Tomotherapy PET-guided dose escalation: A dosimetric feasibility study for patients with malignant pleural...

The aim of this study was to investigate whether a safe escalation of the dose to the pleural cavity and PET/CT-positive areas in patients with unresectable malignant pleural mesothelioma (MPM) is possible using helical tomotherapy (HT).

We selected 12 patients with MPM. Three planning strategies were investigated. In the first strategy (standard treatment), treated comprised a prescribed median dose to the planning target volume (PTV) boost (PTV1) of 64.5 Gy (range: 56 Gy/28 fractions to 66 Gy/30 fractions) and 51 Gy (range: 50.4 Gy/28 fractions to 54 Gy/30 fractions) to the pleura PTV (PTV2). Thereafter, for each patient, two dose escalation plans were generated prescribing 62.5 and 70 Gy (2.5 and 2.8 Gy/fraction, respectively) to the PTV1 and 56 Gy (2.24 Gy/fraction) to the PTV2, in 25 fractions. Dose-volume histogram (DVH) constraints and normal tissue complication probability (NTCP) calculations were used to evaluate the differences between the plans.

For all plans, the 95 % PTVs received at least 95 % of the prescribed dose. For all patients, it was possible to perform the dose escalation in accordance with the Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) constraints for organs at risk (OARs). The average contralateral lung dose was < 8 Gy. NTCP values for OARs did not increase significantly compared with the standard treatment (p > 0.05), except for the ipsilateral lung. For all plans, the lung volume ratio was strongly correlated with the V20, V30, and V40 DVHs of the lung (p < 0.0003) and with the lung mean dose (p < 0.0001).

The results of this study suggest that by using HT it is possible to safely escalate the dose delivery to at least 62.5 Gy in PET-positive areas while treating the pleural cavity to 56 Gy in 25 fractions without significantly increasing the dose to the surrounding normal organs.