Post-Operative Radiation Therapy Contouring Guidelines for Endometrial Carcinoma

Risk Stratification Determines RT Approach and Volumes

The American College of Radiology and other guideline societies recommend that target volume contouring for post-operative radiation therapy in endometrial carcinoma should be risk-adapted, with vaginal brachytherapy alone for intermediate-risk disease and external beam pelvic radiation for high-risk or stage II disease, with consideration for combined modality in stage IIB or high-risk features 1, 2
For low-risk disease, such as Stage IA, Grade 1-2 endometrioid histology with <50% myometrial invasion and no adverse features, observation only is recommended, with no radiation therapy contouring needed 1, 2, 3, 4
For intermediate-risk disease, such as Stage IA-IB with Grade 2-3, or deep myometrial invasion, vaginal brachytherapy alone is warranted, with a target volume that includes the vaginal cuff plus 2-3 cm of proximal vagina 1, 2, 5
The PORTEC-2 trial demonstrated equivalent pelvic control with vaginal brachytherapy compared to external beam RT but with significantly less toxicity, with a typical prescription of 21 Gy in 3 fractions or 15 Gy in 2 fractions to 5mm depth 1, 5, 2

For Stage IIB (cervical stromal invasion) or high-risk Stage I disease, external beam pelvic radiation is indicated, with a clinical target volume (CTV) that should encompass the entire pelvic nodal regions, including common iliac, external iliac, internal iliac, obturator, and presacral nodes 1, 3, 4, 6, 5
The CTV should also include the vaginal cuff and upper 3-4 cm of vagina, as well as parametrial tissues, with an upper border typically at L4-L5 or L5-S1 interspace to cover common iliac nodes 6, 5
A planning target volume (PTV) should be created by adding a 7-10 mm margin to the CTV for setup uncertainty and organ motion, with a typical dose prescription of 45-50.4 Gy in 1.8-2.0 Gy fractions 6, 5, 2

Organs at risk (OARs) to contour include the bladder, rectum, sigmoid colon, small bowel, femoral heads, and bone marrow, with dose constraints of rectum V40Gy <60%, bladder V45Gy <50%, and small bowel V45Gy <200cc 2
Common pitfalls to avoid include inadequate superior coverage, excessive vaginal length in brachytherapy, omitting vaginal boost in Stage IIB, using whole abdominal RT, and overtreatment of low-risk patients 6, 5, 2, 4, 1

The PORTEC-1 and PORTEC-2 trials established that vaginal brachytherapy alone provides equivalent pelvic control to external beam RT for intermediate-risk disease with significantly less toxicity, with a strength of evidence of high 1, 5
The PORTEC-3 trial demonstrated improved 5-year overall survival with chemoradiotherapy versus RT alone for high-risk endometrial cancer, with a strength of evidence of high 2