INTRODUCTION: Both intensity-modulated radiotherapy (IMRT) and image-guided radiotherapy (IGRT) have been shown to independently reduce late rectal toxicity for men with prostate cancer (PC) treated with radiotherapy.
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We explore whether IMRT offers further reductions in late rectal toxicity for men already being managed with IGRT and compare this with more gradual changes over time.
METHODS: Between 2007 and 2009, 103 patients with PC were treated with three-dimensional conformal radiotherapy (3D-CRT n = 52) or IMRT (n = 51) with doses of 74–78 Gy at 2 Gy per fraction. All men had daily IGRT using intra-prostatic gold fiducials. The primary endpoint was incidence of grade ≥2 late rectal toxicity as graded by the Radiation Therapy Oncology Group scale.
RESULTS: The relative risk of late grade ≥2 rectal toxicity in patients treated with IMRT was 68% less than seen with image-guided 3D-CRT at 36 months post-treatment (7% versus 22%; hazard ratio = 0.32, P = 0.03). IMRT remained a significant protective factor in a multivariate analysis. A discriminant analysis showed that the relative volume of rectal wall exposed to doses over 50 Gy was most strongly associated with late rectal toxicity. Controlling for duration of follow-up, a later year of treatment was the strongest clinical predictor of late rectal toxicity in multivariate modelling (P = 0.03).
CONCLUSION: For men with PC managed to doses of 74–78 Gy with IGRT, IMRT leads to reduced rectal toxicity compared with 3D-CRT. Incremental improvements in treatment delivery over time also appear to have an independently strong beneficial effect.
Ratnayake G, Martin J, Plank A, Wong W. Are you the author?
Reference: J Med Imaging Radiat Oncol. 2014 Aug;58(4):503-10.