Textbook of Medical-Surgical Nursing 3e

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Chapter 11

Oncology: Nursing management in cancer care

for the periphery of the tumour to be reoxygenated repeatedly because tumours shrink from the outside inward. This process increases the radiosensitivity of the tumour, thereby increas- ing tumour cell death (Yarbro, Hansen-Frogge & Goodman, 2005). External radiation External beam radiation therapy (EBRT) is the most commonly used form of radiation therapy. The energy utilised in EBRT is either generated from a linear accelerator or from a unit that generates energy directly from a core source of radioactive material such as a GammaKnife™ unit. Through computerised software programs, both approaches are able to shape an invisi- ble beam of highly charged electrons to penetrate the body and target a tumour with pinpoint accuracy. Depending on the size, shape and location of the tumour, different energy levels are generated to produce a carefully shaped beam that will destroy the targeted tumour, yet spare the surrounding healthy tissue and vital organs in an effort to reduce the treatment toxicities for the patient. With advances in computer technology, these beams can be shaped to a two-dimensional or three-dimen- sional shape to conform to the exact shape of the tumour as measured by imaging studies such as positron emission tomogra- phy (PET), CT or MRI scans. Recent treatment enhancements in EBRT include the ability to direct different energy levels at different angles directed at the tumour, called intensity modu- lated radiation therapy (IMRT), which enables higher doses to be delivered to the tumour while sparing the important healthy structures surrounding the tumour. IMRT can be administered as standard daily fractions or as ‘hyperfractionated’ twice daily fractions, which shortens the duration of the patient’s treat- ment schedule. Image-guided radiation therapy (IGRT) uses continuous monitoring of the tumour with ultrasound or CT scans during the treatment to allow for automatic adjustment of the target as the tumour changes shape or position, again in an effort to spare the healthy surrounding tissue and reduce side effects (Sharpe, Craig & Moseley, 2007). The most recent treatment enhancements now include respiratory-gating, where the treatment delivery is actually synchronised with the patient’s respiratory cycle, enabling the beam to be adjusted as the tumour moves (Dawson & Jaffray, 2007). Gamma rays are one of the oldest forms of energy used in EBRT. This energy is produced from the spontaneous decay of naturally occurring radioactive elements such as cobalt 60. The gamma rays also deliver this radiation dose beneath the skin surface, sparing skin tissue from adverse effects. Stereotactic body radiotherapy (SBRT) is another form of EBRT using higher doses of radiation to penetrate very deeply into the body to control deep-seated tumours that cannot be treated by other approaches such as surgery. SBRT is delivered with considerably higher treatment fraction doses over a short span of time, usually 1 to 5 treatment days, in contrast to 6 to 8 weeks for conventional EBRT (Timmerman et al., 2007). Proton therapy is another very different approach to EBRT. The advantage of proton therapy is that it is capable of deliv- ering its high-energy dose to a deep-seated tumour, with no energy exiting through the patient’s healthy tissue behind the tumour, allowing for treatment of deep tumours in close proximity to critical structures such as the heart or major blood vessels (Thornton et al., 2007).

prophylactically to prevent leukaemic infiltration to the brain or spinal cord. Palliative radiation therapy is used to relieve the symptoms of metastatic disease, especially when the cancer has spread to brain, bone or soft tissue, or to treat onco­logical emer- gencies such as superior vena cava syndrome or spinal cord compression. Two types of ionising radiation—electromagnetic rays (x-rays and gamma rays) and particles (electrons [beta par- ticles], protons, neutrons and alpha particles)—can lead to tissue disruption. The most harmful tissue disruption is the alteration of the DNA molecule within the cells of the tissue. Ionising radiation breaks the strands of the DNA helix, leading to cell death. Ionising radiation can also ionise constituents of body fluids, especially water, leading to the formation of free radicals and irreversibly damaging DNA. If the DNA is incapable of repair, the cell may die immediately, or it may initiate cellular suicide (apoptosis), a genetically programmed cell death (Bruner et al., 2006). Cells are most vulnerable to the disruptive effects of radiation during DNA synthesis and mitosis (early S, G2 and M phases of the cell cycle). Therefore, those body tissues that undergo frequent cell division are most sensitive to radiation therapy. These tissues include bone marrow, lymphatic tissue, epithelium of the gastrointestinal tract, hair cells and gonads. Slower-growing tissues or tissues at rest are relatively radioresistant (less sensitive to the effects of radiation). Such tissues include muscle, cartilage and con- nective tissues. However, it is important to remember that radiation therapy is a localised treatment, and only the tissues that are within the treatment field will be affected by the radi- ation therapy. A radiosensitive tumour is one that can be destroyed by a dose of radiation that still allows for cell regeneration in the normal tissue. Tumours that are well oxygenated also appear to be more sensitive to radiation. In theory, there- fore, radiation therapy may be enhanced if more oxygen can be delivered to tumours. In addition, if the radiation is delivered when most tumour cells are cycling through the cell cycle, the number of cancer cells destroyed (cell- killing) is maximal. Radiation sensitivity is also enhanced in tumours that are smaller in size and that contain cells that are rapidly dividing (highly proliferative) and poorly differenti- ated (no longer resembling the tissue of origin) (Bruner et al., 2006). Certain chemicals, including chemotherapy agents, act as radio-sensitisers and sensitise more hypoxic (oxygen-poor) tumours to the effects of radiation therapy. Combinations of chemotherapy and radiation therapy are typically used to take advantage of the radio-sensitising effects of chemo­therapy and achieve an improved survival benefit while minimising side effects of such therapy. Radiation is delivered to tumour sites by external or internal means. Radiation dosage The radiation dosage is dependent on the sensitivity of the target tissues to radiation and on the tumour size. The lethal tumour dose is defined as the dose that will eradicate 95% of the tumour yet preserve normal tissue. The total radiation dose is delivered over several weeks to allow healthy tissue to repair and to achieve greater cell kill by exposing more cells to the radiation as they begin active cell division. Repeated radiation treatments over time (fractionated doses) also allow