What is your approach to a cervical SCC patient in which you're unable to properly place a T&O, due to obliterated cervical os, after completion of EBRT?

In our experience this is an extremely rare circumstance if the implant is done with ultrasound guidance--certainly <1% of cases. Depending on your level of experience and confidence, it may be worth referring the patient to a more experienced brachytherapist. That said, there are rare cases, particularly in elderly patients who have had a cone biopsy, where the os may truly be obliterated. For a stage I tumor with a small cervix, consideration may be given to radical hysterectomy. However, if there is any hint of possible parametrial involvement, this is very risky because there is little that can be done for a close or positive margin.

One thing we have done in very rare cases is to use a hand port to assist sounding of the uterus (a hand is inserted in the pelvis and used to grasp the uterus while the sound is guided using the other hand). This is described in our textbook "Eifel and Klopp, Gynecologic Radiation Oncology..."  In some cases, interstitial brachy may be an option.  External beam alone is a last resort because the ratio between tumor and normal tissue dose is less favorable than with brachy and because there is often a break in treatment while the brachy is being attempted. Such a break decreases the likelihood of control even further.  That said, if none of the above are possible, IMRT to an ITV may be considered, possibly treating bid to partially make up for any break in treatment.

Vaginal brachy alone is of limited value because the penetration is so shallow, usually with a negligible dose delivered to the endocervix. This usually becomes obvious if image guidance is used in planning.

Again, if your experience is limited (e.g., less than 10 or so cases of intact cervix per year), it is always wise to seek assistance of an expert in gyn rad onc in these very rare difficult cases. Cases that seem impossible can sometimes be managed successfully in other hands. 

This is so rare with the options of ring and tandem, tandem and ovoid, hybrid applicator, interstitial, and lastly tandem and cylinder 

Under imaging guidance, (sonogram, CT, AND MRI) it is unlikey one can't get one of the above to get good dose distribution.