GYN Brachytherapy

GYNBrachytherapyHDRCervixVaginal cuffIGABTEQD2D2ccHR-CTVPoint ACylinder
Overview

The brachytherapy part of GYN treatment: an image-guided boost for cervical cancer after pelvic external beam, and vaginal cuff brachytherapy after hysterectomy. The planning concepts here — the high-risk CTV, D90, D2cc and adding doses in EQD2 — are what make GYN brachytherapy different from external beam planning.

Start here: I’m planning my first GYN case — a step-by-step learning roadmap.

Cervix — Insertion & Imaging

After pelvic external beam, applicators are placed in the uterus and vagina and the patient is imaged with them in place. Each insertion is planned on its own images.

Applicators
A tandem with ovoids or a ring, with interstitial needles added when the tumor can't be covered from inside the cavity.

What is it?

An intracavitary applicator — a tandem in the uterus with ovoids or a ring against the cervix — or a hybrid or template-based interstitial implant that adds needles into the tumor and parametria.

Why does it matter?

The choice depends on the anatomy and how much tumor is left after external beam. When the high-risk CTV can't be covered with a tandem and ovoids or ring without exceeding organ limits, adding interstitial needles can improve coverage and reduce organ dose.

Insertion
Under anesthesia, with a Foley catheter, packing to hold the applicator and keep the rectum away, and a fixation device.

What is it?

Usually done under general or spinal anesthesia in lithotomy, after an examination of the residual tumor. A Foley catheter goes into the bladder, the cervix is dilated (often with ultrasound guidance), and the vagina is packed to hold the applicator; a rectal retractor or spatula can add distance from the rectum.

Why does it matter?

Packing and fixation keep the applicator where it was imaged — the plan is only valid if the applicator doesn't move between imaging and treatment. Protocols ask for an applicator check before treatment and re-planning if it has moved.

Image fusion — MRI at brachytherapy
MRI with the applicator in place for at least the first or second insertion; later insertions may be planned on CT using that MRI.

What is it?

Planning images with the applicator in place — CT or MRI, slices 3 mm or less. MRI is suggested for at least the first or second insertion, using T2-weighted images in planes aligned with the applicator; later insertions may be planned on CT with the earlier MRI used as a guide.

Why does it matter?

MRI shows the residual tumor and its relation to the cervix and parametria, which is why the GEC-ESTRO recommendations base the target volumes on it; an NRG consensus atlas compares how the high-risk CTV is drawn on CT and on MRI. Moving the patient between MRI and CT adds uncertainty about applicator and organ position, and one template discourages deformable registration of MRI to CT because it can distort the target.

Applicator reconstruction
The source path is defined in the planning system from the applicator on the images, often with dummy source markers.

What is it?

The channels the source travels through are defined in the planning system, using dummy source markers or the applicator as seen on the images.

Why does it matter?

An error of a few millimeters in where the source dwells moves the high-dose region, and with it the dose to the bladder, rectum and sigmoid. On MRI the applicator can be clearer on some sequences — one template notes T1 images may show less titanium artifact.

Cervix — Target Volumes

Image-guided brachytherapy uses volumes defined at the time of each insertion, not at diagnosis. No planning margin is added.

GTV-res — Residual tumor at brachytherapy

Definition

The macroscopic tumor still present at the time of brachytherapy, from examination and MRI.

Why it matters

Residual tumor carries the highest risk, and EMBRACE II gives it its own dose aim (D98).

Contouring resources

Organ contouring guides →

Relevant protocols

HR-CTV — High-risk CTV

Definition

The residual GTV plus the whole cervix and any presumed tumor extension beyond the cervix at the time of brachytherapy.

Why it matters

The HR-CTV is the volume the brachytherapy dose is prescribed to, and its D90 — the minimum dose to the hottest 90% — is the main measure of the plan.

Contouring resources

Organ contouring guides →

Relevant protocols

IR-CTV — Intermediate-risk CTV

Definition

The HR-CTV with a safety margin, defined at the time of brachytherapy.

Why it matters

It covers tissue that may hold microscopic disease, at a lower dose aim than the HR-CTV.

Contouring resources

Organ contouring guides →

Relevant protocols

Point A — Traditional dose point

Definition

A point defined relative to the applicator — 2 cm up from the cervical os along the tandem and 2 cm to the side — from the era of film-based planning.

Why it matters

Point A is still reported, and some centers still prescribe to it. It doesn't follow the tumor, so with volume-based planning it is a check, not the target.

Contouring resources

Organ contouring guides →

Relevant protocols

Adding External Beam and Brachytherapy

External beam and HDR brachytherapy are given at very different doses per fraction, so their physical doses can't simply be added. Each is converted to EQD2 — the equivalent dose in 2 Gy fractions — and then summed:

EQD2 = D × (d + α/β) / (2 + α/β)

where D is the total dose and d the dose per fraction. Targets use α/β = 10 and organs α/β = 3. The external beam dose is usually counted as its prescription dose, and for organs each brachytherapy fraction's D2cc (the minimum dose to the most exposed 2 cc) is converted and added. Spreadsheets such as the American Brachytherapy Society's dose-equivalence worksheets are commonly used.

As an example from the NRG template, 45 Gy in 25 fractions followed by 4 × 7 Gy HDR gives 83.9 Gy EQD2 at point A, and 50 Gy in 25 followed by 5 × 6 Gy gives 90.0 Gy.

Cervix — Planning Aims & Limits

Totals in EQD2 including 45 Gy in 25 fractions of external beam, from EMBRACE II. Planning aims are what the plan tries to reach; limits are the levels that shouldn't be crossed.

Structure Parameter Planning aim Limit
HR-CTV D90 >90 Gy (and <95 Gy) >85 Gy
HR-CTV D98 >75 Gy —
GTV-res D98 >95 Gy >90 Gy
IR-CTV D98 >60 Gy —
Point A Dose >65 Gy —
Bladder D2cc <80 Gy <90 Gy
Rectum D2cc <65 Gy <75 Gy
Recto-vaginal point Dose <65 Gy <75 Gy
Sigmoid D2cc <70 Gy <75 Gy
Bowel D2cc <70 Gy <75 Gy
  • The NRG cervix template uses the same bladder, rectum and sigmoid D2cc levels as its per-protocol and variation-acceptable criteria, and asks for HR-CTV D90 ≥85 Gy, D98 ≥75 Gy and IR-CTV D98 ≥60 Gy.
  • EMBRACE II notes that sigmoid and bowel D2cc are meaningful only when the loops don't move between fractions.
  • For the vagina, EMBRACE II keeps the 140% isodose out of the vaginal tissue as far as possible.

Source: EMBRACE II, Pötter 2018, Table 4. Organ limits are planning goals; target coverage and organ trade-offs are the physician's decision.

Vaginal Cuff Brachytherapy

After hysterectomy for endometrial cancer, the top of the vagina (the cuff) can be treated with a vaginal cylinder — alone, or as a boost after pelvic external beam.

  • Applicator and imaging. A cylinder (or ovoids) in contact with the vaginal wall. Planning is done on CT, or a standard library plan is used; markers or clips at the apex show whether the applicator sits against the cuff.
  • Prescription point. Either the cylinder surface or 5 mm depth — the same number means a very different dose depending on which is used, so the point is part of the prescription.
  • Length. One template treats 3–5 cm of vagina; another, the upper half or upper 4 cm, whichever is greater.
  • Example schedules (NRG endometrial template): alone, 7 Gy × 3 at 5 mm, 6 Gy × 5 at the surface or 4 Gy × 6 at the surface; as a boost after 45 Gy, 5–6 Gy × 2–3 at 5 mm. The ABS fractionation compendium lists others.
  • Plan check. Dose points along both sides of the cylinder every 2 cm should be within about 10% of the prescription. The NRG template asks for no volumetric organ limits here, given the low toxicity and lack of evidence for cuff constraints, but highly recommends checking the dome position.

Your protocol sets the schedule, the prescription point and the length treated.

Protocols & Literature

Landmark trialSource Verified
The EMBRACE II study: The outcome and prospect of two decades of evolution within the GEC-ESTRO GYN working group and the EMBRACE studies
Pötter R, Tanderup K, Kirisits C, et al. · EMBRACE Collaborative Group / GEC-ESTRO GYN · 2018

The overview of the EMBRACE II study of image-guided IMRT with chemotherapy followed by MRI-based adaptive brachytherapy for locally advanced cervical cancer. It sets out the study's external beam dose constraints (hard and soft, with separate bowel limits when the para-aortic nodes are treated), the brachytherapy planning aims and limits for the high-risk CTV, GTV, point A, bladder, rectum, sigmoid and bowel in total EQD2, and the vaginal dose points. Open access.

View Source Details
Clinical resourceSource Verified
NRG Oncology Protocol Development Template for Radiation Therapy — Gynecological Cancer: Cervix, Uterine Cervix
Lee YC, Benedict SH, Tsai P, Liang X, Padgett K, Portelance L · NRG Oncology Medical Physics Subcommittee / Radiation Oncology Committee · 2024

The template NRG Oncology gives investigators for writing the radiation therapy section of a cervical cancer trial, covering external beam (photon, MR-linac and proton) and brachytherapy. It describes supine or prone setup, full- and empty-bladder simulation scans fused to build an internal target volume, diagnostic MRI and PET/CT fusion, standard structure names (including Spc_Bowel and BoneMarrow), example prescriptions, HDR point A and volume-directed (CTV_HR) brachytherapy, and per-protocol and variation-acceptable compliance criteria for both the external beam plan and the combined EBRT + brachytherapy dose. Its values are examples meant to be edited for each trial. DoseLab's cervix tables quote its per-protocol levels.

View Source Details
Clinical resourceSource Verified
NRG Oncology Protocol Development Template for Radiation Therapy — Gynecological Cancer: Endometrial Cancer (post-operative treatment after hysterectomy)
Lee YC, Kim H, Tsai P, Liang X, Padgett K, Portelance L · NRG Oncology Medical Physics Subcommittee / Radiation Oncology Committee · 2024

The NRG Oncology template for the radiation section of a post-operative endometrial cancer trial. It covers supine or prone setup, vaginal apex markers, full- and empty-bladder scans fused to build the vaginal internal target volume, nodal CTV guidance, standard structure names, example prescriptions (45 or 50.4 Gy), example vaginal cuff brachytherapy schedules alone or as a boost, and per-protocol and variation-acceptable organ goals. For cuff brachytherapy it asks for dose points along the cylinder and verification of the dome position rather than volumetric organ limits. Its values are examples meant to be edited for each trial.

View Source Details
Consensus guidelineUnder Review

The first GEC-ESTRO gynecological working group recommendations, which defined the image-based brachytherapy volumes used today — GTV, high-risk CTV and intermediate-risk CTV — with emphasis on MRI. Citation checked against Europe PMC.

View Source Details
Consensus guidelineUnder Review

The second GEC-ESTRO gynecological recommendations: the dose–volume parameters for image-based cervix brachytherapy (D90 and D100 for the targets, D2cc and D0.1cc for the organs) and how to report them, with notes on radiobiology and EQD2. Citation checked against Europe PMC.

View Source Details
Professional guidelineUnder Review
Compendium of fractionation choices for gynecologic HDR brachytherapy — An American Brachytherapy Society Task Group Report
Albuquerque K, Hrycushko BA, Harkenrider MM, et al. · American Brachytherapy Society · 2019

An American Brachytherapy Society task group report listing published HDR fractionation schedules for gynecologic brachytherapy — cervix, vaginal cuff alone and as a boost, and others — with their EQD2. Citation checked against Europe PMC.

View Source Details
Clinical resourceSource Verified

Endorsed eviQ protocol for the brachytherapy boost in definitive treatment of cervical cancer. It describes the insertion procedure (anesthesia, examination, Foley catheter, ultrasound-guided applicator placement, packing), CT or MRI planning with the GEC-ESTRO MRI sequences, the GTV, high-risk and intermediate-risk CTVs, the traditional ICRU 38 points, HDR schedules of 6–8 Gy in 3–5 fractions to the HR-CTV, and total EQD2 aims for the target and for bladder, rectum, sigmoid and bowel D2cc, most credited to EMBRACE II and GEC-ESTRO. Its review is due 31 December 2026.

View Source Details

All GYN literature →