Intensity-modulated radiotherapy is superior to three-dimensional conformal radiotherapy in the trimodality management of muscle-invasive bladder cancer with daily cone beam computed tomography optimization

Objective Intensity-modulated radiation therapy (IMRT) using a volumetric-modulated arc therapy technique may offer dosimetric and clinical benefits compared to the historical standard of care 3D conformal radiotherapy (3D-CRT) in definitive treatment of bladder cancer. We hypothesized that IMRT with CBCT would reduce dose to the rectum, bowel, and bladder compared to 3D-CRT. Methods We reviewed nineteen patients treated with maximal transurethral resection of bladder tumor followed by concurrent chemotherapy with IMRT. All patients received 45 Gy to the entire empty bladder followed by 19.8 Gy tumor boost treated with full bladder. 3D-CRT treatment plans were created for the same prescription. Paired t test or Wilcoxon matched-pairs signed rank test analyzed dosimetry and bladder volumes. Results The rectum and bowel V40, V45, V50, V55, and V60 were reduced by over 50% in the IMRT plans compared to 3D-CRT (p < 0.0001). IMRT also reduced volume of bladder irradiated compared to 3D-CRT (p < 0.01). After CBCT, patients were likely to undergo clinically significant shifts > 0.5 cm before boost delivery (p = 0.001). Bladder volumes were significantly lower during boost treatments compared to pre-treatment simulation (p = 0.002). There were 4 (21%) grade 3 genitourinary toxicities and 1 (5%) grade 3 gastrointestinal toxicity. Conclusion IMRT is superior to 3D-CRT for bladder cancer and spares dose to bowel, rectum, and bladder with improved acute toxicity compared to published clinical literature. For boost treatment, daily full bladder volume and positioning are not always reproducible, supporting the need for CBCT for optimal localization of the primary bladder tumor.