To evaluate the efficacy and safety of intravesical hyaluronic acid (HA) instillation therapy for the prevention of radiation-induced cystitis in patients undergoing radiotherapy for bladder cancer.

Study Design: Single-blind, Randomized, Controlled trial.

• Primary endpoint

  - To assess patient-reported outcomes (PROs) related to symptoms of radiation-induced cystitis in patients with bladder cancer undergoing radiotherapy.

• Secondary endpoint

  • To evaluate tumor control rates in patients with bladder cancer undergoing radiotherapy.
  • To assess the incidence and severity of radiation-induced cystitis using RTOG/EORTC criteria, CTCAE grading, and cystoscopic findings.
  • To compare healthcare costs between the treatment group receiving intravesical hyaluronic acid instillation and the control group.

Inclusion Criteria:

1. Pathologic confirmed Muscle-Invasive Urothelial Carcinoma I. Clinical stage: T2-T4a MIBC II. No or limited nodal involvement (N0 or partial N1, only isolated or regional) III. No distant metastasis (M0) IV. Transurethral resection of bladder tumor (TURBT): Maximal TURBT is available > Most tumors must be resected, and residual disease should be minimized.

   V. Preserved bladder function is required: patients must have normal bladder capacity and maintain adequate voiding function.

   VI. Unifocal or localized tumor (except multifocal) VII. No extensive carcinoma in situ (CIS)

2. Age ≥ 19

3. Karnofsky performance score (KPS) ≥ 70 or ECOG performance status 0~2

4. Patients who are candidates for bladder-preserving therapy, specifically those scheduled to undergo concurrent chemoradiotherapy (CCRT) instead of radical cystectomy.

5. Patients scheduled to receive radiotherapy in combination with one or more of the following chemotherapeutic agents prior to study enrollment: Cisplatin-based chemotherapy (e.g. weekly cisplatin), Gemcitabine or 5-FU/mitomycin, in accordance with standard clinical practice.

6. Written informed consent obtained from the patients prior to study participation

Exclusion Criteria:

1. Present of distant metastasis (M1)
2. Tumor invasion beyond the bladder wall into adjacent organs (T4b)
3. Non-urothelial carcinoma (including histologic variant) or predominant of non-urothelial components in mixed histology
4. Medically inoperable status or poor general condition (ECOG performance status > 2)
5. History of active cystitis or recurrent urinary tract infections within the past 6 months
6. Known hypersensitivity to hyaluronic acid or related compounds
7. Any condition in which, in the investigator's judgment, administration of the study drug or procedure is deemed inappropriate
8. Pregnant or breastfeeding women, or women of childbearing potential who are unable or unwilling to use adequate contraception during the study period