Ever since radiation proved to be a valuable weapon against cancer, doctors and researchers have been looking for ways to make radiation treatments safer and more effective. The critical issue has been finding a way to deliver enough radiation to destroy abnormal cells while minimizing damage to surrounding healthy tissue. Advanced technology makes it possible to deliver radiation with unprecedented precision.
Tomotherapy is a type of radiation therapy in which the radiation is delivered slice-by-slice (hence the use of the Greek prefix tomo-, which means “slice”). This method of delivery differs from other forms of external beam radiation therapy in which the entire tumor volume is irradiated at one time causing many undesirable effects.
In general, radiation therapy (or radiotherapy) has developed with a strong reliance on homogeneity of dose throughout the tumor. Tomotherapy embodies the sequential delivery of radiation to different parts of the tumor which raises two important issues. First, this method is known as “field matching” and brings with it the possibility of a less-than-perfect match between two adjacent fields with a resultant hot and/or cold spot within the tumor. The second issue is that if the patient or tumor moves during this sequential delivery, then again, a hot or cold spot will result. The first problem can be overcome, or at least minimized, by careful construction of the beam delivery system. The second requires close attention to the position of the target throughout treatment delivery
Escaping the confines of conventional radiation treatment devices developed more than a half century ago, the TomoTherapy®System design combines CT imaging with a radiation treatment delivery system.
With this design, the TomoTherapy System enables efficient daily 3D CT imaging to ensure the accuracy of the patient position before each treatment delivery and leverages the ring geometry to then deliver state-of-the-art radiation treatments, including intensity-modulated radiation therapy (IMRT) and 3D conformal radiation therapy (3DCRT). Radiation delivered by the TomoTherapy System is aided by its sophisticated multi-leaf collimator (MLC), a patented device that opens and closes quickly to permit, or block, the passage of radiation, dividing the radiation beams into many smaller beams lets.
The patterns of movement is precisely calculated before treatment begins, so the intensity of the radiation beam delivered conforms to the patient’s tumor and helps avoid critical structures like the heart, lungs or other organs, as the machine rotates 360 degrees around the patient.
How tomotherapy works?
Tomotherapy combines state-of-theart intensity modulated radiation therapy (IMRT) with the precision of computed tomography (CT) scanning technology. Radiation oncologists create detailed three-dimensional maps of the size and location of a tumor and use these images to plot the tumor’s exact contours, the surrounding organs, and sensitive tissue. Then they prescribe the dose of radiation the tumor should receive.
Based on the prescription, the tomotherapy system programs the appropriate pattern for the treatment, calculating the precise position and intensity of the radiation beams.
Part of tomotherapy’s groundbreaking technology allows a single radiation beam to be divided into thousands of tiny, narrow beamlets that deliver radiation from all angles, in a pattern planned by doctors and coordinated by computers. As the shape or the location of the tumor changes over time, the angles and intensity of the beams are adjusted as well to improve the effectiveness of the treatment.
Treatment with tomotherapy
Tomotherapy is a quick and painless process, with daily treatments that usually take about 20 minutes. The machine is shaped like a large ring, with a bench — sometimes known as a couch — that slides through the ring’s opening. The radiation therapist positions you on the couch, usually on your back. Once treatment starts, you move slowly through the center of the ring while lying on the couch.
The first phase is an initial CT scan using the tomotherapy equipment, so that the doctor can check whether the tumor’s anatomy has changed and adjust the planned dosage and delivery accordingly. The therapist may also change your positioning on the couch as a result of this scan, and may also use special equipment to keep you from moving during treatment. Then the couch once again moves you through the machine, which delivers radiation in the prescribed pattern, typically over the course of five minutes.
Uses of tomotherapy
Tomotherapy can be used to treat many cancers, some of which would have been difficult or unsafe to treat with conventional radiation. Here are some of the ways it’s used:
Prostate Cancer: Tomotherapy produce a cure of the cancer and an early and stable reduction in PSA in a patient with low-risk organ-confined prostate cancer with minimal acute urinary toxicities and no noted chronic toxicities and without damage to other organs like the bladder.
Breast Cancer: Tomotherapy is especially effective for treating the breast cancer due to the treatment plan quality and the added benefit of shorter treatment times as compared to other radiation treatment.
Retreatment: When cancer recurs in a part of the body that has previously been treated with radiation, retreating the area can lead to scarring and ulceration. Because of tomotherapy’s precision, retreatment is now safer and more effective for people who have reached their maximum tolerance for conventional radiation. In these cases, the initial CT scan to map the recurrent cancer is particularly important, since it can sometimes be difficult to distinguish between active recurring cancer and scar tissue from previous treatment.
Total Metastases Irradiation (TMetI): When multiple metastases are present, tomotherapy can target visible tumors in multiple areas of the body with high doses of radiation, while limiting damage to healthy tissue. In this case, doctors typically use tomotherapy in coordination with chemotherapy, which helps treat smaller metastatic sites, called micrometastases that may not be visible or treatable with targeted radiation.
Brain tumors: Tomotherapy allows doctors to treat metastatic brain tumors — cancer that has spread to the brain from other parts of the body — with a two-step process.
First, they treat the whole brain with a moderately low dose of radiation — not strong enough to damage the brain, but enough to eliminate scattered cancer cells that cannot be seen on scans. Then, doctors use tomotherapy to treat all visible brain tumors with extra radiation, while avoiding damage to healthy brain cells.
Head and neck cancer: Tomotherapy makes it possible for doctors to treat the lymph nodes in the tongue, throat, and larynx while avoiding the salivary glands. Damage to those glands can result in permanent dry mouth, a condition known as xerostomia.
What is a typical TomoTherapy radiation treatment course like?
Similar to radiation therapy delivered by other modalities, patients undergo a treatment planning procedure prior to beginning TomoTherapy treatment. During treatment planning, doctors make use of CT or MRI imaging studies to define the size and shape of each tumor so that the appropriate radiation dose may be prescribed for it and the dose limits for the surrounding healthy tissue determined.
A typical TomoTherapy treatment course involves daily (Monday to Friday) visits. The patient may be fitted with a special device to help keep him properly and comfortably positioned as he lies on the treatment couch. Each radiation treatment usually takes 15 to 20 minutes. This includes time for positioning the patient on the treatment couch as well as the daily CT imaging process to be performed and treatment delivered.
In Central America, Caribean and South America our Institute is the only facility that offers this kind of treatment.
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