Abstract
PurposeTo determine the best method to contour the planning organ at risk volume (PRV) for the urethra, this study aimed to investigate the displacement of a Foley catheter in the urethra with a soft and thin guide-wire.MethodsFor each patient, the study used two sets of computed tomography (CT) images for radiation treatment planning (RT-CT): (1) set with a Foley urethral catheter (4.0 mm diameter) plus a guide-wire (0.46 mm diameter) in the first RT-CT and (2) set with a guide-wire alone in the second CT recorded 2 min after the first RT-CT. Using three fiducial markers in the prostate for image fusion, the displacement between the catheter and the guide-wire in the prostatic urethra was calculated. In 155 consecutive patients treated between 2011 and 2017, 5531 slices of RT-CT were evaluated.ResultsAssuming that ≥3.0 mm of difference between the catheter and the guide-wire position was a significant displacement, the urethra with the catheter was displaced significantly from the urethra with the guide-wire alone in > 20% of the RT-CT slices in 23.2% (36/155) of the patients. The number of patients who showed ≥3.0 mm anterior displacement with the catheter in ≥20% RT-CT slices was significantly larger at the superior segment (38/155) than at the middle (14/155) and inferior segments (18/155) of the prostatic urethra (p < 0.0167).ConclusionsThe urethral position with a Foley catheter is different from the urethral position with a thin and soft guide-wire in a significant proportion of the patients. This should be taken into account for the PRV of the urethra to ensure precise radiotherapy such as in urethra-sparing radiotherapy.
Highlights
Radiation therapy is a common treatment modality for localized prostate cancer [1, 2]
If a Foley catheter is used in computed tomography (CT) for treatment planning but not in the actual delivery of urethrasparing radiotherapy (USRT), there is a risk of introducing discrepancies in the urethral position and dose distribution between the planned treatment and the actual treatment
Of 163 eligible patients, eight patients were excluded for the following reasons: cancer infiltration into the urethra (n = 2), refusal to urethral catheter insertion (n = 2), insertion was attempted but the insertion of the urethral catheter failed (n = 2), the guide-wire was accidentally removed before recording the second CT (n = 1), and accidental examination without the guide-wire at the second CT (n = 1)
Summary
Radiation therapy is a common treatment modality for localized prostate cancer [1, 2]. The image-guided intensitymodulated radiotherapy (IG-IMRT) with either conventional or hypofractionated schedules is the standard technology, and the incidences of acute and late gastrointestinal (GI) and genito-urinary (GU) toxicities are Dekura et al Radiation Oncology (2019) 14:226 soft, thin guide-wire in addition to the Foley catheter in the treatment planning for USRT [10]. They did not provide further details of the method. The present study aimed to investigate the magnitude of the positional discrepancy between the urethra with the Foley catheter plus guide-wire and the urethra with only the guide-wire in the CT for treatment planning
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