Potential of dose optimisation in MRI-based PDR brachytherapy of cervix carcinoma.
OBJECTIVE
In this study on PDR treatment planning of utero-vaginal carcinoma, we analysed the dosimetry of traditional X-ray based plans as it presents on MR images. The potential gain of MRI-based dose optimisation was assessed.


METHODS
Sixteen patients boosted with PDR brachytherapy after external beam therapy were included. The clinical X-ray based plans were projected on MR images. The GTV, HR-CTV and IR-CTV were retrospectively contoured, as well as the bladder, rectum and sigmoid colon. The dose in the critical organs and target coverage was investigated. In a second phase, the plans were manually optimised using the MR information. The objectives were to lower the dose in the critical organs (<or= 85 Gy(alphabeta3) for bladder, <or= 75 Gy(alphabeta3) for rectum and sigmoid colon) and to increase the HR-CTV dose to D90 >or= 85 Gy(alphabeta10).


RESULTS
In the X-ray based plans, D(2cc) in bladder and sigmoid colon exceeded the tolerance doses in 10/16 and 7/16 patients, respectively. Coverage of the IR-CTV with the 60 Gy(alphabeta10) was acceptable. D90 of the HR-CTV was below 85 Gy(alphabeta10) in 13 out of 16 patients. After optimisation, the dose constraints in the OAR were not exceeded anymore in any patient. The average D(2cc) dose reduction was 7+/-6 Gy(alphabeta3) in the bladder and 7+/-4 Gy(alphabeta3) in the sigmoid colon for those patients in which the dose constraint was initially exceeded. In addition, an average dose increase of 3 Gy(alphabeta10) was accomplished in the HR-CTV.


CONCLUSIONS
MRI-based dose optimisation can play an important role to reduce the dose delivered to the critical organs and to improve target coverage.
Department of Radiation Oncology, University Hospital Leuven, Belgium. marisol.debrabandere@uzleuven.be
Marisol
M
De Brabandere
Amr Gaber
AG
Mousa
An
A
Nulens
Ans
A
Swinnen
Erik
E
Van Limbergen
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D001918:Brachytherapy / Q000379:methods*; D002277:Carcinoma / Q000188:drug therapy / Q000532:radiotherapy*; D003106:Colon / Q000528:radiation effects; D003131:Combined Modality Therapy; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D011879:Radiotherapy Dosage; D012007:Rectum / Q000528:radiation effects; D012189:Retrospective Studies; D016896:Treatment Outcome; D001743:Urinary Bladder / Q000528:radiation effects; D002583:Uterine Cervical Neoplasms / Q000188:drug therapy / Q000532:radiotherapy*