PCOM

The prefix PCOM indicates the information cited comes from official BBC podcasts — or, prior to the popularisation of that term, webcasts — that were regularly issued during most of the RTD era. It can be compared to DCOM, which indicates DVD commentaries. The necessity for two separate prefixes results from there being two different, BBC-released commentaries for many BBC Wales episodes of Doctor Who.
Thus, PCOM: Last of the Time Lords indicates an entirely different recording than DCOM: Last of the Time Lords.