Brachytherapy permanent seed implant

ALTHAF JOUHAR K

MALABAR CANCER CENTRE

CALICUT UNIVERSITY

INTRODUCTION

Brachytherapy (sometimes referred to as curietherapy or endocurie therapy) is a term used to describe the short distance treatment of cancer with radiation from small, encapsulated radionuclide sources. This type of treatment is given by placing sources directly into or near the volume to be treated.

Permanent brachytherapy, also called seed implantation, involves placing tiny radioactive seeds or pellets (about the size of a grain of rice) in or near the tumor and leaving them there permanently. The seeds stay in the tumor and give a continuous dose of radiation over a few months. After several months, the radioactivity level of the implants eventually diminishes to nothing. The inactive seeds then remain in the body, with no lasting effect on the patient.

TYPE OF IMPLANT DESCRIPTION

Intracavitary Sources are placed into body cavities close to the tumour volume

Interstitial Sources are implanted surgically within the tumour volume

Surface (mould) Sources are placed over the tissue to be treated

Intraluminal Sources are placed in a lumen

Intraoperative Sources are implanted into the target tissue during surgery

Intravascular A single source is placed into small or large arteries

Permanent versus temporary brachytherapy

This type of treatment is given by placing sources directly into or near the volume to be treated.

The dose is then delivered continuously, either over a short period of time (temporary implants)

or over the lifetime of the source to a complete decay (permanent implants). Most common

brachytherapy sources emit photons; however, in a few specialized situations beta or neutron

emitting sources are used.

In addition to permanent brachytherapy, temporary brachytherapy has also been used. In this

technique, the implants deliver radiation to the prostate at a higher dose rate than is provided

by a permanent implant. Currently, the isotope most commonly used for temporary

brachytherapy is iridium (Ir)-192, which provides a higher dose of radiation than the iodine (I)-

125 and palladium (Pd)-103 permanent implants.

Type of implant Description

Temporary Dose is delivered over a short period of time and the source

are removed after the prescribed dose has been reached

Permanent Dose is delivered over the lifetime of the source until

complete decay

COMMONLY USED SEALED SOURCES

ISOTOPE AVERAGE

PHOTON

ENERGY

(MeV)

HALF-LIFESOURCE FORM CLINICAL APPLICATION

Cesium -137 0.662 30 years Tubes and needles LDR intracavitary and interstitial

Iridium-192 0.38 73.8 days Seeds , Wires LDR temporary interstitial, intra vascular ,HDR interstitial and

intracavitary

Cobalt-60 1.25 5.26 years Encapsulated spheres

HDR intracavitary

Iodine-125 0.028 59.6 days Seeds Permanent interstitial

Palladium-103 0.020 17 days Seeds Permanent interstitial

Gold-198 0.412 2.7 days Seeds Permanent interstitial

Strontium/Yitrium-90 2.24 beta 28.9 years Seeds, Plaque Superficial ocular lessions

Prostate

The prostate is a gland that plays an important role in the male reproductive system. It is located in front of the rectum, just below the bladder, and is similar in shape and size to a walnut. The gland partially surrounds the neck of the bladder and the start of the urethra, the tube in which urine flows from the bladder and out the body.

The primary role of the prostate is the production of seminal fluid, the liquid component of the semen. Although the prostate plays no active role in urination, it does help to regulate the flow of urine by slightly compressing the urethra. Consequently, urinary symptoms may occur as the prostate becomes enlarged and presses the urethra.

The three main treatment options for early stage prostate cancer are radical prostatectomy, external beam radiation therapy, and radioactive seed implants.

DETECTION

Digital rectal exam (DRE): the doctor inserts a gloved finger into the rectum to feel the prostate for irregularities or lumps. This exam is extremely effective in identifying a tumour and subsequently detecting cancer even in the absence of symptoms.

PSA blood test (PSA): This test measures the level of certain chemicals (prostate-specific antigen, or PSA) produced by the prostate. PSA is a protein that is produced exclusively by the prostate. A very small quantity of PSA (less than 4 ng/mL) is normal, but a higher level may indicate the presence of cancer.

Needle biopsy: This involves taking a small sample of prostate tissue for examination under a microscope. A grade is then assigned to any cancer discovered to help determine its aggressiveness. According to a system called Gleason’s score (rated on a scale of 1 to 10), the higher the score, the more aggressive the cancer, and the more likely it is to grow quickly and spread outside the prostate.

Brachytherapy is applied in prostate treatment:

• As primary treatment using permanent implantation of short lived radionuclide sources (such as I-125 or Pd-103) emitting low energy photons .

• As a boost to external beam treatments delivered in the form of fractionated or single session treatment using an HDR machine (Ir-192).

• TG-64 is the basic guideline for permanent seed implant which is the report published by the AAPM.

LDR prostate brachytherapy (seed or polymer source implantation) is recommended as a treatment for patients whose cancer is at an early stage (cancer stages T1 to T2), and which has not spread beyond the prostate (localised disease).Doctors use a combination of factors such as cancer stage and grade, PSA level to help them decide if a patient is suitable for LDR brachytherapy

The rectal exam and PSA blood test are the first tests performed when checking for prostate cancer. If one of these two exams is abnormal, a needle biopsy Is performed, since it is the only test that can conclusively confirm the presence of cancerous cells.

Transperineal approach with ultrasound guidance has become the technique of choice, in part because it is carried out as an outpatient one day procedure.

This treatment is most useful for patients whose cancer is still localized to the prostate.

Prostate brachytherapy is reserved for treatment of early stage cancer that has not spread outside the prostate gland.

Prostate seed implants are currently performed using iodine-125 and palladium-103 sources under imaging and template guidance to deliver localized irradiation to high doses. For selected patients, seed implantation alone offers a complete course of treatment; for others, it is used in conjunction with external beam radiation therapy to the pelvis

The seed implant treatment for prostate cancer is also referred to as "interstitial brachytherapy." In this therapy, small pellets of radioactive materials (isotopes such as iodine-125 or palladium-103) are placed inside thin needles, which are inserted through the perineal area (area between the scrotum and anus) into the prostate gland. The permanent types of pellets, which are sometimes called seeds, are implanted through these needles, and become lodged in the cancerous area.

In permanent brachytherapy, also called seed implantation, needles that are pre-filled with the radioactive seeds are inserted into the tumor. The needle or device is then removed, leaving the radioactive seeds behind. Seeds may also be implanted using a device that inserts them individually at regular intervals. X-rays, ultrasound, MRI or CT scans may be used to assist the physician in positioning the seeds. Additional imaging tests may be done after the implantation to verify seed placement.

Seed implantation is a surgical procedure. The potential acute complications may be related to anesthesia and/or include, bleeding, and infection. The late complications of seed implant include irritative voiding symptoms, persistent urinary retention, rectal urgency, increased bowel movements, rectal bleeding or ulceration, and prostatorectal fistulas. The incidence of erectile dysfunction and urinary incontinence appears to be lower than with external beam radiation.

Choice of radionuclide for prostate implant

Introduction of low photon energy emitters iodine-125 and palladium-103 has renewed interest in permanent prostate implants.

• Has a shorter half-life, palladium-103 (17 d) and iodine-125 (60 d).

• Delivers a higher initial dose rate.

• Is useful in treating fast growing high grade tumours.

Pre-planning, seed placement and dose distributions

• Pre-planning of the implant is based on either ultrasound or CT cross-sectional (transverse, axial) images.

• The intended treatment volume generally is the whole prostate gland with a small margin of periprostatic tissue. The seeds are placed and spaced so as to minimize the dose to the urethra to decrease complications.

• The number of seeds and their geometric placement in the target volume is determined through optimized computer dose planning or pre-calculated nomograms.

Prescribed dose and post-treatment evaluation

The recommended total dose to the periphery of the target volume when brachytherapy implant is the sole treatment modality is:

• 150 - 160 Gy for iodine-125 seed implants

• 115 - 120 Gy for palladium-103 seed implants

Post-implant CT imaging:

• Is usually carried out two to three weeks post-implantation to allow for seed migration and volume reduction resulting from oedema.

• Dose calculations are performed and compared with preimplant dose distributions.

Planning

The first step consists of determining the exact size of the prostate. An ultrasound test (using sound waves produced by a probe inserted into the rectum) is performed to determine the shape of the prostate. The shape is analyzed by computer to create three-dimensional model. Then, the number of seeds and where they are placed is customized to match the exact radiation dose with the patient’s needs.

Seed distribution

Different types of seed distributions are in current use and a consensus on the optimal seed distribution does not exist.

Three type of distribution techniques are given below;

o Uniform loading

o Modified peripheral loading

o Peripheral loading

Uniform loading

The classic approach is to space the seeds 1 cm apart, center-to-center, throughout the prostate. This approach, referred to as uniform loading, requires a higher number of lower strength seeds ~typically 0.4 to 0.5 Gy/hr seed for 125I, 1.2 to 1.5 Gy/hr seed for 103Pd!, and is characterized by relatively high doses in the center of the prostate

Modified peripheral loading

In modified peripheral loading, some seeds in the central portion of a uniformly loaded implant are deleted to reduce the central dose. This may require increasing the strength of the remaining seeds or decreasing the needle to needle or seed to seed spacing in the periphery.

Peripheral loading

Peripheral loading is an alternative approach in which the seeds are preferentially limited to the periphery of the prostate. This requires a substantial increase in seed strength ~typically 0.75 to 1.0 Gy/hr seed for 125I, 2.0 Gy/hrseed or higher for 103Pd!. The end result is to produce a dose minimum ~albeit above the prescribed minimum dose, instead of a dose maximum, at the location of the urethra

Disadvantages:

Typical symptoms following prostate brachytherapy (seed implants). Urinary retention lasting up to a week occurs in 10% of the patients and everybody gets frequency, urgency, night-time hesitancy and decreased force of stream. Because of pelvic congestion caused by the implant, hemorrhoids can be a real problem. We tell people to expect these side effects and it will start to get better 3 to 4 weeks after the implant but won't be normal until about 10 to 12 weeks after the implant

Erection problems

The risk of long-term Brachytherapy can affect the blood vessels and nerves that control

erections. This may make it difficult to get and keep an erection (erectile dysfunction).

Erection problems may not happen straight after treatment, but sometimes develop

some time afterwards.

erection problems after brachytherapy varies from man to man. The risk will increase if

patient already had problems with erections before treatment. He may be more likely to

get erection problems if he also having hormone therapy or external beam radiotherapy.

There are treatments available for erection problems.

Having children

Brachytherapy may make you infertile, which means you won’t be able to have children naturally. But there is still a chance that you could make someone pregnant after brachytherapy. It’s possible that the radiation could change your sperm and this might affect any children you conceive. The risk of this happening is very low. But if this is relevant to you, use contraception to avoid having a child during treatment, and for up to two and a half years afterwards.

Tiredness

The effect of radiation on the body can make some men tired. If you are getting up a lot during the night to urinate, this can also make the patient tired in the day. Fatigue is extreme tiredness that can affect patient’s everyday life. It can affect his energy levels, motivation and also the emotions. Fatigue can continue after the treatment has finished and may last several months.

CONCLUSION

Results from centers using I-125 and palladium since 1985 show a higher percentage of implant patients remaining disease-free than with either radical prostatectomy or external beam therapy.

Seed implantation is normally done as an outpatient procedure taking about one hour to perform. The patient usually leaves the hospital the same day as the implant procedure or stays in the hospital for one night and then resumes normal activities within several days.

Because the radioactive sources are placed inside the prostate, seeds actually deliver 2 to 4 times more radiation to the cancer than external radiation therapy or IMRT, which must use a lower dose because they may damage healthy tissue.

This procedure is well suited to older patients because it is much easier to undergo than surgery or external radiation. It is well suited to younger patients who would prefer to avoid the rigors and potential complications of radical prostatectomy

Thank you…