PRACTICE EDUCATION EXERCISES
Question 1
Human errors are present most especially in the medical field. With the use of Linac or linear accelerator, the chances for human errors could significantly cost the life of the patient. Using Linac, it may be possible to further limit the exact amount of radiation that is received by normal tissues that are near the tumor since overexposure of the tissues to the beams could be harmful to normal tissue. In some situations, this may also allow a higher dose of radiation to be delivered to the tumor, increasing the chance of a cure, yet that is not applicable to all situations. Quality assurance is therefore vitally important in all aspects of radiation therapy to ensure that the treatments delivered are safe and effective.
Question 4
The mechanical method of patient contour determination only gives a picture of the tumor in two dimensions – width and height. It leaves little information for the health care practitioner regarding the tumor. It is not possible to see the tumor in three dimensions with this method. An example of this is the X-ray.
The optical method of patient contour determination imaging based treatment planning for radiotherapy is limited due to imaging system related geometrical distortions, especially for patients with large body sizes. In order to use imaging alone for treatment planning the effect of residual distortions on external patient contour determination, especially for the peripheral regions still has to be investigated and corrected.
The radiological method of patient contour determination is advantageous in that it uses sophisticated physical and biological techniques, often accompanied by computer analyses. Ionizing radiation is used for this type of therapy, which involves the use of high-voltage radiation and other radioactive elements to injure or destroy cells. Its disadvantage is that this is localized therapy that is applicable only for a limited number of specific tumors, not for any kind of tumor.
Question 5
It is important to reduce the radiation dose from simulator procedures such as from Linac to patients who will be receiving a high dose of radiation during their treatment because of the fact that radiosurgery performed with linear accelerator machines is only a one session surgical procedure directed by a neurosurgeon and a radiation oncologist. The entire procedure occurs in one day, including immobilization, scanning, planning and the procedure itself. With radiosurgery, the radiation dose given in one session is usually less than the total dose that would be given with radiation therapy since the cancer cells receive a very high one time dose of radiation with radiosurgery, and smaller doses over time with radiation therapy. This is important since more radiation is delivered to surrounding healthy areas when a person undergoes a few (2–5) treatment sessions instead of one; this can result in more side effects, some of which may be permanent. More importantly, a reduced amount of radiation delivered to the tumor with each radiation therapy treatment, rather than a very high one time dose, can result in less tumor control and poorer outcomes than with radiosurgery.
Question 6
The simulator procedure for acquiring and downloading images from simulator to the linear accelerator happens as follows. It is important to remember that the longer a linac is, the higher the energy of the particles it can produce. A synchrotron achieves high energy by circulating particles many times before they hit their targets. Bunches of electrons are accelerated in the copper structure of the linac in much the same way as a surfer is pushed along by a wave. In the linac, the wave is electromagnetic. That means it is made up of changing magnetic and electric fields. The electromagnetic waves that push the electrons in the linac are created by higher energy versions of the microwaves used in the microwave oven in a kitchen. Inside the accelerator structure, the microwaves from the klystrons set up currents in the copper that cause oscillating electric fields pointing along the accelerator as well as oscillating magnetic fields in a circle around the interior of the accelerator pipe.
Question 7
Four compelling arguments can made between obtaining hard copy radiographic portal film compared to electronic portal image. The first shorter time involved in obtaining a hard copy with the use of an electronic portal. The second is less equipment is required for the electronic portal. Third, the linear accelerator incorporates proprietary x-band technology, which can produce high quality images and promotes easier storage and manipulation of the images scanned. All these make the electronic portal more advantageous in obtaining a hard copy, although it is at a disadvantaged higher cost
Question 8
The implantation of radioactive iodine-125 or palladium-103 seeds directly into the anatomical area required for radiation emits a highly localized radiation energy to kill localized cancer cells without excessive harm to nearby healthy cells. Proper placement of these seeds is critical, and a preprocedural map of the area, using ultrasound or CT, is obtained. A grid is then placed over the perineum and ultrasonic or CT imaging used to deliver seeds to the anatomical area alone. These seeds remain in the body, but their radioactivity declines over a period of months ( 2004). The proper placement of the seeds will determine the image quality of the image to be assessed as could be seen in the map obtained from an ultrasound or CT.
Credit:ivythesis.typepad.com
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