S1283
Clinical - Urology
ESTRO 2026
differences in percentage overlap between the expanded prostate and surrounding OOIs, when comparing postures.
one of the most common indications for radiotherapy, this study aimed to quantify posture-induced differences in male pelvic anatomy in order to consider the likely clinical impact of upright positioning on prostate radiotherapy. Material/Methods: 14 Healthy male volunteers were imaged both upright and supine using a FONAR multi-position 0.6T MRI scanner (axial T2-weighted sequences). Participants maintained a full bladder for both upright and supine acquisitions. This dataset was previously used to examine the effects of posture on anatomical marker points[1], but here the analysis was extended to include complete Organs of Interest (OOI) contours generated and validated by radiation oncologists. Our methods (Fig. 1) include: (A) Rigid alignment of paired upright and supine scans using the femoral heads as reference points, with calculation of relative displacements for the prostate and OOIs, based on their centres of mass; (B) Calculation of the separation distance between each OOI voxel and its closest neighbour on the prostate surface, averaged for each OOI; (C) addition of prostate shells/margins (up to 5mm) and calculation of percentage overlap with surrounding OOIs.
Conclusion: The results from analysis B indicate that the average prostate-bladder and prostate-penile bulb separation distances are larger in upright postures. Margin-based analysis C suggests that this increased average separation may not lead to a strong dosimetric impact, but further investigation via full treatment planning studies with consistent bladder filling is warranted. Day-to-day variation in prostate position should also be explored for upright versus supine postures. References: [1] Schreuder, A., Hsi, W. C., Greenhalgh, J., Kissick, M., Lis, M., Underwood, T. S. A., Freeman, H., Bauer, M., Towe, S., & Mackie, R. (2023). Anatomical changes in the male pelvis between the supine and upright positions—A feasibility study for prostate treatments in the upright position. Journal of Applied Clinical Medical Physics, 24(11), e14099. [2] Oguma, K., Yamada, Y., Koike, N., Fukada, J., Yamada, M., Yokoyama, Y., Takeda, A., Shigematsu, N., & Jinzaki, M. (2025). Simulation Study of Upright Prostate Radiation Therapy: Comparison of Upright and Supine Anatomy and Dose-Volumetric Factors. Practical Radiation Oncology, 0(0). Keywords: Prostate, Anatomy, Upright RT The Role of PSMA-PET in Detecting Recurrence in Patients with BCR After Primary RT for Localised Prostate Cancer: A Systematic Review Omar Alghazo 1 , Thomas Milton 2 , Kate Wilson 3 , Mrunal Hiwase 1,4 , Michael S Hofman 5,6 , Matthew Hong 4,1 , Alex Jay 1,4 , Michael O'Callaghan 1,4 1 College of Medicine and Public Health, Flinders University, Adelaide, Australia. 2 Urology, Royal Adelaide Hospital, Adelaiade, Australia. 3 Urology, Royal darwin Hospital, Darwin, Australia. 4 Urology, Flinders Medical Centre, Adelaiade, Australia. 5 Molecular Medicine, petermaccalum cancer Centre, Melbourne, Digital Poster 3966
Results: We found that OOIs typically moved inferiorly with upright positioning (see Figure 1, part II), with the following mean±stdev shifts: prostate (9.81±4.02mm), seminal vesicles (13.43±5.15mm), rectum (5.43±5.15mm), bladder (4.04±5.42mm) (results from analysis A). These inferior shifts under gravity are consistent with previous CT-based findings[2]. In analysis B, the prostate-bladder and prostate-penile bulb separation distances increased significantly in the upright position (p=0.0023 and p=0.0012, respectively, two-tailed t-tests), whereas prostate-rectum and prostate-seminal vesicle separation distances remained consistent between the two positions. Analysis C showed no statistically significant
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