Optimized Adaptive Radiotherapy with Individualized Plan Library for Muscle-Invasive Bladder Cancer Using Internal Target Volume Generation

Patient-specific adaptive planning margin for whole bladder radiation therapy

BACKGROUND

Whole bladder irradiation is an organ preservation treatment approach for muscle-invasive bladder cancer (MIBC). Conventional planning margins, typically 15-20 mm, increase normal tissue toxicity and limit possible dose escalation.

PURPOSE

The study aimed to develop a patient-specific adaptive margin recipe for whole bladder irradiation to minimize the planning target volume (PTV) while preserving adequate dose coverage.

METHODS

Sixteen patients who received whole-bladder irradiation were retrospectively selected for this study. We proposed a patient-specific anisotropic adaptive margin recipe, derived from the first five fractions of kV-CBCTs, to account for inter-fractional bladder changes. This recipe was validated using kV-CBCTs from fractions six to ten and the final five fractions. The goal was to achieve a residual volume, defined as the percentage of daily bladder volume (Vdaily) outside the PTV, of less than 5%. Adaptive and conventional plans were created using proposed and conventional margins, respectively. A dosimetric comparison of targets and organs-at-risk (OARs) was performed between the two approaches.

RESULTS

(Vdaily) decreased throughout the treatment course. The most notable inter-fractional bladder variations were in the superior and anterior directions. The patient-specific anisotropic adaptive margins, averaging 6 mm (± 2.9 mm), achieved a residual volume of less than 5%. Compared to conventional planning, the adaptive approach reduced PTV volume by an average of 135.3 cc (± 46.6 cc). A significant correlation (p < 0.05) was identified between residual volume and adaptive margins in the anterior, superior, left, and right directions. Using the proposed adaptive margins, the median residual volume was 0.71% (interquartile range 0.09%-3.55%), and the median (Vdaily) receiving the prescribed dose was 99.1% (interquartile range 95.3%-99.9%). Adaptive plans demonstrated superior OAR sparing compared to conventional plans.

CONCLUSIONS

The proposed patient-specific adaptive margin recipe for whole bladder irradiation resulted in margins smaller than conventional ones, optimized normal tissue sparing, and maintained adequate PTV coverage.

Adaptive radiotherapy for muscle invasive bladder cancer: a retrospective audit of two bladder filling protocols

BACKGROUND

Radical radiotherapy for muscle-invasive bladder cancer (MIBC) is challenging due to large variations in bladder shape, size and volume during treatment, with drinking protocols often employed to mitigate geometric uncertainties. Utilising adaptive radiotherapy together with CBCT imaging to select a treatment plan that best fits the bladder target and reduce normal tissue irradiation is an attractive option to compensate for anatomical changes. The aim of this retrospective study was to compare a bladder empty (BE) protocol to a bladder filling (BF) protocol with regards to variations in target volumes, plan of the day (PoD) selection and plan dosimetry throughout treatment.

METHODS

Forty patients were included in the study; twenty were treated with a BE protocol and twenty with a BF protocol to a total prescribed dose of 55 Gy in 20 fractions. Small, medium and large bladder plans were generated using three different CTV to PTV margins. Bladder (CTV) volumes were delineated on planning CTs and online pre-treatment CBCTs. Differences in CTV volumes throughout treatment, plan selection, PTV volumes and resulting dose metrics were compared for both protocols.

RESULTS

Mean bladder volume differed significantly on both the planning CTs and online pre-treatment CBCTs between the protocols (p < 0.05). Significant differences in bladder volumes were observed between the planning CT and pre-treatment CBCTs for BF (p < 0.05) but not for BE (p = 0.11). Both protocols saw a significant decrease in bladder volume between first and final treatment fractions (p < 0.05). Medium plans were preferentially selected for BE whilst when using the BF protocol the small plan was chosen most frequently. With no significant change to PTV coverage between the protocols, the volume of body receiving 25.0-45.8 Gy was found to be significantly smaller for BE patients (p < 0.05).

CONCLUSIONS

This work provides evidence in favour of a BE protocol compared to a BF protocol for radical radiotherapy for MIBC. The smaller treatment volumes observed in the BE protocol led to reduced OAR and total body doses and were also observed to be more consistent throughout the treatment course. These results highlight improvements in dosimetry for patients who undergo a BE protocol for MIBC.

TFRC, associated with hypoxia and immune, is a prognostic factor and potential therapeutic target for bladder cancer

BACKGROUND

Bladder cancer is a common malignancy of the urinary system, and the survival rate and recurrence rate of patients with muscular aggressive (MIBC) bladder cancer are not ideal. Hypoxia is a pathological process in which cells acquire special characteristics to adapt to anoxic environment, which can directly affect the proliferation, invasion and immune response of bladder cancer cells. Understanding the exact effects of hypoxia and immune-related genes in BLCA is helpful for early assessment of the prognosis of BLCA. However, the prognostic model of BLCA based on hypoxia and immune-related genes has not been reported.

PURPOSE

Hypoxia and immune cell have important role in the prognosis of bladder cancer (BLCA). The aim of this study was to investigate whether hypoxia and immune related genes could be a novel tools to predict the overall survival and immunotherapy of BLCA patients.

METHODS

First, we downloaded transcriptomic data and clinical information of BLCA patients from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. A combined hypoxia and immune signature was then constructed on the basis of the training cohort via least absolute shrinkage and selection operator (LASSO) analysis and validated in test cohort. Afterwards, Kaplan-Meier curves, univariate and multivariate Cox and subgroup analysis were employed to assess the accuracy of our signature. Immune cell infiltration, checkpoint and the Tumor Immune Dysfunction and Exclusion (TIDE) algorithm were used to investigate the immune environment and immunotherapy of BLCA patients. Furthermore, we confirmed the role of TFRC in bladder cancer cell lines T24 and UMUC-3 through cell experiments.

RESULTS

A combined hypoxia and immune signature containing 8 genes were successfully established. High-risk group in both training and test cohorts had significantly poorer OS than low-risk group. Univariate and multivariate Cox analysis indicated our signature could be regarded as an independent prognostic factor. Different checkpoint was differently expressed between two groups, including CTLA4, HAVCR2, LAG3, PD-L1 and PDCD1. TIDE analysis indicated high-risk patients had poor response to immunotherapy and easier to have immune escape. The drug sensitivity analysis showed that high-risk group patients were more potentially sensitive to many drugs. Meanwhile, TFRC could inhibit the proliferation and invasion ability of T24 and UMUC-3 cells.

CONCLUSION

A combined hypoxia and immune-related gene could be a novel predictive model for OS and immunotherapy estimation of BLCA patients and TFRC could be used as a potential therapeutic target in the future.