Radiation 101: A Guide for Speech-Language Pathologists Dysphagia, or disordered swallowing, is an unfortunate consequence for individuals with a head and neck cancer diagnosis. Swallowing is altered in many ways due to tumor location and presence, and afterwards due to the mechanisms of tumor eradication. As a common treatment, radiation therapy (RT) has been proven to halt ... Article
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Article  |   April 18, 2017
Radiation 101: A Guide for Speech-Language Pathologists
Author Affiliations & Notes
  • Carly Barbon
    Swallowing Rehabilitation Research Laboratory, Toronto Rehabilitation Institute, Toronto, Ontario Canada
  • Andrew Hope
    Department of Radiation Oncology, Princess Margaret Hospital Cancer Centre Ringgold Standard Institution, Toronto, Ontario Canada
    Radiation Medicine Program, Princess Margaret Hospital,, Toronto, Ontario, Canada
  • Catriona Steele
    University Health Network–Research, Toronto Rehabilitation Institute, Toronto, Ontario Canada
  • Disclosures
    Disclosures ×
  • Financial: Carly Barbon has no relevant financial interests to disclose. Andrew Hope has no relevant financial interests to disclose. Catriona Steele has no relevant financial interests to disclose.
    Financial: Carly Barbon has no relevant financial interests to disclose. Andrew Hope has no relevant financial interests to disclose. Catriona Steele has no relevant financial interests to disclose.×
  • Nonfinancial: Carly Barbon has no relevant nonfinancial interests to disclose. Andrew Hope has no relevant nonfinancial interests to disclose. Catriona Steele has no relevant nonfinancial interests to disclose.
    Nonfinancial: Carly Barbon has no relevant nonfinancial interests to disclose. Andrew Hope has no relevant nonfinancial interests to disclose. Catriona Steele has no relevant nonfinancial interests to disclose.×
Article Information
Swallowing, Dysphagia & Feeding Disorders / Special Populations / Part 2
Article   |   April 18, 2017
Radiation 101: A Guide for Speech-Language Pathologists
Perspectives of the ASHA Special Interest Groups, April 2017, Vol. 2, 63-72. doi:10.1044/persp2.SIG13.63
History: Received June 17, 2016 , Revised July 15, 2016 , Accepted July 18, 2016
Perspectives of the ASHA Special Interest Groups, April 2017, Vol. 2, 63-72. doi:10.1044/persp2.SIG13.63
History: Received June 17, 2016; Revised July 15, 2016; Accepted July 18, 2016

Dysphagia, or disordered swallowing, is an unfortunate consequence for individuals with a head and neck cancer diagnosis. Swallowing is altered in many ways due to tumor location and presence, and afterwards due to the mechanisms of tumor eradication. As a common treatment, radiation therapy (RT) has been proven to halt tumor progression and kill quickly growing cancer cells. However, the side effects of such treatments are often prominent in this patient population. As swallowing professionals, it is important that speech-language pathologists (SLPs) understand the repercussions of RT for those patients undergoing such treatments. This paper aims to provide a basic overview of RT for clinicians working with head and neck cancer patients.

Disordered swallowing, or dysphagia, is a common side effect of head and neck cancer. The extent and location of the tumor may impact the swallow directly. In addition, dysphagia may also develop as a consequence of primary cancer treatment. Radiation therapy (RT) is an integral part of cancer treatment protocols and remains the standard of care for tumor eradication and patient survival. The prevalence of long-term dysphagia after RT has been documented to be approximately 40% and higher (Caudell, Schaner, & Meredith, 2009). While the goal of RT is to kill the tumor and prevent spread, maintaining the integrity of tissue that may have otherwise been damaged by surgical procedures is also imperative. It is therefore important to understand radiation and the impacts it may have on the patient's oropharyngeal tissue and swallowing mechanism post-treatment.
Speech-language pathologists (SLP) who work with head and neck cancer patients need to be well-versed in the effects of RT and its impact on speech/swallowing. Understanding the type, schedule, and effects of RT to both the tumor and normal tissues is critical for treatment planning. The purpose of this paper is to provide a basic understanding of radiation and the negative effects it poses in relation to swallowing. The paper will define the basics of RT; the principles and benefits of treatment; negative sequelae and tissue toxicity; and will inform clinicians on how to interpret dose-effects of RT for head and neck cancer patients.
What Is Radiation?
The Chemistry of Radiation
When radiation is administered, and the energy from that radiation is absorbed by tissue, excitation, or ionization of the tissue may occur. Excitation refers to the situation where the energy of an electron in an atom or molecule increases without ejection of that electron. Ionization occurs when enough radiation-associated energy is absorbed to cause ejection of orbital electrons from an atom or molecule. Ionizing radiation involves the localized release of large amounts of energy (Hall & Giaccia, 2012).
Radiation comes in two main forms: electromagnetic or particulate. Electromagnetic rays (x-rays) are a type of electromagnetic radiation and “can be viewed as waves of electrical and magnetic energy” (Hall & Giaccia, 2012). When an x-ray is absorbed into human tissue, energy is deposited in an uneven fashion, in the form of packets. When energy in a beam of x-rays is parsed into large, individual packets, chemical bonds can be broken and biological change is induced. Radiation via x-rays is delivered externally, but there are also internal means of radiation delivery (brachytherapy). The second type of radiation, particulate radiation, is sometimes used experimentally and includes neutrons, electrons, protons, neutrons, and alpha particles. Some of these forms of radiation are in fact used in RT or have potential uses in diagnostic radiology (Hall & Giaccia, 2012). However, this paper will focus on externally delivered RT.
There are two main ways that SLPs may encounter radiation in their clinical work. Firstly, radiation is used as a diagnostic measure for clinicians who manage and rehabilitate swallowing disorders. Precautions are taken specifically to limit radiation exposure to both the patients and clinicians, but some amount of radiation exposure to both parties is ultimately inevitable. A Gray (Gy) is the unit typically used when discussing radiation, and is the amount of radiation that the patient is exposed to/absorbs (1 Gy = energy absorption of 1 J/Kg). Another unit of radiation is the Rad; 1Gy=100 rad (Moro & Cazzani, 2006). While a Gy measures an absorbed dose of ionizing radiation, Sieverts (Sv) measure the health effect of radiation on the human body namely the risk of developing cancerous cells. A dose of 1 Sv equates to a ~5.5% risk of developing cancer later in life within the irradiated area. An absorbed dose of 1 Gy is considered to involve an equivalent dose of 1 Sy. During a standard videofluoroscopic swallow examination (VFSS) of 149 seconds in duration, dose to the clinician is estimated to be <6 micrograys (1 Gy= 1,000,000 μGy) while dose to the patient is estimated to be ~0.35 mSv (0.35 mGy; McLean, 2006; Moro & Cazzani, 2006). According to Moro and Cazzani (2006), this patient dose is associated with a risk of 1 in 39,000 of developing a radiation-induced cancer (Moro & Cazzani, 2006). Therefore, for evaluation purposes, VFSS involves minimal radiation exposure to both the patient and the clinician, and the dose is not likely to cause serious harm. Despite minimal risk, clinicians who are responsible for oversight of the VFSS should follow routine precautions to limit exposure, including wearing lead aprons and thyroid shields, and moving away from the source of exposure.
The second place where SLPs encounter radiation in their practice is with patients who have undergone radiation treatment (RT) to damage the DNA of cancerous cells. Unfortunately, radiation treatment also causes damage to healthy cells within the target field, and this may lead to toxicities along with the possibility of evoking the production of cancerous cells via mutations. It is for this reason that clinical discussion of radiation as a form of treatment should take place. Additionally, although the treatment does cause tumor damage and cell death, there is an extensive list of acute (early) and late secondary effects that may contribute to the development of dysphagia in the head and neck cancer patient.
What Is the Goal of Radiation Treatment?
In order to understand radiation, one must conceptualize what occurs when x-rays are absorbed into human tissue. X-rays are indirectly ionizing, meaning they do not produce biologic and chemical damage directly, but they do so by being absorbed into the material through which they pass. When these rays are absorbed, a process of energy exchange occurs within cells in the area, and fast-moving charged particles are the end result. These charged particles are able to produce biological and chemical damage. The process by which x-ray photons may be absorbed into biologic material during radiotherapy is called the Compton process. Energy from x-ray wavelengths is passed along on its way through the material, and as a result of this exchange in energy, one is left with a large number of fast moving electrons within the tissue. These fast moving electrons then ionize other atoms, and break chemical bonds; this begins a chain of events that can induce biological damage to DNA in the target field (Hall & Giaccia, 2012). Damage to DNA occurs via breaks in the double helix that typically cannot be repaired, resulting in cell death of both oncologic and healthy cells (Hall & Giaccia, 2012).
DNA Strand Breaks
The main purpose of the RT process is to target biological tissue and cause apoptosis (cell death) by DNA damage, in which breaks in the double helix structure occur. This leads to mitotic death, in which the damaged chromosomes prohibit the cell from dividing, causing an inability of the cell to reproduce. Many single DNA strand breaks may occur when smaller doses of radiation are administered, leaving the DNA with repairable damage. Conversely, radiation may also cause more significant double strand breaks, which are unrepairable. In these cases, when single strand breaks on each side are close enough in proximity (i.e., the breaks are directly opposite each other or separated by only a few base pairs), the DNA chromatin snaps into two pieces. Destruction of the DNA double helix interferes with cell proliferation leading to cell death during mitosis. For a clear visual of this concept, see Hall and Giaccia (2012; Figure 2.2).
When two double strand breaks occur in close proximity to one another, one of three consequences may arise:
  1. Cell death may occur, which is beneficial when tumor cells are involved.

  2. Carcinogenesis is also a potential consequence of double strand breaks whereby healthy cells form into cancer cells. This is a risk that comes with the use of radiation treatment, in much the same way that exposure to cigarette smoke is considered to be carcinogenic.

  3. Mutations may occur as a result of critical DNA strand breaks, and when these occur the in the cells of the human body, they may result in cancer or cell death.

Therefore, it is important for SLPs to keep in mind that tumor recurrence is a risk for patients after radiation treatment (Hall & Giaccia, 2012).
Radiation-induced chromosome breaks occur when the ends of the unpaired bases (or broken unpaired ends) of the chromosome fail to join with a normal, unbroken chromosome to form a new pair (Hall & Giaccia, 2012). These aberrations in mitosis may cause chromosome deletion or distortions when the broken ends rejoin with other broken ends. Aberrations may happen when the cell is irradiated early in the mitotic phase, where the chromosomes are yet to be duplicated. Deletions that occur in the mitotic cycle may also be associated with carcinogenesis if the material that is deleted or lost contains a gene that is responsible for tumor suppression. It is important to understand that the occurrence of most radiation-induced aberrations is a function of the overall dose (Hall & Giaccia, 2012).
The Importance of Telomeres in Cell Death
Telomeres are defined as “long arrays of TTAGGG repeats [i.e., sequences of DNA at the end of each chromosome] that cap and protect the ends of chromosomes. Each time a normal somatic cell divides, the terminal end of the telomere is lost” (Hall & Giaccia, 2012). Telomeres decrease and become fewer with age and successive divisions until the cell at some point is unable to divide any further. Cancer cells reproduce and avoid aging by activating the enzyme telomerase. By continuing to activate telomerase, cancer cells avoid the eventual terminal end of telomere, thereby avoiding cell death. Essentially, telomerase activation makes the cell immortal (Hall & Giaccia, 2012).
Fractionation & Dose
Radiation doses for head and neck cancer treatment may range from 40–80 Gy. Higher doses (60–80 Gy) are used for curative intent, while doses of 40–60 Gy are used as adjuvant treatment, and doses from 45–55 Gy are used for subclinical disease or palliation. The total radiation dose is typically divided, or fractioned into smaller doses delivered over a period of weeks or months. The standard fractionation schedule for head and neck cancers (oropharyngeal, laryngeal, tonsillar, or pharyngeal constrictors) is 70 Gy delivered in 35 fractions. Typically, the fractioned dose is delivered once daily, every 5 days over 7 weeks, or on a less frequent basis over a few months.
Fractionation as a technique is more beneficial than providing one large single dose of radiation, because it allows healthy cells to repair damage prior to the next treatment, while allowing cancerous cells to be targeted with the intent of causing cell death. The goal is for healthy cells to be left with a minimal number of single-strand DNA breaks (allowing rapid repair), in addition to causing little to no overall damage to new, dividing cells. In cancer treatment, the ability of the normal tissue surrounding a tumor to tolerate the radiation acts as a natural limit for the dose of the radiation that can be delivered to the tumor.
Since normal tissues have a better repair mechanism than do oncologic cells, fractionation causes a greater amount of damage to cancer cells. As a part of radiation treatment planning, the gross tumor volume (GTV) is defined as well as the clinical target volume (CTV), which contains margins of adjacent tissue, which are considered to be areas of potential tumor proliferation. The dose that may accumulate in normal tissue over the radiation schedule is hard to predict due to differences in patient anatomy that may occur during radiation (Jaffray, 2010). These changes may include extensive edema, or tumor shrinkage. If the GTV decreases quickly after delivery of only a few fractions, the radiation oncologist may need to replan and retrace the radiation fields to avoid including normal tissue in the target area (Jaffray, 2010).
Fractionation Schedules
In addition to the typical fractionation schedule, hyperfractionated radiation or hypofractionated radiation may be used. With a hyperfractionated radiation schedule, the daily dose is divided into two radiation treatments each day. Conversely, hypofractionated radiation schedule doses are divided into larger doses, and delivered in less than one treatment per day during the week (Network, 2006). Finally, an accelerated fractionation schedule option may be used, in which the weekly dose exceeds the typical limit of 10 Gy/week, thereby reducing the total amount of time over which the patient is receiving RT. The schedule will affect how quickly the patient will begin to experience side effects after radiation begins. With more rapid or accelerated schedules, SLPs must be aware that critical toxicities may happen more quickly than with a regular fractioned schedule. For example, when odynophagia (painful swallowing) arises as an early onset toxicity, nutritional support will require special attention. It is important to note that no matter the schedule, a majority of head and neck cancer patients who complete a full course of radiation treatment will experience long-term effects. The risk and impact of these long-term effects is further influenced by factors including age, T-stage, primary cancer site, dosage, and the use of chemotherapy agents used as radiosensitizers (Machtay et al., 2008). Consideration of the fractionation schedule will help clinicians plan treatment accordingly, and anticipate the emergence of potential toxicities.
In addition to radiation-only fractionation schedules, treatment for some patients may include chemotherapy. This treatment process has been shown to significantly improve survival in patients with late stage disease (Network, 2006). Chemotherapy can be combined with radiation (or surgery) in three different ways: it can be given in the weeks before RT (neoadjuvant), during RT (concurrent), or after RT (adjuvant). The most beneficial schedule, in terms of patient survival, is adjuvant chemoradiation (CRT). Although beneficial for survival, the combination of chemotherapy (e.g., cisplatin, gemcitabine, etc.) and radiation (CRT, sometimes seen as x-ray therapy) exacerbates post-radiation swallowing issues for the patient, and particularly involves mucosal toxicity due to increased radiosensitivity of the targeted tissue (Network, 2006; Nguyen & Sallah, 2000).
Radiation Volume Effects
After taking dose and fractionation into consideration, it is also important to understand radiation volume. Volume is typically reported as Vdose=x%, where Vdose is the amount of targeted radiation (or Gy) being absorbed by an organ and x% is the percentage of the organ that is receiving the radiation dose. For example, if one sees dose-volume to a structure in the head and neck written in the format V70Gy=50%, this means that 50% of the structure has received 70Gy of radiation. Dose-volume histograms (Bratengeier, Myer, & Flentje, 2008) provide a quick and effective method for visualizing the dose delivered to the volume or area of the target.
Clinical Response of Normal Tissue
General toxicities are those that occur with all administered RT. The radiated area can become sensitive to touch, much like a bad sunburn that progresses throughout treatment. It is important to note that the skin is one of the most easily observed organs to experience radiation effects. In particular, the mucosal epithelium inside the mouth and pharynx may be affected and become quite irritated. Mucositis is usually considered an acute toxicity because it occurs early but may last weeks after treatment in some patients depending on tumor location, dose, and patient risk. Fatigue is also experienced by many patients who receive radiation, due to the body's response and attempt to heal cells that are under attack. These side effects of radiation treatment are quite common; nausea may be added to this list given the addition of concurrent chemotherapy (Network, 2006).
One main concern regarding radiation is that it is quite difficult to attenuate. Normal tissue complications surrounding the larynx and the pharyngeal constrictors increase by 50% when radiation doses reach or exceed 50–60 Gy (Rancati et al., 2010). After exposure to the maximum dose, desquamation (the shedding of the outer layer of skin) of the oral cavity occurs by approximately day 12, with recovery within 2–3 weeks. This varies from patient to patient, and various risks must also be taken into account (e.g., tumour site, history of RT, and smoking history). Merlotti and colleagues (2014)  conducted a review of IMRT targets for the head and neck, which includes a list of dose constraints to specific structures in the head and neck region. The Radiation Therapy Oncology Group (RTOG; a group focused on radiation based-research) also offers a list of dose constraints online.
Mechanisms of Swallowing Impairment
In addition to the previously mentioned toxicities, radiation can alter the mechanics and the anatomy of critical structures involved swallowing. There are general radiation dose thresholds at which the risk of developing dysphagia arises. When the pharyngeal constrictors receive more than 50 Gy, patients have increased chance of swallow-related complications. For the larynx, doses above 20 Gy have been associated with complications (Avraham Eisbruch et al., 2011).
Acute mucosal toxicity may take 3–6 months to resolve. Other swallowing-related concerns include xerostomia, dysgeusia (altered taste), dysphagia, and odynophagia. Swallowing physiology after radiation is characterized by impaired safety (poor airway protection, with aspiration occurring both before and after the swallow) along with impaired efficiency (inadequate bolus propulsion, leading to increased amounts of residue; Lazarus et al., 1996). These two deficits may lead to severe dysphagia secondary to radiation treatment of head and neck cancer.
Aspiration is one of the most serious aspects of dysphagia following radiation or chemoradiotherapy. The prevalence of aspiration has been reported to be anywhere from 24–62% and is generally thought to be underreported (Eisbruch et al., 2002; Goguen et al., 2006; Hutcheson & Lewin, 2012). A large number of head and neck cancer patients are “silent aspirators,” due to radiation-induced sensory deficits (Hunter et al., 2014). The silent nature of dysphagia in this patient population represents a primary reason for deficits in their swallowing going unnoticed. Fibrosis (tissue hardening) is an additional RT-related effect that has the potential to impact swallowing. Any type of mucosal or submucosal fibrosis in the base of the tongue or affecting the pharyngeal constrictors is likely to cause residue accumulation due to inefficiency in bolus propulsion. Fibrosis affecting the upper esophageal sphincter (UES) may lead to restricted size or duration of sphincter opening, thereby also contributing to residue accumulation and the secondary risk of aspiration after the swallow.
It is important to take into consideration the location of the primary tumor in addition to the dose/fractionation of the radiation when predicting clinical outcomes pertaining to dysphagia. Different primary tumor sites are associated with different rates of pre- and post-radiation abnormalities in swallowing (Logemann et al., 2006). For example, some patients with base of tongue primary tumors may have pre-existing swallowing deficits at baseline.
One study has reported on dysphagia end points after RT and found correlations between swallowing function and the dose delivered to the pharyngeal constrictors and glottis/supraglottic larynx. There are possible benefits associated with the reduction of dose to these areas (Feng et al., 2007). Feng and colleagues (2007)  found that 62% (16/26) patients who had received doses to the pharyngeal constrictors above 60 Gy aspirated. By contrast, in the nine patients who received lower doses to the constrictors (<60 Gy), aspiration was not seen (Feng et al., 2007). This evidence, showing that radiation dose to specific structures may precipitate the occurrence of aspiration, has prompted some authors to propose that limiting radiation dose to these important swallowing structures may minimize impairment (Eisbruch et al., 2004; Feng et al., 2007; Hunter et al., 2014). Data coming out of the MD Anderson Cancer Center in Houston, Texas show that there are specific muscles in the swallow complex that are at particular risk in terms of radiation damage and atrophy (Dale et al., 2016). These muscles are proposed to include those in the floor of the mouth, namely the suprahyoid muscles and the mylohyoid. Eisbruch and colleagues (2004)  aimed to identify those structures in the head and neck that were most vulnerable to radiation damage and most closely associated with dysphagia and aspiration. They reviewed CT scans pre- and post-therapy for evidence of damage and those anatomical structures demonstrating change were termed dysphagia/aspiration-related structures (DARS). The structures included in DARS are the pharyngeal constrictors along with the glottis and supraglottic larynx. It is important for clinicians to expect changes in swallowing during and after radiation and to plan for patient needs based on knowledge of tumor location, radiation field, fractionation and volume, and the involvement of structures that are critical to swallowing within the radiation field.
In addition to the early and late toxicities, late radiation-associated dysphagia (late-RAD) many emerge many months beyond the completion of radiation treatment (Dale et al., 2016). The human papillomavirus (HPV) has been identified as a factor in cancers of the oropharynx (Worden et al., 2008). This new rising phenomenon occurs most commonly in patients who are young (specifically, men aged 50–55). Fortunately, HPV loco-regional control is reported to have good results. However, because these patients have longer post-treatment life expectancies, clinicians are beginning to encounter a greater number of individuals who return with dysphagia and other toxicities 10–15 years post-radiation. Late-RAD induced dysphagia toxicities are ill defined, and the phenomenon of late onset dysphagia involves denervation and multiple cranial neuropathies. A review by the RTOG summarized the different types of late toxicity seen across several clinical trials. Of a total of 230 patients who were studied, 99 had severe late toxicities, and were compared against 131 controls, who did not report late toxicities. Risk factors for the development of late-RAD include age, T-stage and larynx/hypopharynx primary sites, as well as neck dissection post-treatment (Machtay et al., 2008). One study has reported that individuals who have experienced late-RAD with the inclusion of cranial neuropathies had higher radiation doses to the superior pharyngeal constrictors (Awan et al., 2014). The constrictors may then be considered a structure at risk for late-RAD effects in those patients with a history of large doses to this area (Awan et al., 2014; Eisbruch et al., 2004).
Guidelines have been developed for quantifying the amount of radiation to normal tissue and are termed Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC). These guidelines evaluate dose/volume/outcome data for critical organs in order to make RT more efficient and safe for patients. A study conducted by Beetz and colleagues (2014), which followed QUANTEC guidelines for minimizing xerostomia, determined that from week 4 of radiation up to 24 months post-treatment, patients who were considered to be at lower risk (i.e., with at least one parotid gland receiving < 20 Gy and/or both parotids receiving < 25 Gy) reported better recovery. In the same study, the predictors for xerostomia at 6–24 months following RT included the QUANTEC criteria, older age, and pre-irradiation xerostomia.
In addition to aspiration and xerostomia, patients are also likely to experience mucositis, thick mucosal secretions, and pain. When patients reduce the frequency of their swallowing due to these symptoms, disuse atrophy may also occur. For this reason, proactive swallowing therapy is often prescribed and advised (Carnaby-Mann, Crary, Schmalfuss, & Amdur, 2012; Hutcheson et al., 2013). Some retrospective studies suggest that patients report better outcomes given prophylactic swallow therapy regimens (Carroll et al., 2008; Kulbersh et al., 2006). One randomized controlled trial showed superior diet tolerance in the short term amongst those patients who performed prophylactic swallowing exercises (Kotz et al., 2012). Overall, data suggest that per os (PO) status (meaning nutrition/hydration by mouth) at the end of radiation treatment to the head and neck predicts PO status 10 years later (Gillespie, 2004; Langmore, 2012). Recent studies from the MD Anderson Cancer Center have shown that patients who are adherent to an exercise regime and who also maintain oral intake throughout RT/CRT are more likely to maintain some form of oral intake after the completion of treatment (Hutcheson et al., 2013).
Another common sequela of radiation treatment (especially when paired with chemotherapy) is the need for gastrostomy tube feeding to alleviate the burden of oral intake when dysphagia becomes severe (Hutcheson & Lewin, 2012). Some institutions prophylactically place feeding tubes, while others place them only when patients cannot rely on their swallowing for safe and adequate nutrition/hydration. The experience from the MD Anderson trials suggests that treatment should aim to avoid tube dependence, with the specific goal of maintaining oral intake for these patients post-radiation treatment. Other studies have not demonstrated a difference in outcomes when patients rely on enteral means of feeding (Nguyen et al., 2006).
Advances in Radiation
Intensity modulated radiation therapy (IMRT) is a fairly recent advance in head and neck radiation oncology, designed to reduce toxicity to normal tissue. IMRT uses computerized tomography (CT) planning and specific identification of targets, along with careful allocation of radiation dose. Essentially, the region that is being targeted for a high dose of radiation takes on the silhouette image of the structure during planning, as seen on the CT scan. In comparison to conventional radiation therapies, this technique helps to limit dose to specific structures in the radiation field. IMRT utilizes multiple beams to target tumors from multiple angles. This allows for a more specific high-dose target, while also creating low-dose radiation exposure to adjacent areas. IMRT, when compared to conventional radiation, does show reduced toxicity and equivalent outcomes in addition to better specific survival (Beadle et al., 2014; Nutting, 2011). The doses involved in IMRT vary pending the area and volume of the tumor that is to be radiated. Dose prescriptions are defined by the tissue involved and may be low-risk (dose to neck areas for preventative measure, ~55Gy), intermediate-risk (areas contiguous but not involved by the tumor, ~63Gy), or high-risk regions (areas of tumor invasion including affected metastatic nodes, 70Gy; Chao, Low, Perez, & Purdy, 2000). It may be useful for clinicians to estimate areas that may be receiving higher doses related to tumor location. However, patients treated with intensity-modulated RT for oropharyngeal and nasopharyngeal cancers and those with lymph node metastasis are more likely to have their parotid glands irradiated. This is because of the overlap of the planned target volumes with sections of the parotid gland, and it is important for clinicians to realize that these patients are at an increased risk of xerostomia due to the tumor location. Those patients whose parotids can be spared with more ease include those with laryngeal carcinoma, unilateral radiation, early stage disease, and lymph node metastasis from unknown primary tumor sites (Beetz et al., 2014). It is not possible to include an exhaustive discussion of the issues related to xerostomia within this particular paper.
Conclusion
RT continues to be one of the primary treatments for loco-regional tumor control and survival in the head and neck cancer patient. The primary objective of RT is tumor eradication. Given this goal, normal tissues may be irradiated, and dysphagia may develop as a toxicity after cancer has been cured. SLPs are an integral part of the multidisciplinary care team, and are intimately involved in the maintenance of oral nutrition and hydration for these patients during and after treatment. It is ultimately up to the SLP to plan appropriately for the emergence of expected swallowing toxicities and to support patients in maintaining swallowing throughout treatment to the best of their ability. Knowledge of radiation dose, schedule and volume may provide the head and neck clinician with the tools to predict swallowing outcomes. In order to develop and deliver optimal swallowing rehabilitation post-radiation, SLPs must have a clear understanding of RT.
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