Radiotherapy for Cervical Cancer: An Introduction to ASTRO’s Clinical Practice Guideline

The Role of IMRT

For postoperative (adjuvant) RT with or without concurrent chemotherapy, IMRT is strongly recommended because it can reduce the risks of acute and chronic treatment toxicity, according to the ASTRO guideline.But for women undergoing definitive RT (with or without chemotherapy), IMRT is only conditionally recommended to reduce toxicity risks.

The evidence base is equivocal for optimal IMRT roles in some settings. There is no available evidence that IMRT improves disease-specific survival or overall survival compared with 2-dimensional or 3-D conformal RT, according to the guideline. But limited prospective randomized clinical trial data and a meta-analysis suggest decreased acute and late gastrointestinal and urinary tract adverse events associated with IMRT compared with 3-D conformal RT.

“IMRT may be used to boost selective sites of nodal involvement,” the guideline recommends. “The dose required is dependent on the size of the grossly involved node. Generally, between 500 and 6500 cGy is delivered to involved nodes based on size, location, contribution from brachytherapy, and dose per fraction.”

The Role of Brachytherapy

Brachytherapy is an “integral component” of definitive therapy for nonmetastatic cervical cancer, the task force emphasized; omitting brachytherapy more negatively effects patient survival than excluding chemotherapy. Between 2003 and 2011, as use of IMRT and stereotactic body radiation therapy (SBRT) climbed, brachytherapy became less common in the treatment of cervical cancer.The ASTRO guideline authors strongly recommend brachytherapy for patients receiving definitive RT for cervical cancer prior to surgery. For women undergoing postsurgical whole pelvis radiation, a brachytherapy boost is conditionally recommended if there are positive margins, but this recommendation is based on a low quality of available evidence, the authors noted. (Which brachytherapy technique is used depends on the location and volume of positive surgical margins.)

Brachytherapy Technique

The ASTRO task force strongly recommended, albeit based on low-quality available evidence, that intraprocedure imaging be used if available for women undergoing cervical cancer brachytherapy. MRI and CT are standard imaging modalities for brachytherapy treatment planning; MRI offers better soft-tissue definition than CT imaging for cervix and residual cancer visualization.

The authors also offered several other strongly recommended practices based on moderate-quality evidence, regarding the radiation dose, fractionation schedule, and imaging strategies for definitive brachytherapy in treating nonmetastatic cervical cancer. For example, MRI or CT-based planning imaging exams should be undertaken and volume-based dose prescription is recommended for women receiving brachytherapy, and definitive RT should involve a total EBRT and brachytherapy total equivalent dose (EQD2₁₀) of 8000 cGy or more. The volumes of organs at risk (OARs; including the bladder, rectum, vagina, and sigmoid/bowel) should be contoured when brachytherapy is used to treat intact cervical tumors and if volumetric planning is unavailable, 2-D (“points-based”) dose constraints should be applied. The authors provide a table of brachytherapy dose recommendations with EBRT, and dose constraints for OARs.

Radiotherapy “remains an essential component” of curative therapy for women with cervical cancer, the ASTRO guideline authors emphasized.

Reference

Chino J, Annunziata CM, Beriwal S, et al. Clinical Practice Guidelines: Radiation Therapy for Cervical Cancer: Executive Summary of an ASTRO Clinical Practice Guideline. Pract Rad Onc. 2020;10(4):220-234.