Hemithoracic Irradiation With Proton Therapy in Malignant Pleural Mesothelioma

Inclusion criteria: * Patients ≥18 years of age, with biopsy confirmed MPM and histological subtyping (epithelioid or non-epithelioid) * N0 or N1 and M0 disease * Written informed consent * Patient and local/regional MDT opt for active surveillance and deferral of SACT until clinical or radiological progression * WHO Performance Status 0-1 * Disease confined to one hemithorax based on CT assessment * Adequate pulmonary function * ≥ 40% predicted post-FEV1; * ≥ 40% predicted DLCO/TLCO * Agreement to travel to either proton beam therapy centres (i.e. UCLH or The Christie) if randomised to arm 2 * Agreement to be followed up at a local HIT-Meso trial site * Patient likely able to complete PBT planning based on local assessment Exclusion criteria: * Presence of metastatic or contralateral disease * Cytological diagnosis and/or undetermined histological subtype * Prior thoracic radiotherapy, chemotherapy, immunotherapy for MPM * Prior radical surgery for MPM (extrapleural pneumonectomy or extended pleurectomy decortication or pleurectomy decortication) * Initial systemic therapy or surgery is required and the patient and local/regional MDT do not opt for active surveillance * Involvement of contralateral or supraclavicular lymph nodes * T4 disease with invasion of the myocardium * N2 and/or M1 disease * Presence of new effusion that is not amenable to drainage * WHO Performance Status ≥ 2 * Women who are pregnant or breast feeding * Current or previous malignant disease which may impact on the patient's life expectancy * Patient fitted with a pacemaker or implantable cardioverter-defibrillator (ICD)\\ * Diagnosis of clinically significant interstitial lung disease (ILD), excluding mild fibrosis or incidental findings * Chronic non-malignant disease with an estimated three-year survival rate of less than 20% * Patient with prior thoracic / abdominal radiotherapy for malignancy who was not discussed with sponsor before recruitment