VMAT dosimetric study in rectal cancer patients

Abstract

The aim of this study was to evaluate the dosimetric results of patients treated by arc-therapy for rectal cancer at Al Kindy Oncology Center in Casablanca, Morocco. Twenty-five patients with locally advanced rectal cancer (T3, T4, N1, N2) treated by arc-therapy at doses of 46 Gy with a boost of 4 Gy sequentially or simultaneously integrated were collected. We analyzed and compared the dosimetric data of the two techniques using the dose volume histograms as well as the indices of conformity and homogeneity. Statistical analysis was performed using the SPSS v23 system (IBM Inc., Chicago, IL). Arc-therapy with simultaneous or sequential integrated boost allowed better coverage of target volumes. In fact, the D2% and D98% were (104.66 ± 0.50) and (96.62 ± 0.78), respectively. The homogeneity index was (0.078 ± 0.018) and the conformity index was (0.99 ± 0.015). For organs at risk, V30%, V40% and V50% were respectively (15.97 ± 12.97), (7.99 ± 9.15) and (2.36 ± 5.89) for the small bowel. When at the average dose, it was 13.38 Gy. The bladder was largely protected with a V40% of (33.01 ± 18.82) and an average dose of (27.89 ± 13.07) Gy. The V40% of the femoral heads was (3.68 ± 8.25). A comparison of the simultaneous integrated boost with the sequential boost showed that the coverage of the PTVs was similar. For organs at risk, the simultaneous integrated boost has very significantly (P <0.05) reduced doses in the small bowel. For the bladder and femoral heads the results of both techniques were similar. This study clearly shows that the Volumetric Modulated Arc Therapy (VMAT) technique provides a better dose distribution for PTV and OARs. The simultaneous integrated boost reduced the irradiated volumes of the small bowel resulting in a reduction in complications and toxicities.

Keywords:

DVH, ORAs, rectal cancer, target volumes, toxicity, VMAT