Patient Positioning In Radiotherapy Research Articles

Optical Surface Management System for Patient Positioning in Interfractional Breast Cancer Radiotherapy.

Background The Optical Surface Management System (OSMS) is a simple, fast, reproducible, and accurate solution for patient set-up and can minimize random day-to-day set-up errors. However, studies in breast cancer patients are rare. Objective To analyze 200 patient set-ups in 20 patients with breast cancer by comparing the OSMS with the conventional cone-beam computed tomography (CBCT). Method Displacements from concurrent OSMS and CBCT registrations were compared in a total of 200 setups of 20 patients to analyze the interfractional displacement and positioning displacement in three dimensions (lateral, longitudinal, and vertical directions). Results The interfractional displacement on the lateral, longitudinal, and vertical directions for OSMS versus CBCT was 0.049 ± 0.254 versus 0.041 ± 0.244 centimeters (cm); 0.018 ± 0.261 versus 0.040 ± 0.242 cm; 0.062 ± 0.254 versus 0.065 ± 0.240 cm, respectively, without any significant difference (all P > 0.05). The duration for CBCT scan was about 60 seconds (s), while that for image processing, matching, and couch displacement was at least 5 minutes (min). The average scanning time with OSMS was less than 20 s, and the total duration for positioning was less than 1 min. Conclusion OSMS is an efficient tool to improve the accuracy and increase the speed for verifying the patient positioning in radiotherapy for breast cancer.

Patient positioning in radiotherapy based on surface imaging using time of flight cameras.

To evaluate the patient positioning accuracy in radiotherapy using a stereo-time of flight (ToF)-camera system. A system using two ToF cameras was used to scan the surface of the patients in order to position them daily on the treatment couch. The obtained point clouds were registered to (a) detect translations applied to the table (intrafraction motion) and (b) predict the displacement to be applied in order to place the patient in its reference position (interfraction motion). The measures provided by this system were compared to the effectively applied translations. The authors analyzed 150 fractions including lung, pelvis/prostate, and head and neck cancer patients. The authors obtained small absolute errors for displacement detection: 0.8 ± 0.7, 0.8 ± 0.7, and 0.7 ± 0.6 mm along the vertical, longitudinal, and lateral axes, respectively, and 0.8 ± 0.7 mm for the total norm displacement. Lung cancer patients presented the largest errors with a respective mean of 1.1 ± 0.9, 0.9 ± 0.9, and 0.8 ± 0.7 mm. The proposed stereo-ToF system allows for sufficient accuracy and faster patient repositioning in radiotherapy. Its capability to track the complete patient surface in real time could allow, in the future, not only for an accurate positioning but also a real time tracking of any patient intrafraction motion (translation, involuntary, and breathing).

Verification Films: A Study of the Daily and Weekly Reproducibility of Breast Patient Set-up in the START Trial

Verification of patient position in radiotherapy by the use of portal images is a current practice in most radiotherapy departments. All patients within the Standardisation of Breast Radiotherapy Trial (START) were required to have on-treatment verification images. Measurements of maximum lung and breast depth from these were used to provide details for the case-report forms. This study was undertaken to validate these measurements, assess the reproducibility of patients' set-up within the START trial and to compare reproducibility on a day-to-day basis with reproducibility over a longer period. Analysis also included a subjective assessment of image quality. Fifty-three patients from 29 departments were studied. Some centres used electronic portal imaging and others used film. Where film verification was the method of choice, information was collected about the type of film and cassette used. The correlation coefficients for inter- and intra-observer variability of breast and lung depth were 0.99. Comparing maximum breast depth on weekly and daily images, the median per cent standard deviation of breast depth was 4% and 3%, respectively. The mean standard deviation of breast depth for all patients, which gives an indication of the individual patient variability, was 5.5 +/- 2.2 mm for weekly and 3.9 +/- 1.5 mm for daily measurements. For lung depth, mean standard deviation was 6.8 +/- 2.5 mm for weekly and 6.8 +/- 2.8 mm for daily measurements. Images taken using Kodak X-omat V film were inferior to those taken with films in corresponding cassettes. Differences between lung depth measured in simulator and on the treatment unit were evident for many patients. There was little difference in the standard deviations of breast and lung depth for daily and weekly verification films on the treatment machine.

Automated determination of patient setup errors in radiation therapy using spherical radio-opaque markers.

Patient positioning accuracy can be quantified by the three-dimensional (3-D) translations and rotations required to transform the patient back to the desired position. Results of the current study show that the translations and rotations could be obtained from two projection images obtained radiographically on a linear accelerator when spherical radio-opaque markers were implanted inside or affixed to the surface of a skull phantom. In this study, film used to record the images were converted into digital gray scale images using a laser film digitizer. The marker images were located automatically by the computer using image processing techniques. By combining information from both projections, the 3-D locations of the markers were determined to submillimeter precision. Pairs of films were also analyzed for the phantom displaced from its original location by known amounts. The accuracy of the computed translations and rotations required for realignment of the phantom were found to be better than 1 mm and 0.3 degrees, respectively; comparable to the accuracy of the readout system of the equipment used. The general methodology could be coupled with an electronic portal imaging device for use in computer aided or automated correction of patient position in radiotherapy.