Does using a tandem-ring applicator lower rectal doses compared to a tandem-ovoid?

In cervical cancer brachytherapy, the applicator type can affect how much radiation reaches nearby organs like the rectum and sigmoid colon. A recent randomized trial directly compared the tandem-ring (T-R) and tandem-ovoid (T-O) applicators. The study found that T-R significantly reduced the radiation dose to the rectum and sigmoid, while still delivering the same dose to the tumor. This suggests T-R may help lower the risk of bowel side effects.

What the research says

A 2025 randomized trial of 36 cervical cancer patients compared tandem-ring and tandem-ovoid applicators during CT-guided brachytherapy ³⁹. The T-R applicator reduced the mean rectal dose by 2.7 Gy (p=0.04) and the sigmoid dose by 6.8 Gy (p=0.005) compared to T-O ³⁹. Bladder doses were similar between the two groups ³⁹. Importantly, the dose to the tumor (high-risk clinical target volume) was the same for both applicators, meaning T-R did not compromise tumor coverage ³⁹. Early clinical outcomes, including tumor response and acute side effects, were also similar ³⁹. A separate meta-regression of brachytherapy studies noted that tandem-ring applicators were associated with improved dose distributions, though it did not specifically compare ring vs. ovoid ⁴. The trial's short follow-up (median 7 months) means long-term side effect differences are not yet known ³⁹.

What to ask your doctor

• What type of brachytherapy applicator (tandem-ring or tandem-ovoid) does my treatment plan use?
• How does the choice of applicator affect the radiation dose to my rectum and sigmoid colon?
• What are the potential short-term and long-term bowel side effects I should watch for?
• Are there any other techniques, like interstitial needles, that could further reduce bowel doses?
• How will my tumor coverage and overall treatment effectiveness be ensured with the chosen applicator?