Radiation oncology is a subspecialty of oncology. Not all tumors are treated the same way. In fact, there are three types of treatment modalities used to treat tumors. They are surgery, radiation and systemic treatment (chemotherapy and immunotherapy). Although some tumors may be best treated with only one of these modalities, many tumors, both malignant and benign, are best treated with a combination of these modalities.
Radiation oncology specializes in the treatment of tumors using radiation for tumor control. Radiation treatment often follows surgery when a tumor cannot be removed completely by surgical procedures in order to clean up microscopic disease that may be left behind. If a tumor is in a location where surgery cannot be performed without significant risk of causing detrimental dysfunction, then radiation is often administered as the primary treatment for local disease control. Whether coupled with surgery or not, the main goal of radiation treatment is the targeting of primary local disease. It should be noted that although radiation may assist in controlling the spread of cancer by targeting the primary nodes draining the tumor location, in most cases, radiation does not target microscopic spread that cannot be visibly identified with imaging. For tumors that have a potential risk of distant microscopic spread at the time of radiation therapy treatment, the patients are typically referred to the medical oncology service to discuss options such as chemotherapy and/or immunotherapy, which are systemic treatments primarily designed to target distant microscopic disease.
What Types of Tumors can be Treated with Radiation?
All tumors can potentially be treated with radiation therapy but not all tumors respond the same to radiation and recommended treatments will, therefore, depend on the anatomical location, the type of tumor, the anticipated behavior of the tumor and prognosis, the overall health status and patient medical history as well as many other factors.
Tumors frequently referred for radiation therapy include:
- Skin tumors and Soft tissue tumors of the limbs and trunk (soft tissue sarcomas, mast cell tumors, carcinomas, melanomas)
- Bone tumors (of limbs, skull, spine and pelvis)
- Joint tumors
- Nasal and oral tumors (sarcomas, carcinomas, melanomas, odontogenic tumors, lymphoma, tonsillar and tongue tumors)
- Tumors of the larynx, pharynx and trachea
- Brain tumors/spinal cord tumors
- Periocular and facial tumors
- Ear tumors
- Thyroid tumors
- Anal sac adenocarcinoma
- Anal/rectal tumor
- Bladder/prostate and urethral tumors
- Heart base and mediastinal tumors (thymoma, chemodectoma, ectopic thyroid, lymphoma, and other less common)
- Non-resectable lung masses and other thoracic tumors
- Non-surgical abdominal/pelvic tumors
Working as a Team: Our staff supervises the treatment of every patient that receives radiation. Our doctors work closely with a team of trained and experienced technicians and assistants, as well as with The AMC’s medical oncology service, surgical services and other specialists to ensure that your pet receives the best overall care possible. Our specialists all take part in the initial diagnosis of cancer patients and also sometimes in the staging process of the cancer. In most cases, a biopsy is the most important step towards a definitive diagnosis of a tumor. This is required in order to determine whether a tumor is malignant or benign and whether or not your pet could benefit from our radiation oncology services. There are exceptions however where a biopsy is NOT recommended: such as, for example, certain brain tumors or some patients being referred for palliative purposes.
Staging the pet: Once a patient is diagnosed with a specific type of cancer and referred to us for treatment, the patient first needs to be fully evaluated. Staging the patient is important before determining what treatment is most appropriate for us to recommend. Some pets may have already been staged at their referring or regular veterinarian’s office and therefore may not need further staging tests performed at AMC. Staging means first determining to what extent a cancer has progressed and invaded the body (is it still limited to a single local tumor or has it already had the chance to escape that local site to then go on to travel to another part of the body?). This requires taking images of your pet’s body (x-rays, ultrasound, CT or CAT scans, MRI, endoscopy ) as well as possibly taking tissue samples of lymph nodes and any area suspicious of spread with either a needle (for cytology) or a biopsy (for histopathology). This information can then allow us to give you a better idea of the prognosis so that we can help you make the best decisions regarding your pet’s treatments. In addition to evaluating the extent of the cancer, we must also evaluate the patient’s overall health so that we can assure that any recommended treatment is safe and appropriate taking into account any other health problem your pet may have. This typically will require a minimum of blood tests and urinalysis.
Treatment planning: Once the appropriate treatment has been determined, your pet will be scheduled for treatment planning set up. This may be performed on the same day of the first treatment in cases where the set-up is simple. For more complex areas of the body, computer planning may be necessary. For computer planning, your pet must first be scheduled for a CT planning set-up procedure. This consists of performing a CT scan of your pet placed in the position required for his/her radiation treatment. A custom molding bed will be fabricated to support your pet’s body in the correct position. For treatments of head and necks, a mold of your pet’s teeth will also be made to assist with precise head positioning. Once the images are taken, they are sent to the planning computer to create your pet’s treatment plan. This treatment planning can take many hours. Therefore your pet will be sent home and scheduled to return another day to start actual treatments.
Treatments: Depending on the determined treatment course, your pet may need to come in once a week for a few weeks, or may need to come more frequently up to three to five days per week for one to 5 weeks. Treatment recommendations vary a great deal depending on each individual patient’s diagnosis, condition and special needs. Again, not all tumors respond the same and not all patients have the same medical concerns and needs. Here at AMC we custom design your pet’s treatment based on that pet’s diagnosis as well as his/her needs. Many factors come into play when deciding what is best for your pet. The FIRST DAY of your pet’s treatment course is typically the longest since we must first perform simulation of the treatment plan to confirm that the plan will work as anticipated. If adjustments need to be made, then the procedure may take longer. Your pet will likely need to stay most of the day for the first treatment. Our doctors work closely with our nurses and therapists to discuss all special concerns of each patient on the first day as well as along the entire course of treatments as various new factors, anesthetic needs or other special needs and potential side effects may develop along the way. For the most part, the required anesthesia is very mild and light and usually requires only fast acting agents that allow treatments to be performed on an out-patient basis. For pets that live far away or for owners who cannot take time off work every day, AMC does offer day boarding as well as weekly boarding to facilitate daily treatments when needed.
After Radiation Graduation: Once your pet’s entire course of treatments is completed, discharge instructions will be given to you. This will include your pet’s full radiation prescription description, what type of side effects to look for as well as how to care for any side effects that may have developed during the course of treatment. Not all patients will develop significant side effect, but some will, depending on the location being treated, the radiation dose prescription and the location that was treated. Your pet will need re-check appointments to follow-up on any side effect until they are fully healed. Follow-up exams will also be recommended to assess the tumor response and to monitor for regression or progression of the cancer. Depending on the type of tumor your pet has, other treatment modalities may be recommended to follow radiation. If this is the case, then your radiation oncologist may refer you to another specialist.
Types of Radiation Therapy:
There are many types of radiation therapies:
External beam radiation (administration of radiation from outside of the body, most often using x-rays). This requires radiation that penetrates deep into the tissues but to a very focused target. It is administered by a machine (such as a Linear accelerator or x-ray unit) which produces the radiation only when turned on for treatment. Once the treatment is done, the patient goes home and is NOT radioactive.
Plesiotherapy and Brachytherapy (direct administration of a radioactive source placed in, through or on the tumor). These radioactive sources (seeds or needles or applicators) administer a type of radiation that does not travel deep. It is used for treatment of very superficial administration and only treats a very small area around the source. This is typically only available at very few specialized facilities.
Systemic radiation (systemic administration through the blood stream meant to target a very specific receptor, organ or cell type). The most common type of systemic radiation used in veterinary medicine is the use of I-131 for treatment of hyperthyroidism in cats. This is typically only available at very few specialized facilities.
The Animal Medical Center is mostly specialized in External Beam Radiation using a Linear Accelerator, but does also offer a form of plesiotherapy using a strontium-90 applicator for very selective superficial tumors.
External Beam Radiation Therapy:
Radiation treatments at The Animal Medical Center are performed using a Varian state-of-the-art Linear Accelerator equipped with a multi-leaf collimator and an on-board KVP imaging system. This allows our doctors to deliver radiation in the most precise way possible to avoid normal structures.
Benefits of the Linear Accelerator include:
- Can treat tumors anywhere in the body guiding the dose specifically to the tumor while minimizing dose to surrounding critical normal tissues.
- Can administer either electron beam radiation or photon (x-ray) beam radiation depending on which is most appropriate based on tumor size, depth and location. The benefit of both types of radiation available gives the oncologist more flexibility to manipulate dose distribution as needed.
- Customizes the area treated to fit the shape of your pet’s tumor to better spare adjacent structures.
- Delivers treatment very rapidly to minimize anesthesia time.
- Offers much more flexibility for treatment planning and type of course administration. Adapts to simple manual plans, or to computer 3D conformal treatment planning (3DCRT), to advanced technology Intensity Modulated Radiation Therapy (IMRT) and to more recent advanced technology Stereotactic Radiosurgery (SRS), Stereotactic Radiation Therapy (SRT) and Stereotactic Body Radiation Therapy (SBRT).
3D Computer Treatment Planning
The advancement of imaging as technology has continued to flourish ove these past decades, has allowed medicine to markedly improve the ability to define tumors in their entirety. Tumors that invade into the deeper tissues, cannot be well delineated on simple examination without sophisticated imaging. The progression of 3D imaging such as CT (computed tomography), MRI (Magnetic Resonance Imaging) and PET (Positron Emission Tomography) has facilitated the computerization of radiation therapy planning, increasing accuracy of dose distribution and administration of complex tumor locations. Locations such as head and neck tumors, chest and abdominal tumors, spinal and pelvic tumors require advanced imaging to precisely determine their exact extent and to evaluate the involvement of the surrounding structures. Complex plans can be designed on computer now allowing the radiation oncologist to attempt multiple variations to then better identify the most optimal angles to use for a specific tumor treatment.
Intensity Modulated Radiation Therapy (IMRT)
In the Spring of 2009, The AMC became the first facility in New York City to begin treating patients with intensity modulated radiation therapy (IMRT). IMRT has been made possible by the use of advanced technology and specialized delivery system added to modern Linear Accelerator treatment machines. This type of computer planning and radiation administration requires a multi-leaf collimator (MLC), which allows us to very tightly mold around targeted structures while better sparing other structures that we intend to avoid. The lead leaflets of the MLC move in and out during the course of treatment of each beam to modify the dose distribution across the treated area such that not all structures get the same dose but rather, each area (or tissue/structure) receives its individually assigned dose. The end result is that we can now further minimize dose to the critical organs at risk that reside adjacent to the targeted tumor and therefore side effects to the patient have been greatly reduced while still achieving the desired prescription dose to the tumor. Since treating with IMRT, the radiation therapy patients treated at AMC maintain a much better quality of life because of reduced side effects! The Animal Medical Center is still the only cancer facility in the State of New York to offer IMRT treatments to our veterinary patients.
Stereotactic Radiation Treatments (SRS, SRT and SBRT)
IMRT planning is also used for Stereotactic radiation treatment. The dose is also greatly modulated across the treatment fields when administering SBRT, SRT and SRS treatments and therefore the same equipment and techniques are used. SBRT stands for Stereotactic Body Radiation Therapy. SRT stands for Stereotactic Radiation therapy. And SRS stands for Stereotactic Radiosurgery. When administered in the brain using only ONE dose, the correct term is SRS. If the dose is administered over 2- 5 treatments in the brain, the correct term is SRT. If the dose is administered over 1-5 treatment anywhere else OUTSIDE of the brain, then the correct term is SBRT. For simplicity, I will refer to stereotactic radiation (SR) for all three terms.
Stereotactic radiation differs from traditional radiation (such as conformal radiation and fractionated IMRT) because the total prescription dose is delivered to the patient over a very short period of time (within 5 days) using very high individual doses. This very high dose administered in a very short time, overwhelms the tumor cells much more aggressively resulting to a faster tumor shrinkage, faster tumor induced pain relief and often longer disease control time of large measureable tumors. It is meant specifically for treatment of tumors that cannot be surgically removed and reduced to microscopic disease in a safe manner. The first types of tumors to be treated this way in human medicine were brain tumors. This treatment technique was given the name of Stereotactic Radiosurgery because it was designed as an alternative to brain surgery in the hope to avoid causing so much damage to the healthy surrounding brain, which so often resulted to devastating neurological deficits in patients post-operatively. Because of the great success of this approach, experts decided to further explore this technique for treatment of other tumors located outside of the brain. At this point, to differentiate this treatment from Radiosurgery, they gave it the term stereotactic BODY Radiotherapy (SBRT). This procedure was later used frequently for the treatment of primary lung masses, and since has been developed for treatments of all parts of the body. In veterinary medicine, the most common tumors treated with this new technology and modalities include: brain, nasal and bone tumors. But with the fast progressing new developments in veterinary medicine, SBRT is now offered for the treatment of multiple other tumor types as well all over the body.
AMC used particularly Linac Based Stereotactic radiation. This differs from similar types of Stereotactic Radiotherapy equipment called the Cyberknife and Tomotherapy. It differs particularly from Cyberknife SR as Linac-based SR has the ability to administer radiation through much larger fields and variable field sizes resulting in much faster treatment administrations and greatly reducing treatment time under anesthesia. AMC is one of the few facilities that offer both IMRT and Stereotactic Radiotherapy and the ONLY facility that has an on-site radiation oncologist performing these two new advanced technologic radiotherapies in the Tri-State area. An on-site radiation oncologist is essential for offering the high quality radiation treatments that AMC patients receive. Treatments such as IMRT and Stereotactic Radiotherapy need to be very accurately verified to assure proper dose distribution to the appropriate structures. Even small mistakes can result to devastating tissue damage and unsuccessful tumor control. Patient response during the course of treatment needs to be assessed in case custom treatment adjustments are needed because not all tumors and patients necessarily respond the same. Individual patient assessments and treatment adjustments in the absence of an on-site radiation oncologist cannot be performed appropriately and this significantly increases the risk of performed mistakes which can result in serious complications and poor patient care.
Plesiotherapy: Strontium-90 Radiation Therapy (Plesiotherapy)
Stontium-90 Plesiotherapy uses a radioactive probe to deliver high doses of radiation to surface tumors on the patient. This treatment is limited to treating only very small tumor lesions that do not require dose administration any deeper than 3mm. It is not a frequently recommended type of treatment but comes in very handy for treating tiny less invasive lesions located in very delicate locations such as around the eyes and nostril, ears etc…
- Gives off shallow penetrating radiation so as not to impact deeper tissues in the patient
- Treats small, superficial tumors (e.g. tumors of the skin, lining of the mouth and eyelids, etc.)
- Delivers treatment rapidly and requires only 1 to few treatments total
Palliative Radiation versus Definitive Radiation Therapy
The goal of a Palliative Radiation Course is to relieve pain or discomfort caused by the cancer or to shrink a mass that is compressing important structures and interfering in normal function. Because these treatments are designed to have as little impact on your pet’s quality of life as possible, treatments are few and side effects are minimal. This consists of a protocol designed to be easy on the patient and less time consuming for patients with a more guarded prognosis where our primary goal is to offer COMFORT and not necessarily LONGEVITY. Typical patients to whom this is offered are patients with advanced spread of cancer who still have a good quality of life but are uncomfortable due to their tumors and for whom euthanasia is not yet recommended or not an option. Other patients that may benefit from palliative radiation are patient who may have a tumor with a good prognosis but have other life threatening health issues that make them high risk anesthetic patients (such as severe heart failure, advanced end-stage renal failure, aged geriatric patients etc…).
For patients for whom our primary goal is LONGEVITY because of a better prognosis, then we are aiming for Long term tumor control, which requires typically a higher total cumulative dose. These patients are treated with a Definitive Radiation Course. This consists of a protocol designed to allow a higher dose of radiation delivered to the tumor while focusing mostly at minimizing later tissue side effects that might lead to dysfunction of organs and important body structures. This is important because patients with a good prognosis may live long enough for these later side effects to develop. If these side effects develop later in life, they can greatly take away from the patient’s quality of life. Definitive protocols focus more on preventing these side effects. In some cases however, in order to prevent late effects and still achieve long term tumor control, some of these protocols may result to acute temporary discomforting side effects (such as swelling of tissues and temporary skin wounds/burn). These side effects can take 1-2 weeks to completely resolve and may require some care and pain medications. The severity of side effects depend greatly on the protocol as well as on the individual patient’s sensitivity to radiation and is not the same for all patient (similar to the sensitivity to sun burning differs among all of us).
To conclude, Palliative versus Definitive are terminology that refer to the primary GOAL of treatment and NOT to the type of planning and technology. All mentioned technologies (3DCRT, IMRT, SRT, SRS, SBRT and Strontium-90) can be utilized for both Palliative and Definitive purposes.
What Types of Equipment and Technology does AMC have for our Radiation Therapy Patients?
For those who understand advanced technology and want to know where AMC stands in the technology of Radiation therapy, here is a brief summary of our setting at The Animal Medical Center. We are quite fortunate to offer our companion friends the state-of-the-art equipment, including a Varian 2100 C-series linear accelerator with multiple electron energies (6, 9, 12, 16 and 20 MeV) and 6MV photon energy capability, equipped with a Millennium 120 MLC and an on-board mounted Theraview KVP imaging system. Custom electron therapy blocking is prepared in an on-site blocking room. For treatment planning, we also utilize the most recent version of the Varian Eclipse computer treatment planning system (version 13.6) complemented by the most recent version of the RadCalc point dose and MU verification software package. MapCHECK equipment and software by Sun Nuclear is used for IMRT and Stereotactic radiation therapy QA verification. Our KVP-IGRT system improves accuracy in IMRT treatment administration as well as to facilitate Linac based Stereotactic Radiosurgery and Radiotherapy (SRS and SRT) and Stereotactic Body Radiotherapy (SBRT). This Theraview system also significantly benefits the level of accuracy in positioning required in the treatment of very small patients coming from our Exotic Pet Service for all computer planned cases (3D, IMRT and Stereotactic). Atracurium anesthesia is also routinely practiced for SBRT of the thoracic or abdominal trunk to eliminate respiratory motion for optimal accuracy. AMC has a full time Board certified Anesthesiologist on-site to assist in difficult cases and to discuss optimal anesthesia protocols as needed on a case by case basis. Our imaging capabilities include standard digital radiography, an on-site 1.5 tesla MRI and a 4th generation CT unit, two-dimensional and color-flow Doppler ultrasonography units, rigid and flexible video-endoscopy, laparoscopy, and arthroscopy equipment. A fully equipped intensive care and emergency room with ventilator machines, along with extensive point-of-care laboratory equipment is also available on-site. The AMC also has on-site, full-service anatomical and clinical pathology laboratories allowing urgent bloodwork results to be processed same day within an hour.