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Published on: June 7, 2015
Impact of intrafractional respiratory-induced prostate mobility on PTV size
Dawid Bodusz1, Leszek Miszczyk1
1Radiotherapy Department, Maria Skłodowska-Curie Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Gliwice - Poland.
Purpose:
Daily image-guided radiation therapy significantly reduces setup errors, but it does not minimize intrafractional target mobility; respiratory-induced target motion is one of the reasons for this. Therefore, the main aim of this study was to evaluate the impact of respiratory-induced prostate motion on the clinical target volume (CTV) margins.
Methods:
The analysis comprised 50 videos stored in digital format and recorded in a group of 50 patients during image-guided radiation therapy for prostate cancer. Fluoroscopy time was 10 seconds. Respiratory motion of the prostate in the anterior-posterior and lateral direction was assessed on the basis of a fiducial marker (GoldAnchor) implanted into the prostate before the treatment planning procedure.
Results:
The average values and standard deviations of respiratory-induced prostate motion in the superior-inferior and left-right (lateral) directions were 2.6 ± 2.1 mm and 0.7 ± 0.7 mm, respectively. The CTV margins calculated according to the van Herk formula based on respiratory prostate motion were 8 mm in the superior-inferior direction and 2 mm in the lateral direction.
Conclusions:
Respiratory-induced prostate mobility during radiotherapy is significant especially in the superior-inferior direction, and can thus induce a geographical error. This confirms the need for determining CTV margins for this type of respiratory-induced mobility.
