Adaptive radiation therapy (ART) for patients with limited?stage small cell lung cancer (LS?SCLC): A dosimetric evaluation

Background: Adaptive radiation therapy (ART) refers to redesigning of radiation therapy (RT) treatment plans with respect to dynamic changes in tumor size and location throughout the treatment course. In this study, we performed a comparative volumetric and dosimetric analysis to investigate the impact of ART for patients with limited-stage small cell lung cancer (LS-SCLC). Methods: Twenty-four patients with LS-SCLC receiving ART and concomitant chemotherapy were included in the study. ART was performed by replanning of patients based on a mid-treatment computed tomography (CT)-simulation which was routinely scheduled for all patients 20� days after the initial CT-simulation. While the first 15 RT fractions were planned using the initial CT-simulation images, the latter 15 RT fractions were planned using the mid-treatment CT-simulation images acquired 20� days after the initial CT-simulation. In order to document the impact of ART, target and critical organ dose-volume parameters acquired from this adaptive radiation treatment planning (RTP) were compared with the RTP based solely on the initial CT-simulation to deliver the whole RT dose of 60 Gy. Results: Statistically significant reduction was detected in gross tumor volume (GTV) and planning target volume (PTV) during the conventionally fractionated RT course along with statistically significant reduction in critical organ doses with incorporation of ART. Conclusion: One-third of the patients in our study who were otherwise ineligible for curative intent RT due to violation of critical organ dose constraints could be treat

Clinical implementation of MR-Linac systems in adaptive radiation therapy for head and neck cancer / 中华放射肿瘤学杂志

Adaptive radiation therapy (ART) has been proposed as a method to account for changes in head and neck cancer and normal tissues to enhance the therapeutic ratios. Online magnetic resonance-guided radiotherapy (MRgRT) using hybrid MR-Linac systems is a novel innovative application in ART for head and neck cancer. The concept of MR-Linac systems is the ability to acquire MR images for ART and also online imaging during treatment delivery. Daily ART allows to improve the targeting accuracy while avoiding organs at risk for head and neck cancer. Although an increasing number of studies related to clinical application and technical aspect of MRgRT in head and neck cancer have been published, MRgRT for ART of head and neck cancer remains in its infancy. The purpose of this article is to summarize and discuss the rationale, clinical implementation, and prospect of this promising adaptive radiotherapy modality for treating head and neck cancer.

Advances in magnetic resonance imaging guided radiation therapy / 生物医学工程学杂志

Image-guided radiation therapy using magnetic resonance imaging (MRI) is a new technology that has been widely studied and developed in recent years. The technology combines the advantages of MRI imaging, and can offer online real-time tracking of tumor and adjacent organs at risk, as well as real-time optimization of radiotherapy plan. In order to provide a comprehensive understanding of this technology, and to grasp the international development and trends in this field, this paper reviews and summarizes related researches, so as to make the researchers and clinical personnel in this field to understand recent status of this technology, and carry out corresponding researches. This paper summarizes the advantages of MRI and the research progress of MRI linear accelerator (MR-Linac), online guidance, adaptive optimization, and dosimetry-related research. Possible development direction of these technologies in the future is also discussed. It is expected that this review can provide a certain reference value for clinician and related researchers to understand the research progress in the field.

Target setup margin and dose evaluation for cervical cancer cases based on the off-line adaptive radiotherapy / 中华放射医学与防护杂志

Objective To study the target setup margin and dose evaluation for cervical cancer patients with volume-modulated arc therapy in the off-line adaptive radiation therapy (off-line ART),Methods A total of fifty patients with cervical cancer were randomly divided into test group and control group.Cone beam CT scanning was performed twice a week,the setup errors in directions of LR,AP and CC were recorded in the whole treatment process.The target setup formula was used to calculate the new CTV-PTV setup margin.At the same time,the setup error was returned to planning isocenter (ISO).For the control group,the dose was recalculated on the basis of the original PTV after considering ISO shift.For the test group,the dose was also recalculated after the new extended boundary of the target.The dosimetric parameters of CTV and organs at risk (OAR) were evaluated between two groups after dose recalculation.Results According to the target setup formula,extended boundaries of CTV in the direction of LR,AP,CC were 0.45,0.46 and 0.82 cm,respectively.The test group increased in CTV with D100％ and D95％ (t =-8.16,-6.73,P ＜0.05) and decreased in femoral head with V40,V30 and D (t=3.14,-9.52,-7.48,P＜0.05) than the control group.The test group decreased in the pelvis with V34 and D than control group (t =10.14,-9.38,P ＜0.05).Conclusions The CTV-PTV setup margin and the dose of OAR were effectively reduced,and the coverage of target area was extended when the off-line ART technology was conducted in the volume-modulated arc therapy for cervical cancer.

Feasibility study on the application of accelerator MV CBCT images in adaptive radiation therapy / 中华放射医学与防护杂志

Objective To investigate whether the accelerator image beam line (IBL) full scan and extend field of view(EFOV) scan mode megavoltage cone beam CT(MV CBCT) images can be used for dose calculation in adaptive radiotherapy.Methods The large aperture CT and MV CBCT were used to scan the CIRS 062M electron density modules,the CT value was established to electron density curves in the Pinnacle treatment planning system.Also,CT and MV CBCT were used to scan the head and neck,chest,abdomen and pelvis phantom.The intensity modulated radiotherapy(IMRT) plans were made with CT images and transplanted to MV CBCT images.The dose of targets and organs with their electron density curves was calculated,and two type IMRT plans with different CT images were compared.Results The dose distribution of head and neck phantom was acceptable,compared with the reference plan,the difference was within 3 ％.The dose distribution of chest and.pelvis was significantly reduced from reference plans,and the difference was 5％ and 10％ separately.This difference was beyond the scope of clinical acceptance.Conclusions MV CBCT images of accelerator IBL full scan mode in patients with head and neck site scan could be used for dose calculation in adaptive radiotherapy,chest and pelvic sites in EFOV mode scanning MV CBCT images could only be used for image guidance.

Image-guided radiation therapy in lymphoma management

Image-guided radiation therapy (IGRT) is a process of incorporating imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI), Positron emission tomography (PET), and ultrasound (US) during radiation therapy (RT) to improve treatment accuracy. It allows real-time or near real-time visualization of anatomical information to ensure that the target is in its position as planned. In addition, changes in tumor volume and location due to organ motion during treatment can be also compensated. IGRT has been gaining popularity and acceptance rapidly in RT over the past 10 years, and many published data have been reported on prostate, bladder, head and neck, and gastrointestinal cancers. However, the role of IGRT in lymphoma management is not well defined as there are only very limited published data currently available. The scope of this paper is to review the current use of IGRT in the management of lymphoma. The technical and clinical aspects of IGRT, lymphoma imaging studies, the current role of IGRT in lymphoma management and future directions will be discussed.

Improvement of the Dose Calculation Accuracy Using MVCBCT Image Processing / 의학물리

The dose re-calculation process using Megavoltage cone-beam CT images is inevitable process to perform the Adaptive Radiation Therapy (ART). The purpose of this study is to improve dose re-calculation accuracy using MVCBCT images by applying intensity calibration method and three dimensional rigid body transform and filtering process. The three dimensional rigid body transform and Gaussian smoothing filtering process to MVCBCT Rando phantom images was applied to reduce image orientation error and the noise of the MVCBCT images. Then, to obtain the predefined modification level for intensity calibration, the cheese phantom images from kilo-voltage CT (kV CT), MVCBCT was acquired. From these cheese phantom images, the calibration table for MVCBCT images was defined from the relationship between Hounsfield Units (HUs) of kV CT and MVCBCT images at the same electron density plugs. The intensity of MVCBCT images from Rando phantom was calibrated using the predefined modification level as discussed above to have the intensity of the kV CT images to make the two images have the same intensity range as if they were obtained from the same modality. Finally, the dose calculation using kV CT, MVCBCT with/without intensity calibration was applied using radiation treatment planning system. As a result, the percentage difference of dose distributions between dose calculation based on kVCT and MVCBCT with intensity calibration was reduced comparing to the percentage difference of dose distribution between dose calculation based on kVCT and MVCBCT without intensity calibration. For head and neck, lung images, the percentage difference between kV CT and non-calibrated MVCBCT images was 1.08%, 2.44%, respectively. In summary, our method has quantitatively improved the accuracy of dose calculation and could be a useful solution to enhance the dose calculation accuracy using MVCBCT images.

Enhancement of the Deformable Image Registration Accuracy Using Image Modification of MV CBCT / 의학물리

To perform the Adaptive Radiation Therapy (ART), a high degree of deformable registration accuracy is essential. The purpose of this study is to identify whether the change of MV CBCT intensity can improve registration accuracy using predefined modification level and filtering process. To obtain modification level, the cheese phantom images was acquired from both kilovoltage CT (kappaV CT), megavoltage cone-beam CT (MV CBCT). From the cheese phantom images, the modification level of MV CBCT was defined from the relationship between Hounsfield Units (HUs) of kappaV CT and MV CBCT images. 'Gaussian smoothing filter' was added to reduce the noise of the MV CBCT images. The intensity of MV CBCT image was changed to the intensity of the kappaV CT image to make the two images have the same intensity range as if they were obtained from the same modality. The demon deformable registration which was efficient and easy to perform the deformable registration was applied. The deformable lung phantom which was intentionally created in the laboratory to imitate the changes of the breathing period was acquired from kappaV CT and MV CBCT. And then the deformable lung phantom images were applied to the proposed method. As a result of deformable image registration, the similarity of the correlation coefficient was used for a quantitative evaluation of the result was increased by 6.07% in the cheese phantom, and 18% in the deformable lung phantom. For the additional evaluation of the registration of the deformable lung phantom, the centric coordinates of the mark which was inserted into the inner part of the phantom were measured to calculate the vector difference. The vector differences from the result were 2.23, 1.39 mm with/without modification of intensity of MV CBCT images, respectively. In summary, our method has quantitatively improved the accuracy of deformable registration and could be a useful solution to improve the image registration accuracy. A further study was also suggested in this paper.

Error Analysis of Delivered Dose Reconstruction Using Cone-beam CT and MLC Log Data / 의학물리

We aimed to setup an adaptive radiation therapy platform using cone-beam CT (CBCT) and multileaf collimator (MLC) log data and also intended to analyze a trend of dose calculation errors during the procedure based on a phantom study. We took CT and CBCT images of Catphan-600 (The Phantom Laboratory, USA) phantom, and made a simple step-and-shoot intensity-modulated radiation therapy (IMRT) plan based on the CT. Original plan doses were recalculated based on the CT (CTplan) and the CBCT (CBCTplan). Delivered monitor unit weights and leaves-positions during beam delivery for each MLC segment were extracted from the MLC log data then we reconstructed delivered doses based on the CT (CTrecon) and CBCT (CBCTrecon) respectively using the extracted information. Dose calculation errors were evaluated by two-dimensional dose discrepancies (CTplan was the benchmark), gamma index and dose-volume histograms (DVHs). From the dose differences and DVHs, it was estimated that the delivered dose was slightly greater than the planned dose; however, it was insignificant. Gamma index result showed that dose calculation error on CBCT using planned or reconstructed data were relatively greater than CT based calculation. In addition, there were significant discrepancies on the edge of each beam while those were less than errors due to inconsistency of CT and CBCT. CBCTrecon showed coupled effects of above two kinds of errors; however, total error was decreased even though overall uncertainty for the evaluation of delivered dose on the CBCT was increased. Therefore, it is necessary to evaluate dose calculation errors separately as a setup error, dose calculation error due to CBCT image quality and reconstructed dose error which is actually what we want to know.