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Intensity-Modulated Radiation Therapy Is Not Associated With Either Short-Term or Long-Term Benefit Over 3D-Conformal Radiotherapy for Rectal Cancer
Zhifei Sun*1, Mohamed A. Adam1, Mithun Shenoi1, Brian Czito2, John Migaly1, Christopher R. Mantyh1
1 Surgery, Duke University, Durham, NC; 2Radiation Oncology, Duke University, Durham, NC
Background
Use of intensity-modulated radiation therapy (IMRT) in rectal cancer has steadily increased over traditional 3D conformal radiotherapy (3D-CRT) due to perceived benefit of delivering higher treatment doses while minimizing exposure to surrounding tissues. However, IMRT is technically challenging and costly, and its effects on rectal cancer outcomes are unclear.
Methods
Adults with clinical stage II and III rectal adenocarcinomas who underwent neoadjuvant chemoradiotherapy with 45-54Gy of radiation and surgery were included from the 2006-2013 National Cancer Data Base. Patients were grouped based the modality of radiation received: IMRT or 3D-CRT. Multivariable regression modeling adjusting for demographic, clinical, and treatment characteristics was used to examine the impact of IMRT vs. 3D-CRT on resection margin positivity, need for permanent colostomy, 30-day unplanned readmission and mortality after surgery, and overall survival.
Results
Among 7,386 patients included, 3,330 (45%) received IMRT and 4,056 (55%) received 3D-CRT. Utilization of IMRT steadily increased over the study period from 24% in 2006 to 50% in 2013. While the mean radiation dose delivered was higher with IMRT (4735 vs. 4608 cGy, p<0.001), 3D-CRT was associated with lower risks of positive surgical margins (adjusted odds ratio [OR]: 0.64; 95% confidence interval [CI]: 0.49-0.83; p<0.001) and the need for permanent colostomy (OR: 0.76; CI: 0.66-0.87; p<0.001). There were no differences between IMRT and 3D-CRT in the rates of 30-day unplanned readmission (OR: 1.27; CI: 0.98-1.65; p=0.07) or 30-day mortality (OR: 1.63; CI: 0.64-4.18; p=0.31) after surgery. Additionally, there were no differences in overall survival at 8 years (3D-CRT vs. IMRT: 64.3% vs. 64.2%; adjusted hazard ratio: 0.96; CI: 0.8-1.14; p=0.61).
Conclusions
IMRT is associated with worse local tumor control without any long-term survival benefit for patients with locally advanced rectal cancer. Given the lack of significant advantage and the higher cost of IMRT, caution should be exercised when using IMRT instead of traditional 3D-CRT for rectal cancer.
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