Volumetric image-guidance: does routine usage prompt adaptive re-planning? An institutional review.
OBJECTIVE
To investigate how the use of volumetric image-guidance using an on-board cone-beam computed tomography (CBCT) system impacts on the frequency of adaptive re-planning.


METHODS
Treatment courses of 146 patients who have undergone a course of external beam radiation therapy (EBRT) using volumetric CBCT image-guidance were analyzed. Target locations included the brain, head and neck, chest, abdomen, as well as prostate and non-prostate pelvis. The majority of patients (57.5%) were treated with hypo-fractionated treatment regimens (three to 15 fraction courses). The frequency of image-guidance ranged from daily (87.7%) to weekly or twice weekly. The underlying medical necessity for adaptive re-planning as well as frequency and consequences of plan adaptation to dose-volume parameters was assessed.


RESULTS
Radiation plans of 34 patients (23.3%) were adapted at least once (up to six time) during their course of EBRT as a result of image-guidance CBCT review. Most common causes for adaptive planning were: tumor change (mostly shrinkage: 10 patients; four patients more than one re-plan), change in abdominal girth (systematic change in hollow organ filling; n=7, two patients more than one re-plan), weight loss (n=5), and systematic target setup deviation from simulation (n=5). Adaptive re-plan was required mostly for conventionally fractionated courses; only 5 patient plans undergoing hypo-fractionated treatment were adjusted. In over 91% of adapted plans, the dose-volume parameters did deviate from the prescribed plan parameters by more than 5% for at least 10% of the target volume, or organs-at-risk in close proximity to the target volume.


CONCLUSIONS
Routine use of volumetric image-guidance has in our practice increased the demand for adaptive re-planning. Volumetric CBCT image-guidance provides sufficient imaging information to reliably predict the need for dose adjustment. In the vast majority of cases evaluated, the initial and adapted dose-volume parameters differed to a degree that was considered clinically significant.
Tanyi
James A
JA
Department of Radiation Medicine, Oregon Health and Science University, Portland, OR, USA. tanyij@ohsu.edu
Fuss
Martin H
MH
D002294:Carcinoma, Squamous Cell / Q000532:radiotherapy; D054893:Cone-Beam Computed Tomography; D006801:Humans; D008297:Male; D008545:Melanoma / Q000532:radiotherapy / Q000556:secondary; D018358:Neuroendocrine Tumors / Q000532:radiotherapy; D011860:Radiography, Abdominal; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014067:Tonsillar Neoplasms / Q000532:radiotherapy