A hybrid IMRT/VMAT technique for the treatment of nasopharyngeal cancer

Optimal plan target in cases with locally advanced nasopharyngeal cancer: Comparison of VMAT, IMRT, hybrid, and tomotherapy results

PURPOSE

In locally advanced nasopharyngeal cancer (NC), the spread of the disease, proximity to critical structures, and high dose requirement for tumor control may complicate the treatment plan. In this study, VMAT/IMRT/hybrid/tomotherapy plans were made to reach the safest and most effective dose distribution for each of the patients and the results were compared.

METHODS

Double volumetric-modulated arc therapy (VMAT) and 7- and 9-field intensity-modulated radiation therapy (IMRT) plans were made to 21 locally advanced NCs with Varian Trilogy System. It was observed that appropriate dose distributions could not be achieved with IMRT or VMAT, and hybrid IMRT-VMAT plans were made. All cases were also planned with Tomotherapy Precision System, and the data of four different techniques were compared retrospectively.

RESULTS

For normal tissue tolerances in 73 structures could not be obtained with VMAT and 38 structures with IMRT whereas the desired tolerance was provided with the hybrid plan. Hybrid plans were made with an average of 14 VMATs and 20 IMRTs. The maximum brainstem and spinal cord doses were found significantly lower in hybrid and tomotherapy techniques. Homogeneity index (HI) and conformity index (CI) values were the best in hybrid plans. No statistically significant difference between the hybrid plan and tomotherapy in terms of normal tissue tolerance doses and HI whereas a significant difference was found in the hybrid plan for CI.

CONCLUSION

It was observed that the most ideal plans for the locally advanced NC could be obtained with tomotherapy and hybrid plan techniques that the better protection in critical structures and desired dose distribution at target volumes.

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.

Volumetric modulated arc therapy versus tomotherapy for late T-stage nasopharyngeal carcinoma

Purpose

To compare the dosimetric parameters and clinical outcomes between volumetric modulated arc therapy (VMAT) and tomotherapy for treating late T-stage nasopharyngeal carcinoma (NPC).

Methods

Patients with non-metastatic late T-stage NPC who received definitive radiotherapy with tomotherapy or VMAT were selected. 1:1 propensity score matching (PSM) was used to control the balance of confounding factors. The dosimetric parameters and clinical outcomes were compared.

Results

A total of 171 patients were enrolled before matching, with 61 patients in the VMAT group and 110 patients in the tomotherapy group. In the post-PSM cohort, 54 sub-pairs of 108 patients were included after matching. Tomotherapy was superior to VMAT in the dosimetric parameters of planning target volumes, brainstem, spinal cord, lenses, and parotid glands but inferior in the optic nerves and optic chiasm. The tomotherapy group had a lower incidence of grade ≥ 3 acute mucositis (22.2% vs. 40.7%, p = 0.038) and a higher rate of complete response (83.3% vs. 66.7%, p = 0.046) after radiotherapy. However, there were no significant differences in locoregional failure-free survival (p = 0.375), distant metastasis-free survival (p = 0.529), or overall survival (p = 0.975) between the two groups.

Conclusion

Tomotherapy is superior to VMAT in terms of most dosimetric parameters, with less acute mucositis and better short-term efficacy. There are no significant differences in the survival outcomes between the VMAT and tomotherapy groups.

Hybrid Tomo-Helical and Tomo-Direct radiotherapy for localized prostate cancer

PURPOSE

The aim of the study is to present a new planning approach to provide better planning target volume (PTV) coverage and reduce bladder and rectum dose with hybrid Tomo-Helical (TH)/Tomo-Direct (TD) radiotherapy (RT) for localized prostate cancer (LPC).

METHODS

Twenty-five LPC patients were included in this retrospective study. TH plans, TD plans, and hybrid TH/TD plans were created. Lateral beams were used for the hybrid TD plan and the prescribed dose was 70 Gy in 28 fractions (hybrid plans were combined 45 Gy/ 18 fxs for TH and 25 Gy/10 fxs for TD). Doses of PTV (D2%, D98%, D50%, homogeneity index (HI), conformity index (CI), coverage) and organs at risk (OARs) (V50%, V35%, V25%, V5%, and V95%) were analyzed. The Wilcoxon signed-rank test was used to analyze the difference in dosimetric parameters. p-Value < 0.05 was considered statistically significant.

RESULTS

TH plans showed better CI, and target coverage (p < 0.01) than TD and hybrid plans in all patient plan evaluations. However, TD plans D2%, D98%, and D50% doses were better than TH and hybrid plans. The HI values were similar between the three plans. Significant reductions in bladder and rectum V50%, V35%, and V25% doses (p < 0.001) were observed with hybrid plans compared to TH and TD. Penile bulb V95% and bowel V5% doses were better in the hybrid plans. Left and right femoral head V5% doses were higher in the hybrid plan compared to others (p < 0.001).

CONCLUSION

Concurrently hybrid TH/TD RT plan can be a good option to reduce the doses of the rectum and bladder in the RT of LPC.

[Segmentation of organs at risk in nasopharyngeal cancer for radiotherapy using a self-adaptive Unet network]

OBJECTIVE

To investigate the accuracy of automatic segmentation of organs at risk (OARs) in radiotherapy for nasopharyngeal carcinoma (NPC).

METHODS

The CT image data of 147 NPC patients with manual segmentation of the OARs were randomized into the training set (115 cases), validation set (12 cases), and the test set (20 cases). An improved network based on three-dimensional (3D) Unet was established (named as AUnet) and its efficiency was improved through end-to-end training. Organ size was introduced as a priori knowledge to improve the performance of the model in convolution kernel size design, which enabled the network to better extract the features of different organs of different sizes. The adaptive histogram equalization algorithm was used to preprocess the input CT images to facilitate contour recognition. The similarity evaluation indexes, including Dice Similarity Coefficient (DSC) and Hausdorff Distance (HD), were calculated to verify the validity of segmentation.

RESULTS

DSC and HD of the test dataset were 0.86±0.02 and 4.0±2.0 mm, respectively. No significant difference was found between the results of AUnet and manual segmentation of the OARs (P > 0.05) except for the optic nerves and the optic chiasm.

CONCLUSIONS

AUnet, an improved deep learning neural network, is capable of automatic segmentation of the OARs in radiotherapy for NPC based on CT images, and for most organs, the results are comparable to those of manual segmentation.

Feasibility of a Skin Dose Reduction for Nasopharyngeal Carcinoma Treated With High-Intensity-Modulated Delivery Techniques

Acute skin toxicity observed in radiotherapy treatment of head and neck cancer is a big concern. The purpose of this work is to evaluate the feasibility of a skin dose reduction in the treatment of nasopharyngeal carcinoma without compromising the overall plan quality. This research focused on comparison of the skin dose reduction that can be obtained for the main high conformal radiotherapy delivery techniques. Sixteen cases of early-stage nasopharyngeal carcinoma were included in this study. For each case, a dynamic intensity-modulated radiation therapy, a volumetric modulated arc therapy, and a helical tomotherapy treatment plans were performed with and without the skin as a sensitive structure in the inverse plan optimization. The dosimetric results obtained for the different treatment techniques and plan optimizations were compared. Dose–volume histogram cutoff points of D95%, D98%, and the homogeneity index were used for target comparison, while Dmean and Dmax/D1cc were used for the organs at risk. The skin volume receiving 5 Gy and then 10 to 70 Gy of radiation dosage registered at step of 10 Gy and Dmean were used for the skin dose comparison. One-way analysis of variance was used to assess the dosimetric results obtained for the different types of treatment plans and techniques investigated. A total of 96 treatment plans were analyzed. When the neck skin was considered in the treatment optimization process, the skin volume that received more than 30 Gy was reduced by 3.7% for dynamic intensity modulated, 4.1% for volumetric modulated arc, and 4.3% for dynamic intensity modulated, while the target dose coverage and organs at risk dosages remained unvaried (p > .05).