Tomotherapy improves local control and changes failure patterns in locally advanced malignant pleural mesothelioma

The purpose of the study was to determine whether intensity modulated radiation therapy delivered via helical tomotherapy improves local control (LC) after pleurectomy/decortication (P/D) for malignant pleural mesothelioma compared with 3-dimensional conformal radiation therapy (3D-CRT).

Forty-five consecutive patients were treated with adjuvant radiation to 45 Gy in 1.8 Gy fractions after P/D between 2006 and 2014; 23 received 3D-CRT, and 22 received tomotherapy. Kaplan-Meier analysis was used to calculate overall survival, time to in-field or local failure (LF), and time to out-of-field failure. The Student t test and Fisher exact test were used to detect between-group differences.

Median follow-up time was 19.4 months and 12.7 months for the 3D-CRT and tomotherapy groups, respectively. Eighty-two percent of patients had T3/T4 disease, and 64% had positive nodes; 17.4% and 41% of patients in the 3D-CRT and tomotherapy groups had nonepithelioid histology, respectively. Mean planning target volume dose, percentage of planning target volume receiving 100% of the prescription dose, and lung doses were significantly greater with tomotherapy (P < .05), but toxicity rates (including radiation pneumonitis rates) were equivalent. LC was significantly improved with tomotherapy on Kaplan-Meier analysis with outcomes censored at 2 years (P < .05); uncensored, this became a trend (P = .06). Median time to LF was 19 months with tomotherapy and 10.9 months in 3D-CRT (the latter interval being less than the median follow-up in the tomotherapy group). On univariate analysis, treatment modality was the only significant predictor of LC (P < .05). Isolated LF was significantly more frequent with 3D-CRT (P < .05). Conversely, isolated out-of-field failure was significantly more frequent with tomotherapy (P < .05). Overall survival and out-of-field control were not significantly different.

Tomotherapy after P/D for malignant pleural mesothelioma is associated with improved target coverage that translates into improved LC compared with 3D-CRT. This is related to a change in failure patterns, with isolated LF being more common in the 3D-CRT group and isolated out-of-field failures predominating in the tomotherapy group.