Cone-Beam Computed Tomography-Guided Online Adaptive Radiotherapy: Promising Results for Bladder Cancer Case

Area of Science:

• Radiation oncology
• Medical physics

Background:

• Bladder radiotherapy faces challenges from daily anatomical variations and unpredictable bladder filling, especially for cranial tumors.
• Conventional non-adaptive radiotherapy (non-ART) necessitates large planning target volume margins, increasing radiation dose to healthy tissues and toxicity risk.

Observation:

• This study compared daily online adaptive radiotherapy (oART) with non-ART in a bladder cancer patient with a challenging cranial tumor location.
• Liquid fiducial markers were used for precise tumor bed localization during simultaneous integrated boost delivery.
• Dose distributions from clinical oART fractions were compared against simulated non-ART fractions using post-treatment cone-beam computed tomography (CBCT).

Findings:

• Both oART and non-ART maintained 100% target coverage for the bladder and gross tumor volume.
• oART significantly reduced high-dose exposure to organs-at-risk, particularly the small bowel, compared to non-ART (p ≤ 0.05).
• The median volume of small bowel receiving 95% of the prescribed dose was 20 cm³ lower with oART. Total irradiated healthy tissue volume was also significantly reduced with oART (p ≤ 0.05).

Implications:

• CBCT-guided oART provides a conformal treatment for challenging bladder cancer cases.
• oART demonstrates a clear advantage in reducing toxicity by sparing healthy tissues.
• Long-term follow-up showed no toxicity effects in the treated patient, supporting oART's efficacy and safety.