bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐282: Preliminary Simulation Study for 3 Dimensional Dose Delivery in Carbon Beam Active Scanning System of KHIMA
Authors: Kim C , Kim H , Yang T , Han G , Lee H , Jang H , Kim J , Park D , Hong S
Published: June 2012

Purpose: KHIMA (Korea Heavy Ion Medical Accelerator) project has a plan to develop and construct a research beam line for carbon beam active scanning system. The carbon beam line consists with scanning magnet, beam‐monitoring system, energy modulation system. In this study, the significant components, scanning magnets and ridge filter, were designed for the carbon beam active scanning beam line. Methods: The designed scanning magnet and ridge filter were used for 3 dimensional active beam dose delivery simulation by Geant4 Monte Carlo code. The target volume of the active scanning was 10 × 10 × 5 cm2 on the water phantom with 400 MeV/u of carbon beam. The transvers plane on the target was scanned by 3mm of step size. And, the optimized weighting factors of transverse scanning were obtained by MINUIT fitting package of ROOT. An aluminum ridge filter was designed to generate 5 cm of physical SOBP through step shape, which was optimized through in‐house iteration method and the MINUIT package.The simulation was performed with Geant4 through applying the transverse scanning with the obtained weighting factor and the designed ridge filter. Results:The uniformity on the transverse plan will be expected below 4% when it considered scattered beam. Also, the uniformity for longitudinal plane will be expected lower then 5%. Conclusions: This preliminary computational study was shown a possibility of using ridge filter for acceptable 3 dimensional uniformity on active beam delivery system in carbon beam therapy line. The optimization process to reach an acceptable uniformity on clinical use should be followed. In addition, it would be used for the design of treatment planning system software for KIHMA project.
SU‐E‐T‐286: Verification of Treatment Delivery Monitor Unit (MU) Calculation and Dose Estimation of Bilateral Total Body Irradiation (TBI)
Authors: Li S , Driewer J , Lin C
Published: June 2012

Purpose: TBI treatment delivery MU and patient dose estimation are calculated manually at our institution. This study was to verify the accuracyof MU calculation and dose estimation of bilateral TBI by application of tissue heterogeneity correction. Methods: Twelve TBI patients were simulated from neck to thigh in bilateral TBI position. CT images were imported into the treatment planning system (Philips, Pinnacle3). Treatment dose was prescribed to the midpoint at the level of the umbilicus. Treatment distance was 519 cm. Both 6MV and 23 MV opposite lateral beams delivered 200 cGy to the dose prescription point with a 40 ×40 cm2 field size and 45o collimator angle. A 1 cm thick spoiler was placed about 15 cm from patient skin. Adaptive convolution superposition with and without heterogeneity correction was used for calculation of MUs and doses at the midpoints of the shoulder, chest, abdomen, and pelvis. Results:Monitor units calculated with heterogeneity correction were 1.1% and 0.9% smaller on average than those without heterogeneity correction for 6MV and 23MV beams respectively. The maximum deviations of MU were 3.8% and 2.8% smaller. Average percentage differences of point doses with and without heterogeneity corrections were −0.2%, 17.0%, −0.3%, and −2.7% at the levels of shoulder, chest, abdomen, and pelvis for 6MV beam and 0.4%, 11.0%, 0.2%, and ‐1.7% for 23MV beam. Discrepancy of doses to the points at the shoulder level varied from −6.8% to 8.9% for 6MV beam and from −1.6% to 5.1% for 23MV beam. Conclusions: Bilateral TBI MU calculation errors caused by ignoring tissue inhomogeneity would be less than 4% and 3% for 6MV and 23 MV beam. Dose estimation is less accurate using 6MV beam and the inaccuracy could be more than 8% for shoulder midpoint and 4% for pelvis midpoint.
SU‐E‐T‐292: New Technique for Developing Proton Range Compensator Using Three‐Dimensional Printer
Authors: Ju S , Kim M , Hong C , Yim D , Kim J , Shin D , Lee S , Han Y , Shin J , Shin E , Ahn S , Choi D
Published: June 2012

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‐296: Optimization of the Energy Selection System with Varying Magnetic Field for Laser‐Accelerated Proton Beams
Authors: Kim D , Yoo S , Cho W , Kim M , Jung J , Lee S , Suh T
Published: June 2012

Purpose: Laser‐based accelerated proton beams are unsuitable for clinical use because of their broad energy spectra. For this reason, it is essential to employ an energy selection system (ESS). The purpose of this study is to determine optimum parameters of the ESS which uses a varying magnetic field to generate Bragg‐peak. Methods: We simulated an accelerated proton beams using radiation pressure acceleration mechanism with carbon‐proton mixture target. The density ratio (n = 6) between the protons and the carbon ions is one of optimization parameters in determining the accelerating mechanisms. The ESS was implemented by the Geant4 Monte Carlo toolkit. In order to optimize the hole size and position of the energy selection collimator, and magnetic field at ESS, these parameters were simulated for acquiring energy and dose distributions by changing each values. Results: The proton energy distributions had a poly‐energetic distribution after passing through the ESS. As the magnetic field was increased, the mean energy of the proton beams also was increased. Also as the hole size was increased, the energy bandwidth of proton passed through the ESS was increased. The hole size and position of the energy selection collimator were effectively optimized to 2 cm and 5 cm from the z‐axis, respectively. Conclusions: We simulated laser‐accelerated proton beams using ESS for generation of Bragg‐peak. Our results suggest that the ESS with magnetic field variation can effectively generate a Bragg‐peak suitable for use in proton radiation therapy. Our ESS can be applied to pencil beam scanning proton therapy.
SU‐E‐T‐297: Proton‐Therapy System for Treatment of Macular Degeneration and Ocular Malignancies
Authors: Slopsema R , Mamalui‐Hunter M , Yeung D , Li Z
Published: June 2012

Purpose: To commission a proton‐therapy system for the treatment of uveal melanoma and age‐related macular degeneration. Methods: Proton therapy system is the proto‐type of a commercial product developed by Ion Beam Applications. Proton beam is brought into the treatment room at 105 MeV through a fixed beam line. A single‐scattering system with absorber/scattering foils spreads the beam into a Gaussian profile. A library of 10 range‐modulator wheels and 16 range‐modulator blocks generate spread‐out Bragg peaks of various range and modulation width. Source‐to‐axis distance of the system is 169 cm. Two orthogonal digital x‐ray panels are used for alignment. EyePlan software is used both for both treatment planning and in‐room alignment. Results: Range can be varied continuously between 0.5 and 3.4 g/cm2. Range accuracy is measured to be better than 0.05 g/cm2. Modulation width can be varied in steps of =0.3 g/cm2 with an accuracy of 0.05 g/cm2 or 2%. Maximum aperture diameter is 2.5 cm and maximum dose rate >32 Gy/min. Strong dependence of output on range (7%/mm) and dose rate (0.2%/(Gy/min)) is found. Distal and lateral fall‐off (80%‐20%) are =0.23 and =0.18 g/cm2 and do not depend much on range or depth. When reducing the aperture diameter to 6 mm no significant change is observed in shape of depth‐dose curve or absolute dose (<2.5%). Measurements show a significant portion of the dose at shallow depth (=0.7 g/cm2) is delivered by protons scattering off of snout elements. Simple collimation could reduce this effect. Conclusion: The dosimetric and positioning properties of the IBA ocular proton system are adequate to treat ocular lesions with acceptable clinical margins. Suggested improvements include limiting the output‐dependence on range and reducing snout scatter.
SU‐E‐T‐299: Proton Pencil Beam Spot Scanning Phase Space in the IBA System and the Clinical Implications for Superficial Targets
Authors: Lin L , Ainsley C , Dolney D , Closset M , Dessy F , De Wilde O , Maughan R , McDonough J
Published: June 2012

Purpose: In the treatment of superficial lesions with proton Pencil Beam Scanning (PBS), spot size is dominated by the nozzle contribution. Accuracy of phase‐space modeling is therefore paramount. IBA's Dedicated (DN) and Universal Nozzles (UN) have different designs and, consequently, characteristics. Here we report the phase spaces of these two nozzles, without and with a range shifter (RS). Methods: In‐air spot fluence measurements were made for five proton energies: 225, 210, 180, 150 and 115 MeV and at five distances from isocenter pertinent to SAD‐type treatments: +33, +20, +10, 0 and −10 cm (‘+’ implies upstream), without and with a 7.5 cm water‐equivalently‐thick RS (sufficient to pull back the lowest energy Bragg peak to patient surface), fixed with its upstream side 41 cm from isocenter. Data collected on a fixed horizontal beam‐line with a DN and a gantry‐mounted UN were compared. The full‐width‐at‐half‐maximum (FWHM) of a Gaussian fit to each spot fluence profile was extracted along the two principal axes. Results: With no RS, the proton spots are ∼20–70% larger at isocenter in the UN than in the DN. Spots are less asymmetric, and eccentricity increases more slowly with energy, in the UN than in the DN. Over the 33 cm in‐air travel upstream of isocenter, the spot FWHM varies by less than ∼2 mm. However, spot asymmetry becomes more severe upstream (for 115 MeV spots, 30–40% compared to <20% at isocenter for DN, but similar and <10% for UN). With an RS, spot FWHM at isocenter increases by 12.7 mm from 8.3 mm (DN) and 10.7 mm from 13 mm (UN) for 150 MeV protons (typical for brain treatments). With no RS, relatively distance‐independent spot size facilitates SAD‐type treatments. For patients with superficial lesions, where an RS is required and the phase space varies rapidly with distance, the RS should be permitted at two additional locations. US Army Medical Research and Materiel Command under Contact Agreement No. DAMD17‐W81XWH‐04‐2‐0022
SU‐E‐T‐302: A Simulation Study with Geant4 Investigating the Secondary Prompt Gamma Emissions from Incident 40 MeV Protons Onto Various Materials
Authors: Lau A , Chen Y , Ahmad S
Published: June 2012

Purpose: This study aims to investigate the prompt secondary gamma spectrum and thedepth‐dose distributions of incident 40 MeV protons onto various phantom materials.The goal is to find a relationship between the secondary prompt gamma emissions andthe range of the incident particles. Methods: An application was constructed using the Geant4 Monte CarloToolkit utilizing various physics packages. Several phantom materials were irradiatedwith a pencil beam of 40 MeV protons. These materials include PMMA (C5H8O2,density 1.18 g/cm3) and the built‐in Geant4 materials bone, soft‐tissue, and water. Foreach simulation, the energy deposited from the incident proton was recorded every 1 mmincrement of depth in the phantom. The resulting prompt secondary gamma emissionswere recorded from 0 to 10 MeV in energy bins of 10 keV. Results: The secondary prompt gamma spectrum has various peaks. The peaks locatedabout 4.4 and 6 MeV correspond to the carbon and oxygen de‐excitation photons,respectively. Our simulations show greater production of the higher‐energy gammaparticles closer to the Bragg‐Peak. When we plot the oxygen peak against the normalizedBragg‐Peak we found that in all materials the difference between Bragg‐Peak and theoxygen de‐excitation photon peak to be about 2 mm. The oxygen peak could be used inthe clinic for range verification of the incident proton beam. Conclusions: Our Geant4 Monte Carlo application was used to investigate the secondaryprompt gamma emissions from incident 40 MeV protons. A relationship was betweenthe 6 MeV peak and the incident proton Bragg Peak. We believe that prominent peaksaround 4 and 6 MeV can be used to locate the range of the incident beam provided adetector system is built that can count these high‐energy gamma particles.
SU‐E‐T‐309: Dosimetric Study and Clinical Implementation of an HDR Applicator of SAVI for Partial Breast Irradiation
Authors: Dou K , Lerma F , Jacobs M , Ottinger M , Seidel M , Herchko M , Reynolds S
Published: June 2012

Purpose: To present clinical implementation and quality assurance for a new HDR applicator of Strut‐Adjusted Volume Implant (SAVI) for partial breast irradiation and the higher‐order DVH examined. Methods: The SAVI applicator with multi‐peripheral struts can be differentially loaded with the HDR source for a conformal dose distribution to the lumpectomy cavity. The treatment plan is evaluated by a dose volume histogram (DVH) as follows: V90 > 90%, V150 < 50 cc, and V200 < 20 cc. A higher‐order DVH which may reflect radiation‐induced toxicity, such as V300, was studied. The SAVI device status was verified by the 3D CT images and image fusion. Tissue invagination was investigated using an ion chamber and film with the cavity filled with air and water merged into a water phantom. Results: Twenty‐nine patients to date at Mercy Medical Center, Baltimore, Maryland were treated with SAVI device. The dosimetric data demonstrated the achievements of greater than 90% coverage for V90 at 96.8% and 94.1% for V95 while keeping a low V150 at 33.9 cc and V200 at 16.5 cc. V300 was found to be 2.7 cc in average. Potential uncertainties introduced by the SAVI applicator motion were a 3% variation in dose caused either by a 3‐mm} translation or a rotation of 3 degree. Conclusions: Multiple catheters of the SAVI applicator allows for optimal and conformal dose distribution around a lumpectomy cavity while minimizing the dose to adjacent normal structures such as skin and ribcage. Multiple imaging techniques are capable to verify cavity variation, strut collapse or relative motion, and device shift. A nearly fully loaded dwell source position produced the discrepancy of less than 3% and allow for optimal and conformal dose distribution to a lumpectomy cavity. Advantages of the SAVI applicator have been shown in treating breast cancer with the shallower, elliptical, and asymmetric cavity.
SU‐E‐T‐312: Optically Stimulated Luminescent Dosimeter Performance in High Dose Rate Brachytherapy
Authors: Tien C , Hiatt J , Curran B , Sternick E
Published: June 2012

Purpose: To investigate the use of optically stimulated luminescent dosimeters (OSLDs) for high dose rate (HDR) Ir‐192 brachytherapy. While common in megavoltage radiotherapy applications, the performance of OSLDs using kilovoltage energies, high dose gradient and high dose rate regions ubiquitous to HDR has not been demonstrated. Methods: Commercially available nanoDotTM (Landauer, Glenwood, IL) OSLDs ‐ 5mm diameter and 0.2mm thickness ‐ were irradiated using an Ir‐192 source in various geometries to determine dose rate dependence. Angular geometries were created using a circular applicator designed for accelerated partial breast irradiation by Accuboost®. Results: Response remained linear for high doses and was independent of dose rate. Specifically, the OSLDs were shown to be linear with dose up to 200 cGy then became slightly supra‐linear up to 600 cGy. There was a slight angular dependence for OSLDs which becomes significant in ‘edge‐on’ scenarios. An asymmetry in this angular dependence was discovered, but was attributed to cable curvature, point source approximation, and positioning within its plastic casing. Conclusions: Clinical HDR doses of 300 cGy fall within the linear, dose‐rate‐independent region. Angular independence can be maintained by avoiding extreme ‘edge‐on’ measurement geometries. Because of re‐ readability, OSLDs can serve as a permanent record or alternatively be annealed within a few hours using conventional fluorescent light. Lastly, OSLDs are produced for only $5 each. Due to these features, in conjunction with the dosimetric performance, OSLDs should be considered a reliable tool for in vivo HDR brachytherapy measurements.
SU‐E‐T‐313: Probe‐Type Experimental Dosimetry in Terms of Absorbed Dose to Water in Photon‐Brachytherapy a Proposal for a Radiation‐Quality Index
Authors: Quast U , Kaulich TW , Zakaria GA , Ahnesjö A , Alvarez‐Romero JT , Medich D , Mourtada F , Pradhan A , Rivard M
Published: June 2012

Purpose: In photon‐brachytherapy (BT), all data for clinical dosimetry (e.g., the dose‐rate constant) are not measured in water, but calculated, based on MC‐simulation. To enable the measurement of absorbed dose to water, DW, in the vicinity of a source, the complex energy‐dependence and other influence quantities must be considered. Methods: The detectors response, R=M/D, is understood as product of a detector‐material dependent ‘absorbed dose response’, Ren, and Rin, the ‘intrinsic response’. Ren is described by the Burlin‐theory and because of dissimilarities between the detector‐material and water, will have energy dependent correction factors which convert Ren into the clinically relevant DW,Qo=MQo × ND,W,Qo. To characterize BT‐ source‐types, we propose a new ‘radiation‐quality index’ QBT=Dprim(2cm)/Dprim(1cm), the ratio of the primary‐dose to water at r=2cm to that at the reference distance r=1cm, similar to external beam dosimetry. Although QBT cannot be measured directly, it can be derived from primary and scatter separated dose‐data, published as consensus data e.g., in the Carlton AAPM‐TG‐43‐database. Results: Mean QBT‐values are: for nine HDR and four PDR 192Ir‐sources: 0.2258±0.5%; one 169Yb‐ source: 0.2142; and one 125I‐source: 0.1544. Conclusions: The main benefit of this new QBT‐concept is that a type of BT‐dosimetry‐detector needs to be calibrated only for one reference radiation‐quality, e.g., for Q0=192Ir. To measure the dose for different source‐types, DW can be determined using calculated radiation‐quality conversion factors kQ,QoBT, to be included in the AAPM‐database and to be provided by the manufacturer for each detector‐type. Typical BT‐dosimetry‐detectors are plastic scintillation detectors, radiochromic film, thermoluminescence detectors, optically stimulated detectors, and small volume ionization chambers. Recently, different DW(1cm)‐primary standards have been developed in several European NMIs, enabling to calibrate BT‐radiation‐ sources and BT‐dosimetry‐detectors and allowing to verify MC‐calculated dose‐rate constant values. The proposed definition of QBT has to be discussed internationally to find broad consensus.
SU‐E‐T‐314: Evaluation of Dosimetric Impact of Catheter‐Position Uncertainty in Balloon High Dose Rate Brachytherapy of Breast Cancer
Authors: Kim Y , Trombetta M
Published: June 2012

Purpose: To evaluate the dosimetric impact of catheter‐position uncertainty prior to each fraction in balloon high dose rate (HDR) brachytherapy for breast cancer. Methods: For 30 balloon HDR patients, each dwell position of the catheters was manually shifted distally (+) and proximally (−) with a magnitude of ±1 mm, ±2 mm, ±3 mm and ±4 mm. A total of 240 plans were retrospectively produced and compared to clinical treatment plans to simulate catheter‐position uncertainty. The following dosimetric data were evaluated: PTV_EVAL V90[%] after subtracting air/seroma volume, skin and rib maximal dose (Dmax[%]) and normal breast tissue V200[cc]. Results: PTV_EVAL V90 was decreased in 93% of cases while increased with maximum value of < 0.7% in 7% of cases. Average/maximal reduction was increased from 0.3%/1.2% (±1 mm), 1.0%/3.5% (±2 mm) and 2.6%/6.2% (±3 mm) to 5.0%/9.2% (± 4 mm) as catheter‐position error was increased. Change of skin and rib Dmax values was case‐specific. They were increased in 52% of cases while decreased in 48% of cases. As catheter‐position error was increased, the average/maximal deviation was increased from 1.6%/9.3% (±1 mm), 3.1%/19.1% (±2 mm) and 4.6%/29.1% (±3 mm) to 6.3%/40.2% (± 4 mm). Normal breast tissue V200 was increased in 90% of cases while decreased with maximum value of < 0.4cc in 10% of cases. Average/maximal increase was elevated from 0.3cc/1.2cc (±1 mm), 0.8cc/2.9cc (±2 mm) and 1.8cc/4.8cc (±3 mm) to 2.9cc/6.7cc (± 4 mm) as catheter‐position error was increased. Conclusions: The catheterposition tolerance of ±2 mm set by the AAPM TG 56 is clinically acceptable for most clinical cases. However, in a case where the dosimetric data of treatment plan are close to the dosimetry limits of the clinical protocol, smaller tolerances such as ±1 mm or zero tolerance is clinically recommended to minimize delivered dose discrepancy from the planned dose.
SU‐E‐T‐315: Planning and Verification of CT‐Based HDR Intraluminal Brachytherapy Treatment for Malignant Obstructive Jaundice
Authors: Svoboda A , Lo Y , Sheu R , Dumane V , Rosenzweig K
Published: June 2012

Purpose: To present our experience using CT to plan and verify intraluminal HDR treatment for a patient with obstructive jaundice. Due to the obstruction's proximity to the small bowel, along with small bowel adhesions from past surgical history, it was imperative to verify source position relative to the bowel before each treatment. Methods: Treatment was administered to a total dose of 2000cGy in 5 fractions via a 6F intraluminal catheter inserted into the patient's 14F percutaneous drainage catheter. Graduations on the intraluminal catheter were used to measure the exact length of catheter inserted in to the patient's drainage tube allowing reproducibility. Dummy seeds inserted during CT were identified by iteratively aligning the planning system's 3D reconstruction axis to the catheter at multiple points as it snaked through the liver. Taking in to account the known offset between actual dwell positions and dummy source positions, we determined what dwell positions to activate for planning. CT verification was performed prior to each treatment to insure that the drainage catheter had not moved and that the distance from treatment site to small bowel was adequate. Dummy seeds and anatomical landmarks were identified on the scout image and correlated to the CT. Results: Verification CTs showed remarkable consistency in the day‐to‐day drainage catheter position. The physician was able to easily identify the small bowel of concern on the CT and determine if a safe distance existed for treatment. Conclusions: The method outlined in this work provides a safe means by which to treat bile duct obstructions using HDR when critical structures are nearby. We were prepared to make real‐time adjustments to our treatment plan to account for significant variation, but found it unnecessary to do so in this particular case.
SU‐E‐T‐324: Evaluation of Prostate Volume and Shape Change after Permanent Prostate Brachytherapy Using Implanted Seed Displacement Analysis
Authors: Le Y , He Q , Lee J , Song D
Published: June 2012

Purpose: To investigate a novel method of characterizing prostate volume and shape changes after permanent prostate brachytherapy (PPB) by using the implanted seeds as a surrogate. Methods: In twenty‐one patients undergoing PPB, multiple 2D C‐arm based fluoroscopy (CF) were taken intraoperatively immediately after seed implantation (day 0) and CT scan was performed the next day (day 1). The 3D coordinates of seed locations for each patient were reconstructed from both CF and CT, respectively. The volume of seed cloud was calculated as the volume of its convex hull. The CT and CF seed clouds were registered using iterative closest point (ICP) algorithm. The boundary seed shifts in each dimension between CF and CT seeds were calculated and student's t‐test was used to test if the seeds shifts were significantly different from zero. Results: Twelve patients show average of 7%±5% volume increase between day one CT seeds and day 0 CF seeds and nine patients show 9%±5% volume decrease. A positive correlation is found between seed‐calculated volume and intraoperative preplanning ultrasound volume. For patients with volume increase, there is significant expansion in both z dimension (SI) with p<0.001. For patients with volume decrease, there is shrinkage in both x dimension (LR) with p<0.05. An average 23±8 degree pitch angle around x (LR) axis was observed between two seed clouds, corresponding to the change of patient position from lithotomy position during the implant to supine position during CT. Conclusions: A method to use implanted seeds to determine prostate volume changes is demonstrated. The prostate volume can increase or decrease between end of implantation and day one CT, indicating edema either reaches its maximum intraoperatively, or still continues development after implantation. The ability to characterize immediate postoperative prostate volume and shape changes allows for correlation of intraoperative dynamic dosimetry to post‐implant CT dosimetry.
SU‐E‐T‐342: Evaluation of Volumetric Change and Dosimetric Discrepancy with Daily Cone‐Beam CT for Patients with Head‐And‐Neck Cancer
Authors: Liu H , Greskovich J , Koyfman S , Xia P
Published: June 2012

Purpose: To evaluate volumetric changes in the target and critical organs during IMRT treatment for patients with head‐and‐neck cancer, and investigate discrepancy between the planned doses and doses of the day using daily CBCTs. Methods: Four head‐and‐neck patients with 150 daily kilo‐voltage CBCTs were selected for this study. For each patient, CBCTs were rigidly registered with the planning CT based on the bony structures. Contours of the target and critical organs were then deformed from the planning CT to each CBCT using a commercial deformable registration algorithm. After rigid imaging registration, the planning dose matrix was mapped to the corresponding CBCT images. The doses of the day to the deformed structures were compared with the planned doses. Results: Significant volume shrinkage in PTV was observed with a mean volume of 27.8 ± 8.1cc (range: 20.7cc – 38.4cc). The volume variations were 2.6 ± 2.4cc (range: 0.2cc – 5.9cc) for the right parotid, and 4.0 ± 4.8cc (range: 0.4cc – 11.0cc) for the left parotid. The differences in D95 between the dose of the day and planned dose were 0.4 ± 1.2% for the GTV and 1.8 ± 2.4% for the PTV. The difference in the mean dose for right parotid and left parotid were from −9.3% to 24.3% (mean 8.4%) and from −11.4% to 26.1% (mean 8.7%), respectively. The average mean dose variations were 1.9 ± 1.2% for the spinal cord, 2.3 ± 3.3% for the mandible, and 2.6 ± 3.7% for the larynx. Conclusions: No significant changes in daily dose coverage of the tumor were observed despite of tumor shrinkage and anatomic changes. The daily mean dose changes in the parotid glands were greater than other sensitive structures. With deformable contours from the planning CT, daily CBCT along with rigid dose transformation can provide quantitative dose guidance for re‐planning.
SU‐E‐T‐353: Dosimetric Verification of Rectal Wall Sparing Effect in Intensity‐Modulated Radiation Therapy for Prostate Cancer Patients with and Without the Use of a Rectal Balloon
Authors: Lee S , Lee J , Park H , Park J , Suh T
Published: June 2012

Purpose: To evaluate dosimetric effect of a rectal balloon and calculation accuracy due to dose perturbation by air cavities in the rectum, rectal wall doses with and without a rectal balloon were verified using rolled‐up and ‐ out techniques of radiochromic films in prostate cancer cases. Methods: The prescribed dose of 74 Gy in 37 fractions was delivered to the 6 patients with similar sized‐intact prostates using the same plan parameters and constraints in intensity‐modulated radiation therapy. The rectum was contoured from the anus to the rectosigmoid flexure for all divided patient groups according to the rectal filling status. Calculated rectal wall doses were evaluated by the analytical anisotropic algorithm (AAA) and the pencil beam convolution (PBC) algorithm. The acrylic inserts dedicated to measure rectal wall doses were developed for simulating the 70 cc air‐filled and the empty rectum. Rolled‐up Gafchromic EBT2 films are closely placed in the interspaces film layer thick between 2 hollow cylinders and in the innermost inside of the rectal wall 4 mm thick and 4.5 mm in diameter. Results: The AAA algorithm more accurately yielded perturbed doses near the air‐tissue interfaces by describing anterior rectal wall sparing and higher doses at the posterior rectal wall than estimated values in PBC. Delivered doses on rolled‐up films showed more than 93% gamma pass rate. Although the air‐filled rectum achieved rectal wall sparing at the doses very close to the prescribed one, the rectal wall volumes received 70% or adjacent to the prescribed dose were increased. Conclusion:
Delivered rectal wall doses to the rolled‐up films suggested that the AAA algorithm reflected more accurate dosimetric effect by the air cavity in the rectum. The rectal balloon can be useful to spare the small fraction of rectal volume where high doses reaching up to the prescribed level were delivered.
SU‐E‐T‐354: Comparative Evaluation of EBT2 Film, Matrixx and PTW729 for Patient Specific, Small‐Field, High Dose IMRT Plans
Authors: Kim S , Stathakis S , Esquivel C , Papanikolaou N , Gutierrez A
Published: June 2012

Purpose: To compare the use of Gafchromic EBT2 film and 2D array ionchamber detectors (IBA Matrixx and PTW729) as a QA tool for patient specific QA of small‐field, high dose IMRT plans. Method and Materials: EBT2 film is designed to detect high dose gradients with excellent spatial resolution power‘”100um. The film has wide dose coverage of 1cGy ‐ 1000 cGy in red color channel and therefore can serve for high dose applications. In the study, the film was calibrated by a 6MV photon beam in a water‐equivalent phantom. Measuring the performance of the EBT2 film and 2D array ionchamber detectors was proceeded simultaneously by inserting a film between the top build up and top of the ionchamber array. In all, eight previous patient cases, planned on BrainLab iPlan Version 4.1.1 and delivered by Varian TX Novalis, were re‐delivered. Differences were evaluated using dose profile and Gamma Index comparisons. Results: For EBT2 vs. planar dose, X and Y profiles of the film were similar to the planar dose. Dose profiles from the film showed better agreement than Matrixx and PTW729 due to improved spatial resolution in high dose region. The high gradient dose region is also very well matched. For Matrixx and PTW729 vs. calculated dose, the Matrixx and PTW729 dose profile were unable to resolve the smaller peaks within the target region. The overall Gamma evaluation results showed that the stricter the analysis criteria were, the lower the percentage pass rate occurs on Matrixx and PTW729. Conclusions: Results show that EBT2 film is able to better characterize the calculated dose distribution for small fields due to its better spatial resolution as compared to Matrixx and PTW729. Additionally, Matrixx and PTW729 appear to show lower Gamma Index values as the evaluation criteria is restricted.
SU‐E‐T‐356: Dose Response of a 2D Diode Array for Non‐Primary Photon Radiation from a Dynamic MLC
Authors: Chu A , Feng W , Chen Z , Nath R
Published: June 2012

Purpose: To quantify the dose responses of a 2D‐diode array for ‘non‐primary’ radiations (scatter and transmission from MLC and gantry‐head) under dynamic MLC dose deliveries. The ‘non‐primary doses' have been overlooked by the 2D‐diode dose‐calibration because the primary radiation dominates over a large calibration field (10×10cm2). If non‐primary dose responses of diode are significant, it would cause systematic errors when non‐primary radiations become important (in small field). Methods: The dose response is the diode‐dose normalized by chamber‐dose. Three setups under a 6MeV photon beam (Trilogy) were measured by detector (diode and chamber) at central‐axis (CAX): (1) the CAX diode was accurately located at places: either within MLC‐leaf collimation (2.5 mm) or between leaves. This measurement field is entirely blocked by MLC. (2) Dynamic MLC exposures are tested by 6 different MLC‐gaps (1, 5, 10, 20, 50 and 100 mm) sweeping over the CAX detector. (3) To estimate the scatter dose but without MLC involved, the CAX detector is blocked from primary beam by jaws only but received scatter doses from narrow‐slit apertures with distances from CAX. Results: (1) Results showed the diodes tends to underestimate dose of lower energy radiation, e.g. scatters. Experiment (3) confirmed this by showing its decreased dose response by scatter source away from CAX; i.e. more lower‐energy scatters in larger lateral scattered angles. As the slit is narrowed, less scatters and higher diode response were observed. (2) 3% difference in diode response to MLC‐leakage vs. non‐leakage was detected. However the impact of MLC leakage is not substantial in dynamic MLC delivery unless MLC‐gap is narrow enough (e.g. 1 mm). (3) Overall non‐primary radiations still significantly present as gap<10mm by 3% criterion. Conclusions: The diode dose responses to non‐primary radiations can cause more than 3% systematic errors for small‐aperture dynamic MLC QA unless appropriate corrections are made.
SU‐E‐T‐360: The Effect of Delivery Parameter Errors to the Patient Quality Assurance Result for RapidArc Treatment in Head‐And‐Neck Patients
Authors: Peng J , Hu W , Zhang Z
Published: June 2012

Purpose: To investigate how the delivery parameter errors (DPEs) act on the patient quality assurance (QA) results in RapidArc treatment for head and neck cancer. Methods: Three DPEs (MLC gap, gantry angle and dose MU error) were scrutinized and quantified by comparing delivery parameters between the planed and actual delivered. The actual delivered parameters were recorded in dynalog‐files by computer controller during delivery. Sixteen clinically approved head‐and‐neck RapidArc plans were checked. Sixty‐four error induced plans were reconstructed by applying four types of errors (three DPEs separately and one integrally) to the original 16 plans. The gamma passing rate (GPR) and dose endpoint variations caused by these DPEs was analyzed. Results: For all patients, the mean error of MLC gap, gantry angle and Dose MU were 0.19±0.06 mm, −0.36±0.03 degree, and 0.5E‐4±1.8E‐4 MU, respectively. The GPR results were most vulnerable to MLC gap error among three DPEs (ANOVA test, p<0.001). A strong negative correlation (r=−0.538, 2‐tailed p<0.05, Pearson correlation analysis) existed between GPR and absolute mean MLC gap error for RapidArc treatment plans in head‐and‐neck patients. Compared to original plans, the DPEs induced plans showed mean dose variations of 0.6–1.01% on the target of PGTV, PTV and some normal tissues (including spinal cord, brain stem, parotid and larynx). The MLC gap error played the prominent role on affecting the dose differences (ANOVA test, p<0.001) among the three DPEs. Conclusions: The MLC gap error, Dose MU error and gantry angle error can affect the GPR and differ the actual dose distribution from the planned one. The MLC gap error is the most prominent factor that affects the GPR and clinical dose distribution for head and neck cancer patients. A mean MLC gap error of 0.19mm will increase dose by 1–3% for head and neck cancer patients treated with Rapidarc.
SU‐E‐T‐364: Verification of MLC Motion Error during IMRT/VMAT Delivery by Using an In‐House Program
Authors: Ehara I , Hayashi N , Adachi Y , Yada R , Matsunaga T , Kato H
Published: June 2012

Purpose: In intensity modulated radiation therapy (IMRT) and/or volumetric modulated arc therapy (VMAT), it is important to ensure the accuracy of multi‐leaf collimator (MLC) motion during delivery. However, the commercially available software can evaluate only summary of MLC motion during delivery as the error's root‐mean‐square (RMS). The purposeof this study is to construct the suitable procedure to evaluate MLC‐motion continuously with an in‐house program. Method: This study was composed into two sections. First, we created the in‐house program to import MLC‐log file during delivery. The in‐house program was built by using visual basic language. The in‐house program includes some additional: 1) visualization of MLC motion during delivery with an animation, 2) classification whether the MLC‐motion error was over the tolerance or not, and 3) visualization of the location of MLC‐motion error during delivery. Second, we evaluated the MLC‐log during VMAT delivery by using our in‐house program. The VMAT plan was created by Eclipse ver.8.9 (Varian). The Clinac 21EX linear accelerator (Varian) equipped with Millenium multi‐leaf collimator was used for this study. Results: We confirmed the functions of our in‐house program as follows. The in‐house software was available to import the Varian's formatted MLC‐log file. The animation of MLC motion during delivery was expressed in 2 fr/sec. The tolerance value of MLC motion error could be defined optimally. If the MLC motion error happened, the location became colored from default color to red color. For prostate VMAT, the MLC motion error in all cases passed the tolerance value. We defined the tolerance value based on AAPM TG‐119 and 142. Conclusion:We conclude that our in‐house program should be useful to evaluate the accuracy of MLC motion during IMRT and/or VMAT delivery because the users can analyze the MLC motion error simply.
SU‐E‐T‐393: Using TG119 to Assess RapidArc at Hamad Medical Corporation
Authors: Nobah A , El‐Kaissi T , Hammoud R , Al‐Hammadi N
Published: June 2012

Purpose: To provide a confidence level within our clinic relating to the implementation and administration of RapidArc, the AAPM TG1 19 has been implemented. This task group provides a sound and relatively simple methodology for determining the accuracy of the overall IMRT process administered in the day‐to‐day clinicMethods: Six different test plans, of varying complexity, were created on mock structure sets, downloaded from AAPM, and delivered. The treatment planning system results were then compared with the delivered results. Plans were created and delivered on a solid water phantom, using 25×25cm water equivalent slabs of varying thicknesses. Delivered point and planar dose measurements were obtained using an ionization chamber and film, respectively. Results: The confidence limit (CL), averaged for all test plans, was calculated for the high dose point in the PTV and for the low dose point in the avoidance structure. This was used as an indicator of the uncertainty of the average difference between measured and planned dose. Where the precision of the delivery is based on how small the CL value is.For both the high and low dose points, the local CL's were determined to be 0.036 and 0.011, respectively. The range of results for the CL presented in TG1 19 varies from 0.015 to 0.098 for the high dose point, and from 0.014 to 0.086 for the low dose point. Conclusions: Our results indicate the accurate implementation of RapidArc within our clinic, especially when compared to the results of other institutions, published in TG1 19. Furthermore, the CL value for the low dose measurements is lower than any of the results published in TG119. We recommend that any clinic conducting IMRT should implement this task group. This will not only provide a greater understanding of the delivery and its limitations, but will also give the overall accuracy and consistency of the technique as it applies to the various treatment sites.
SU‐E‐T‐394: Comparison of Planned Dose Distribution Vs. Delivered Dose Distribution for Both IMRT and Proton Therapy Using Weekly Repeat 4DCT Data Sets
Authors: Chen Y , Zhang L , Court L , Liao Z , Zhu X , Mohan R , Dong L
Published: June 2012

Purpose: To evaluate treatment deviations and the impact of treatment modality in the presence of breathing motion and anatomical changes during the course of lung cancer radiotherapy. Methods: Two non‐small cell lung cancer patients were enrolled in a randomized clinical trial to compare IMRT and proton therapy. To rigorously evaluate the impact of motion and anatomical changes, we used a ‘5D' dose accumulation approach to sum dose distributions from phase‐to‐phase and week‐to‐week to the reference (end‐expiration) phase of the original planning 4DCT data set. Six to eight weekly 4DCT data sets that consisted of 10 breathing phases were acquired during the treatment course. The original plan was re‐calculated for each phase and deformably mapped to the reference phase to compare the ‘delivered’ dose distribution with the planned dose distribution of both the IMRT plan and the proton plan for each patient. DVHs derived from delivered dose distribution were compared to that from the planned dose distribution. Results: The delivered dose showed 3% and 2% increase in the dose to the CTV for IMRT and proton plan respectively. Target coverage remained acceptable despite tumor shrinkage from 29% to 49%. The doses to normal structures, such as lung and heart, increased more in the proton plan than in the IMRT plan. The V20 of the total lung volume increased by 4% and 6% from the delivered dose compared to the planned dose for IMRT and proton plan, respectively. Conclusions: The results showed sufficient target coverage was maintained for both modalities. Increases in lung dose were observed in both modalities, but more in the proton arm, perhaps due to weight loss and tumor shrinkage. Adaptive proton therapy strategy is recommended to minimize normal tissue doses. Supported in part by NCI P01 CA021239‐29A1
SU‐E‐T‐395: Achievability and Optimization of Synchrotron‐Based Respiratory Gated Spot Scanning Proton Beam Delivery
Authors: Tsunashima Y , Sahoo N , Sakae T , Poenisch F , Umezawa M , Briere T , Zhu X , Mohan R , Dong L
Published: June 2012

Purpose: The purpose was to investigate the interplay of residual motion in realistically delivered respiratory gated spot scanning proton beam by a synchrotron. Methods: A MatriXX 2D ion‐chamber array detector was placed on a moving platform. The platform with the 2D ion‐chamber array detector was moved based on sin4 motion with 3s and 5s cycle and 20 mm amplitude. Its motion was monitored by a laser displacement sensor (ZS‐LDS2VT, omron, Japan). The respiration gate threshold level was set at 30% duty cycle and the residual motion within the gate window was approximately 6 mm. A 10×10 cm2 uniform field was delivered by a matrix of 13×13 spots with ∼ 8 mm spot size (s) and 8 mm spot spacing. Measurements were done for the field delivered with a single painting and multiple re‐painting, from 2 to 12 times, for both orthogonal and parallel scan directions. The same field was also measured without moving the detector, defined as the static reference dose. Dose homogeneity was compared between with gated and the static dose distributions. Results: The worst single painting result of the dose homogeneity ratio was 0.90 in 3s motion cycle and 0.93 in 5s motion cycle with the orthogonal scan pattern, and 0.97 in 3s and 0.98 in 5s motion with the parallel scan pattern, respectively . The homogeneity ratio improved to over 0.98 by 4∼6 times repainting in orthogonal and only 2 times re‐painting with the parallel scan. Conclusions: The respiratory gated spot scanning proton beam delivery is sensitive to spot movement direction relative to the residual motion of the target. A proper selection of the number of repainting and the scan direction can improve beam delivery quality. The study offers a basic understanding when implementing respiratory gated spot scanning proton beam treatment.
SU‐E‐T‐398: Verification of Gamma Knife EXtend System Based Fractionated Treatment Planning Using EBT2 Film
Authors: Gopishankar N , Bisht R K
Published: June 2012

Purpose: To present EBT2 film verification of treatment planning with the eXtend System, a relocatable frame system for multiple‐fraction or serial multiple‐session radiosurgery. Methods: A human head shaped phantom simulated the verification process for fractionated Gamma Knife (GK) treatment. Phantom preparation for eXtend Frame based treatment planning involved creating a dental impression, fitting the phantom to the frame system, acquiring a stereotactic computed tomography (CT) scan. A CT scan (Siemens, Emotion6) of the phantom was obtained with following parameters: Tube Voltage ‐ 110 kV, Tube Current ‐ 280 mA, pixel size ‐ 0.5 mm × 0.5 mm and 1 mm slice thickness. A treatment plan with two 8 mm collimator shots and three sector blocking in each shot was made. Dose prescription of 4.0 Gy at 100% was delivered for the first fraction out of the two fractions planned. Gafchromic EBT2 film (ISP Wayne, NJ) was used as 2D verification dosimeter in this process. Films were cut and placed inside the film insert of the phantom for treatment dose delivery. Meanwhile a set of films from the same batch were exposed from 0 Gy to 12 Gy doses for calibration purpose. EPSON (Expression 10000XL) scanner was used for scanning the exposed films in transparency mode. Scanned films were analyzed with in‐house made Matlab codes. Results: Gamma index analysis of film measurement in comparison with TPS calculated dose resulted in high pass rates >90% for different tolerance criteria of 2%/2mm, 1%/1mm, and 0.5%/0.5mm. The isodose overlay and linear dose profiles of film measured and computed dose distribution on sagittal and coronal plane was in close agreement. Conclusions: Through this study we propose a treatment verification QA method for eXtend frame based fractionated Gamma Knife radiosurgery using EBT2 film. Acknowledgement: Authors acknowledge the help of Andre Micke, ISP for sharing his expertise on EBT2 film.