Cm In Lateral Direction Research Articles

207. Impact of IGRT on correct set-up of patients with prostate cancer: Experience of our center

Purpose The purpose of this study is to quantify displacements in image-guided radiotherapy (IGRT) for prostate cancer patients and to evaluate the impact of IGRT on the quality of radiotherapy treatments in terms of rectal toxicities. Methods From January to October 2017, 46 patients with prostate cancer were treated. All patients were planned with volumetric-modulated arc therapy (VMAT) technique, receiving hypofractionated radiotherapy for a total dose of 67.5 Gy in 25 fractions or conventionally fractionated radiotherapy for a total dose of 70–80 Gy in 35–40 fractions. Daily IGRT using cone-beam computed tomography (CBCT) was performed for all patients. Setup corrections were determined and corrected by means of registrations of CBCT images with the planning CT using online 3D fusion and for each session displacements were evaluated to analyze the setup errors. Weekly clinical visits were made to all patients; rectal toxicities were evaluated according to CTCAE (Common Terminology Criteria for Adverse Events) scales and compared with a group of prostate cancer patients treated with intensity modulated radiotherapy without daily CBCT from January 2013 to July 2014. Results Significative differences in setup displacements were found for each treatment session. The range of displacements in the three space directions was calculated for each patient, as showed in Fig. 1, and the average of all ranges was 1.6 cm in vertical direction, 1.3 cm in lateral direction and 1.4 cm in longitudinal direction. Symptomatic grade 1 (G1) rectal toxicity was found in 17% of daily IGRT patients and in 49% of no-daily IGRT patients; asymptomatic G1 rectal toxicity was found in 79% and 47% of IGRT and no-daily IGRT patients, respectively (Fig. 2). Conclusions Daily CBCT allows real-time verification and correction of set-up and organ-motion errors and improves treatment quality by reducing rectal toxicity. More cases and a longer follow-up are needed to confirm the preliminary results of this study. Download : Download high-res image (413KB) Download : Download full-size image Download : Download high-res image (236KB) Download : Download full-size image

Numerical Modeling of Shallow Foundation on Liquefiable Soil Under Sinusoidal Loading

In seismic areas, most of the light and heavy structures resting on saturated soil are prone to liquefaction behavior. It occurs in the form of cyclic mobility of soil mass, reduction in bearing capacity, increment in lateral pressure and settlement of structure which must be inspected before constructing any civil engineering structures so that respective precautionary measures can be taken at early stage. The aim of this paper is to model the behavior of shallow foundation on liquefiable soil using Biot’s basic theory of porous media. The non-linear behaviors like dilitancy, loading–unloading, hardening and other behaviors of the soil mass are modelled using Pastor–Zienkiewicz Mark III model. Generalized Newmark-beta method is employed for integration in time. A computer code based on finite element method is developed in FORTRAN 90 to simulate a surface footing resting on loose liquefiable soil deposit. The models is subjected to input ground motion of sinusoidal nature to observe the settlement, excess pore pressures, and liquefaction susceptibility of the soil deposits. Some of the key parameters like soil permeability, shear modulus and contact pressure has been also explored on foundation response during numerical study. The results show that settlement of foundations increased with the increase of soil permeability i.e. at higher permeability, maximum settlement in vertical direction and lateral direction are 9.55 cm and 4.20 cm respectively. When shear modulus increases from 8 to 20 MPa, the settlement decreases from 9.55 cm to 2.47 cm in vertical direction and 4.20 cm to 0.98 cm in lateral direction. Excess pore pressures increases with the depth and decreases with the increases in shear modulus.

Evaluation of Set-up Accuracy for Frame-based and Frameless Lung Stereotactic Body Radiation Therapy

The purpose of this study was to evaluate the set up accuracy using stereotactic body frame and frameless immobilizer for lung stereotactic body radiation therapy (SBRT). For total 40 lung cancer patients treated by SBRT, 20 patients using stereotactic body frame and other 20 patients using frameless immobilizer were separately enrolled in each group. The setup errors of each group depending on the immobilization methods were compared and analyzed. All patients received the dose of 48∼60 Gy for 4 or 5 fractions. Before each treatment, a patient was first localized to the treatment isocenter using room laser s, and further aligned with a series of image guidance procedures; orthogonal kV radiographs, cone-beam CT, o rthogonal fluoroscopy. The couch shifts during these procedures were recorded and analyzed for systematic and random errors of each group. Student t-test was performed to evaluate significant difference depending on the immobilization methods. The setup reproducibility was further analyzed using F-test with the random errors excluding the systematic setup errors. In addition, the ITV-PTV margin for each group was calculated. The setup errors for SBF were 0.05±0.25 cm in vertical direction, 0.20±0.38 cm in longitudinal direction, and 0.02±0.30 cm in lateral direction, respectively. However the setup errors for frameless immobilizer showed a significant increase of -0.24±0.25 cm in vertical direction while similar results of 0.06±0.34 cm, −0.02±0.25 cm in longitudinal and lateral directions. ITV-PTV margins for SBF were 0.67 cm (vertical), 0.99 cm (longitudinal), and 0.83 cm (lateral), respectively. On the other hand, ITV-PTV margins for Frameless immobilizer were 0.75 cm (vertical), 0.96 cm (longitudinal), and 0.72 cm (lateral), indicating less than 1 mm difference for all directions. In conclusion, stereotactic body frame improves reproducibility of patient setup, resulted in 0.1∼0.2 cm in both vertical and longitudinal directions. However the improvements are not substantial in clinic considering the effort and time consumption required for SBF setup.

SU-FF-T-391: Study of Treatment Couch Leveling and Sagging Related to Patient Weight and Couch Longitudinal Positions

Purpose: The weighted couch appears leveling and sagging inheriting from its design and material used. The amount of leveling and sagging depend on longitudinal position and patient weight since the couch experiences different amounts of torque. This phenomenon could affect patient setup accuracy, especially for stereotactic radiosurgery.Material and Method: An infrared camera based ExacTrac system (BrainLab) of high accuracy was used to measure the leveling and sagging. Four infrared reflecting makers were placed on a piece of graphic paper attached on the couch‐top, with a 10 cm separation in superior/inferior direction, and 6cm in lateral direction. Couch base is ExactCouch (Varian) with a new fiberglass couch top (Brainlab). The measurements were taken at a 5cm increment step on longitudinal direction in a range of 80cm couch movement, repeated with weight loads of 40LB and 60 LB on the couch front end. The graphic paper was repositioned for each couch movement so that the center of the four markers was always at the isocenter. The average horizontal position change of four markers represented the sagging, and the position difference between the superior and inferior markers represented the leveling. Result: Couch sagging was Z(mm) = 0.011*Y(cm) + 0.26 for zero load, Z(mm) = −0.0048*Y(cm) + 0.08 for 40Lb, and Z(mm) = −0.011Y(cm ) + 0.03 for 60Lb, where Y is the amount of couch longitudinal movement. The maximum sagging was 1.9mm compared the difference between 60Lb loading and 0 loading. Couch leveling was 0.316±0.084mm, 0.58±0.12mm, 0.71±0.059mm, for three different loading with the range of 11 cm around the isocenter, however, it changed little with different couch position. Conclusion: Couch sagging depends on its longitudinal extension and the patient weight. The maximum sagging at isocenter position was about 2mm. Couch leveling only depend on the weight of loading.

TH‐C‐M100E‐05: Fabricating a Customized Gating System for Large Bore AcQSim CT Scanner

Purpose: A customized gating system was developed for a large bore CT scanner to produce gated images for use with an active breathing control (ABC) system. Operator triggering following a breath hold is replaced by an electronic gating signal from a bellows. A breathing phantom was constructed and imaged to insure accurate gating. Methods and Materials: A bellows strap wraps around the patient to monitor breathing during CT scans. A universal serial port (USB) cable provides power to the bellows sensor via the circuit box. Bellows signals route to the computer from the circuit box via another USB cable. Operators can set a threshold point in the breathing cycle that corresponds to an ABC breath‐hold to trigger the CT scanner. Software generated signals gate the CT through the circuit box. Unique to this system is an option to scan continuously while the patient is holding a breath, in contrast to commercial gated‐CT systems which take one image per breathing cycle. A breathing phantom was created using a computer programmed actuator, step‐motor, and off‐set ball. A sine wave modeled on human breathing was fed to the actuator. The moving range was 2.10 cm anterior‐posterior and 1.05 cm in lateral direction. The diameter and motion period was 6.4 cm and 5.54 sec. Phantom images taken were: stationary non‐gated, moving gated, and three un‐gated while moving. All image sets were analyzed with the Pinnacle planning system. Volumes generated from contours where used as a metric to determine imaging accuracy. Results: Target volumes of stationary and gated imaging were 146.8 and 145.5cm3, respectively (1% agreement). However, the discrepancies between stationary and all three un‐gated scans ranged from 4.84 to 5.45% with significant shape distortion.Conclusions: We successfully created a custom gating system for a large‐bore CT simulator.

SU-FF-J-37: Generic Motion Kernels for Treatment Planning Incorporating Interfraction Motion

Purpose: To generate motion kernels for treatment planning incorporating interfraction motion. Method and Materials: Patients undergo MVCT guided tomotherapy treatments were enrolled in this study. Patients were set up using skin markers and lasers; daily MVCT images were acquired; the MVCT images were then registered to treatment planning KCVT by automatic and/or manual rigid body image registration. Patient shift was recorded and analyzed. Up to date, data from seven lung cancer and nine prostate cancer patients were acquired. Patient shifts were grouped according to the diseases and plotted in histogram. Generic motion kernels were derived by fitting distribution profiles into functions. For verification purpose, the daily shifts for each individual patient were also analyzed and compared to the generic ones. Results: The daily patient shifts are principally normal distributions. Generic motion kernels were obtained for lung patients and prostate patients by fitting the distributions into Gaussian functions. The standard deviations in x, y and z directions were 0.4, 0.62 and 0.62 cm for the lung and 0.32, 0.74 and 0.63 cm for the prostate. The standard deviations of individual patients range from 0.21 to 0.33 cm in lateral direction, 0.19 to 0.57 cm in longitudinal direction and 0.21 to 1.47 in vertical direction. The mean values significantly deviated from zero. Conclusion: Generic interfraction motion kernels obtained from large group of patients can be used for inverse or forward treatment planning to account for interfraction motion. This work was partially supported by a grant from the NIH (P01CA088960).

Internal organ motion in prostate cancer patients treated in prone and supine treatment position

Background and Purpose: To compare supine and prone treatment positions for prostate cancer patients with respect to internal prostate motion and the required treatment planning margins. Materials and Methods: Fifteen patients were treated in supine and fifteen in prone position. For each patient, a planning computed tomography (CT) scan was used for treatment planning. Three repeat CT scans were made in weeks 2, 4, and 6 of the radiotherapy treatment. Only for the planning CT scan, laxation was used to minimise the rectal content. For all patients, the clinical target volume (CTV) consisted of prostate and seminal vesicles. Variations in the position of the CTV relative to the bony anatomy in the four CT scans of each patient were assessed using 3D chamfer matching. The overall variations were separated into variations in the mean CTV position per patient (i.e. the systematic component) and the average ‘day-to-day’ variation (i.e. the random component). Required planning margins to account for the systematic and random variations in internal organ position and patient set-up were estimated retrospectively using coverage probability matrices. Results: The observed overall variation in the internal CTV position was larger for the patients treated in supine position. For the supine and prone treatment positions, the random components of the variation along the anterior-posterior axis (i.e. towards the rectum) were 2.4 and 1.5 mm (1 standard deviation (1 SD)), respectively; the random rotations around the left-right axis were 3.0 and 2.9 degrees (1 SD). The systematic components of these motions (1 SD) were larger: 2.6 and 3.3 mm, and 3.7 and 5.6 degrees, respectively. The set-up variations were similar for both treatment positions. Despite the smaller overall variations in CTV position for the patients in prone position, the required planning margin is equal for both groups (about 1 cm except for 0.5 cm in lateral direction) due to the larger impact of the systematic variations. However, significant time trends cause a systematic ventral-superior shift of the CTV in supine position only. Conclusions: For internal prostate movement, it is important to distinguish systematic from random variations. Compared to patients in supine position, patients in prone position had smaller random but somewhat larger systematic variations in the most important coordinates of the internal CTV position. The estimated planning margins to account for the geometrical uncertainties were therefore similar for the two treatment positions.

Quantitative photogrammetric analysis of digital underwater video imagery

This paper presents a photogrammetric model for digital underwater video imagery, which has been mostly applied to qualitative analysis in the marine environment. With this model, quantitative analysis of underwater images is possible, e.g., to locate positions, calculate sizes, and measure shapes of objects from image features. The underwater photogrammetric model is based on a three-dimensional optical ray tracing technique which rigorously models imaging systems with multilens configurations and multiple refractions. The calibration procedure with two independent phases has been proven to be efficient in simplifying the computation and improving the calibration accuracy. With the current imaging system configuration and photogrammetric model, an accuracy of 0.8 cm in lateral directions and 1.2 cm along the depth direction for objects located about 2-3 m from the camera system in the object space is attainable. A PC-based digital underwater photogrammetric prototype system has been developed to implement the underwater photogrammetric model.