Day-to-day reproducibility of prostate intrafraction motion assessed by multiple kV and MV imaging of implanted markers during treatment.
OBJECTIVE
When one is performing online setup correction for prostate positioning displacements prior to daily dose delivery, intrafraction motion can become a limiting factor to prostate targeting accuracy. The aim of this study was to quantify and characterize prostate intrafraction motion assessed by multiple kilovoltage (kV) and megavoltage (MV) imaging of implanted markers during treatment in a large patient group.


METHODS
Intrafraction motion in the sagittal plane was studied by retrospective analysis of displacements of implanted gold markers on (nearly) lateral kV and MV images obtained at various time points during the treatment fractions (mean, 27 per patient) in 108 consecutive patients. The effective prostate motion in a fraction was defined as the time-weighted mean displacement.


RESULTS
Prostate displacements in the sagittal plane increased during the fraction (mean, 0.2 ± 0.2 mm/min). Forty percent of patients had a systematic (i.e., appearing in all fractions) effective displacement in the sagittal plane greater than 2 mm. Observed effective population mean-of-means (μeff) +/- systematic (Σeff) intrafraction motion (μ(eff) ± Σ(eff)) was 0.9 ± 1.1 mm and 0.6 ± 1.0 mm for the anterior-posterior and superior inferior directions, respectively. Corresponding random motion (σ(eff)) was 1.2 mm and 1.1 mm. Mean effective prostate motion in the first 5 fractions was predictive for mean effective displacement in the remaining fractions (p < 0.001).


CONCLUSIONS
For a large subgroup of patients, the systematic component of intrafraction prostate motion was substantial. Intrafraction motion correction prior to each beam delivery or offline corrections could likely be beneficial for the subgroup of patients with significant motion. The systematic component is well predicted by measurements in the initial fractions.
Department of Radiation Oncology, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands.
Theodore F
TF
Mutanga
Hans C J
HC
de Boer
Vinayakrishnan
V
Rajan
Maarten L P
ML
Dirkx
Luca
L
Incrocci
Ben J M
BJ
Heijmen
D019583:Dose Fractionation, Radiation; D057918:Fiducial Markers; D006046:Gold; D006801:Humans; D008297:Male; D009068:Movement; D009426:Netherlands; D011467:Prostate; D011471:Prostatic Neoplasms / Q000532:radiotherapy*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors / Q000517:prevention & control*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D016683:Supine Position; D013997:Time Factors
D006046:Gold