Assessing the daily consistency of bladder filling using an ultrasonic Bladderscan device in men receiving radical conformal radiotherapy for prostate cancer

Abstract

Objective: Consistency in target organ and organ at risk position from planning to treatment is an important basic principle of radiotherapy. This study evaluates the effectiveness of bladder-filling instructions in achieving a consistent and reproducible bladder volume at the time of planning CT and daily during the course of radical radiotherapy for prostate cancer. It also assessed the rate of bladder filling before and at the end of radiotherapy. Methods: 30 men attending for radiation therapy planning for prostate cancer received written and verbal bladder-filling instructions. They had their bladder volume assessed using a bladder ultrasound scanner post-void, immediately prior to planning CT scan and then daily immediately prior to treatment while in the therapy position. The inflow was calculated using the void and full bladder volumes and the time for the bladder to fill. Results: The mean bladder volume at the time of planning was 282 ml (range 89-608 ml, standard deviation (SD)5144.5 ml). This fell during treatment, with a mean value for all treatments of 189 ml (range 11-781 ml, SD5134 ml). During radiotherapy, 76% (828/1090), 53% (579/1090) and 36% (393/1090) of bladder volumes had .50 ml, .100 ml and .150 ml difference, respectively when compared with their volume at the time of planning. Inflow reduced from 4.6 ml min -1 , SD52.9 min -1 at planning to 2.5 min -1 , SD51.8 min -1 after radiotherapy. Conclusion: The Bladderscan device (BVI 6400 Bladderscan, Verathon Medical UK, Sandford, UK) provides an effective means of assessing bladder volume prior to radiotherapy for prostate cancer. The evaluated bladder-filling protocol does not produce consistent, reproducible bladder volumes for radiotherapy. Reproducibility of target volume position is a fundamental component of external beam radiotherapy at any site, but is of particular importance where a doseescalated regimen is being employed and where the surrounding organs are both dose and volume sensitive. For men receiving dose-escalated radical prostate radiotherapy, a consistent bladder volume between planning and treatment is vital. Although there are differing opinions on the influence of bladder volume on interfraction prostate position [1][2][3][4][5][6][7], the influence of the irradiated bladder volume on acute and late urinary [8] and bowel toxicity [2,9] has been well documented.Despite the apparent importance of controlling bladder volume for prostate radiotherapy, there is surprisingly limited research into the provision of bladder-filling instructions that produce acceptable dose-volume histograms (DVHs) and provide a reproducible bladder volume from planning through to treatment [1-2, 10, 11] rather than an unreliable and misleading snapshot at the time of planning.This study was designed to first validate bladder volume measurements using a non-invasive transabdominal bladder ultrasound device (BVI 6400 Bladderscan, Verathon Medical UK, Sandford, UK) before using it to evaluate the effectiveness of standardised bladder-filling instru...

Assessing the consistency of bladder filling using an ultrasonic Bladderscan® device: Author response

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The Editor, We acknowledge and agree with the majority of comments on our paper published in the September issue of BJR [1] made by Dr Dudley and thank him for his input. The study protocol stipulated that men entering the study had no previous pelvic surgery, an anatomically normal functioning bladder and an International Prostate Symptom Score of ,15 without the use of either alpha-blockade or antimuscarinic therapy.

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“…When we examined data points that were beyond twice the limits of agreement, 25.6% (279/1090) were identified, with 22.2% (242/1090) on the inferior side. As such, we continue to look into how we can achieve a bladder volume at the time of planning which is more representative, consistent and reproducible over the course of radical prostate radiotherapy than in the current study [1]. …”

“…Dr Dudley is entirely correct, correlation assesses the degree of association between two measurements and not how closely they agree, which is why we calculated the limits of agreement as demonstrated in figure 1 [1]. We accept that our comment on the relationship between the difference between the bladder volumes on BUS and CT and the average bladder volume was poorly worded and would have been more correctly stated as ''at higher volumes CT tended to over estimate the bladder volume''.…”

Prostate Bed Radiation Therapy: The Utility of Ultrasound Volumetric Imaging of the Bladder

“…Overall, large bladder volumes have caused some concern with our CBCT protocol due to the limited field of view of the CBCT, resulting in the inability to identify and hence measure the bladder length. Additionally there was the concern regarding the ability of patients to maintain large volumes through their course of treatment [16,17]. By contrast, by allowing patients to proceed with treatment with a greatly reduced bladder volume not only risks compromised target volume coverage but increases the risk of excess dose to normal tissues, including the bladder itself and the small bowel.…”

Assessing the consistency of bladder filling using an ultrasonic Bladderscan® device

“…The Editor, Hynds et al [1] assessed the daily consistency of bladder filling using a BVI 6400 BladderscanH (Verathon Medical UK, Sandford, UK). This device is marketed to help in the diagnosis of urinary retention as an aid in prevention of unnecessary catheterisation and is widely and successfully used for this purpose.…”