Brachytherapy Versus Stereotactic Body Radiotherapy for Cervical Cancer Boost: A Dosimetric Comparison

Background: The standard treatment for locally advanced cervical cancer involves chemo-radiation followed by brachytherapy. However, some patients are unable to undergo brachytherapy intensification. Recent advancements in radiation technology have provided several techniques, with stereotactic body radiation therapy (SBRT) theoretically able to mimic the dose distribution of brachytherapy with a high dose gradient. Methods: We analyzed 20 high-dose-rate intra-cavity brachytherapy plans for women with cervical cancer and simulated an adjunctive stereotactic radiotherapy plan at the same doses used for brachytherapy (21 Gray [Gy] in three fractions). No planning tumoral volume (PTV) margin was added for SBRT dosimetry. We used the dose constraints for brachytherapy from the EMBRACE trial and the dose constraints for SBRT in three fractions. Dose distribution, maximum dose points on target volumes, bladder, rectum, and dose-volume histograms were compared between the two techniques. Results: The mean volume of the high-risk clinical tumoral volume (CTV) was 64 cm3, and the mean volume of the intermediate-risk CTV was 93 cm3. The mean minimum dose received by 90% of the high-risk CTV (D90 CTV HR) was 17 Gy for brachytherapy versus 8.3 Gy for SBRT. The average minimum dose received by 90% of the intermediate-risk CTV (D90 CTV IR) was 7.5 Gy for brachytherapy versus 8.9 Gy for SBRT. The mean minimum dose delivered to 2cc of the bladder was 74.6 Gy for brachytherapy versus 84.7 Gy for SBRT. The mean minimum dose delivered to 2cc of the rectum was 71.8 Gy for brachytherapy versus 74.7 Gy for SBRT. Conclusion: We confirmed the dosimetric superiority of brachytherapy over SBRT in terms of target volume coverage and organ-at-risk sparing. Therefore, pending the results of further clinical studies, no current radiotherapy technique can replace brachytherapy for cervical cancer boost after external radiotherapy.