Room: AAPM ePoster Library
In radiotherapy of prostate cancer interfractional differences in rectum- or bladder-volume lead to dose deviations. As the precise effects of these are largely unknown, this analysis investigates the dosimetric consequences of weekly and daily adaptive replanning.
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 position-control-CT (fx-CT) was performed (SOMATOM® Emotion, SIEMENS). Based on the fx-CT, the target volumes (TV) and all OARs were contoured. Using a deformable registration algorithm, applied doses were tracked and weekly as well as daily (only for 3 patients, because of software limitations) adaptive replanning was done. The dosimetric effects were quantitatively compared.
The applied dose D50 to the PTV with use of weekly replanning almost corresponded the planned dose. The D98 to the PTV was 1.33Gy lower than prescribed but 3.35Gy higher than without adaption. Using weekly replanning, the D50 to the bladder was 5.7Gy higher than the prescribed dose and 0.75Gy higher than without adaption. Weekly replanning effected an increase of the D50 to the rectum (0.53Gy) but a marginally decrease of 0.25Gy compared to no adaption. The applied dose D50 to the PTV with use of daily replanning was 1.2Gy higher than prescribed. Daily replannig effected a marginally increase of the D98 to the PTV, but a significant increase of 10Gy compared to no adaption. Daily replanning slightly reduced the D50 to bladder and rectum.
The analysis showed, that with use of weekly/daily replanning we achieved a dose coverage of the TV comparable to the planning and a significant better coverage of the TV compared to no adaption. It was however difficult to reach a more conformal dose to the TV and a better sparing of OARs at once.