Tomotherapy as a neoadjuvant treatment for locally advanced esophageal cancer might increase bone marrow toxicity in comparison with intensity-modulated radiotherapy and volumetric-modulated arc therapy.
This study compares dosimetric parameters in these following 3 neoadjuvant chemoradiotherapy (NCRT) methods in treating locally advanced esophagus cancer: helical tomotherapy (TOMO), volumetric modulated arc therapy (VMAT), and intensity-modulated radiotherapy (IMRT). It is aimed to ascertain the efficient technique that kept high target coverage and availed the dose sparing of bone marrow (BM). This research collected data on 11 patients from October 2014 to June 2017 who received NCRT for pathologically confirmed esophageal cancer. The prescription doses to the planning target volume (PTV) were all given as 60 Gy (2 Gy per fraction, 5 days a week). Three physicists via Varian Eclipse Treatment Planning System and Accuray planning stations redesigned 5 radiotherapy plans (fixed 5-field IMRT, fixed 7-field IMRT, 2-arc VMAT, 3-arc VMAT, and TOMO) for each of the patients. At the end of the planning, we then appraised the dosimetric quality based on the PTV parameters and the doses to organs at risk (OARs). In the study VMAT reached the highest conformity index (CI; 2 arcs VMAT: 0.74 ± 0.10; 3 arcs VMAT: 0.78 ± 0.07; p< 0.05), and IMRT the lowest homogeneity index (HI; fivefields IMRT: 0.12 ± 0.03; sevenfields IMRT: 0.10 ± 0.02; p< 0.05). Besides, 7 fields IMRT (0.10 ± 0.02) achieved superior HI to that of 5 fields IMRT (0.12 ± 0.03, p< 0.01). TOMO (p< 0.05) and VMAT (p< 0.05) were both significantly superior to IMRT in terms of the dose to lung (V5, V10, V15, V20, and V30). These 5 radiation techniques were similar regarding the dose to heart (V5, V20, and V30), but IMRT (5 fields IMRT: 19.27 ± 5.33; 7 fields IMRT: 20.05 ± 4.19) significantly raised the dose to the V50 of the heart when compared to VMAT (2 arcs VMAT: 16.6 ± 5.68; 3 arcs VMAT: 15.04 ± 5.75; p< 0.05) and TOMO (15.05 ± 4.7, p< 0.05). VMAT reduced the dose to BM (V5, V10, V20, and V30) as compared to TOMO (p< 0.05) and IMRT (p< 0.05). The CI of VMAT was the supreme one in those of the techniques in this study, so was the HI of IMRT. VMAT also provided another advantage that it reduced the dose to the BM. TOMO ameliorated the dose sparing of the lung, but the dose that the BM absorbed from TOMO was of some concern about BM toxicity.
Wang Y
，Xiao Q
，Zeng B
，Ni Q
，Liu X
，Liu X
，Tian L
，Sheng C
，Peng L
，Wang H
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Dosimetric comparison of TomoDirect, helical tomotherapy, VMAT, and ff-IMRT for upper thoracic esophageal carcinoma.
The new TomoDirect (TD) modality offers a nonrotational option with discrete beam angles. We aim to compare dosimetric parameters of TD, helical tomotherapy (HT), volumetric-modulated arc therapy (VMAT), and fixed-field intensity-modulated radiotherapy (ff-IMRT) for upper thoracic esophageal carcinoma (EC).
Twenty patients with cT2-4N0-1M0 upper thoracic esophageal squamous cell carcinoma (ESCC) were enrolled. Four plans were generated using the same dose objectives for each patient: TD, HT, VMAT with a single arc, and ff-IMRT with 5 fields (5F). The prescribed doses were used to deliver 50.4 Gy/28F to the planning target volume (PTV50.4) and then provided a 9 Gy/5F boost to PTV59.4. Dose-volume histogram (DVH) statistics, dose uniformity, and dose homogeneity were analyzed to compare treatment plans.
For PTV59.4, the D2, D98, Dmean, and V100% values in HT were significantly lower than other plans (all p < 0.05), and those in TD were significantly lower than VMAT and ff-IMRT (all p < 0.05). However, there was no significant difference in the D2 and Dmean values between VMAT and ff-IMRT techniques (p > 0.05). The homogeneity index (HI) differed significantly for the 4 techniques of TD, HT, VMAT, and ff-IMRT (0.03 ± 0.01, 0.02 ± 0.01, 0.06 ± 0.02, and 0.05 ± 0.01, respectively; p < 0.001). The HI for TD was similar to HT (p = 0.166), and had statistically significant improvement compared to VMAT (p < 0.001) and ff-IMRT (p = 0.003). In comparison with the 4 conformity indices (CIs), there was no significant difference (p > 0.05). For PTV50.4, the D2 and Dmean values in HT were significantly lower than other plans (all p < 0.05), and those in TD were significantly lower than VMAT and ff-IMRT (all p < 0.05). However, there was no significant difference in the D2 and Dmean values between VMAT and ff-IMRT techniques (p > 0.05). No D98 and V100% parameters differed significantly among the 4 treatment types (p > 0.05). HT plans were provided for statistically significant improvement in HI (0.03 ± 0.01) compared to TD plans (0.05 ± 0.01, p = 0.003), VMAT (0.08 ± 0.03, p < 0.001), ff-IMRT (0.08 ± 0.01, p < 0.001). The HI revealed that TD was superior to VMAT and ff-IMRT (p < 0.05). The CI differed significantly for the 4 techniques of TD, HT, VMAT, and ff-IMRT (0.59 ± 0.10, 0.69 ± 0.11, 0.64 ± 0.09, and 0.64 ± 0.11, respectively; p = 0.035). The best CI was yielded by HT. We found no significant difference for the V5, V10, V15, V30, and the mean lung dose (MLD) among the 4 techniques (all p > 0.05). However, the V20 differed significantly among TD, HT, VMAT, and ff-IMRT (21.50 ± 7.20%, 19.50 ± 5.55%, 17.65 ± 5.45%, and 16.35 ± 5.70%, respectively; p = 0.047). Average V20 for the lungs was significantly improved by the TD plans compared to VMAT (p = 0.047), and ff-IMRT (p = 0.008). The V5 value of the lung in TD was 49.30 ± 13.01%, lower than other plans, but there was no significant difference (p > 0.05). The D1 of the spinal cord showed no significant difference among the 4 techniques (p = 0.056).
All techniques are able to provide a homogeneous and highly conformal dose distribution. The TD technique is a good option for treating upper thoracic EC involvement. It could achieve optimal low dose to the lungs and spinal cord with acceptable PTV coverage. HT is a good option as it could achieve quality dose conformality and uniformity, while TD generated superior conformality.
Zhang Y
，Wang H
，Huang X
，Zhang Q
，Ren R
，Sun R
，Zheng Z
，Dong S
，Zheng A
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