Intensity-Modulated Radiation Therapy Is Not Associated with Perioperative or Survival Benefit over 3D-Conformal Radiotherapy for Rectal Cancer

Zhifei Sun, Mohamed A Adam, Jina Kim, Brian Czito, Christopher Mantyh, John Migaly

The 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 remain unclear. Adults with clinical stage II and III rectal adenocarcinoma who underwent neoadjuvant chemoradiotherapy with 45-54 Gy 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 pathologic downstaging, resection margin positivity, sphincter loss surgery, 30-day unplanned readmission and mortality after surgery, and overall survival. Among 7386 patients included, 3330 (45 %) received IMRT and 4056 (55 %) received 3D-CRT. While the mean radiation dose delivered was higher with IMRT (4735 vs. 4608 cGy, p < 0.001), it was associated with higher risks of positive margins (adjusted odds ratio (OR) 1.57; p < 0.001) and sphincter loss surgery (OR 1.32; p < 0.001). There were no differences between IMRT and 3D-CRT in the likelihood of pathologic downstaging (OR 0.89, p = 0.051), unplanned readmission (OR 0.79; p = 0.07), or 30-day mortality (OR 0.61; p = 0.31) after surgery. Additionally, there were no differences in overall survival at 8 years (IMRT vs. 3D-CRT: 64 vs. 64 %; adjusted hazard ratio 1.06, p = 0.47). 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.