Abstract
There are no quantitative selection criteria for identifying high-grade glioma (HGG) patients who are suited for volumetric-modulated arc therapy (VMAT). This study aimed to develop selection criteria that can be used for the selection of the optimal treatment modality in HGG. We analyzed 20 patients with HGG treated by 3D conformal radiotherapy (3DCRT). First, VMAT plans were created for each patient retrospectively. For each plan, the normal tissue complication probability (NTCP) for normal brain was calculated. We then divided the patients based on the NTCPs of the 3DCRT plans for normal brain, using the threshold of 5%. We compared the NTCPs of the two plans and the gross tumor volumes (GTVs) of the two groups. For the GTVs, we used receiver operating characteristic curves to identify the cut-off value for predicting NTCP < 5%. We determined the respective correlations between the GTV and the GTV’s largest cross-sectional diameter and largest cross-sectional area. In the NTCP ≥ 5% group, the NTCPs for the VMAT plans were significantly lower than those for the 3DCRT plans (P = 0.0011). The NTCP ≥ 5% group’s GTV was significantly larger than that of the NTCP < 5% group (P = 0.0016), and the cut-off value of the GTV was 130.5 cm3. The GTV was strongly correlated with the GTV’s largest cross-sectional diameter (R2 = 0.82) and largest cross-sectional area (R2 = 0.94), which produced the cut-off values of 7.5 cm and 41 cm2, respectively. It was concluded that VMAT is more appropriate than 3DCRT in cases in which the GTV is ≥130.5 cm3.
Highlights
Post-operative radiotherapy is absolutely essential for high-grade glioma (HGG)
With respect to the PTV-boost, the median conformity index (CI) value in the volumetric-modulated arc therapy (VMAT) plan (0.93) was significantly superior to that in the 3D conformal radiotherapy (3DCRT) plan (0.59) (P < 0.001), there were no significant differences between the 3DCRT and VMAT plans in the median values of D95% (57.3 Gy vs 57.2 Gy, P = 0.85), D98% (54.7 Gy vs 56.3 Gy, P = 0.23), D2% (62.5 Gy vs 63.0 Gy, P = 0.14), V90% (98.2% vs 99.7%, P = 0.079), V95% (95.9% vs 95.7%, P = 0.90) and HI (0.14 vs 0.11, P = 0.33), respectively
There were no significant differences in the median value of the mean dose and V5 Gy–V50 Gy for normal brain and D2% for each planning OAR volume (PRV) in the 3DCRT or VMAT plans
Summary
With the technical advances in radiotherapy, the use of intensity-modulated radiation therapy (IMRT) and/or volumetric-modulated arc therapy (VMAT) for the radiation of HGGs is increasingly common as a substitute for 3D conformal radiotherapy (3DCRT) [1]. Several studies have reported that IMRT including VMAT can achieve high conformity for the target while reducing the dose to organs at risk (OARs), compared with 3DCRT [2,3,4,5,6,7]. Wagner et al [2] described their dosimetric comparison of IMRT and 3DCRT plans for 14 consecutive patients with malignant glioma, and they reported that if the planning target 249. Sakanaka et al [7] reported that VMAT could reduce the number of monitor units, while maintaining target coverage comparable with that of IMRT. It is difficult to use VMAT for all HGG patients, because it requires a longer preparation time and more human resources compared with 3DCRT
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