Purpose: To determine whether partial volume lung irradiation influences the risk of developing acute radiation pneumonitis after the treatment of non-small-cell lung cancer with continuous hyperfractionated accelerated radiotherapy (CHART).
Methods and materials: We conducted an analysis of 32 patients treated with CHART at the Gloucestershire Oncology Center. Twelve patients were treated using conventional two-dimensional treatment techniques and received elective nodal irradiation (ENI). Their treatment plans were subsequently recapitulated using a three-dimensional treatment planning system. Twenty patients were planned using this system from the outset. For these patients, elective nodal irradiation was omitted. Dose-volume histograms (DVH) were constructed and several parameters analyzed for their ability to predict for the development of pneumonitis.
Results: Univariate analysis revealed that the percentage lung volume receiving more than 20 Gy (V20) and the mean lung dose are of predictive value for the development of pneumonitis after CHART. There is a strong correlation between these two parameters. Importantly, partial volume lung irradiation using CHART appears to be better tolerated than conventionally fractionated radiotherapy. The omission of ENI considerably reduces V20. Using a commonly employed 3-beam technique it was also noted that the shape of the planning target volume (PTV) in the transverse plane (expressed as an elliptical index) affects the conformity of the V20 isodose to the PTV. This influences the scope for dose escalation with irregularly shaped tumors.
Conclusions: In relation to acute radiation pneumonitis, CHART appears to have a superior therapeutic index than conventionally fractionated radiotherapy. V20 and mean lung dose are useful factors for predicting the risk of this complication. The use of these parameters will aid the selection of optimal treatment plans and provides a basis for future dose escalation studies.