Comparison of Intrafraction Variation of Dose-volume Parameters in Hybrid Brachytherapy for Carcinoma Cervix.

PURPOSE: The present study aimed to compare the dosimetric parameters for a fractional re-imaging approach using computed tomographic (CT) scans before the first and third fractions with hybrid brachytherapy for carcinoma cervix patients.

MATERIALS AND

METHODS

Patients with cervical carcinoma who received radical chemoradiation and hybrid brachytherapy were prospectively included for the analysis. The first fraction was delivered on day 1 after applicator insertion and the second and third fractions were delivered on day 2, 6 h apart. Two plans were created for each patient using CT-based planning, one before the first fraction (Plan 1) and the other before the third fraction (Plan 2). The dose prescribed was 7 Gy per fraction to high-risk clinical target volume (HRCTV). The dosimetric parameters compared between the two plans were D90 HRCTV, D98 IRCTV, TRAK, D0.1cc, and D2cc to the bladder, rectum, sigmoid, and dose to the ICRU 89 radiation therapy (RV) point, respectively.

RESULTS

Fifteen patients were included for the analysis. The mean HRCTV volume was 31 cc. The mean D90 HRCTV was 87.86 Gy EQD2 for Plan 1 versus 84.64 Gy EQD2 for Plan 2, respectively (P = 0.018). On analysis, there was a significant difference between the mean D0.1cc rectum between Plan 1 and Plan 2 (89.57 Gy vs. 115.27 Gy) and the D2cc of the rectum between Plan 1 and Plan 2 (70.9 Gy vs. 77.2 Gy). The bladder, sigmoid, and RV ICRU 89 point dose between the two plans were not significantly different.

CONCLUSION

In carcinoma cervix patients undergoing hybrid brachytherapy in a single application multiple fraction approach, there can be significant variations in rectum doses. These results indicate that fractional re-imaging is necessary to optimize the plan and spare organ-at-risk.