Which Is Better for Liver SBRT: Dosimetric Comparison Between DCAT and VMAT for Liver Tumors

Treating early-stage centrally-located non-small cell lung cancer with DCAT-SBRT in centers lacking the VMAT technique: a comprehensive study

Background

Volumetric-modulated arc therapy (VMAT) may have the highest overall performance for stereotactic body radiotherapy (SBRT) treatment of inoperable early-stage NSCLC. However, in centers lacking the VMAT technique, the dynamic conformal arc therapy (DCAT) technique is potentially the best option for small and rounded NSCLC-SBRT. Therefore, we will comprehensively analyze the advantages of the DCAT versus the other techniques except VMAT in terms of dosimetry, plan complexity, delivery time, γ-passing rates and the interplay effect.

Methods

36 patients with early-stage centrally located NSCLC with PTV volumes < 65 cc were enrolled. All patients were redesigned with 50Gy/5f, and 100% of the prescribed dose was normalized to cover 95% of the PTV. The other two delivery techniques compared to the DCAT technique include 3-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT), which use the same parameters for all three techniques.

Results

The dosimetric parameters of the 3-group plans all met the RTOG 0813 protocol. Unsurprisingly, plan complexity parameters such as segments and MUs were significantly reduced in the DCAT plans by 159.56 and 925.90 compared to the IMRT plans, respectively (all P < 0.001). The delivery time of the DCAT plans was the least of 164.51 s (all P < 0.05). Compared to the IMRT plans, the γ-passing rates were higher in the DCAT plans (P < 0.001), with the most significant difference of 6.01% in the (2%, 1 mm) criteria. As for the interplay effect, the mean dose difference (MDD) in the DCAT plans was as good as the 3DCRT plans at different respiratory amplitudes but better than the IMRT plans (all P < 0.05), and the MDD of DCAT plans did not exceed 3% in all respiratory amplitude.

Conclusion

In centers lacking the VMAT technique, implementing SBRT treatment based on the DCAT technique for inoperable early-stage centrally-located NSCLC patients with PTV volumes < 65 cc achieves better treatment efficiency and delivery accuracy while maintaining the plan quality.

Planning issues on linac-based stereotactic radiotherapy

This work aims to summarize and evaluate the current planning progress based on the linear accelerator in stereotactic radiotherapy (SRT). The specific techniques include 3-dimensional conformal radiotherapy, dynamic conformal arc therapy, intensity-modulated radiotherapy, and volumetric-modulated arc therapy (VMAT). They are all designed to deliver higher doses to the target volume while reducing damage to normal tissues; among them, VMAT shows better prospects for application. This paper reviews and summarizes several issues on the planning of SRT to provide a reference for clinical application.

Multi-Planar VMAT Plans for High-Grade Glioma and Glioblastoma Targeting the Hypothalamic-Pituitary Axis Sparing

Background: This study aimed to identify the better arc configuration of volumetric modulated arc therapy (VMAT) for high-grade glioma and glioblastoma, focusing on a dose reduction to the hypothalamic–pituitary axis through an analysis of dose-volumetric parameters, as well as a correlation analysis between the planned target volume (PTV) to organs at risk (OAR) distance and the radiation dose. Method: Twenty-four patients with 9 high-grade glioma and 15 glioblastomas were included in this study. Identical CT, MRI and structure sets of each patient were used for coplanar VMAT (CO-VMAT), dual planar VMAT (DP-VMAT) and multi-planar VMAT (MP-VMAT) planning. The dose constraints adhered to the RTOG0825 and RTOG9006 protocols. The dose-volumetric parameters of each plan were collected for statistical analysis. Correlation analyses were performed between radiation dose and PTV-OARs distance. Results: The DP-VMAT and MP-VMAT achieved a significant dose reduction to most nearby OARs when compared to CO-VMAT, without compromising the dose to PTV, plan homogeneity and conformity. For centrally located OARs, including the hypothalamus, pituitary, brain stem and optic chiasm, the dose reductions ranged from 2.65 Gy to 3.91 Gy (p < 0.001) in DP-VMAT and from 2.57 Gy to 4 Gy (p < 0.001) in MP-VMAT. Similar dose reduction effects were achieved for contralaterally located OARs, including the hippocampus, optic nerve, lens and retina, ranging from 1.06 Gy to 4.37 Gy in DP-VMAT and from 0.54 Gy to 3.39 Gy in MP-VMAT. For ipsilaterally located OARs, DP-VMAT achieved a significant dose reduction of 1.75 Gy to D_max for the optic nerve. In the correlation analysis, DP-VMAT and MP-VMAT showed significant dose reductions to centrally located OARs when the PTV-OAR distance was less than 4 cm. In particular, DP-VMAT offered better sparing to the optic chiasm when it was located less than 2 cm from the PTV than that of MP-VMAT and CO-VMAT. DP-VMAT and MP-VMAT also showed better sparing to the contralateral hippocampus and retina when they were located 3–8 cm from the PTV. Conclusion: The proposed DP-VMAT and MP-VMAT demonstrated significant dose reductions to centrally located and contralateral OARs and maintained the high plan qualities to PTV with good homogeneity and conformity when compared to CO-VMAT for high-grade glioma and glioblastoma. The benefit in choosing DP-VMAT and MP-VMAT over CO-VMAT was substantial when the PTV was located near the hypothalamus, pituitary, optic chiasm, contralateral hippocampus and contralateral retina.

Dosimetric benefits of dynamic conformal arc therapy-combined with active breath-hold in lung stereotactic body radiotherapy

To test the hypothesis that dynamic conformal arc therapy (DCAT) in Monaco, compared with volumetric modulated arc therapy (VMAT), maintains plan quality with higher delivery efficiency for lung stereotactic body radiotherapy (SBRT) and to investigate dosimetric benefits of DCAT with active breath-hold (DCAT+ABH), compared with free-breathing (DCAT+FB) for varying tumor sizes and motions. Fifty DCAT plans were used for lung SBRT. Randomly selected 17 DCAT plans were evaluated with respect to the retrospectively generated volumetric modulated arc therapy (VMAT) plans. The maximum dose at 2 cm from planning target volume (PTV) in any direction (D2cm/Rx), the ratio of 50% prescription isodose volume to the PTV (R50%), conformity index (CI), the lung volume receiving ≥20 Gy (V20), and monitor unit (MU) were evaluated. A t-test was used to evaluate the difference of plan quality between DCAT and VMAT. Internal target volume (ITV)/integrated-gross target volume (GTV) attributed by intra-fraction motion and lung V20 were stratified for DCAT+ABH and DCAT+FB across varying GTVs. DCAT maintained plan quality (p = 0.154 for D2cm/Rx, p = 0.089 for R50%, p = 0.064 for CI, and p = 0.780 for lung V20) while reducing MUs up to 30% (p <0.001) from 2748 MU (VMAT) to 1868 MU (DCAT). DCAT+ABH, compared to DCAT+FB, reduced tumor motion, resulting in 19% volume reduction of PTV and 60% reduction in lung V20, on average. The difference in lung V20 between DCAT+ABH and DCAT+FB increased as the target size increased. The DCAT is a favorable approach compared with VMAT. These results support the utility of DCAT as a routine planning platform for lung SBRT, especially when utilized with respiratory motion management using the ABH.