What is brachytherapy (internal radiation therapy) in the treatment of cervical cancer?

What is Brachytherapy in Cervical Cancer

Brachytherapy is a form of internal radiation therapy that involves precise placement of radioactive sources directly into or adjacent to the cervical tumor, and it is a critical, non-negotiable component of definitive radiotherapy for all cervical cancer patients with an intact cervix who are not surgical candidates. 1, 2, 3

Definition and Technical Approach

Brachytherapy delivers extremely high doses of radiation (>80-90 Gy total when combined with external beam) directly to the tumor while minimizing exposure to surrounding normal tissues. 1, 2 The technique typically uses an intracavitary approach with an intrauterine tandem combined with vaginal applicators (colpostats, ovoids, ring, or cylinder), depending on patient and tumor anatomy. 1, 2

Role in Treatment Strategy

Primary Definitive Treatment

• Brachytherapy combined with external beam radiotherapy (EBRT) is the standard of care for locally advanced cervical cancer (stages IB2-IV) and for early-stage patients who are not surgical candidates. 1, 2
• The combination achieves superior outcomes compared to EBRT alone, with significantly better primary remission rates (92.5% vs 73.3%), 5-year cancer-specific survival (68.5% vs 35.4%), and lower recurrence rates (31.3% vs 37.2%). 4
• Conformal external beam techniques like IMRT or SBRT should never be used as routine alternatives to brachytherapy for central disease in patients with an intact cervix, as this compromises survival. 1, 3

Specific Stage-Based Applications

• Stage IA2: Brachytherapy alone (without external beam) may be used as sole treatment in highly selected cases, or when surgery is contraindicated. 1, 2
• Stages IB-IIA (<4 cm): Brachytherapy can be sole radiotherapy for tumors <4 cm when anatomical conditions are appropriate, with external beam directed only to lateral pelvic regions. 1
• Stages IB2-IV: Brachytherapy is combined with pelvic EBRT (40-46 Gy) and concurrent cisplatin-based chemotherapy. 1, 2

Post-Surgical Setting

• Vaginal cylinder brachytherapy may be used as a boost to EBRT in selected post-hysterectomy patients, particularly those with positive vaginal mucosal surgical margins. 1, 5

Critical Dosing Parameters

Total Dose Requirements

• Point A must receive at least 80 Gy for small tumors and ≥85 Gy for larger tumors from the combined EBRT and brachytherapy. 2
• For limited-stage disease, the combination must deliver 60 Gy to the central pelvis and 45-50 Gy to the lateral pelvic area. 2
• The point A dosing system remains the standard based on extensive validation and tumor control results. 1, 2

Timing Imperatives

• The entire radiation course (EBRT plus brachytherapy) must be completed within 8 weeks, as extending beyond 6-8 weeks results in approximately 0.5-1% decrease in pelvic control and survival for each extra day of delay. 2
• Brachytherapy is typically initiated toward the latter part of EBRT, after sufficient tumor regression permits satisfactory applicator geometry. 1, 2

Technical Delivery Methods

Low-Dose-Rate (LDR) vs High-Dose-Rate (HDR)

• Traditional LDR brachytherapy delivers 40-70 cGy/hour. 1
• HDR brachytherapy uses multiple fractions (commonly 5 insertions with tandem and colpostats) with biologically equivalent dosing based on linear-quadratic model conversions. 1
• HDR at 9 Gy/fraction in 2-5 fractions has demonstrated safety and efficacy with 5-year local control of 74.5% and disease-free survival of 62%, with Grade 3+ late toxicity risk of only 3.31%. 6

Image-Guided Approaches

• 3D image-guided adaptive brachytherapy is evolving as the preferred method, using CT or MRI to optimize tumor coverage while reducing dose to bladder, rectum, and bowel. 2, 3, 7
• MRI remains the gold standard for soft tissue assessment with 86% agreement with surgical pathology for tumor size. 2
• Critical caveat: When implementing image-guided techniques, traditional point A dosing must not be abandoned to avoid underdosing tumors. 1, 2

Special Circumstances

Interstitial Brachytherapy

• In rare cases where tumor geometry renders intracavitary brachytherapy infeasible, interstitial brachytherapy may be used, but only by individuals and institutions with appropriate experience and expertise. 1, 2

Contraindications to Standard Approach

• When positive lymph nodes or parametrial invasion are present, vaginal brachytherapy alone is NOT appropriate—these patients require concurrent cisplatin-based chemoradiation with EBRT, with brachytherapy potentially added as a boost. 5

Evidence Base and Survival Impact

The importance of brachytherapy is supported by Level I evidence showing that omitting brachytherapy significantly compromises outcomes. 4, 3 The decline in brachytherapy use has been associated with negative impacts on survival even in the era of modern EBRT techniques. 3 Brachytherapy improves overall survival as an integral part of definitive radiotherapy, particularly when combined with concurrent chemotherapy for locally advanced disease. 8, 7