Aims

Radiotherapy with radiosensitisation offers opportunity for cure with organ preservation in muscle-invasive bladder cancer (MIBC). Treatment response assessment and follow-up are reliant on regular endoscopic evaluation of the retained bladder. In this study we aim to determine the role of diffusion-weighted magnetic resonance imaging (DWI) and apparent diffusion coefficient (ADC) analysis to assess bladder radiotherapy response.

Materials and methods

Patients with T2-T4aN0-3M0 MIBC suitable for radical radiotherapy were recruited prospectively to an ethics approved protocol. Following transurethral resection of the bladder tumour and prior to any treatment, magnetic resonance imaging including DWI was performed on a 1.5T system using b values of 0, 100, 150, 250, 500, 750 s/mm². DWI was repeated 3 months after completing radiotherapy. Cystoscopy and tumour site biopsy were undertaken following this. The response was dichotomised into response (<T2) or poor response (≥T2). Tumour region of interest was delineated on b750 s/mm² image and transferred to the ADC map to calculate per pixel ADC values for all b values (ADC_all) and high b values (ADC_b100). ADC mean, percentiles, skew, kurtosis and their change (ΔADC and %ΔADC) were determined. Threshold predictive of response with highest specificity was ascertained using receiver operating characteristic analysis.

Results

Thirty-four patients were evaluated. Response was associated with a significant increase in ΔADC mean compared with poor response at ΔADC_all (0.57 × 10⁻³ mm²/s versus –0.01 × 10⁻³ mm²/s; P < 0.0001) and ΔADC_b100 (0.58 × 10⁻³ mm²/s versus –0.10 x 10⁻³ mm²/s; P = 0.007). A 48.50% increase in %ΔADC_all mean was seen in response compared with a 1.37% decrease in poor response (P < 0.0001). This corresponded to a %ΔADC_b100 mean increase of 50.34% in response versus a 7.36% decrease for poor response (P < 0.0001). Significant area under the curve (AUC) values predictive of radiotherapy response were identified at ΔADC and %ΔADC for ADC_all and ADC_b100 mean, 10th, 25th, 50th, 75th and 90th percentiles (AUC >0.9, P < 0.01). ΔADC_all mean of 0.16 × 10⁻³ mm²/s and ΔADC_b100 mean 0.12 × 10⁻³ mm²/s predicted radiotherapy response with sensitivity/specificity/positive predictive value/negative predictive value of 92.9%/100.0%/100.0%/75.0% and 89.3%/100.0%/100.0%/66.7%, respectively.

Conclusions

Quantitative DWI analysis can successfully provide non-invasive assessment of bladder radiotherapy response. Multicentre validation is required before prospective testing to inform MIBC radiotherapy follow-up schedules and decision making.

中文翻译：

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通过定量扩散加权磁共振成像分析评估膀胱放疗反应

 目标

放射增敏放射治疗为肌层浸润性膀胱癌 (MIBC) 的器官保留治疗提供了机会。治疗反应评估和随访依赖于对保留膀胱的定期内窥镜评估。在本研究中，我们的目的是确定弥散加权磁共振成像 (DWI) 和表观弥散系数 (ADC) 分析在评估膀胱放疗反应中的作用。

 材料和方法

前瞻性招募适合根治性放疗的 T2-T4aN0-3M0 MIBC 患者，按照伦理批准的方案进行治疗。在经尿道切除膀胱肿瘤之后和任何治疗之前，在1.5T系统上使用0、100、150、250、500、750 s/mm ²的b值进行包括DWI的磁共振成像。完成放疗后 3 个月重复 DWI。此后进行膀胱镜检查和肿瘤部位活检。响应被二分为响应（ 2 图像并传输到 ADC 图，以计算所有 b 值 (ADC _all ) 和高 b 值 (ADC _b100 ) 的每像素 ADC 值。确定 ADC 平均值、百分位数、偏斜、峰度及其变化（ΔADC 和 %ΔADC）。使用接受者操作特征分析确定具有最高特异性的反应阈值预测。

 结果

对 34 名患者进行了评估。与 ΔADC _all （0.57 × 10 ⁻³ mm ² /s 对比 –0.01 × 10 ⁻³ mm ² /s； P < 0.0001）和 ΔADC _b100 （0.58 × 10）的不良响应相比，响应与 ΔADC 平均值显着增加相关。 ⁻³ mm ² /s 与 –0.10 x 10 ⁻³ mm ² /s； P = 0.007)。响应中 %ΔADC_均值增加了 48.50%，而响应较差时则下降了 1.37% ( P < 0.0001)。这对应于响应的 %ΔADC _b100平均增加 50.34%，而响应差则平均减少 7.36% ( P < 0.0001)。在_所有ADC 和 ADC _b100平均值、第 10、25、50、75 和 90 个百分位数的 ΔADC 和 %ΔADC 处确定了预测放疗反应的显着曲线下面积 (AUC) 值（AUC >0.9， P < 0.01）。 ΔADC_均值为 0.16 × 10 ^-3 mm ² /s，ΔADC _b100均值为 0.12 × 10 ^-3 mm ² /s 预测放疗反应，敏感性/特异性/阳性预测值/阴性预测值为 92.9%/100.0%/100.0%分别为/75.0%和89.3%/100.0%/100.0%/66.7%。

 结论

定量 DWI 分析可以成功地提供膀胱放疗反应的无创评估。在前瞻性测试之前需要进行多中心验证，以告知 MIBC 放疗随访时间表和决策。