RETROSPECTIVE RECONSTRUCTION OF 3-DIMENSIONAL RADIOTHERAPY TREATMENT PLANS OF THE THORAX FROM 2-DIMENSIONAL PLANNING DATA

Purpose: A method for the retrospective reconstruction of three-dimens ional (3-D) radiotherapy treatment plans from two-dimensional (2-D) pl anning data is detailed in this paper. Methods and Materials: With the se techniques the user can register an arbitrarily shaped portal on a simulation film with a diagnostic computed tomography study of the pat ient and then generate the resultant 3-D dose distribution or dose-vol ume histogram. Seven treatment plans were reconstructed of patients wh o had previously undergone 3-D treatment planning for fields involving the thorax and who had had a diagnostic computed tomography (CT) scan . The dose-volume histograms and the spatial positions of the beams on the reconstructed plans were then compared to those of the original 3 -D plan, which until then, were not made available to the investigator s. Results: The dose-volume histograms of the reconstructed plans did not differ from those of the original plans by more than 3% except in the low dose region. The error in positioning the beam in the reconstr ucted plan was determined to be approximately 5 mm. Conclusion: The te chnique of 3-D treatment plan reconstruction can be used, through retr ospective studies, to obtain better assessments of normal tissue compl ication probabilities and tumor control probabilities.