Room: AAPM ePoster Library
Adaptive radiotherapy takes the constant changes in the anatomy and physiology of the patient during the course of treatment into account. Therefore, plan adaptation strategies are necessary. This analysis was aimed at investigating dosimetric consequences of a novel concept for adaptive radiotherapy using an individualized plan-database.
The data of ten patients with prostate carcinoma (salvage radiotherapy to the prostatic bed, 68Gy in 34 fx, step-and-shoot IMRT) were investigated. Prior to each fraction, a diagnostic in-room position-control-CT (fx-CT) was performed. Based on the daily fx-CT, the target volume and all OARs were contoured. Two additional plans were calculated based on the bladder filling observed using the first five fx-CTs, thereby creating a plan database that contained plans for low, intermediate and high bladder volume for each patient. Using a deformable registration algorithm for each daily fx-CT, applied doses were tracked and analyzed against the planned doses.
Interfractional variabilities resulted in an increase of D50 (0.40±0.38Gy) and a decrease of D95 (2.03±5.40Gy) to the PTV and effect a dose deviation to the bladder of at mean 7.76±6.05Gy of the D50. By using a plan database, the applied dose to the bladder could be reduced by 4.55±5.81Gy. The D50 to the PTV was marginally lower (-0.23±0.31Gy) and the D95 to the PTV was marginally higher (1.00±0.9Gy) than without using plan database and thus closer to the planning value.
The observed variability resulted in significant dose increases of the D50 to the bladder, whereas in the PTV, only small non-significant dose deviations could be detected. By using an individualized plan-database a significantly lower dose to the OAR was achieved, while the target volume coverage was virtually unchanged.