volume of more than 5cm3, a brain-tumor interface of >1 cm, the presence of pretreatment edema, and parasagittal location. These factors should be considered when deciding whether or not to include none of the dural tail or only a portion of it within the clinical target volume. Small meningiomas can be controlled with radiosurgery in the majority of patients, with initial results comparable to those of complete resection.
WhichoneofthefollowingistrueofSRSfor acoustic neuroma?
a. Microsurgery is associated with better preservation of serviceable hearing than radiotherapy.
b. Microsurgery is preferred for lesions smaller than 3 cm.
c. Radiotherapy is associated with reduced facial nerve and trigeminal nerve toxicity compared to microsurgery.
d. Stereotactic radiosurgery is more effec- tive than fractionated stereotactic radio- therapy.
e. Stereotactic radiosurgery is preferred for lesions bigger than 3 cm.
c. Radiotherapy is associated with reduced facial nerve and trigeminal nerve toxicity compared to microsurgery.
Vestibular schwannomas represent 6-8% of pri- mary intracranial tumors, arising at the point where nerve sheaths are replaced by fibroblasts (Obersteiner-Redlich zone; usually in IAC). Though benign, the lesions can cause severe local symptoms. Typical growth rates are less than 2 mm per year. Common symptoms include unilateral sensorineural hearing loss (>90%), tinnitus, unsteady gait, facial numbness or weakness, mastoid pain, and headaches. Late presentations can include brain stem compres- sion. The typical appearance on T1-weighted MRI with contrast shows a homogenously enhancing mass within the cerebellopontine angle with widening of the internal auditory canal. Treatment options include observation, microsurgical resection, SRS, or fractionated radiotherapy; recommendations are influenced by age, comorbidities, tumor size, presenting symptoms, hearing loss/presence of serviceable hearing, proximity to the brainstem or cochlea, and patient preference. The goals of treatment include maximizing tumor control while pre- serving hearing and facial nerve and trigeminal nerve function. All interventions (surgery, SRS, FSRT) appear to result in a tumor control probability of more than 90%, and utility is sum- marized below:
* Microsurgery is preferred for lesions larger than 2.5 cm. The risk of cranial nerve injury with microsurgical resection is highly dependent on tumor size, operative approach (retrosigmoid, middle cranial fossa, or translabyrinthine), and the sur- geon’s skill and experience.
* SRS is an option for lesions smaller than 2.5 cm. The risk of sensorineural hearing loss is related to the dose of radiation deliv- ered to cranial nerve VIII, the cochlea, and the ventral cochlear nucleus. Compared to microsurgery for similar tumors, SRS shows better serviceable hearing preserva- tion (50-89%) and reduced facial nerve and trigeminal nerve toxicity (<5%).
* Fractionated stereotactic radiotherapy (FSRT) has comparable efficacy with SRS; some series have reported poorer hearing preservation and increased trigem- inal nerve injury with SRS.
What is the risk of secondary neoplasm after SRS at 15 years?
a. 0.004%
b. 0.04%
c. 0.4%
d. 4.0%
e. 4.4%
f. 44%
b. 0.04%
Which one of the following is most accurate about stereotactic radiosurgery for pituitary adenomas?
a. At doses above 5 Gy, the rate of impaired thyrotropic function at 5 years was 50%.
b. Contraindicated for tumors within 5 mm
of the optic chiasm
c. For secretory tumors there is no significant
difference in response by tumor subtype.
d. Improved rates of tumor control are seen when radiation therapy is combined with
dopamine agonists.
e. Radiation-induced hypopituitarism occurs
in 10% of patients undergoing SRS
b. Contraindicated for tumors within 5 mm
of the optic chiasm
Pituitary adenomas represent 10-15% of intracra- nial neoplasms. Irradiation is generally reserved for patients who have incompletely resected tumors or recurrent disease. Based on the size and location, either SRS or conformal EBRT may be considered. SRS is typically contraindi- cated for tumors within 3-5 mm of the optic chi- asm, respecting a maximum dose constant of 10 Gy or less to the optic nerves and chiasm. Frac- tionated radiotherapy, used successfully for more than 50 years to treat pituitary adenomas, should be recommended for tumors abutting optic nerve or chiasm and for diffuse or large tumors. Local
control using SRS is generally in excess of 90% for non-secretory tumors. Radiation-induced hypopituitarism occurs in more than 50% of patients and is the most common late toxicity. A mean pituitary dose of 15 Gy was found to pose little risk of subsequent thyrotropic, gonado- tropic, or adrenocorticotropic function; but at 5 years half of patients had low gonadotropic and thyrotropic function at doses above 17 Gy and low adrenocorticotrophic function at doses above 20 Gy. Dose to the pituitary stalk and hypo- thalamus may also contribute to hypopituitarism following SRS. For secretory tumors, SRS appears to result in a shorter time to hormone normalization than fractionated radiotherapy. Though tumor control remains high, hormonal remission is seen in 25-75% of patients and depends on the tumor subtype (i.e., prolactinoma, Cushing’s disease, Nelson’s syndrome, or acro- megaly). Cytostatic medical management of secreting pituitary adenomas is often employed, but should be discontinued pre-radiotherapy if symptoms allow because patients receiving octreotide or dopamine agonists show markedly inferior control rates in several series.
Which one of the following is most accurate about radiation treatment for craniopharyngiomas?
a. Bleomycin can be used for intracystic irradiation.
b. Intracystic interferon alpha is utilized to sensitize the cystic component to SRS.
c. Fractionated conformal radiotherapy is
commonly used to treat residual tumour.
d. SRS with intracystic irradiation is effec-
tive for mixed-type tumors.
e. There is no significant role for radiother-
apy in management.
d. SRS with intracystic irradiation is effec-
tive for mixed-type tumors.
Maximal safe resection is the mainstay of treatment for craniopharyngiomas and leaving residual tumour is often necessary to preserve vision or hypothalamic function. Radiotherapy (RT) has emerged as a valuable adjuvant treatment modality for recurrent or residual craniopharyngiomas. Sev- eral radiotherapeutic modalities, including confor- mal radiotherapy, single-fraction stereotactic radiosurgery, fractionated stereotactic radiother- apy, and proton beam therapy offer reasonable rates of tumor control. With advances in neuroimaging and RT modalities, dose delivery is more accurate and focused, resulting in decreased long-term com- plication rates over time (hypopituitarism, visual deterioration, cranial nerve deficit, radiation effects). The cystic component of a craniopharyn- gioma commonly presents a problem for radiation therapy and radiosurgery. Tumor growth and cyst enlargement can be independent: the solid compo- nent of the tumor can usually be controlled by radi- ation while the cystic component may require treatment with one of the following options:
* Stereotacticaspiration(e.g.,acutepresenta- tion or poor surgical candidate)
* Placement of an Ommaya reservoir allow- ing intermittent aspiration of a cyst that cannot be completely resected
* Sclerosis of the cyst wall by chemothera- peutic drugs for treatment-resistant cysts (e.g., bleomycin, interferon alpha)
* Internal irradiation (i.e., brachytherapy) with implanted radioisotopes for treatment- resistant cysts (Phosphorus-32)
Although the beneficial effect of radiation in the treatment of craniopharyngiomas has been well recognized, several issues remain sources of sig- nificant controversy:
1. Onthebasisofthecomplicationsassociated with aggressive resection and the proven efficacy of radiation for craniopharyngio- mas, several authors have recommended subtotal resection and RT as an acceptable alternative to gross-total resection. Further support for this approach comes with increasing recognition that while neurolog- ical deficits and endocrine dysfunction due to radical resection can be managed, the associated psychosocial consequences for pediatric patients growing into adults sig- nificantly affect quality of life.
2. TheroleofRTimmediatelyafterresection without first monitoring for tumor pro- gression (up-front vs. salvage treatment) is debated with early radiotherapy showing some evidence of lower rates of morbidity and improved tumor control in children but not adults.
3. SRS as a primary treatment has shown higher tumor control rates in single-type tumors (solid or cystic) compared to mixed solid-cystic tumors. Solid-type tumors and the solid portions of mixed tumors may be less responsive to brachytherapy than cystic tumors, hence a combination of radioisotope instillation and SRS has been suggested as primary treatment for mixed solid-cystic tumors.
Has a single fraction maximal tolerated dose of 3.7 Gy
a. Brain lesion 0-2 cm
b. Brain lesion 2-3 cm
c. Brain lesion 3-4 cm
d. Brainstem
e. Cochlea
f. Cranial nerves III, IV, VI
g. Facial nerve
h. Optic chiasm/nerve
i. Pituitary
j. Trigeminal nerve
e. Cochlea
With increasing international experience with SRS, guidelines for reducing the risk of normal- tissue toxicity have emerged. In general, normal tissues at risk depend on the location of the target volume. These include the brain parenchyma (edema, necrosis), brainstem (edema, necrosis, neuropathy), cranial nerves (neuropathy), and hypothalamic-pituitary axis (hypopituitarism). The interaction of dose and volume irradiated has not been clearly defined for most structures at risk.
