World J Nephrol Urol

World Journal of Nephrology and Urology, ISSN 1927-1239 print, 1927-1247 online, Open Access

Article copyright, the authors; Journal compilation copyright, World J Nephrol Urol and Elmer Press Inc

Journal website https://wjnu.elmerpub.com

Original Article

Volume 15, Number 3, July 2026, pages 71-81

Association Between Bladder Volume Changes and Organ-at-Risk Dose Constraints in a Moderate Hypofractionation for Prostate Cancer

↓ Figure 1. Participant flow diagram. CBCT: cone beam computed tomography; CT: computed tomography; DVH: dose–volume histogram.

↓ Figure 2. Correlation between bladder volume (mL) and bladder dose (dose–volume constraints) in the 70 Gy/28 fractions radiotherapy protocol. LOWESS: locally weighted regression plots.

↓ Figure 3. Correlation between bladder volume (mL) and rectal dose (dose–volume constraints) in the 70 Gy/28 fractions radiotherapy protocol. LOWESS: locally weighted regression plots.

↓ Figure 4. Correlation between bladder volume (mL) and bladder dose (dose–volume constraints) in the 60 Gy/20 fractions radiotherapy protocol. BC: bladder constraint; LOWESS: locally weighted regression plots.

↓ Figure 5. Correlation between bladder volume (mL) and rectal dose (dose–volume constraints) in the 60 Gy/20 fractions radiotherapy protocol. LOWESS: locally weighted regression plots; RC: rectal constraint.

↓ **Table 1.** Patient Characteristic
Patient characteristic, n (%)	70 Gy/28 Fr (n = 11)	60 Gy/20 Fr (n = 4)
Fr: fraction; Gy: gray; NCCN: National Comprehensive Cancer Network; SD: standard deviation.
Age (year), mean (± SD)	73 (5.0)	69 (6.3)
NCCN risk group
Low-risk	1 (9.1)	1 (25.0)
Favorable intermediate-risk	0	2 (50.0)
Unfavorable intermediate-risk	3 (27.3)	0
High-risk	7 (63.6)	1 (25.0)
Clinical stage
T1	2 (63.6)	0
T2	6 (54.6)	3 (75.0)
T3	2 (18.2)	1 (25.0)
T4	1 (9.1)	0
Bladder filling time (min), mean (± SD)	52 (12.3)	47.5 (8.6)

↓ Table 1. Patient Characteristic

Patient characteristic, n (%)

70 Gy/28 Fr (n = 11)

60 Gy/20 Fr (n = 4)

Fr: fraction; Gy: gray; NCCN: National Comprehensive Cancer Network; SD: standard deviation.

Age (year), mean (± SD)

73 (5.0)

69 (6.3)

NCCN risk group

Low-risk

1 (9.1)

1 (25.0)

Favorable intermediate-risk

2 (50.0)

Unfavorable intermediate-risk

3 (27.3)

High-risk

7 (63.6)

1 (25.0)

Clinical stage

2 (63.6)

6 (54.6)

3 (75.0)

2 (18.2)

1 (25.0)

1 (9.1)

Bladder filling time (min), mean (± SD)

52 (12.3)

47.5 (8.6)

↓ **Table 2.** Bladder Volume Thresholds (95th and 100th Percentiles) and Adjusted Dose Constraint Correlations by Radiotherapy Protocol and Organ at Risk
	P₉₅ BV (mL)	P₁₀₀ BV (mL)	Adjusted BV vs. dose constraint correlation
Statistical analysis was performed using multilevel mixed-effects regression, adjusting for age, prostate cancer recurrence risk (unfavorable/high), and bladder filling session number. ^a–eThe reported bladder volume values correspond to the following percentiles: ^a95.9th percentile; ^b96.2th percentile; ^c97.6th percentile; ^d96.4th percentile; ^e99th percentile. P95 BV and P100 BV: Bladder volumes at which 95% and 100% of radiotherapy sessions, respectively, did not exceed the dose constraint (i.e., no overdose observed). NA: No session exceeded the dose threshold for the specified constraint. BV: bladder volume; CI: confidence interval; Fr: fraction; Gy: gray; RD: risk difference; SE: standard error.
70 Gy/28 Fr dose constraint
Bladder constraints (%)
V79 < 15%	NA
V74 < 25%	NA
V69 < 35%	173.9	238.2	–6.4 (–7.3, –5.6)	0.45	< 0.001
V64 < 50%	85.2	238.2	–7.8 (–8.7, –6.8)	0.49	< 0.001
Rectum constraints (%)
V74 < 15%	NA
V69 < 25%	< 43.4^a	243.9	–1.0 (–2.0, –0.1)	0.47	0.029
V64 < 35%	< 43.4^b	323.3	–1.4 (–2.6, –0.3)	0.59	0.017
V50 < 50%	288.4	537.5	–2.2 (–3.7, –0.8)	0.74	0.003
60 Gy/20 Fr dose constraint
Bladder constraints (%)
V60 < 5%	223	364.2	–3.1 (–4.3, –1.9)	0.61	< 0.001
V48.6 < 25%	166.6	243.9	–5.6 (–7.1, –4.1)	0.78	< 0.001
V40.8 < 50%	< 81.1^c	125	–7.8 (–9.6, –6.0)	0.90	< 0.001
Rectum constraints (%)
V60 < 3%	293.9	362.4	–0.1 (–0.9, 0.7)	0.40	0.755
V57 < 15%	< 112.7^d	265.3	–0.4 (–1.7, 0.8)	0.64	0.519
V52.8 < 30%	< 112.7^d	282.6	–0.9 (–2.7, 0.9)	0.91	0.351
V48.6 < 50%	< 228.9^e	265.3	–0.8 (–3.0, 1.4)	0.11	0.463
V40.8 < 60%	223	282.7	–1.0 (–3.5, 1.5)	0.13	0.424

↓ Table 2. Bladder Volume Thresholds (95th and 100th Percentiles) and Adjusted Dose Constraint Correlations by Radiotherapy Protocol and Organ at Risk

P₉₅ BV (mL)

P₁₀₀ BV (mL)

Adjusted BV vs. dose constraint correlation

RD per 100 mL BV (95% CI)

P value

Statistical analysis was performed using multilevel mixed-effects regression, adjusting for age, prostate cancer recurrence risk (unfavorable/high), and bladder filling session number. ^a–eThe reported bladder volume values correspond to the following percentiles: ^a95.9th percentile; ^b96.2th percentile; ^c97.6th percentile; ^d96.4th percentile; ^e99th percentile. P95 BV and P100 BV: Bladder volumes at which 95% and 100% of radiotherapy sessions, respectively, did not exceed the dose constraint (i.e., no overdose observed). NA: No session exceeded the dose threshold for the specified constraint. BV: bladder volume; CI: confidence interval; Fr: fraction; Gy: gray; RD: risk difference; SE: standard error.

70 Gy/28 Fr dose constraint

Bladder constraints (%)

V79 < 15%

V74 < 25%

V69 < 35%

173.9

238.2

–6.4 (–7.3, –5.6)

0.45

< 0.001

V64 < 50%

85.2

238.2

–7.8 (–8.7, –6.8)

0.49

< 0.001

Rectum constraints (%)

V74 < 15%

V69 < 25%

< 43.4^a

243.9

–1.0 (–2.0, –0.1)

0.47

0.029

V64 < 35%

< 43.4^b

323.3

–1.4 (–2.6, –0.3)

0.59

0.017

V50 < 50%

288.4

537.5

–2.2 (–3.7, –0.8)

0.74

0.003

60 Gy/20 Fr dose constraint

Bladder constraints (%)

V60 < 5%

223

364.2

–3.1 (–4.3, –1.9)

0.61

< 0.001

V48.6 < 25%

166.6

243.9

–5.6 (–7.1, –4.1)

0.78

< 0.001

V40.8 < 50%

< 81.1^c

125

–7.8 (–9.6, –6.0)

0.90

< 0.001

Rectum constraints (%)

V60 < 3%

293.9

362.4

–0.1 (–0.9, 0.7)

0.40

0.755

V57 < 15%

< 112.7^d

265.3

–0.4 (–1.7, 0.8)

0.64

0.519

V52.8 < 30%

< 112.7^d

282.6

–0.9 (–2.7, 0.9)

0.91

0.351

V48.6 < 50%

< 228.9^e

265.3

–0.8 (–3.0, 1.4)

0.11

0.463

V40.8 < 60%

223

282.7

–1.0 (–3.5, 1.5)

0.13

0.424

↓ **Table 3.** Association Between Patient and Treatment Factors and the Risk of Weighted Overdose Counts, Analyzed Using Zero-Inflated Poisson Regression
Variables	Bladder constraint	Rectal constraint
60 Gy/20 Fr: One of the two radiation therapy protocols used in the study; the other was 70 Gy/28 Fr. Recurrence risk: High-risk or unfavorable intermediate-risk prostate cancer. BV: bladder volume; Fr: fraction; Gy: gray; IRR: incidence rate ratio; SE: standard error.
Age	1.08 (0.96, 1.21)	0.06	0.217	0.99 (0.90, 1.08)	0.05	0.760
Effect of sessions	1.00 (0.98, 1.01)	0.01	0.705	1.02 (0.99, 1.04)	0.01	0.148
BV per 100 mL	0.37 (0.17, 0.79)	0.14	0.011	0.80 (0.50, 1.25)	0.18	0.321
Recurrence risk	2.41 (1.12, 5.16)	0.94	0.024	1.48 (0.88, 2.48)	0.39	0.141
Filling time	1.05 (0.97, 1.14)	0.04	0.210	1.02 (0.97, 1.08)	0.03	0.387
60 Gy/20 Fr	15.4 (2.93, 81.02)	13.04	0.001	4.71 (1.45, 15.35)	2.83	0.010

↓ Table 3. Association Between Patient and Treatment Factors and the Risk of Weighted Overdose Counts, Analyzed Using Zero-Inflated Poisson Regression

Variables

Bladder constraint

Rectal constraint

IRR (95% CI)

P value

IRR (95% CI)

P value

60 Gy/20 Fr: One of the two radiation therapy protocols used in the study; the other was 70 Gy/28 Fr. Recurrence risk: High-risk or unfavorable intermediate-risk prostate cancer. BV: bladder volume; Fr: fraction; Gy: gray; IRR: incidence rate ratio; SE: standard error.

Age

1.08 (0.96, 1.21)

0.06

0.217

0.99 (0.90, 1.08)

0.05

0.760

Effect of sessions

1.00 (0.98, 1.01)

0.01

0.705

1.02 (0.99, 1.04)

0.01

0.148

BV per 100 mL

0.37 (0.17, 0.79)

0.14

0.011

0.80 (0.50, 1.25)

0.18

0.321

Recurrence risk

2.41 (1.12, 5.16)

0.94

0.024

1.48 (0.88, 2.48)

0.39

0.141

Filling time

1.05 (0.97, 1.14)

0.04

0.210

1.02 (0.97, 1.08)

0.03

0.387

60 Gy/20 Fr

15.4 (2.93, 81.02)

13.04

0.001

4.71 (1.45, 15.35)

2.83

0.010