When you hear about radiation therapy, your mind may be brought to images of the Toxic Avenger, or news stories about victims of radiation accidents. Radiation therapy and how it works may seem like a mystery, and mystery can lead to apprehension. Rest assured that this treatment for cancer has evolved along with many advances in technology, resulting in highly accurate and safe treatments.
One main goal of radiation therapy is to deposit high doses of radiation in the unwanted tumor tissue, while exposing the surrounding normal tissue to the least amount of radiation possible. It is the normal tissues in the treatment area that limit the overall dose of radiation that we can safely prescribe. Quality of life is of utmost importance, and so the way radiation treatments are planned is to limit the number and severity of radiation side effects as much as possible. As with other treatments in veterinary medicine, there are side effects that must be managed to provide the best experience for the patient.
Perhaps you have heard of “radiation burns” from previous accounts of treatment with radiation therapy. This is a bit of a misnomer, as radiation does not incite a thermal injury. Rather, if tissues close to the skin surface experience some radiation dose, we get what is called “moist desquamation”.
Moist desquamation is when the lower layer of skin cells are affected on the first day of radiation therapy, and it typically takes these cells three or four weeks to rise to the surface during natural skin replenishment. When these cells reach the surface, they turn wet and fall off in a layer, leaving the underlying pink, healthy tissues. This is similar to if you’ve ever scraped your knee on asphalt: the underlying pink tissue gives off a fluid (plasma) that hardens into a crust (scab).
Moist desquamation may occur with mild inflammation. Our patients at VRC are prescribed a non-steroidal anti-inflammatory drug (NSAID) and other low-dose pain medication to help with comfort while this early radiation side effect heals. Whether treated or not, most early effects of radiation therapy are healed within two-to-three weeks after treatment. It has been found that daily cleansing of the radiation site will help to hydrate the crusts that form and allow them to exfoliate naturally, accelerating the healing process.
Many accounts of “radiation burns” from therapeutic radiation come from older treatment plans using orthovoltage. This treatment modality utilized a lower energy beam that had higher radiation dose deposition in skin and preferential radiation dose absorption by bone. The early radiation effects from orthovoltage treatment included severe inflammation of the skin, while the late side effects (effects present 6 months after radiation therapy) included death of bone tissue, scarring of soft tissues, and secondary tumor formation. With the advent of the linear accelerator, which treats with a higher energy radiation beam (megavoltage), there is a skin sparing effect and no preferential bone absorption of radiation dose. This is why our patients look so good after treatment!
Another way to limit radiation dose to the normal surrounding tissues is to dose radiation over multiple beams from different angles. The multiple beams converge on the treated tumor, while the surrounding tissues experience a fraction of the dose. High dose conformity over the tumor is further enhanced by planning with Intensity-Modulated Radiation Therapy (IMRT), which uses individual lead leaves in the machine’s radiation window that are in constant motion during treatment. This action shapes the radiation field, “painting” the dose across the tumor and sparing more normal tissue than is possible with conventional radiation planning. IMRT can be used with nasal tumors, heart base tumors, prostate tumors, and more tumor types are being added to the list.
To learn more about Radiation Therapy at VRC or any other services that we offer, please give us a call at 610-647-2950 or email us at firstname.lastname@example.org.