bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐120: Reduction in Breathing Motion Intra‐Fraction Variability through Prone Body Positioning
Authors: Rosu M , Chen S , Hugo G , Weiss E
Published: November 2011

Purpose: Simplicity in treatment is preferable, whenever possible: it reduces errors, execution time and effort, and increases patient confidence. We aim at this benefit by using a natural body compression approach through positioning the patient prone, instead of the habitual (albeit unsubstantiated) supine positioning. The innovative premise tested in this work is that prone positioning can moderate the respiratory‐induced motion and make it more consistent from cycle‐to‐cycle, compared to supine positioning. Methods: Breathing traces from 8 patients positioned supine, then prone, were used to evaluate cycle‐to‐cycle variances in end‐of‐exhale(EoE), end‐of‐inhale(EoI) and average(AVE) locations, and to quantify the statistical significance at a p‐value=0.05. Population variances were also evaluated for these locations. Results: Prone positioning has improved EoE‐location consistency for all patients, and was superior in all but one case for AVE‐location. EoI reproducibility was poorer (improved in 5 out of 8 cases). Data analysis for the entire population reveals an overall improvement through prone positioning for all locations of interest. Variance reduction implies a corresponding reduction in the random component of the respiratory motion. Conclusions: Our analysis demonstrates statistically significant improvements in breathing pattern consistency in prone position. This conclusion can be extended to the tumor motion as well, under the assumption that the RPM traces and the tumor trajectories exhibit similar motion pattern characteristics, a condition often fulfilled. Radiotherapy with prone body positioning is straightforward and non‐invasive, and can be implemented without using complex respiration control technology (therefore could become widespread available). The reduction in breathing variability through prone positioning offers the potential for 4DCT image acquisition with even fewer motion artifacts and for radiation delivery under anatomical conditions resembling more closely those from the pre‐treatment CT scans, while enabling the possibility of tumor dose escalation at similar or reduced normal tissue doses compared to the conventional supine treatment position.
SU‐E‐J‐124: Comparison of Infrared Marker‐Based Positioning System and EPID for the Measurement of Setup Errors
Authors: Cao Y , Gao C , Wang L , Chi Z , Han C
Published: November 2011

Purpose: To measure the setup errors with infrared marker‐based positioning system (IM‐BPS) and electronic portal imaging device （EPID） for patients with esophageal carcinoma and lung cancer and investigate the accuracy and practicality of IM‐BPS. Methods: From January 2007 to January 2008, 40 patients with esophageal carcinoma and 27 patients with lung cancer received three‐dimensional conformal radiotherapy or intensity‐modulated radiotherapy, setup errors during the treatment were measured with IM‐BPS and EPID, and the data of setup errors were compared with paired t‐test and agreement with χ2‐ test. Results: ⑴It takes 10–12mins to complete the validating for each patient by EPID system, while IM‐BPS system only needs 2–5mins. ⑵The mean setup errors along x‐axis, y‐axis, z‐axis for patients with esophageal carcinoma measured by IM‐BPS and EPID were 3.49mm, 3.19mm, 3.31mm and 4.03mm, 3.41mm, 3.43mm, respectively. For the patients with lung cancer, the setup errors were 4.23mm, 3.51mm, 3.39mm and 4.85mm, 3.53mm, 3.74mm, respectively. ⑶The difference of setup errors measured by the two systems was within 1mm for 65% esophageal carcinoma patients (χ2=51.09，P=0.000), the difference of setup errors measured by the two systems was within 1 mm for 55% lung cancer patients (χ2=53.35,P=0.000). ⑷The rotation errors along sagittal plane, coronal plane and transverse plane for patients with esophageal carcinoma and lung cancer measured by IM‐BPS were 0.31o, −0.90o, 0.34o and 0.05o, −1.12o, 0.22o, respectively. Conclusions: The measurement results of setup errors for patients with esophageal carcinoma and lung cancer show that IM‐BPS is mostly better than EPID. Though validating for patients can be measured accurately and be well quality controlled, IM‐BPS is used easily because of macroscopic, homely, spare time and real‐time monitoring.
SU‐E‐J‐133: Accuracy of Cone Beam CT, X‐Ray Imaging in Conjunction with Optical Image Guidance in Stereotactic Body Radiation Therapy
Authors: Liu Y , Campbell J , Chen S
Published: November 2011

Purpose: Stereotactic body radiation therapy (SBRT) requires high precision of patient position and target localization. For SBRT patients positioning, cone beam CT imaging has been widely used, generally with zero couch rotation. The purpose of this study is to implement Stereotactic radiation surgery (SRS) patient positioning technology to SBRT by expanding patient positioning with couch rotation. Methods: Currently we are using Varian® Novlis Tx for treating SBRT patients implementing CBCT. BrainLAB® X‐ray imaging system in conjunction with optical guidance is primarily used for SRS patients. CBCT and X‐ray imaging system were independently calibrated with 1.0 mm accuracy. For daily imaging QA, we set up a Penta™ imaging phantom with infrared markers. The imaging phantom has two image isocenters for CBCT and X‐ray imaging respectively with CBCT isocenter offset from the X‐ray imaging isocenter. The X‐ray imaging system was implemented through BrainLAB® ExacTrac system with CBCT localized position at the initial zero position for the X‐ray imaging system. For the other couch positions, X‐ray images were fused with patient DRRs for positioning. Results: For daily imaging QA, the longitudinal, vertical and lateral coordination between CBCT and X‐ray imaging average 0.4+/−0.6, 0.1+/−0.6 and 0.6+/−0.7 mm. The shift from the CBCT imaging isocenter to the X‐ray imaging isocenter is 0.7+/−0.5 mm accuracy for a 6‐month period of tracking.Patient position accuracy: After initially localizing the patient with CBCT at the zero couch position, we then position the patient with the X‐ray imaging system. The computed translational and rotational shift accuracy are 0.6+/− 0.6 mm and 0.5+/−0.3 degree respectively, based on 39 SBRT patients couch rotations. Conclusion: Accurate coordination of CBCT and X‐ray imaging in conjunction with optical imaging guidance can be expanded to patient positioning with couch rotation. The X‐ray imaging capability at rotated‐couch positions improved the physician confidence level during SBRT treatment.
SU‐E‐J‐141: The Development of Real Time Automatic Patient Position Correction System
Authors: Shin D , Jeong H , Min B , Yoo S , Park S , Lee S
Published: November 2011

Purpose: According as the previous scattering mode is being converted to a uniform scanning and a PBS, the methods of proton therapy are characterized by prolonged treatment time. Nevertheless, most of the gating or tracking methods correspond to patientsˈ respiration. There are no considerations about the mobility of patients during the treatment. Given this background, the current study was conducted to confirm the movement of patients during the treatment and to adjust the position of patients using an automatic couch on a real‐time basis. Methods: A cruciate form of tattoo was drawn on the body of patients and it was photographed using CCD. With the use of image pattern matching method of NI Vision assistant, the current location was confirmed. A real‐time image of tattoo was done to confirm the set‐up position of patients. In regard to the movement of patients within a tolerance range, a couch was moved and the location was adjusted accordingly. In cases in which the movement was measured to a higher level than the tolerance range, to prevent the fluctuation of patientsˈ body due to the abrupt movement of table for the position correction, a beam‐off was attempted and the set‐up of patients was adjusted accordingly. Following the adjustment of patientsˈ location, with the use of methods where a beam‐on gating and a tracking were synchronously performed, the location of patients was adjusted. Results: To develop and then to investigation the program algorithm for automatic couch correction and tracking, a small‐sized 3D phantom was prepared. Following the preliminary experiment, a correction of couch position was effectively achieved according to the movement of target. Conclusion: From now on, further practical studies are warranted to make an application of moving couch apply to a clinical use.
SU‐E‐J‐147: Effect of Audio Instruction on the Tracking Accuracy for a Four‐ Dimensional Image‐Guided Radiotherapy System, MHI‐TM2000 (VERO)
Authors: Nakamura M , Sawada A , Mukumoto N , Takahashi K , Miyabe Y , Takayama K , Matsuo Y , Mizowaki T , Kokubo M , Hiraoka M
Published: November 2011

Purpose: To assess the effect of audio instruction on tracking accuracy for MHI‐TM2000 (VERO).Methods: Anterior‐posterior abdominal skin surface displacements for ten patients with a lung tumor were measured by a respiratory monitoring system with and without audio instruction. Based on the obtained twenty respiratory patterns, a three‐dimensional movable phantom with a steel ball target of 9.5 mm in diameter was driven along the superior‐inferior direction. The target position was measured in real time by the laser displacement gauge and the orthogonal kV x‐ray imaging subsystem. Simultaneously, the kV x‐ray imaging subsystem predicted the future target position, and then the system controller calculated the corresponding rotation angles. Thereafter, the gimbaled x‐ray head tracked the target based on the command. Total tracking system error (ET) was computed by both target prediction errors and mechanical response errors of the gimbaled x‐ray head, and then compared between with and without audio instruction.Results: By applying audio instruction, the reproducibility of respiratory pattern was significantly improved (p < 0.01), although motion amplitude was increased by a factor of 2.1 on average. The root mean squares of the ET (RMSET) were up to 1.18 mm without audio instruction and 1.26 mm with audio instruction, respectively. There was no significant difference between free breathing and audio instruction in the RMSET (p = 0.26). The correlation between the RMSET and the 90th percentile of respiratory speed (v) was stronger under the conditions of audio instruction (R2 = 0.77) than under the conditions of free breathing (R2 = 0.29) Conclusions: Audio instruction improved reproducibility of respiratory pattern but increased to the v that negatively affected the tracking accuracy. The tracking errors can be deduced from the v for regular respiratory pattern, suggesting upper limit of the v to achieve high tracking accuracy.

This research was in part sponsored by Mitsubishi Heavy Industries, Ltd., Japan.
SU‐E‐J‐157: Investigation of Gated Cone‐Beam CT to Reduce Respiratory Motion Blurring
Authors: Kincaid R , Yorke E , Rimner A , Mageras G
Published: November 2011

Purpose: Respiration‐correlated cone‐beam CT (RC‐CBCT) using slow continuous gantry rotation is commonly used to reduce respiratory motion blurring but image quality is limited by uneven projection spacing. This study investigates the efficacy of a novel gated CBCT technique (gantry motion and imaging only within gate) in reducing motion blur with improved image quality using a new type of computer‐controlled linac (Varian TrueBeam).Methods: For gated CBCT, the linac is programmed to gate gantry rotation and kV image acquisition with approximately 25% duty cycle around end expiration. The two‐part study examines images in phantom and prospectively in patients with thoracic and abdominal tumors. A motion phantom is programmed to follow a patient respiratory trace (1.4cm mean excursion) and CBCT scans are performed in standard “free‐breathing”, RC‐CBCT, and gated CBCT modes. A standard CBCT of the stationary phantom serves as ground truth. Evaluation of phantom image quality compares contrast‐to‐noise ratios (CNR) of spheres embedded in acrylic, delineated on the static image and aligned to the other images. In patient studies, image fidelity in standard free‐breathing and gated CBCT is compared relative to a respiration‐correlated CT (RCCT) on the same day, by computing a cross‐correlation metric (CCM) in an ROI around the internal target volume following rigid registration.Results: CNR in motion phantom for gated CBCT is nearly that for static phantom (ratio gated/static 0.95) and larger than for RC‐CBCT (ratio 1.64) and standard CBCT (1.22). CCM of the tumor ROI in gated CBCT is larger than standard CBCT in all three thoracic cases thus far (ratio gated/standard mean 1.04 range 1.03–1.06), indicating higher congruence with the ground‐truth RCCT Conclusions: Gated CBCT visibly reduces image blurring caused by respiratory motion. By exploiting recent computer‐controlled linac technology, complete projection sets can be acquired within a gate, yielding improved reconstruction image quality relative to RC‐CBCT.
SU‐E‐J‐167: Estimation of Effective Dose from a Single KV Imager for Real‐Time Intrafraction Tumor Position Monitoring
Authors: Ng J , Poulsen P , Kuncic Z , Keall P
Published: November 2011

Purpose: A novel kV guidance method has been proposed in which the tumor position is continuously measured during IMRT and arc therapy by a single kV imager. Adding kV imaging during therapy adds radiation dose. We quantify the dose delivered and compare it to other imaging doses. Methods: The software PCXMC2.0 was used to calculate effective dose delivered to a mathematical human phantom. The Varian OBI system was simulated. The beam axis was set to intersect the geometric center of the prostate. Tube voltage and mAs settings were fixed. The imager angle, field size, height and mass (statistics from ten countries) of the phantom were varied. For different treatment scenarios, the effective dose was averaged over all angles to obtain an average angular effective dose. The field size was fixed to the minimum area sufficient to cover all markers and the average effective dose was obtained by weighting all the countries by their populations. This average effective dose per projection was used to calculate the effective dose based on treatment technique, fractionation and imaging frequency. The dose was compared to the Navotek radioactive fiducial and CBCT. Results: Effective dose varied with imager angle. For a 6cm×6cm field, the highest average angular dose per projection is 1.2 microSv (India), while the lowest is 0.6 microSv (Germany). The average dose weighted by population is 0.9 microSv. The effective dose increases linearly with field size, imaging frequency and treatment duration but decreases with height or mass. A 15 minute single fraction IMRT treatment delivers 0.84 mSv at 1 Hz. For comparison, a pre‐treatment CBCT pelvic scan delivers 4.3 mSv while the Navotek radioactive fiducial delivers 64 mSv of lifetime dose. Conclusion: Intrafraction kV guidance for tumor tracking gives less than 1mSv imaging dose with reasonable settings. This is lower than Navotek and CBCT.

Conflict of interest: Supported by NCI R01 CA93626.
SU‐E‐J‐170: Influence of Technique and Filtration on Kilovoltage Cone Beam CT Dose
Authors: Alaei P
Published: November 2011

Purpose: To quantify the effect of changing imaging techniques and addition of filtration on the dose delivered to patient. The variation of dose with technique in kilovoltage beams is well understood in diagnostic radiology but is not commonly measured in therapeutic radiology. Occasionally, the beam techniques may be changed to improve image quality without proper attention given to patient dose. The bowtie filtration commonly added to the beam to improve image quality also affects the dose on surface and at depth. Methods: The dose from Elekta XVI CBCT beam was measured in phantom. Measurements were made for the clinical presets and after changing the imaging techniques (mA and/or ms) as well as for beams with and without bowtie filter. The measurements were performed at 1 cm depth and at surface. Results: The dose measurements exhibit a linear increase with the increase of mAs, as expected. There is a slight difference between changing the ms (keeping mA constant) and changing the mA (keeping ms constant). Addition of bowtie filter does not result in an appreciable change in the depth dose in shallow depths (< 1 cm) but reduces the overall dose at depth and skin by approximately 25%, providing the technique is not changed. Conclusions: Variation of dose with technique and addition of filtration has been studied. Since the dose tracks the technique settings (mAs) linearly, techniques should not be changed to improve image quality without quantifying the image dose. Addition of filtration does reduce the dose but does not affect the depth dose at shallow depths. It should be noted that the “filtered” beams often have higher technique settings for the same cassette size in the clinical presets, so this dose reduction is not achieved by using these presets.
SU‐E‐J‐182: Development of a Tomosynthesis Algorithm to Reduce Cone Beam Imaging Dose
Authors: Izaguirre E. W. , Price S , Silvius A A
Published: November 2011

Purpose: To develop a tomosynthesis cone beam reconstruction algorithm for LINAC cone beam CT with the goal to achieve a dose reduction better than 1/5 in current cone beam imaging protocols for patient positioning and portal beam verification while maintaining the required image quality for patient positioning and beam delivery verification. Methods: Tomosynthesis is the process of reconstructing tomographic images with fewer acquired projection images and additional synthetically generated projections to preserve image resolution and contrast. We developed a tomosynthesis cone beam reconstruction algorithm based on combining Feldkampˈ s cone beam reconstruction algorithm and an iterative maximum likelihood reconstruction algorithm. The Feldkamp method is used to reconstruct the first estimate of the tomographic data and the iterative maximum likelihood algorithm improves the resolution, contrast and considerably eliminates ghost images from the first estimate. Results: The algorithm tests show image reconstruction with the adequate image quality, contrast and resolution for patient positioning and beam delivery verification with a 1/8 dose delivered reduction using current cone beam imaging set‐up protocols. Imaging time is reduced with the same proportion allowing higher patient throughput. The algorithm has been tested using patient data for head and neck and brain treatment sites. On both treatment sites, portal beam and patient localization can be effectively performed within 3 mm accuracy using digitally reconstructed radiographs generated from the tomosynthesis reconstructed patient anatomical image. The reconstruction is executed on a desktop computer with 2GHz CPU and 4 Gb RAM in less than 5 minutes. Conclusions: We developed a tomosynthesis algorithm capable of reconstructing images with adequate resolution to perform beam delivery verification and patient positioning. This dose reduction will allow the daily use of cone beam CT in patients that require daily set‐up verification which currently is impractical because of dose and time constraints.
SU‐E‐T‐02: Reduced Tumor Control Probability Becaused of the Interplay between Tumor Motion and IMRT
Authors: Sheng K , Saraiya S , Read P , Yang W
Published: November 2011

Purpose: To study the change of the tumor control probability (TCP) caused by variation in the fractional dose from the interplay between tumor motion and intensity modulated radiation therapy (IMRT). Methods: A numerical simulation was performed to simulate the dose perturbation induced by the interplay. 107 tumor clonogens were divided into 1, 10 and 100 sub‐volumes that received an expected fractional dose of 2 Gy with dose variations following either a normal distribution or a sine distribution. The variation was generated independently to each sub‐volume. Two different groups of alpha/beta values were used to represent fast and slow proliferation tumors, respectively. TCP was calculated for 10,000 independent histories using the linear quadratic model, with or without the repopulation of the tumor cells. Results: The interplay did not significantly change the TCP for tumors with 1 sub‐volume. On the other hand, a significant decrease in the TCP was observed in a more probable scenario with different dose variation in different tumor subvolumes. Higher radiation doses are required to achieve the same TCP for 95% of the patients. Approximately, for alpha/beta=1 1.9 Gy, an additional 0.69 Gy and 0.37 Gy are required for an additional 0.1 Gy of uncertainty with the normal and sine distributions, respectively; for alpha/beta=3 Gy, the additional doses are 0.73 Gy and 0.41 Gy. Tumor repopulation exacerbates the problem for the normal distribution by increasing additional doses required to 0.92 Gy (alpha/beta=11.9 Gy) and 1.05 Gy (alpha/beta=3 Gy) for every additional 0.1 Gy of uncertainty in the delivered dose. Conclusions: Interplay between tumor motion and IMRT contributes negligibly to the total physical dose but significantly to the tumor control probability. A higher dose is needed to achieve the same TCP if random variation in the fractional dose is present.
SU‐E‐T‐15: GEANT4 Microdosimetry for Simulation of Dose Enhancement in Vivo at Orthovoltage Energy
Authors: Ackerman N , Graves E , Bazalova M
Published: November 2011

Purpose: This study simulates at the cellular scale the microscopic dose enhancement from high Z materials (such as gold nanoparticles) in tissue as a function of concentration and intracellular localization. Methods: Monte Carlo (MC) simulations were performed using Geant4 9.3p02 for a simple 3D geometry of 125 cubic cells with centered nuclei. Contrast materials of gold, iodine, and tungsten were simulated in a 150 kVp beam. The extra‐ and intra‐cellular contrast concentration was varied, and internal cellular contrast was placed either throughout the cytoplasm or in localized vesicles. Results: The enhancement factor for the nucleus is well described by a linear function of tissue contrast, regardless of whether the enhancement agent was contained in vesicles or throughout the cytoplasm. The predicted enhancement is smaller than previous simulations using macroscopic methods and is smaller than measured values. Conclusions: Cellular scale simulations show that macroscopic simulations overestimate the enhancement seen in the nucleus, but that intermediate energy secondaries interacting in the nucleus would not provide the enhancement measured experimentally.

N. Ackerman is supported by a Weiland Family Fellowship
SU‐E‐T‐18: Nanoscale Proton Dose Distributions Using GEANT4‐DNA Simulation
Authors: Chen Y , Ahmad S
Published: November 2011

Purpose: To simulate the energy deposition patterns of 1 MeV proton beam in three different nanoscale size spherical water targets. Methods: In this study, GEANT4 version 9.4 with the DNA physics package demonstrated in one of the advanced examples “microdosimetry” was used. In order to mimic typical cell geometry, three spherical targets of water with diameters of 200, 20 and 2 nanometer were placed in a cube of water (10 × 10 × 10 micrometer3). The interactions listed in the DNA package were applied to these three spherical targets where secondary electrons were tracked down to 5 eV. The standard electromagnetic interaction processes were used in the volume of the cube outside the spherical targets. Proton beams of 1 MeV were used to travel through the spherical targets. One thousand incident proton histories per spherical target were studied in the simulations. The frequency distributions of energy deposited (eV) per nanometer in the Results: With the decrease of the of the target dimensions, the shapes of the frequency distribution of the energy depositions per nanometer in the spherical targets were observed to gradually become asymmetric. The mean energy depositions were found to be 29, 24.5 and 14.8 eV/nanometer for 200, 20 and 2 nanometer diameter targets, respectively. Conclusions: The energy deposition patterns at the DNA environment directly affect sub‐cellular radiation damage and lesion repair mechanism and thus are essential for biophysics models to estimate the radiobiological effects. The trend of increasing asymmetry showed in this study in dose distributions for smaller nanoscale target demonstrate the usefulness of GEANT4‐DNA package as a powerful tool to better understand the physical basis of dose deposition in realistic size of DNA to accurately predict the cellular radiobiological effect due to particle irradiation.
SU‐E‐T‐19: The Use of Probability Volume Histograms (PVH) and Iso‐Probability of Response Charts in Treatment Plan Evaluation
Authors: Mavroidis P , Ferreira B , Papanikolaou N , Lopes M
Published: November 2011

Purpose: This study demonstrates new methods for treatment plan evaluation and comparison. The clinical importance of these methods is examined in relation with standard radiobiological and dosimetric treatment plan evaluation criteria. Methods: Typical head and neck, breast and prostate cancer cases were selected to quantify the benefits of the proposed treatment plan evaluation method. In each case, conformal radiotherapy (CRT) and IMRT treatment plans were produced. The different treatment plans were evaluated based on the dose distribution converted to D2Gy, iso‐probabilty and iso‐BED dose charts and corresponding probability volume histograms. Results: For the head & neck cancer case, at the prescribed dose level of the CRT and IMRT dose distributions, the P+ values are 0.0% and 24.9% for a BEUD to the target of 54.6 Gy and 63.5%, respectively. For the breast cancer case, the P+ values are 88.0% and 89.1% for a BEUD of 61.6 Gy and 61.4%, respectively. For the prostate cancer case, the P+ values are 28.7% and 51.3% for a BEUD of 69.3 Gy and 70.7%, respectively. The use of local iso‐probability charts is very useful for plan evaluation since the visual information focuses on the doses that may cause an effect in a particular organ by considering its radiosensitivity. Also, since these low doses may not have an actual clinical effect, the dosimetric information provided by low doses in the normal tissues is reduced eliminating some visual noise. At the same time, cold spots in the target volumes and hot spots in the normal tissues are immediately visualized. Conclusions: The proposed D2Gy, iso‐probabilty and iso‐BED dose charts and histograms illustrated better the difference in the effectiveness of the different treatment plans, which shows the benefits that these evaluation tools can offer in the process of treatment planning.
SU‐E‐T‐35: Comparison of IMRT Verses 3D‐CRT Dose and Acute Toxicity for Rectal Cancer Patients
Authors: Levinson L , Jabbour S
Published: November 2011

Purpose: To compare the doses and toxicities in patients treated with radiation therapy for rectal cancer using 3‐dimensional conformal radiotherapy (3DCRT) verses intensity‐modulated radiation therapy (IMRT). Materials: Thirty six patients treated for Stage II–IV rectal cancer were retrospectively reviewed: 19 using 3DCRT and 17 using IMRT. A median dose of 5040cGy was delivered. The dose volume histogram statistics for the initial 45Gy delivered for small bowel, large bowel, bladder, femoral heads, and iliac crest were compared between the two treatment groups. Toxicities such as pain, proctitis, urinary urgency, dehydration, fatigue, and anorexia were graded according to the CTCAE version 3.0 and compared between the two groups. Student t‐tests were used to determine the statistical significance of the data. Results: The patients treated with IMRT showed larger volumes receiving low doses and smaller volumes receiving higher doses in normal structures than 3DCRT. To list a few, Large bowel >30Gy (3D=112cc, IMRT=60cc); Large bowel >40Gy (3D=93, IMRT=39); Femoral Heads >40Gy (3D=18%, IMRT=2%); Bladder >45Gy (3D=47%, IMRT=19%); Iliac Crest >45Gy (3D=22%, IMRT=4%). The patients treated with 3DCRT showed more Grade 2+ toxicities than the patients treated with IMRT — total percent of patients with toxicity greater than Grade 1: Pain (3D=42%, IMRT=0%); Proctitis(3D=53%, IMRT=12%); Urinary Frequency/Urgency (3D=26%, IMRT=0%); Dehydration (3D=32%, IMRT=0%); Fatigue (3D=21%, IMRT=6%); Anorexia (3D=16%, IMRT=0%). However, due to the relatively low number of patients, correspondence between the DVH data and the individual toxicity data did not prove to be strongly statistically significant. Conclusions: The data shows that IMRT has the potential to greatly reduce high grade acute toxicities when compared with 3DCRT. A stronger correlation between dose levels and toxicities is anticipated with more patient data. Specifically, we expect that further research would produce insight into correlating which dose factors contribute to which toxicities.
SU‐E‐T‐42: Changes in Submandibular Gland Volume during Radiotherapy
Authors: Niedzielski J , Court L , Cheung J , Beadle B , Dong L
Published: November 2011

Purpose: To examine submandibular gland volume changes by CT throughout the course of Intensity Modulated Radiation Therapy treatment for head and neck cancers. Method and Materials:CT images from 15 patients were analyzed to evaluate the change in volume of the left and right submandibular glands over the course of treatment (30–35 fractions). Each patient had received daily CT imaging using a CT‐on‐rails unit. Eleven of these patients had pre‐ and post‐treatment measurements of the stimulated and unstimulated saliva flow. Submandibular gland contours were drawn on the first fraction CT. The contours were then deformably mapped to the weekly CTs using an in‐house deformable registration tool. The volume of each gland was extracted, and changes in volume assessed. The changes in gland volume were compared with saliva flow measurements using using the R2 value from a linear fit. Results: All 15 patients showed decreases in gland volume over the course of treatment. The mean gland volume at the start of treatment was 10.6cc (range: 6.9–16.4cc). The mean volume reduction was 32.8% (range: 10.8 – 46.6%), 3.6cc (1.3 – 5.6cc). There was no clear statistical correlation between gland volume decrease and either stimulated or unstimulated salivary function. Conclusions: This study shows a significant reduction in submandibular gland volume over the course of radiation therapy. A more thorough study should be conducted to try and link gland volume decrease with saliva production.
SU‐E‐T‐44: Model Prediction of Radiation Induced Duodenal Toxicity for a Dose Escalation in Radiation Therapy of Pancreatic Cancer Using Published Reports
Authors: Prior P , Erickson B , Li X
Published: November 2011

Purpose: Safe dose escalation for RT of pancreatic cancer is limited by the surrounding organs at risk, particularly the duodenum, which is adjacent to the pancreas. The purpose of this work is to estimate the radiation induced duodenal toxicity using dose‐volume response data extracted from the literature for a proposed dose escalation of 72 Gy in 28 fractions via IMRT simultaneously integrated boost.Methods: Two patients treated for pancreatic cancer at our institution were randomly selected to retrospectively alter their treatment plan to simulate the testing dose escalation of 50.4 and 72 Gy in 28 fractions to the pancreatic head and the GTV, respectively. The report by Murphy et al. on SBRT of Grade 2 or higher duodenal toxicity was used to estimate NTCP using testing protocol DVHs. The Modified LQ model by Guerrero and Li was used to calculate the iso‐effective dose in the testing protocol producing the same effect as doses in the SBRT regime. Additional analysis of NTCP variation considered alpha‐beta ratios of 3 to 5 Gy for small bowel/duodenum late effects. Results: The testing protocol iso‐effective dose, D, associated with 25 Gy in a single fraction had a median value of 61.2 Gy and ranged from 56.3 to 68.0 Gy. The first patient had a high estimated risk of toxicity (0.45) due to the duodenal volume being greater than 0.21 cubic centimeters. A lower risk of toxicity was estimated for the second patient due to the duodenal volume being less than 0.21 cubic centimeters. Conclusion: Estimates of duodenal toxicity can be made despite the limited number of toxicity data available. A conservative dose‐volume constraint would limit 0.21 cubic centimeters of the duodenal volume to no more than 56 Gy. The estimates of duodenal toxicity exhibit a dependence on the value of alpha‐beta ratio of the duodenum.
SU‐E‐T‐107: Dosimetric Characteristics of a Glass Dosimeter for Proton Beam Measurements
Authors: Rah J , Kim D , Park S
Published: November 2011

Purpose: The purpose of this study was to investigate the dosimetric characteristics of the GD‐301 glass dosimeter for clinical dosimetry in a high‐energy proton beam and to compare it with LiF TLD‐100. Materials: The dose distribution measured with the glass dosimeter was evaluated by comparing them to those from GEANT4 MC simulation. We also compared dose measured with glass dosimeter and calculated with treatment planning system, Eclipse calculated dose of plan delivery in order to evaluate its potential as a new dosimeter in clinical proton beams. All measurements were performed in a proton beam (IBA Proton Therapy System‐Proteus 235) at the National Cancer Center in Korea. Dosimeters were irradiated in a water phantom using a stair‐like holder specially designed for this study. Maximum height was 100 mm with each step of 1 mm in ten layers. Results: Reproducibility in the 200 MeV proton beam was within 1.5% for the glass dosimeter, and within 1.7% for TLD‐chip responses. The glass dosimeter signal was linear as a function of applied dose in the range of 1—10 Gy. The fading effect of the glass dosimeter after a received dose of 2 Gy was initially found to be within 1.6% for six months. Angular dependence of the glass dosimeter was measured to be approximately 1.3% for angles ranging 80° from the beam axis using a cylindrical phantom. Depth‐dose distributions in the non‐modulated and modulated proton beams obtained with the glass dosimeter were estimated to be within 3.0% lower than those with the ionization chamber and simulation model using GEANT4 code. The difference between delivery dose calculated by the Eclipse and measured by the glass dosimeter is within 5.0%. Conclusions: Measurements comparing the glass dosimeter and TLD‐100 dosimetric characteristics demonstrated the suitability of the glass dosimeter for dose measurement in high‐energy proton beam therapy.
SU‐E‐T‐116: Measuring Dose Distribution Accuracy in Stereotactic Radiosurgery and Gamma Knife Treatment Using MR Or CT Imaging
Authors: Best R , Bennett M , Gersh J , Wiant D , Bourland J
Published: November 2011

Purpose: This study aimed to establish a standard dosimetry protocol for HDR Ir‐192 sources using an ion chamber calibrated with a Co‐60 beam. We developed a dedicated device for ion chamber measurements with a sandwich method and examined its measurement accuracy. Methods: A microSelectron‐v2 HDR Ir‐192 source was modeled with the EGSnrc/egs_chamber code. The accuracy of modeling was confirmed by comparing calculated results for gL (r) and F(r, angle) with those of TG‐43. First, an optimal source‐to‐chamber (SCD) separation for Ir‐192 dosimetry was determined from measurements with a PTW 31010 chamber at distances of 1.5–5 cm from the source center in water. The measured ionization chamber reading was corrected with the Monte Carlo‐calculated energy response for Co‐60 and Ir‐192, and was converted to the absorbed dose to water. The measured doses were compared with TPS values based on TG‐43. We developed a dedicated device for ion chamber measurements with a sandwich method at the optimal SCD separation. The average dose measured with two EXRADIN A1SL chambers was compared with the TPS value. Results: Calculated gL (r) and F(r, angle) values agreed well with those of TG‐43. The absorbed dose to water measured with the PTW31010 chamber was 3% lower than that of TPS at a distance of 5 cm and was 3%‐7% lower at distances less than 5 cm. This was addressed to the uncertainty of the chamber positioning. We made a sandwich measurement device with the separation of 5 cm, considering the uncertainty of positioning and measurement time. The dose to water with the sandwich method was in agreement with that of TG‐43 within −1.2%. Conclusions: The optimal distance for ion chamber measurements was at 5 cm from the Ir‐192 source. The dose to water measurement with the sandwich method is useful for daily dose management for Ir‐192 sources.
SU‐E‐T‐118: The Beam Quality Dependence of a Radiophotoluminescent Glass Dosimeter in Megavoltage Photon and Electron Beams
Authors: Araki F , Ohno T , Yoshiyama F , Kohno T , Wulff J
Published: November 2011

Purpose: This study investigated the beam quality dependence of a radiophotoluminescent glass dosimeter (RGD) in megavoltage photon and electron beams. Methods: The RGD response for 4–18 MV photons and 6–20 MeV electrons was investigated by comparison with ion chamber measurements and Monte Carlo (MC) simulations in solid water phantom. The beam quality response in electron beams was determined at reference depth. The energy response for photon and electron beams was calculated with EGSnrc/egs_chamber and cavity user‐codes, respectively. The photon energy dependence was also analyzed according to Burlinˈs cavity theory. The fraction of dose due to photon interactions 1‐d for Burlinˈs theory was calculated with a modified version of egs_chamber, which allowed discarding electrons generated in surrounding medium and entering the detector. Results: The calculated and measured RGD response in photons was lower by up to 2.5% with increasing beam quality in a range of 4–18 MV. The RGD response of 20×20 cm2 for 5×5 cm2 increased by 4% in 4 MV. The RGD response as function of depth was constant within 1% except for dmax in a range of 4–18 MV. The dose in RGD resulting from 1‐d decreased with increasing photon energy and with decreasing the field size. 1 ‐d is related to the photon energy response of RGD. The RGD response at dref in electron beams was constant within 1 % but 4% lower than that for 6 MV photons. The RGD response estimated by comparison with the ion chamber measurements agreed within 1% with the MC calculations. Conclusions: The energy dependence of RGD depends on the photons energy and the field size. In electron beams, the beam quality dependence at a reference depth is insignificant but was 4% lower than 6 MV photons. The beam quality dependence depends on 1‐d in RGD, demonstrating its behavior according to Burlinˈs theory.
SU‐E‐T‐119: A Phenomenological Model of the Al2O3:C Optically Stimulated Luminescence Detector (OSLD) Fading
Authors: Sawakuchi G , Yukihara E
Published: November 2011

Purposes: To explain the causes of fading in the Al2O3:C optically stimulated luminescence detectors (OSLDs). Methods: A phenomenological band diagram model with three electron traps and two recombination centers was used to represent the entities that are related to the OSL of Al2O3 :C OSLDs. The electron traps consist of a shallow trap, the main dosimetric trap and a deep trap. The shallow trap is unstable at room temperature (activation energy of 1.03 eV). Both recombination centers are radiative, however, the OSL signal is due only to one of the recombination centers. This model was based on experimental data of the thermoluminescence, optical absorption and OSL of Al2O3:C. A system of differential equations representing the transport and storage of charge carriers during irradiation, relaxation and stimulation phases was solved numerically. The system of equations was solved at room temperature conditions (T = 295 K). Results: The simulated shape of the OSL decay curve was in good qualitative agreement with experimental data. The simulated dose response of the OSL signal was linear in the interval of doses investigated (up to 10 Gy). The simulated fading of the OSL signal occurred in the first 10 min elapsed since irradiation and then became stable. Conclusions: The fading behavior of the OSL signal of Al2O3:C OSLDs can be explained by the existence of a shallow trap that is unstable at room temperature.
SU‐E‐T‐123: Evaluation of Integrated Gating Systems on a Novalis Tx System Using Quantitative Motion Tracking Analyses and Efficient Time‐Delay Measurements
Authors: Chang Z , Liu T , Cai J , Chen Q , Wang Z , Yin F
Published: November 2011

Purpose: To investigate accuracy of motion tracking and radiation delivery controlling of integrated gating systems on a Novalis Tx system. Methods: The study was performed on a Novalis Tx system, which is equipped with Varian RPM and BrainLAB ExacTrac gating systems. In this study, the two systems were assessed on accuracy of both motion tracking and radiation delivery controlling. To evaluate motion tracking, one artificial sinusoidal profile and three patientsˈ respiratory profiles were used. The motion trajectories acquired by the two gating systems were compared against the references. To assess radiation delivery controlling, time‐delays were measured using a single‐exposure method. More specifically, radiation is delivered with a 4‐mm diameter cone within 10%–45% phases for BrainLAB ExacTrac system and within 0%–25% phases for Varian RPM system during expiration, each with three times. Radiochromic films were used to record the radiation exposures and to calculate the time‐delays. In the work, the discrepancies were quantified using mean and standard deviation (SD). Pearsonˈs product moment correlational analysis was used to test correlation, which is quantified using a parameter of r. Results: The trajectory profiles acquired by the gating systems show good agreement with those references. A quantitative analysis shows that the average mean discrepancy between BrainLAB ExacTrac system and known references is 1.68 mm for artificial and patient profiles, with the maximum motion amplitude of 28.0 mm. As for Varian RPM system, the corresponding average mean discrepancy is 1.54 mm for artificial and patient profiles. With the single‐exposure method, the time‐delays are found to be 0.20±0.03 seconds and 0.09±0.01 seconds for BrainLAB ExacTrac and Varian RPM systems, respectivelyConclusions: The results indicate the gating systems on the Novalis Tx system can track motion and control radiation delivery with reasonable accuracy. The single‐exposure method has been demonstrated feasible in measuring time‐delays efficiently.
SU‐E‐T‐124: Feasubility Study of Absorbed Dose Estimation Using Radiophotoluminescence Glass Dosimeter for Proton Therapeutic Beam
Authors: Chang W , Kadoya N , Hashimoto S , Fujita Y , Kato T , Saitoh H
Published: November 2011

Purpose: Ion chamber is one of the fewer detectors that can be used to measure absolute dose for proton beam at present. However ion chamber is not proper for in vivo dose measurement as the large volume. Although a great number of studies reported on the in vivo dosimetry. But there is no study carried out on the topic for feasibility of the absolute dose measurement by radiophotoluminescence glass dosimeter (RGD) with the stopping power correction. The purpose of the study is to investigate the performance of RGD in the therapeutic proton beam by means of Monte Carlo simulation and experiments, and evaluate the feasibility of RGD for therapeutic proton beam. Methods: In this work, Monte Carlo simulation toolkit Geant4 was used to obtain the detailed information of dosimetric performance of the RGD. Firstly, the proton stopping power ratio of water to RGD (GD301, Asahi Techno Glass Co.) was calculated. Secondly, the beam modeling of proton beam in Southern Tohoku Proton center was held and then absorbed dose and proton energy fluence in the RGD at different depth was calculated for acquiring the stopping power correction factors. Finally the stopping power correction factor calculated by Geant4 will be applied to the measured data for confirming the usefulness of stopping power correction and the usability of RGD for dose measurement in therapeutic proton beam. Results: The simulation results showed that the stopping power ratio of RGD to water increased with the decreasing energy. The measured data showed good agreement between ion chamber and RGD with stopping power correction except the region behind of Bragg peak. Conclusions: The experiment results revealed that the usefulness of stopping power correction for correct proton dose measurement using RGD. More research is needed for correct dose measurement around the deeper region of Bragg peak.
SU‐E‐T‐126: Analysis of Uncertainties for the RPC Remote Dosimetry Using Optically Stimulated Light Dosimetry (OSDL)
Authors: Aguirre J , Alvarez P , Ibbott G , Followill D
Published: November 2011

Purpose: Determine the uncertainty of the Radiological Physics Centerˈs (RPC) remote audit dose measurement of photon and electron beam outputs using Optically Stimulated Luminescence Dosimeters (OSLD). Methods: In June 2010 the RPC implemented a switch from TLD to an OSLD mailed dosimetry audit using Landauerˈs InLight nanoDot™ OSL dosimeters and microStar reader System™. The steps and factors for the calculation of dose with OSLD were designed to follow those already in use with TLD including the use of the same acrylic mini‐phantoms and irradiation instructions. The OSLD sensitivity was referenced to Co‐60, and corrections for linearity, individual dosimeter response, fading, use of mini‐phantoms and energy were determined for the OSLD. An analysis of the uncertainty of each of the correction factors was determined to give an overall uncertainty of the OSLD dose measurement under Co‐60 reference conditions and megavoltage beam audits. Results: The expectation was that with the physical processes for OSLD, being so closely resembling those of TLD, the uncertainties of OSLD would be comparable to those of TLD. A combined uncertainty of 0.8% for irradiations with Co‐60 under controlled reference conditions and 1.8% for irradiations with high‐energy X‐rays was determined as compared to 1% and 2% for the previously used TLD, respectively. The OSLD energy block correction factor (KE) is the primary source of the overall OSLD dose measurement uncertainty. To date, the OSLD audit results after a year are essentially identical to the previous 5 years of TLD results both showing a mean TLD/Inst. Ratio of 1.00 ± 0.018.Conclusion: The uncertainty of the RPCˈs new OSLD remote dosimetry audit programˈs dose measurement is equal to if not less than that for the historical TLD program.

Work supported by PHS CA010953, awarded by NCI, DHHS.
SU‐E‐T‐134: Angular Dependence of the NanoDot Dosimeter
Authors: Kerns J , Kry S , Sahoo N , Followill D , Ibbott G
Published: November 2011

Purpose: Optically stimulated luminescence detectors (OSLDs) are quickly gaining popularity as passive dosimeters, with applications in medicine for linac output calibration verification, brachytherapy source verification, treatment plan quality assurance, and clinical dose measurements. With such wide applications, these dosimeters must be characterized for numerous factors affecting their response. The purpose of this study was to examine the angular dependence of the nanoDot OSL dosimeter, which is part of the InLight series from Landauer, Inc. Methods: Relative dosimeter response data were taken at several angles in 6 and 18 MV photon beams, as well as in clinical proton beams. These measurements were done within a phantom at a depth beyond the build‐up region. Measurements were conducted over several sessions to provide confidence in the data. To examine the reasons for the observed angular dependence Monte Carlo simulations were performed with MCNPX. Results: In photon beams, the nanoDot had an angular dependence of 4% at 6 MV and 3% at 18 MV respectively, at angles where the dosimeter was parallel to the beam. Monte Carlo simulations at 6 MV showed similar results to the experimental values. In proton beams, no angular dependence was found. Conclusions: A significant angular response of this OSLD was observed in photon beams. This factor must be accounted for when evaluating doses from photon beams impinging from non‐normal directions.