Dynamic Electron Arc Radiotherapy Research Articles

Technical Note: A dose calculation framework for dynamic electron arc radiotherapy (DEAR) using VirtuaLinac Monte Carlo simulation tool.

Dynamic electron arc radiotherapy (DEAR) is a novel dynamic technique that achieves highly conformal dose through simultaneous couch and gantry motion during delivery. The purpose of this study is to develop a framework integrating a Monte Carlo dose engine (VirtuaLinac) to a treatment planning system (TPS, Eclipse) for DEAR. A quality assurance (QA) procedure is also developed. The interfaces include the following: computed tomography image export and conversion for VirtuaLinac; VirtuaLinac computation tasks management through application programming interface (API); and dose matrix processing and evaluation. The framework was validated with both static beam and DEAR plan with a 3×3cm2 cutout for both 6 and 9MeV electrons. Verification plans for DEAR were created on flat phantom and a hybrid dose calculation technique was developed which convolves precalculated small field kernel with the beam trajectory, and the resulting dose was compared with the full VirtuaLinac calculation and film measurement. Excellent agreement between VirtuaLinac and eMC was observed with three-dimensional γ pass rate of 98% at 1%/1mm criteria for both 6 and 9MeV electrons. Film measurement shows two-dimensional (2D) γ passing rate of 99.8 % (6MeV) and 97.1% (9MeV) at 2%/2mm criteria. For DEAR plans the comparison of VirtuaLinac and measurement shows the 2D γ passing rates of 94% at 2%/2mm for 6MeV. The dose distributions from hybrid method in phantom are identical to the full VirtuaLinac simulations, but can be done instantly. A framework has been developed for DEAR dose calculation using VirtuaLinac Monte Carlo dose engine. The VirtuaLinac calculated dose was validated against measurement. A feasible and practical DEAR QA method has been developed for dose measurement in phantom. The hybrid dose calculation technique is efficient and suitable for DEAR QA purpose.

A Technique to Irradiate Scar-like Line Target With Dynamic Electron Arc Radiation Therapy

For superficial target such as surgical scar, standard radiotherapy technique is the static electron beam. Its use can become cumbersome when target area is long and/or the skin has large curvature, because the combination of multiple beams often produces hot and cold spots in the junction regions and surrounding healthy tissues can be over-irradiated. In addition, manual setup of each field is required which is often impractical clinically. In this study, we investigate a new technique to irradiate any line target with the dynamic electron arc radiotherapy (DEAR) where both the couch position and Linac gantry angle are synchronized with the radiation beam. The electron applicator is kept in DEAR to preserve beam penumbra. To avoid collision between Linac and patient, couch is moved simultaneously with gantry rotation to maintain a constant source to skin distance (SSD) and an en face beam direction at all times. The DEAR plan, in the form of XML, follows the MU-position trajectory model using control point (CP) similar to IMRT and VMAT, is currently deliverable on Truebeam Linac in research mode. The line target is represented by a series of connected points whose 3D coordinates are first extracted from treatment planning system. They are used to determine the gantry angle, couch position, collimator angle, and MU at each CP. The XML plan also includes some fixed parameters: energy, applicator, cutout, and dose rate. The plan and CT are fed to the Virtual Linac Monte Carlo simulation platform for the final dose calculation and prescription normalization. Finally the plan is verified dosimetrically on phantom with radiochromic film. Various target orientations and lengths were studied on flat, cylindrical, and anthropomorphic phantoms. Either 6 or 9 MeV electron beams were chosen depending on the depth of the target. The smallest applicator (6 × 6 cm2) is used for increased clearance. Cutout shape is in square (3 × 3 cm2), rectangular (3 × 1 cm2), or circular (dia = 3 cm). Dose rate is based on the prescription dose, speed of couch motion and gantry rotation, and delivery time. Plans are generated in both forward and reverse motion directions. Any number of setup beams during the motion trajectory can be created and mode up during the dry run. Gantry angle is chosen so that beam is always perpendicular to the target. For circular cutout, the collimator angle is fixed; for others, it is parallel to the scanning direction. Finally, the MU at each CP is proportional to the distance between the current and the neighboring target points. For a 20 cm long target with 200 cGy prescription dose, the delivery can be completed within 2 minutes at dose rate of 1000 MU/min. The film measurements agree well with the Monte Carlo dose calculations. We have developed a technique to irradiate any line target using DEAR. It improves dose distributions substantially over the standard electron beam. Further investigations are in progress to expand into two dimensional targets.

TH‐AB‐BRB‐05: Using a Research Real‐Time Control Interface to Go Beyond Dynamic MLC Tracking

Current state‐of‐the art digital C‐arm medical linear accelerators are capable of delivering radiation treatments with high level of automation, which affords coordinated motions of gantry, couch, and multileaf collimator (MLC) with dose rate modulations. The new machine capacity has shown the potential to bring substantially improved radiation dosimetry and/or delivery efficiency to many challenging diseases. Combining an integrated beam orientation optimization algorithm with automated machine navigation, markedly improved dose conformity has been achieved using 4ρ therapy. Trajectory modulated radiation therapy (TMAT) can be used to deliver highly conformal dose to partial breast or to carve complex dose distribution for therapy involving extended volumes such as total marrow and total lymph node treatment. Dynamic electron arc radiotherapy (DEAR) not only overcomes the deficiencies of conventional electron therapy in dose conformity and homogeneity but also achieves so without patient‐specific shields. The combination of MLC and couch tracking provides improved motion management of thoracic and abdominal tumors. A substantial body of work has been done in these technological advances for clinical translation. The proposed symposium will provide a timely review of these exciting opportunities. Learning Objectives: Recognize the potential of using digitally controlled linacs for clinically significant improvements in delivered dose distributions for various treatment sites. Identify existing approaches to treatment planning, optimization and delivery for treatment techniques utilizing the advanced functions of digital linacs and venues for further development and improvement. Understand methods for testing and validating delivery system performance. Identify tools available on current delivery systems for implementation and control for such treatments. Obtain the update in clinical applications, trials and regulatory approval.K. Sheng, NIH U19AI067769, NIH R43CA183390, NIH R01CA188300, Varian Medical SystemsV. Yu, Varian Medical Systems, AAPM Summer Undergraduate Fellowship, NSF graduate fellowshipS. Nill, Elekta AB. Cancer Research UK under Programme C33589/A19727, NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.

TH‐AB‐BRB‐04: Quality Assurance for Advanced Digital Linac Implementations

Current state‐of‐the art digital C‐arm medical linear accelerators are capable of delivering radiation treatments with high level of automation, which affords coordinated motions of gantry, couch, and multileaf collimator (MLC) with dose rate modulations. The new machine capacity has shown the potential to bring substantially improved radiation dosimetry and/or delivery efficiency to many challenging diseases. Combining an integrated beam orientation optimization algorithm with automated machine navigation, markedly improved dose conformity has been achieved using 4ρ therapy. Trajectory modulated radiation therapy (TMAT) can be used to deliver highly conformal dose to partial breast or to carve complex dose distribution for therapy involving extended volumes such as total marrow and total lymph node treatment. Dynamic electron arc radiotherapy (DEAR) not only overcomes the deficiencies of conventional electron therapy in dose conformity and homogeneity but also achieves so without patient‐specific shields. The combination of MLC and couch tracking provides improved motion management of thoracic and abdominal tumors. A substantial body of work has been done in these technological advances for clinical translation. The proposed symposium will provide a timely review of these exciting opportunities. Learning Objectives: Recognize the potential of using digitally controlled linacs for clinically significant improvements in delivered dose distributions for various treatment sites. Identify existing approaches to treatment planning, optimization and delivery for treatment techniques utilizing the advanced functions of digital linacs and venues for further development and improvement. Understand methods for testing and validating delivery system performance. Identify tools available on current delivery systems for implementation and control for such treatments. Obtain the update in clinical applications, trials and regulatory approval.K. Sheng, NIH U19AI067769, NIH R43CA183390, NIH R01CA188300, Varian Medical SystemsV. Yu, Varian Medical Systems, AAPM Summer Undergraduate Fellowship, NSF graduate fellowshipS. Nill, Elekta AB. Cancer Research UK under Programme C33589/A19727, NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.

TH‐AB‐BRB‐01: Trajectory Modulated Arc Therapy: Application to Partial Breast Irradiation

Current state‐of‐the art digital C‐arm medical linear accelerators are capable of delivering radiation treatments with high level of automation, which affords coordinated motions of gantry, couch, and multileaf collimator (MLC) with dose rate modulations. The new machine capacity has shown the potential to bring substantially improved radiation dosimetry and/or delivery efficiency to many challenging diseases. Combining an integrated beam orientation optimization algorithm with automated machine navigation, markedly improved dose conformity has been achieved using 4ρ therapy. Trajectory modulated radiation therapy (TMAT) can be used to deliver highly conformal dose to partial breast or to carve complex dose distribution for therapy involving extended volumes such as total marrow and total lymph node treatment. Dynamic electron arc radiotherapy (DEAR) not only overcomes the deficiencies of conventional electron therapy in dose conformity and homogeneity but also achieves so without patient‐specific shields. The combination of MLC and couch tracking provides improved motion management of thoracic and abdominal tumors. A substantial body of work has been done in these technological advances for clinical translation. The proposed symposium will provide a timely review of these exciting opportunities. Learning Objectives: Recognize the potential of using digitally controlled linacs for clinically significant improvements in delivered dose distributions for various treatment sites. Identify existing approaches to treatment planning, optimization and delivery for treatment techniques utilizing the advanced functions of digital linacs and venues for further development and improvement. Understand methods for testing and validating delivery system performance. Identify tools available on current delivery systems for implementation and control for such treatments. Obtain the update in clinical applications, trials and regulatory approval.K. Sheng, NIH U19AI067769, NIH R43CA183390, NIH R01CA188300, Varian Medical SystemsV. Yu, Varian Medical Systems, AAPM Summer Undergraduate Fellowship, NSF graduate fellowshipS. Nill, Elekta AB. Cancer Research UK under Programme C33589/A19727, NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.

TH‐AB‐BRB‐02: ET‐Reloaded

Current state‐of‐the art digital C‐arm medical linear accelerators are capable of delivering radiation treatments with high level of automation, which affords coordinated motions of gantry, couch, and multileaf collimator (MLC) with dose rate modulations. The new machine capacity has shown the potential to bring substantially improved radiation dosimetry and/or delivery efficiency to many challenging diseases. Combining an integrated beam orientation optimization algorithm with automated machine navigation, markedly improved dose conformity has been achieved using 4ρ therapy. Trajectory modulated radiation therapy (TMAT) can be used to deliver highly conformal dose to partial breast or to carve complex dose distribution for therapy involving extended volumes such as total marrow and total lymph node treatment. Dynamic electron arc radiotherapy (DEAR) not only overcomes the deficiencies of conventional electron therapy in dose conformity and homogeneity but also achieves so without patient‐specific shields. The combination of MLC and couch tracking provides improved motion management of thoracic and abdominal tumors. A substantial body of work has been done in these technological advances for clinical translation. The proposed symposium will provide a timely review of these exciting opportunities. Learning Objectives: Recognize the potential of using digitally controlled linacs for clinically significant improvements in delivered dose distributions for various treatment sites. Identify existing approaches to treatment planning, optimization and delivery for treatment techniques utilizing the advanced functions of digital linacs and venues for further development and improvement. Understand methods for testing and validating delivery system performance. Identify tools available on current delivery systems for implementation and control for such treatments. Obtain the update in clinical applications, trials and regulatory approval.K. Sheng, NIH U19AI067769, NIH R43CA183390, NIH R01CA188300, Varian Medical SystemsV. Yu, Varian Medical Systems, AAPM Summer Undergraduate Fellowship, NSF graduate fellowshipS. Nill, Elekta AB. Cancer Research UK under Programme C33589/A19727, NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.

TH‐AB‐BRB‐00: Research Opportunities with Digital Linear Accelerators

Current state‐of‐the art digital C‐arm medical linear accelerators are capable of delivering radiation treatments with high level of automation, which affords coordinated motions of gantry, couch, and multileaf collimator (MLC) with dose rate modulations. The new machine capacity has shown the potential to bring substantially improved radiation dosimetry and/or delivery efficiency to many challenging diseases. Combining an integrated beam orientation optimization algorithm with automated machine navigation, markedly improved dose conformity has been achieved using 4ρ therapy. Trajectory modulated radiation therapy (TMAT) can be used to deliver highly conformal dose to partial breast or to carve complex dose distribution for therapy involving extended volumes such as total marrow and total lymph node treatment. Dynamic electron arc radiotherapy (DEAR) not only overcomes the deficiencies of conventional electron therapy in dose conformity and homogeneity but also achieves so without patient‐specific shields. The combination of MLC and couch tracking provides improved motion management of thoracic and abdominal tumors. A substantial body of work has been done in these technological advances for clinical translation. The proposed symposium will provide a timely review of these exciting opportunities. Learning Objectives: Recognize the potential of using digitally controlled linacs for clinically significant improvements in delivered dose distributions for various treatment sites. Identify existing approaches to treatment planning, optimization and delivery for treatment techniques utilizing the advanced functions of digital linacs and venues for further development and improvement. Understand methods for testing and validating delivery system performance. Identify tools available on current delivery systems for implementation and control for such treatments. Obtain the update in clinical applications, trials and regulatory approval.K. Sheng, NIH U19AI067769, NIH R43CA183390, NIH R01CA188300, Varian Medical SystemsV. Yu, Varian Medical Systems, AAPM Summer Undergraduate Fellowship, NSF graduate fellowshipS. Nill, Elekta AB. Cancer Research UK under Programme C33589/A19727, NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.

TH‐AB‐BRB‐03: 4n Radiotherapy

Current state‐of‐the art digital C‐arm medical linear accelerators are capable of delivering radiation treatments with high level of automation, which affords coordinated motions of gantry, couch, and multileaf collimator (MLC) with dose rate modulations. The new machine capacity has shown the potential to bring substantially improved radiation dosimetry and/or delivery efficiency to many challenging diseases. Combining an integrated beam orientation optimization algorithm with automated machine navigation, markedly improved dose conformity has been achieved using 4ρ therapy. Trajectory modulated radiation therapy (TMAT) can be used to deliver highly conformal dose to partial breast or to carve complex dose distribution for therapy involving extended volumes such as total marrow and total lymph node treatment. Dynamic electron arc radiotherapy (DEAR) not only overcomes the deficiencies of conventional electron therapy in dose conformity and homogeneity but also achieves so without patient‐specific shields. The combination of MLC and couch tracking provides improved motion management of thoracic and abdominal tumors. A substantial body of work has been done in these technological advances for clinical translation. The proposed symposium will provide a timely review of these exciting opportunities. Learning Objectives: Recognize the potential of using digitally controlled linacs for clinically significant improvements in delivered dose distributions for various treatment sites. Identify existing approaches to treatment planning, optimization and delivery for treatment techniques utilizing the advanced functions of digital linacs and venues for further development and improvement. Understand methods for testing and validating delivery system performance. Identify tools available on current delivery systems for implementation and control for such treatments. Obtain the update in clinical applications, trials and regulatory approval.K. Sheng, NIH U19AI067769, NIH R43CA183390, NIH R01CA188300, Varian Medical SystemsV. Yu, Varian Medical Systems, AAPM Summer Undergraduate Fellowship, NSF graduate fellowshipS. Nill, Elekta AB. Cancer Research UK under Programme C33589/A19727, NIHR Biomedical Research Centre at The Royal Marsden and The Institute of Cancer Research.

WE-A-207-02: Electron Beam Therapy - Current Status and Future Directions

In memory of the significant contribution of Dr. Jacques Ovadia to electron beam techniques, this session will review recent, advanced techniques which are reinvigorating the science of electron beam radiation therapy. Recent research efforts in improving both the applicability and quality of the electron beam therapy will be discussed, including modulated electron beam radiotherapy (MERT) and dynamic electron arc radiotherapy (DEAR). Learning Objectives: 1. To learn about recent advances in electron beam therapy, including modulated electron beam therapy and dynamic electron arc therapy (DEAR). 2. Put recent advances in the context of work that Dr. Ovadia pursued during his career in medical physics.

TU‐CD‐304‐07: Intensity Modulated Electron Beam Therapy Employing Small Fields in Virtual Scanning Mode

Purpose:Dynamic electron radiation therapies such as dynamic electron arc radiotherapy (DEAR) utilize small fields to provide target conformity and fluence modulation. The purpose of this study is to demonstrate the feasibility of virtual scanning mode using small fields.Methods:Monte Carlo simulations (EGSnrc/BEAMnrc/DOSXYZnrc) were performed using validated Varian TrueBeam phase space files for electron beam energies of 6, 9, 12, and 16 MeV and square/circular fields (1×1/1, 2×2/2, 3×3/3, 4×4/4, 5×5/5 cm2/cm diameter). Resulting dose distributions (kernels) were used for subsequent calculations. The following analyses were performed: (1) Comparison of composite square fields and reference 10×10 cm2 dose distributions and (2) Scanning beam deliveries for square and circular fields realized as the convolution of kernels and scanning pattern. Preliminary beam weight and pattern optimization were also performed. Two linear scans of 10 cm with/without overlap were modeled. Comparison metrics included depth and orthogonal profiles at dmax.Results:(1) Composite fields regained reference depth dose profiles for most energies and fields within 5%. Smaller kernels and higher energies increased dose in the build‐up and Bremsstrahlung region (30%, 16MeV and 1×1 cm2), while reference dmax was maintained for all energies and composite fields. Smaller kernels (<2×2 cm2) maintained penumbra and field size within 0.2 cm, and flatness within 2%. Deterioration of penumbra for larger kernels (5×5 cm2) were observed. Balancing desirable dosimetry and efficiencies suggests that smaller kernels are used at edges and larger kernels in the center of the target. (2) Beam weight optimization improved cross‐plane penumbra (0.2 cm) and increased the field size (0.4 cm) on average. In‐plane penumbra and field size remained unchanged. Overlap depended on kernel size and optimal overlap resulted in flatness ±2%.Conclusion:Dynamic electron beam therapy in virtual scanning mode is feasible by employing small fields to achieve desired dose distributions and acceptable efficiencies.

A Monte Carlo simulation framework for electron beam dose calculations using Varian phase space files for TrueBeam Linacs.

To develop a framework for accurate electron Monte Carlo dose calculation. In this study, comprehensive validations of vendor provided electron beam phase space files for Varian TrueBeam Linacs against measurement data are presented. In this framework, the Monte Carlo generated phase space files were provided by the vendor and used as input to the downstream plan-specific simulations including jaws, electron applicators, and water phantom computed in the EGSnrc environment. The phase space files were generated based on open field commissioning data. A subset of electron energies of 6, 9, 12, 16, and 20 MeV and open and collimated field sizes 3 × 3, 4 × 4, 5 × 5, 6 × 6, 10 × 10, 15 × 15, 20 × 20, and 25 × 25 cm(2) were evaluated. Measurements acquired with a CC13 cylindrical ionization chamber and electron diode detector and simulations from this framework were compared for a water phantom geometry. The evaluation metrics include percent depth dose, orthogonal and diagonal profiles at depths R100, R50, Rp, and Rp+ for standard and extended source-to-surface distances (SSD), as well as cone and cut-out output factors. Agreement for the percent depth dose and orthogonal profiles between measurement and Monte Carlo was generally within 2% or 1 mm. The largest discrepancies were observed within depths of 5 mm from phantom surface. Differences in field size, penumbra, and flatness for the orthogonal profiles at depths R100, R50, and Rp were within 1 mm, 1 mm, and 2%, respectively. Orthogonal profiles at SSDs of 100 and 120 cm showed the same level of agreement. Cone and cut-out output factors agreed well with maximum differences within 2.5% for 6 MeV and 1% for all other energies. Cone output factors at extended SSDs of 105, 110, 115, and 120 cm exhibited similar levels of agreement. We have presented a Monte Carlo simulation framework for electron beam dose calculations for Varian TrueBeam Linacs. Electron beam energies of 6 to 20 MeV for open and collimated field sizes from 3 × 3 to 25 × 25 cm(2) were studied and results were compared to the measurement data with excellent agreement. Application of this framework can thus be used as the platform for treatment planning of dynamic electron arc radiotherapy and other advanced dynamic techniques with electron beams.

SU-E-T-358: Monte Carlo Dose Calculation of Small Field Electron Beams

Purpose: Dynamic radiotherapy involving electron beams such as Dynamic Electron Arc Radiotherapy (DEAR) requires accurate dose modelling of small field sizes, similar to the requirement of IMRT field on the small photon field. The current commercial electron Monte Carlo algorithms such as eMC v11 in Eclipse were developed for standard field sizes and do not support the planning of dynamic therapy yet. The purpose of this study is to develop a method to accurately model small field electron beam dosimetry using Monte Carlo simulations. Methods: Comparison between eMC, phantom measurements (diode), and Monte Carlo (MC) simulations (BEAMnrc/DOSYZnrc) were performed for a Varian TrueBeam linac. MC simulations utilized Varian TrueBeam phase space files which had been validated in another study. Static single small field was assessed by comparing dose distributions in water for a 16 MeV beam for circular (2 cm diameter) and rectangular (1×10 cm{sup 2}) cut-out. MC was performed with a resolution of 2.5×2.5×2 mm{sup 2} and statistical uncertainty < 4%. The dose distribution was averaged over adjacent bins to improve precision. Depth dose and orthogonal profiles were evaluated. Results: Small field PDDs differ from those with standard cones. For both circular and rectangular cutouts, the difference in rangemore » R8 0-R1 0 is less than 2 mm and in dose within 2%. For the orthogonal profiles, field size and penumbra differences were within 1 mm at depth of maximum dose. The eMC displayed a distinctive “step” in the out-field dose profile in disagreement with both measurement and MC results and needs further investigation. Conclusion: MC was able to characterize the small field dosimetry with good agreement with the measurement data, and thus offers the opportunity for treatment planning of dynamic radiotherapy. Analyses for all other electron energies and cut-out sizes are under way and results will be included in the presentation.« less

Dynamic electron arc radiotherapy (DEAR): a feasibility study

Compared to other radiation therapy modalities, clinical electron beam therapy has remained practically unchanged for the past few decades even though electron beams with multiple energies are widely available on most linacs. In this paper, we present the concept of dynamic electron arc radiotherapy (DEAR), a new conformal electron therapy technique with synchronized couch motion. DEAR utilizes combination of gantry rotation, couch motion, and dose rate modulation to achieve desirable dose distributions in patient. The electron applicator is kept to minimize scatter and maintain narrow penumbra. The couch motion is synchronized with the gantry rotation to avoid collision between patient and the electron cone. In this study, we investigate the feasibility of DEAR delivery and demonstrate the potential of DEAR to improve dose distributions on simple cylindrical phantoms. DEAR was delivered on Varian's TrueBeam linac in Research Mode. In conjunction with the recorded trajectory log files, mechanical motion accuracies and dose rate modulation precision were analyzed. Experimental and calculated dose distributions were investigated for different energies (6 and 9 MeV) and cut-out sizes (1×10 cm2 and 3×10 cm2 for a 15×15 cm2 applicator). Our findings show that DEAR delivery is feasible and has the potential to deliver radiation dose with high accuracy (root mean square error, or RMSE of <0.1 MU, <0.1° gantry, and <0.1 cm couch positions) and good dose rate precision (1.6 MU min−1). Dose homogeneity within ±2% in large and curved targets can be achieved while maintaining penumbra comparable to a standard electron beam on a flat surface. Further, DEAR does not require fabrication of patient-specific shields. These benefits make DEAR a promising technique for conformal radiotherapy of superficial tumors.

SU‐E‐T‐602: Dynamic Electron Arc Radiotherapy (DEAR): A Planning Study

Purpose: Electron beam therapy is under‐utilized in radiation treatment of cancer and has remained practically unchanged for decades. We propose a new technique, Dynamic Electron Arc Radiotherapy (DEAR) with synchronized couch motion. In DEAR, gantry rotation, dose rate, and intensities are modulated to create desirable dose distributions free of hot and/or cold spots, with high homogeneity, and narrow penumbra. This study demonstrates the potential of DEAR in improving dose distributions. Methods: Dose distributions for single‐field and two‐field were compared to DEAR with equal and optimized beam weights on a 32 cm diameter cylindrical phantom. Plans were designed to irradiate equivalent field size on the phantom surface, with the target dimension extending from 315° –45° in radial angle and target depth at 1 cm (6 MeV) or 2 cm (9 MeV). Penumbra (20–80%), dose homogeneity, and dose area histogram (DAH) were evaluated at target depths. Plans were calculated with the eMC algorithm in Eclipse v10. Results: In‐plane (longitudinal direction) penumbra was comparable across all plans as expected. Cross‐plane (along curved surface) penumbra was 5.0, 1.5, and 2.0 cm (6 MeV) and 5.6, 1.7, and 2.1 (9 MeV), for single‐field, two‐field, and DEAR, respectively. While the two‐field penumbra was better, it exhibited a hot spot 60% higher than the target mean at the beam junction covering approximately 20% of the target. DEAR plans displayed homogenous dose distributions with variations of less than ±1.5%. DAH of the single‐field failed to achieve optimal coverage, while the two‐field displayed a high‐dose tail (&gt;100%). 90% of the target receives at least 95% (two‐field) and 88% (DEAR) of the target dose. Conclusion: Preliminary findings show that DEAR can produce homogenous dose distributions over large and curved targets without hot and/or cold spots while maintaining narrow penumbra. Future work includes planning for various target shapes and desired dose distributions.

TU‐E‐108‐02: Dynamic Electron Arc Radiotherapy (DEAR): A Feasibility Study

Purpose: Electron beam therapy is under‐utilized in radiation treatment of cancer and has remained practically unchanged for decades. We propose a new technique, Dynamic Electron Arc Radiotherapy (DEAR) with synchronized couch motion. DEAR utilizes modulation in gantry rotation, dose rate, and intensity to create desirable dose distributions. This study investigates the feasibility of DEAR in terms of deliverability and dosimetry. Methods: DEAR plans were designed and delivered across various energies, doses, and dose rates on a cylindrical phantom. Deliverability was evaluated by verifying the accuracy of the MU, gantry, and couch axes: The agreement between planned and actual axes values recorded in the trajectory log during delivery was quantified by the root mean square error (RMSE). Subsequently, couch, gantry, and collimator velocities were derived and evaluated. Maximum velocities were verified by delivering 10 MU at 1000 MU/min while an axis covered a large distance/rotation, thus forcing a dose rate drop resulting in maximum velocity. Dosimetry was evaluated with radiographic film for static and DEAR plans by comparing in‐plane and cross‐plane beam penumbra (20–80%) to those calculated with the eMC algorithm in Eclipse v10. Dose homogeneity within target region was evaluated. Results: Trajectory log analysis of planned and actual axes values for DEAR plans had small RMSE (&lt;0.1 MU, &lt;0.1° gantry, &lt;0.1 cm couch positions). Velocities for couch lateral, vertical, and gantry ranged from 0.1–1.1cm/s, 0.1–1.7cm/s, and 0.3– 6° /s, respectively. Maximum velocities agreed with manufacturer's specifications and were 3.8, 2, and 7.4cm/s for couch lateral, vertical, and longitudinal, respectively; and 2.9, 5.9, and 14.2°/s for couch rotational, gantry, and collimator, respectively. Dosimetric evaluation showed good agreement for the penumbrae (within 1 mm). Further, dose homogeneity was within ±2% of the mean dose. Conclusion: Preliminary findings show that DEAR has the potential to deliver electron beam therapy with high accuracy and dose homogeneity.