bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐12: A Comparative Dosimetric Study of Pre and Post Prostate Iodine‐125 Permanent Seed Implants
Authors: Liu X , Rahimian J , Goy B , Cosmatos H , Qian Y 
Published: June 2015

Purpose:Post‐implant dosimetry has become the gold standard for prostate implant evaluation. The goal of this research is to compare the dosimetry between pre‐plan and post‐plan in permanent prostate seed implant brachytherapy.Methods:A retrospective study of 91 patients treated with Iodine‐125 prostate seed implant between year 2012∼2014 were performed. All plans were created using a VariSeed 8.0 planning system. Pre‐plan ultrasound images were acquired using 0.5 cm slice thickness. Post‐plan CT images acquired about 1–4 weeks after implant, fused with the preplan ultrasound images. The prostate and urethra contours were generated using the fusion of ultrasound and CT images. Iodine‐125 seed source activities varied between 0.382 to 0.414 mCi per seed. The loading patterns varied slightly between patients depending on the prostate size. Statistical analysis of pre and post plans for prostate and urethra volumes, V100%, V150% and D90, and urethra D10 were performed and reported.Results:The pre and post implant average prostate size was 36.90cc vs. 38.58cc; V100% was 98.33% vs. 96.89%; V150% was 47.09% vs. 56.95%; D90 was 116.35Gy vs. 116.12Gy, urethra volume was 1.72cc vs. 1.85cc, urethra D10% was 122.0% vs. 135.35%, respectively. There was no statistically significant difference between the pre and post‐plan values for D90(p‐value=0.43). However, there are significant differences between other parameters most likely due to post surgical edema; prostate size (p‐value= 0.00015); V100% (p‐value=3.7803E‐07); V150% (p‐value=1.49E‐09); urethra volume (p‐value= 2.77E‐06); Urethra D10 (p‐value=7.37E‐11).Conclusion:The post‐plan dosimetry using CT image set showed similar D90 dose coverage to the pre‐plan using the ultrasound image dataset. The study showed that our prostate seed implants have consistently delivered adequate therapeutic dose to the prostate while sparing urethra. Future studies to correlate dose versus biochemical response using patients’ PSA values as well as patients’ survival are warranted.
SU‐E‐T‐14: A Comparative Study Between Forward and Inverse Planning in Gamma Knife Radiosurgery for Acoustic Neuroma Tumours
Authors: Gopishankar N , Agarwal Priyanka , Bisht Raj Kishor , Kale S S , Rath G K , Chander S , Sharma B S 
Published: June 2015

Purpose:To evaluate forward and inverse planning methods for acoustic neuroma cases treated in Gamma Knife Perfexion.Methods:Five patients with acoustic neuroma tumour abutting brainstem were planned twice in LGP TPS (Version 10.1) using TMR10 algorithm. First plan was entirely based on forward planning (FP) in which each shot was chosen manually. Second plan was generated using inverse planning (IP) for which planning parameters like coverage, selectivity, gradient index (GI) and beam‐on time threshold were set. Number of shots in IP was automatically selected by objective function using iterative process. In both planning methods MRI MPRAGE sequence images were used for tumour localization and planning. A planning dose of 12Gy at 50% isodose level was chosen. Results and Discussion: Number of shots used in FP was greater than IP and beam‐on time in FP was in average 1.4 times more than IP. One advantage of FP was that the brainstem volume subjected to 6Gy dose (25% isodose) was less in FP than IP. Our results showed use of more number of shots as in FP results in GI less than or equal to 2.55 which is close to its lower limit. Dose homogeneity index (DHI) analysis of FP and IP showed average values of 0.59 and 0.67 respectively. General trend in GK for planning in acoustic neuroma cases is to use small collimator shots to avoid dose to adjacent critical structures. More number of shots and prolonged treatment time causes inconvenience to the patients. Similarly overuse of automatic shot shaping as in IP results in increased scatter dose. A compromise is required in shot selection for these cases.Conclusion:IP method could be used in acoustic neuroma cases to decrease treatment time provided the source sector openings near brainstem are shielded or adjusted appropriately to reduce brainstem dose.
SU‐E‐T‐15: A Comparison of COMS and EP917 Eye Plaque Applicators Using Different Radionuclides
Authors: Aryal P , Molloy JA , Rivard MJ 
Published: June 2015

Purpose:To investigate the effect of plaque design and radionuclides on eye plaque dosimetry.Methods:The Monte Carlo N‐particle Code version 6 (MCNP6) was used for radiation transport simulations. The 14 mm and 16 mm diameter COMS plaques and the model EP917 plaque were simulated using brachytherapy seeds containing I‐125, Pd‐103, and Cs‐131 radionuclides. The origin was placed at the scleral inner surface. The central axis (CAX) doses of both COMS plaques at −1 mm, 0 mm, 1 mm, 2 mm, 5 mm, 10 mm, 15 mm, 20 mm, and 22.6 mm were compared to the model EP917 plaque. Dose volume histograms (DVHs) were also created for both COMS plaques for the tumor and outer sclera then compared to results for the model EP917 plaque.Results:For all radionuclides, the EP917 plaque delivered higher dose (max 343%) compared to the COMS plaques, except for the 14 mm COMS plaque with Cs‐131 at 1 mm and 2 mm depths from outer sclera surface. This could be due to source design. For all radionuclides, the 14 mm COMS plaque delivered higher doses compared to the 16 mm COMS plaque for the depths up to 5 mm. Dose differences were not significant beyond depths of 10 mm due to ocular lateral scatter for the different plaque designs. Tumor DVHs for the 16 mm COMS plaque with Cs‐131 provided better dose homogeneity and conformity compared to other COMS plaques with I‐125 and Pd‐103. Using Pd‐103, DVHs for the 16 mm COMS plaque delivered less dose to outer sclera compared to other plaques.Conclusion:This study identified improved tumor homogeneity upon considering radionuclides and plaque designs, and found that scleral dose with the model EP917 plaque was higher than for the 16 mm COMS plaque for all the radionuclides studied.
SU‐E‐T‐16: A Comparison of Expected Dwell Times and Dose Variations for NAMD Patients Treated with An Episcleral Brachytherapy Device
Authors: Hamilton R , Patel P , Balaggan K , Restori M , Ilginis T , Drew M , McGovern M , Vitali J , Marsteller L 
Published: June 2015

Purpose:To evaluate the variations in dwell times and doses expected when using an episcleral brachytherapy device for treatment of neovascular agerelated macular degeneration (n‐AMD) based on accurate imaging modalitiesMethods:Data from 40 eyes from 40 subjects with known n‐ AMD acquired through the Distance of Choroid Study (DOCS) conducted at Moorfields Eye Hospital was used to determine the target depth; the distance from the outer scleral surface of the eye, through the choroid, to the apex of the choroidal neovascularization (CNV). Each subject underwent, in triplicate, enhanced‐depth Spectral Domain Optical Coherence Tomography (SD‐OCT), Swept Source Optical Coherence Tomography, (SS‐OCT) and Ocular Ultrasound (O‐US). These data are the most comprehensive and accurate measurements of the dimensions of the CNV and adjacent layers of the eye for this cohort of patients. During treatment of n‐AMD, patients receive a dose of 24Gy to the apex at the target depth. Using the percentage depth dose for a Sr‐90 episcleral brachytherapy device, dwell times and doses to the apex were computed to determine the expected variations.Results:The mean target depth and the 95% confidence interval (CI) determined by combining O‐US with SD‐OCT were 1326 (956,1696)µm and with SS‐OCT were 1332 (970,1693)µm. The calculated corresponding mean dwell times and 95% (CI) were 334 (223,445)s and 335 (226,445)s for SD‐OCT and SS‐OCT determined depths, respectively. The corresponding mean apex dose and 95% (CI) were 24 (35.9,18.0)Gy (SD‐OCT) and 24 (35.6,18.1)Gy (SS‐OCT).Conclusion:For episcleral brachytherapy treatment of n‐AMD, using a patient population average target depth for treatment planning is inadequate, resulting in dose variations of a factor of approximately two over the 95% CI and larger variations for a nontrivial segment of the population. Each patient should have individualized imaging studies to determine the target depth for use in the dwell time calculation.Study was sponsored by Salutaris Medical Devices, Ltd., a subsidiary of Salutaris Medical Devices, Inc. Hamilton and Marsteller are founders of Salutaris Medical Devices, Inc. Drew, McGovern and Vitali are minor equity holders in Salutaris Medical Devices, Inc.
SU‐E‐T‐18: A Comparison of Planning Techniques for Bilateral Reconstructed Chest Wall Patients Undergoing Whole Breast Irradiation
Authors: Volpe T , Margiasso R , Saleh Z , Kuo L , Hong L , Ballangrud A , Gelblum D , Zinovoy M , Deasy J , Tang X 
Published: June 2015

Purpose:As we continuously see more bilateral reconstructed chest wall cases, new challenges are being presented to deliver left‐sided breast irradiation. We herein compare three Deep Inspiration Breath Hold (DIBH) planning techniques (tangents, VMAT, and IMRT) and two free breathing techniques (VMAT and IMRT).Methods:Three left‐sided chest wall patients with bilateral implants were studied. Tangents, VMAT, and IMRT plans were created for DIBH scans. VMAT and IMRT plans were created for free breathing scans. All plans were normalized so that 95% of the prescription dose was delivered to 95% of the planning target volume (PTV). The maximum point dose was constrained to less than 120% of the prescription dose. Since the success of DIBH delivery largely depends on patient's ability to perform consistent breath hold during beam on time, smaller number of Monitor Units (MU) is in general desired. For each patient, the following information was collected to compare the planning techniques: heart mean dose, left and right lung V20 Gy, contra‐lateral (right) breast mean dose, cord max dose, and MU.Results:The average heart mean dose over all patients are 1561, 692, 985, 1245, and 1121 cGy, for DIBH tangents, VMAT, IMRT, free breathing VMAT and IMRT, respectively. For left lung V20 are 60%, 28%, 26%, 30%, and 29%. For contra‐lateral breast mean dose are 244, 687, 616, 783, 438 cGy. MU are 253, 853, 2048, 1035, and 1874 MUs.Conclusion:In the setting of bilateral chest wall reconstruction, opposed tangent beams cannot consistently achieve desired heart and left lung sparing. DIBH consistently achieves better healthy tissue sparing. VMAT appears to be preferential to IMRT for planning and delivering radiation to patients with bilaterally reconstructed chest walls being treated with DIBH.
SU‐E‐T‐19: A Comparison of the Dosimetric Effects of Brass Mesh and Superflab Boluses
Authors: Irwin JS , Gong J , Pavord D 
Published: June 2015

Purpose:We compared the dosimetric effects of brass mesh (Whiting and Davis, Attleboro Falls, MA) and Superflab (CNMC, Nashville, TN) boluses to verify equivalence between the two. Brass mesh bolus may be a convenient alternative to traditional bolus as it better conforms to the skin surface.Methods:Measurements were taken using a 6MV 10×10cm field produced by an Infinity linear accelerator (Elekta, Stockholm, Sweden) in a solid water phantom using a parallel plate ion chamber (Model 96035, Keithley Instruments, Cleveland, OH). Measurements compared 0.5cm and 1cm of Superflab to one to six layers of brass bolus mesh. Measurements were performed at depths from 0cm (‘skin’) to 10cm. Oblique beams were not studied.Results:Four layers of brass mesh were equivalent to 0.5cm Superflab within 5% at all depths. Six layers of brass compares most favorably with 0.5cm Superflab, with doses at all depths within 3%. Six layers of brass were not fully equivalent to 1cm Superflab, although the agreement was within 5% for depths greater than 3mm. Surface dose was 12% lower than 1cm Superflab. Surface dose can be up to 34% different between Superflab and brass mesh, but is less than 5% different with 4–6 layers of brass when compared to 0.5cm Superflab. To achieve surface dose agreement better than 5% compared to 1cm Superflab, more than 6 layers would be needed. The attenuation at depth was a maximum of 0.17cm per layer.Conclusion:Between four and six layers of brass mesh can be equivalent to 0.5cm Superflab, depending on the level of agreement desired. Equivalence within 5% at all depths to 1cm Superflab was not achieved even with six layers. This data agrees with measurements taken by Utsunomiya et al. (2010). More point measurements at shallower depths should be taken prior to clinical implementation of brass bolus mesh.
SU‐E‐T‐26: A Dosimetric Comparison of Two Treatment Setups for Lung Stereotactic Body Radiation Therapy (SBRT) Patients
Authors: Lewis D , Wang X , Gao S , Nitsch P , Pollard J , Sadagopan R , Balter P 
Published: June 2015

Purpose:To assess the feasibility of treating lung SBRT patients with the ipsilateral arm adducted beside the body instead of elevated above the head.Methods:Patients receiving lung SBRT at our institution are typically treated with both arms raised above their head. However, several patients had difficulty maintaining their arms in an elevated position. In this study, lung SBRT patients who underwent PET‐CT imaging with an adducted ipsilateral arm were selected to investigate the dosimetric effects of this treatment setup. PET‐CT datasets were fused with treatment planning CT images to simulate the adducted arm position. One VMAT treatment plan was created per patient using the Pinnacle treatment planning system. Plans were optimized to achieve minimal dose to the ipsilateral arm while keeping the target coverage and critical structure doses within clinical limits. The target dose coverage, conformity index (CI) for the target, and DVHs of critical structures for the adducted arm plan were calculated. These parameters were compared with the clinical plan and reported along with the mean and maximum doses of the ipsilateral arm.Results:The target coverage, CI and DVHs for the adducted arm plans of two patients (one with peripheral lesion and one with central lesion) were comparable with the clinical plans. Dose constraints for the chest wall limited further reduction of ipsilateral arm doses for the peripheral lesion plan. The mean ipsilateral arm doses for the central and peripheral lesions were 0.33 Gy and 2.4 Gy, respectively. The maximum ipsilateral arm doses for the central and peripheral lesions were 1.0 Gy and 6.2 Gy, respectively.Conclusion:The results suggested patients with central lung SBRT tumors were more suitable for treatment with the adducted arm position. More patients with various lung tumor locations will be studied to find optimal tumor locations for treatment with this arm position.
SU‐E‐T‐27: A Dosimetric Evaluation of Boney Anatomy Versus Fiducial Marker Alignment for the Treatment of Prostate Cancer Using Scanned Beam Proton Therapy
Authors: Freund D , Ding X , Zhang J , Rosen L , Wu H 
Published: June 2015

Purpose:In prostate proton radiotherapy, three fiducial markers are used for patient daily alignment. However fiducial alignment can change beamline heterogeneity in proton therapy. The purpose of this study is to determine the difference in fiducial and boney anatomy alignment for patient treatment.Methods and materials:Prostate cancer patients who received proton treatment were included in this study. 3 fiducial markers were implanted before the initial CT. All the patients were re‐CT'd every 2 weeks to check the fiducial marker position reproducibility as well as dosimetric consistence of target coverage. In geometry study, re‐CT were fused to the initial CT base on the boney anatomy and the average fiducial marker displacement was measured the centers of the fiducials. Dosimetrically, the initial plan was recalculated directly to re‐CT image set based on the boney alignment and fiducial alignment to determine the difference from daily treatment. Prostate coverage and hotspots were evaluated using the dose to 98% of the CTV (D98) and dose to 2% (D2), respectively.Results:The shift from the initial 6 patient CT image sets resulted in an average change in the fiducial location of 5.70 +/− 3 mm. Dosimetric comparison from a single patient revealed that differences from the planned dose resulted from both boney and fiducial alignment. Planned clinical treatment volume coverage resulted in a D98 of 70.44Gy and D2 of 70.84Gy compared to a D98 of 70.13Gy and D2 70.94Gy for boney alignment and a D98 of 70.08Gy and D2 71.18Gy for fiducial alignment respectively.Conclusion:This study demonstrates that with boney anatomy alignment there is little change to CTV coverage and only slightly worse CTV coverage and hotspot production with fiducial alignment. An increase patient cohort and further investigation is necessary to determine the whether boney alignment can help better control dose heterogeneity.
SU‐E‐T‐28: A Dosimetric Evaluation of IMRT Versus 4 Arc VMAT in the Treatment of Bilateral Head and Neck Cancer Using Concavity Ratio Defined PTVs
Authors: Ulizio V , Pearson D 
Published: June 2015

Purpose:VMAT has been shown to produce dosimetrically equivalent or superior plans than step and shoot IMRT for many different common cancer types. Bilateral H&N treatment plans are particularly challenging due to the concave shape of the target volume. We aim to compare the two techniques for various levels of concavity and we quantify the concavity of the target, and thus the difficulty of the plan, with a simple but novel ratio.Methods:20 bilateral H&N patients were chosen for this study, all with different concavity ratios (CR). The original treatments were generated using 9‐field 6 MV IMRT. The plans were then converted to 4 arc VMAT and planned using the same constraints. A ratio was created to quantify the concave shape of each PTV. The patients were then initially split into two categories; CR >2 and CR<2. Each plan was evaluated for two conformity indices, as well as OAR doses.Results:Initial results show better IMRT conformity indexes, averaged over all patients. The spinal cord maximum dose was lower for VMAT but the mandible mean dose was higher. The parotid mean dose was lower in VMAT plans that had CR<2, but higher with CR>2. This was also the case for the oral cavity mean dose and the mandible maximum dose.Conclusion:In the preliminary results, VMAT plans with CR< 2 spare OARs better. The conformity indices in these plans are worse but are insignificant. The RTOG conformity index as well as OAR sparing, excluding the spinal cord, is significantly worse when CR>2. Thus, when a patient is targeted, the CR should be calculated and if the ratio is below two then it should be planned with VMAT, but if the ratio is above two then the traditional IMRT planning should be used.
SU‐E‐T‐35: A General Fill Factor Definition Serving to Characterise the MLC Misalignment Detection Capabilities of Two‐Dimensional Detector Arrays
Authors: Stelljes T.S. , Looe H.K. , Harder D. , Poppe B. 
Published: June 2015

Purpose:To present a general definition of the fill factor realistically characterizing the “field coverage”, i.e. the MLC misalignment detection capabilities of a detector array.Methods:According to Gago‐Arias et al.1 the fill factor of a 2D array is defined as the ratio of the area enclosed by the FWHM of the fluence response function KM(x) of a single detector and its cell area defined by the detector spacing. More generally ‐ accounting also for the possible overlap between FWHM's of neighboured detectors ‐ the fill factor is here defined as that fraction of the sum of the detector cell areas in which a defined MLC misalignment is detectable when the induced percentage signal changes exceed a detection threshold d. Ideally the generalized fill factor may reach 100 %. With user code EGS_chamber and a 2 MeV photon slit beam 0.25 mm wide, both types of the fill factor were calculated for an array with total cell area 100 cm2 for chamber widths 1–9 mm, using =1mm, d=5%.Results:For single chamber width 5 mm, fill factors were 0.49 (FWHM) and 0.61 (generalized). For chamber width 2 mm the FWHM fill factor was 0.13 whereas the generalized fill factor was 0.32. For chamber widths above 7 mm, the FWHM fill factor exceeds unity, and the general fill factor is exactly 1.00.Conclusions:An updated fill factor definition is introduced which, as a generalization of the FWHM‐based definition, more closely estimates the performance of small array chambers and gives a realistic value in the case of overlapping sensitive areas of neighboured chambers. References:1A. Gago‐Arias, L. Brualla‐Gonzalez, D.M. Gonzalez‐Castano, F. Gomez, M.S. Garcia, V.L. Vega, J.M. Sueiro, J. Pardo‐Montero, “Evaluation of chamber response function influence on IMRT verification using 2D commercial detector arrays,” Phys. Med. Biol. 57, 2005–2020 (2012).
SU‐E‐T‐40: A Method for Improving Dose Gradient for Robotic Radiosurgery
Authors: Li T , Burton S , Flickinger J , Heron D E , Huq M Saiful 
Published: June 2015

Purpose:For targets with substantial volume, collimators of relatively large sizes are usually selected to minimize the treatment time in robotic radiosurgery. Their large penumbrae may adversely affect the dose gradient around the target. In this study, we implement and evaluate an inner‐shell planning method to increase the dose gradient.Methods:Ten patients previously treated with CyberKnife M6 system were randomly selected with the only criteria that PTV be larger than 2cm3. A new plan was generated for each patient, in which the PTV was split into two regions: an inner shell and a core, where the core was created by shrinking the PTV by 5mm using 3D erosion, and the shell was obtained by subtracting the core from the PTV; then a 7.5mm Iris collimator was exclusively applied to the shell, with other appropriate collimators applied to the core depending on its size. The optimization objective functions and constraints were kept the same as the corresponding clinical plans. The results were analyzed for V12Gy, V9Gy, V5Gy, and gradient index (GI).Results:Volume reduction is found for the inner‐shell method at all studied dose levels as compared to the clinical plans. The absolute dose volume reduction ranged from 0.05cm3 to 18.5cm3 with a mean of 5.6cm3 for 12Gy, from 0.2cm3 to 38.1cm3 with a mean of 9.8cm3 for 9Gy, and from 1.5cm3 to 115.7cm3 with a mean of 24.8cm3 for 5Gy, respectively. The relative GI reduction ranged from 3.2% to 23.6%, with a mean of 12.6%. Paired t‐test for GI has a p‐value of 0.0014. The range for treatment time increase is from −3 min to 20 min, with a mean of 7.0 min.Conclusion:The inner‐shell planning method can significantly increase the dose gradient outside the PTV, while maintaining good coverage, conformity, and reasonable treatment time.