bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐377: Dose Calculation Accuracy of Various Commercially Available Algorithms for Treatment of Targets in Heterogeneous Media
Authors: Saini J , Mathews B , Grant E
Published: June 2012

Purpose: Lack of lateral electron equilibrium is a concern when treating lung lesions through IMRT. A comparison is made for the accuracy of dose calculation algorithms for IMRT and 3D conformal arc (CA) plans calculated by three algorithms; Iplan Monte Carlo (MC), Iplan Pencil Beam (PB), and Pinnacle Superposition‐Convolution (SC). Methods: An in‐house heterogeneous phantom was constructed to mimic the electron disequilibrium conditions that arise for lung tumors. The phantom has a cylindrical piece of polystyrene, used as a tumor surrogate, placed in balsa wood, whose density and CT# resemble that of lung tissue. A number of real patient cases with lesions of varying sizes were selected for this study. For each lesion, an IMRT and a CA plans were generated. These plans were then calculated with MC, PB, SC algorithms and mapped onto phantom for ion chamber and film measurement in three orthogonal plains. Results: Preliminary results for three lesions are given. The ion chamber/ plan measurements are, (i) Tumor1 (10cc): IMRT (MC 0.99, PB 0.94, SC 1.00) CA (MC 0.98, PB 0.90, SC 1.03); (ii) Tumor2 (20cc): IMRT (MC 1.01, PB 0.92, SC 0.97) CA (MC 0.98, PB 0.89, SC 0.97); (iii) Tumor3 (80cc): IMRT (MC 0.98, PB 0.93, SC 1.01) CA (MC 0.99, PB 0.91, SC 0.98). The percentage of points passing the 3%/3mm gamma index criteria are; (i) Tumor1: IMRT (MC 99.9%, PB 96.9%, SC 99.5%) CA (MC 97.7%, PB 97.2%); (ii) Tumor2: IMRT (MC 92.1%, PB 85.7%, SC 91.5%) CA (MC 97.7%, PB 89.5%); (iii) Tumor3: (MC 92.3%, PB 85.7%, SC 92.5%) CA (MC 97.8%, PB 91.6%). Conclusions: MC and SC algorithms accurately predict the dose while PB algorithm can under dose the target by up to 10%. IMRT is a viable option for lung tumors if dose is calculated by MC or SC algorithms. Project support provided by CARTI.
SU‐E‐T‐379: Assessment of the Dosimetric Significance of Isocenter Shift by Means of EPIDQA
Authors: Papanikolaou N , Quino L Vazquez , Stathakis S , Gutierrez A , Esquivel C , Alkhatib H
Published: June 2012

Purpose: An EPID based tool for IMRT quality assurance was used to investigate the dosimestric significance of an isocenter shift. Methods: The MU‐EPID software was used to calculate the dose of the measured QA and compare this against the TPS dose calculation in the original CT patient anatomy. Once the dose has been calculated, the isocenter is shifted and a new dose calculation was obtained and compared against the original dose calculation of the plan. Isocenter shifts ranged from 1mm to 5mm were introduced in order to compute the dose based on the EPID based QA images. Once the dose with the isocenter shift was calculated, a dose comparison against the un‐shifted plan was performed. In addition, a gamma index analysis was performed between the two plans. Results: Preliminary results comparing the percent dose difference of the shifted plan to the original plan show that lateral shift of the isocenter has the maximum impact in the absolute point dose at the isocenter with a maximum percent difference of 4.58%. Anterior‐posterior shifts exhibit minimum variation in the dose calculation of the dose at isocenter with an average of 1.69 % dose differences at the isocenter. For the gamma analysis, the lateral shift had the minimum impact while anterior‐posterior isocenter shift had the greatest impact with a gamma of 89.9% passing with a 3% dose and 3mm distance to agreement criteria. Deviation of the original QA results is detectable down to a shift that is as small as 1mm based on our results. Conclusions: The present investigation shows the importance of the patient positioning during treatment delivery since very small deviation of the isocenter can have a great impact in the dosimetry of the IMRT plan.
SU‐E‐T‐385: Accelerated Beam Delivery with MLC Gaps in IMRT Fields
Authors: Yang Y , Wong J , McNutt T , Tryggestad E , Le Y
Published: June 2012

Purpose: By default, the 4‐mm wide leaf‐pairs of the Elekta Beam Modulator MLC not used for field shaping are moved to under the primary collimator to minimize the leakage dose. The trade‐off is the increased beam delivery time in the case of IMRT. This study examines the dosimetric impact and improved delivery efficiency by allowing the unused leaf‐pair as 2mm gap to stay within the PTV aperture during beam‐on. Methods: The capability of the treatment planning system (Pinnacle) in modeling the central and off‐axis dose through 2mm MLC gaps, respectively, was investigated. EBT film measurement performed in a solid water phantom was compared with the computed dose. For two representative IMRT cases, the dosimetric features of treatment plans generated with and without MLC gaps in the field were compared. Similarly, the delivery times for 13 IMRT cases with and without MLC gaps were compared. Results: The peak dose of the leaf gap computed with Pinnacle was dependent on dose grid resolution. The difference between a 0.5mm and 2mm dose grid was about 16.5% for 6MV and 15MV beam respectively. Using a 0.5mm dose grid, the maximum difference between measured and calculated dose was < 1% for a central axis gap, and < 3% for an off‐axis gap. The maximum dose through a 2mm×4mm leaf gap was estimated < 10cGy for a typical IMRT plan. DVH comparison showed an increase of target dose up to 2% for the IMRT plans with gap, with minimal dose change to all critical structures. For the 13 IMRT cases, the beam delivery times were reduced by 27+/−9.7%, from 8.7+/−4.5 minutes to 6.5+/−4.0 minutes. Conclusions: The beam delivery is accelerated by utilizing minimal gaps in the IMRT fields. The increased dose to the target is acceptable and is minimal to all critical structures.
SU‐E‐T‐388: Verification of Monitor Units and Dose Distributions in IMRT Plans Using Monte Carlo Algorithms on the E‐IMRT Web Platform
Authors: Pereira L , Martin Z , Mera M , MeilÃ¡n E , Vazquez J , Salgado M , Medina A
Published: June 2012

Purpose: Currently, quality control (QC) for each IMRT treatment is performed by dose distribution measurements. These techniques are very time‐consuming and require long accelerator downtime. QC could be only based in verification of monitor units and dose distributions, if precise control of MLC is carried out. In such a manner, the e‐IMRT platform (http://eimrt.cesga.es/) is a remote distributed computing tool, which allows comparison between the dose distributions calculated by a TPS and those calculated by Monte Carlo (MC). Methods: Previously, our linear accelerator (Oncor Impression, Siemens) was commissioned. For this purpose, comparison of experimental and MC simulated data was carried out. Several IMRT treatments plans were calculated in superposition algorithm (TPS Xio®CMS 4.60.00) and used as input data for the e‐IMRT platform. These treatment plans were previously verified employing a 2D array MapCheckTM, Sun Nuclear. The gamma index (3%, 3mm) was used for validating results. Results: The platform displays calculated doses using MC, also gamma map (in the CT images, not only statistical data) and histogram shown in Figures 1a), b) and d). The gamma map illustrates the differences between the input and calculated doses. According to the legend in Figure 1 d), these differences correspond to less than 1%. Results show good agreement between the doses calculated by TPS and those computed by e‐IMRT platform. Conclusions: If a rigorous quality control is established for MLC and optimisation criteria (number of gantry angles, minimum segment size, levels of intensity for fluency map) are used. Then, QC for IMRT standard treatment plans would be only based on the verification of monitor units and dose distributions using e‐IMRT II.This work has been funded by the Xunta de Galicia, Project R&D Grant 09SIN007CT. We would like to thank Centro de SupercomputaciÃ3n de Galicia for the computational resources and support.
SU‐E‐T‐401: Evaluation of Initial Setup Accuracy and Intra‐Fraction Motion for Spine SBRT Using Stereotactic Body Frames
Authors: Hacker F , Bondeson J , Lewis J , Mannarino E , Friesen S , Balboni T , Alexander B , Sher D
Published: June 2012

Purpose: Quantify initial setup accuracy and intra‐fraction motion using stereotactic body frames (SBF) for spine SBRT. Methods: 10 patients (11 sites, 31 fractions) treated with spine SBRT using SBF immobilization were evaluated for initial setup accuracy and intra‐fraction motion. Either the commercial Elekta SBF or an in‐house developed SBF (BHS‐SBF) were used. The BHS‐SBF uses the same setup/immobilization principle as the Elekta but with increased interior space and couch indexing. Both frames include sidewalls to conform the vac‐loc rigidly to the patient's sides. All patients were setup using the Brainlab ExacTrac system which includes IR and stereoscopic kV x‐ray based positioning. Patients were initially positioned in the frame using skin tattoos then shifted to treatment isocenter based on IR markers affixed to the frame with known geometry relative to isocenter. kV imaging was acquired and automatic 6‐D bony fusion performed. Resulting translations and rotations give the initial setup accuracy. Calculated shifts and rotations were performed using a robotic couch and verification imaging acquired. The imaging/fusion process was repeated multiple times during treatment providing intra‐fraction motion data. Results: Mean initial setup error in the VRT, LNG and LAT directions was 0.1+/−3.0 mm (0.1+/−0.6 deg), 0.5+/−5.2 mm (0.1+/−1.1 deg) and −0.3+/− 3.7 mm (0.4+/−0.8 deg) respectively. Mean 3‐D error magnitude was 6.6 mm with a 95% certainty of 11.2 mm. Mean intra‐fraction shifts observed in the VRT, LNG and LAT directions were −0.1+/−0.4 mm, −0.1+/−0.4 mm and 0.1+/−0.3 mm respectively. Mean 3‐D intra‐fraction shift magnitude was 0.6 mm with a 95% certainty of 1.4 mm. No significant difference was observed between the SBFs. Conclusions: Patient positioning is not sufficiently reproducible with the evaluated SBF to allow non‐image guided treatment. However, provided image guidance is used for patient positioning, these frames provide excellent immobilization which is on par with mask based cranial radiosurgery.
SU‐E‐T‐404: A Prototype Program for Analyzing 4D Image Guidance Shifts for Lung SBRT
Authors: Wang B , Sarkar V , Busselberg C , Rassiah‐Szegedi P , Zhao H , Huang Y , Szegedi M , Salter B
Published: June 2012

Purpose: A prototype in‐house program was developed to assist deriving image guidance shifts clinically using our 4DCT method for lung SBRT. Methods: Our in‐house prototype program was implemented in MATLAB. The 4D DICOM CT dataset of interest is imported by the program from AW and subsequently accepts input from the user regarding the desired relative IGRT shifts. The DICOM header information defining the relative 4D dataset origin is then read in and the desired relative IGRT shifts are applied to re‐define the origin for the dataset that is to be shifted. Lastly, the redefined (shifted) origin coordinates are written to the header of the 4D dataset and the dataset is then exported to AW as DICOM files. We used this program to process 4DCT datasets for four patients with 3–5 fractions each. The clinical shifts that were derived previously, without this program, were applied to the images and the acceptability of these shifts were evaluated. Results: All slices and planes of the shifted 4D dataset were reviewed and, in general, demonstrated acceptable re‐centering of the target within the ITV. However, it is noted that some small adjustments to the shift coordinates would likely have been made had we had the opportunity to visualize the shifted 4D dataset as facilitated by the new in‐house software. The additional adjustments for the four patient cases studied here had an average of lmm and maximum of 2mm in three principle directions. We look forward to exploring the potential for implementing this software into our clinical workflow, and we believe that such a workflow is worthy of consideration by vendors for implementation as an available feature in future versions of their software. Conclusions: We presented a prototype program to shift 4DCT image set for lung SBRT applications and demonstrated four clinical cases.
SU‐E‐T‐406: Online Image‐Guidance for Prostate SBRT: Dosimetric Benefits and Margin Analysis
Authors: Li T , Yuan L , Lee W , Yin F , Wu QJ
Published: June 2012

Purpose: To evaluate the dosimetric benefits of online image guidance during prostate stereotactic body radiotherapy (SBRT) and the potential on margin reduction. Methods: 28 prostate SBRT patients were retrospectively studied, each treated with 37Gy in 5 fractions. RTOG recently opened a similar protocol (0938). During treatments, per‐beam couch corrections were made based on the actual target motion provided by dynamic tracking with either Calypso or per‐beam OBI imaging. Dosimetric benefits of online correction were evaluated by comparing delivered dose distributions with and without such correction. The dose distribution without correction was generated in the same treatment planning system by accumulating doses without online correction from the each beam and each fraction. Quantitative analyses include the dosimetric difference between delivered doses with and without correction; the correction magnitude and frequency; and the potential on margin reduction based on the margin recipe by Van Herk et al. Results: (1) Delivery without online correction results in small reduction on target mean dose (0.03±0.05Gy), maximal dose (0.01±0.06Gy), and conformity index (<0.06). (2) Delivery without online correction has small impact on OAR dose: 26 out of 28 patients have <1%/1.5cc differences in V18.5Gy/V24Gy/V28Gy/V33Gy/V37Gy for both the bladder and the rectum. Maximal differences are 4cc of the bladder and 1.6cc of the rectum in mid‐dose regions (V18.5Gy). (3) For femoral heads, <1cc/1Gy differences are observed in V20Gy/Dmean/D1cc.(4) Average number of couch corrections per fraction is 0.49. The magnitudes are: (−0.2±2)mm vertically, (−0.1±2.1)mm longitudinally, and (−0.2±1.4)mm laterally. (5) Margin determined by actual target motion in this patient population is 2.5mm isotropic. Conclusion: For both target coverage and OAR sparing, overall small benefit is seen from per‐beam couch correction under dynamic tracking. The target motion between beams is small and random, and indicates a population‐based margin size of 2.5mm.
SU‐E‐T‐407: Freedom from Conventional: Application of RapidArc for SBRT Lung Treatments
Authors: Guida K , Luo G , Morales M , Coffey C , Ding G
Published: June 2012

Purpose: Stereotactic body radiotherapy (SBRT) has been applied in treating early stage small lung lesions, delivering hypofractionated doses in a conformai manner. Studies have shown that SBRT has similar outcomes compared with surgery. Conventionally, SBRT lung treatments rely on utilization of multiple small, conformai, static fields in coplanar and non‐ coplanar arrangements. With the advent of RapidArc, it is important to evaluate the differences in dosimetry and delivery of conformai SBRT lung treatments for both conventional static field and VMAT techniques. Methods: A retrospective study of 12 patients at our institution who have received SBRT for primary lung lesions was used to evaluate the application of RapidArc for such cases. Originally treated plans utilized eight to ten conformai static coplanar and non‐coplanar fields. RapidArc plans were generated in Eclipse using single and multiple arc setups. Results: As an ntensity‐modulated modality, RapidArc provides greater freedom as compared to conventional static field delivery, as one can achieve dose uniformity throughout the PTV or replicate the dosimetry synonymous with conventional SBRT. RapidArc is capable of reproducing the high conformality achieved by conventional SBRT; dual arc plans, delivering uniform dose distributions, yielded an average CI100% of 1.11 and D2cm maximum of 63% of the prescribed dose, compared to 1.33 and 77% (p‐ values of .002 and .005, respectively) for conventional SBRT. Application of a short, non‐coplanar arc, in conjunction with dual coplanar arcs, improved sparing of OARs in direct proximity of the PTV at the expense of treatment time. RapidArc allows for faster treatment delivery; conventional SBRT delivery averages 13.7 minutes at our institution, whereas coplanar dual arcs are estimated to average treatment durations of 4.2 minutes. Conclusions: RapidArc is capable of generating conformai dose distributions and sparing of OARs, allows greater freedom in plan optimization, and reduces treatment time significantly.
SU‐E‐T‐408: Enhancing Stereotactic Radiosurgery for Neovascular Age‐Related Macular Degeneration, Using Gold Nanoparticles
Authors: Ngwa W , Makrigiorgos M , Berbeco R
Published: June 2012

Purpose: Age‐related macular degeneration (AMD) is the leading cause of irreversible vision loss for people over the age of 60 in the United States. In this study the dosimetric feasibility of using gold nanoparticles (AuNP) as radiosensitizers to enhance stereotactic radiosurgery for neovascular AMD is investigated. Methods: Analytic calculations were carried out to estimate the nucleus dose enhancement factor (nDEF) due to photon‐induced photo‐ /Auger electrons from AuNP targeting neovascular AMD endothelial cells (EC). The nDEF represents the ratio of the dose to the nucleus with and without the presence of AuNP. As in previous studies, the EC is modeled as a slab of 2 μm (thickness) × 10 μm (length) × 10 μm (width) containing a nucleus of 5 μm diameter and thickness of 0.5 – 1 μm. The targeted AuNP are attached to the exterior of the EC. The nDEF was calculated for a range of feasible AuNP local concentrations (1–7 mg/g) using the clinically applicable 100 kVp x‐rays employed by the IRayTM system (Oraya Therapeutics Inc. Newark, CA), with total filtration of 0.75 mm Al and 0.8 mm Be. For comparison the nDEF for other energies: 80 kVp, 90 kVp, 110 kVp, and 120 kVp was also investigated. Results: For 100 kVp x‐rays, the results revealed nDEF values of 1.30 – 3.26 for the investigated concentration range of 1 – 7 mg/g, respectively. In comparison, for the same concentration range, nDEF values of 1.32 – 3.40, 1.31–3.33, 1.29 – 3.19, 1.28 – 3.12 were calculated for 80 kVp, 90 kVp, 110 kVp, and 120 kVp x‐rays, respectively. Conclusions: The results predict substantial dose enhancement to the sensitive nucleus of neovascular endothelial cells, targeted by AuNP during kilovoltage stereotactic radiosurgery. This suggests that AuNP may be employed as radiosensitizers to enhance therapeutic efficacy during radiosurgery for neovascular AMD.
SU‐E‐T‐413: Dose Verification for Linac‐Based SRS Commissioning and Patient Specific QA
Authors: Wu J , Wu H
Published: June 2012

Purpose: Stereotactic Radiosurgery (SRS) program commissioning is currently relied on Radiological Physics Center (RPC) Head Neck phantom with Thermo Luminescent Dosimeters (TLDs) for dose verification. However, due to the limited accessibility of RPC Head Neck phantom, ongoing QA or patient specific dose verification is not performed in most clinics. In this study, we proposed an SRS dose verification approach for both SRS commissioning and patient specific dose verification with widely available clinical instruments. Methods: SRS treatment plans were imposed onto a 14cm thick conventional solid water phantom (30cm × 30cm), with a PTW micro‐chamber in the middle. Treatment couch angles were renormalized to 90 or 270 degrees for two reasons: 1) micro‐chamber's axis was parallel to gantry rotation axis during all the arc beam delivery, which minimizes the angle dependence effect (axis tilt) of micro‐chamber. 2) Any collision between the cone and conventional solid water phantom would be avoided and there would be minimum attenuation effect from the couch. The arc verification plan was then recalculated and compared to the measured absolute dose by PTW micro‐chamber. An End‐to‐End test with a CyberKnife Head Neck phantom and GAFChromic EBT2 film was utilized as secondary dose delivery verification. Results: Cones with all twelve different sizes in SRS commissioning were tested. For the cone size from 10mm to 30mm, the micro‐chamber measurements agreed with the computer calculations within 3%. However, when the cone size was reduced to 5mm, micro‐chamber measurement was 10% lower than planned dose, indicating underdose effect for small cone size. Additional measurements with Cyberknife head phantom confirmed the dose delivery accuracy was within 5%. Conclusions: A simple SRS dose verification method which only requires micro‐chamber and conventional solid water phantom has been presented and verified. This approach will be valuable for SRS commissioning and ongoing SRS QA.
SU‐E‐T‐419: MU Verification for Small Lesions in Lung SBRT
Authors: Ellerbusch D
Published: June 2012

Purpose: To determine if a secondary MU calculation can validate the treatment planning system MU calculation for objects less than 4cm in diameter in small field lung SBRT. To determine the small object modifier to better predict the correct MU. Methods: Four polystyrene spheres were embedded into lung mimicking material. The sphere diameters are 4cm, 3cm, 2cm, and 1.2cm. The spheres are made up of two dome TLD‐100 chip holders. Each TLD holder holds two 0.125′ square × 0.035′ TLDs. The output (cGy/MU) was measured at the center of each sphere for three depth and effective depth combinations. The depth, effective depth, field size, and energy were kept constant. The effective depth was kept constant by adding tissue equivalent water to the top of the phantom as the sphere diameter got smaller. The three depths were 5cm, 10cm, and 15cm, with an effective depth of 5cm, 6cm, and 7cm, respectively. The collimator field size and the effective field size was 3cm × 3cm. The energy was 6MV. The measured results were compared with the output predicted by our treatment planning system. Results: Dose measurements were made with both TLD and film and the results were averaged. The secondary MU calculation predicted that the output would be the same for each sphere. However, the measured output dropped as the sphere diameter got smaller, especially for the 1.2cm diameter sphere. The output dropped by 5% at a 10cm depth and by 9% at a depth of 15cm. Conclusions: Secondary MU calculations cannot reliably predict the MU's for small objects less than 3cm in diameter without modifiers. A modifier of 3% is needed for a 2cm sphere and 7% for a 1.2cm diameter sphere.
SU‐E‐T‐424: Inter‐Fraction Variation of High Dose Regions of OARS in MR Image Based Cervix Brachytherapy Using Rigid Registration
Authors: Swamidas Jamema , Mahantshetty U , Deshpande D , Shrivastava S
Published: June 2012

Purpose: To quantify the inter fraction variation of spatial location of high dose regions of OARs in MR‐image based cervix brachytherapy using rigid registration algorithm. Methods: : Retrospective analysis of 27 previously treated patients under EMBRACE multi‐centric trial was evaluated. Each patient had two applications, API and AP2 with Vienna applicator. As part of the protocol, all patients underwent MR imaging for each application, followed by volume delineation (Oncentra v3.3) treatment planning & optimization (Plato sunrise, Nucletron), documentation of DVH parameters based on GEC‐ESTRO recommendations. The volume receiving the dose D2cc from the plan with which the patient was treated was contoured in each of the image series for OARs rectum, bladder, sigmoid and small bowel region. Both the image series were exported to Eclipse planning system (v8.6.14, VMS) and were co‐registered with applicator as the reference using rigid registration Results: Out of 27 patients, the overlapping D2cc volumes were found in 21, 20, 10 and 4 patients for rectum, bladder, sigmoid and small bowel respectively between AP1 and AP2. The mean(SD) volume of overlap of D2cc was 0.20(0.23), 0.17(0.20), 0.07(0.14), and 0.09(0.11) for rectum, bladder, sigmoid and small bowel respectively. The overlap volume had a wide range which is evident from its standard deviation. The mean(SD) difference of the absolute volumes between AP1 and AP2 was 22(20), 5(6), and 11(11) for bladder, rectum and sigmoid respectively. The uncertainties include the calculation of small overlapping volumes of D2cc, co‐registration and variation between applications. Conclusions: The inter‐fraction variation of spatial location of high dose regions were more consistent in rectum and bladder and less in sigmoid and much lesser in small bowel region
SU‐E‐T‐432: Comparison of HDR Treatment Plans for Interstitial Brachytherapy with Intracavitary Savi Brachytherapy for Post Lumpectomy Breast Cancer
Authors: Nair M , Anderson P , Neumann T , Vance W , White M , Davis J
Published: June 2012

Purpose: To compare the dose distributions from HDR brachytherapy using interstitial catheter implants and Intracavitary Savi applicator for breast cancer patients following lumpectomy. Methods: We have treated over 200 post lumpectomy breast patients with brachytherapy and Savi applicator (Cianna Medical) . The interstitial technique used a custom built template for placement of catheters under the image guidance. The Savi applicator was placed into the resected cavity and the applicator was expanded to cover the cavity under CT image guidance. The criteria used for plan evaluation was prescription dose covered 95 to 100% of the volume 1.5× prescribed dose to cover <30% of the PTV and 2.0 × prescribed dose covered <10% of the PTV. The Savi plans were evaluated with PTVeval to cover 90 to 95% of the prescribed dose and 1.5×PTVeval not to exceed 50cc, 2×PTVeval to cover <10% of volume. Results: The PTV for interstitial ranged from 29 to 170cc, and that for Savi the PTVeval varied from 28 to 111. For interstitial the 1.5× dose reference expressed as % of PTV varied from 11% to 30% with a median at 24.9%. For Savi the 1.5× dose reference volume expressed as % of PTVeval ranged from 30 to 50% with a median of 40%. The 2× dose reference covered volume expressed as % of PTV varied from 5.5 to 30% of PTV at a median value of 8.5%. The same for Savi varied from 13 to 31% at a median value of 19.4%. The skin dose for interstitial implant was less than 70% whereas same for Savi application was <100%Conclusions: We conclude that the dose uniformity for V1.5 and V2 were better with interstitial implant as compared to Savi application. Also the interstitial implant allowed covering the desired margin of resection without restriction imposed due to air gap. Savi application, being less invasive was better preference by the patient over interstitial
SU‐E‐T‐436: Feasibility of Using the ‘Irregular Surface Compensator’ Planning Feature of the Eclipse TPS for Total Body Irradiation (TBI) Treatment Planning
Authors: Ayan A , Lu L , Rong Y , Cunningham M , Weldon M , Welliver M , Woollard J , Gupta N
Published: June 2012

Purpose: To investigate the feasibility of using the Irregular Surface Compensator (ISC) planning feature of the Eclipse treatment planning system (TPS) for Total Body Irradiation (TBI). Methods: TBI treatments require that the whole body receives within +−10% of the prescribed dose. Different body parts with different thicknesses compared to the umbilicus separation may receive higher or lower doses compared to the prescribed dose. Another challenge is to keep the lung dose below 10Gy to avoid complications. To mitigate this problem, physical compensators and blocks are used during the treatment for different body parts and lungs. This method presents a challenge during the treatment delivery and prolongs the treatment time due to patient setup, in‐vivo on‐line dosimetric monitoring and the adjustment of the compensators frequently during the treatment. We investigated the use of ISC planning feature of Eclipse TPS which is an electronic compensation method that calculates a fluence map based on the body contour from the CT image. The fluence map is delivered with dynamic MLCs . This TBI treatment technique was tested using a Rando phantom in Head First Supine position with lateral beams at SSD=250cm.The calculated fluence were edited so that the lung received <∼10Gy for 12Gy prescription. A single fraction of 2Gy was delivered and the in‐vivo measurements were performed in the neck, lung and the umbilicus by using OSLDs. Results: OSLD measurements and the Eclipse TPS predictionswere 200.4/195.0, 162.2/168.9, and 196.1/208.9 cGy for the neck, lung and the umbilicus respectively. Conclusions: The feasibility of using the ‘Irregular Surface Compensator’ feature of Eclipse TPS for TBI treatment planning was demonstrated. Good agreement (<6%) between the predicted and measured doses was obtained. The proposed planning and delivery simplifies the compensation and blocking to achieve uniform dose distributions and reduces the treatment time.
SU‐E‐T‐437: Interfractional Dosimetric Verification of Lung Patients Treated by Passive Double Scattering Proton Radiotherapy
Authors: Tang S , Yin L , Rengan R , James P , Hahn S , Both S
Published: June 2012

Purpose: Proton radiotherapy, with the ability to confine the dose at desired depth, can potentially benefit lung tumor patients by significantly sparing the healthy lung tissue. However, the superior proton dose distribution could be affected by tumor shrinkage due to the quick response and by motion especially related to the respiration. Thus the treatment should be frequently verified and be adjusted accordingly if necessary to achieve the initial treatment goal.Material and Methods: A cohort of 20 patients were selected from lung patients treated with passive proton radiotherapy. All those patients were evaluated via 4D‐CT scans and found to have tumor motion less than 1 cm. The internal target volumes (ITV) were derived based on the full inspiration and expiration phases. The average of the 4D‐CT scan, full inspiration and expiration phases were used for the initial treatment planning. The planning objective was 95% of the prescription dose to at least 95% volume of the ITV. Bi‐weekly verification 4D‐CT scans were performed to assess the robustness of the initial treatment plan and no replanning was required for target dose variations less then 3%. Results: Compared with the initial treatment plan, the standard deviations of target coverage on inspiration, expiration, and average verification CT scans are within 3% for all the patients, with the maximum difference up to 7%. No statistically significant differences were found among the initial and verification plans (p>0.1). The percentage deviations of OAR sparing were highly variable, e.g., up to 40% for mean lung dose, 100% for mean heart dose, 50% for max cord dose, particularly for OARs receiving small amount of doses. However, the absolute dose deviations are all with OAR's tolerance. Conclusion: Overall, the passive double scattering proton modality allows for robust proton treatment planning and delivery to treat the lung tumors with limited motion.
SU‐E‐T‐439: First Experience of Three Dimensional Conformai Radiotherapy (3DCRT) Planning with Helical Tomotherapy
Authors: Chao M , Corry P , Zhang X , Penagaricano J , Ratanatharathorn V
Published: June 2012

Purpose: A three‐dimensional conformal radiotherapy (3DCRT) has been recently introduced to helical tomotherapy, allowing the user to plan and treat patients that do not require sophisticated IMRT planning and delivery. This study aims to test treatment planning on this modality and evaluate its performance by comparing to conventional LINAC‐based 3DCRT planning. Methods: Four clinical cases (whole brain, extremity, lung, and partial breast irradiation) were retrospectively selected from a Pinnacle planning system (Philips Medical System, Fitchburg, WI) and planned on Tomotherapy (Accuray Inc., Sunnyvale, CA). Computed tomography (CT) images together with contours of target and critical structures were exported from Pinnacle to the Tomotherapy planning station. The same prescription and fractionation scheme was adopted. The pitch factor for all clinical cases was set to 0.287. A 2.5 cm jaw was employed except in the lung case the field size was set to 1.0 cm for better dose conformity. The dose grid size was chosen to be half of that of the planning CT images. On Pinnacle 100% prescription dose was delivered to the treatment isocenter while onTomotherapy it was stipulated that at least 95% of the target volume received the prescribed dose. Comparison between two planning strategies was performed, in terms of dose volume histograms (DVH), dosimetric and radiobiological parameters, for plan quality assessment. Results: Comparison of DVHs reveals that up to 25% healthy tissue sparing in volume can be accomplished with Tomotherapy 3DCRT while the same target coverage is ensured. Dosimetric and radiobiological indices between Tomotherapy and Pinnacle planning agree to within 3.0%. Additional beam modifiers and non‐coplanar beams associated with LINAC‐based 3DCRT are not needed on Tomotherapy, making it more favorable. Conclusions: Tomotherapy 3DCRT has similar dosimetric performance when compared to conventional LINAC‐based 3DCRT while it is substantially easier to use.
SU‐E‐T‐446: Effect of Dose Calculation Grid Size Variability on the Specification of Spinal Cord Dose Tolerance for Spinal Stereotactic Body Radiation Therapy
Authors: Gros S , Descovich M , Barani I , Ma L
Published: June 2012

Purpose: To investigate the effect of the dose grid resolution variability on the spinal cord dose for spinal SBRT treatments. Method: 10 CyberKnife plans were selected for the proximity of the PTV to the spinal cord. All dose distributions were calculated with Monte Carlo using high spatial resolution and minimal relative uncertainty. The plans were renormalized to a 16 Gy prescription dose and to ensure a target coverage > 95% in order to compare the calculated dose distributions. Each dose matrix was resampled 12 times, covering a grid resolution range of 0.95 mm to 13.52 mm. The spinal cord DVHs were generated for each resampled dose grid. The variations of the maximum point dose (DmaxCord) and dose‐coverage to partial volumes (D[V]) up to 5 cc were investigated against the grid resolution. Results: The mean variation of DmaxCord with grid resolution is characterized by an inverse power law, with a sharp initial decrease leading to potentially large underestimates of DmaxCord (24%, 40% and 55% at resolutions of 2 mm, 4 mm and 8 mm). The variability of mean D[V] values decreases from smaller to larger grid resolutions, however large disparities are observed between patient plans. We introduced the variability threshold volume (Vth) as a constraint to express the dose coverage independently from the grid resolution. For resolutions up to 8 mm, the mean Vth value is (0.96±0.10) cc with a corresponding dose coverage of (26± 12) % relative to the initial DmaxCord value. Conclusions: Dose distributions calculated with grid resolutions larger than 2 mm could Result in significant underestimates of DmaxCord. Furthermore, the sensitivity of the dose coverage to grid resolution variability is patient dependent. Consequently, a specified cord dose tolerance should be quoted at a particular grid resolution uniformly adopted between institutions; 2 mm or less is an appropriate value.
SU‐E‐T‐449: Dosimetric Comparison of Beam Arrangements for Stereotactic Body Radiotherapy of Lung Lesion
Authors: Liu R , Meeks S
Published: June 2012

Purpose: Dosimetric comparison of beam arrangements of coplanar, non‐ coplanar and conformal arc for Stereotactic body radiotherapy of lung lesion. Methods: Four spherical targets with diameters of 2, 4, 6 and 7cm are contoured in the geometric center of right lung of a selected SBRT CT scan. For each target, treatment plans of optimized 7, 9 and 11 coplanar, non‐ coplanar and conformal arc beam arrangements are generated in Pinnacle (Pinnacle Version 9.0, Philips Radiation Oncology Systems, WI). Prescription isodoses are chosen to cover at least 95% of target volumes. The volumes enclosed by the prescription and 50% of prescription isodose surfaces are computed. Conformality index (CI) and effective dose fall off gradient are computed for dosimetric comparison. Results: All plans with optimized coplanar and conformal arc beam arrangements have similar CIs while optimized non‐coplanar beam arrangements have the smallest CIs. For each target size, optimized 7 and 9 coplanar beam arrangements have the largest half prescription isodose volumes while optimized 11 coplanar beam arrangements have slightly less half prescription isodose volumes than conformal arc plans. All 3 optimized non‐coplanar beam arrangements Result in faster dose gradient than conformal arcs except for the smallest target cases, for a 2cm diameter target, 9 or 11 non‐coplanar beams are needed to achieve better dose gradient than their rival conformal arc plan. Conclusions: Treatment plans using optimized 9 and 11 non‐coplanar beam arrangements are superior to conformal arc plans for SBRT of lung lesions based on dosimetric comparison. To achieve a superior plan for small lesions, 11 or more optimized coplanar beams may be required.
SU‐E‐T‐450: An Evaluation Study of Dose Calculation Algorithms for Stereotactic Body Radiation Therapy in Heterogeneous Phantom
Authors: Shosha M , Deiab N , Eldib A , Tohamy K
Published: June 2012

Purpose: In Stereotactic body radiation therapy (SBRT) higher dose per fraction is delivered to patients and thus the need for an accurate dose computation is further elevated. However under such conditions of small field geometries, the electronic equilibrium can be lost, making it challenging for the dose‐calculation algorithm to accurately predict the dose, especially in the presence of tissue heterogeneities. Thus the aim of this study is to evaluate the performance of the algorithms implemented in our treatment planning system. Methods: In this study different phantoms were designed to model the lung with a small tumor volume of sizes that are usually encountered in SBRT. Solid water and cork slabs were used in constructing the phantom body. Perspex pieces of different diameters were created to be inserted in precut holes in the cork to simulate the tumor. The various dose calculation algorithms that are implemented in our CMS XIO planning system were then used for dose calculation inside the target. Results: A significant discrepancies between maximum, minimum and mean dose for PTV was found between Clarkson, FFT Convolution, Fast superposition and superposition algorithms in dose calculation for the lung tumor. The FFT Convolution and Clarkson algorithms have higher calculated minimum dose than that predicted by the superposition and the fast superposition algorithm. A percentage difference as high as 62.5% was obtained between Clarkson and the superposition algorithm in the estimated minimum dose. A percentage difference up to 13.4% was obtained between the FFT Convolution and the superposition algorithm for the estimated maximum dose. Superposition and fast superposition showed little discrepancies for maximum, minimum and mean dose for the PTV. Conclusion: It is very critical to address the accuracy of dose computation for SBRT as a significant dose overestimation can occur inside the target due to the heterogeneous geometries.
SU‐E‐T‐458: Radiobiological Comparison of Single and Dual‐Isotope Prostate Seed Implants
Authors: Knaup C , Mavroidis P , Esquivel C , Stathakis S , Swanson G , Papanikolaou N
Published: June 2012

Purpose: Several isotopes are available for low dose‐rate brachytherapy of the prostate. Currently, most implants use a single isotope. However, the use of dual‐isotope implants may yield an advantageous combination of characteristics such as half‐life and relative biological effectiveness. However, the use of dual‐isotope implants complicates treatment planning and quality assurance. Do the benefits of dual‐isotope implants outweigh the added difficulty? The goal of this work was to use a linear‐quadratic model to compare single and dual‐isotope implants. Methods: Ten patients were evaluated in this study. For each patient, six treatment plans were created with single or dual‐isotope combinations of 1251, 103Pd and 131Cs. For each plan the prostate, urethra, rectum and bladder were contoured by a physician. The biologically effective dose was used to determine the tumor control probability and normal tissue complication probabilities for each plan. Each plan was evaluated using favorable, intermediate and unfavorable radiobiological parameters. The results of the radiobiological analysis were used to compare the single and dual‐isotope treatment plans. Results: Iodine‐125 only implants were seen to be most affected by changes in tumor aggressiveness. Significant differences in organ response probabilities were seen at common dose levels. It was recognized that these differences were likely a result of suboptimal initial seed strengths. After adjusting the initial seed strength to maximize complication‐free tumor control the differences between isotope combinations were minimal. This result was true even for unfavorable tumors. Conclusions: The objective of this work was to perform a radiobiologically based comparison of single and dual‐isotope prostate seed implant plans. For all isotope combinations, the plans were improved by varying the initial seed strength. For the minimally‐optimized treatment plans, no substantial differences in predicted treatment outcomes were seen among the different isotope combinations.
SU‐E‐T‐466: TCP and NTCP: Is That All?
Authors: Sánchez‐Nieto B , Expósito MR , Terrón JA , Paiusco M , Cagni E , Ghetti C , Filice S , Grishchuk D , Mateos JC , Roselló J , Planes D , NÃ°ñez L , Sánchez‐Doblado F
Published: June 2012

Purpose: Concerns about the secondary cancer risks associated to the peripheral neutron and photon contamination in photon modern radiotherapy (RT) techniques (e.g., Intensity Modulated RT ‐IMRT‐ or Intensity Modulated Arc Therapy ‐IMAT) have been widely raised. Benefits in terms of better tumor coverage have to be balanced against the drawbacks of poorer organ at risk sparing and secondary cancer risk in order to make the decision on the optimum treatment technique. The aim of this study was to develop a tool which estimates treatment success taking into consideration the neutron secondary cancer probability. Methods: A methodology and benchmark dataset for radiotherapy real time assessment of patient neutron dose and application to a novel digital detector (DD) has been carried out (submitted to PMB, 2011). Our DD provides real time neutron equivalent dose distribution in relevant organs along the patient. This information, together with TCP and NTCP estimated from the DVH of target and organs at risks, respectively, have been built into a general biological model which allows us to evaluate the success of the treatments (SÃ¡nchez‐Nieto et al., ESTRO meeting 2012). This model has been applied to make estimation of treatment success in a variety of treatment techniques (3DCRT, forward and inverse IMRT, RapidArc, Volumetric Modulated Arc Therapy and Helical Tomotherapy) to low and high energy. Results: MU‐demanding techniques at high energies were able to deliver treatment plans with the highest complicated‐free tumour control. Nevertheless, neutron peripheral dose must be taken into consideration as the associated risk could be of the same order of magnitude than the usually considered NTCPs. Conclusions: The methodology developed to provide an online organ neutron peripheral dose can be successfully combined with biological models to make predictions on treatment success taking into consideration secondary cancer risks.
SU‐E‐T‐472: Characterization of the Very High Energy Electrons, ISO ‐ 250 MeV (VHEE) Beam Generated by ALPHA‐X Laser Wakefield Accelerator Beam Line for Utilization in Monte Carlo Simulation for Biomedical Experiment Planning
Authors: Moskvin V , Subiel A , Desrosiers C , Wiggins M , Maryanski M , Mendonca M , Boyd M , Sorensen A , Cipiccia S , Issac R , Welsh G , Brunetti E , Aniculaesei C , Jaroszynski DA
Published: June 2012

Purpose: Progress in the development of compact high‐energy pulsed laser‐ plasma wakefield accelerators is opening up the potential for using Very High Energy Electron (VHEEs) beams in the range of 150 – 250 MeV for biomedical studies. Initial experiments using VHEE for this purpose have been carried out using the ALPHA‐X laser‐plasma wakefield accelerator beam line at the University of Strathclyde, Glasgow, UK. The purpose of this investigation is to use Monte Carlo simulations to plan experiments and compare with characterization of the interaction of the VHEE beam using a dosimeter. Methods: An experiment using the VHEE beam to irradiate a muscle‐equivalent BANG polymer gel dosimeter has been carried out. Simulations have been used to prepare for the experiments. These were undertaken using the expected average energy for a pulse set and an energy spread approximated by Gaussian distribution. The model was implemented in FLUKA Monte Carlo code with follow up modeling using the Geant4 toolkit. The results have been compared with 1mm̂3 voxel laser CT based measurements of the dose deposited in the BANG dosimeter and with measurement of the induced radioactivity. Results: The results of the measured dose from induced radioactivity have been compared with data from the FLUKA simulations. The beam model based on an average energy of particles in irradiation gives an acceptable estimate of the induced radioactivity and the dose deposited in the BANG dosimeter. Comparison with the dosimeter scanned profiles shows that the structure of the spectra of VHEE beams in the experiment and secondary scattered particles in the beam line should be accounted for in any model. Such model description of the VHEE beam for the ALPHA‐X beam line has been developed. Conclusions: Monte Carlo simulations using the FLUKA code is an efficient way to plan a VHEE experiment and analyze data from measurements.
SU‐E‐T‐474: Monte Carlo Phase Space Production to Model Magnetically Scanned Proton Beams for IMPT
Authors: Titt U , Mirkovic D , Perles L , Sell M , Peeler C , Liu A , Mohan R
Published: June 2012

Purpose: Accurate dose predictions in proton beam therapy using magnetically scanned beams are highly dependent on the accurate modeling of the lateral dose profiles. This study was performed to provide proton phase spaces for Monte Carlo simulations, used to accurately simulate doses at distances up to 12 cm from the central axis of the beam. Methods: Measured lateral dose profiles at various depths in water were compared to Monte Carlo simulations of doses for 90 discreet initial proton energies. Phase spaces were produced using a one dimensional energy distribution, and a combination of several two dimensional spatial and directional distributions. Simulations were performed iteratively using variations in the initial phase space distributions to achieve acceptable agreement between measured and simulated lateral dose profiles, i.e. differences in FWHM < 0.5 mm and dose differences less that 0.1% at distances up to 12.5 cm. Results: 90 phase spaces of proton sources for different initial beam energies were created for use in Monte Carlo simulations of scanned proton beam therapy patient plans. At a depth of 2 cm in water, the simulated and measured FWHM of the lateral dose profiles differed in in‐plane direction by an average of 0.05 mm, in cross‐plane direction by 0.13 mm. All simulated profiles were within 0.1% of the measured doses at distances between 2cm and 12.5 cm from the central beam axis. Conclusions: A library of 90 phase space files has been created to accurately simulate magnetically scanned proton beams for IMPT, providing accurate dose distributions up to 12 cm distance from the central beam axis. This project is supported in part by P01CA021239 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health.