A century ago, brachytherapy—the specific placement of radiation within diseased tissue—was found to cause cancers to shrink. However, concerns about exposure to radiation and accuracy in dosing led to a decline in using the treatment. But recent advances in medical imaging and discoveries in radiation have made brachytherapy more accurate and successful, creating renewed interest in this ancient treatment.
BrachyVision from Varian Medical Systems provides several types of dose optimization, which can be used alone or in combination. Here, surface dose on critical organs helps identify trouble spots. Also, the green patient icon (lower left corner) connotes body direction.
Small Distance, Big Treatment
According to the history recorded by the American Brachytherapy Society (ABS of Reston, Va), Pierre Curie introduced brachytherapy in 1901 when he suggested that a small radiation tube be inserted into a tumor to aide in its treatment. In 1903, Alexander Graham Bell developed the same idea independently, making a similar suggestion in a letter to the editor of Archives of the Roentgen Ray. Early experiments found that radiation did indeed cause the cancers to shrink; thus, brachytherapy was born.
Its name was taken from the Greek words for “short distance” (brachios) and “treatment” (therapy). The use of brachytherapy is intended to allow the physician to target a small area with radiation, sparing the healthy tissue surrounding the cancerous tissue. Though most commonly discussed in relation to prostate cancer, brachytherapy also can be used to treat cervical, endometrial, lung, esophageal, uterine, and tongue cancers; anal and neck tumors; sarcomas; and even coronary heart disease.
Typically, the treatment is performed on an outpatient basis. Radioactive seeds are positioned inside the cancerous tissue in ways intended to most effectively treat the tumor. Two types of seeds can be used: temporary or permanent. Temporary seeds are implanted and removed after treatment; permanent seeds remain in place forever, long after their radiation has decayed.
At its outset, brachytherapy was not a foolproof treatment, and accurate placement of the seeds and radiation exposure from high-energy nucleotides created major concerns. With the introduction of high-voltage telemetry for deeper tumors, brachytherapy declined in use in the middle of the 20th century.
However, the past 30 years have seen a renewed interest, and use of the treatment has increased. ABS cites three reasons:
- The discovery of man-made radioisotopes and remote after-loading techniques, which reduce exposure hazards;
- Newer imaging modalities—such as CT scans, MRI, and transrectal ultrasound and sophisticated computerized treatment planning, which have helped increase positional accuracy and provide superior, optimized dose distribution; and
- The treatment’s usefulness in nonmalignant diseases.
The Role of Medical Imaging
Medical imaging plays a role before, during, and after the actual brachytherapy procedure; hence, advances in the field have had a powerful impact on the treatment’s effectiveness. “The use of modern imaging modalities, coupled with computerized treatment planning and delivery systems, have dramatically improved the accuracy in locating the tumor, determining its size and shape, and placing the radioactive seeds and other treatment devices,” says Joe Barden, global oncology market manager with Vidar Systems Corp (Herndon, Va).
In the very early stages of treatment, medical imaging—as part of the patient’s workup—helps to determine the diagnosis as well as the degree of the disease’s progress. Ultrasound, for instance, can be used to guide a biopsy.
“Imaging is an integral part of diagnosing cancer in the first place,” Barden says. “Being able to ‘see’ into the body to find tumors [that are] still small and treatable is a wonderful tool.”
David Hall is the marketing manager of brachytherapy at Varian Medical Systems (Palo Alto, Calif). He says, “Volume images from all of the modalities can be used to delineate target tissues and evaluate whether brachytherapy is an appropriate technique or not.”
When the diagnosis is confirmed and brachytherapy has been found to be the appropriate treatment, medical imaging is again used to help plan and perform the actual procedure.
“Once diagnosed, tumor volumes can be measured, and different dosing plans can be tried in simulation to make sure that optimum radiation is delivered to the tumor while sparing healthy tissue,” Barden explains. “During treatment, imaging can confirm that the treatment is following the plan, record and verify processes using images to validate that the result matched the plan, and better estimate the success of the outcome with less post-treatment waiting.”
After treatment, medical imaging is used to determine the procedure’s accuracy and success. “After brachytherapy, imaging is less common, except as associated with later patient follow-up,” Hall clarifies. “But prostate seed implants, for example, are permanently placed, and a CT scan 30 days following the procedure is often used to quantify the quality of the implant and for reporting purposes.”
Varian Medical Systems offers VariSeed dosimetry for permanent seed prostate brachytherapy. With the real-time planning features of the Implant View module (optional), users can create a volume study, a proposed plan, and a completed post-plan, all as part of the implant process.
Real-Time Imaging
It is during the actual treatment where advances in medical imaging have had—and will continue to have—their greatest impact. According to Michael Zelefsky, MD, chief of brachytherapy service at Memorial Sloan-Kettering Cancer Center (New York) and president of ABS, the past 10 years in particular have seen major advances. “Medical imaging has transformed prostate brachytherapy from a crude technique to a more accurate one with significantly improved results,” he says.
Zelefsky attributes the poor results of brachytherapy in the 1960s and 1970s to the inability to plan or target the radiation accurately. “Ultrasound and CT scans came along and provided more focus,” he explains. “The role of MRI has grown and will increase even further. Currently, we are using intraoperative imaging to map out brachytherapy planning in the operating room so that we can target the radiation in real time. This use has created better results and reduced side effects.”
The real-time information allows the doctor to make modifications to the plan and the procedure as necessary. Areas showing greater abnormality can receive a greater dose, and changes can be made to account for disease progress. The prostate, for instance, can change significantly during the 2 weeks between treatment planning and the actual procedure.
“Often, the prostate looks very different, and the physician must match the plan to an organ that has altered in size, volume, and/or shape,” says Roger Szafranski, senior product manager at Capintec Inc (Ramsey, NJ). “The physician also must align the urethra, bladder, and other organs. So preplanning has not been the most effective way to perform the procedure.”
Intraoperative imaging has been found to be much more effective. Recently completed research studies on brachytherapy for prostate cancer show similar long-term survival rates as those produced with prostatectomy.
Exploring the Modalities
Most often, the live imaging is performed using ultrasound, although some facilities are working with MRI, CT, and fluoroscopy. Ultrasound was one of the first modalities used during the brachytherapy implant procedure.
“It started with ultrasound. Physicians could see the needles inside the body and where the sources were being placed,” explains Cliff Burdette, PhD, director and VP of research for CMS Inc (St Louis). “More recently, ultrasound developed the ability to localize images within the body and know where they are. Digital imaging permits accurate guidance and dose feedback to the physician.”
Zelefsky notes that over the past 5 to 10 years, such facilities as Harvard have begun to use CT and/or MRI to guide and plan their brachytherapy procedures. He also suggests that PET scanning has a role for a number of investigators.
Burdette agrees that ultrasound is the more widely used modality, noting that a small number of research programs in the United States are also using open MRI to perform seed implants.
Varian’s Hall states, however, that “each treatment site lends itself to its own preferred imaging modality. Transrectal ultrasound is most commonly used for diagnostic, preplan, and placement guidance for prostate implants. Plane film is still most common for intraluminal treatments, where the source is guided into place by a body cavity or channel, such as bronchus, esophagus, nasopharynx, vascular brachytherapy, and many gynecological and rectal procedures.”
He suggests looking at medical imaging’s role before and after the treatment. “Of course, CT, MRI, or PET might have been useful in the definitive diagnosis of these patients,” Hall explains. “And while plane film or fluoroscopic images might be used for placement, a follow-up CT scan might still be used for dosimetry planning for high dose rate brachytherapy.”
Burdette notes that fluoroscopy can confirm that “things are where the physician thinks they are.”
Szafranski concurs. “It removes the element of the unknown. A doctor will leave the operating room thinking that the implant has gone well, but it hasn’t. So some doctors will use fluoroscopy to see the seeds and check their placement before letting the patient go. A CT scan 2 weeks later assists with postimplant assessment.”
And Hall adds, “There is no way to overestimate how much more confidence these images give a physician when the procedure [progresses] the way they would want it to.”
Benefits for the Patient
“Patients benefit from more accurate treatment, which has a greater chance of maximizing damage to the target with the best possible morbidity as a result of sparing tissue,” Hall explains. “In some cases—prostate seed implants, for example—the patient also clearly benefits from a procedure that is over in a couple of weeks, allowing him to return to his normal life in a day or so. [This aspect is] a major improvement over surgical techniques, where recovery from the surgery might last weeks.”
In fact, according to Hall, the great strength of brachytherapy is its ability to deliver a very high dose that is close to the source location and that falls off very rapidly with distance.
Zelefsky adds, “Imaging helps to target brachytherapy to regions of cancer more precisely and, with that information, further reduce side effects and improve the patient’s quality of life.”
Future Trends
Zelefsky believes image-guided therapy will become more implemented among the radiation oncologists who practice brachytherapy.
Adds Hall: “In working with our physician customers, the striking thing I see is the desire to have better information about the extent of disease they are treating. Further, as we become more successful at early diagnosis and successful eradication of an increasing number of cancers, the question of reducing morbidity—which, in brachytherapy, means identifying and avoiding sensitive normal tissues—begins to become a major concern.”
Others feel great strides will be made with technology. Barden says, “I would suspect the new 3-D, real-time imaging modalities that are just taking off will marry with image-guided surgical technology to allow faster and more precise procedures.”
Looking ahead, he adds, “Tremendous further potential exists for incorporating medical imaging to better target brachytherapy, and with the use of functional imaging and other new modalities, the field of brachytherapy will be elevated to a new level.” And, of course, this elevation will further increase precision, reduce side effects, and improve quality of life.
Renee DiIulio is a contributing writer for Medical Imaging.
