S2857
RTT - RTT education, training, and advanced practice
ESTRO 2026
parameters were analyzed: V95% for PTV55, Dmean for the rectum, V25.8 Gy and V45.8 Gy for the bowel. Results: In the analysis of all delivered plans (Figure 1), the median V95% for PTV55 was 89.7%, 96.2%, and 93.4% for the planned, adapted, and delivered plans, respectively. The dosimetric evaluation showed improved target coverage with the adapted and delivered plans compared with the initial scheduled plans. For OARs, similar results were observed across all plan types.Adapted plans were then stratified according to the bladder volume ratio: session bladder volume (Vol_S) divided by planning bladder volume (Vol_P) (Figure 2). The median mean rectal dose was higher when the bladder volume during treatment was smaller than at simulation, 15.1 Gy vs. 11 Gy when larger. For the bowel, dose–volume values increased when the bladder volume was larger during the treatment. In this case, the median volume receiving 45.8 Gy increases by 10 cc.
Conclusion: Adaptive treatment enables margin reduction while maintaining target coverage and minimizing irradiated volume. OAR exposure remains influenced by bladder volume variations between planning and treatment. Keywords: Bladder adaptative radiotherapy References: Dees-Ribbers, et al. (2014). Inter-and intra-fractional bladder motion during radiotherapy for bladder cancer: a comparison of full and empty bladders.Radiotherapy and Oncology,113(2), 254- 259.Åström, Lina M., et al. "Online adaptive radiotherapy of urinary bladder cancer with full re- optimization to the anatomy of the day: Initial experience and dosimetric benefits." Radiotherapy and Oncology 171 (2022): 37-42.
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