A dosimetric evaluation of IGART strategies for cervix cancer treatment.
OBJECTIVE
Image guided adaptive radiotherapy (IGART) strategies can be used to include the temporal aspects of radiotherapy treatment. A dosimetric evaluation of on- and off-line adaptive strategies are done in this study.


METHODS
A library of equivalent uniform dose (EUD)-based Intensity Modulated Radiotherapy Treatment plans with incrementally increasing clinical target volume (CTV)-to-planning target volume (PTV) margins were developed for 10 patients. Utilizing daily computed tomography (CT) images an on-line strategy using a margin-of-the-day (MOD) concept that selects the best plan from the library was employed. This was compared to an off-line strategy with full analysis of accumulated dose between fractions where dosimetric deviations from the treatment intent triggered plan adaptation. A fixed margin treatment approach was used as benchmark.


RESULTS
Using fixed margins of <15mm lead to under-dosages of more than 5Gy in total delivered dose. The average CTV EUD for the off-line and on-line strategy was 50.0±5.0Gy and 50.4±2.0Gy respectively and OAR doses were comparable.


CONCLUSIONS
A fixed margin treatment approach yields a significant probability of CTV under-dosage. Using EUD dose metrics CTV coverage can be restored in both the off-line and on-line adaptive strategies at acceptable OAR dose levels. Considering the workload and time on the treatment machine, the off-line strategy proves to be sufficient and more practical.
Department of Medical Physics (G68), University of the Free State, Nelson Mandela Drive, Park West, Bloemfontein 9300, South Africa. Electronic address: oreillyfhj@ufs.ac.za.
Frederika H J
FH
O'Reilly
Department of Medical Physics (G68), University of the Free State, Nelson Mandela Drive, Park West, Bloemfontein 9300, South Africa. Electronic address: shaww@ufs.ac.za.
William
W
Shaw
D055592:Biophysical Phenomena; D003198:Computer Simulation; D005260:Female; D006801:Humans; D009862:Online Systems; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000706:statistics & numerical data*; D061089:Radiotherapy, Image-Guided / Q000706:statistics & numerical data*; D050397:Radiotherapy, Intensity-Modulated / Q000706:statistics & numerical data; D014057:Tomography, X-Ray Computed / Q000706:statistics & numerical data; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*
Cervix cancer; EUD; IGART; Off-line; On-line