The Principles of Radiation Therapy are described in the algorithm and are summarized in this Discussion (see the NCCN Guidelines for Malignant Pleural Mesothelioma). The NCCN Guidelines for Non-Small Cell Lung Cancer are also a useful resource. In patients with MPM, RT can be used as part of a multimodality regimen; however, RT alone is not recommended for treatment (see next paragraph). RT can also be used as palliative therapy for relief of chest pain, bronchial or esophageal obstruction, or other symptomatic sites associated with MPM such as metastases in bone or in the brain (see the NCCN Guidelines for Malignant Pleural Mesothelioma and NCCN Guidelines for Central Nervous System Cancers, available at NCCN The dose of radiation should be based on the purpose of treatment. The most appropriate timing of delivering RT (ie, after surgical intervention, with or without chemotherapy) should be discussed with a multidisciplinary team. After EPP, adjuvant RT may reduce the local recurrence rate. Patients are candidates for RT if they have good PS, pulmonary function, and kidney function (see Principles of Radiation Therapy in the NCCN Guidelines for Malignant Pleural Mesothelioma). However, in patients with limited or no resection of disease (ie, in the setting of an intact lung), high-dose RT to the entire hemithorax has not been shown to improve survival and is associated with significant toxicity.
It has been controversial whether immediate (prophylactic) RT is useful for preventing instrument-tract recurrence after pleural intervention. A French trial reported that prophylactic RT was useful for preventing recurrence, but 2 more recent trials did not find any benefit. A phase 3 randomized trial (SMART trial) compared prophylactic radiotherapy with deferred radiotherapy to assess the rate of recurrences in patients who had had procedures for MPM. Patients in the deferred RT arm did not receive RT until procedure-tract metastases were evident. Data showed that there was no difference in procedure-tract recurrence in the prophylactic RT (9% [9/102]) versus deferred RT (16% [16/101]) arms (odds ratio [OR], 0.51 [95% CI, 0.19–1.32]). In addition, prophylactic RT did not improve the quality of life, decrease chest pain, or decrease the need for analgesic drugs.
However, if patients did not receive chemotherapy, prophylactic RT did decrease the risk for procedure-tract metastases (OR, 0.16 [95% CI, 0.02–0.93]; P = .021). For the 2018 update, the NCCN Panel revised the recommendations for use of prophylactic RT to prevent instrument-tract recurrence after pleural intervention based on the SMART trial. The recommendation was softened to state that RT may prevent instrument-tract recurrence after pleural intervention; previously the recommendation had stated that RT can be used to prevent recurrence (see Principles of Radiation Therapy in the NCCN Guidelines for Malignant Pleural Mesothelioma). The prophylactic RT doses were also deleted, because panel members felt they were overly prescriptive and only included one regimen when several regimens are cited in the literature.
CT simulation–guided planning using either intensity-modulated RT (IMRT) or conventional photon/electron RT is acceptable. For treatment planning, PET scans can be used as indicated. The clinical target volumes should be reviewed with the thoracic surgeon to ensure coverage of all the volumes at risk. The total doses of radiation are described in the algorithm (see Principles of Radiation Therapy in the NCCN Guidelines for Malignant Pleural Mesothelioma). A dose of 60 Gy or more is recommended for macroscopic residual tumors, if the doses to normal adjacent structures are limited to their tolerances (see the NCCN Guidelines for Non-Small Cell Lung Cancer, available at NCCN) The volume of postoperative radiation should cover the surgical bed within the thorax. The optimal dose of RT for palliative purposes remains unclear. For patients with chest pain from mesothelioma, total doses of 20 to 40 Gy appear to be effective in providing relief from pain.
IMRT allows a more conformal high-dose RT and improved coverage to the hemithorax at risk. Advanced technologies, such as image-guided RT may be used for treatments involving IMRT, stereotactic radiosurgery, or stereotactic body radiation therapy. The NCI and ASTRO/ACR IMRT guidelines are recommended. The ICRU-83 (International Commission on Radiation Units & Measurements Report 83) recommendations are also a useful resource. RT to the contralateral lung should be minimized, because fatal pneumonitis may occur with IMRT if strict limits are not applied. The mean lung dose should be kept as low as possible, preferably less than 8.5 Gy. The volume of contralateral lung receiving low-dose RT (eg, 5 Gy) should be minimized.
Hemithoracic IMRT immediately followed by EPP was assessed in 25 patients with stage III or IV MPM on final pathologic review; for patients with epithelial subtypes of MPM, 3-year survival reached 84%. However, 13 patients had grade 3+ surgical complications and one patient died from treatment.