3364 - Spatial and Dosimetric Analysis of Local Recurrence Patterns after Trimodality Therapy for Bladder Cancer

12:45pm - 02:00pm PT

Hall F

Screen: 2

POSTER

Presenter(s)

Matthew Whitmill, MD - UNC Health, Chapel Hill, NC

M. A. Whitmill¹, B. M. Anderson¹, K. H. Gessner², Z. Feuer², D. Melwani³, M. C. Repka¹, S. Sud¹, C. Fahey⁴, H. J. Tan², M. A. Bjurlin², M. Milowsky⁴, W. Y. Kim⁴, T. L. Rose⁴, and A. Wijetunga⁵; ¹Department of Radiation Oncology, University of North Carolina, Chapel Hill, NC, ²Department of Urology, University of North Carolina, Chapel Hill, NC, ³Chicago College of Osteopathic Medicine, Chicago, IL, ⁴Division of Oncology, University of North Carolina, Chapel Hill, NC, ⁵Department of Radiation Oncology, University of North Carolina School of Medicine, Chapel Hill, NC

Purpose/Objective(s):

Trimodality therapy (TMT) is a bladder-preserving approach for muscle-invasive bladder cancer (MIBC) that achieves oncologic outcomes comparable to radical cystectomy. However, local recurrence (LR) remains a significant challenge, highlighting the need for improved understanding of failure patterns. This study uses a novel bladder subregion mapping strategy to evaluate the relationship between radiation dose distribution and LR, aiming to identify dose-related factors that may contribute to treatment failure.

Materials/Methods:

A retrospective analysis was conducted on patients who received TMT for MIBC within a large academic health system since 2009. A standardized bladder subregion template was deformably registered to each patient’s simulation scan to extract dose-volume histograms (DVHs) for six anatomical bladder regions (trigone [TG], dome [DM], anterior wall [AW], posterior wall , left lateral wall and right lateral wall). For cases with grossly visible tumor at simulation, a subregional analysis of 32 template bladder subregions was performed.

Radiotherapy doses were converted to EQD2Gy(a/B=10). D95 and D80 were computed for each region and subregion. Cohort-wide median D95 and D80 values were calculated for each anatomical region. For each patient, differences between region-specific doses and cohort-wide medians were analyzed for both initially involved and recurrence sites to assess dose deviations associated with LR.

Results:

A total of 105 patients who received RT as part of TMT for MIBC were included. The median age was 76 (range: 45-91) years, with 74% male and 26% female. Histology was predominantly urothelial with 30% of cases having at least a component of variant histology. Clinical stage distribution was 3% T1, 85% T2, 12% T3, and 4% T4, with 95% N0 and 5% N+. Concurrent chemotherapy was given in 98% of cases (39% Gemcitabine alone, 33% 5FU+MMC, 28% other).

LR occurred in 27 patients (19.3%), and 17 (63%) involved a lateral bladder wall. TG involvement before TMT (n=10, 37%) was associated with involvement at LF (p<0.001). Among patients with LR, the median D95 for each anatomical region ranged from 53.3 Gy to 58.9 Gy and the median D80 ranged from 56.1 Gy to 59.4 Gy.

Of anatomic regions which were scored by a urologist as being grossly involved pre-treatment, the median D95 in cases with recurrence in the same region was 2.8Gy lower than when the recurrence did not involve the same region (54.9Gy vs 57.7Gy, p=0.67).

The anatomic region with the highest rate of recurrence relative to the baseline involvement was the bladder dome (9 vs 6 cases), which also had the lowest median D95 of any region (53.3Gy vs 57.9Gy for non-dome regions, p=0.08)

Conclusion:

There is substantial local dosimetric variation in TMT for MIBC which can be quantified with an unbiased template approach. Future studies are needed to clarify whether regional dose differences correlate with local failure.