RCR11: Characterisation of tumour boost with diffusion weighted MRI (DW-MRI) to inform biological target volume for radical radiotherapy in muscle invasive bladder cancer (MIBC)
1The Institute of Cancer Research, London, UK,2The Royal Marsden NHS Foundation Trust, Sutton, Surrey, UK
DW-MRI quantifies water molecule motion within tissue using the apparent diffusion coefficient (ADC). As an imaging biomarker it has been related to tumour response. We investigate use of DW-MRI to personalise radiation dose delivery in MIBC.
21 MIBC patients suitable for radiotherapy were prospectively recruited. The tumour boost volume (GTV) was delineated using anatomical information on the radiotherapy planning CT scan. DW-MRI was performed on a 1.5T system using b values 0, 50,100, 250, 500 and 750s/mm2. GTV drawn on 750 s/mm2 images were transferred to the corresponding ADC map to determine mean values. Skew and kurtosis values were used to assess tumour heterogeneity. Volumes were compared using conformity index and Wilcoxon signed rank.
All tumours seen on T2 weighted images were identified on DW-images. In 3 patients no tumour was seen on T2 images or DW-image. GTV mean ADC value was 1.5 x10-3mm2/s (std.deviation 0.3; range 1.0-2.3). Mean skew and kurtosis was 2.1 (std.deviation 1.9; range 0.3-6.8) and 12.5 (std.deviation 23.6; range 0.9-83.5) respectively. Mean anatomical GTV was 34.1cm3 (std. deviation 21.1; range 6.7-78.7). Mean DW-MRI GTV was 15.6cm3 (std. deviation 23.4; range 0-104.4). Mean conformity index was 38% (std.deviation 32.5; range 0-132.6). There was significant reduction in DW-MRI GTV (p=0.001).
Acquiring DW-MRI for radiotherapy planning may complement target volume delineation and inform non-uniform dose delivery to biological sub-volumes for bladder radiotherapy dose escalation trials.