radiation and in the case of photon emitting sources, the ? radiation produced during decay. The brachytherapy sources usually comprises of ? rays which are the majority of the components of radiation released in brachytherapy. Electron capture or in some internal conversion which may occur at the source may result to the emission of characteristics X-rays. Finally the source capsule may also emit other characteristics X-rays and bremsstrahlung radiations. Usually various factors may influence the choice of a radionuclide, the photon emitting source. The choice is dictated by physical and dosimetric features which are required such as the photon energies and beam penetration into the tissues and the shielding materials to be used. The source strength, half-life, and the shielding material half-life layer (HVL) should also be put into consideration. Several millimeters (mm) of lead may be required as shielding material. This treatment allows clinicians to deliver high dose of radioactive treatment with very low negative effect to the surrounding tissues. Brachytherapy involves prescribing a radiation dose to an isodose encircling a small target volume as opposed to external beam radiation therapy where the volume treated is large. Two forms of this treatment exist, low dose rate (LDR) and high dose rate (HDR). The LDR is usually temporary and is applied to prostate cancer whereas HDR is usually permanent and is applied in many forms of cancer such as breast, lung, and sarcoma among other types of cancers. In LDR, a source with a low strength is used accompanied by longer treatment times. For instance, in the treatment of prostate cancer, tiny radioactive seeds are placed permanently in the prostate. However, in the case of HDRs, a source with a high radioactivity is contained within an afterloader device. This device delivers the radioactive source in short periods of time to gadgets such as needles, catheters which may be placed in the tumor site. These delivery devices are doubly shielded to ensure that the radioactive material does not leak and also to provide adequate shielding from ? and ? radiation from the source. In comparison to LDR, HDR takes a shorter treatment time ranging to a few minutes to days and does not necessary require multiple treatments (Varian Medical Systems, 2012, ¶1). Pulse dose rate and image guided brachytherapy are also techniques in brachytherapy. Brachytherapy treatments may be classified under different categories one of them being, the classification based on dose rate, namely; low dose rate (LDR), medium dose rate (MDR) and high dose rate (HDR). Table 1: Classification of brachytherapy based on dose rate Dose rate Numerical value of the dose rate at the dose specification point (s) Low dose rate 0.4 – Gy/h Medium dose rate 2 – 12 Gy/h High dose rate >12 Gy/h High Dose Rate (HDR) Brachytherapy In this technique the ultimate goal is to use a dose that targets the size of the cancerous tissue. A single, tiny highly radioactive source approximately 1 mm x 3 mm in size is used as the radioactive source of Iridium -192 which is welded at the end of a thin, flexible stainless steel cable. The radioactive source is placed in an afterloader which is the device housing the radioactive source. This afterloader is computer-guided and it is the one that directs the radioactive source into the catheters. Catheters are placed beforehand in the patients by the physician into the
Subject: Health sciences and Medicine, Research Paper Topic: High Dose Rate (HDR) Brachytherapy Introduction Brachytherapy is a type of internal radiation treatment in which radioactive source is placed into cancerous tissues. Brachytherapy is also referred as curietherapy or enducurie therapy (Suntharalingam et al., n.d, ¶451)…
Dever (1991, p.210) states that “To make statistically valid comparisons…crude rates may be used if it is reasonably certain that the age and sex structures of the population under investigation are similar.” Weaknesses: Taylor (1989, p.10) asserts that using crude mortality rates for comparisons is dangerous.
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