Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “DOSE LIMITS”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

EVALUATION OF EXISTING PUBLIC DOSE LIMITS APPLIED TO RECREATIONAL SPACEFLIGHT

Abstract Establishing realistic radiation dose limits with a solid scientific basis is a key component of the ‘as low as reasonably achievable’ (ALARA) principle. Although existing occupational dose limits have been established for civil astronauts, with the rise in popularity and technological maturation of the ‘space tourism’ sector, there does not appear to be considerable discussion on the subject of non-occupational astronaut dose limits. The necessity to come to a collective decision on dose limits and radiation safety procedures for recreational spaceflight is urgent and imperative to maintain ALARA goals, as existing federal dose limits to the public cannot be adequately or universally applied to the space tourism sector. Development of an entirely new set of regulations and guidelines should also provide long-term benefits in public perception as evidence of safety commitments from decision makers and the community in protecting passengers from radiological risks balanced with other spaceflight hazards.

Long, Michael A. (ORCID:0000000181363476)↗
DOE OSTI2020

Applicability of Public Dose Limits to Individuals on the Nevada National Security Site

Historically all persons working on the Nevada National Security Site (NNSS) were considered subject to worker dose limits when calculations of potential dose from the air pathway were conducted to demonstrate compliance with Title 42 United States Code (USC) Chapter 85, “The Clean Air Act,” and Title 40 Code of Federal Regulations (CFR) Part 61, Subpart H, “National Emission Standards for Hazardous Air Pollutants (NESHAP).” Calculations were also conducted for the all-pathways potential dose to demonstrate compliance with U.S. Department of Energy (DOE) Order DOE O 458.1 Chg. 3, “Radiation Protection of the Public and the Environment.” The need to evaluate environmental air sampling locations and past regulator questions about the existence of persons potentially subject to public dose limits being on the NNSS drove this assessment (letter from EPA [U.S. Environmental Protection Agency] Region 9 to DOE/Nevada Operations Office, dated September 3, 1999). This assessment also supports determining those persons subject to public dose limits from the all pathways perspective. A person that is a member of the public is subject to public dose limits.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Decreasing Irradiated Rat Lung Volume Changes Dose-Limiting Toxicity From Early to Late Effects

Purpose: Technological developments in radiation therapy result in smaller irradiated volumes of normal tissue. Because the risk of radiation therapy-induced toxicity generally depends on irradiated volume, changing volume could change the dose-limiting toxicity of a treatment. Recently, in our rat model, we found that early radiation-induced lung dysfunction (RILD) was closely related to irradiated volume dependent vascular remodeling besides inflammation. The exact relationship between early and late RILD is still unknown. Therefore, in this preclinical study we investigated the dose-volume relationship of late RILD, assessed its dependence on early and late pathologies and studied if decreasing irradiated volume changed the dose-limiting toxicity. Methods and Materials: A volume of 25%, 32%, 50%, 63%, 88%, or 100% of the rat lung was irradiated using protons. Until 26 weeks after irradiation, respiratory rates were measured. Macrovascular remodeling, pulmonary inflammation, and fibrosis were assessed at 26 weeks after irradiation. For all endpoints dose-volume response curves were made. These results were compared to our previously published early lung effects. Results: Early vascular remodeling and inflammation correlated significantly with early RILD. Late RILD correlated with inflammation and fibrosis, but not with vascular remodeling. In contrast to the early effects, late vascular remodeling, inflammation and fibrosis showed a primarily dose but not volume dependence. Comparison of respiratory rate increases early and late after irradiation for the different dose-distributions indicated that with decreasing irradiated volumes, the dose-limiting toxicity changed from early to late RILD. Conclusions: In our rat model, different pathologies underlie early and late RILD with different dose-volume dependencies. Consequently, the dose-limiting toxicity changed from early to late dysfunction when the irradiated volume was reduced. In patients, early and late RILD are also due to different pathologies. As such, new radiation techniques reducing irradiated volume might change the dose-limiting toxicity of the radiation therapy treatment.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Dose-limiting Urinary Toxicity With Pembrolizumab Combined With Weekly Hypofractionated Radiation Therapy in Bladder Cancer

There is currently significant interest in the potential benefits of combining radiation and immune checkpoint blockade (ICB) to stimulate both regional and distant abscopal immune responses. In melanoma and lung cancer, patients who have received radiation therapy during ICB appear to have prolonged survival. The PLUMMB trial (Pembrolizumab in Muscle-invasive/Metastatic Bladder cancer) (NCT02560636) is a phase I study to test the tolerability of a combination of weekly radiation therapy with pembrolizumab in patients with metastatic or locally advanced urothelial cancer of the bladder. In the first dose-cohort, patients received pembrolizumab 100 mg 3-weekly, starting 2 weeks before commencing weekly adaptive bladder radiation therapy to a dose of 36 Gy in 6 fractions. The first dose-cohort was stopped after 5 patients, having met the predefined definition of dose-limiting toxicity. Three patients experienced grade 3 urinary toxicities, 2 of which were attributable to therapy. One patient experienced a grade 4 rectal perforation. In view of these findings, the trial has been paused and the protocol will be amended to reduce radiation therapy dose per fraction. The authors advise caution to those combining radiation therapy and ICB, particularly when radiation therapy is given at high dose per fraction for pelvic tumours. The PLUMMB trial met the protocol-defined definition of dose-limiting toxicity and will be amended to reduce radiation therapy dose.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2011

Consideration of Dose Limits for Organs at Risk of Thoracic Radiotherapy: Atlas for Lung, Proximal Bronchial Tree, Esophagus, Spinal Cord, Ribs, and Brachial Plexus

Purpose: To review the dose limits and standardize the three-dimenional (3D) radiographic definition for the organs at risk (OARs) for thoracic radiotherapy (RT), including the lung, proximal bronchial tree, esophagus, spinal cord, ribs, and brachial plexus. Methods and Materials: The present study was performed by representatives from the Radiation Therapy Oncology Group, European Organization for Research and Treatment of Cancer, and Soutwestern Oncology Group lung cancer committees. The dosimetric constraints of major multicenter trials of 3D-conformal RT and stereotactic body RT were reviewed and the challenges of 3D delineation of these OARs described. Using knowledge of the human anatomy and 3D radiographic correlation, draft atlases were generated by a radiation oncologist, medical physicist, dosimetrist, and radiologist from the United States and reviewed by a radiation oncologist and medical physicist from Europe. The atlases were then critically reviewed, discussed, and edited by another 10 radiation oncologists. Results: Three-dimensional descriptions of the lung, proximal bronchial tree, esophagus, spinal cord, ribs, and brachial plexus are presented. Two computed tomography atlases were developed: one for the middle and lower thoracic OARs (except for the heart) and one focusing on the brachial plexus for a patient positioned supine with their arms up for thoracic RT. The dosimetric limits of the key OARs are discussed. Conclusions: We believe these atlases will allow us to define OARs with less variation and generate dosimetric data in a more consistent manner. This could help us study the effect of radiation on these OARs and guide high-quality clinical trials and individualized practice in 3D-conformal RT and stereotactic body RT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

The kinetic dose limit in room-temperature time-resolved macromolecular crystallography

Protein X-ray structures are determined with ionizing radiation that damages the protein at high X-ray doses. As a result, diffraction patterns deteriorate with the increased absorbed dose. Several strategies such as sample freezing or scavenging of X-ray-generated free radicals are currently employed to minimize this damage. However, little is known about how the absorbed X-ray dose affects time-resolved Laue data collected at physiological temperatures where the protein is fully functional in the crystal, and how the kinetic analysis of such data depends on the absorbed dose. Here, direct evidence for the impact of radiation damage on the function of a protein is presented using time-resolved macromolecular crystallography. The effect of radiation damage on the kinetic analysis of time-resolved X-ray data is also explored.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2019

Ultra-low-dose limited renal CT for volumetric stone surveillance: advantages over standard unenhanced CT

Purpose: To describe and validate a novel CT approach using volumetric analysis for renal stone surveillance. Materials and methods: This prospective trial consisted of a standard low-dose non-contrast CT (SLD) of the abdomen and pelvis, immediately followed by an ultra-low-dose non-contrast CT (ULD) with reconstruction limited to the kidneys. A novel dedicated software tool was applied that automates stone volume, density, and maximum linear size. Manual linear stone size was measured by a radiology fellow and urology resident for comparison. CT dose and clinical charges were considered. Results: Twenty-eight stones in 16 patients were analyzed. Mean effective dose of ULD CT was 0.57 mSv, an average 92% lower than the SLD CT dose. For SLD, mean size ± SD (range) (mm) was 7.9 ± 6.2 (2.6–30.5) for Reader 1, 7.3 ± 6 (2.4–30.7) for Reader 2, and 9.3 ± 6.4 (3.7–33.1) for the automated software. For ULD, mean size ± SD (range) (mm) was 7.3 ± 6 (2.5–30.5) for Reader 1, 7.2 ± 6.1 (2.1–30.7) for Reader 2, and 9.1 ± 6.4 (4.2–32.8) for the automated software. Automated stone diameters were larger than manual diameters for 27/28 stones (mean difference, 23%); difference was ≥ 2 mm in 30%. Average variability between manual measurements was 8.6% (SLD) and 7.8% (ULD), but was 0% for the automated technique. Our institutional charge for ULD renal CT is slightly less than renal US, and > 4× less than SLD CT. The Medicare global fee for the ULD renal CT is less than the SLD CT of the abdomen and pelvis. Conclusions: This focused stone surveillance CT protocol is lower cost and lower dose compared to the standard CT approach. Automated assessment of stone burden provides improved reproducibility over manual linear measurement and offers the advantages of 3D measurements and volumetry. We now offer and perform this protocol in routine clinical practice for stone surveillance.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2020

Radiation damage and dose limits in serial synchrotron crystallography at cryo- and room temperatures

Radiation damage limits the accuracy of macromolecular structures in X-ray crystallography. Cryogenic (cryo-) cooling reduces the global radiation damage rate and, therefore, became the method of choice over the past decades. The recent advent of serial crystallography, which spreads the absorbed energy over many crystals, thereby reducing damage, has rendered room temperature (RT) data collection more practical and also extendable to microcrystals, both enabling and requiring the study of specific and global radiation damage at RT. Here, we performed sequential serial raster-scanning crystallography using a microfocused synchrotron beam that allowed for the collection of two series of 40 and 90 full datasets at 2- and 1.9-Å resolution at a dose rate of 40.3 MGy/s on hen egg white lysozyme (HEWL) crystals at RT and cryotemperature, respectively. The diffraction intensity halved its initial value at average doses ( D 1/2 ) of 0.57 and 15.3 MGy at RT and 100 K, respectively. Specific radiation damage at RT was observed at disulfide bonds but not at acidic residues, increasing and then apparently reversing, a peculiar behavior that can be modeled by accounting for differential diffraction intensity decay due to the nonuniform illumination by the X-ray beam. Specific damage to disulfide bonds is evident early on at RT and proceeds at a fivefold higher rate than global damage. The decay modeling suggests it is advisable not to exceed a dose of 0.38 MGy per dataset in static and time-resolved synchrotron crystallography experiments at RT. This rough yardstick might change for proteins other than HEWL and at resolutions other than 2 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Initial Results of a Phase I Dose-Escalation Trial of Concurrent and Maintenance Erlotinib and Reirradiation for Recurrent and New Primary Head-and-Neck Cancer

Purpose: To present the first report of a Phase I trial evaluating concurrent and maintenance erlotinib and reirradiation in patients with recurrent or secondary primary head-and-neck cancer (HNC). Methods and Materials: Patients with recurrent or new primary HNC with an interval of at least 6 months since prior radiation were eligible. Patients were treated in 3 sequential cohorts: Cohort I, 100 mg of erlotinib daily with reirradiation at 61.6 Gy in 28 fractions; Cohort II, 150 mg of erlotinib with 61.6 Gy in 28 fractions; and Cohort III, 150 mg of erlotinib with 66 Gy in 30 fractions. Maintenance erlotinib started immediately after reirradiation at 150 mg daily and was continued for 2 years or until disease progression or dose-limiting toxicity. Dose-limiting toxicities were defined as any Grade 4 or 5 toxicity or a toxicity-related delay in radiation therapy of greater than 7 days. Results: Fourteen patients were accrued, 3 to Cohort I, 4 to Cohort II, and 7 to Cohort III. Thirteen patients were evaluable for toxicity. Median follow-up was 8.4 months overall and 15.1 months for surviving patients. One patient had a dose-limiting toxicity in Cohort III. This patient declined initial percutaneous endoscopic gastrostomy tube placement, was hospitalized with Grade 3 dysphagia and aspiration, and required a delay in radiation therapy of greater than 7 days. No Grade 4 acute toxicity was observed. Acute Grade 3 toxicity occurred in 9 of 13 patients. No erlotinib-related toxicity of Grade 3 or greater was observed during maintenance therapy. One patient had Grade 5 carotid hemorrhage 6 months after reirradiation, and another patient had Grade 3 osteoradionecrosis. Conclusions: Reirradiation (66 Gy in 2.2 Gy fractions) with concurrent and maintenance erlotinib (150 mg daily) for recurrent or new primary HNC is feasible.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2011

Correction Factors Applied to Finger Dosimetry: A Theoretical Assessment of Appropriate Values for Use in Handling Radiopharmaceuticals

United States Nuclear Regulatory Commission (USNRC) regulations limit the dose to the skin to 500 mSv per year. This is also the dose limit recommended by the International Commission on Radiological Protection (ICRP). The operational quantity recommended by ICRP for quantifying dose to the skin is the personal dose equivalent, Hp(0.07) and is identical to NRC s shallow dose equivalent, Hs, also measured at a skin depth of 7 mg cm 2. However, whereas ICRP recommends averaging the dose to the skin over an area of 1 cm2 regardless of the size of the exposed area of skin, USNRC requires the shallow dose equivalent to be averaged over 10 cm2. To monitor dose to the skin of the hands of workers handling radioactive materials and particularly in radiopharmaceutical manufacturing facilities, which is the focus of this work, workers are frequently required to wear finger ring dosimeters. The dosimeters monitor the dose at the location of the sensitive element, but this is not the dose required to show compliance (i.e., the dose averaged over the highest exposed contiguous 10 cm2 of skin). Therefore, it may be necessary to apply a correction factor that enables estimation of the required skin dose from the dosimeter reading. This work explored the effects of finger ring placement and of the geometry of the radioactive materials being handled by the worker on the relationship between the dosimeter reading and the desired average dose. A mathematical model of the hand was developed for this purpose that is capable of positioning the fingers in any desired grasping configuration, thereby realistically modeling manipulation of any object. The model was then used with the radiation transport code MCNP to calculate the dose distribution on the skin of the hand when handling a variety of radioactive vials and syringes, as well as the dose to the dosimeter element. Correction factors were calculated using the results of these calculations and examined for any patterns that may be useful in establishing an appropriate correction factor for this type of work. It was determined that a correction factor of one applied to the dosimeter reading, with the dosimeter placed at the base of the middle finger, provides an adequate estimate of the required average dose during a monitoring period for most commonly encountered geometries. Different correction factors may be required for exceptional or unusual source geometries and must be considered on a case-by-case basis.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

Waste Generator Instructions: Key to Successful Implementation of the US DOE's 435.1 for Transuranic Waste Packaging Instructions (LA-UR-12-24155) - 13218

In times of continuing fiscal constraints, a management and operation tool that is straightforward to implement, works as advertised, and virtually ensures compliant waste packaging should be carefully considered and employed wherever practicable. In the near future, the Department of Energy (DOE) will issue the first major update to DOE Order 435.1, Radioactive Waste Management. This update will contain a requirement for sites that do not have a Waste Isolation Pilot Plant (WIPP) waste certification program to use two newly developed technical standards: Contact-Handled Defense Transuranic Waste Packaging Instructions and Remote-Handled Defense Transuranic Waste Packaging Instructions. The technical standards are being developed from the DOE O 435.1 Notice, Contact-Handled and Remote-Handled Transuranic Waste Packaging, approved August 2011. The packaging instructions will provide detailed information and instruction for packaging almost every conceivable type of transuranic (TRU) waste for disposal at WIPP. While providing specificity, the packaging instructions leave to each site's own discretion the actual mechanics of how those Instructions will be functionally implemented at the floor level. While the Technical Standards are designed to provide precise information for compliant packaging, the density of the information in the packaging instructions necessitates a type of Rosetta Stone that translates the requirements into concise, clear, easy to use and operationally practical recipes that are waste stream and facility specific for use by both first line management and hands-on operations personnel. The Waste Generator Instructions provide the operator with step-by-step instructions that will integrate the sites' various operational requirements (e.g., health and safety limits, radiological limits or dose limits) and result in a WIPP certifiable waste and package that can be transported to and emplaced at WIPP. These little known but widely productive Waste Generator Instructions (WGIs) have been used occasionally in the past at large sites for treatment and packaging of TRU waste. The WGIs have resulted in highly efficient waste treatment, packaging and certification for disposal of TRU waste at WIPP. For example, a single WGI at LANL, combined with an increase in gram loading, resulted in a mind boggling 6,400% increase in waste loading for {sup 238}Pu heat source waste. In fact, the WGI combined with a new Contact Handled (CH) TRU Waste Content (TRUCON) Code provided a massive increase in shippable wattage per Transuranic Package Transporter-II (TRUPACT-II) over the previously used and more restrictive TRUCON Code that have been used previously for the heat source waste. In fact, the use of the WGI process at LANL's TA-55 facility reduced non-compliant drums for WIPP certification and disposal from a 13% failure rate down to a 0.5% failure rate and is expected to further reduce the failure rate to zero drums per year. The inherent value of the WGI is that it can be implemented in a site's current procedure issuance process and it provides documented proof of what actions were taken for each waste stream packaged. The WGI protocol provides a key floor-level operational component to achieve goal alignment between actual site operations, the WIPP TRU waste packaging instructions, and DOE O 435.1. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2014

Limitations of the TG-43 formalism for skin high-dose-rate brachytherapy dose calculations

Purpose: In skin high-dose-rate (HDR) brachytherapy, sources are located outside, in contact with, or implanted at some depth below the skin surface. Most treatment planning systems use the TG-43 formalism, which is based on single-source dose superposition within an infinite water medium without accounting for the true geometry in which conditions for scattered radiation are altered by the presence of air. The purpose of this study is to evaluate the dosimetric limitations of the TG-43 formalism in HDR skin brachytherapy and the potential clinical impact. Methods: Dose rate distributions of typical configurations used in skin brachytherapy were obtained: a 5 cm × 5 cm superficial mould; a source inside a catheter located at the skin surface with and without backscatter bolus; and a typical interstitial implant consisting of an HDR source in a catheter located at a depth of 0.5 cm. Commercially available HDR{sup 60}Co and {sup 192}Ir sources and a hypothetical {sup 169}Yb source were considered. The Geant4 Monte Carlo radiation transport code was used to estimate dose rate distributions for the configurations considered. These results were then compared to those obtained with the TG-43 dose calculation formalism. In particular, the influence of adding bolus material over the implant was studied. Results: For a 5 cm × 5 cm{sup 192}Ir superficial mould and 0.5 cm prescription depth, dose differences in comparison to the TG-43 method were about −3%. When the source was positioned at the skin surface, dose differences were smaller than −1% for {sup 60}Co and {sup 192}Ir, yet −3% for {sup 169}Yb. For the interstitial implant, dose differences at the skin surface were −7% for {sup 60}Co, −0.6% for {sup 192}Ir, and −2.5% for {sup 169}Yb. Conclusions: This study indicates the following: (i) for the superficial mould, no bolus is needed; (ii) when the source is in contact with the skin surface, no bolus is needed for either {sup 60}Co and {sup 192}Ir. For lower energy radionuclides like {sup 169}Yb, bolus may be needed; and (iii) for the interstitial case, at least a 0.1 cm bolus is advised for {sup 60}Co to avoid underdosing superficial target layers. For {sup 192}Ir and {sup 169}Yb, no bolus is needed. For those cases where no bolus is needed, its use might be detrimental as the lack of radiation scatter may be beneficial to the patient, although the 2% tolerance for dose calculation accuracy recommended in the AAPM TG-56 report is not fulfilled.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

User Guide for GoldSim Model to Calculate PA/CA Doses and Limits

A model to calculate doses for solid waste disposal at the Savannah River Site (SRS) and corresponding disposal limits has been developed using the GoldSim commercial software. The model implements the dose calculations documented in SRNL-STI-2015-00056, Rev. 0 “Dose Calculation Methodology and Data for Solid Waste Performance Assessment (PA) and Composite Analysis (CA) at the Savannah River Site”.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2017

Bladder radiotherapy treatment: A retrospective comparison of 3-dimensional conformal radiotherapy, intensity-modulated radiation therapy, and volumetric-modulated arc therapy plans

To examine tumor's and organ's response when different radiotherapy plan techniques are used. Ten patients with confirmed bladder tumors were first treated using 3-dimensional conformal radiotherapy (3DCRT) and subsequently the original plans were re-optimized using the intensity-modulated radiation treatment (IMRT) and volumetric-modulated arc therapy (VMAT)-techniques. Targets coverage in terms of conformity and homogeneity index, TCP, and organs' dose limits, including integral dose analysis were evaluated. In addition, MUs and treatment delivery times were compared. Better minimum target coverage (1.3%) was observed in VMAT plans when compared to 3DCRT and IMRT ones confirmed by a statistically significant conformity index (CI) results. Large differences were observed among techniques in integral dose results of the femoral heads. Even if no statistically significant differences were reported in rectum and tissue, a large amount of energy deposition was observed in 3DCRT plans. In any case, VMAT plans provided better organs and tissue sparing confirmed also by the normal tissue complication probability (NTCP) analysis as well as a better tumor control probability (TCP) result. Our analysis showed better overall results in planning using VMAT techniques. Furthermore, a total time reduction in treatment observed among techniques including gantry and collimator rotation could encourage using the more recent one, reducing target movements and patient discomfort.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2025

URC/HRC Selection Guidance

Given the importance of the URC and HRC thresholds as part of a physical security program that is designed to protect against radiological sabotage, it is important to provide guidance on how to assign those thresholds consistent with a State’s level of risk tolerance. Without such guidance, most States will be challenged to establish appropriate thresholds or appropriately establish regulations. This document provides guidance on establishing dose limits and where they apply, as well as the timeframe for which the dose limits should be measured. For dose limits, it offers examples of established thresholds based on safety and emergency response thresholds. Whereas, for timeframes, a process to identify possible timeframes is offered.

45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
DOE OSTI2016

SU-G-201-11: Exploring the Upper Limits of Dose Sculpting Capacity of the Novel Direction Modulated Brachytherapy (DMBT) Tandem Applicator

Purpose: To explore and quantify the upper limits in dose sculpting capacity of the novel direction modulated brachytherapy (DMBT) tandem applicator compared with conventional tandem design for {sup 192}Ir-based HDR planning. Methods: The proposed DMBT tandem applicator is designed for image-guided adaptive brachytherapy (IGABT), especially MRI, of cervical cancer. It has 6 peripheral holes of 1.3-mm width, grooved along a 5.4-mm diameter nonmagnetic tungsten alloy rod of density 18.0 g/cc, capable of generating directional dose profiles – leading to enhanced dose sculpting capacity through inverse planning. The external dimensions are identical to that of conventional tandem design to ensure clinical compatibility. To explore the expansive dose sculpting capacity, we constructed a hypothetical circular target with 20-mm radius and positioned the DMBT and conventional tandems at the center. We then incrementally shifted the positions laterally away from the center of up to 15 mm, at 1-mm steps. The in-house coded gradient projection-based inverse planning system was then used to generate inverse optimized plans ensuring identical V100=100% coverage. Conformity index (CI) was calculated for all plans. Results: Overall, the DMBT tandem generates more conformal dose distributions than conventional tandem for all lateral positional shifts of 0-15 mm (CI=0.91–0.52 and 0.99–0.34, respectively), with an exception at the central position due to the ideal circular dose distribution, generated by the {sup 192}Ir, fitting tightly around the circular target (CI = 0.91 and 0.99, respectively). The DMBT tandem is able to generate dose conformity of CI>0.8 at up to 6-mm positional shift while the conventional tandem violates this past 2-mm shift. Also, the CI ratio (=DMBT/conv.) increases rapidly until about 8 mm and then stabilizes beyond. Conclusion: A substantial enhancement in the dose sculpting capacity has been demonstrated for the novel DMBT tandem applicator. While further studies are warranted, the concept is promising for potential clinical translation.

60 APPLIED LIFE SCIENCES↗