Treatment of malignant pleural mesothelioma with a conformal dynamic arc

Abstract

Malignant pleural mesothelioma is a relatively rare disease affecting approximately 3000 people annually in the United States. The treatment of malignant mesothelioma in traditional radiotherapy involves opposed hemithorax fields or an electron arc that encompasses the pleural cavity as well as the entire lung. However, these treatments usually result in radiation-induced pneumonitis and fibrosis along with significant loss of lung function. Patients presenting with mesothelioma at the Thompson Cancer Survival Center (TCSC) are considered for conformal dynamic arc (CD-ARC) therapy with the goal of treating the pleural lining while sparing lung tissue. The CD-ARC is designed using the ADAC Pinnacle 3-D treatment planning system. A series of static fan-shaped beams is created using multileaf collimators (MLC) fields in fifteen-degree intervals around the patient. The MLC shapes are designed at each gantry angle by exposing the tumor volume along the edge of the lung while blocking the lung itself. The result of modulating across the fan-beam is a more uniform dose distribution. The MLC shapes are used to design a 360-degree dynamic arc treatment. CD-ARC delivery is performed with a Varian Clinac 2100C accelerator with 52-leaf MLC. The Varian MLC controller moves the MLC leaves to the planned positions at the specified gantry angles during the arc. Between the specified gantry angles, the MLC controller interpolates between the MLC shapes. Dosimetric and patient quality assurance procedures are described as well as dosimetry verification methods. The CD-ARC therapy offers more optimal dose distribution than typically experienced during radiation treatment of pleural mesothelioma.