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Thursday, March 01, 2007

TNPG 2006 RADIODIAGNOSIS & RADIOTHERAPHY

RADIODIAGNOSIS & RADIOTHERAPHY

169) Left Atrial EnlargeMent Seen In

a. AP View

b. PA View

c. Left Oblique View

d. Right Anterior Oblique View

Answer (d) Right Anterior Oblique View

Reference: Braunwald, Chapter 7 - Radiology of the Heart

RIGHT ANTERIOR OBLIQUE (RAO) PROJECTION.

Ä Chest radiography in this projection is performed with the patient in a 45-degree right anterior oblique relationship to the film cassette (right shoulder toward the cassette). In this view there is elongation of the ventricles; the long axes of the ventricles are in view and the atrioventricular groove is in profile. This position permits optimal visualization of a calcified mitral or tricuspid valve. The right anterior oblique view is used by angiographers to determine the presence of left atrial enlargement, a common feature in mitral stenosis. It is also helpful to the fluoroscopist when studying the function of a mechanical mitral valve prosthesis. The aortic arch is foreshortened in this view, so that the arch and proximal descending aorta are often superimposed and obscured. The anterior border of the heart consists of the sinus portion of the right ventricle inferiorly and the right ventricular outflow tract and the main pulmonary artery superiorly. The right-sided or posterior heart border consists of the right atrium superiorly and the left atrium inferiorly.

LEFT ANTERIOR OBLIQUE (LAO) PROJECTION.

Ä The left anterior oblique projection is performed with the patient in a 60-degree oblique relationhip to the cassette. This is a useful angiographic view to diagnose the presence of left ventricular enlargement. Since the ventricular septum is in profile in the LAO projection, septal defects, dyskinesia, and displacement, due to right heart enlargement, can be identified. In this projection the aortic and pulmonary valves are in profile, so that aortic valve calcifications can be clearly visualized and aortic or pulmonary stenosis and regurgitation can be assessed. The aortic arch is also in profile in the LAO projection so that abnormalities of the arch including dissection, contained rupture, aortitis, aneurysm, and coarctation can be detected with aortography or cross-sectional imaging. The anterior (right) heart border consists of the right atrium above and right ventricle below. Along the left posterior heart border, the left atrium is border-forming superiorly and the left ventricle inferiorly. The LAO projection is superior to other projections for detecting right ventricular enlargement, characterized by an increase in the convexity of the anterior border of the cardiac silhouette. An enlarged right atrium may cause bulging of the upper anterior border of the cardiac shadow, producing a shelf-like configuration.

170) NMR is based on the properties of

a. Protons

b. Spin

c. Both

d. None

Answer © Both

Reference: Nelson 15th Edition Chapter 381.7

Nuclear magnetic resonance (NMR) is a physical phenomenon based upon the magnetic properties of an atom's nucleus. All nuclei that contain odd numbers of nucleons and some that contain even numbers of nucleons have an intrinsic magnetic moment. The most commonly used nuclei are hydrogen-1 and carbon-13, although certain isotopes of many other elements nuclei can also be observed. NMR studies a magnetic nucleus, like that of a hydrogen atom (protium being the most receptive isotope at natural abundance) by aligning it with a very powerful external magnetic field and perturbing this alignment using an electromagnetic field. The response to the field by perturbing is what is exploited in nuclear magnetic resonance spectroscopy and magnetic resonance imaging.

NMR spectroscopy is one of the principal techniques used to obtain physical, chemical, electronic and structural information about a molecule. It is the only technique that can provide detailed information on the exact three-dimensional structure of biological molecules in solution. Also, nuclear magnetic resonance is one of the techniques that has been used to build elementary quantum computers.

171) Lentiform appearance

a. Extradural Haemorrage

b. Subdural

c. Sub Arachnoid Hemorrhage

d. Intra Cerebral hemorrhage

Answer (a) Extradural Hemorrhage

Reference:

Concise Textbook of Surgery - 3rd Edition - Das Page 546 Fig 31.2

Schwartz Surgery : 7th Edition Page 1882 : Fig 40-1

Bailey 22nd Edition Page 395

Facts

1. Lentiform-shaped hyperdense lesion is Acute Extradural Hemorrahge.

2. Cresent-shaped hypodense lesion is Chronic Subdural Hematoma.

3. Cresent-shaped hyperdense lesion is Acute Subdural Hematoma.

4. Lentiform-shaped hypodense lesion is Chronic Extradural Hematoma.

Ä This is easy to understand. When the blood is between Skull and Dura, as in the case of Extra dural haemorrhage, it is limited by the inner aspect of skull and the dura and gives the classical biconvex or lentiform shaped (Remember that the common lens (including the lens in our eye) is biconvex)

Ä When the blood is between Dura and Arachnoid, as in the case of Sub Dural, it assumes a concavo convex shape, limited by Dura on the outer aspect and Arachnoid on the inner aspect to produce a crescent shaped lesion

172) A patient presents with mass in lung with hyperosmolality of urine. The probable cause of this is

a. SIADH

b. Lab Error

c. Renal Secondaries

d. None of the above

Answer (a) SIADH

Reference: Robbins 7th Edition Page 334

173) Most common cause of lymph edema of developed countries-

a. Malignancy

b. Filaria

c. Trauma

d. None of the above

Answer (a) Malignancy

Reference: Bailey and Love 24th Edition Page 981

174) Which of the following Techniques and Instruments allow more accurate placement of radiation beams than is possible using conventional X-rays, where soft-tissue structures are often difficult to assess and normal tissues difficult to protect and to measure cancer volume for Rx for Tele therapy in Radio therapy

a. Virtual simulation,

b. 3-dimensional conformal radiotherapy,

c. and intensity-modulated radiotherapy

d. All of the above

Answer (d) All of the above

Reference: Bucci M, Bevan A, Roach M (2005). "Advances in radiation therapy: conventional to 3D, to IMRT, to 4D, and beyond.". CA Cancer J Clin 55 (2): 117-34. PMID 15761080.

The planning of radiotherapy treatment has been revolutionized by the ability to delineate tumors and adjacent normal structures in three dimensions using specialized CT scanners and planning software.[2] Virtual simulation, the most basic form of planning, allows more accurate placement of radiation beams than is possible using conventional X-rays, where soft-tissue structures are often difficult to assess and normal tissues difficult to protect.

An enhancement of virtual simulation is 3-Dimensional Conformal Radiotherapy (3DCRT), in which the profile of each radiation beam is shaped to fit the profile of the target from a beam's eye view (BEV) using a multileaf collimator (MLC) and a variable number of beams. When the treatment volume conforms to the shape of the tumour, the relative toxicity of radiation to the surrounding normal tissues is reduced, allowing a higher dose of radiation to be delivered to the tumor than conventional techniques would allow.

An enhancement of 3DCRT is intensity-modulated radiotherapy (IMRT), employing dynamic multileaf collimation not only to shape the profile of the beam, but also to vary the intensity of the beam over its area. The goal is to achieve greater conformality than 3DCRT provides. IMRT also improves the ability to conform the treatment volume to concave tumour shapes, for example when the tumour is wrapped around a vulnerable structure such as the spinal cord or a major organ or blood vessel.

3DCRT is used extensively. Use of IMRT is growing but is limited by its need for additional time from medical personnel. Proof of improved survival benefit from either of these techniques over conventional radiotherapy is limited to a few tumor sites, but the ability to reduce toxicity is generally accepted. Both techniques may enable dose escalation, potentially increasing usefulness. There has been some concern, particularly with IMRT, about increased exposure of normal tissues to radiation and the consequent potential for secondary malignancy. Overconfidence in the accuracy of imaging may increase the chance of missing lesions that are invisible on the planning scans (and therefore not included in the treatment plan) or which may move between treatments or during a treatment (for example, due to respiration or inadequate patient immobilization). New techniques are being developed to better control this uncertainty — for example, real-time imaging combined with real-time adjustment of the therapeutic beams. This new technology is called image-guided radiation therapy (IGRT) or four-dimensional radiotherapy.

175) Cell Most Sensitive to Radiotherapy

a. Rapidly Proliferating Cell

b. Slowly dividing cells

c. Central Nervous system

d. None of the above

Answer (a) Rapidly Proliferating Cell

Reference: Robbins 7th Edition Page 437

176) Which one of the following radioisotope is not used as permanent implant?

a. Iodine- 125.

b. Palladium - 103.

c. Gold - 198.

d. Caesium - 137.

Answer

4. Caesium - 137.

Reference

Radiation in Medicine: A Need for Regulatory Reform (1996) Page 71 TABLE 2.13 published by the institute of Medicine http://www.iom.edu/

Oxford Textbook of Surgery, Chap 35.7

http://books.nap.edu/books/0309053862/html/71.html

http://mrcas.mpe.ntu.edu.sg/groups/urobot/bt/brachytherapy.html

Discussion

The original method of brachytherapy is now sometimes called "low dose rate" (LDR) brachytherapy. The radioactivity of sources available at the time of brachytherapy's development was such that, to give a tumor-killing dose, sources had to be left in place for days. Because of the low activity, these sources could be handled manually. LDR therapy typically involves tumor dose rates of from 0.3 to 0.6 Gy per hour.

For interstitial brachytherapy, sources are either inserted directly into tissues or are afterloaded into hollow needles or plastic catheters that pierce the tumor. In some cases, seeds are implanted directly into tissues and left permanently. For radiation safety and radiobiological considerations, permanent implants are feasible only with nuclides having a fairly short half-life.

In the early days of brachytherapy, radium-226 (Ra-226) was the only radionuclide available. After World War II, reactor-produced nuclides became available and the use of Ra-226 gradually declined. The radionuclides commonly applied in brachytherapy are listed in in the table below in approximate order of prevalence of use.

Some Properties of Radionuclides Commonly Used for Brachytherapy

Element

Isotope

Half-Life

Source Forms

Implant Type

Gold

Au-198

2.7 days

Seeds

Permanent

Palladium

Pd-103

17 days

Seeds

Permanent

Iodine

I-125

60 days

Seeds

Permanent

Iridium

Ir-192

74 days

Seeds, wire

Temporary

Cesium

Cs-137

30 years

Tubes, needles

Temporary

Strontium

Sr-90

29 years

Plaque

Temporary

Explanation

Self Explanatory

Comments

In a permanent implant, the radioactive sources are permanently implanted into the tumor and allowed to decay. Hence, neither the dose nor the dose distribution can be changed after the initial insertion. It is, however, a simple procedure, and some of them can be done on an out-patient basis. Other advantages of the permanent implant are that, in deep-seated tumors, it is safer because of the lower risk of infection and that a second operation for its removal is not required. Permanent implantations are performed with relatively short half-life radiosotopes like iodine-125, palladium-103, or gold-198

Tips

Ä I 125 PERMANENT IMPLANTS are used in prostate cancer

Ä Palladium is used for Prostate cancers and Choroidal melanoma

Ä Gold is used in the following cases

    1. Palliative treatment of inoperable tumours obstructing the trachea can be achieved using a number of techniques. A diathermy loop can be used to core out large volumes of tumour from within the lumen. Laser resection is more elegant but no more effective. Local radiotherapy can be achieved by inserting radioactive gold grains; this technique may be supplanted by placing a cannula into the tumour site and inserting iridium-199.
    2. Although nasopharyngeal carcinoma is radiosensitive, local failure in the form of persistent or recurrent tumour is not uncommon. Administration of further external radiation is limited by the tolerance of structures such as the inner ear and brain-stem. Brachytherapy has been successfully employed in the management of local disease. This requires adequate exposure of the nasopharynx to allow accurate insertion of radioactive implants. Under general anaesthesia, the hard and soft palates can be split in the midline to expose the tumour in the nasopharynx; radioactive gold grains can then be inserted into the tumour under direct vision. The operative procedure is simple and the complication rate is minimal. Small recurrent or persistent tumours in the nasopharynx can be managed successfully in this way.

177) half life of Cobalt 60

a. 5 hours

b. 5 days

c. 8 days

d. 8 months

Answer : (For this question, all choices are wrong)

The correct answer is 5.2 Years

Important Radioactive elements

Rays

Mass

Symbol

Atomic Number

Actual Mass

Element

t ½

t ½

b

32

P

15

30

Phosphorus

14.3

Days

b

90

Sr

38

87

Strontium

28

Years

b

90

Y

39

88

Yttrium

2.54

Days

b,g

226

Ra

88

226

Radium

1622

Years

b,g

198

Au

79

197

Gold

2.7

Days

b,g

131

I

53

127

Iodine (Mainly b)

8

Days

g

Ir

77

192

Iridium

74.5

Days

g

60

Co

27

57

Cobalt

5.2

Years

g

137

Cs

55

133

Caesium

30

Years

N,g

252

Cf

98

252

Californium

2.6

Years

182

Ta

73

180

Tantulum

4

Months

Tritium

12.4

Years

g

133

Xe

54

131

Xenon

5.2

Days

123

I

53

127

Iodine

13

Hours

132

I

53

127

Iodine

2.3

Hours

g

99

Tc

43

99

Technetium

6

Hours

Ga

31

70

Gallium Citrate

3.2

Days

g

201

Tl

81

204

Thallous Chloride

3.1

Days

222

Rn

76

222

Radon

3 to 6

Days

51

Cr

24

52

Chromium

3.8

g

81

K

36

Krypton

g

Se

34

Selenium

178) Phantom used in

a. Stereotactic Surgery.

b. Electron Beam CT

c. Both

d. None

Answer (c) Both

Reference:

Robert Levy, A Short History of Stereotactic Surgery, Cyber Museum of Neurosurgery. This is based on

Patrick J. Kelly, "Introduction and Historical Aspects", Tumor Stereotaxis, Philadelphia: W.B. Saunders Company (1991)

Philip L. Gildenberg, "Stereotactic Surgery: Present and Past", Stereotactic Neurosurgery, (Editor: M. Peter Heilbrun) Baltimore: Williams and Wilkins (1988)

Stereotactic neurosurgery

Ä Stereotactic neurosurgery has become an indispensable portion of the neurosurgeon's repitoire, a method allowing three dimensional localization of specific sites within the complex and compact human nervous system.

Ä The word stereotactic is derived from the Greek word stereos, meaning three dimensional, and the Latin word tactus, meaning to touch. Originally used to create accurate maps of the human brain, its first clinical application occurred at the end of World War II. At this time physicians attempted to treat patients with movement disorders, such as Parkinson's disease, by creating defects within abnormal portions of the brain.

Ä Stereotactic guidance was used to increase the accuracy of the lesion produced. Despite the initial attempts, stereotactic neurosurgery did not become popularized until the late 1970's when dramatic improvements in neuroimaging occurred. At this time computed tomography, CT, redefined the ability of a physician to identify diseases within the brain. More recently magnetic resonance imaging, MRI, has also been applied to stereotactic procedures, increasing the neurosurgeon's accuracy and the diversity of disease processes treated.

Ä Combined with these neuroimaging techniques, stereotactic neurosurgery has found a role in both the therapeutic as well as diagnostic approaches to treating diseases of the nervous system.

How is stereotactic neurosurgery performed?

Ä There are a number of different stereotactic systems, each employs the same basic principle to localize a specific site within the brain. The system pictured is known as the Cosman-Roberts-Wells System. At Columbia Presbyterian Medical Center this system, as well as the Brown-Roberts-Wells System, is utilized. Although a number of different procedures can be performed with stereotactic techniques, the following description is for a stereotactic brain biopsy.

Ä The initial step to stereotactic localization is the application of the base ring. With the help of an anesthesiologist, the patient is mildly sedated and four points on the scalp are infiltrated with local anesthetic. The ring is then fastened to the patient's skull with four pins, inserted through the anesthetized regions. The exact pin sites are determined based on the location of the lesion. The localizing ring is then attached to the base ring and the patient is taken to the neuroradiology department where a CT or MRI is performed. Brain Targeting

Ä The image obtained in conjunction with the localizing ring allows the neurosurgeon to compute the exact three dimensional position of the region of interest. The patient is then taken to the operating room and placed on the operating table. The base ring is attached to the operating table. This maintains the base ring in a fixed position and avoids the patient having to support the weight of the apparatus. The entry site is selected, and both the entry site and point of interest are mapped onto a "phantom," which relates each point to the patient's head. Coordinates are obtained from the phantom and entered into a computer which determines the final trajectory.

Ä The localizing ring is removed and an arc ring is attached to the base ring. The arc ring will guide the neurosurgeon in the proper trajectory. A small incision, about 0.5 cm, is made in the scalp at the entry site, and a hole is drilled through the skull which has a diameter smaller than a pencil. The biopsy needle is inserted, guided by the arc ring, to the point of interest. Samples of tissue are obtained and sent for analysis. Once enough specimens have been obtained the biopsy needle is removed and the scalp incision is sutured, often requiring only one stitch. The arc ring is then disassembled and the base ring removed from the patient's skull by unscrewing the four pins. The entry sites for the pins are small and do not require any stitches. The patient is taken to the recovery room, observed overnight, and returns home the next day.

What are the applications of stereotactic neurosurgery?

Ä The description above is for a stereotactic brain biopsy, which is one of the more common procedures employing stereotactic techniques. This type of procedure is purely diagnostic, and will only identify a disease process. Stereotactic techniques also aid in the diagnosis of abnormal brain in patients with epilepsy. Such patients often do not have discrete areas which can be identified as the seizure focus. The implantation of electrodes is required to record the activity of brain tissue. Based on these recordings the abnormal tissue is located. Stereotactic insertion of these electrodes insures that the electrodes will be placed in the suspected region of pathology.

Ä Besides diagnostic applications, there are therapeutic procedures performed with stereotactic techniques. One procedure gaining increasing popularity is stereotactic radiosurgery. There are numerous advantages to combining radiation treatments with stereotactic techniques. As opposed to conventional radiation therapy, stereotactic radiosurgery allows a higher dose of radiation to be focused onto the lesion of interest. In addition there is a decreased spread of radiation into the normal brain. The type of radiation employed is either gamma rays or heavy charged particles, such as protons or helium ions. Stereotactic radiosurgery allows a more effective treatment of brain tumors with a decreased incidence of complications.

Ä Certain disease processes produce an abnormal collection of fluid within the brain. These collections produce pressure on the surrounding brain and can lead to damage of normal structures. Examples of abnormal fluid collections include neoplastic and non-neoplastic cysts, hydrocephalus, and traumatic fluid collections. Utilizing stereotactic procedures the neurosurgeon is able to precisely insert a catheter into the fluid collection. The fluid can then be drained with a temporary catheter, or a permanent draining device. Stereotactic techniques are also employed to determine the exact location of a skull opening, known as a craniotomy, in order to remove lesions within the brain.

Ä Finally, stereotactic techniques are also utilized in the treatment of various neurological diseases that produce movement disorders, such as Parkinson's disease, Hemiballismus, Essential Tremor, or Huntington's Chorea. The procedures utilized to treat such conditions are known as Pallidotomy and Thalamotomy. Such procedures are designed to create an ablative lesion within various brain structures, such as the pallidum or the thalamus. Precise localization is required so as not to include adjacent structures within this compact area of the brain. Such precision is only obtained with stereotactic techniques.

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