What does brachytherapy use to treat cancer?

Brachytherapy Uses Radioactive Isotopes to Treat Cancer

Brachytherapy primarily uses radioactive isotopes such as iodine-125, palladium-103, iridium-192, and cesium-137 to deliver targeted radiation directly into or adjacent to tumor tissue for cancer treatment. 1, 2

Types of Radioactive Sources Used in Brachytherapy

Brachytherapy involves the precise placement of radioactive sources either directly into or next to tumor tissue. The choice of isotope depends on the cancer type, treatment goals, and delivery method:

Common Isotopes

• Iodine-125 (125I): Commonly used for permanent prostate implants; emits lower energy photons 1, 3
• Palladium-103 (103Pd): Used for permanent prostate implants; shorter half-life than iodine-125 1, 3
• Iridium-192 (192Ir): Higher energy photons; typically used for temporary implants 3, 4
• Cesium-137 (137Cs): Traditional source for various applications 3, 4

Delivery Methods

1. Low-Dose Rate (LDR) Brachytherapy:

   • Permanent implantation of radioactive seeds (typically iodine-125 or palladium-103)
   • Commonly used for prostate cancer 1, 3
   • Seeds remain in the body and decay over time

2. High-Dose Rate (HDR) Brachytherapy:

   • Temporary placement of radioactive sources
   • Can be used as a boost with external beam radiation therapy
   • Recommended for intermediate and high-risk prostate cancer patients 1

Clinical Applications

Brachytherapy is indicated for multiple cancer types based on high-level evidence:

• Prostate Cancer:

  • Low-risk: LDR brachytherapy alone is an effective treatment option 1
  • Intermediate-risk: Brachytherapy boost (LDR or HDR) with external beam radiation therapy 1
  • High-risk: Brachytherapy boost with external beam radiation and androgen-deprivation therapy 1

• Other Cancer Sites:

  • Cervical cancer: Standard treatment in combination with chemoradiation 2
  • Endometrial cancer: Reduces risk of vaginal vault recurrence 2
  • Breast cancer: Used for tumor bed boost or accelerated partial breast irradiation 2
  • Head and neck cancers: Used for certain tumor locations 2, 3

Isotope Selection Considerations

When selecting an isotope for brachytherapy, several factors are considered:

• Energy level: Lower energy photons (like iodine-125) are easier to shield but have less tissue penetration 4
• Half-life: Longer-lived isotopes can be reused, while shorter-lived ones may provide higher initial dose rates 4
• Cancer type and location: Different isotopes are optimal for different treatment sites
• Treatment intent: Permanent vs. temporary implantation 5

Specific Isotope Recommendations

For prostate cancer specifically, the American Society of Clinical Oncology/Cancer Care Ontario guideline states:

• Iodine-125 and palladium-103 are both reasonable isotope options for patients receiving LDR brachytherapy 1
• No definitive recommendation can be made for or against using cesium-131 or HDR monotherapy 1

Technical Considerations

Brachytherapy requires specialized expertise and equipment:

• Waterproof gloves and adequate shielding must be maintained during handling 6
• Modern techniques use transrectal ultrasound, CT imaging, and computerized dosimetry systems for precise placement 5
• The procedure may be performed as outpatient treatment with high patient acceptance 5

Pitfalls and Caveats

• Patient selection is critical for successful outcomes; poor selection can lead to suboptimal results 5
• Adequate coverage of the entire target volume is essential; inconsistent coverage was a historical problem 5
• Radiation safety protocols must be strictly followed when handling radioactive materials 6, 3
• Different isotopes have unique characteristics that must be matched to the specific clinical situation 4

Brachytherapy's main advantage is its ability to deliver very high radiation doses to the tumor while minimizing exposure to surrounding normal tissues, potentially improving the therapeutic ratio compared to external beam radiation alone 2, 4.