Target Volume Delineation Variability and the Effect of Contouring Training during Stereotactic Body Radiation Therapy (SBRT) Planning for Lung Cancer
Matthew Orton, Michael Chang, Drew Moghanaki, Keith Neiderer, Alfredo Urdaneta, Jessica Schuster and Elisabeth Weiss
World Journal of Surgical Medical and Radiation Oncology 2014, 3:7
To investigate the variability of target volume delineation, analyze its dosimetrical importance, and evaluate the effect of contouring training during treatment planning for early stage lung cancers treated with SBRT.
Nine radiation oncologists independently delineated lung tumor volumes in 6 patients after 4D-CT simulation. Tumor delineation occurred in 3 sessions: prior to contouring training, after completing training, and >2 weeks after the second session to assess intraobserver variability. Target volumes were evaluated for variations in the magnitude of volumes (coefficient of variation (COV) = standard deviation/mean volume), volume overlap (conformality index (CI) = common volume/encompassing volume), and 3D vector displacements. To evaluate the dosimetrical effect of target volume variability, treatment plans were created for all 54 planning target volumes of session 2 and compared to the reference treatment plan.
From sessions 1 to 3 the mean interobserver 3D vector displacements (0.8 to 0.5 mm, p=0.01), COV (0.25 to 0.19, p=0.03), and CI (0.35 to 0.44, p=0.03) demonstrate significant improvements. Intraobserver variability in 3D vector displacements and CI demonstrated statistically non-significant improvements from session 1 to 3. Planning target volume underdosage by 3% or more compared to the reference plan was found in 23% of all session 2 contours.
Intra- was smaller than interobserver variability; both could be improved with repeat contouring and contouring training. Planning target volume variability demonstrated underdosing most commonly in lesions located centrally, showing spiculations, or with pleural attachments suggesting a need for a standardized approach to delineate such lesions