Impact of image guidance on toxicity and tumour outcome in moderately hypofractionated external-beam radiotherapy for prostate cancer

To report toxicity and efficacy outcome of moderately hypofractionated image-guided external-beam radiotherapy in a large series of patients treated for prostate cancer (PCa). Between 10/2006 and 12/2015, 572 T1-T3N0M0 PCa patients received 70.2Gy in 26 fractions at 2.7Gy/fraction: 344 patients (60%) with three-dimensional conformal radiotherapy (3D-CRT) and 228 (40%) with intensity-modulated radiotherapy (IMRT). Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria and Houston definition (nadir+2) were used for toxicity and biochemical failure evaluation, respectively. Median age was 74years (interquartile range 69-77). Compared with 3D-CRT, in IMRT group more high-risk patients (29% vs 18%; P=0.002) and more high-volume target (75% vs 60%; P<0.001) were included. Acute gastro-intestinal (GI) toxicity G>1 were registered in 8% and in 11% IMRT and 3D-CRT patients, respectively, whereas late GI G>1 were observed in 2% and 16% IMRT and 3D-CRT patients, respectively. Acute genito-urinary (GU) toxicity G>1 were registered in 26% and 40% IMRT and 3D-CRT patients, respectively, whereas late GU G>1 occurred in 5% IMRT and 15% 3D-CRT patients. Multivariate proportional hazard Cox models confirmed significantly greater risk of late toxicity with 3D-CRT compared to IMRT for GU>1 (P=0.004) and for GI>1 (P<0.001). With a median 4-year follow-up, overall survival (OS), clinical progression-free survival (cPFS) and biochemical PFS (bPFS) for the whole series were 91%, 92% and 91%, respectively. cPFS and bPFS were significantly different by risk groups. Multivariate Cox models for bPFS and cPFS showed no difference between irradiation techniques and a significant impact of risk group and initial PSA. Moderately hypofractionated radiotherapy is a viable treatment option for localized PCa with excellent tumour control and satisfactory toxicity profile. IMRT seems associated with a reduction in toxicity, whereas tumour control was equal between IMRT and 3D-CRT patients and depended mainly on the risk category.