The most commonly used radiation technique used in cancer treatment is External Beam Radiation Therapy (EBRT). This practice involves radiation beams that are generated outside of the patient, typically by devices such as LINACS and particle accelerators. However, another method, called Brachytherapy, consists of the precise placement of radioactive seeds directly into or next to the tumor. Brachytherapy can be utilized alone; however, it is most commonly used in combination with EBRT to improve disease control and survival. The dosimetric advantages of this technique include its ability to provide high radiation doses to the tumor while having rapid fall-off doses at distances away from the source. In other words, it is an optimal tool for delivering very high doses to the tumor while minimizing the probability of normal tissue complications. Additionally, there is less uncertainty in dose distribution since the implanted seed moves with the tumor during treatment. In this blog, the developmental, mechanical, and treatment processes will be discussed.
History of Development
The discovery of radioactivity in 1896 by Becquerel is directly related to the invention of Brachytherapy. In the early 1900s, Pierre Curie and Alexander Graham Bell independently observed the shrinkage of malignant tumors when radioactive sources were implanted directly into the mass. The first successful brachytherapy treatment was completed in 1903 when two patients with basal cell carcinoma were irradiated with radium. Radium remained the primary source for brachytherapy radiation until it was replaced with cobalt-60 and cesium-137 in the 1950s. In the 1960s, iridium-192 became the most commonly used source of brachytherapy and the “afterloading” technique that is used today was developed.
Overview of Technical Process
Brachytherapy treatments are either integrated during EBRT treatment or given as a boost after EBRT is complete. A boost is designed to allow for maximal tumor shrinkage and to treat the gross disease that may not be seen in the diagnostic images. Additionally, brachytherapy is commonly given after tumor resection surgery to treat the surrounding tissue, thus decreasing disease reoccurrence.
To start Brachytherapy the radiation therapy team may position special applicators into the area in which irradiation will occur. Some of these applicators may require a surgical team to install. The doctor may insert the delivery device into a body cavity (intracavitary) or body tissues (interstitial). Medical imaging is required after the insertion of these devices to ensure the device’s correct positioning and calculate the most effective tumor treatment. Computer calculation from these images helps the physicist decide where the sources should be placed and how long those sources should stay in place to achieve the optimal treatment plan. Once the applicator’s position is verified and treatment planning has concluded, radioactive seeds can then be inserted during brachytherapy sessions.
Brachytherapy can be divided into two categories: Temporary and Permanent. Temporary brachytherapy places radioactive material inside a catheter for a specific amount of time and then removes it. Permanent brachytherapy (aka seed implantation) inserts needles pre-filled with radioactive seeds into the tumor. The doctor will remove the needle and leave the seeds behind permanently. Over time the radiation source will decay to the degree that irradiation will no longer take place.
There are three types of ways that doses can be delivered in temporary brachytherapy: 1) continuous low-dose-rate (LDR) irradiation, 2) low-intensity pulses repeated every hour for up to a few days (pulse-dose-rate irradiation), or 3) a few fractions delivering high doses each time (high-dose-rate [HDR] irradiation). LDR treatment delivers radiation at a continuous rate over one to two days, which allows the applicator to remain in place throughout the treatment period. To achieve a continuous rate over this length of time a hospital stay is required. Pulse-dose-rate irradiation (PDR) is a hybrid form of treatment that deploys a source for a brief period of time, hourly, over an extended treatment delivery period. PDR has potential radiobiologic advantages, but it requires prolonged patient immobilization and hospitalization.
HDR is the most prevalent treatment form as it offers several advantages including more precise positioning of the source, shorter treatment times, greater protection of health care personnel from radiation exposure, and better dose conformity. HDR treatment delivers a specified dose of radiation to the tumor in a short burst using remote afterloading technology. This technology allows a small radioactive seed attached to the end of a cable to be robotically driven through multiple channels of applicators, stopping at predetermined points for varying lengths of time. HDR treatments deliver radiation over 2-15 minutes per session and are typically done as an outpatient procedure; however, some patients are admitted to the hospital for one to two days to have several treatments using the same applicator.
Brachytherapy can be utilized to treat several different types of cancer; however, the most common utilization of this technique is for cervical, endometrial, breast, and prostate cancer.
Intracavitary brachytherapy remains the most commonly practiced form of brachytherapy for cervical cancer. Generally, the procedure consists of inserting a plastic tube into the uterine cavity and an applicator within the vaginal cavity. Afterloading technology is applied to automatically place non-permanent sources into the applicator. The two main types of applicators are the Tandem and Ovoid (T&O) or Tandem and Ring (T&R) design. The T&O consists of a tandem, an intrauterine tube, placed through the cervix, and two ovoids that are placed on either side of the cervix. The T&R also consists of a tandem and utilizes a ring that sits on either side of the cervix. Both of these devices require surgical placement and follow-up imaging to ensure proper positioning. Most commonly, patients are hospitalized for 3 days to complete 5 fractions of brachytherapy.
Brachytherapy for endometrial cancer consists of the placement of an applicator within the vaginal cavity to irradiate the upper vaginal vault. Typically, the device used is a hollow cylinder of variable width that allows a radioactive seed to be driven through a central channel. This treatment is usually conducted through 3 to 4 fractions given on an outpatient basis. The advantages of this therapy include the ability to eradicate residual cancers cells while avoiding harsh doses to the bowel and bladder, which are located nearby. Overall, endometrial brachytherapy decreases the risk of vaginal recurrence while avoiding the harmful side effects of pelvic EBRT.
Typically performed as perioperative or postoperative lumpectomy treatment and consists of placing non-permanent sources within the tumor bed to decrease the risk of local recurrence by delivering focused irradiation. The most common device used in this treatment is called a SAVI. The SAVI system consists of a tube-like applicator and an expandable bundle of tiny catheters that are positioned interstitially into the breast tissue. Comparatively to conventional EBRT, it spares healthy breast, lung, and heart tissue while shortening the course of treatment.
Most frequently treated with LDR brachytherapy and consists of placing permanent radioactive iodine-125 seeds into the prostate. Compared to radical prostatectomy, it is a minimally invasive technique that has fewer side effects and more rapid recovery. Additionally, Prostate HDR brachytherapy can be also performed over a few sessions and consists of inserting catheters within the gland using high-activity radioactive sources of iridium-192. This technique is mainly used as a boost to the prostate in combination with EBRT.
Conclusion and Further Resources
Although there are several advantages to brachytherapy, it is only as accurate as the positioning of the device. Improper positioning of the source may expose the tumor to under dosage or excessive toxicity if the sources are too close to a critical organ. Additionally, brachytherapy is more invasive than traditional EBRT and may result in infections if not properly managed. These disadvantages along with the advent of stereotactic body radiotherapy (SBRT) have led to decreasing national use. SBRT uses many precisely focused radiation beams to treat tumors with high doses while having rapid fall-off doses similar to brachytherapy. In next month’s blog, SBRT will be discussed in more detail. In the meantime, check out the links below for more information on brachytherapy.