Pocket Oncology (Pocket Notebook Series), 1st Ed.

BRACHYTHERAPY

Michael R. Folkert and Michael J. Zelefsky

Definition

• Derived from “brachy” meaning “short,” refers to the treatment of targets using radiation sources in close proximity to a target; this allows treatment of a target w/o radiation dose delivery to nl tissues that would be traversed by an external beam.

• Interstitial: Inserted w/in a target

• Contact: Placed close to a target, w/in a natural or surgical cavity, lumen, or vascular route

• The high degree of dose localization depends on the inverse-square law, where the dose rate ↓ w/square of the distance from the source (1/distance2)

Figure 3-1 Permanent low–dose-rate prostate seed implant under TRUS guidance; U/S cradle & template shown w/needles placed through the perineum into the prostate gland.

Figure 3-2 Intracavitary brachytherapy for cervical cancer using ring-and-tandem high–dose-rate applicator; applicator is shown in place in the vagina w/tandem inserted into the uterus.

Sources Used

• Low–dose-rate (LDR) treatments (<12 cGy/h) typically use palladium-103 (Pd-103, T½ = 17 d) or iodine-125 (I-125, T½ = 59.4 d)

• These are generally used for permanent implants

• High–dose-rate (HDR) treatments (>12 cGy/h) use sources such as iridium-192 (Ir-192, T½ = 74 d)

• Uses a remote afterloader & preplaced catheters to guide a physically small, high-activity source to the target rather than direct handling

• Used for temporary implants

• Many other sources exist, including cesium-137, ruthenium-106, radium-226, cobalt-60, & gold-198

Intraoperative Radiation Therapy

• Treatment, generally of a surgical cavity, to sterilize at-risk margins

• Can be performed w/a multichannel HDR applicator & a remote afterloader, solid applicators loaded w/high-activity isotopes such as phosphorus-32 (P-32, T½ = 14.3 d) or yttrium-90 (Y-90, T½ = 64 h)

• Low-energy photon & electron generators have been designed & also have been used, particularly in breast cancer

Complications

• Nl tissues near the brachytherapy source receive very high radiation dose

• Interstitial treatments & many intracavitary treatments require anesthesia & carry risk of bleeding & infxn

• Site-specific examples:

• Breast: Cosmetic changes to breast tissue, fat necrosis

• Prostate: Acute urinary retention (15%), urethral irritation, chronic stricture (4%), proctitis (2%), erectile dysfunction (30%)

• Esophagus: Esophagitis/dysphagia, tracheoesophageal fistula (up to 12%)

• Anorectal: Proctitis, mucosal ulceration

• Bronchial: Fistula (5–10%), hemoptysis (7–22%), stenosis, tracheomalacia

• Gynecologic: Vaginal shortening/stenosis, dyspareunia