Brachytherapy

Brachytherapy (Greek brachys = short) is short-distance radiotherapy in which the distance between the radiation source and the clinical target volume is less than 10 cm. The main advantage of brachytherapy is that the radiation source is in close proximity to the tumor, thus maximally sparing the surrounding healthy tissue. This type of radiotherapy is particularly recommended when it is necessary to increase the radiation dose (boost) or when a tumor volume is to be irradiated without its spreading pathways. Nowadays, point or linear gamma/beta emitters of only a few millimeters in length and about 1 mm in diameter are used as the radiation source. These can be inserted into very different applicators, so that even coronary vessels of the heart are accessible to short-distance irradiation. A basic distinction is made between three principles of brachytherapy:

Surface contact therapy: the radiation source is brought into contact with the patient’s surface (e.g., skin).
Intracavitary therapy: the radiation source is introduced into a body cavity (e.g., uterus/uterine).
Interstitial therapy: the radiation source is implanted via an applicator directly into the tumor tissue temporarily or permanently (e.g., seed implantation into the prostate).

Depending on the dose rate, one also distinguishes:

LDR brachytherapy (LDR stands for “low dose rate”): in this case, thin hollow needles about 4 mm long thin pins (technically “seeds”) of weakly radioactive iodine-125 are introduced into the prostate (= seed implantation into the prostate); indication: smaller and less aggressive tumors of the prostate (low-risk prostate cancer).
HDR brachytherapy (HDR stands for “high dose rate”); is usually combined with percutaneous irradiation, i.e. irradiation from the outside; indication: localized tumors of the prostate gland

Indications (areas of application)

Brachytherapy is suitable for easily accessible tumors, i.e., these are located, for example, on the surface of the body or in hollow organs or can be exposed surgically.

Surface contact therapy: this is often used in dermatology and ophthalmology when the tumors are located, for example, on the skin, in the epipharynx (nasopharynx) or eyeball.
Intracavitary brachytherapy:
- Gynecology: carcinomas of the corpus uteri (uterine body), cervix uteri (cervix), vagina, bladder.
- Insertion into ductal systems previously occluded by tumor and opened with the use of a laser device: Bile ducts, bronchi, esophagus (esophagus), etc.
- Intracoronary radiotherapy after coronary artery dilatation (coronary artery dilation) for stenosis prophylaxis in the context of PTCA (percutaneous transluminal coronary angioplasty).
Interstitial brachytherapy: carcinomas in the cervical lymph nodes, floor of the mouth, cervix uteri (cervix), prostate, or mammary (breast) gland; in low-risk patients.

The procedure

Due to radiation protection reasons, brachytherapy is nowadays performed according to the principle of afterloading (reloading procedure). For this purpose, non-radioactive applicators (e.g., sleeves, tubes, etc.) are first placed in the desired position. After radiographic verification of the correct fit and fixation, the radioactive sources are introduced into or through the applicators by remote control only afterwards. As a result, personnel are outside the irradiation room.

Surface contact therapy: the target volume in this therapy is very superficial, so the radiation only needs to penetrate a few millimeters. The radiation sources are pure beta emitters such as Sr-90 (strontium) preparations or Ru-106 (ruthenium)/Rh-106 (rhodium) emitters with a small gamma fraction (1-2%) and a therapeutic range of approximately 7 mm. As an applicator, small shells are used for application to the eyeball or plastic deformable material from which moulages can be made on the basis of external contours (e.g. skin surface) or internal cavities (e.g. pharyngeal roof) and into which radiation sources can be introduced in afterloading.
Intracavitary therapy: today, the radiation source is usually iridium-192 as a gamma emitter or, more rarely, iodine-125, strontium-90/yttrium-90, and phosphorus-60. The applicators are adapted in shape and size to the respective body cavity (cylinder, egg, pen, plate, etc.) and are first positioned according to the afterloading principle and then remotely loaded with the radioactive source. The dosage of radiation is measured from the mucosal surface to a certain tissue depth. After a radiotherapy session, all applicators are removed from the body again.
Interstitial therapy: radioactive sources are introduced directly into the tumor tissue or its immediate surroundings. As with intracavitary therapy, an applicator (needles/seed therapy or tubing) is placed first and the radiation source is not introduced until the reloading procedure. A distinction is made between temporary (source is removed from the tissue after irradiation) and permanent implantation (source remains in the tissue for life). Today, iodine, palladium-103 or iridium-192 are considered as sources.

Possible complications

Not only tumor cells, but also healthy body cells are damaged by radiotherapy. Therefore, it is always necessary to pay careful attention to radiogenic side effects and to prevent them, if necessary, detect them in time and treat them. This requires a good knowledge of radiation biology, radiation technique, dose and dose distribution as well as permanent clinical observation of the patient. The possible complications of radiotherapy are essentially dependent on the localization and size of the target volume. Prophylactic measures must be taken especially if there is a high probability of side effects occurring. Common complications of radiation therapy:

Intestinal disorders: Enteritides (intestinal inflammation with nausea, vomiting, etc.), strictures, stenoses, perforations, fistulas.
Limitations of the hematopoietic system (blood-forming system), especially leukopenias (decreased number of white blood cells (leukocytes) in the blood compared to the norm) and thrombocytopenias (decreased number of platelets (thrombocytes) in the blood compared to the norm)
Lymphedema
Mucositides (mucosal damage) of the respiratory and digestive tracts.
Pericarditis (inflammation of the pericardium) (6 months to 2 years after therapy).
Radiogenic dermatitis (radiation dermatitis; radiation-induced skin inflammation).
Radiogenic pneumonitis (collective term for any form of pneumonia (pneumonia), which does not affect the alveoli (alveoli), but the interstitium or the intercellular space) or fibrosis.
Radiogenic nephritis (radiation nephropathy; radiation-induced inflammation of the kidneys) or fibrosis.
Secondary tumors (secondary tumors).
Radiation syndromes in the central nervous system (a few months to several years after therapy).
Teleangiectasias (visible dilatations of superficially located small blood vessels).
Tooth and gum damage
Cystitis (inflammation of the urinary bladder), dysuria (difficult emptying of the bladder), pollakiuria (frequent urination).

Other indications

LDR brachytherapy as monotherapy for men with prostate cancer (PC) is performed when the following conditions are present:
- Stage cT1b-T2a, ISUP grade 1 (Gleason 3+3), provided that no more than half of the biopsy punches (specimen collections) are affected, or for ISUP grade 2 (Gleason 3+4), provided that no more than one-third of the punches are positive.
- PSA value of no more than 10 ng/ml and a prostate volume of no more than 50 ml.
- Absence of severe micturition disorders (bladder emptying disorders).
RESULT: After ten years, an estimated 85% of patients treated with LDR brachytherapy are recurrence-free (No recurrence of disease).
Accelerated Partial Breast Irradiation with Interstitial Brachytherapy (APBI-IBT) shortens the several weeks of radiotherapy after breast-conserving surgery from early-stage breast cancer (up to stage IIA) to a few days. The procedure was also not subject in terms of disease-free as well as overall survival.