Emerging evidence for the role of an endorectal balloon in prostate radiation therapy

Purpose: To reassess and update the role of an endorectal balloon (ERB) in prostate radiotherapy (RT) based on emerging evidence by reviewing various aspects of treatment methodologies and clinical outcomes. Methods and materials: A literature review based on a PubMed/MEDLINE database search using keywords such as: ERB, prostate RT, toxicities, real-time, image-guided radiotherapy (IGRT), radiofrequency-guided radiotherapy (RGRT), and inter- and intrafraction prostate motion for articles published over the past two years. Ten articles were identified and subdivided into three categories: (I) Issue of Motion, (II) Dosimetry, (III) Clinical Outcomes. Results: With the advent of real-time prostate tracking, analysis of intrafraction motion as a function of treatment time for patients treated with a daily-ERB was performed and revealed an overall reduction in 3D prostate motion, especially in the anterior-posterior direction. Two different groups of authors found that this reduction in intrafraction prostate motion allowed for tighter internal margins. Dosimetric studies showed overall improved dose distributions which for proton therapy were maximized when using ERBguided range verification for anteriorly oriented beams. Clinical outcomes showed favorable early GI toxicities however late toxicity results are still awaited. Conclusions: Utilizing a daily-ERB shows favorable early GI toxicity as well as reduced prostate intrafraction motion based on real-time tracking data. Reduced intrafraction motion improves the feasibility to use anteriorly oriented proton beams, which may further improve dosimetry.