Copenhagen, Denmark
Onsite/Online

ESTRO 2022

Session Item

Sunday
May 08
09:00 - 10:00
Poster Station 1
09: Inter-fraction motion & adaptive radiotherapy
Mirjana Josipovic, Denmark
Poster Discussion
Physics
Analysis of the internal motion of the urethra caused by urethral catheters
David Sevillano, Spain
PD-0405

Abstract

Analysis of the internal motion of the urethra caused by urethral catheters
Authors:

David Sevillano1, Asunción Hervás2, Rafael Rodríguez-Patrón3, Juan David García-Fuentes4, Rafael Colmenares4, Carmen Vallejo2, Fernando López-Campos2, José Antonio Domínguez-Rullán2, Teresa Muñoz2, Miguel Cámara4, Belén Capuz4, Rafael Morís4, Pablo Galiano5, Pedro Retorta4, Sandra Williamson4, María José Béjar4, Daniel Prieto4, Feliciano García-Vicente4

1Hospital Universitario Ramón y Cajal., IRYCIS, Medical Physics, Madrid, Spain; 2Hospital Universitario Ramón y Cajal, IRYCIS, Radiation Oncology, Madrid, Spain; 3Hospital Universitario Ramón y Cajal, IRYCIS, Urology, Madrid, Spain; 4Hospital Universitario Ramón y Cajal, IRYCIS, Medical Physics, Madrid, Spain; 5Hospital Universitario Ramón y Cajal, IRYCIS, Medial Physics, Madid, Spain

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Purpose or Objective

To study differences between the real position of the urethra and that observed when a Foley catheter is used for its definition.

Material and Methods

10 prostate SBRT patients were included in this study. For each patient, two CT scans were performed. The first one with a 4mm-wide Foley urethral catheter and the second with a thin (0.9mm) guide-wire alone.

                Both CTs were registered based on 4 fiducial markers in the prostate. The urethra was contoured in both situations and data was exported to an in-house software designed for analysis purposes.

For each patient, the contours of the urethra in both CTs were divided into 21 sectors according to their relative longitudinal position along the prostate. Hence, population-based data on urethral position regardless the size of the prostate was obtained.

For each subsector the mean and SD of the differences between the urethra contoured with the Foley catheter and that contoured with the guide-wire were obtained for lateral and Anterior-Posterior directions.

Margins needed to design a PRV accounting for 90% of the population were also calculated by multiplying the standard deviation at each subsector by a factor of 2.15, as a 2D geometry was considered. 

Results

Differences between urethral positions in both cases are shown in Figure 1. Larger differences can be observed in the AP direction compared to those in the lateral direction. Differences are also larger in areas closer to the base of the prostate. While no systematic difference is observed in lateral direction, a 5mm difference occurs in the posterior direction.

Margins calculated in Table 1 increase as the urethra is closer to the base of the prostate. Margins needed in that area much larger than those usually applied by assuming urethral diameters of 8-10mm.

                According to these data, the use of a guide-wire to represent the urethra has become the common practice in our department, as it better represents the real position of the urethra.

Conclusion

                The use of a Foley catheter in the urethra causes an internal motion of the urethra relative to the prostate that might have dosimetric consequences. This motion is of larger importance close to the base of the prostate, where differences in position caused by the catheter might be larger than 1cm.

The use of a guide-wire to contour the urethra may avoid the need for larger PRV margins.

Conclusion

The use of a Foley catheter in the urethra causes an internal motion of the urethra relative to the prostate that might have dosimetric consequences. This motion is of larger importance close to the base of the prostate, where differences in position caused by the catheter might be larger than 1cm.

The use of a guide-wire to contour the urethra may avoid the need for larger PRV margins.