Radiation Therapy: What is it? Radiation therapy (megavoltage) is supplied by a Linear Accelerator. This device generates high energy photons or electrons used to treat many kinds of cancer. Radiation therapy is typically applied to one site in an attempt to provide local therapy (local control or cure) of a cancer that only affects one part of the body. What is the goal? When choosing radiation therapy for any patient, we have to consider what the goals of therapy are – are we trying to “cure” or eradicate all local tumor cells, or are we trying to shrink a cancer to make it operable or more amenable to chemotherapy, or are we simply trying to make pain control easier? Full course treatments.  Radiation therapy is delivered to a total dose of between 45-54 Gray for most types of cancer. This dose is more than 500 times what a diagnostic xray (radiograph) would be so it cannot be tolerated by any normal tissue as a single dose. We divide up that dose into many “fractions” which are then delivered on a Monday-Friday basis until the total dose needed for that cancer’s control has been given.  Radiation therapy is a key feature in the treatment of patients with the following cancers:             Nasal carcinomas             Nasal sarcomas             Nasal lymphoma             Laryngeal lymphoma             Brain tumors             Pituitary tumors             Oral squamous cell carcinomas in dogs             Skull tumors             Incompletely excised (but not yet recurrent) mast cell tumors             Incompletely excised (but not yet recurrent) soft tissue sarcomas (oral and other locations)             Non-resectable plasma cell tumors Treatment of these patients typically involves a CT-based 3D radiation treatment plan, and 15 – 18 treatments over a 3-4 week time period. Lymphoma/plasmacytoma therapy takes many fewer treatments as these tumor types are very sensitive to radiation therapy and we do not need to treat to as high a total dose. Palliative: Radiation therapy can also be used in palliative fashion to try to slow an aggressive/non-resectable tumor’s growth, to shrink an oral tumor, decrease the vascularity of a cancer, or to kill pain associated with a cancer such as the following:             Oral melanoma             Bulky soft tissue sarcoma             Bulky carcinomas             Oral squamous cell carcinoma in cats             Osteosarcoma Typically, palliative radiation therapy is given on a 0-7-21 day basis (three treatments) or once weekly for four treatments. A two dimensional radiation treatment plan is usually used for this type of patient (may be radiographic based, or CT based). How is it performed? All radiation therapy requires perfect positioning of patients to avoid side effects to portions of the body that should not be in the treatment field!  That means that each patient will have to be anesthetized for each therapy. Radiation therapy anesthesia protocols are designed for safety in repetitive use – often in an elderly patient population. Fentanyl, propofol and/or gas anesthesia are used to try to have patients back on their feet as quickly as possible. The treatment field may be shaved and marks placed on the skin during the first imaging session to be certain that the treatment field stays the same with each treatment. Admitting patients: Patients for radiation therapy must first be seen by one of our oncologists to discuss treatment options, prognosis, and overall state of health. Imaging for treatment planning would be accomplished next so that a detailed treatment plan can be designed. Once imaging and treatment planning are complete, radiation therapy would typically be begun on a Monday (for full course treatments) – although schedules can be adjusted to meet patient needs. Clients can either drop their pets off for the day, or set up a defined time for radiation therapy. Pets must be fasted for at least 12 hours prior to their radiation therapy (due to anesthesia needs). Side Effects: Radiation therapy cannot tell the difference between normal and cancer tissues – it simply kills cells as they divide. Since most cancers divide much faster than normal tissues, we get a selective effect on the cancer cells. We expect, however, to see side effects of radiation therapy. Acute (or short term) effects include loss of hair, moist desquamation of skin/mucus membranes (radiation burn like a blistering sunburn), and corneal irritation – if these tissues are in the treatment field. Common late side effects of radiation therapy include permanent hair loss, permanent hair color change, cataracts, retinal degeneration, keratoconjunctivitis sicca – again only if these tissues are in the treatment field.  Some organs have more difficulties with radiation than others – eyes are clearly sensitive, but tubular organs (esophagus, colon, rectum, urethra) can also be – they could heal from acute radiation effects by scarring (stricture). The heart and lungs can only tolerate a limited amount of radiation therapy – so we try to avoid these structures. Bone marrow is very sensitive to radiation if used in an “whole or half body” therapy.  Bone density within a treatment field decreases. One in 10,000 patients could develop a bone tumor in a treated bone 5-10 years following therapy.  The spinal cord and brain’s vasculature can also be sensitive to some types of radiation therapy (late effects). Because we want to minimize side effects, imaging and treatment planning are essential for most patients. Symptom care for side effects: Dogs and cats getting full course radiation therapy WILL develop acute side effects. Palliative or short course radiation therapy rarely causes acute side effects other than the hair loss needed in order to shave/mark the treatment field. Dogs with moist desquamation (cats more commonly get dry desquamation with dry flaky skin and itchiness) need to have their treatment sites kept clean and dry (with water – not other products). We try NOT to bandage as we don’t want dirt and moisture to build up – that means that E-collars are often necessary as a dog’s licking will only make the side effects worse. If a pet is scratching, sometimes T-shirts, socks or hobbles must be used to prevent self-trauma. Anti-inflammatories and rarely narcotics can be used to help through this time period. Typically, these radiation burns form in the second to third week of full course therapy, and then form crusts, and then the skin heals under the crusts. The whole process takes about 2-3 weeks. Mucositis is seen when the gums, tongue, cheeks, throat or other mucus membrane-lined tissue is in the treatment field (often with nasal or oral tumors). The mucosa will get very red, and may ulcerate or blister during the second week of full course  radiation therapy. Bad smell to the breath (halitosis), drooling, and difficulty eating can occur. Oral rinses are often helpful. Some cats and small dogs could require a temporary feeding tube if a large portion of their mouths are in the treatment field. Mucosa heals quickly following the conclusion of radiation therapy. Ocular side effects are of concern if the eyes are in the treatment field. Acute side effects include dry eye and corneal irritation – so artificial tears and tacrolimus ointments are often needed. Eyes are checked for corneal ulcer formation at least weekly if they are in the treatment field – but let your oncology nurse know right away if your pet is squinting, or if the eyes look abnormal to you at home. Late side effects of radiation (permanent keratoconjunctivitis sicca or dry eye, cataracts, and retinal degeneration can be irreversible side effects of radiation therapy if the eye gets full dose or even scatter radiation.  It takes between 6-12 months for cataracts to form following radiation therapy – cataract surgery could be considered if the tumor is under control. Certain types of delayed side effects are very dangerous or deadly (spinal cord malacia, kidney fibrosis or scarring, lung fibrosis, death of bone) so every effort to avoid late side effects is made in full course radiation therapy – the risks of developing these problems is small (5-10%). The multiple fractions of radiation therapy as well as careful treatment planning are the ways that we attempt to avoid late side effects. What if patient also needs other types of treatment? If a patient has a type of cancer that would benefit from multimodality therapy (surgery, chemotherapy, etc), then there are additional timing concerns – healing from surgery may be altered based upon when radiation therapy is started. Some chemo drugs make anti-cancer activity of radiation therapy stronger – while some cause worsened radiation burns.  Your SouthPaws oncology team will help to design the best treatment plan to take into consideration all of these variables for your patient. Click here for printable information for Clients (.PDF)