Presenter(s)
G. Kalinauskaite1,2, L. A. Künzel1, K. Rubarth1,3, J. Dannehl1, B. Bräutigam1, M. De Santis4, M. Beck1, J. Bauer1, D. Zips1, and C. Senger1; 1Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt Universität zu Berlin, Department of Radiation Oncology, Augustenburger Platz 1, 13353 Berlin, Germany, Berlin, Germany, 2Berlin Institute of Health at Charité – Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany, Berlin, Germany, 3Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and Humboldt Universität zu Berlin, Institute of Biometry and Clinical Epidemiology, Charitéplatz 1, 10117 Berlin, Germany, Berlin, Germany, 4Charité – Universitätsmedizin Berlin, corporate member of Freie Universität Berlin and HumboldtUniversität zu Berlin, Department of Urology, Charitéplatz 1, 10117 Berlin, Berlin, Germany
Purpose/Objective(s):
Online adaptive radiotherapy (oART) compensates for daily anatomical changes in bladder cancer; however, it remains unclear whether all patients derive comparable dosimetric benefit. We aimed to exploratively identify patterns of adaptive benefit and to determine how many patients demonstrate improvement in PTV coverage or organ-at-risk (OAR) sparing compared with non-adaptive plans.Materials/Methods:
In this prospective cohort study, twelve patients with histologically confirmed node-negative muscle-invasive bladder cancer undergoing trimodality therapy received CBCT-guided oART (55 Gy in 20 fractions). Target volumes were defined as: GTV= bladder; CTV= sex-specific extension (men: prostate base +1.5 cm; women: urethra +1 cm cranially); ITV = CTV +5 mm excluding bowel; and PTV = ITV +7 mm isotropic. Patients were instructed to empty their bladder before planning CT and each fraction. For each fraction, adapted and scheduled plans (reference plan recalculated on daily CBCT) were compared with respect to PTV D98% and small bowel dose–volume parameters. Per patient, median values across 20 fractions were calculated. Adaptive gain (?) was defined as adapted minus scheduled plan values; negative ? for bowel parameters indicates reduced irradiated volume with oART. Patients were exploratively stratified according to the dominant dosimetric effect into: coverage-rescue, OAR-sparing, and stable anatomy phenotypes. Results are reported as median (Q1–Q3).Results:
Adapted plans maintained PTV coverage comparable to reference plans and improved coverage relative to scheduled plans (D98%: 96.7% [96.30–96.90] adapted vs 93.7% [87.90–95.90] scheduled). The coverage-rescue group (n=3) demonstrated marked restoration of PTV coverage (median ? D98% of11.3%, Table 1). The OAR-sparing group (n=6) showed limited coverage change (median ? D98% of 1.7%) but substantial reductions in bowel high-dose exposure (median ?V50 of18 cc). Patients with stable anatomy (n=2) exhibited minimal change of both target coverage and OAR sparing. Overall, 9 of 12 patients demonstrated relevant adaptive benefit. Rectal dose changes did not define a distinct response pattern.Conclusion:
Online adaptive radiotherapy preserves robust target coverage while providing patient-specific OAR sparing. Exploratory pattern analysis suggests that adaptive benefit differs between patients, supporting individualized application of oART strategies.| Table 1. Patient-level adaptive gain by phenotype. | |||
| Parameter | Coverage-rescue (n=3) | OAR-sparing (n=6) | Stable-anatomy (n=2) |
| PTV DD98% [%] | 11.3 (8.8, 18.0) | 1.7 (0.0, 3.2) | 2.3 (2.1, 2.5) |
| Bowel DV54 [cc] | -0.3 (-5.9 to 5.3) | -9.9 (-20.8 to 1.7) | -10.3 (-11.9 to -9.2) |
| Bowel DV50 [cc] | -3.3 (-4.9 to -1.8) | -18 (-32.4 to -11.5) | -8.4 (-9.0 to -7.8) |
| Bowel DV41 [cc] | -5.2 (-8.15 to 1.5) | -20.1 (-34.5 to -14.3) | -8.4 (-11.0 to -5.8) |
| Values represent ? (adapted - scheduled) as median (Q1–Q3). | |||