Intensity-modulated radiotherapy might increase pneumonitisnrisk relative to three-dimensional conformal radiotherapy innpatients receiving combined chemotherapy and radiotherapy: anmodeling study of dose dumping.
PURPOSE:
To model the possible interaction between cytotoxic chemotherapynand the radiation dose distribution with respect to the risk ofnradiation pneumonitis.
METHODS AND MATERIALS:
A total of 18 non-small-cell lung cancer patients previouslyntreated with helical tomotherapy at the University of Wisconsinnwere selected for the present modeling study. Three treatment plansnwere considered: the delivered tomotherapy plans; anthree-dimensional conformal radiotherapy (3D-CRT) plan; and anfixed-field intensity-modulated radiotherapy (IMRT) plan. The IMRTnand 3D-CRT plans were generated specifically for the present study.nThe plans were optimized without adjusting for the chemotherapyneffect. The effect of chemotherapy was modeled as an independentncell killing process by considering a uniform chemotherapynequivalent radiation dose added to all voxels of the organ at risk.nThe risk of radiation pneumonitis was estimated for all plans usingnthe Lyman and the critical volume models.
RESULTS:
For radiotherapy alone, the critical volume model predicts thatnthe two IMRT plans are associated with a lower risk of radiationnpneumonitis than the 3D-CRT plan. However, when the chemotherapynequivalent radiation dose exceeds a certain threshold, thenradiation pneumonitis risk after IMRT is greater than after 3D-CRT.nThis threshold dose is in the range estimated from clinicalnchemoradiotherapy data sets.
CONCLUSIONS:
Cytotoxic chemotherapy might affect the relative merit ofncompeting radiotherapy plans. More work is needed to improve ournunderstanding of the interaction between chemotherapy and thenradiation dose distribution in clinical settings.
]]>