Dosimetric Comparison of Volumetric Modulated Arc Therapy (VMAT), 5F Intensity Modulated Radiotherapy (IMRT) and 3D Conformal Radiotherapy (3DCRT) in Rectal Carcinoma Receiving Neoadjuvant Chemoradiotherapy

Abstract

Objective: To investigate better dosimetric distribution of volumetric modulated arc therapy (VMAT) vs. 5F intensity modulated radiotherapy (IMRT) and 3D conformal radiotherapy (3DCRT) in patients with locally advanced rectal cancer (LARC) when treated with neoadjuvant chemoradiotherapy. Methods: 3D-CRT, 5F-IMRT and VMAT plans for preoperative radiotherapy were designed in 12 patients with locally advanced rectal cancer. The conformity index (CI) and homogeneity index (HI) in target volume, and the dose and volume of the organs at risk (OAR) irradiated including small bowel, bladder and bilatera1 femoral heads were compared among the three plans. Results: The CI for planning target volume (PTV) 2 and HI for PTV1 of VMRT and 5F-IMRT were superior to 3D-CRT. The CI of VMAT, 5F-IMRT and 3D-CRT plans were 0.71, 0.69 and 0.62 (p = 0.011 and p = 0.019, respectively). The HI of the VMAT and 5F-IMRT plans were both 1.04 and 3D-CRT planning was 1.06 (p = 0.022 and p = 0.006, respectively). The V35 -V45 of small bowel * Corresponding authors. G. Wen et al. 55in VMAT were significantly less than in 5F-IMRT and 3D-CRT. V35 was 47.0, 56.4, and 72.8 cm 3 for VMAT, 5F-IMRT, and 3D-CRT (p = 0.021 and p = 0.034, respectively), while V40 was 30.5, 35.5, 45.1 cm 3 (p = 0.024 and p = 0.032, respectively) and V45 was 15.1, 18.1, 30.0 cm 3 (p = 0.033 and p = 0.032, respectively). The D5, V30 and V50 of bladder in 3D-CRT were less than in VMAT and 5F-IMRT planning (p = 0.034, 0.004, 0.002 and p = 0.027, 0.003, 0.002, respectively). The Dmean of left femoral head in VMAT and 5F-IMRT were less than in 3D-CRT planning (p = 0.028 and p = 0.022, respectively) and the Dmean, V30 of right femoral head in VMAT and 5F-IMRT were better than in 3D-CRT planning (p = 0.044, 0.036 and p = 0.023, 0.028, respectively). Conclusions: Dosimetric analyses demonstrated that IMRT is superior to 3D-CRT in the conformity and homogeneity of dose distribution to the target volume, and provide a better protection to OARs sparing in patients with locally advanced rectal cancer for preoperative radiotherapy. With similar target coverage, VMRT is superior to 5F-IMRT in normal tissue sparing.

A Review of Neoadjuvant Chemoradiotherapy for Locally Advanced Rectal Cancer

“…Studies also compared volumetric modulated arc therapy (VMAT) and IMRT in patients with locally advanced rectal cancer (LARC) when treated with neoadjuvant chemoradiotherapy. Wen's study found that VMRT showed similar target coverage as IMRT does but with superior normal tissue sparing 40 . This indicates VMAT may be better in neoadjuvant radiotherapy, but this need more studies and evidence.…”

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“…They concluded that VMAT provided better dose conformity with significant savings of femoral heads and a significant reduction in full and average doses to normal tissues. In a dosimetric comparative study, Wen et al (2015) delivered a dose of 50 Gy on PTVG in 23 fractions of 2.17 Gy and 46 Gy on PTV in 23 fractions of 2 Gy. They concluded that VMAT allows good conformity (0.37 ± 0.09 vs 0.71 ± 0.06) and homogeneity (1.04 ± 0.01 vs 1.13 ± 0.01) of PTVG and PTV.…”

“…In the majority of published studies, VMAT has achieved the dose constraint objectives. Indeed, Wen et al (2015) had a good DVH for the small bowel with a Dmean of 16.92Gy and D5% of 35.53 Gy. In a study comparing VMAT to 3D radiotherapy, Droge et al (2015) demonstrated better protection of the small bowel by VMAT (V40 = 28.4% and Dmean = (16.24 ± 3.09) Gy).…”

Importance of neoadjuvant treatment in management of locally advanced rectal cancer

“…Novi pravac u istraživanju predstavlja studija Wen-a i sar. [13] u kojoj se poredi efekat primene volumetrijski modulisane lučne terapije (VMAT -Volumetric Modulated Arc Therapy) u odnosu na IMRT. VMAT tehnika obezbeđuje sličnu homogenost u ozračivanju zračnog volumena, ali je superiornija u zaštiti normalnog okolnog tkiva u odnosu na IMRT.…”

“…VMAT tehnika obezbeđuje sličnu homogenost u ozračivanju zračnog volumena, ali je superiornija u zaštiti normalnog okolnog tkiva u odnosu na IMRT. Smatra se da će odgovor na pitanje da li VMAT tehniku treba koristiti u neadjovantnom pristupu lečenja dati buduće studije sa većim brojem bolesnika [13].…”