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About Brachytherapy

By Gene Carter,2014-04-29 21:44
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About Brachytherapy

    Janusz Skowronek MD, PhD

    Greatpoland Cancer Center

    Poznań, January 2004

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1. About Brachytherapy

     Derived from ancient Greek words for short distance (brachios) and treatment (therapy) and refers to the therapeutic use of encapsulated radionuclides within or close to a tumor. It is sometimes called seed implantation and is an outpatient procedure used in the treatment of different kinds of cancer.

     Two general types of radiation techniques are used clinically - brachytherapy and

    teletherapy. In brachytherapy, the radiation device is placed within or close to the target volume. Teletherapy uses a device located at a distance from the patient, as is the case in most orthovoltage or supervoltage machines. The advent of high voltage teletherapy for deeper tumors and the problems associated with radiation exposure from high-energy radionuclides led to a decline in the use of brachytherapy towards the middle of last century. However, over the past three decades, there has been renewed interest in the use of brachytherapy for a number of reasons. The discovery of man-made radioisotopes and remote afterloading techniques has reduced radiation exposure hazards. Newer imaging modalities (CT scan, magnetic resonance imaging, transrectal ultrasound) and sophisticated computerized treatment planning has helped to achieve increased positional accuracy and superior, optimized dose distribution. Finally, while brachytherapy was initially used only for treatment of cancer, it has now been found to be useful in non-malignant diseases (for example, in the prevention of vascular restenosis) as well. It is clear that brachytherapy is the optimum way of delivering conformal radiotherapy tailored to the shape of the tumor while sparing surrounding normal tissues.

     The efficacy of brachytherapy, as compared with the efficacy of external beam alone,

    is attributable to the ability of radioactive implants to deliver a higher concentrated radiation dose more precisely to tissues, which contributes to improved local control, provided that the

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    tissue is clinically delimitable and accessible. At the same time, the surrounding healthy tissues are spared irradiation.

     In contrast to external-beam irradiation, brachytherapy is invasive, requiring

    insertion of site-specific applicators under sedation or anaesthesia. The surgeon who is sometimes involved in these procedures, particularly if laparotomy or craniotomy is required for the insertion of applicators, or if tumour resection is required prior to applicator insertion, should be aware of the indications for brachytherapy and the associated techniques

     Brachytherapy is an internal radiation therapy that is applied either in a permanent manner, (sometimes called seed implantation), or in a temporary manner, often through the use of catheters into which the radioactive sources are placed. The radioactive materials (seeds or in catheters) are placed inside the body, and positioned in a manner that will most effectively treat the disease. When permanent brachytherapy is being employed, the radioactive “seeds” are left inside of the body. The half-life of the radioactive isotope used, gauges how long they will be radioactive within the body since the radioactivity of the seeds diminishes over time. Temporary brachytherapy usually involves either an in-patient procedure (low dose rate brachytherapy, or LDR), whereby the patient lies in bed for several days while the radioactive sources treat the disease, or in an out-patient setting (high dose rate brachytherapy, or HDR, whereby the patient usually undergoes several treatments of radiation in a short period of time.

     Because the radiation source is close to or within the target volume with

    brachytherapy, the dose is determined largely by inverse-square considerations. This means

    that the geometry of the implant is important. Spatial arrangements have been determined for different types of applications based on the particular anatomic considerations of the tumor and important normal tissues. The dose decreases rapidly as the distance from the applicator increases. This emphasizes the importance of proper placement.

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     Brachytherapy has now been used for over a century. Some of the diseases now

    treated with brachytherapy include prostate cancer, cervical cancer, head and neck cancer, endometrial cancer, and coronary artery disease. Brachytherapy has been proven to be very effective and safe, providing a good alternative to surgical removal of the prostate, breast, and cervix , while reducing the risk of certain long-term side effects.

2. History

     Historically, the removable interstitial and intracavitary sources used were radium

    and radon, the latter primarily for permanent implants. Henri Becquerel discovered natural radioactivity in 1896 when he found that Uranium produced a black spot on photographic plates that had not been exposed to sunlight. Two years later, Marie and Pierre Curie working in Becquerel's laboratory extracted Polonium from a ton of Uranium ore and later in the same year, extracted Radium. In 1901, Pierre Curie suggested to Danlos at St. Louis Hospital in Paris that a small radium tube be inserted into a tumor thus heralding the birth of brachytherapy. In 1903, Alexander Graham Bell made a similar suggestion, completely independently, in a letter to the Editor of Archives Roentgen Ray. It was found in these early experiences that inserting radioactive materials into tumors revealed that radiation caused cancers to shrink.

     In the early twentieth century, major brachytherapy work was done at the Curie Institute in Paris and at Memorial Hospital in New York. Dr. Robert Abbe, the chief surgeon at St. Lukes Hospital of New York, placed tubes into tumor beds after resection, and later inserted removable Radium sources thus introducing the afterloading technique as early as 1905. Dr. William Myers at Ohio State University developed several radioisotopes, including 1986012532Gold, Cobalt, Iodine, and Phosphorus for clinical brachytherapy. These were

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    implanted surgically by Drs. Arthur James (surgeon) and Ulrich Henschke (radiation oncologist).

     Marie Curie, the discoverer of radium, recognized its importance early and

    championed the medical use of these isotopes. They were important tools in early cancer therapy but now have been largely replaced by manmade isotopes, which overcome most of the disadvantages of the naturally occurring ones.

     Initially, even removable isotopes were used by directly applying the isotope, and thereby exposing the operator to significant radiation doses. This problem has largely been

    13719260circumvented through the use of Cs, Ir, and Co. The first two have a lower energy and

    are much easier to shield. Afterloading techniques are used for removable implants as often as possible. Receptacles for the radioactive material are placed in the patient in the form of needles, tubes, or intracavitary applicators. When they have been satisfactorily placed they are afterloaded with the radiation sources.

    198125 Permanent implants are primarily done today with Au and I. In the treatment of

    prostate cancer, the radioactive seeds are about the size of a grain of rice, and give off radiation that travels only a few millimeters to kill nearby cancer cells. With permanent implants (for example, prostate) the radioactivity of the seeds decays with time while the actual seeds permanently stay within the treatment area.

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3. Kinds of brachytherapy

    a. characterized by the duration of the irradiation:

    there are 2 different kinds of brachytherapy: permanent, when the seeds remain inside of the

    en the seeds are inside of the body and then removed. body, and temporary, wh

    b. characterized by the positioning of the radionuclides:

    - interstitial brachytherapy: radioactive sources are inside the tumour

    - contact brachytherapy or plesiobrachytherapy: radioactive sources are close to the

    tumour. Contact brachytherapy is divided into four different kinds of brachytherapy: intracavitary, intraluminal, endovascular and surface brachytherapy

    c. characterized by the dose rate (ICRU definitions):

    - low dose rate (LDR) 0.4 - 2.0 Gy/h

    - pulsed dose rate (PDR) 0.5 - 1.0 Gy/h

    - medium dose rate (MDR) 2 - 12 Gy/h

    - high dose rate (HDR) > 12 Gy/h

     Low Dose Rate (LDR) remote afterloading systems radiation protection, but do not provide as much flexibility in the design of alter native isodose volumes as that obtained with higher dose rate sources with adjustable stepping positions and dwell times. At the other end of the spectrum of brachytherapy methods is the use of High Dose Rate

    (HDR) afterloading with a single source of 192 Ir moved by computer to a series of dwell positions. In that case the choice of isodose volume is very flexible. Large doses can be given within a few minutes. Sources of that kind require well-shielded bunkers similar to linear accelerator rooms.

    One radiobiological disadvantage in the use of such high dose rates, of 1-3 Gy/min (greater ratio of late tissue effects), can in practice be overcome by careful placement of catheters and by good immobility achievable with very short exposures.

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Pulsed Dose Rate (PDR) treatment is a recent brachytherapy modality that combines

    physical advantages of high-dose-rate (HDR) technology (isodose optimization, planning flexibility and radiation safety) with radiobiological advantages of low-dose-rate (LDR) brachytherapy (repair advantages).

    192PDR uses a single stepping Iridium source of 15-37 GBq (0,5 1Ci). This produces

    treatment dose rates of up to about 3 Gy per hour, which can be utilized (pulsed) every hour, 24 pulses per day. The source is enclosed in a 2,5 mm long capsule 1.1 mm in diameter. The single radioactive stepping source moves through all the implanted catheters during each pulse. A typical pulse length lasts 10 minutes per hour, which may be increased to

    192approximately 30 minutes three month later when the Ir source has decayed.

    Pulsed brachytherapy uses a stronger radiation source than that employed in LDR brachytherapy and gives a series of short 10 to 30 minute exposure long every hour amounting to approximately the same total dose in the same overall time as that in LDR The trajectory of a single high activity source through the implanted catheter can be precisely programmed by a dedicated computer and carried out by a remote source projector. The resulting isodoses can be optimized by modulating the dwell time of the source as a function of its trajectory within the implanted volume. This allows individualization of dose distributions, while essentially eliminating radiation exposure to the medical staff. The source strength is 10 to 20 times lower than that used in HDR, and the requirements for shielding are less stringent. An ordinary brachytherapy room would require less than two extra half, value thickness of protection, and an accelerator type bunker is not necessary. Nursing care is facilitated compared with LDR brachytherapy, since patients can be attended between the treatment sessions, without concern about problems of radioprotection. PDR brachytherapy offers several advantages over conventional LDR brachytherapy:

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    (1) The distribution of radiation doses can be more easily controlled and tailored permitting the following improvements:

    (a)/ more precise application (then LDR) of the prescribed dose to the treatment volume, (b) better reproducibility of treatment plans,

    (c) greater flexibility to change the dose distribution through the course of treatment if necessary,

    (2) Improved radiation safety for clinical and physics staff,

    (3) Only one source to replace every three months, and

    (4) All brachytherapy procedure feasible with one machine: intracavitary, interstitial, intraoperative and intraluminal.

    Compared with HDR brachytherapy

    (1) PDR offers similar quality of treatment,

    (2) Similar treatment procedure and technical verification,

    (3) Improved radiation safety for clinical and physics staff,

    (4) Requirements for shielding are less stringent - an accelerator type bunker is not necessary, (5) Theoretical radiobiological advantage: the technique allows some repair in late-reacting normal tissue due to intervals between pulses,

    (6) patient comfort is believed to be worse, and

    (7) few indications for palliative treatment.

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4. Indications for brachytherapy.

    a. prostate brachytherapy

     Prostate brachytherapy usually involves an out-patient procedure for either permanent seed implantation or HDR brachytherapy to the prostate gland. It has been shown to have comparable 10-year survival rates to radical prostatectomy, and has fewer side effects including a lower incidence of impotence and incontinence.

    According to the American Cancer Society, prostate cancer is one of the most common forms of cancer among American men, mainly affecting men over the age of 65. As men get older, the likelihood of developing prostate cancer increases, therefore, physicians usually recommend that prostate cancer screening begin at age 50. For African American men, or men with a family history of prostate cancer, physicians recommend screening beginning at age 40.

    b. breast brachytherapy

     Treatment of breast cancer with brachytherapy usually involves a five-day treatment course with either LDR (in-patient) or HDR (out-patient) brachytherapy, rather than six weeks as with traditional radiation treatment following a lumpectomy. This offers excellent cure rates without the need for a mastectomy.

     Breast conservation treatment has long since been established as an effective treatment alternative to mastectomy for early stage breast cancer. Standard breast conservation treatment consists of breast conserving surgery for tumor removal (lumpectomy) followed by external radiation to the whole breast. Although this treatment approach offers many advantages over mastectomy and provides in-breast cancer control rates that approach 95-100% with good to excellent cosmetic results in nearly all patients, six weeks of daily treatment has proved prohibitive for some patients. As a result, some women refuse external radiation (putting themselves at higher risk for recurrence) or choose mastectomy and have

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    the breast unnecessarily removed. Those finding six weeks of daily treatment inconvenient or impossible include working women, elderly patients, and those who live a significant distance from a treatment center. Breast brachytherapy as the sole method of radiation following lumpectomy is a new treatment approach that offers equivalent local control, breast conservation and improved convenience of treatment delivery. Although most women with breast cancer are appropriate candidates for standard breast conservation treatment and can be treated with lumpectomy and external radiation, only a subgroup of these women will be appropriate candidates for breast brachytherapy. However, even with strict selection criteria it is estimated that 71,000 women each year in USA would be appropriate candidates for breast brachytherapy.

    c. cervical brachytherapy

     Historically, cervical cancer has been treated with a hysterectomy (the surgical removal of the uterus), which carries many side effects for the patient. Brachytherapy is usually used in combination with external beam radiation therapy in the treatment of cervical cancer and has been found to be at least as effective as a hysterectomy.

    d. head and neck brachytherapy

     The use of brachytherapy in the treatment of head and neck cancers causes

    practitioners hesitation, owing to the proximity to vital structures including the carotid arteries, the jugular veins, other major blood vessels and in some cases the brain. There is a limited amount of clinical data available but, there are several safe and efficacious ways to use brachytherapy in the treatment of head and neck cancers.

    e. skin brachytherapy

    f. lung cancer

     The use of brachytherapy in the treatment of lung cancer dates to the 1920s, though the applications varied widely. Brachytherapy is one of the most efficient methods in the

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