Assessment of an ultrasound bladder scanner in prostate radiotherapy: A validation study and analysis of bladder filling variability

Abstract

Introduction During prostate radiotherapy treatment, it is important to ensure the position of the bladder and prostate is consistent between treatments. The aim of this study was to provide a quantitative basis for incorporating ultrasound bladder volume estimates into local practice for prostate radiotherapy. Methods Agreement between bladder volume estimates obtained using computed tomography (CT) and ultrasound was assessed. Analysis of bladder volumes between planning and treatment scans was used to quantify expected variations in bladder volume over the course of radiotherapy. Dose–volume statistics were estimated and compared to planned dose constraints to propose a target bladder volume and tolerance. Results Bladder volume measurements were obtained from 19 radiotherapy patients using ultrasound and CT. Ultrasound underestimated bladder volume compared to CT with a mean bias of –28 ± 30 ml. Pre-treatment (planning) bladder volumes varied from 71 to 383 ml with a mean of 200 ml. Treatment bladder volumes reduced by more than half in 9% of patients during the course of their treatment, potentially leading to a 30% increase in mean bladder dose. Patients with pre-treatment bladder volumes < 200 ml were most likely to exhibit differences in bladder volume, resulting in ‘out of tolerance’ increases in dose. Conclusions A pragmatic individualised drinking protocol, aimed at achieving a minimum ultrasound bladder volume of 200 ml at planning CT, may be beneficial to reproducibility in radiotherapy treatment. Ultrasound measurements prior to treatment should ideally confirm that bladder volume is at least half the volume measured at planning.

A prospective comparative study on bladder volume measurement with portable ultrasound scanner and CT simulator in pelvic tumor radiotherapy

“…Yoon et al [ 19 ] and Chang et al [ 7 ] conducted separate studies involving 20 patients with rectal cancer receiving RT, demonstrating a strong correlation between BV measured by BioCon-700 (Mcube Technology, Seoul, Korea) and CT ( r = 0.87, 0.93). Claxton et al [ 20 ] and Smith et al [ 6 ] measured BV in 20 patients with cervical/endometrial cancer and 19 patients with prostate cancer treated with RT, respectively, using BioCon-700 and CT, and obtained similar strong correlations. Stam MR et al [ 14 ] and O’Doherty et al [ 21 ] enrolled 26 and 41 patients with prostate cancer, respectively, and showed a strong correlation between BV measured by BladderScan BVI3000(Verathon Medical Europe, Washington State, USA) and CT ( r = 0.95, r = 0.88).…”

“…Bladder volume (BV) is a significant factor in determining the target volume for cervical/cervical cancer [ 3 , 4 ], prostate cancer [ 5 , 6 ], and rectal cancer [ 7 , 8 ]. Variations in BV among treatment fractions have been observed; Ahmad et al [ 4 ] found an average reduction of 71% in bladder capacity among patients with cervical cancer.…”

“…Therefore, a more objective approach to maintaining consistent BV is required to reduce the impact of bladder-volume changes on pelvic tumor radiation therapy. Daily Megavoltage Computed Tomography (MVCT) [ 5 ] and Cone Beam Computed Tomography (CBCT) [ 6 ] scans allow visualization of radiation targets and organs before each treatment. However, this method will only find that the filling material is insufficient when the patient is already on the treatment table.…”