Physical aspects of external beam radiotherapy for the treatment of malignant pleural mesothelioma.

The optimization of radiotherapy for the treatment of malignant mesothelioma highlights many of the currently outstanding problems in clinical radiation physics. The experimental investigation of an intuitively attractive irradiation technique with combined photon and electron beams using a specially constructed phantom has established that, due to the penetration in low density material of both primary electrons and those secondary to photon irradiation, the normal lung tissue is not spared to any significant degree by such a technique. Furthermore, great care needs to be exercised in the treatment planning calculations for this approach if absolute dosimetry errors as large as 50% are to be avoided.