Simple opposed tangential fields were defined by surface anatomy in the conventional manner in 221 consecutive patients. After MRI, fields were modified by a single radiation oncologist to ensure encompassment of the POCx with a 10-mm margin. Genetic analysis was performed on all local relapses (LRs) to distinguish true recurrences (TRs) from new primaries (NPs).
This was a high risk cohort at 5 years: only 9.5 % were classified as low risk (St Gallen): 43.4 % were Grade 3 and 19.9 % had surgical margins <1 mm; 62.4 % of patients received boosts. Adjustments of standard field margins were required in 69 % . After a median follow-up of 5 years, there were 3 LRs (1.3 % ) as the site of first relapse in 221 patients, comprising two TRs (0.9 % ) and one NP (0.4 % ).
Accurate targeting of the true tumor bed is critical. MRI may better define the tumor bed.