Volumetric modulated arc therapy for malignant pleural mesothelioma after pleurectomy decortication
Treatment of malignant pleural mesothelioma (MPM) has historically presented a treatment challenge due to the aggressive nature of the tumor, the size and complexity of the target volume and its proximity to critical organs. Two types of surgery are performed for mesothelioma: extrapleural pneumonectomy (EPP) and pleurectomy/decortication (P/D) EPP involves an en bloc resection of the entire pleura, lung, diaphragm and ipsilateral, half of the pericardium, and is a high risk surgery for patients with this disease. P/D is a lung sparing surgery that involves the removal of gross tumor along with the visceral pleura, parietal pleura, pericardium and/or hemidiaphragm if needed for macroscopic complete resection, but spares the underlying ipsilateral lung. Studies have shown that P/D is a less morbid procedure compared to EPP, suggesting a survival benefit and, thus, is becoming increasingly used for these patients.1,2 Surgery alone, however, does not offer adequate long term local control or survival rates. Multimodality therapy that combines surgery, chemotherapy and radiation therapy has shown favorable clinical outcomes both for patients who have received EPP3 or P/D4 as part of their surgical management. Adjuvant radiation therapy with conventional techniques has been given through anterior and posterior fields that encompass the entire hemithorax.5,6 Since the ipsilateral lung remains in situ after P/D, traditionally these techniques have attempted to spare the lung by adding a block on the central part of the lung.6 Anterior and posterior parts of the chest wall underneath the lung are boosted with an electron field. However, this technique has resulted in disappointing local control, survival rates and high levels of toxicity.5 Since conventional radiation techniques in these patients have been unable to provide adequate local control without compromising toxicity, we must examine advanced radiation planning and delivery techniques. Intensity modulated radiation therapy (IMRT) a highly conformal radiation delivery technique, has been shown to effectively spare normal tissues while enabling the delivery of higher radiation doses to the tumor, potentially providing safer and less toxic treatments compared to conventional techniques.7 Initial experience with pleural IMRT in 36 patients with 2 intact lungs has shown the safety and feasibility of this technique.8 The risk of grade 3 pneumonitis was 20% an acceptable result given the high risk of this patient population. An expanded analysis published using this technique in 67 patients with definitive or adjuvant hemithoracic pleural IMRT showed a median survival of 2 years from the time of diagnosis, with a 1and 2 year overall survival (OS) rate of 85% and 50% respectively.9 A recent 2 center phase II trial in which 27 of 45 patients completed hemithoracic IMRT following chemotherapy and surgery reported that 8 of these patients (30% experienced either grade 2 (n 6) or grade 3 (n 2) RP with no grade 4 or 5, and 1 and Volumetric modulated arc therapy for malignant pleural mesothelioma after pleurectomy/decortication