Radiologically if the radiolucency is close enough to pulp chamber, RCT might be indicated, not always. Clinic symptoms are considered more. If tooth pain triggered by cold (some times relieved by cold) lingers(from minutes to hours) or it comes by itself without contacting anything cold and/or sometimes wakes you up during sleep the irreversible pulpitis can be diagnosed and RCT is for sure. If there is no pain, or the tooth pain only lasts within ten seconds, irreversible pulpitis cannot be diagnosed and RCT is not indicated clinically.