Comparison of dosimetric analysis of organs at risk and target volumes for ovoids and cylinders in endometrial carcinoma

Purpose:
To compare dose volume parameters of target and organs at risk in vaginal vault brachytherapy using ovoids or cylinder in post-operative endometrial carcinoma.

Material and methods:
The study was done among 25 histologically proven post-operative endometrial carcinoma patients requiring vaginal brachytherapy. All patients underwent both cylinder and ovoids application alternatively on weekly basis. Ovoids size ranged from 2 to 3 cm diameter. Diameters of cylinder ranged between 2.5 and 3.5 cm. Bladder, rectum, urethra, and clinical target volume (CTV) were contoured on CT simulation images. Prescribed dose was 6-7 Gy in 2-3 fractions at 0.5 cm from the surface of applicator.

Results:
The mean values of D₉₀, D₅₀, V₁₅₀, V₁₀₀, V₉₀, and V₅₀ of CTV were comparable between cylinder and ovoids plans. The mean dose of CTV was significantly higher with cylinder than with ovoids, and D₁₀₀ was significantly higher with ovoids (mean = 15.63 Gy vs. 14.64 Gy, p = 0.016, and D₁₀₀ = 37.82% vs. 42.86%, p = 0.042, for cylinder vs. ovoids). In the dosimetry of the vault, D₉₀, D₅₀, V₁₀₀, V₉₀, V₅₀, and mean of the vault did not show any significant difference between cylinder and ovoids. The V₁₅₀ was significantly higher with cylinder plans than ovoids, and D₁₀₀ of the vault was significantly higher with ovoids plans (V₁₅₀ = 14.81% vs. 6.86%, p = 0.02, and D₁₀₀ = 37.77% vs. 44.80%, p = 0.029, for cylinder vs. ovoids). D_0.1cc, D_1cc, D_2cc, and mean for the bladder, rectum, and urethra were comparable between the cylinder and ovoid plans.

Conclusions:
The present study showed that the dose to organs at risk, most of the dosimetric parameters of CTV, and vault were comparable between the cylinder and ovoid plans. Both applicators provide good reproducibility. The choice of applicator will ultimately depend on the institutional policies and oncologist decision. However, in patients with dog-ear configuration of the vagina, ovoids may be preferred as per ABS guidelines.