Study of lung density corrections in a clinical trial (RTOG 88-08). Radiation Therapy Oncology Group

To investigate the effect of lung density corrections on the dose delivered to lung cancer radiotherapy patients in a multi-institutional clinical trial, and to determine whether commonly available density-correction algorithms are sufficient to improve the accuracy and precision of dose calculation in the clinical trials setting.

A benchmark problem was designed (and a corresponding phantom fabricated) to test density-correction algorithms under standard conditions for photon beams ranging from 60Co to 24 MV. Point doses and isodose distributions submitted for a Phase III trial in regionally advanced, unresectable non-small-cell lung cancer (Radiation Therapy Oncology Group 88-08) were calculated with and without density correction. Tumor doses were analyzed for 322 patients and 1236 separate fields.

For the benchmark problem studied here, the overall correction factor for a four-field treatment varied significantly with energy, ranging from 1.14 (60Co) to 1.05 (24 MV) for measured doses, or 1.17 (60Co) to 1.05 (24 MV) for doses calculated by conventional density-correction algorithms. For the patient data, overall correction factors (calculated) ranged from 0.95 to 1.28, with a mean of 1.05 and distributional standard deviation of 0.05. The largest corrections were for lateral fields, with a mean correction factor of 1.11 and standard deviation of 0.08.

Lung inhomogeneities can lead to significant variations in delivered dose between patients treated in a clinical trial. Existing density-correction algorithms are accurate enough to significantly reduce these variations.