Triple-tandem high-dose-rate brachytherapy for early-stage medically inoperable endometrial cancer: Initial report on acute toxicity and dosimetric comparison to stereotactic body radiation therapy.

PURPOSE: Stereotactic body radiotherapy (SBRT) may be appealing in medically inoperable endometrial cancer to avoid procedural risks. We performed a dosimetric comparison to triple-tandem, high-dose-rate (HDR) brachytherapy.

METHODS AND MATERIALS: Six consecutive clinical stage I, grade 1-2, medically inoperable endometrial cancer patients were treated with triple-tandem HDR brachytherapy. We report patient factors and acute toxicity. Also, we performed dosimetric comparison to SBRT using both 3D conformal arc (3DArc) and volumetric-modulated arc therapy. D2cc values for normal tissues were calculated and compared to the HDR plans.

RESULTS: Median age was 57 years. Patient comorbidities included morbid obesity, congestive heart failure, diabetes, and pulmonary emboli. In three patients who received prior external beam radiation (EBRT), median EBRT and HDR doses were 46 Gy and 20 Gy, respectively. The median dose with HDR brachytherapy monotherapy was 35 Gy. Acute toxicities during EBRT included gastrointestinal (3/3 with grade 1-2) and genitourinary (3/3 with grade 1-2). Acute toxicities during HDR brachytherapy were gastrointestinal (2/6 total with grade 1-2) and genitourinary (2/6 total with grade 1). The mean D2cc/Gy of prescription dose for rectum, sigmoid, and bladder were 0.58, 0.40, and 0.47 respectively. Overall, doses to normal tissues were higher for SBRT plans as compared to HDR. Also, the R50 (ratio of the 50% prescription isodose volume to the PTV) was lowest with HDR brachytherapy.

CONCLUSIONS: In medically inoperable, clinical stage I endometrial cancer patients with multiple comorbidities, definitive triple-tandem, HDR brachytherapy results in mild acute toxicity. In addition, HDR brachytherapy achieves relatively lower doses to surrounding normal tissues as compared to SBRT.