Migration of intraprostatic fiducial markers and its influence on the matching quality in external beam radiation therapy for prostate cancer.
OBJECTIVE
To assess the influence of fiducial marker (FM) migration on the matching quality in external beam radiation therapy (EBRT) for prostate cancer.


METHODS
The position of FMs were identified using on-board kV imaging (OBI) and their 3-D position established using an in-house reconstruction algorithm for 31 patients with prostate adenocarcinoma. To carry out the match, the positions were overlaid on the digitally reconstructed radiographs (DRR) generated from the planning CT. The distance between each FM was calculated for seven treatments throughout the EBRT course. Four radiotherapy technologists were asked to independently perform and rate the match from OBI to DRR which was then correlated to the extent of FM migration.


RESULTS
All the matches were rated by at least three radiotherapy technologists as "very easy" ("easy" subgroup) for 24 patients (77%), while the other seven patients had their match rated less than "very easy" and considered the "not easy" subgroup. The average daily FM migration was 0.93+/-0.34 mm for the "easy" subgroup vs. 1.82+/-0.75 mm for the latter. An average migration >2 mm was seen in five/seven patients in the "not easy" subgroup as compared to none in the "easy" subgroup. There was a trend towards less FM migration and better matching if the planning CT was done later than the day of the FM implant (p=0.093).


CONCLUSIONS
FM migration >2 mm predicts for a more difficult matching process; PTV margins might have to be adjusted or the planning CT repeated.
Delouya
Guila
G
Département de Radio-Oncologie, Centre Hospitalier de l'Université de Montréal-Hôpital Notre-Dame, Montreal, Quebec, Canada.
Carrier
Jean-François
JF
Béliveau-Nadeau
Dominic
D
Donath
David
D
Taussky
Daniel
D
D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D000368:Aged; D016009:Chi-Square Distribution; D015331:Cohort Studies; D005548:Foreign-Body Migration / Q000209:etiology*; D006050:Gold Radioisotopes / Q000009:adverse effects* / Q000627:therapeutic use; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D019736:Prostheses and Implants; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D011882:Radiotherapy, High-Energy / Q000379:methods*; D018570:Risk Assessment; D018709:Statistics, Nonparametric; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
D006050:Gold Radioisotopes