Clinical impact of margin reduction on late toxicity and short-term biochemical control for patients treated with daily on-line image guided IMRT for prostate cancer.

To evaluate the impact of PTV reduction when delivering image-guided IMRT (IG-IMRT) for patients with prostate cancer. Between 2001 and 2007, 165 men were treated with daily IG-IMRT using a 3D ultrasound-based system. Median dose prescribed to the prostate was 78 Gy [74 Gy-78 Gy]. Patients were stratified regarding the CTV to the PTV margin: group A (n=87)=5mm or group B (n=78)=10mm. Late toxicity was scored using the CTC v3.0 scale. Biochemical progression-free survival (bPFS) was calculated using the Phoenix definition. Grade 2 genitourinary toxicity was 7.0% for group A and 6.6% for group B (p=1.00). Grade 2 gastrointestinal toxicity was 1.2% and 2.6% (p=0.38). With a median follow-up of 38.3 months [5.25-87.3], bPFS at 3 years was 92.5% [82.4%-96.9%] in group A and 94.3% [85.5%-97.8%] in group B (p=0.84). IG-IMRT yielded very low rates of late toxicity. Margin had impact neither on short-term bPFS nor late toxicity.