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


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Orton
C G
CG
Gershenson Radiation Oncology Center, Karmanos Cancer Institute and Wayne State University, Detroit, Michigan 48201, USA.
Chungbin
S
S
Klein
E E
EE
Gillin
M T
MT
Schultheiss
T E
TE
Sause
W T
WT
D000465:Algorithms; D017326:Clinical Trials, Phase III as Topic; D006801:Humans; D008168:Lung / Q000473:pathology*; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D015337:Multicenter Studies as Topic; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*