A parameterized model for mean urinary inflow rate and its preliminary application in radiotherapy for cervical cancer

Abstract

Forty-nine patients with stage IIb cervical cancer were included to investigate the changes in bladder volume in response to different approaches to maintaining consistent bladder filling. The impacts of age (P age), water consumption (P wat), and body mass index (BMI, P bmi) on the mean urinary inflow rate (v tot) were analysed. The bladder volume (BV) increased linearly over time. A large variation in v tot among individuals was observed, ranging from 0.19 to 5.13 ml/min. The v tot was correlated with P age (R = −0.53, p = 0.01) and P wat (R = 0.84, p = 0.00), and no correlation between v tot and P bmi was found (p > 0.05). Therefore, v tot could be parameterized using two methods: multivariable linear regression and iterative fitting. There was no statistically significant difference between the two methods. The model accuracy was successfully assessed with several validation tests for patients with good compliance (79.2% of all patients), and the proportion of radiotherapy (RT) fractions with zero wait time (one ultrasound (US) scan) increased from 6.5% to 41.2%. The optimal US scanning number and RT time could be provided using this model. This adaptive RT approach could reduce patient discomfort caused by holding onto urine and reduce technician labour as well as cost.

Dynamic Changes in Bladder Morphology Over Time in Cervical Cancer Patients

“…A previous study reported large variations in the urinary filling rate among different patients. 11 In this study, the mean urinary filling rate also largely varied among patients. Fortunately, the approximate value can be calculated using a water-drinking- and age-based linear formula, and the result was also consistent with the previous findings.…”

“…The accuracy of the model was successfully assessed in patients with good compliance (79.2% of all patients), and the proportion of RT fractions with zero wait time (one US scan) increased from 6.5% to 41.2%. 11 However, these findings of previous studies covered a wide BV range, and it is unknown whether the variations in bladder shape and position were similar across the entire range, which was directly correlated with the RT dose coverage. Hence, the aims of this study were to further investigate the patterns of bladder motion, and to characterize the temporal and spatial changes of the bladder as a function of the BV (10-800 mL).…”

“…Fortunately, the approximate value can be calculated using a water-drinking- and age-based linear formula, and the result was also consistent with the previous findings. 11 Coincidentally, many age-based formulae for the bladder capacity benchmark are available. 16 These formulae can also be used to evaluate the movement of the bladder during treatment.…”

“…The accuracy of the model was successfully assessed in patients with good compliance (79.2% of all patients), and the proportion of RT fractions with zero wait time (one US scan) increased from 6.5% to 41.2%. 11 …”

“…10 Recently, we have investigated strategies for maintaining a consistent BV. 10,11 A "comfortably full bladder" approach was adopted using measurements with a portable ultrasound (US) scanner. Consistent BV was mostly achieved after multiple measurements within 2 h after water intake, and target margins were reduced in the superior-inferior (SI) direction.…”