632 Background: To compare the areas of residual disease after neoadjuvant pelvic radiation with 5-FU based chemotherapy for rectal cancer using Intensity Modulated Radiation Therapy (IMRT) with simultaneous integrated boost (SIB) technique compared to 3D Conformal Radiation Therapy (3DCRT) Methods: Fourty nine (49) consecutive rectal cancer patients treated with pelvic radiation and concurrent 5-FU based chemotherapy were analyzed. We compared twenty-eight (28) patients treated on an institutional IMRT protocol versus twenty-one (21) patients treated with 3DCRT. All patients received 45-50.4 Gy to the pelvis in 3DCRT group. All patients with IMRT received 45 Gy in 25 fractions to the pelvic no des. The primary rectal tumor recieved a simultaneous integrated boost to a dose of 50 Gy in 25 fractions. IMRT planning was done with dose constraints for bladder, rectum, and small bowel and bone marrow. All patients in both groups received 5-FU based chemotherapy during radiation. Evaluation of toxicity was based on RTOG criteria. 2 patients in the 3DCRT group and 2 in IMRT group received either growth factors or blood-products transfusion and needed hospitalization during treatment secondary to acute toxicities. Results: All patients completed their prescribed course of radiation. CR rates were 5/21(23%) in 3DCRT and 4/28(25%) in the IMRT-SIB (p-value 0.74). 9/21(42%) in 3D and 19/29(65%) in the IMRT group underwent Low anterior resection according to the location of the tumor. There was no grade 4 toxicity in the IMRT-SIB group. Overall grade 2 toxicity in 3D Vs IMRT-SIB group was - GI -52% Vs 19%, GU- 8% Vs 8%, skin 42 Vs 4%, hematologic 33 Vs 47%. Overall Grade 1 toxicity in 3DCRT Vs IMRT group was- GI- 33% Vs 52%, GU 23% vs 28%, Skin 52% Vs 38%, hematologic 4% Vs 33%. Conclusions: Neoadjuvant pelvic radiation with 5 FU for rectal cancer has similar local control rates. There is less GI, skin and hematologic toxicity when delivered via IMRT-SIB versus 3DCRT. IMRT is safe and may allow dose escalation with potential probability of increased tumor response.
Dosimetric comparisons of VMAT, IMRT and 3DCRT for locally advanced rectal cancer with simultaneous integrated boost