Dosimetric comparison of bladder, rectal, and vaginal surface doses between ovoids and cylinder-based vaginal brachytherapy in carcinoma of the endometrium.

Purpose: The study aims to estimate the differences in vaginal surface, bladder, and rectal doses when adjuvant intracavitary brachytherapy is carried out with ovoids or with vaginal cylinders, in postoperative carcinoma endometrium and to assess the difference in variability in organs at risk (OAR) doses and thereby the reproducibility of application in subsequent sittings.

Materials and Methods: Fifteen patients each received vaginal brachytherapy with ovoid and cylindrical applicators. The dose received by 0.1 cc, 1.0 cc, 2.0 cc, 5.0 cc, and 10.0 cc volumes of the OAR, namely, bladder, and rectum were analyzed using independent t-test. Interfractional variation in dose to OAR was evaluated using a two-way repeated ANOVA test. The dose received by the upper 2 cm of vagina was assessed using volume receiving 100% (V100 ) and dose received by 100% (D100 ) for documenting dose distribution to the target volume.

Results: The mean dose to rectum and bladder were significantly lesser with ovoids (P < 0.0001). This difference was seen in all volumes analyzed. V100 (99.05% vs. 67.7%, P < 0.0001) and D100 (95.70% vs. 53.08%, P < 0.0001) were significantly better with cylinders compared to ovoids. There was no statistically significant interfractional variation between sittings with either applicator.

Conclusion: The two applicators studied have different dosimetric properties conferring specific advantages and disadvantages as far as dose to OARs and target is concerned. Both applicators provide good reproducibility. The choice of applicator would ultimately depend on the clinical outcomes of these dosimetric differences which need to be prospectively analyzed.