Evaluating Inter- and Intra-Fractional Variations In Bladder Cancer Precision Radiotherapy Using Fbct and Epid: Implications for Bladder Management
Abstract
Purpose
To investigate the inter- and intra-fractional morphological and dosimetric variations in precision radiotherapy for bladder cancer using Fan Beam CT (FBCT) and Electronic Portal Imaging Device (EPID), providing evidence for motion management.
Methods
A retrospective analysis was conducted on 17 patients who underwent radiotherapy with daily FBCT for image guidance and in vivo dose monitoring using EPID during treatment. Morphological and dosimetric parameters of the initial plan (Plan0) and plans calculated on FBCTs (PlanF) were obtained, as well as the gamma passing rate (GPR) of PlanF and invivo plans(PlanI: plans reconstructed from EPID dose during the radiotherapy).
Results
The overall 2D GPRs of 3%/3 mm of 263 fractions was 92.78% ± 4.91%. The 3D GPRs of 3%/3 mm, 2%/3 mm, 2%/2 mm, and 3 mm/5%, were 96.18% ± 5.47%, 94.43% ± 7.21%, 90.07% ± 9.07%, and 98.45% ± 3.20%, respectively. Group comparisons showed the GPRs was significantly higher in bladder-filling group than the bladder-empty group; the . GPRs was significantly higher in group with immobilization devices calculated than the group without. For the bladder-filling group (128 fractions), GPRs showed weak positive correlations with morphological changes of bladder (Dice and Jaccard index), and negative correlations with changes of Body (HD and Jaccard index). Inter-fraction difference between Plan0 and PlanF showed the Plan0 delivered higher doses to GTV D98%, D95% , bladder Dmean, rectum (Dmean and V10Gy ) ( P < 0.01). Intra-fraction difference between between PlanF and PlanI revealed that PlanF delivered slightly higher GTV(D98%, D95%) and lower bladder Dmean than PlanI (P<0.05). Additionally, the Inter- and Intra-fractional dose deviation of GTV showed positive correlations with the morphological changes of the bladder and rectum (Dice,HD) ( p<0.05)
Conclusion
The inter- and intra-fractional dose deviation was both correlated with changes of bladder and more attention should be payed to bladder management.