Radioactive Implants (Brachytherapy): How They Treat Cancer

Principle

Brachytherapy places sealed radioactive sources (seeds, wires, catheters) directly into or adjacent to a tumor, delivering a high radiation dose to the target while sparing surrounding normal tissue via rapid dose falloff (inverse square law).

Common Isotopes

• Iodine-125 (I-125): Low energy (28 keV), half-life 60 d – permanent prostate seeds.
• Palladium-103 (Pd-103): Similar to I-125, shorter half-life (17 d).
• Cesium-137 (Cs-137): Higher energy (662 keV), half-life 30 y – temporary intracavitary (gynecologic).
• Iridium-192 (Ir-192): High dose rate (HDR) – temporary interstitial (breast, prostate, head/neck).

Procedure Types

• Permanent (LDR): Seeds implanted (e.g., prostate); remain forever, decay to background.
• Temporary (LDR/HDR): Applicators placed, sources loaded for calculated time, then removed.

Advantages

• Highly conformal dose distribution.
• Minimally invasive (percutaneous or intracavitary).
• Shorter overall treatment time (HDR: minutes per fraction).
• Organ preservation (e.g., breast, prostate, cervix).

Clinical Uses

Prostate, cervical, endometrial, breast, head/neck, skin, sarcoma. Often combined with EBRT.

Patient may require brief hospitalization (LDR) or outpatient visits (HDR). Radiation safety protocols protect staff/family.