Heart Dosimetry is Correlated with Risk of Radiation Pneumonitis after Lung-Sparing Hemithoracic Pleural IMRT for Malignant Pleural Mesothelioma

Abstract

Purpose/Objective

To determine clinically helpful dose-volume and clinical metrics correlating with symptomatic radiation pneumonitis (RP) in malignant pleural mesothelioma (MPM) patients with two lungs treated with hemithoracic intensity modulated pleural radiation therapy (IMPRINT).

Methods and Materials

Treatment plans and resulting normal organ dose-volume histograms of 103 consecutive MPM patients treated with IMPRINT (2/2005–1/2015) to the highest dose ≤50.4 Gy satisfying departmental normal tissue constraints were uniformly recalculated. Patient records provided maximum RP grade (CTCAE v4.0), clinical and demographic information. Correlations analyzed with the Cox model were: ≥ Grade 2 RP (RP2+) and ≥ Grade 3 RP (RP3+) with clinical variables, with volumes of PTV and PTV-Lung overlap and with mean dose, percent volume receiving dose D, (V _D), highest dose encompassing % volume V, (D _V), and heart, total, ipsilateral, and contralateral lungs volumes.

Results

Twenty-seven patients had RP2+ (14 with RP3+). Median prescription dose was 46.8 Gy (39.6 to 50.4 Gy, 1.8Gy/fraction). Median age was 67.6 years (42 to 83 years). There were 79 males, 40 never-smokers, 44 with left-sided MPM. There were no significant (p≤0.05) correlations with clinical variables, prescription dose, total lung dose-volume metrics and PTV-Lung overlap volume. Dose-volume correlations for heart were RP2+ with V _D (35≤D≤47 Gy, V ₄₃ strongest at p=0.003), RP3+ with V _D (31 ≤D≤ 45 Gy), RP2+ with D _V (5 ≤V≤ 30%), RP3+ with D _V (15 ≤V≤ 35%) and mean dose. Significant for ipsilateral lung were RP2+ with V _D (38 ≤D≤44 Gy), RP3+ with V ₄₁, RP2+ and RP3+ with minimum dose; for contralateral lung, RP2+ with maximum dose. Correlation of PTV with RP2+ was strong (p<0.001) and also significant with RP3+.

Conclusions

Heart dose correlates strongly with symptomatic RP in this large cohort of MPM patients with two lungs treated with IMPRINT. Planning constraints to reduce future heart doses are suggested.