Evaluation of bladder dose in intensity-modulated radiation therapy of the prostate

Bladder volume reproducibility after water consumption in patients with prostate cancer undergoing radiotherapy: A systematic review and meta-analysis

BACKGROUND

To minimize toxicity due to radiotherapy in patients with prostate cancer, high bladder volume reproducibility is essential. Water consumption is often used to increase bladder volume reproducibility, but the optimal amount of water required to be consumed remains unclear. We aimed to analyzed the relationship between water consumption and bladder volume reproducibility in patients undergoing radiotherapy for prostate cancer.

METHODS

We conducted a systematic review and meta-analysis of randomized controlled trials and cohort studies that assessed bladder volume change after water consumption in patients with prostate cancer undergoing radiotherapy. MEDLINE, Embase, and Cochrane Central Register of Controlled Trials were searched for relevant studies published from database inception up until July 4, 2020. The Newcastle-Ottawa Scale was used to evaluate the risk of bias in the included studies. The outcome was the mean difference (MD) of bladder volume after water consumption, evaluated through meta-analysis using a random-effects model.

RESULTS

Ten cohort studies and one randomized controlled trial with a total of 417 patients were included. For 300-400 ml water consumption, the bladder volume MD between during treatment and at computer tomography-simulation (95% confidence interval [CI]) was -11.97 (-51.68 to 27.74), was -45.99 (-82.85 to -9.13) for 500-540 ml water consumption and -45.92 (-78.86 to -12.98) for water consumption until full-bladder sensation was reached.

CONCLUSION

Consuming 300-400 ml of water potentially leads to the best bladder volume reproducibility; moreover, the higher the water consumption volume, the lower the bladder volume reproducibility.

Planned versus 'delivered' bladder dose reconstructed using solid and hollow organ models during prostate cancer IMRT

BACKGROUND AND PURPOSE

All studies to date have evaluated the dosimetric effect of bladder deformation using an organ model that includes the dose to the urine. This research reconstructed bladder dose using both hollow and solid organ models, to determine if dose/volume differences exist.

MATERIALS AND METHODS

35 prostate IMRT patients were selected, who had received 78Gy in 39 fractions and full bladder instructions. Biomechanical modelling and finite element analysis were used to reconstruct bladder dose (solid and hollow organ model) using every third CBCT throughout the treatment course.

RESULTS

Reconstructed dose (ReconDose) was 11.3Gy greater than planned dose (planDose) with a hollow bladder model (p<0.001) and 12.3Gy greater with a solid bladder model (p<0.0001). Median reconstructed volumes within the 30Gy, 65Gy and 78Gy isodoses were 3-4 times larger with the solid organ model (p<0.0001). The difference between planning bladder volume and median treatment volume was associated with the difference between the planDose and reconDose below 78Gy (R(2)>0.61).

CONCLUSIONS

Substantial differences exist between planned and reconstructed bladder dose, associated with the differences in bladder filling between planning and treatment. Dose reconstructed using a solid bladder model over-reports the volume of bladder within key isodose levels and overestimates the differences between planned and reconstructed dose. Dose reconstruction with a hollow organ model is recommended if the goal is to associate that dose with toxicity.

Timing Variability of Bladder Volumes in Men Receiving Radiotherapy to the Prostate

BACKGROUND AND PURPOSE

Dose-escalated external-beam radiotherapy improves outcomes for localized prostate cancer but risks increasing the toxicity. One strategy to decrease this toxicity may be larger and more consistent bladder volumes. The primary objective of this study was to determine the time required for 95% of patients on a dose-escalated external-beam radiotherapy protocol to comfortably achieve a 180-cc bladder volume. In addition, measurement of patients' subjective assessment of urgency related to bladder filling was obtained to determine the feasibility of bladder-filling instructions.

METHODOLOGY

Thirty consenting patients with localized prostate cancer treated with external-beam radiotherapy were assigned 1:1 to 250-cc vs. 500-cc water preload. After voiding, patients drank the specified fluid preload and had their bladder volume and urinary urgency assessed at regular intervals over 2 hours, repeated at weeks 1, 4, and 7.

RESULTS

The time required for 95% of patients to achieve a bladder volume of 180 cc was 75 and 57 minutes for groups 1 and 2, respectively (P = .03). Serum creatinine and use of bladder medications did not influence time to optimal bladder filling. Participants in group 2 reported moderate to severe urinary severity more frequently than participants in group 1.

CONCLUSIONS

Time to optimal bladder volume was highly varied and was faster with a 500-cc fluid preload. Customizing the wait times based on calculated ultrasound-based filling rates appears feasible in a busy radiotherapy department.

A randomized trial comparing bladder volume consistency during fractionated prostate radiation therapy

PURPOSE

Organ motion is a contributory factor to the variation in location of the prostate and organs at risk during a course of fractionated prostate radiation therapy (RT). A prospective randomized controlled trial was designed with the primary endpoint to provide evidence-based bladder-filling instructions to achieve a consistent bladder volume (BV) and thus reduce the bladder-related organ motion. The secondary endpoints were to assess the incidence of acute and late genitourinary (GU) and gastrointestinal (GI) toxicity for patients and patients' satisfaction with the bladder-filling instructions.

METHODS AND MATERIALS

One hundred ten patients were randomly assigned to 1 of 2 bladder-filling protocols; 540 mL (3 cups) of water or 1080 mL (6 cups) of water, in a single institution trial. A portable ultrasound device, BladderScan BVI 6400 (Verathon Inc, Bothell, WA), measured BVs at treatment planning computed tomography (TPCT) scan and 3 times per week during RT. Maximum bladder dose and BV receiving ≥ 50, 60, and 70 Gy were recorded. Acute and late GU and GI toxicity were evaluated, as were patients' comfort, perception of urinary symptoms, and quality of life (QoL).

RESULTS

There was significantly less BV variation in the 540 mL arm when compared with 1080 mL (median: 76 mL vs 105 mL, P = .003). Larger BVs on initial TPCT correlated with larger BV variations during RT (P < .0005). There were no statistically significant associations between arm and GU/GI toxicity, dose median comfort scores, or median QoL scores.

CONCLUSIONS

The 540 mL bladder-filling arm resulted in reproducible BVs throughout a course of RT, without any deterioration in QoL or increase in toxicities for prostate patients.