External Beam Radiation
Cancer treatment often requires a multi-disciplinary approach, which includes chemotherapy and radiation therapy. Everyone at Central Care Cancer Center plays an important role as an active team member. This team-oriented approach is the key to ensuring optimum patient care.
External radiation is delivered by a radiation therapist using a machine called a linear accelerator. The treatment beam is only on for a matter of seconds, although it is not measured by time. The linear accelerator runs on electricity, so when the machine is turned off there is no radiation in the treatment room.
Image-Guided Radiation Therapy (IGRT)
Precise patient positioning and real-time tumor monitoring are vital to accurate treatment of defined areas while sparing surrounding normal tissues. The advancement of conformal radiotherapies has been supplemented by image-guided radiotherapy, or IGRT, enabling clinicians to compensate for the geometric uncertainties inherent in the treatment delivery process. Tumors can move, because of breathing and other naturally occurring processes within the body. IGRT allows physicians to locate and track the tumor just prior to and during radiation treatment to enhance the precision of the radiation beam and protect healthy tissues, ultimately reducing side effects and improving outcomes.
Central Care Cancer Center utilizes a diverse set of imaging tools, such as kV and MV imaging with our electronic portal imager, Cone Beam CT (CBCT), fluoroscopy, and respiratory gating technology. These tools make it possible to deal with inter-fraction motion (i.e., changes in target position due to setup error or naturally-occurring changes in organ position over time) and intra-fraction motion (i.e., organ motion during treatment, usually due to respiration or other physiological processes). Our radiation oncologists can then make immediate technical adjustments when a tumor moves outside of a planned treatment range. As a result, the radiation treatment is targeted precisely to the tumor, helping to limit radiation exposure to healthy tissue and reduce common radiation side effects.
The physicians can choose from a multitude imaging tools for patient repositioning based on bony anatomy, implanted or external fiducial markers, soft tissue structures, and/or respiratory gating verification. Images are usually acquired just after the patient has been positioned for treatment, and then special matching software is used to compare the images to reference images from the treatment plan. The system then calculates a “shift” and sends instructions to the treatment couch, which moves to bring the targeted tumor into precise alignment for treatment. Patient positioning is then verified prior to treatment delivery. For some cases, target positioning may occur during the treatment delivery as well.
Central Care Cancer Center has developed specific protocols for IGRT based on nationally published guidelines and verified using a rigorous internal quality assurance and peer review program. IGRT allows the treatment team to obtain high-resolution, three-dimensional images to pinpoint tumor sites, adjust patient positioning when necessary, and complete a treatment—all within the standard treatment time slot of 15-20 minutes. IGRT enables pinpoint accuracy of treatment delivery by ensuring reproducible, stable and accurate patient positioning.
The picture you initially see is of a Varian Trilogy machine with on-board imaging (OBI) and the setup CBCT images of a pelvis field. The video shows the process of using the acquired CBCT and utilizing the robotic couch to remotely position a patient for treatment. OBI with CBCT is just one of the many IGRT options available at Central Care Cancer Center facilities.
Intensity Modulated Radiation Therapy (IMRT)
Intensity-modulated radiation therapy (IMRT) is an advanced treatment method that uses computer-controlled linear accelerators to deliver high doses of radiation directly to cancer cells in a very targeted way, much more precisely than is possible with conventional radiotherapy. IMRT enables an oncology team to direct and narrowly concentrate potent doses of high-energy X rays at a patient’s tumor while minimizing complications to surrounding healthy tissue.
IMRT uses multiple small radiation beams of varying intensities to precisely irradiate a tumor. This method involves varying (or modulating) the intensity of the radiation beam while simultaneously changing the geometric profile of the delivery area so that the shape of the resulting dose delivery is tightly matched to the shape of the tumor. IMRT targets a tumor with intensity-modulated beams delivered from multiple angles. The area where the radiation beams intersect creates a finely sculpted radiation cloud that envelops and has the same shape as the tumor. The goal of IMRT is to conform the radiation dose to avoid or reduce exposure of healthy tissue and limit the side effects of treatment.
Treatment planning for IMRT is more complex than for conventional radiation therapy. The IMRT process starts with planning images, for example, computed tomography (CT), magnetic resonance (MR) and/or positron emission tomography (PET) images, of the patient’s tumor and surrounding anatomy. These images are converted into a custom three-dimensional model of the patient’s internal anatomy. A sophisticated computer program is used to determine the dose intensity pattern that will best conform to the tumor shape, creating a treatment plan based on tumor size, shape, and location within the body, combined with the doctor’s dose prescription. Typically, combinations of multiple intensity-modulated fields coming from different beam directions produce a custom tailored radiation plan that maximizes tumor dose while also minimizing the dose to adjacent normal tissues.
The equipment used to deliver radiation treatment is called a medical linear accelerator, which is equipped with a special beam-shaping device called a multi-leaf collimator (MLCs). IMRT utilizes conformal MLCs that can turn on or off dynamically changing the field during dose delivery. The linear accelerator rotates around the patient to send beams from multiple angles in order to give the tumor a high dose of radiation while preserving important healthy tissues.
The number of IMRT treatments is typically more than conventional radiation therapy because of the highly conformal beam which allows a higher dose to be delivered safely. Actual treatment time for each session may be slightly longer than with conventional radiation therapy because of the complexity of the treatment and the additional quality assurance checks and precision targeting.
Historically, the maximum radiation dose that could be given to a tumor site has been restricted by the tolerance and sensitivity of the surrounding nearby healthy tissues. IMRT delivers higher doses of radiation directly to tumors and cancer cells, while surrounding organs and tissues are protected. The level of normal tissue sparing achieved with IMRT is significant, resulting in fewer complications and side effects.
IMRT offers very high-resolution delivery, giving an oncology team the ability to conform the dose tightly to a small or irregularly shaped target. Precision targeting is especially important when delivering dose around small or oddly shaped structures such as the optic nerves or salivary glands. IMRT can more effectively shape the dose around such critical structures, severely limiting or even eliminating unnecessary exposures to radiation dose.
IMRT differs from conventional radiation therapy by employing complex software to plan a therapeutic dose of radiation based on tumor dimensions and location. IMRT delivers radiation in sculpted doses that exactly match the 3D shape of the tumor, adjusting the intensity of the radiation beams across the tumor area with unparalleled accuracy. Because of its greater degree of accuracy, IMRT may be a treatment option for recurrent or persistent tumors after conventional doses have been delivered.
Because the ratio of normal tissue dose to tumor dose is reduced to a minimum with the IMRT approach, higher and more effective radiation doses can safely be delivered to tumors with fewer side effects compared with conventional radiotherapy techniques. IMRT also has the potential to reduce treatment toxicity, even when doses are not increased. The end result is better tumor control, less damage to healthy tissues and structures in the treatment area, and a better quality of life for the patient.
The initial picture seen is a depiction of an IMRT plan of a pelvis constructed using our Eclipse Treatment Planning software. Eclipse software and IMRT technology are two tools used by Central Care Cancer Centers to optimize your treatment outcomes.
Certain tumors are treated using Rapid Arc technology. The radiation is delivered in a circular pattern as the linear accelerator rotates around the patient’s body.
Respiratory gating allows treatment to be given in sync with a patient’s breathing pattern. The radiation is delivered in small portions during a chosen portion of a normal breathing cycle. This allows maximum dose to a tumor volume that may be mobile during normal breathing.
Stereotactic Radiation Therapy (SRT)
SRT is used to deliver extremely high doses of radiation in a short amount of time. A disease must meet very specific criteria related to tumor size, type, and location, and a patient must be able to follow careful instructions related to positioning.
Stereotactic Body Radiation Therapy (SBRT)
Stereotactic treatments delivered to areas within the body but not the head.
Stereotactic Radiosurgery (SRS)
Stereotactic treatments delivered usually to a head or spine region, consisting of one very large dose of radiation delivered in one treatment.