Dosimetric comparison of intra-cavitary brachytherapy technique with free-hand (intra-cavitary + interstitial) technique in cervical cancer

Abstract

Purpose:
The aim of the study was to dosimetrically compare intra-cavitary brachytherapy technique (ICBT) with free-hand (intra-cavitary + interstitial, IC + IS) technique.

Material and methods:
Twenty seven locally advanced carcinoma cervix patients were included in the study. Patients with more than medial 1/3^rd parametrial residual disease without extending upto lateral pelvic wall were included, following external beam radiotherapy (EBRT), in which cobalt-60 high-dose-rate (⁶⁰Co HDR) brachytherapy source was used. Dose for both plans were 6.5 Gy × 4 fractions, 2 fractions per day, 6 hours apart, over 2 days. Free-hand brachytherapy technique, consisted of placement of central tandem and 2 ovoids along with needles without using template, was applied. Two plans were generated by activating and deactivating the needles, and compared by normalizing to V₁₀₀.

Results:
A total of 79 needles were applied. Using paired-t test, dosimetric comparison of both the plans was done. Free-hand plan had a significant higher mean V90 (volume receiving 90% of the dose) of 94.2% compared with 87.22% in ICBT plan (p ≤ 0.0001). Free-hand and ICBT plans presented a mean V₁₀₀ values of 89.06% and 81.51% (p ≤ 0.0001), respectively, favoring free-hand plan. The mean _D90 (dose to 90% volume), D₉₈, and D₁₀₀ of free-hand plan were 6.28 Gray (Gy), 4.91 Gy, and 3.62 Gy, respectively, but equivalent parameters in ICBT plan were 5.26 Gy, 3.72 Gy, and 2.61 Gy, with p value ≤ 0.0001. In both the plans, D_2cc of the bladder, rectum, and sigmoid were 4.59 Gy, 3.98 Gy, 2.77 Gy, and 4.46 Gy, 3.90 Gy, 2.67 Gy, respectively, with no statistical significance.

Conclusions:
Free-hand brachytherapy (IC + IS) achieves a statistically significant better dose distribution to high-risk clinical target volume (HR-CTV) comparing with ICBT technique with similar dose to organs at risk.