Prospective Trial of Hydrogel Visualization and Dosimetric Effects on Rectum and Tumor Dose in Gynecologic Brachytherapy.

Abstract

PURPOSE/OBJECTIVE(S)\nPolyethylene glycol hydrogel has increasingly been used in brachytherapy for organ-at-risk sparing. This study evaluated visualization and dosimetry with hydrogel in gynecologic brachytherapy.\n\n\nMATERIALS/METHODS\nWomen with gynecologic cancer received hydrogel injection prior to brachytherapy on a prospective clinical trial. Two researchers rated the appearance immediately after hydrogel injection and measured volume at initial injection, and at 3 and 6 months follow-up on T2w MRI. Visualization was rated as: (1) not visualized; (2) faint or trace visibility (shadow or haze); (3) visible but indistinct borders (definable entity, not just haze); (4) partially distinct border, partial haze; and (5) clearly visualized, unequivocal. Cohen s Kappa statistic assessed interobserver variability. For patients that had spacer injected during the second implant of brachytherapy, EQD2 rectal D2cc and CTVHR D90 absolute and ratio values were calculated between the first and second implants to determine the difference in dose to tumor after placement of hydrogel. A paired t-test was performed.\n\n\nRESULTS\n28 women were enrolled and had an average patient age of 57.2 years (38-77). Brachytherapy applicators used in treatment included the Syed (33.3%, n\u202f=\u202f9), Tandem and Ring (29.6%, n\u202f=\u202f8), and Syed and Tandem (37.04%, n\u202f=\u202f11). Diagnoses included cervical cancer (57.1%, n\u202f=\u202f16), vaginal (23.4%, n\u202f=\u202f6), endometrial (17.9%, n\u202f=\u202f5), and urethral cancer (3.6%, n\u202f=\u202f1). The average rating of hydrogel amount was 3.4/5, and did not differ by type of applicator used or by diagnosis. Inter-rater reliability (kappa statistic) for the 2 readers on the 5-point scale was 0.37. Average hydrogel volumes on 3 and 6 month T2 MRIs were 69.3 ± 53.4% and 43.7 ± 34.2%, relative to day of injection. Five patients had spacer placed at the time of the second fraction, and when compared to the first fraction, the EQD2 CTVHR D90 increase (per fraction) was 1.43 Gy10 (P\u202f=\u202f0.006) and the average reduction in rectum EQD2 D2cc dose to the rectum was 0.39 Gy3 (P\u202f=\u202f0.34) per fraction. The rectum EQD2 D2cc to CTVHR D90 ratio decreased from 0.65 to 0.49, on average, after hydrogel injection.\n\n\nCONCLUSION\nHydrogel demonstrated moderate inter-rater reliability and progressive decrease in size over 6 months on MRI. There was a significant increase in D90 and decrease in the ratio of rectal D2cc/D90 after hydrogel injection in those that had first (without) and second (with hydrogel) fraction comparative implants.\n\n\nAUTHOR DISCLOSURE\nM. Morcos: None. R. Bhatia: None. K. Li: None. A.N. Viswanathan: Research Grant; National Cancer Institute. Honoraria; NCI Uterine Cancer Task Force Chair.