Skin Dose Reduction Research Articles

Feasibility of a Skin Dose Reduction for Nasopharyngeal Carcinoma Treated With High-Intensity-Modulated Delivery Techniques.

Acute skin toxicity observed in radiotherapy treatment of head and neck cancer is a big concern. The purpose of this work is to evaluate the feasibility of a skin dose reduction in the treatment of nasopharyngeal carcinoma without compromising the overall plan quality. This research focused on comparison of the skin dose reduction that can be obtained for the main high conformal radiotherapy delivery techniques. Sixteen cases of early-stage nasopharyngeal carcinoma were included in this study. For each case, a dynamic intensity-modulated radiation therapy, a volumetric modulated arc therapy, and a helical tomotherapy treatment plans were performed with and without the skin as a sensitive structure in the inverse plan optimization. The dosimetric results obtained for the different treatment techniques and plan optimizations were compared. Dose–volume histogram cutoff points of D95%, D98%, and the homogeneity index were used for target comparison, while Dmean and Dmax/D1cc were used for the organs at risk. The skin volume receiving 5 Gy and then 10 to 70 Gy of radiation dosage registered at step of 10 Gy and Dmean were used for the skin dose comparison. One-way analysis of variance was used to assess the dosimetric results obtained for the different types of treatment plans and techniques investigated. A total of 96 treatment plans were analyzed. When the neck skin was considered in the treatment optimization process, the skin volume that received more than 30 Gy was reduced by 3.7% for dynamic intensity modulated, 4.1% for volumetric modulated arc, and 4.3% for dynamic intensity modulated, while the target dose coverage and organs at risk dosages remained unvaried (p > .05).

Influence of a Commercial Lead Apron on Patient Skin Dose Delivered During Oral and Maxillofacial Examinations under Cone Beam Computed Tomography (CBCT).

The purpose of this paper is to investigate the impact of a commercial lead apron on patient skin dose delivered during maxillofacial CBCT in five critical regions by means of solid-state-dosimetry. Five anatomical regions (thyroid gland, left and right breast, gonads, back of the phantom torso) in an adult female anthropomorphic phantom were selected for dose measurement by means of the highly sensitive solid-state dosimeter QUART didoSVM. Ten repeated single exposures were assessed for each patient body region for a total of five commercial CBCT devices with and without a lead apron present. Shielded and non-shielded exposures were compared under the paired Wilcoxon test, with absolute and relative differences computed. Reproducibility was expressed as the coefficient of variation (CV) between the 10 repeated assessments. The highest doses observed at skin level were found at the thyroid (mean shielded ± SD: 450.5 ± 346.7 μGy; non-shielded: 339.2 ± 348.8 μGy, p = 0.4922). Shielding resulted in a highly significant (p < 0.001) 93% dose reduction in skin dose in the female breast region with a mean non-shielded dose of approximately 35 μGy. Dose reduction was also significantly lower for the back-region (mean: -65%, p < 0.0001) as well as for the gonad-region (mean: -98%, p < 0.0001) in the shielded situation. Reproducibility was inversely correlated to skin dose (Rspearman = -0.748, p < 0.0001) with a mean CV of 10.45% (SD: 24.53 %). Skin dose in the thyroid region of the simulated patient was relatively high and not influenced by the lead apron, which did not shield this region. Dose reduction by means of a commercial lead apron was significant in all other regions, particularly in the region of the female breast.

Bolus Effect to Reduce Skin Dose of the Contralateral Breast During Breast Cancer Radiation Therapy

Bolus Effect to Reduce Skin Dose of the Contralateral Breast During Breast Cancer Radiation Therapy

Influence of exposure and geometric parameters on absorbed doses associated with common neuro-interventional procedures

PurposeThe purpose of this study was to investigate the effects of routine exposure parameters on patient’s dose during neuro-interventional radiology procedures. MethodsWe scrutinized the routine radiological exposure parameters during 58 clinical neuro-interventional procedures such as, exposure direction, magnification, frame rate, and distance between image receptor to patient’s body and evaluate their effects on patient’s dose using an anthropomorphic phantom. Radiation dose received by the occipital region, ears and eyes of the phantom were measured using MOSkin detectors. ResultsDSA imaging technique is a major contributor to patient’s dose (80.9%) even though they are used sparingly (5.3% of total frame number). The occipital region of the brain received high dose largely from the frontal tube constantly placed under couch (73.7% of the total KAP). When rotating the frontal tube away from under the couch, the radiation dose to the occipital reduced by 40%. The use of magnification modes could increase radiation dose by 94%. Changing the image receptor to the phantom surface distance from 10 to 40cm doubled the radiation dose received by the patient’s skin at the occipital region. ConclusionOur findings provided important insights into the contribution of selected fluoroscopic exposure parameters and their impact on patient’s dose during neuro-interventional radiology procedures. This study showed that the DSA imaging technique contributed to the highest patient’s dose and judicial use of exposure parameters might assist interventional radiologists in effective skin and eye lens dose reduction for patients undergoing neuro-interventional procedures.

Real-time colour pictorial radiation monitoring during coronary angiography: effect on patient peak skin and total dose during coronary angiography.

The aim of this study was to evaluate whether a real-time (RT) colour pictorial radiation dose monitoring system reduces patient skin and total radiation dose during coronary angiography and intervention. Patient demographics, procedural variables and radiation parameters were recorded before and after institution of the RT skin dose recording system. Peak skin dose as well as traditionally available measures of procedural radiation dose were compared. A total of 1,077 consecutive patients underwent coronary angiography, of whom 460 also had PCI. Institution of the RT skin dose recording system resulted in a 22% reduction in peak skin dose after accounting for confounding variables. Radiation dose reduction was most pronounced in those having PCI but was also seen over a range of subgroups including those with prior coronary artery bypass surgery, high BMI, and with radial arterial access. This was associated with a significant reduction in the number of patients placed at risk of skin damage. Similar reductions in parameters reflective of total radiation dose were also demonstrated after institution of RT radiation monitoring. Institution of an RT skin dose recording reduced patient peak skin and total radiation dose during coronary angiography and intervention. Consideration should be given to widespread adoption of this technology.

Planning Considerations for Skin Dose Reduction in Proton Beam Accelerated Partial-Breast Irradiation

Planning Considerations for Skin Dose Reduction in Proton Beam Accelerated Partial-Breast Irradiation

복합부가여과에서 알루미늄 여과판 사용 시 양자검출효율과 화질평가를 통한 효율성 분석

본 연구는 복합부가여과에서 높은 원자번호 물질에서 발생된 특성방사선을 제거하기 위해 사용되는 알루미늄 여과판의 효율성을 분석하고자 양자검출효율, 화질평가를 실시하였다. 구리 0.1, 0.2, 0.3 mm 에 알루미늄 1mm 사용 전, 후를 평가하였다. IEC 규정에 의해 선질, 양자검출효율을 실험하고 화질평가는 PSNR, MAE, MSE, CNR, SNR 정성적 평가로는 국가암검진 흉부 평가표의 해상, 대조도 평가 7문항을 이용하였다. MTF 10, 50%에서 4.6, 2.54 cycle/mm 모두 동일했고 NPS, DQE, PSNR MAE, MSE, CNR, SNR, 정성적 평가는 모두 알루미늄 미사용 시 같거나 약간 우수했다. PSNR은 30 dB이상으로 모두 의미있는 수치였고 정성적 평가에서 T-test 검정은 p>0.05였다. 알루미늄 여과판은 광자검출효율과 화질 평가에서 사용 전, 후 큰 차이가 없으므로 특성 방사선 제거를 통한 피부선량 감소를 위해 사용됨이 효율적이라고 사료된다. This study analysed the effectiveness of aluminium(Al) filter in the added compound filtration for the removal of characteristic radiation from high atomic number material by DQE and image evaluation. 1mm Al was applied to each 0.1, 0.2, 0.3 mm copper and befere and after use were evaluated. Beam quality and DQE were tested by IEC regulations and image quality was evaluated by PSNR, MAE, MSE, CNR, SNR and qualitative analysis was performed by 7 items for resolution and contrast from chest x-ray criteria of national cancer checkup. MTF 10 and 50% were the same by 4.6, 2.54 cycle/mm and NPS, DQE, PSNR MAE, MSE, CNR, SNR and qualitative analysis were all the same or slightly better when Al was not used. PSNR is over 30dB and all significant and at the qualitative analysis, the p-value of t-test was over 0.05. The DQE and image quality evaluation have little difference between before and after use of Al filter and it is effective to use the Al filter for the reduction of skin dose by removal of characteristic radiation.

Potential for reduced radiation-induced toxicity using intensity-modulated arc therapy for whole-brain radiotherapy with hippocampal sparing.

The purpose of this study was to retrospectively investigate the accuracy, plan quality, and efficiency of using intensity‐modulated arc therapy (IMAT) for whole brain radiotherapy (WBRT) patients with sparing not only the hippocampus (following RTOG 0933 compliance criteria) but also other organs at risk (OARs). A total of 10 patients previously treated with nonconformal opposed laterals whole‐brain radiotherapy (NC‐WBRT) were retrospectively replanned for hippocampal sparing using IMAT treatment planning. The hippocampus was volumetrically contoured on fused diagnostic T1‐weighted MRI with planning CT images and hippocampus avoidance zone (HAZ) was generated using a 5 mm uniform margin around the hippocampus. Both hippocampi were defined as one paired organ. Whole brain tissue minus HAZ was defined as the whole‐brain planning target volume (WB‐PTV). Highly conformal IMAT plans were generated in the Eclipse treatment planning system for Novalis TX linear accelerator consisting of high‐definition multileaf collimators (HD‐MLCs: 2.5 mm leaf width at isocenter) and 6 MV beam for a prescription dose of 30 Gy in 10 fractions following RTOG 0933 dosimetric criteria. Two full coplanar arcs with orbits avoidance sectors were used. In addition to RTOG criteria, doses to other organs at risk (OARs), such as parotid glands, cochlea, external/middle ear canals, skin, scalp, optic pathways, brainstem, and eyes/lens, were also evaluated. Subsequently, dose delivery efficiency and accuracy of each IMAT plan was assessed by delivering quality assurance (QA) plans with a MapCHECK device, recording actual beam‐on time and measuring planed vs. measured dose agreement using a gamma index. On IMAT plans, following RTOG 0933 dosimetric criteria, the maximum dose to WB‐PTV, mean WB‐PTV D2%, and mean WB‐PTV D98% were 34.9±0.3 Gy,33.2±0.4 Gy, and 26.0±0.4 Gy, respectively. Accordingly, WB‐PTV received the prescription dose of 30 Gy and mean V30 was 90.5%±0.5%. The D100%, and mean and maximum doses to hippocampus were 8.4±0.3 Gy,11.2±0.3 Gy, and 15.6±0.4 Gy, on average, respectively. The mean values of homogeneity index (HI) and conformity index (CI) were 0.23×0.02 and 0.96×0.02, respectively. The maximum point dose to WB‐PTV was 35.3 Gy, well below the optic pathway tolerance of 37.5 Gy. In addition, compared to NC‐WBRT, dose reduction of mean and maximum of parotid glands from IMAT were 65% and 50%, respectively. Ear canals mean and maximum doses were reduced by 26% and 12%, and mean and maximum scalp doses were reduced by 9 Gy (32%) and 2 Gy (6%), on average, respectively. The mean dose to skin was 9.7 Gy with IMAT plans compared to 16 Gy with conventional NC‐WBRT, demonstrating that absolute reduction of skin dose by a factor of 2. The mean values of the total number of monitor units (MUs) and actual beam on time were 719×44 and 2.34×0.14 min, respectively. The accuracy of IMAT QA plan delivery was (98.1±0.8) %, on average, with a 3%/3 mm gamma index passing rate criteria. All of these plans were considered clinically acceptable per RTOG 0933 criteria. IMAT planning provided highly conformal and homogenous plan with a fast and effective treatment option for WBRT patients, sparing not only hippocampi but also other OARs, which could potentially result in an additional improvement of the quality life (QoL). In the future, we plan to evaluate the clinical potential of IMAT planning and treatment option with hippocampal and other OARs avoidance in our patient's cohort and asses the QoL of the WBRT patients, as well as simultaneous integrated boost (SIB) for the brain metastases diseases.PACS number: 87

SU-D-304-02: Magnetically Focused Proton Irradiation of Small Field Targets

Purpose: To investigate the use of magnetic focusing for small field proton irradiations. It is hypothesized that magnetic focusing will provide significant dose distribution benefits over standard collimated beams for fields less than 10 mm diameter. Methods: Magnets consisting of 24 segments of radiation hard samarium-cobalt adhered into hollow cylinders were designed and manufactured. Two focusing magnets were placed on a positioning track on our Gantry 1 treatment table. Proton beams with energies of 127 and 157 MeV, 15 and 30 mm modulation, and 8 mm initial diameters were delivered to a water tank using single-stage scattering. Depth dose distributions were measured using a PTW PR60020 diode detector and transverse profiles were measured with Gafchromic EBT3 film. Monte Carlo simulations were also performed - both for comparison with experimental data and to further explore the potential of magnetic focusing in silica. For example, beam spot areas (based on the 90% dose contour) were matched at Bragg depth between simulated 100 MeV collimated beams and simulated beams focused by two 400 T/m gradient magnets. Results: Preliminary experimental results show 23% higher peak to entrance dose ratios and flatter spread out Bragg peak plateaus for 8 mm focused beams compared with uncollimated beams. Monte Carlo simulations showed 21% larger peak to entrance ratios and a ∼9 fold more efficient dose to target delivery compared to spot-sized matched collimated beams. Our latest results will be presented. Conclusion: Our results suggest that rare earth focusing magnet assemblies could reduce skin dose and beam number while delivering dose to nominally spherical radiosurgery targets over a much shorter time compared to unfocused beams. Immediate clinical applications include those associated with proton radiosurgery and functional radiosurgery of the brain and spine, however expanded treatment sites can be also envisaged.

WE-AB-303-06: Combining DAO with MV + KV Optimization to Improve Skin Dose Sparing with Real-Time Fluoroscopy

Purpose: Real-time fluoroscopy may allow for improved patient positioning and tumor tracking, particularly in the treatment of lung tumors. In order to mitigate the effects of the imaging dose, previous studies have demonstrated the effect of including both imaging dose and imaging constraints into the inverse treatment planning object function. That method of combined MV+kV optimization may Result in plans with treatment beams chosen to allow for more gentle imaging beam-on times. Direct-aperture optimization (DAO) is also known to produce treatment plans with fluence maps more conducive to lower beam-on times. Therefore, in this work we demonstrate the feasibility of a combination of DAO and MV+kV optimization for further optimized real-time kV imaging. Methods: Therapeutic and imaging beams were modeled in the EGSnrc Monte Carlo environment, and applied to a patient model for a previously treated lung patient to provide dose influence matrices from DOSXYZnrc. An MV + kV IMRT DAO treatment planning system was developed to compare DAO treatment plans with and without MV+kV optimization. The objective function was optimized using simulated annealing. In order to allow for comparisons between different cases of the stochastically optimized plans, the optimization was repeated twenty times. Results: Across twenty optimizations, combined MV+kV IMRT resulted in an average of 12.8% reduction in peak skin dose. Both non-optimized and MV+kV optimized imaging beams delivered, on average, mean dose of approximately 1 cGy per fraction to the target, with peak doses to target of approximately 6 cGy per fraction. Conclusion: When using DAO, MV+kV optimization is shown to Result in improvements to plan quality in terms of skin dose, when compared to the case of MV optimization with non-optimized kV imaging. The combination of DAO and MV+kV optimization may allow for real-time imaging without excessive imaging dose. Financial support for the work has been provided in part by NIH Grant T32 EB002103, ACS RSG-13-313-01-CCE, and NIH S10 RR021039 and P30 CA14599 grants. The contents of this submission do not necessarily represent the official views of any of the supporting organizations.

SU-D-304-04: Pre-Clinical Feasibility Study for Intensity Modulated Grid Proton Therapy (IMgPT) Using a Newly Developed Delivery System

Purpose: The purpose of the current study was to characterize and evaluate intensity-modulated proton grid therapy (IMgPT) using a clinical proton beam. Methods: A TOPAS MC model of a new developmental mode (pre-clinical) of the Hitachi proton therapy system (PROBEAT) was used for simulation and characterization of proton grid therapy. TOPAS simulations of different energy ranges, depths and spot separation distances were performed. LET spectra for various energies and depths were produced with FLUKA MC code for evaluation potential interplay between planning parameters and their effect on the characterization of areas (valley) between spots. IMgPT planning aspects (spot spacing, skin dose, peak-to-valley ratios, beam selection, etc.) were evaluated for different phantom and patient cases. Raysearch software (v4.51) was used to perform the evaluation. Results: Calculated beam peak-to-valley ratios scenarios showed strong energy and depth dependence with ratios to be larger for higher energies and shallower depths. Peak-to-valley ratios for R90 range and for spot spacing of 1cm varied from 30% (E = 221.3 MeV, depth 30.6 cm) to 80% (E = 70.3 MeV, depth 4 cm). LET spectra calculations showed spectral hardening with depth, which might potential increase, spot separation distance and improve peak-to-valley ratios. IMgPT optimization, using constant spot spacing, showed skin dose reduction between peak regions of dose due to the irradiation of less skin. Single beam for bulky shallower tumors might be a potential candidate for proton grid therapy. Conclusions: Proton grid therapy using a clinical beam is a promising technique that reduces skin dose between peak regions of dose and may be suitable for the treatment of shallow tumors. IMgPT may be considered for use when bystander effects in off peak regions would be appropriate.

SU‐E‐T‐704: Skin Dose in Proton Pencil Beam Scanning for Pediatric Patients

Purpose:Optimize intensity modulated proton therapy (IMPT) treatment planning guidelines with regard to skin dose reduction in pediatric patients.Methods:Phantom and patient CTs were used to evaluate skin dose using a pre‐clinical proton beam modeled using Monte Carlo (TOPAS) in a commercial radiotherapy planning system (RTP). Single‐spot and single‐beam doses were analyzed in phantom environment. Fractional surface dose was evaluated vs. spot spacing and maximum range for beams optimized for increasingly deep targets. Both RTP automatic variable spacing (0.5xσprojected) and constant spacing (0.2–1.2cm) were evaluated. 3 spine IMPT plans were obtained with/without objectives for skin dose, with automatic and constant spot spacing. Dosimetric parameters and spot weight/energy statistics were evaluated.Results:Single‐spot primary fluence depletion raises the spot axial relative skin dose above Bragg peak dose for E0&gt;139MeV. Dose heterogeneity and maximum skin dose increases with maximum beam energy and spot spacing non‐linearly. Exponential fitting of maximum skin‐to‐target dose ratio against spot spacing suggested an optimum constant spacing &lt;3mm for minimizing skin dose. Automatic spacing did not produce optimal results for deep tumors. For patient plans, heterogeneous and high skin dose were observed where &gt;50% MU weight was carried by spots with energy &gt;135MeV, and had spots &gt;155MeV. Introducing skin optimization objectives/constraints, decreased high energy spots weights, while that for &gt;135MeV spots increased. Hence, skin D50 increased with skin‐optimized plans, while coverage remained constant. Average dose, D1 and D0.1cc decreased compared to plans without skin objectives. Constant spacing did not produce superior skin dose distributions without skin optimization objectives.Conclusion:IMPT inverse planning can produce high skin doses with heterogeneous distributions, effects that can be mitigated via optimization. Careful coordination between RTP techniques and accurate skin dosimetric parameters will allow minimization of clinical skin effects and establishment of threshold doses for acute/late effects in pediatric population treated with IMPT.

PD4-03 A COMPARISON OF CALCULATED ABSORBED RADIATION ORGAN DOSES AND IMAGE QUALITY FOR ITERATIVE VERSUS FILTERED BACK PROJECTION CT IN KIDNEY STONE PATIENTS

You have accessJournal of UrologyImaging/Radiology: Uroradiology I1 Apr 2015PD4-03 A COMPARISON OF CALCULATED ABSORBED RADIATION ORGAN DOSES AND IMAGE QUALITY FOR ITERATIVE VERSUS FILTERED BACK PROJECTION CT IN KIDNEY STONE PATIENTS Rishi Modh, Akira Yamamoto, James Mason, Elizabeth Vorhis, Lori Deitte, Cyrus Monroe, Anna Mench, Rebecca H. Lamoureux, Izabella Lipnharski, Jacob Batson, Derek Lee, Carl Henriksen, Manuel Arreola, and Benjamin Canales Rishi ModhRishi Modh More articles by this author , Akira YamamotoAkira Yamamoto More articles by this author , James MasonJames Mason More articles by this author , Elizabeth VorhisElizabeth Vorhis More articles by this author , Lori DeitteLori Deitte More articles by this author , Cyrus MonroeCyrus Monroe More articles by this author , Anna MenchAnna Mench More articles by this author , Rebecca H. LamoureuxRebecca H. Lamoureux More articles by this author , Izabella LipnharskiIzabella Lipnharski More articles by this author , Jacob BatsonJacob Batson More articles by this author , Derek LeeDerek Lee More articles by this author , Carl HenriksenCarl Henriksen More articles by this author , Manuel ArreolaManuel Arreola More articles by this author , and Benjamin CanalesBenjamin Canales More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2015.02.315AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Methods commonly used to reduce patient radiation exposure, such as standard Filtered Back Projection CT (FBP CT), may still result in significant image noise and decreased image quality. Adaptive Iterative Dose Reduction (AIDR), a CT image reconstruction algorithm, has been touted to lower patient radiation dose while maintaining adequate diagnostic quality. Our group recently developed a validated method to estimate CT patient absorbed dose based on statistical modeling and post-mortem dosimetry. The purpose of this study is to determine absorbed dose in urinary stone patients undergoing FBP CT compared to AIDR CT and compare the quality of the scans. METHODS After IRB approval, we reviewed records of all patients who underwent stone protocol CT scan from 11/1/12 – 7/1/13 at our single institution which houses 2 ADR-capable and 4 FBP CT scanners, a modified form of random assignment. Clinical and radiological data was then recorded from patients found to have urinary tract stones. Two blinded, board-certified radiologists independently reviewed data sets for image quality (1–5), noise (1–3), and calculi (number, size, location),and discrepancies were resolved by a blinded third board-certified radiologist. Absorbed skin and internal abdominal organ doses were calculated using equations that utilize the scanner-reported CT dose Index (CTDI) and the patient central effective diameter. Statistical analysis was performed using Fisher's Exact and paired t tests. RESULTS Of the 54 patients who met inclusion criteria, 28 patients underwent FBP CT while 26 underwent AIDR. Both groups were similar in regard to gender, race, BMI(31.7 +/- 9.9), stone burden detected, image quality, and image noise. Absorbed skin dose was 42.9 ± 19.9 mGy for FBP CT and 27.4 ± 35.0 mGy (p<0.001) for AIDR CT, while mean internal organ doses were 20.12 ± 9.7 mGy (FBP CT) and 6.9 ± 3.8 mGy (p<0.001, ADIR). Mean CTDI for all stone protocol FBP CT studies was 31.4 ± 11.8 mGy compared to 15.4 ± 13.9 mGy (p<0.05) for AIDR CT. CONCLUSIONS In our random cohort and using a validated absorbed dose formula, urinary stone patients who underwent AIDR CT had 36% and 65% reduction in skin and internal organ dose (respectively) compared to FBP CT, without compromising scan readability. Measured CT output using CTDI did not correlate to calculated patient absorbed dose and should not be used as a valid patient dose parameter. AIDR technology decreases radiation doses in urinary stone formers undergoing stone protocol CT and may replace FBP CT as the standard of care in CT imaging. © 2015 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 193Issue 4SApril 2015Page: e87 Advertisement Copyright & Permissions© 2015 by American Urological Association Education and Research, Inc.MetricsAuthor Information Rishi Modh More articles by this author Akira Yamamoto More articles by this author James Mason More articles by this author Elizabeth Vorhis More articles by this author Lori Deitte More articles by this author Cyrus Monroe More articles by this author Anna Mench More articles by this author Rebecca H. Lamoureux More articles by this author Izabella Lipnharski More articles by this author Jacob Batson More articles by this author Derek Lee More articles by this author Carl Henriksen More articles by this author Manuel Arreola More articles by this author Benjamin Canales More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Single-Plane Magnetically Focused Elongated Small Field Proton Beams.

We previously performed Monte Carlo simulations of magnetically focused proton beams shaped by a single quadrapole magnet and thereby created narrow elongated beams with superior dose delivery characteristics (compared to collimated beams) suitable for targets of similar geometry. The present study seeks to experimentally validate these simulations using a focusing magnet consisting of 24 segments of samarium cobalt permanent magnetic material adhered into a hollow cylinder. Proton beams with properties relevant to clinical radiosurgery applications were delivered through the magnet to a water tank containing a diode detector or radiochromic film. Dose profiles were analyzed and compared with analogous Monte Carlo simulations. The focused beams produced elongated beam spots with high elliptical symmetry, indicative of magnet quality. Experimental data showed good agreement with simulations, affirming the utility of Monte Carlo simulations as a tool to model the inherent complexity of a magnetic focusing system. Compared to target-matched unfocused simulations, focused beams showed larger peak to entrance ratios (26% to 38%) and focused simulations showed a two-fold increase in beam delivery efficiency. These advantages can be attributed to the magnetic acceleration of protons in the transverse plane that tends to counteract the particle outscatter that leads to degradation of peak to entrance performance in small field proton beams. Our results have important clinical implications and suggest rare earth focusing magnet assemblies are feasible and could reduce skin dose and beam number while delivering enhanced dose to narrow elongated targets (eg, in and around the spinal cord) in less time compared to collimated beams.

The choice of IMRT for early-stage right breast cancer.

81 Background: The benefit of Intensity Modulated Radiation Therapy (IMRT) has been established for left breast cancer. However, IMRT is not routinely employed for right breast cancer. The purpose of this study is to (1) compare dosimetric parameters in women with early stage right breast cancer undergoing whole breast radiation therapy using 3-dimensional conformal radiation (3DCRT) versus intensity modulated radiation therapy (IMRT) (2) determine treatment planning and/or anatomical correlates for patients who may benefit from IMRT. Methods: IMRT versus 3DCRT treatment plans were compared for 20 consecutive female patients with early stage (T1-T2 N0M0 ) right breast cancer treated at our center from 1/2012 to 12/2012. The planned target volume (PTV), contoured according to the RTOG atlas guidelines, was prescribed to 46-8-50.4 Gy in 26-28 fractions with PTV coverage goal of ≥ 95 % receiving the prescription dose. Dosimetric and anatomic parameters: % right lung receiving 20 Gy (lung V20), maximum breast dose (Dmax), maximum skin dose (Dmax skin), chest wall separation (CWS) and medial gantry angle (MGA) were determined for each paired treatment plan. Wilcoxon-signed rank test was utilized to compare IMRT and 3DCRT dosimetric parameters. Univariate analysis was used to identify planning or anatomic correlates associated with favorable dosimetric outcomes. Results: The lung V20Gy for IMRT ( 10.86±2.81%) was significantly lower than for 3DCRT (12.92±3.45 %, p &lt; 0.043). IMRT significantly reduced Dmax to 53.79 ± 2.17 Gy from 56.7 ± 2.24 Gy with 3DCRT (p 0.001). 3DCRT yielded significantly higher Dmax skin (33.47±3.21 Gy) than IMRT (24.16 ±2.65 Gy, p&lt; 0.0001). Mean CWS and MGA were 22.4 ± 2.6 cm and 126 ± 5.1° respectively. There was a significant association between CWS and Dmax for 3DCRT (p &lt; 0.026). Conclusions: The most significant impact of IMRT for right breast cancer was the reduction of Dmax and Dmax skin, with a more tempered advantage in the reduction of lung V20. Reduction of maximum breast and skin dose harbors clinical relevance as it relates to acute skin toxicity, long- term fibrosis and adverse cosmetic outcomes. Chest wall separation may be a potential planning surrogate marker to determine which right-sided breast cancer patients may benefit from IMRT.

Reversed C-arm projection for reduction of focal skin radiation exposure: experimental analysis and first clinical experience

Radiodermatitis, predominantly over the right scapula, is a well-known complication of complex percutaneous coronary interventions (PCI). To reduce focal radiation exposure, we analyzed an inversed X-ray beam direction using a reversed C-arm position. On phantom experiment, we found that 130° right anterior oblique projection reduced skin dose over the right scapula by 98.2 % (P < 0.001) compared with conventional 50° left anterior oblique projection. A 73-year-old man with history of bypass surgery, multiple PCI and chronic radiodermatitis over the right scapula presented with recurrent chest pain. After successful PCI using the reversed C-arm projection, no aggravation of radiodermatitis was found.

SU-E-T-139: Evaluation of Surface, Peripheral,and Buildup Dose in MR-IGRT

Purpose: To determine the effect of the magnetic field on surface and buildup dose in radiotherapy using MR-IGRT, specifically measured with a Co-60 system. Methods: A commercially-available MR-IGRT system was used to measure surface, peripheral, and build-up dose due to thermoplastic head immobilization masks. Both radiographic (Kodak EDR2) and radiochromic (EBT2) film types were used for surface measurements. A small-volume ionization chamber was used for peripheral dose measurements. Several types of thermoplastic masks from three different manufacturers were chosen; radiochromic film was used to measure possible dose to skin under the masks. Comparisons were made using these masks with 6-MV photon beams delivered by a Varian Truebeam machine. Results: For a 10×10 cm field size at 100 SSD, the surface dose as normalized to maximum dose (at 0.5 cm) was determined to be about 30% as measured by both EDR and EBT2 films. Peripheral dose with an open 10x10 field at 10 cm depth matched previously published data for Co-60. Skin dose due to thermoplastic mask buildup was at least 30% higher (depending on mask construction) with Co-60 as compared to 6-MV due to its lower energy. Conclusion: While the magnetic field of an integrated MR-IGRT system is expected to reduce skin dose by sweeping away contamination electrons, the use of Co-60 introduces the added challenge of carefully choosing immobilization devices in order to preserve the skin-sparing effect of the MR. Drs. Green, Hu, and Mutic have served as consultants to ViewRay, Inc.

Contura Multi-Lumen Balloon Breast Brachytherapy Catheter: Comparative Dosimetric Findings of a Phase 4 Trial

Final dosimetric findings of a completed, multi-institutional phase 4 registry trial using the Contura Multi-Lumen Balloon (MLB) breast brachytherapy catheter to deliver accelerated partial breast irradiation (APBI) in patients with early-stage breast cancer are presented. Three dosimetric plans with identical target coverage were generated for each patient for comparison: multilumen multidwell (MLMD); central-lumen multidwell (CLMD); and central-lumen single-dwell (CLSD) loading of the Contura catheter. For this study, a successful treatment plan achieved ideal dosimetric goals and included the following: ≥ 95% of the prescribed dose (PD) covering ≥ 95% of the target volume (TV); maximum skin dose ≤ 125% of the PD; maximum rib dose ≤ 145% of the PD; and V150 ≤50 cc and V200 ≤ 10 cc. Between January 2008 and February 2011, 23 institutions participated. A total of 318 patients were available for dosimetric review. Using the Contura MLB, all dosimetric criteria were met in 78.93% of cases planned with MLMD versus 55.38% with the CLMD versus 37.66% with the CLSD (P ≤.0001). Evaluating all patients with the full range of skin to balloon distance represented, median maximum skin dose was reduced by 12% and median maximum rib dose by 13.9% when using MLMD-based dosimetric plans compared to CLSD. The dosimetric benefit of MLMD was further demonstrated in the subgroup of patients where skin thickness was <5 mm, where MLMD use allowed a 38% reduction in median maximum skin dose over CLSD. For patients with rib distance <5 mm, the median maximum rib dose reduction was 27%. Use of the Contura MLB catheter produced statistically significant improvements in dosimetric capabilities between CLSD and CLMD treatments. This device approach demonstrates the ability not only to overcome the barriers of limited skin thickness and close rib proximity, but to consistently achieve a higher standard of dosimetric planning goals.

DUAL-AXIS ROTATIONAL CORONARY ANGIOGRAPHY CAN REDUCE PEAK SKIN DOSE AND SCATTERED DOSE: A PHANTOM STUDY

Objectivesto evaluate the peak skin dose received by the patient and scattered dose to the operator during the dual-axis rotational coronary angiography and compared to standard coronary angiography.MethodsAn anthropomorphic phantom...

SU‐C‐217A‐06: A Collaborative Approach to Dose Optimization in Fluoroscopy Guided Lumbar Spine Injection Procedures

Purpose: To observe and evaluate technical acquisition and operating procedures used for lumbar spine injection procedures under fluoroscopy guidance performed by multiple neuroradiologists for potential patient dose reduction opportunities. Methods: Baseline skin dose measurements were acquired on patients undergoing lumbar spine injection procedures on a biplane fluoroscopy unit. Optically stimulated luminescent dosimeters were placed on the patient's abdomen corresponding to the anterior‐posterior plane beam entrance location and on the patient's right side corresponding to the lateral plane beam entrance location. Technical acquisition factors, treated levels, and patient demographics were recorded. In addition, observations were made of operating procedures such as the use of collimation and magnification, patient and equipment positioning, beam angulations, and exposure techniques used by individual neuroradiologists. Results: Baseline data and observations were reviewed with neuroradiologists. Opportunities to reduce dose were discussed and a series of acquisition and practice changes accepted. Changes were implemented and skin dose measurements repeated. Results showed a reduction in skin dose of 64% and 79% respectively for anterior‐posterior and lateral planes from baseline data. No adverse outcomes to procedure time, fluoroscopy time, or image quality were observed. Conclusions: Practices among physicians can vary substantially. Collaboration and standardization of acquisition and operating procedures can Result in substantial dose reduction for patients without compromising image quality or clinical productivity.