What is the procedure for performing brachytherapy (internal radiation therapy)?

How to Perform Brachytherapy

Brachytherapy for cervical cancer is performed using an intracavitary approach with an intrauterine tandem and vaginal applicators (ovoids, ring, or cylinder), typically initiated after 40-45 Gy of external beam radiation when sufficient tumor regression permits optimal applicator geometry. 1

Patient Selection and Timing

• Brachytherapy is a critical component of definitive therapy for all patients with intact cervical cancer who are not surgical candidates 1
• Initiate brachytherapy toward the latter part of external beam radiotherapy (EBRT) treatment, after sufficient primary tumor regression has occurred to permit satisfactory applicator geometry 1
• For highly selected very early disease (stage IA2), brachytherapy alone without external beam radiation may be an option 1

Pre-Procedure Planning

Imaging Requirements

• MRI remains the gold standard for soft tissue assessment, with 86% agreement with surgical pathology for tumor size and 71-88% sensitivity for invasion extent 2
• CT-based treatment planning with conformal blocking and dosimetry is considered standard care for external beam component 1
• Real-time transabdominal ultrasound-guided applicator placement is strongly recommended to ensure ideal positioning 3

Treatment Planning Approach

• Perform individual treatment planning for every single applicator insertion to ensure dose accuracy 3
• Initial EBRT of 40-45 Gy to the whole pelvis is necessary to obtain tumor shrinkage before optimal intracavitary placements 1

Applicator Selection and Placement

Standard Intracavitary Technique

• Use an intrauterine tandem combined with vaginal colpostats (ovoids, ring, or cylinder) based on patient and tumor anatomy 1
• The vaginal component selection depends on anatomical factors and tumor extent 1
• Applicator reconstruction is easier on CT than MRI because the applicator image is more clearly visible 3

Alternative Approaches

• Interstitial brachytherapy should only be used in rare cases when tumor geometry renders intracavitary brachytherapy infeasible, and only by individuals and institutions with appropriate experience and expertise 1
• For posthysterectomy patients with positive vaginal mucosal surgical margins, vaginal cylinder brachytherapy may be used as a boost to EBRT 1

Dosing Parameters

Point A Dosing System (Standard)

• Total doses from brachytherapy and external beam radiation to point A must reach at least 80 Gy for small tumors and ≥85 Gy for larger tumors 1, 2
• The point A dosing system remains the standard based on extensive experience and tumor control results 1
• When implementing 3D image-guided approaches, traditional point A dosing must not be abandoned to avoid underdosing tumors 1, 2

Dose Rate Options

Low-Dose-Rate (LDR) - Standard:

• Delivery at 40-70 cGy/hour remains the standard approach 1
• No survival advantage has been demonstrated for high-dose-rate compared to low-dose-rate delivery 1

High-Dose-Rate (HDR) - Common Alternative:

• One common HDR approach uses 5 insertions with tandem and colpostats, each delivering 6 Gy nominal dose to point A 1
• This results in a nominal HDR point A dose of 30 Gy in 5 fractions, generally accepted as equivalent to 40 Gy using LDR 1
• HDR uses radionuclides at dose rates of 20 cGy per minute (12 Gy per hour) or more 4
• Use the linear-quadratic model equation to convert nominal HDR dose to biologically equivalent LDR dose 1

Treatment Delivery Sequence

Integration with External Beam

• Complete the entire radiation course (including both external beam and brachytherapy components) within 8 weeks 1
• Extending treatment beyond 6-8 weeks results in approximately 0.5-1% decrease in pelvic control and cause-specific survival for each extra day 1
• Avoid delays or splits in radiation treatment whenever possible 1

Concurrent Chemotherapy

• For most patients receiving EBRT for cervical cancer, administer concurrent cisplatin-based chemotherapy (either cisplatin alone or cisplatin + 5-fluorouracil) during EBRT 1

Image-Guided Brachytherapy Considerations

3D Planning Advantages

• Current 3D image-guided techniques optimize implant dose coverage of tumor while potentially reducing dose to adjacent bladder, rectum, and bowel structures 1
• Image-based brachytherapy improves tumor coverage (especially for large volume disease) and decreases dose to critical organs 5
• Confirmation of applicator placement and accounting for sigmoid colon dose are key advantages 5

Critical Caution

• Highly conformal external beam therapies (such as IMRT) should not be used as routine alternatives to brachytherapy for treatment of central disease in patients with an intact cervix 1
• Attempts to improve dosing with image-guided brachytherapy must take care not to underdose tumors relative to the point A system dose recommendations 1

Dosimetry Standards

• Use dosimetry according to International Commission of Radiation Units recommendations 1
• Calculate doses at standardized point A, point B, and bladder and rectal points 1
• For limited-stage disease, the combination of external radiotherapy/brachytherapy must deliver a total dose of 60 Gy to the central pelvis and 45-50 Gy to the lateral pelvic area 1

Special Anatomical Considerations

• For lesions in the lower third of the vagina, the inguinal lymph nodes must be treated 1
• When ovaries are conserved, mark them with radio-opaque labels at the time of surgery for potential shielding during postoperative radiotherapy 1
• The inferior radiation limit depends on vaginal involvement, with a minimal safe margin of 4 cm below the lowest tumor level 1