Ovoid shields reduce radiation dose to the rectum during ICRT for cervical cancer

Gifford KA et al. (2005) A three-dimensional computed tomography-assisted Monte Carlo evaluation of ovoid shielding on the dose to the bladder and rectum in intracavity radiotherapy for cervical cancer. Int J Radiat Oncol Biol Phys 63: 615–621

Fletcher Suit Delclos (FSD) (Nucletron Trading, Leersum, The Netherlands) ovoid shields were developed with the aim of protecting nontarget tissues in patients undergoing intracavitary radiotherapy (ICRT). Gifford and colleagues at the MD Anderson Cancer Center, Houston, TX, have recently assessed the effectiveness of FSD ovoid shields in reducing radiation dose to the rectum and bladder in 12 patients undergoing low-dose-rate ICRT for carcinoma of the uterine cervix.

The effect of ovoid shields on the radiation dose distributions in patient CT scans was determined using the Monte Carlo dosimetry method and cumulative dose-difference surface histograms. Dose–volume histograms were used to calculate the minimum radiation doses to the 2 cm³ and 5cm³ of bladder (D_BV2 and D_BV5) and rectum (D_RV2 and D_RV5) receiving the highest dose.

Although shielding did not significantly reduce the radiation dose to the bladder, rectal tissue was shown to be protected by the shields, with 10.1% and 11.1% dose reductions to D_RV2 and D_RV5, respectively. The average dose reduction to 5% of the rectal surface area, as calculated by the cumulative dose-difference surface histograms, was 195 cGy, with a 405 cGy reduction recorded in one patient. The authors conclude that FSD ovoid shields are beneficial in protecting rectal tissue from radiation in patients receiving ICRT for cervical cancer, and should be included in 3D CT-based dosimetry.