What clinical factors would lead to utilizing a tandem and cylinder rather than tandem and ovoid for cervical cancer brachytherapy?  

Tandem and cylinder should be used with caution as it is hard to cover the entire cervix and paracervical region with tandem and cylinder. If the patient has lower vaginal disease with good response to chemo RT, one can use tandem and cylinder but may need some needles to cover entire cervix.

When we decide to use tandem-cylinder for cervical cancer, anatomy and tumor factors need to be considered. Most often, tandem-cylinder brachytherapy has been used when the regular tandem-ovoid cannot be performed due to sub-optimal anatomy such as narrow vaginal vault, even though there is a higher...

The most common situations are the following: 1) conical vaginal apex in which anatomy does not favor ovoid placement, 2) upper vaginal constriction ring or lack of distensibility (possibly due to upper vaginal tumor infiltration) that does not lend itself to ovoid placement, and 3) tumor extension ...