Utilization of cone-beam CT for offline evaluation of target volume coverage during prostate image-guided radiotherapy based on bony anatomy alignment
Abstract
To assess target volume coverage during prostate image-guided radiotherapy based on bony anatomy alignment and to assess possibility of safety margin reduction. Implementation of IGRT should influence safety margins.
Utilization of conebeam CT provides current 3D anatomic information directly in irradiation position. Such information enables reconstruction of the actual dose distribution.
In 12 % of reconstructed plans the prostate coverage was not sufficient. The prostate underdosage was observed in 5 patients.
Coverage of seminal vesicles was not satisfactory in 3 % of plans. Most of the target underdosage corresponded to excessive rectal of bladder filling.
Evaluation of alternative plans assuming a smaller 7 mm margin revealed 22 % and 11 % of plans where prostate and seminal vesicles coverage, respectively, was compromised. These were distributed over 8 and 7 patients, respectively.
Sufficient dose coverage of target volumes was not achieved for all patients. Reducing of safety margin is not acceptable.
Initial rectal and bladder volumes cannot be considered representative for subsequent treatment.