Inside job.

Top Line: Stereotactic body radiation therapy (SBRT) in lieu of a brachytherapy boost for cervical cancer is happening.

The Study: And it’s happening mainly because of a variety of logistical, geographic, and economic forces at play rather than because of overwhelming data. Here we have a single arm, phase 2 trial from UT Southwestern. 15 patients with IB2-IVB cervical cancer were enrolled if they were medically unfit for or refused intracavitary brachytherapy. They received 1.8 Gy x 25 = 45 Gy of pelvic IMRT with concurrent chemo +/- a simultaneous integrated boost of 10 Gy to any involved lymph nodes. SBRT planning was based on pelvic MRI and used the GEC-ESTRO guidelines to define the high-risk target. The prescription was a homogeneous 7 Gy x 4 = 28 Gy. This was, of course, in contrast to the typically inhomogeneous dose distribution of intracavitary brachytherapy. Two year local and regional control were both roughly 70%, but 2 year progression-free survival was only 47%. Most importantly, enrollment was stopped earlier than the planned 21 patients due to excess toxicity. Over a quarter of patients (n=6) had grade 3+ late GI toxicity at a median of 8 months, including 2 rectal ulcers and 3 rectovaginal fistulas with 2 deaths from sepsis and/or bleeding. The only good predictor of late GI toxicity was >62.7% of the rectal circumference receiving 15 Gy.

TBL: Let’s be honest, using SBRT in place of brachytherapy for cervical cancer remains highly investigational with relatively high rates of late grade 3+ GI toxicity. | Albuquerque, Int J Radiat Oncol Biol Phys 2019