# Implementation of Cone Beam Computed Tomography-Guided Online Adaptive Radiotherapy for Challenging Trimodal Therapy in Bladder Preservation: A Report of Two Cases

## TL;DR

This paper presents two cases where advanced imaging-guided radiotherapy helped treat bladder cancer while preserving the bladder and managing complex patient conditions.

## Contribution

The paper demonstrates the clinical application of CBCT-guided online adaptive radiotherapy in complex bladder cancer cases.

## Key findings

- CBCT-guided oART was successfully used in patients with complex target-OAR interfaces.
- Patients experienced minimal side effects and no disease recurrence.
- The system enabled efficient treatment of complex clinical scenarios requiring bladder preservation.

## Abstract

Muscle invasive bladder cancer (MIBC) is an aggressive disease with a high risk of metastasis. Bladder preservation with trimodality therapy (TMT) is an option for well-selected patients or poor cystectomy candidates. Cone beam computed tomography (CBCT)-guided online adaptive radiotherapy (oART) shows promise in improving the dose to treatment targets while better sparing organs at risk (OARs). The following series presents two cases in which the capabilities of a CBCT-guided oART platform were leveraged to meet clinical challenges. The first case describes a patient with synchronous MIBC and high-risk prostate cancer with challenging target-OAR interfaces. The second recounts the case of a patient with a history of low dose rate (LDR) brachytherapy to the prostate who was later diagnosed with MIBC and successfully treated with CBCT-guided oART with reduced high-dose volume bladder targeting. To date, both patients report minimal side effects and are without disease recurrence. These cases illustrate how CBCT-guided online adaptive systems may efficiently aid radiation oncologists in treating patients with more complex clinical scenarios who desire bladder-sparing therapy.