Feasibility and potential benefits of defining the internal gross tumor volume of hepatocellular carcinoma using contrast-enhanced 4D CT images obtained by deformable registration

Advances in gross tumor target volume determination in radiotherapy for patients with hepatocellular carcinoma

Hepatocellular Carcinoma (HCC) is one of the most common malignant neoplasms. With the advancement of technology, the precision of radiotherapy (RT) for HCC has considerably increased, and it is an indispensable modality in the comprehensive management of HCC. Some RT techniques increase the radiation dose to HCC, which decreases the radiation dose delivered to the surrounding normal liver tissue. This approach significantly improves the efficacy of HCC treatment and reduces the incidence of Radiation-induced Liver Disease (RILD). Clear imaging and precise determination of the Gross Target Volume (GTV) are prerequisites of precise RT of HCC. The main hindrances in determining the HCC GTV include indistinct tumor boundaries on imaging and the impact on respiratory motion. The integration of multimodal imaging, four-dimensional imaging, and artificial intelligence (AI) techniques can help overcome challenges for HCC GTV. In this article, the advancements in medical imaging and precise determination for HCC GTV have been reviewed, providing a framework for the precise RT of HCC.

The status of medical physics in radiotherapy in China

PURPOSE

To present an overview of the status of medical physics in radiotherapy in China, including facilities and devices, occupation, education, research, etc. MATERIALS AND METHODS: The information about medical physics in clinics was obtained from the 9-th nationwide survey conducted by the China Society for Radiation Oncology in 2019. The data of medical physics in education and research was collected from the publications of the official and professional organizations.

RESULTS

By 2019, there were 1463 hospitals or institutes registered to practice radiotherapy and the number of accelerators per million population was 1.5. There were 4172 medical physicists working in clinics of radiation oncology. The ratio between the numbers of radiation oncologists and medical physicists is 3.51. Approximately, 95% of medical physicists have an undergraduate or graduate degrees in nuclear physics and biomedical engineering. 86% of medical physicists have certificates issued by the Chinese Society of Medical Physics. There has been a fast growth of publications by authors from mainland of China in the top international medical physics and radiotherapy journals since 2018.

CONCLUSIONS

Demand for medical physicists in radiotherapy increased quickly in the past decade. The distribution of radiotherapy facilities in China became more balanced. High quality continuing education and training programs for medical physicists are deficient in most areas. The role of medical physicists in the clinic has not been clearly defined and their contributions have not been fully recognized by the community.

Use of lung treatment plans to evaluate DIR algorithms

The purpose of the study is to evaluate the accuracy of two deformable image registration algorithms by examining their influence on the dose summation results obtained using 4DCT (four dimensional computed tomography) dose distributions based on '4D' planned and '4D optimal' IMRT (intensity modulated radiation therapy) plans. For ten lung cancer patients, 4D step and shoot IMRT plans were produced. The breathing cycle was divided into ten parts and for each part a set of CT images was acquired. For each patient the treatment plan was copied to the CTs of each phase and subsequently recalculated. Each phase CT was then registered to the average intensity projection (AIP) CT using a deformable image registration (DIR) algorithm and the composite dose distribution was then calculated by summing up the deformed dose distributions from all the phases ('4D' treatment plan). The '4D optimal' treatment plan was created by producing an optimal plan on the CTs of each phase of the respiratory cycle and summing up the deformed dose distributions from all the phases. The results indicate that it is possible to map the dose distributions of different breathing phases in lung using DIR, and that different DIR methods and target characteristics (motion amplitude, size, location) affect the differences between original plan, '4D' and '4D optimal' dose distributions. Although the '4D optimal' plans were designed to achieve 95% target coverage, both of the used DIR methods failed to translate that coverage in some instances. The same variation between these methods was also observed in the '4D' plan comparison. This study shows that it is feasible to perform an acceptably accurate calculation of the composite deformed dose. However, it is important to account for tumor motion and body deformation especially when the tumor volume is small and/or located in the lower lobe of the lung.

Reduction of breathing irregularity-related motion artifacts in low-pitch spiral 4D CT by optimized projection binning

Background

Respiration-correlated CT (4D CT) is the basis of radiotherapy treatment planning of thoracic and abdominal tumors. Current clinical 4D CT images suffer, however, from artifacts due to unfulfilled assumptions concerning breathing pattern regularity. We propose and evaluate modifications to existing low-pitch spiral 4D CT reconstruction protocols to counteract respective artifacts.

Methods

The proposed advanced reconstruction (AR) approach consists of two steps that build on each other: (1) statistical analysis of the breathing signal recorded during CT data acquisition and extraction of a patient-specific reference breathing cycle for projection binning; (2) incorporation of an artifact measure into the reconstruction. 4D CT data of 30 patients were reconstructed by standard phase- and local amplitude-based reconstruction (PB, LAB) and compared with images obtained by AR. The number of artifacts was evaluated and artifact statistics correlated to breathing curve characteristics.

Results

AR reduced the number of 4D CT artifacts by 31% and 27% compared to PB and LAB; the reduction was most pronounced for irregular breathing curves.

Conclusions

We described a two-step optimization of low-pitch spiral 4D CT reconstruction to reduce artifacts in the presence of breathing irregularity and illustrated that the modifications to existing reconstruction solutions are effective in terms of artifact reduction.

Electronic supplementary material

The online version of this article (doi:10.1186/s13014-017-0835-7) contains supplementary material, which is available to authorized users.

Magnitude and influencing factors of respiration-induced liver motion during abdominal compression in patients with intrahepatic tumors

PURPOSE

The purpose of this study was to use 4-dimensional-computed tomography (4D-CT) to evaluate respiration-induced liver motion magnitude and influencing factors in patients with intrahepatic tumors undergoing abdominal compression.

METHODS

From January 2012 to April 2016, 99 patients with intrahepatic tumors were included in this study. They all underwent 4D-CT to assess respiratory liver motion. This was performed during abdominal compression in 53 patients and during free-breathing (no abdominal compression) in 46 patients. We defined abdominal compression as being effective in managing the breath amplitude if respiration-induced liver motion in the cranial-caudal (CC) direction during compression was ≤5 mm and as being ineffective if >5 mm of motion was observed. Gender, age, body mass index (BMI), transarterial chemoembolization history, liver resection history, tumor area, tumor number, and tumor size (diameter) were determined. Multivariate logistic regression analysis was used to analyze influencing factors associated with a breath amplitude ≤5 mm in the CC direction.

RESULTS

The mean respiration-induced liver motion during abdominal compression in the left-right (LR), CC, anterior-posterior (AP), and 3-dimensional vector directions was 2.9 ± 1.2 mm, 5.3 ± 2.2 mm, 2.3 ± 1.1 mm and 6.7 ± 2.1 mm, respectively. Univariate analysis indicated that gender and BMI significantly affected abdominal compression effectiveness (both p < 0.05). Multivariate analysis confirmed these two factors as significant predictors of effective abdominal compression: gender (p = 0.030) and BMI (p = 0.006). There was a strong correlation between gender and compression effectiveness (odds ratio [OR] = 7.450) and an even stronger correlation between BMI and compression effectiveness (OR = 10.842).

CONCLUSIONS

The magnitude of respiration-induced liver motion of patients with intrahepatic carcinoma undergoing abdominal compression is affected by gender and BMI, with abdominal compression being less effective in men and overweight patients.