Image-guided radiation therapy for muscle-invasive bladder cancer
Organ preservation protocols that incorporate chemoradiotherapy have shown good efficacy in bladder cancer. Owing to changes in rectal filling, urinary inflow and subsequent bladder volume with bladder wall deformations, irradiation must take into account interfractional and intrafractional internal target motion. Growing evidence suggests that image guidance during irradiation is essential in order to appropriately treat bladder cancer in this way. We performed a literature search on the imaging techniques and margins used for radiation therapy planning in the context of whole-bladder and partial-bladder irradiation. The most common image-guided radiation therapy (IGRT) method was based on cone-beam CT using anisotropic margins. The role of cine-MRI for the prediction of intraindividual bladder changes, in association with cone-beam CT or ultrasonography, is promising. Drinking protocols, diet and laxatives were used in most cases to minimize large variations in bladder size and shape. IGRT is crucial for avoiding tumor undercoverage and undue toxicity during radiation therapy for bladder cancer. IGRT-based adaptive radiation therapy can be performed using cone-beam CT or ultrasonography: modeling of bladder changes with cine-MRI or other imaging techniques might also be useful for facilitating adaptive radiation therapy with personalized margins.