Study Characteristics
The characteristics of the studies included in this systematic review
are summarised in table 1. The studies were published between 2002 and
2021 and originate from centres in the USA (51,53,55,57), Europe
(50,52,56,64), Asia (58,59,61–63) and Australia (54). There were no
eligible studies from the UK. One of the studies was based on extraction
of data from a national cancer database (51), while the remainder were
single institution or multi-centre studies from a single geographical
region. Three studies were based on prospective databases (53–55) that
were retrospectively analysed, and the remainder were all retrospective
studies. All the studies identified patients based on diagnosis and
reported outcomes with respect to treatments given, and as such, were
observational cohort studies. None of the studies directly compared ND
alone to radiotherapy alone in a prospective or matched cohort manner,
although some retrospectively commented on outcomes for both groups.