Moderate dose escalation with volumetric modulated arc therapy improves outcome in rectal cancer

Locally advanced rectal cancer is frequently treated with a long course of preoperative chemoradiotherapy. We investigated the effect of moderate dose escalation with volumetric modulated arc therapy (VMAT) up to 50 Gy in 25 fractions compared to 3D conformal radiotherapy (3D-CRT) to 45 Gy in 25 fractions in rectal cancer patients. Dose-volume parameters, acute toxicity, and complete response rates were compared.

For both groups, 65 patients were selected from our database through availability. Dose-volume parameters and acute toxicity data were compared using a Mann-Whitney U-test. Univariate and multivariate analyses correcting for tumor and nodal stage, distance to the mesorectal fascia and interval to surgery were used to compare complete response rates.

Lower mean doses to the small and large bowel were observed in the VMAT group compared to the 3D-CRT group (21 Gy vs. 29 Gy [p < .001] and 26 Gy vs. 30 Gy [p = .002], respectively). Similar beneficial dose-volume parameters were observed for the bladder, sacrum and femoral heads. Furthermore, patients receiving VMAT experienced significantly less diarrhea, flatulence, non-infective cystitis, urinary frequency, dermatitis, and fatigue. In univariate analysis, a significant increase in complete response rate after moderate dose escalation with VMAT was observed (34% vs. 15%, p = .015). However, this did not remain significant when corrected for tumor and nodal stage, distance to the mesorectal fascia, and interval to surgery.

Moderate dose escalation with VMAT resulted in superior dose-volume parameters compared to 3D-CRT, translating into lower acute toxicity. Additionally, improved tumor response after VMAT up to 50 Gy might contribute to a higher percentage of patients achieving a complete response.