Image-guided brachytherapy ties applicator choice, HRCTV contouring, and dose prescription to findings seen at the time of implantation. For a broader view of the topic, read our Target Volume Delineation and Field Setup – Complete Clinical Guide.
This article stays with the chapter’s practical workflow for cervix, endometrium, vagina, and vulva. If you want to compare the brachytherapy boost with whole pelvic external beam coverage, our dedicated article on definitive gynecologic target delineation is the most relevant companion piece.
General principles of image-guided brachytherapy
The chapter starts from a straightforward position: staging has to be complete before planning can be precise. Every patient should have a history, physical examination with pelvic exam, and radiographic workup with contrast-enhanced CT, PET/CT, and/or pelvic MRI to define local extent and metastatic spread.
Applicator choice is driven by histopathology, tumor size, topography, extension to nearby organs, and response to radiotherapy or chemoradiotherapy when applicable. Planning and delivery are anchored in American Brachytherapy Society and GEC-ESTRO guidance. For cervical and uterine cancer, brachytherapy remains the standard central boost technique; SBRT is restricted to clinical trials or patients who refuse brachytherapy. The chapter also insists on counseling about long-term toxicity, vaginal dilator use when needed, and multidisciplinary follow-up.
Cervical cancer
In definitive cervical treatment, brachytherapy improves local control, disease-free survival, and overall survival. It should start during weeks 3 to 5 of EBRT, and the total treatment time should stay at 56 days or less.
Initial evaluation and applicator choice
The initial workup includes full history and physical examination plus CBC and chemistry panels with liver function tests, BUN, and creatinine. Imaging at diagnosis includes contrast-enhanced CT of the chest, abdomen, and pelvis, whole-body PET/CT, and pelvic MRI with cystoscopy and/or sigmoidoscopy when bladder or rectal invasion is a concern. For tumors larger than 4 cm, pelvic MRI is also recommended for brachytherapy planning.
Applicator selection follows tumor size, parametrial extension, and vaginal extension. Intracavitary alone fits tumors smaller than 4 cm with less than 1 cm of vaginal involvement and non-bulky parametrial disease. Hybrid intracavitary-interstitial treatment is used for tumors 3 to 5 cm, parametrial disease, irregular topography, or difficulty meeting OAR constraints. Interstitial alone is reserved for tumors larger than 5 cm, vaginal involvement greater than 1 cm, bulky parametrial disease, or persistent OAR limitation. Transabdominal or transrectal ultrasound can guide tandem placement, and transrectal ultrasound is also useful when a tandem tract must be created or needles must be guided. If a fistula already exists, the chapter recommends considering diverting nephrostomy tubes for vesicovaginal fistula and diversion before radiation for rectovaginal fistula.
Implant evaluation
Three-dimensional planning after insertion requires thin-slice CT or MRI with the applicator in place. The tandem should sit in the cervix and uterus; a ring should be flush against the cervix; ovoids should be bisected by the tandem; and vaginal packing should not displace the device. Whenever interstitial needles are used, coverage and distance from critical structures must be reviewed before treatment is approved.
Volume delineation
The practical split in the chapter is clear: CT often overestimates disease extent, while MRI allows actual GTV definition. If the uterus is involved, full uterine dose coverage is required. In postoperative cervical cancer with a positive vaginal margin, the upper third of the vagina should be treated.
Table 22.1. Target volumes and OARs for intact cervix brachytherapy
This table lays out how the chapter defines GTV, HRCTV, IRCTV, and the key organs at risk that must be contoured during 3D planning for intact cervical cancer.
| Structure | Description |
|---|---|
| GTV | Macroscopic tumor at the time of brachytherapy seen on MRI. |
| HRCTV | GTV, cervix, macroscopic extension, or parametrial involvement at the time of brachytherapy. |
| IRCTV(3) | HRCTV + 1 cm margin; it can include the initial disease extension at diagnosis, often used in Europe and less commonly used in the United States. |
| Bladder | Contour the outer bladder wall. |
| Rectum | Contour the outer rectal wall from above the anal sphincter to the level of transition into the sigmoid. |
| Sigmoid | Contour the outer sigmoid wall from the rectosigmoid flexure to 2 cm superior to the uterus and parametria. |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.1)
The figure below shows the multimodality logic behind the chapter: PET/CT, pelvic MRI, applicator geometry, and dose distribution reviewed together.
Treatment planning
The chapter lists common HDR schedules for intact cervix cases and pairs them with explicit dosimetric goals. In the postoperative setting with a positive vaginal margin, the usual sequence is 45 Gy in 25 fractions of EBRT followed by vaginal cuff brachytherapy to 15 Gy in 3 fractions prescribed to the surface of the upper vagina.
Table 22.2. Common HDR schedules for intact cervical cancer
These schedules combine 45 Gy of EBRT with HDR brachytherapy and show dose per fraction, total HRCTV dose, and the resulting EQD2.
| Total EBRT (Gy) | # HDR fractions | HRCTV dose per fraction (Gy) | Total HRCTV dose (Gy) | Total HRCTV EQD2 (Gy) |
|---|---|---|---|---|
| 45 | 4 | 7.0 | 28.0 | 83.9 |
| 45 | 5 | 5.5 | 27.5 | 79.8 |
| 45 | 5 | 6 | 30 | 81.8 |
| 45 | 3 | 8.0 | 24.0 | 80.3 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.2)
Dose contribution from EBRT is assumed to be the prescription dose of 45 Gy, and doses are cumulative. EQD2 (α/β = 10 for target, α/β = 3 for normal tissues) for HDR and physical doses for PDR/LDR.
Table 22.3. Dose goals for cervical targets and OARs
The chapter keeps the planning focus on adequate HRCTV coverage while still enforcing bladder, rectum, and sigmoid constraints.
| Structure | Dosimetric parameter | Ideal EQD2 goal (Gy) | Maximum EQD2 constraint (Gy) |
|---|---|---|---|
| HRCTV | D90% | ≥80 | – |
| Bladder | D2cc | ≤80 | ≤90 |
| Rectum | D2cc | ≤65 | ≤75 |
| Sigmoid | D2cc | ≤70 | ≤75 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.3)
Endometrial cancer
For endometrial cancer, brachytherapy is used in postoperative adjuvant treatment, medically inoperable disease, and recurrent disease. Upfront surgery remains standard for operable patients, and lymph node assessment should be considered in grade 2 to 3 disease, gross intraoperative disease larger than 2 cm, or myometrial invasion greater than 50%.
Postoperative adjuvant treatment
Adjuvant radiotherapy lowers the risk of local recurrence in patients with adverse pathologic features such as high-grade disease, deep myometrial invasion, cervical stromal extension, LVSI, and regional nodal involvement. Vaginal brachytherapy should start within 12 weeks of surgery and only after pelvic examination confirms cuff healing. When brachytherapy is used as a boost after EBRT, it should begin within 2 weeks after EBRT finishes.
Clinical stage I patients do not require routine imaging workup, but patients with locally advanced disease should undergo contrast-enhanced CT of the chest, abdomen, and pelvis. Implant evaluation uses thin-slice CT with the applicator. The vaginal cylinder should be the largest diameter the patient tolerates, it must sit flush with the cuff apex, and it must achieve mucosal contact while vaginal length is verified.
For target definition, brachytherapy alone treats the upper third to upper half of the vagina depending on tumor features. After EBRT, the same upper third to upper half of the vagina remains the target.
Table 22.4. Adjuvant treatment recommendations for endometrial cancer
The adjuvant algorithm changes according to AJCC stage, grade, LVSI, pelvic lymph node dissection, and cervical involvement before deciding on chemotherapy, pelvic EBRT, and brachytherapy.
| AJCC stage | Grade | LVSI | PLND | Cervical involvement | Chemo | Pelvic EBRT | Brachytherapy |
|---|---|---|---|---|---|---|---|
| IA | 1 | Any | Any | N/A | No | No | No |
| IA | 2 | No | Any | N/A | No | No | No |
| IA | 2 | Yes | Any | N/A | No | No | Yes |
| IA | 3-Adeno | Any | Any | N/A | No | Noa | Yes |
| IA | 3-PS/CC | Any | Any | N/A | No/Yes | Yes | No |
| IA | 3-PS/CC | Any | Any | N/A | Yes | No | Yes |
| IB | 1 | No | Any | N/A | No | No | No |
| IB | 1 | Yes | Any | N/A | No | No | Yes |
| IB | 2 | No | Any | N/A | No | No | Yes |
| IB | 2 | Yes | Any | N/A | No | No | Yes |
| IB | 3-Adeno | No | Any | N/A | No | Noa | Yes |
| IB | 3-Adeno | Yes | Any | N/A | No | Yes | No |
| IB | 3-PS/CC | Any | Any | N/A | Yes | Yes | No |
| IB | 3-PS/CC | Any | Any | N/A | Yes | No | Yes |
| II | 1-2 | No | No | Yes | No | No | Yes |
| II | 1-2 | Yes | No | Yes | No | Yes | Yes |
| II | 1-2 | No | Yes | Yes | No | No | Yes |
| II | 1-2 | Yes | Yes | Yes | No | No | Yes |
| II | 3-Adeno | Any | Any | Yes | No | Yes | Yes |
| II | 3-PS/CC | Any | Any | Yes | Yes | No | Yes |
| II | 3-PS/CC | Any | Any | Yes | Yes | Yes | Yes |
| IIIA | 1 | Any | Any | No | Yes | No/Yes | No |
| IIIA | 1 | Any | Any | Yes | Yes | Yes | Yes |
| IIIA | 2-3 | No | Any | No | Yes | Yes | No |
| IIIA | 2-3 | Yes | Any | Any | Yes | Yes | Yes |
| IIIA | 2-3 | Any | Any | Yes | Yes | Yes | Yes |
| IIIB | Any | Any | Any | Any | Yes | Yes | Yes |
| IIIC1 | 1 | Any | Any | No | Yes | Yes | No |
| IIIC1 | 1 | Any | Any | Yes | Yes | Yes | Yes |
| IIIC1 | 2-3 | No | Any | No | Yes | Yes | No |
| IIIC1 | 2-3 | Yes | Any | Any | Yes | Yes | Yes |
| IIIC1 | 2-3 | Any | Any | Yes | Yes | Yes | Yes |
| IIIC2 | 1 | Any | Any | No | Yes | N/A | No |
| IIIC2 | 1 | Any | Any | Yes | Yes | N/A | Yes |
| IIIC2 | 2-3 | No | Any | No | Yes | N/A | No |
| IIIC2 | 2-3 | Yes | Any | Any | Yes | N/A | Yes |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.4)
LVSI = lymphovascular space invasion; PLND = pelvic lymph node dissection; PS = papillary serous histology; CC = clear cell histology. EFRT depends on uterine risk factors and lymph node status or risk of involvement. a Denotes patients eligible for GOG 249, and pelvic RT should be considered.
Table 22.5A. Vaginal cuff brachytherapy alone schedules
For postoperative treatment, the chapter separates schedules prescribed at 0.5 cm depth from schedules prescribed at the vaginal surface.
| Prescription point | # fractions | Dose per fraction (Gy) |
|---|---|---|
| 0.5 cm depth from the vaginal surface | 3 | 7 |
| 0.5 cm depth from the vaginal surface | 4 | 5.5 |
| 0.5 cm depth from the vaginal surface | 5 | 5 |
| 0.5 cm depth from the vaginal surface | 6 | 2.5 |
| Vaginal surface | 4 | 8.5 |
| Vaginal surface | 5 | 6 |
| Vaginal surface | 6 | 4 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.5A)
Table 22.5B. Vaginal cuff boost schedules after EBRT
When brachytherapy is used as a boost after EBRT, the prescription stays at the surface and the number of HDR fractions decreases.
| EBRT dose and fractionation | Prescription point | # HDR fractions | Dose per fraction (Gy) |
|---|---|---|---|
| 45 Gy in 25 fractions | Surface | 3 | 5 |
| 50.4 Gy in 28 fractions | Surface | 2 | 6 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.5B)
Medically inoperable endometrial cancer
When surgery is not an option, definitive radiotherapy with brachytherapy, with or without EBRT, is the standard approach. EBRT alone is specifically not preferred and should only be offered if the patient refuses brachytherapy or cannot receive it.
Baseline pelvic MRI is recommended to determine the full extent of disease. Patients with uterine width below 4 cm may be treated with tandem and cylinder or tandem and ring; above 4 cm, a double tandem applicator is required. Thin-slice CT with the applicator remains the planning study, and the tandem position has to be checked carefully, especially when double tandems are meant to reach the bilateral cornua.
MRI should guide GTV delineation, and the CTV should include the entire uterus, cervix, and upper 1 to 2 cm of vagina. In practice, that keeps uterine disease from being undercovered when the cavity is broad or irregular.
Table 22.6. Definitive radiotherapy for inoperable uterine cancer
For medically inoperable uterine cancer, the chapter keeps brachytherapy at the center of definitive treatment and adjusts EBRT according to stage and grade.
| AJCC stage | Grade | EBRT | Brachytherapy |
|---|---|---|---|
| I | 1 | No | Yes |
| I | 2-3 | Yes | Yes |
| II | Any | Pelvic RT | Yes |
| IIIC1 | Any | Pelvic RT | Yes |
| IIIC2 | Any | EFRT | Yes |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.6)
Table 22.7A. Brachytherapy-alone schedules for inoperable uterine cancer
These brachytherapy-alone regimens show how different fractionation patterns can reach a similar biological dose range.
| # HDR fractions | Dose per fraction (Gy) | EQD2 (Gy) |
|---|---|---|
| 4 | 8.5 | 52.4 |
| 5 | 8 | 60 |
| 5 | 7.3 | 52.6 |
| 6 | 6.4 | 52.5 |
| 6 | 6 | 48 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.7A)
Table 22.7B. Brachytherapy boost schedules after EBRT for inoperable uterine cancer
Once EBRT is delivered, these combinations are used to bring the final EQD2 into the definitive range described in the chapter.
| EBRT dose and fractionation | # HDR fractions | Dose per fraction (Gy) | EQD2 (Gy) |
|---|---|---|---|
| 45 Gy in 25 fractions | 2 | 8.5 | 70.5 |
| 45 Gy in 25 fractions | 3 | 6.5 | 71.1 |
| 45 Gy in 25 fractions | 3 | 6.3 | 69.9 |
| 45 Gy in 25 fractions | 4 | 5.2 | 70.6 |
| 45 Gy in 25 fractions | 5 | 5 | 75 |
| 50.4 Gy in 28 fractions | 2 | 6 | 65.6 |
| 50.4 Gy in 28 fractions | 6 | 3.75 | 75.3 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.7B)
For combined treatment, the chapter cites EBRT to 45 Gy in 25 fractions and a total EQD2 goal of 70 to 80 Gy. In previously irradiated patients with vaginal recurrence, salvage surgery may be considered, but if surgery is not feasible the chapter describes reduced-dose EBRT of 30.6 to 36 Gy in 17 to 20 fractions plus brachytherapy with or without chemotherapy. For non-vaginal pelvic recurrence after prior pelvic radiation, reduced-dose EBRT and/or SBRT with or without chemotherapy is the listed option.
Vaginal cancer
For vaginal cancer, brachytherapy as part of definitive organ-preserving treatment improves overall survival. Definitive radiation is preferred in stage I disease, with surgery reserved for selected non-bulky distal non-urethral cases, while definitive chemoradiation is preferred for stage II to IVA disease.
Initial evaluation and applicator choice
The basic workup again includes history, physical examination, CBC, chemistry, liver function tests, BUN, and creatinine. Imaging consists of contrast-enhanced CT of the chest, abdomen, and pelvis for initial staging and pelvic MRI, with cystoscopy and/or sigmoidoscopy when bladder or rectal invasion is suspected. Interstitial brachytherapy is the standard approach, except in very small tumors with thickness of 5 mm or less, where intracavitary applicators may be considered.
Transrectal ultrasound can guide needle placement and help avoid bowel puncture. At the end of an interstitial procedure, digital rectal examination should confirm that no catheter has perforated the rectum.
Implant evaluation and volume delineation
Three-dimensional planning uses thin-slice CT or MRI with the applicator in place. Diluted contrast may be placed in the bladder and rectosigmoid region to improve organ visualization. If needles are used, coverage and distance from rectum and bowel must be reviewed before treatment proceeds.
Pelvic MRI helps determine superior and paravaginal extent. Target volumes depend on initial disease involvement, treatment response, and whether the disease is multifocal or discontinuous.
Table 22.8. Target volumes and OARs for primary vaginal cancer
For vaginal cancer, the HRCTV expands laterally, inferiorly, and superiorly, while the IRCTV incorporates microscopic vaginal extension and the full initial disease extent.
| Structure | Description |
|---|---|
| GTV | Macroscopic tumor at the time of brachytherapy seen on MRI. |
| HRCTV | GTV + 1 cm margin in lateral, inferior, and superior directions. |
| IRCTV | HRCTV + microscopic extension in the vagina, including all initial disease. |
| Bladder | Contour the outer bladder wall. |
| Rectum | Contour the outer rectal wall from above the anal sphincter to the level of transition into the sigmoid. |
| Sigmoid | Contour the outer sigmoid wall from the rectosigmoid flexure to 2 cm superior to the uterus and parametria. |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.8)
Treatment planning
The total dose goal is 70 to 80 Gy, adjusted to vaginal location and nearby normal structures such as the urethra. The chapter gives a practical split: proximal vagina may receive 75 to 80 Gy, while distal vagina should be reduced to 70 to 75 Gy. In multifocal or discontinuous spread, treating the full vaginal length to an equivalent dose of 60 Gy and boosting gross residual disease to 70 to 80 Gy is considered reasonable.
Table 22.9. Common schedules for primary vaginal cancer
The final dose depends on EBRT fractionation and brachytherapy dose per fraction, but the planning aim is consistent: bring the HRCTV to the intended biological range.
| EBRT dose and fractionation | # HDR fractions | HRCTV dose per fraction (Gy) | HRCTV EQD2 (Gy) |
|---|---|---|---|
| 45 Gy in 25 fractions | 3 | 7 | 74.1 |
| 45 Gy in 25 fractions | 4 | 6 | 76.3 |
| 45 Gy in 25 fractions | 5 | 4.5-5.5 | 71.5-79.8 |
| 45 Gy in 25 fractions | 9 | 3 | 76.8 |
| 45 Gy in 25 fractions | 10 | 3 | 73.6 |
| 50.4 Gy in 28 fractions | 3 | 7 | 79.4 |
| 50.4 Gy in 28 fractions | 5 | 4-5 | 72.9-80.9 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.9)
Table 22.10. Dose goals for primary vaginal cancer
The chapter explicitly separates the HRCTV target for the lower third of the vagina from the upper two thirds while keeping conservative bladder, rectum, and sigmoid limits.
| Structure | Dosimetric parameter | Ideal EQD2 goal (Gy) | Maximum EQD2 constraint (Gy) |
|---|---|---|---|
| HRCTV | D90% | Lower third of vagina: 70-75 Upper two thirds of vagina: 75-80 |
– |
| Bladder | D2cc | ≤80 | ≤90 |
| Rectum | D2cc | ≤65 | ≤75 |
| Sigmoid | D2cc | ≤75 | ≤75 |
Source: Target Volume Delineation and Field Setup, 2nd Edition (Table 22.10)
Vulvar cancer
For vulvar disease, brachytherapy is not presented as a routine standalone solution. Concurrent chemoradiotherapy is the preferred approach for stage II to IVA disease, with consideration of a brachytherapy boost in patients who have vaginal extension or tolerate the initial EBRT phase poorly. In stage I disease, brachytherapy is not standard except in medically inoperable patients.
