S Ju

Stereotactic Device for Gamma Knife Radiosurgery in Experimental Animals: Technical Note

Objective: Radiosurgery has become a well-established treatment modality for many intracranial lesions and the information obtained from animal experiments is crucial in devising new strategies with improved efficacy and less risk. We constructed a stereotactic device for rats which can be used for both usual laboratory work and radiosurgery using a Gamma Knife. Materials and Methods: The stereotactic device was made by modifying the basic design of the ordinary stereotactic frames used for usual laboratory work. It was developed for both Gamma Knife model B and C. An auxiliary tool was also devised which facilitates the placement of the target point at the radiation isocenter. Results: The reliability of the device was verified by checking the radiation profile and absorbed dose. The results of the experimental irradiation in normal and tumor-cell-inoculated rats demonstrated the usefulness of the device. Conclusions: The modified animal stereotactic frame described herein can be used for both the production of experimental animal models and for performing radiosurgery with a common apparatus.

SU‐E‐J‐172: Development of a Video Guided Real‐Time Patient Motion Monitoring System for Helical Tomotherpay

PURPOSE We developed a video image-guided real-time patient motion monitoring system for helical Tomotherapy (VGRPM-Tomo), and its clinical utility was evaluated using a motion phantom. METHODS The VGRPM-Tomo consisted of three components: an image acquisition device consisting of two PC-cams, a main control computer with a radiation signal controller and warning system, and patient motion analysis software, which was developed in house. The system was designed for synchronization with a beam on/off trigger signal to limit operation during treatment time only and to enable system automation. In order to detect the patient motion while the couch is moving into the gantry, a reference image, which continuously updated its background by exponential weighting filter (EWF), is compared with subsequent live images using the real-time frame difference-based analysis software. When the error range exceeds the set criteria (δ_movement) due to patient movement, a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.1, 0.2, 0.5, and 1.0 cm for 1 and 2 sec, respectively, was used to evaluate the system performance at maximum couch speed (0.196 cm/sec) in a Helical Tomotherapy (HD, Hi-art, Tomotherapy, USA). We measured the optimal EWF factor (a) and δ_movement, which is the minimum distance that can be detected with this system, and the response time of the whole system. RESULTS The optimal a for clinical use ranged from 0.85 to 0.9. The system was able to detect phantom motion as small as 0.2 cm with tight δ_movement, 0.1% total number of pixels in the reference image. The measured response time of the whole system was 0.1 sec. CONCLUSIONS The VGRPM-tomo can contribute to reduction of treatment error caused by the motion of patients and increase the accuracy of treatment dose delivery in HD. This work was supported by the Technology Innovation Program, 10040362, Development of an integrated management solution for radiation therapy funded by the Ministry of Knowledge Economy (MKE, Korea). This idea is protected by a Korean patent (patent no. 10-1007367).

SU-E-T-438: Motion Induced Dose Artifact of Multi-Fractional Tomotheapy

Purpose: Treating moving oragan has been an issue due to the dynamic nature of Tomotheapy. Non of study has investigated throughly the multi‐ fractional effects of treatments. Therefore, we designed a study to evaluate the cumulative error in moving target and nearby normal tissues. Methods: A moving phantom whose motion pattern could be rogrammed by a user was produced. Four plans which used different jaw width (1.05 cm, 2.5 cm), pitch (0.660, 0,287) and modulation factor (1.5, 2.5) to deliver 1.49 Gy to 95% of PTV in each fraction were made. For each plan, 5 different motions ( amplitude 1–3cm, Period 3–5sec) and irregular motion were tested. Film measurements for accumulated dose were made with Gafchromic@EBT films from 1 to 5 fractions. Dose distribution on each film was compared with that measured in static phantom. Profile shapes, DoseArea Histogram (DAH)s and gamma index were used for comparison Results: The dose distortion increased up to 3rd fractions and, after 3rd fractions dose distributions in the target and OAR converged to some constant distribution. The distortion level inside the target was affected by motion parameters; larger motion amplitude and larger motion period resulted in increased dose. However dose at the center of the critical organ was rather affected by the motion amplitude than the motion period . The irregularity of the motion was not thought to cause large dose artifact. More complicated plan with larger modulation factor (2.5) resulted in larger dose distortin than the plan with modulation factor 1.5. The observed phenomena is thought to be reproducible since 3 different measurements of accumulated 5 fraction of treatments showed very similar dose distributions Conclusions: When treating moving organ in small number of fractions, verifying the dose artifact is necessary. (This work was supported by Korea Government (MEST, Grant No2010‐0011771)

SU-E-T-63: Carotid Sparing Tomohelical Three Dimensional Conformal Radiotherapy for T1N0 Glottic Cancer

PURPOSE We investigated the dosimetric benefit and treatment efficiency of carotid-sparing TomoHelical (TH) three-dimensional conformal radiotherapy (3DCRT) for early glottic cancer. METHODS Computed tomography (CT) simulation was performed for 10 patients with early-stage (T1N0M0) glottic squamous cell carcinoma. The clinical target volume, planning target volume (PTV), carotid artery (CA), and spinal cord (SP) were delineated for each CT data set. Two-field 3DCRT (2F-3DCRT), three-field intensity-modulated radiation therapy (IMRT) (3F-IMRT), TomoHelical-IMRT (TH-IMRT), and TH-3DCRT plans were generated, with a total prescribed dose of 67.5 Gy in 30 fractions to the PTV for each patient. In order to evaluate plan quality, dosimetric characteristics were compared in terms of the conformity index (CI) and homogeneity index (HI) for the PTV, V35, V50, and V63 for the CAs and in terms of the maximum dose for the SP. Additionally, treatment planning and delivery times were compared to evaluate treatment efficiency. RESULTS The CIs for 3F-IMRT (0.650±0.05), TH-IMRT (0.643±0.03), and TH-3DCRT (0.631±0.03) were much better than that for 2F-3DCRT (0.318±0.03). The HIs for TH-IMRT (1.053±0.01) and TH-3DCRT (1.055±0.01) were slightly better than those for 2F-3DCRT (1.062±0.01) and 3F-IMRT (1.091±0.007). 2F-3DCRT showed poor CA sparing in terms of the V35, V50, and V63 compared to 3F-IMRT, TH-IMRT, and TH-3DCRT (p<0.05), whereas there was no significant dose difference between 3F-IMRT, TH-IMRT, and TH-3DCRT (p>0.05). The maximum dose to the SP with all plans was below 45 Gy. The treatment planning times for 2F-3DCRT (5.9±0.66 min) and TH-3DCRT (7.32±0.94 min) were much lower than those for 3F-IMRT (45.51±2.76 min) and TH-IMRT (35.58±4.41 min), whereas the delivery times with all plans was below 3 minutes. CONCLUSION TH-3DCRT showed excellent carotid sparing capability, comparable to that with TH-IMRT, with high treatment efficiency and short planning and treatment times, comparable to those for 2F-3DCRT, while maintaining good PTV coverage. This work was supported by the Technology Innovation Program, 10040362, Development of an integrated management solution for radiation therapy funded by the Ministry of Knowledge Economy (MKE, Korea).

SU-E-T-195: Gantry Angle Dependency of MLC Leaf Position Error

PURPOSE The aim of this study was to investigate the gantry angle dependency of the multileaf collimator (MLC) leaf position error. METHODS An automatic MLC quality assurance system (AutoMLCQA) was developed to evaluate the gantry angle dependency of the MLC leaf position error using an electronic portal imaging device (EPID). To eliminate the EPID position error due to gantry rotation, we designed a reference maker (RM) that could be inserted into the wedge mount. After setting up the EPID, a reference image was taken of the RM using an open field. Next, an EPID-based picket-fence test (PFT) was performed without the RM. These procedures were repeated at every 45° intervals of the gantry angle. A total of eight reference images and PFT image sets were analyzed using in-house software. The average MLC leaf position error was calculated at five pickets (-10, -5, 0, 5, and 10 cm) in accordance with general PFT guidelines using in-house software. This test was carried out for four linear accelerators. RESULTS The average MLC leaf position errors were within the set criterion of <1 mm (actual errors ranged from -0.7 to 0.8 mm) for all gantry angles, but significant gantry angle dependency was observed in all machines. The error was smaller at a gantry angle of 0° but increased toward the positive direction with gantry angle increments in the clockwise direction. The error reached a maximum value at a gantry angle of 90° and then gradually decreased until 180°. In the counter-clockwise rotation of the gantry, the same pattern of error was observed but the error increased in the negative direction. CONCLUSION The AutoMLCQA system was useful to evaluate the MLC leaf position error for various gantry angles without the EPID position error. The Gantry angle dependency should be considered during MLC leaf position error analysis.

SU‐E‐T‐292: New Technique for Developing Proton Range Compensator Using Three‐Dimensional Printer

PURPOSE A new system for manufacturing proton range compensator (PRC) was developed by using a three-dimensional printer (3DP). The physical accuracy and dosimetrical characteristics of the new PRC (PRC-3DP) was compared with conventional PRC (PRC-CMM) manufactured by computerized milling machine (CMM). METHODS A PRC for brain cancer treatment, with passive scattered proton beam, was calculated in the TPS (Eclipse, Varian, USA) and its data was converted into a new format for 3DP (Projet HD3000, 3D Systems, USA), using the in-house developed software. PRC-3DP was printed with UV curable acrylic plastic, while PRC- CMM was milled into PMMA using a CMM (V-CNC500, CINCINNATI, USA). We measured the 5 randomly selected points for its physical thickness of both PRCs to evaluate its physical accuracy. Stopping power ratio (SPR), spread-out bragg peak (SOBP, 90∼90%) and distal fall-off (DFO, 20∼80%) at the central axis, +2.5, and 2.5 cm in the lateral direction, and FWHM of dose profile in depth 6, 8, and 10 cm were measured to evaluate for its dosimetrical characteristics. All measured data was compared with TPS data. RESULTS There was no significant difference in the physical depths between the calculated and the measured value of both RPC-3DP and RPC-CMM (p<0.05). SPR of both PRC showed similarity in value (1.022) when compared with that of the water. Average difference of SOBP between the TPS and the measured data from both PRC was 0.3773±0.0075 and 0.2762±0.0235 cm, while DFO was 0.06±0.005 and 0.0471±0.0042 cm, respectively. Average differences of FWHM between the TPS and the measured data from PRC-3DP and PRC-CMM were 0.1799±0.025 and 0.137±0.0181 cm, respectively. There was no significant difference in dosimetrical characteristic between the RTP and both PRCs (p<0.05). CONCLUSIONS Physical accuracy and dosimetrical characteristics of the PRC-3DP were comparable to that of the conventional PRC-CMM, while significant system minimization was provided. This work was supported by the Technology Innovation Program, 10040362, Development of an integrated management solution for radiation therapy funded by the Ministry of Knowledge Economy (MKE, Korea). This idea was applied for a Korea patent (no. 10-2012-0010812).

SU‐E‐T‐504: Development of An Offline Based Internal Organ Motion Verification System during Treatment Using Sequential Cine EPID Images

Purpose: We developed an offline based organ motion verification system using cine EPIDimages and evaluated its accuracy and availability through phantom study. Methods: The system was designed for import of cine EPIDimages, which are obtained sequentially during treatment through a DICOM format and reconstructed into a live image. For verification of organ motion, a pattern matching algorithm using an internal surrogate was employed in the self‐developed analysissoftware. For the system performance test, we developed a linear motion phantom, which consists of a human body shaped phantom with a fake tumor in the lung and linear motion cart with control software. The phantom was operated with a motion of 2 cm at 4 sec per cycle and cine EPIDimages were obtained at a rate of 3.3 frames/sec with 1024 × 768 pixel counts in a linear accelerator (10 MVX). Organ motion of the target was tracked using self‐developed analysissoftware and compared with data from the RPM system (Varian, USA). For quantitative analysis, we analyzed correlation between two data sets in terms of average cycle, amplitude, and pattern (root mean square, RSM) of motion. Results: Averages for the cycle of motion from cine EPID and RPM system were 3.95±0.02 and 3.98±0.11 sec, respectively, and showed good agreement on real value (4 sec). Average of the amplitude of motion tracked by our system (1.71 ±0.02 cm) showed a slightly different value, compared with the actual value (2 cm), due to time resolution for image acquisition. The value of the RMS from the cine EPIDimage (0.379) grew slightly, by 3.8%, compared with data from the RPM (0.365). Conclusions: Our system showed good representation of its motion in a preliminary phantom study. The system can be implemented for clinical purposes, which include organ motion verification and its feedback for accurate dose delivery to the moving target.

SU‐E‐T‐263: Development of a Video Guided Real‐Time Patient Motion Monitoring System

Purpose: Using conventional CCDcamera systems, we developed a video image guided real‐time patients motion monitoring (VGRPM) system; a motion phantom was used for evaluation of its performance for clinical use. Methods: The VGRPM system consists of three parts: an image acquisitiondevice, a main control computer, and in‐house developed patient motion analysissoftware. For development of an intelligent patient motion monitoring system that works only during treatment time and for system automation, the system was designed for synchronization with a beam on/off trigger signal. Patient movement during radiation is detected by real‐time frame difference based in‐house developed analysissoftware. When the error range exceeds the set criteria, (Cmove), a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.5, 1, and 2 cm for 1 and 2 sec, respectively, was used for evaluation of system performance. We measured optimal Cmove for clinical use, minimum distance, which can be detected in this system, and response time of the whole system. The stability of the system in a linear accelerator unit was evaluated for a period of 6 months. Results: : As a result of the moving phantom test, the Cmove for detection of all simulated phantom motion was determined to be 0.5%. The system can detect phantom motion as small as 0.5 cm. The measured response time from detection of phantom movement to warning signal through video analysis was 0.1 sec. During this testing period, no significant functional disorder was observed. Conclusions: The VGRPM system can contribute to reduction of treatment error by patients motion and increase the accuracy of treatment dose delivery.

SU‐GG‐T‐549: Development of Respiration Verification Program and Procedure for 4‐Dimensional Stereotactic Body Radiation Therapy

Purpose: In order to verify the behavior of tumor motion caused by breathing, respiration & tumor motion verification procedure was designed and its feasibility was tested. Method and Materials: Visual software was developed using LabView 7.0 to analyzerespiration by detecting peak/valley points from RPM signals. The software displays the number of detected peaks/valleys, peak/valley locations, amplitude of signals, and 2nd order differential coefficients at each data points. It calculates mean, standard deviation, variance, maximum and minimum of all detected peak/valley points. It can analyze data for user defined intervals and exports the results in excel file. The program performance was tested using known RPM signals which were sine waves with period of 3 and 6 sec with amplitude of 1 and 2 cm. Also irregular signals obtained from patients breathing were used to generate irregular respiratory signals by moving a phantom and the software performance was tested. In clinical application, the analyzed respiratory data were converted into tumor motion by applying scaling factor defined by tumor‐motion amplitude to respiration amplitude. To determine the scaling factor, gated On‐Board‐Image (OBI)s were acquired at 0% and 50% of respiratory phases and the imaging times were recorded. From the RPM file, the respiratory signal values at imaging times were read and displacement of tumor was measured from the OBI images. The scaling factor was, then, determined as the ratio of tumor displacement between 0% and 50% phases to difference of two respiratory signals values at corresponding phases. Results: The computed results by the software were extremely consistent with true values within 0.1% difference for regular and irregular motions. Conclusion: Developed software was proven to have sufficient accuracy for clinical application. The proposed method has advantages of non‐invasive, fine temporal resolution without extra radiation, thereby providing a useful tool for 4‐dimensional body stereotactic radiotherapy.

SU-GG-J-32: Analysis of Imaging Doses for Optimal Management of 4D-IGRT Treatments

Purpose: Introducing 4D‐IGRT potentially increases an accumulated dose to patients from imaging and verification processes compared to conventional practice. It is therefore essential to investigate the level of imaging dose to patients when 4D‐IGRT devices are installed. We monitored the imaging dose level and compared with that of pre‐IGRT practice. Method and Materials: A 4D‐CT (GE, Ultra Light Speed 16), a simulator (Varian Acuity), and a linear accelerator (Varian IX) equipped with kVp (OBI) and MVp (aSi 1000) imaging devices were installed for 4D‐IGRT. The surface doses to a RANDO phantom were measured with newly installed devices and with pre‐existing devices; single slice CT(GE,Light Speed), a simulator (Varian Ximatron) and L‐gram with a Varian 2100CLinac. The surface doses were measured using TLDs (HASHOW, Model T‐100) at 8 different sites of the phantom; the brain, eye, thyroid, chest, abdomen, ovary, prostate, pelvis. Results: Compared to the imaging with single slice non‐gated CT, the gated MDCT imaging increased the dose to the chest and abdomen more than tenfold (1.74 ± 0.34 vs 23.23 ± 3.67 cGy ). But the imaging doses with Acuity at all measured sites were smaller than those with Ximatron due to a function that reduced irradiation time for fluoroscopy, which were 0.91 ± 0.89 vs 6.77 ± 3.56 cGy, respectively. The portal imaging doses with MVp EPID were about the half of the dose with conventional L‐gram (1.83 ± 0.36 vs 3.80 ± 1.67 cGy). The dose from OBI was 0.97 ± 0.34 cGy for fluoroscopy mode. Conclusion: Gated CT is the major source of increasing the imaging dose to patients. OBI imaging dose was small, but the accumulated dose associated with everyday verification for accurate treatments needs to be taken into account.