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

Abstract

Purpose: 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).

Methods and materials: 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.

Results: 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.

Conclusion: 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.