The Clinical Implementation of 2D Dose Distribution QA System for the Patient Specific Respiratory-gated Radiotherapy / 의학물리

Emerging technologies such as four-dimensional computed tomography (4D CT) is expected to allow clinicians to accurately model interfractional motion and to quantitatively estimate internal target volumes (ITVs) for radiation therapy involving moving targets. A need exists for a 4D radiation therapy quality assurance (QA) device that can incorporate and analyze the patient specific intrafractional motion as it relate to dose delivery and respiratory gating. We built a 4D RT prototype device and analyzed the patient-specific 4D radiation therapy QA for 2D dose distributions successfully. With more improvements, the 4D RT QA prototype device could be an integral part of a 4D RT decision process to confirm the dose delivery.

The Analysis of Predictive Factors for the Identification of Patients Who Could Benefit from Respiratory-Gated Radiotherapy in Non-Small Cell Lung Cancer / 대한방사선종양학회지

PURPOSE: 4DCT scans performed for radiotherapy were retrospectively analyzed to assess the possible benefits of respiratory gating in non-small cell lung cancer (NSCLC) and established the predictive factors for identifying patients who could benefit from this approach. MATERIALS AND METHODS: Three treatment planning was performed for 15 patients with stage I~III NSCLC using different planning target volumes (PTVs) as follows: 1) PTVroutine, derived from the addition of conventional uniform margins to gross tumor volume (GTV) of a single bin, 2) PTVall phases (patient-specific PTV), derived from the composite GTV of all 6 bins of the 4DCT, and 3) PTVgating, derived from the composite GTV of 3 consecutive bins at end-exhalation. RESULTS: The reductions in PTV were 43.2% and 9.5%, respectively, for the PTVall phases vs. PTVroutine and PTVgating vs. PTVall phases. Compared to PTVroutine, the use of PTVall phases and PTVgating reduced the mean lung dose (MLD) by 18.1% and 21.6%, and V20 by 18.2% and 22.0%, respectively. Significant correlations were seen between certain predictive factors selected from the tumor mobility and volume analysis, such as the 3D mobility vector, the reduction in 3D mobility and PTV with gating, and the ratio of GTV overlap between 2 extreme bins and additional reductions in both MLD and V20 with gating. CONCLUSION: The additional benefits with gating compared to the use of patient-specific PTV were modest; however, there were distinct correlations and differences according to the predictive factors. Therefore, these predictive factors might be useful for identifying patients who could benefit from respiratory-gated radiotherapy.

Development of Respiratory Signal Analysis Program for Accurate Phase Reassignment in 4D CT Reconstruction / 의학물리

Patient's respiration can have an effect on movement of tumor range and peripheral organs. Therefore, the respiratory signal was acquired by relation between external markers and movement of patient's abdomen during radiational therapy in order to minimize the effect of respiration. Based on this technique, many studies of rational therapy to irradiate at particular part of stable respiratory signals have executed and they have been clinically applied. Nevertheless, the phase-based method is preferred to the amplitude-based method for the rational therapy related to respiration. Because stabilization of the respiratory signal are limited. In this study, a in-house respiratory signal analysis program was developed for the phase reassignment and the analysis of the irregular respiratory signals. Various irregular respiratory patterns was obtained from clinical experimental volunteers. After then, the in-house program analyzed the factors affecting to phase assignment which is directly related to irradiated sector. Subsequently, accuracy of phase assignment was improved with removement of irregular signals by self-developed algorithm. This study is considered to be useful for not only image reconstruction and elevation of irradiating accuracy through phase assignment of RPM system but also analysis of respiratory signals. Moreover, development of 4D CT image is planed with phantom researches or clinical experiments based on this program.

Analysis on the Decrease of Planning Target Volume in the Case of Lung Radiation Surgery with the Application of Respiratory Gated Radiotherpy Method / 의학물리

The application of a respiratory gated radiotherpy method to the lung radiation surgery was evaluated compared with the conventional method in which the whole tumor motion range is considered in the delineation of PTV (Planning target volume). The four dimensional CT simulation images were acquired for the five NSCLC (Non-small cell lung cancer) patients for radiation surgery. The respiratory gated plan was prepared with the 50% phase CT images and the conventional method was planned based on the ITV (Internal target volume) which include all the target volumes created in each phase CT images within a whole respiratory period. The DVH (Dose volume histogram) of OAR (Organ at risk) which calculated in each method was compared for the evaluation of the plan properness. The relative decrease of OARs' DVH were verified in the application of respiratory gated method. The average decrease rate were 16.88+/-9.97% in the bronchus, 34.13+/-19.15% in the spinal cord, 28.42+/-18.49% in the chest wall and 32.48+/-16.66% in the lung. Based on these results, we can verified the applicability and the effectiveness of the respiratory gated method in the lung radiation surgery.