Brachytherapy

Question 1

What is brachytherapy?

Answer 1

Brachytherapy is a special procedure in Radiation Oncology that uses radioactive sources placed at short distances (hence brachy) from the target. Brachytherapy generates highly conformal dose distributions in a target volume because radioactive seeds (or sources) are placed directly within or in the vicinity of the target tissue.

Question 2

What are the types of brachytherapy?

Answer 2

Interstitial brachytherapy—radioactive sources are placed in the target tissue directly either permanently or temporarily.
Intracavitary brachytherapy—radioactive sources are contained in an applicator that is inserted into body cavities such as the vagina or uterus.
Intraluminal brachytherapy—subclass of intracavitary brachytherapy in which the radioactive sources are inserted in the lumen of the patient such as the blood vessel, bronchus, esophagus, or bile duct. Surface–Radioactive sources (or seeds) are placed in the surface plaques or molds, which are then placed on the treatment area such as the eye or skin.

Question 3

What are different types of brachytherapy loading systems?

Answer 3

Manual “hot” loading: used for low dose rate seeds such as prostate or eye plaque. Manual afterloading: this technique is not frequently used anymore.
Remote afterloading: most frequently used for high dose rate treatment.

Question 4

What are permanent versus temporary implants in brachytherapy?

Answer 4

Permanent implants—the radioactive sources are permanently implanted into the tumor, the patient is released from the hospital with radioactive materials in them.
Temporary implants—the radioactive material is implanted into or close to the tumor and is removed once the prescribed radiation dose has been delivered

Question 5

What are the advantages of the high-dose-rate (HDR) brachytherapy compared with low-dose-rate (LDR) brachytherapy?

Answer 5

Out-patient procedure
Safety—reduction or elimination of radiation exposure to the radiation therapy staff Optimization—moving source allows optimization of the dose distribution by adjustment of the dwell times for each dwell position in each channel (catheter or needle), permitting very fine control of the dose distribution
Stability—HDR intracavitary treatments take less time (usually under an hour), and the movement of the applicators during treatment is minimized.
Dose reduction to normal tissue—shorter duration of HDR treatments allows for physical displacement of normal tissue structure during treatment
Applicator size—the small size of the HDR source permits the use of smaller applicators

Question 6

What are the disadvantages of the high-dose-rate (HDR) brachytherapy compared with low-dose-rate (LDR) brachytherapy?

Answer 6

Investment—machine’s cost can be anywhere between $1M and $2M.
Radiobiology—as the dose rate increases, the radiosensitivity (damage per unit dose) increases for both normal tissues and tumors, the radiosensitivity for the normal tissue increases faster, increasing the likelihood of injuring the patient while controlling the tumor. Overcoming this requires the use of the advantages of optimization, geometry, stability, and dose reduction to normal tissues, and multiple fractionation treatment.
Safety—if the HDR machine has a malfunction or if a patient has an emergency situation, the risk of accidental radiation exposure to the patient and the staff is much higher in HDR than in LDR.