A Feasibility Study on the Role of Ultrasound Imaging of Bladder Volume as a Method to Improve Concordance of Bladder Filling Status on Treatment with Simulation

Abstract

Purpose: Accurate positioning of the prostate is of paramount importance to ensure optimal target coverage and normal tissue sparing in stereotactic ablative body radiation when large doses per fraction are delivered with tight margins around the prostate. Bladder and rectal filling play an important part in controlling the accuracy of a patient's setup and therefore the overall toxicities and outcomes. The aim of this study was to establish the value of characterizing patients' bladder filling kinetics at the time of simulation with ultrasound scans so that a predictive model can be used to ensure that a bladder volume at treatment would match at simulation.

Daily Ultrasound Imaging for Patients Undergoing Postprostatectomy Radiation Therapy Predicts and Ensures Dosimetric Endpoints

“…5 Analyses on optimal bladder filling have shown that it takes about 57 to 75 minutes after consumption of 500 cm 3 of water to achieve bladder filling measured at 180 cm 3 . 3,6 These studies, however, did not analyze the effect of bladder filling variability on dosimetry.…”

“…This protocol is either based on treatment with a "comfortably full-bladder" or one that is centered around a voiding-filling-timing regimen to replicate the bladder filling at time of computed tomography (CT) simulation. [1][2][3][4][5][6] Treating patients with a full bladder is based on established dosimetric studies that demonstrate better sparing for the bladder and other organs at risk. 2,[7][8][9][10][11][12][13] However, studies based on daily and weekly on-treatment imaging have shown that bladder filling varies and can result in dosimetric variances that differ from the initial CT scan (and planning dose volume histogram [DVH]).…”

“…Pretreatment and on-treatment bladder volumes have also been measured through a wide range of techniques. 1,[4][5][6][15][16][17][18] Some of the most common regimens use daily or weekly cone beam computed tomography (CBCT) to compare the volumes with those at the time of simulation. 1,4,8,13,14,19 However, the bladder is a highly distensible organ and is unlikely to have a dose-volume represented by the planning DVH because of inconsistencies of the on-treatment bladder volume.…”

“…Ultrasound (US) has been used to evaluate pretreatment bladder volumes. 5,6,16,17 The volume calculation has been shown to be an easy and reliable real-time method to obtain bladder volume with reasonable accuracy. Clinics have also used custom filling instructions and wait times based on US bladder filling rates to achieve a consistent and reproducible bladder volume.…”

“…3 Several groups have compared and validated daily US bladder volumes with pretreatment CBCT bladder volumes and found strong correlation in their results. 6,17 Prior work related to daily US and CBCT imaging has focused on 2 separate components involved in patients' treatment: (1) daily/weekly CBCT to evaluate dosimetric bladder and rectum DVH values to report "true" endpoints based on daily anatomic variation and (2) the use of US to ensure a consistent and reproducible bladder volume. Our goal was to connect the 2 components, and to establish a data-driven process, via daily bladder US imaging and comparative CBCT, that defines bladder volume required to meet V40/65 constraints before placing a patient on the treatment table.…”