IR Source Research Articles

Estimating blurless and noise-free Ir-192 source images from gamma camera images for high-dose-rate brachytherapy using a deep-learning approach

Objective. Precise monitoring of the position and dwell time of iridium-192 (Ir-192) during high-dose-rate (HDR) brachytherapy is crucial to avoid serious damage to normal tissues. Source imaging using a compact gamma camera is a potential approach for monitoring. However, images from the gamma camera are affected by blurring and statistical noise, which impact the accuracy of source position monitoring. This study aimed to develop a deep-learning approach for estimating ideal source images that reduce the effect of blurring and statistical noise from experimental images captured using a compact gamma camera. Approach. A double pix2pix model was trained using the simulated gamma camera images of an Ir-192 source. The first model was responsible for denoising the Ir-192 images, whereas the second model performed super resolution. Trained models were then applied to the experimental images to estimate the ideal images. Main results. At a distance of 100 mm between the compact gamma camera and the Ir-192 source, the difference in full width at half maximum (FWHM) between the estimated and actual source sizes was approximately 0.5 mm for a measurement time of 1.5 s. This difference has been improved from approximately 2.7 mm without the use of DL. Even with a measurement time of 0.1 s, the ideal images could be estimated as accurately as in the 1.5 s measurements. This method consistently achieved accurate estimations of the source images at any position within the field of view; however, the difference increased with the distance between the Ir-192 source and the compact gamma camera. Significance. The proposed method successfully provided estimated images from the experimental images within errors smaller than 0.5 mm at 100 mm. This method is promising for reducing blurring and statistical noise from the experimental images, enabling precise real-time monitoring of Ir-192 sources during HDR brachytherapy.

Clinical use of high dose-rate brachytherapy in treatment of patients with localized prostate cancer and infravesical obstruction

Background. High dose-rate brachytherapy is a new method of interstitial radiation therapy for treatment of localized prostate cancer. The difference from low dose therapy is temporary implantation of radiation sources with targeted high dose-rate irradiation of the affected organ.Aim. To evaluate 3-year effectiveness and safety of high dose-rate brachytherapy in patients with infravesical obstruction. Materials and methods. Between January of 2017 and December of 2019 at the Central Clinical Hospital “RZD-medicine”, 49 patients (mean age 67.8 ± 7.5 years) with verified prostate cancer diagnosis underwent high dose-rate brachytherapy in the regimen of 2 sessions of 15 Gy with 192Ir source. The inclusion criteria were disease stage ≤сТ2с, Gleason score ≤7. Patients were divided into 2 groups: 1st – patients with incidental prostate cancer (n = 21) who previously (more than 6 months ago, mean time 9.4 ± 2.4 months) underwent transurethral prostatectomy; 2nd – patients with verified prostate cancer (mean prostate volume 56 cm3) and obstructive symptoms without previous transurethral prostatectomy (n = 28).Results. In both groups, no intraoperative complications were observed. In 6 (28 %) patients of the 1st group and 2 patients of the 2nd group, grade II genitourinary toxicity in the form of moderate dysuria and nocturia was observed. Acute gastrointestinal toxicity was observed in 3 (14 %) patients of the 1st group, in the 2nd group such complications were absent. In the 2nd group during the postoperative period after the 2nd session, 4 patients (14 %) experienced acute urinary retention requiring cystostomy.Conclusion. High dose-rate brachytherapy is a safe and effective radical treatment method for patients with localized prostate cancer with obstructive symptoms who have contraindications for surgical treatment.

Development of Gamma Flaw Detectors for Non-Destructive Testing

The radiographic method of control is implemented by a set of control tools in the form of gamma flaw detectors, which are distinguished by: mobility, reliability, radiation safety, adaptability to a wide climatic range, ease of operation, and the ability to control products with small and large radiation thicknesses. The paper describes portable gamma flaw detectors manufactured by JSC NIITFA: Gammarid 2010R, UNIGAM R, Stapel-5 Se75 Ir192, Stapel-5 Se75W, gamma flaw detector γ-RID-75/80R and stationary gamma flaw detectors RID K-100 and RID K-400. Also paper describes a brief technology for the production of ionizing radiation sources Ir-192 with activity of 120 Curie, a technology for rolling the source holder with Ir-192 source and completing the Ir-192 source with a portable gamma flaw detector Gammarid-192/120M in the INP AS.

A Novel Brachytherapy Needle Design to Reduce Urethra Dose in HDR Prostate Brachytherapy.

Ultrasound-guided high-dose-rate (HDR) prostate brachytherapy is a safe and effective treatment option for prostate cancer patients; however, some patients still experience acute and late genitourinary (GU) toxicity. It has been reported that urethra dose is associated with the incidence and severity of GU toxicity. Therefore, a technique that can further spare the urethra while ensuring adequate target coverage is highly desirable. Intensity modulated brachytherapy (IMBT) designs, such as rotating shield brachytherapy (RSBT), offer ideal dosimetry on-paper but are challenging to implement clinically due to the need for high precision in moving mechanisms and the use of non-conventional HDR sources, such as 153Gd, electronic, and 169Yb. In this study, we propose a novel clinically implementable solution based on the direction modulated brachytherapy (DMBT) design concept, which has no moving parts and works effectively with the commercially available 192Ir sources. The widely used GammaMedPlus (GMP) 192Ir sources, with outer diameters of 0.9 mm, was simulated using the GEANT4 Monte Carlo (MC) simulation code. The novel DMBT needle concept consists of a 14-gauge nitinol needle with an outer diameter of 2.1 mm and a crust thickness of 0.1 mm, which housed a platinum shield inside. A single groove, consistent with the outer diameter of each source, was incorporated inside the platinum shield to accommodate the HDR source. The maximum thickness of the shield was 0.8 mm. To evaluate the effectiveness of the DMBT needle concept in reducing urethra dose, two proof-of-concept in silico DMBT plans were created from the standard clinical plan by replacing two needles close to the urethra with the DMBT needles. The dosimetrical comparisons between the two DMBT plans, and the clinical BT plan were done by assessing the target coverage, and urethral, bladder and rectum dose. The MC results showed that the use of the novel DMBT needle could reduce the radiation dose by approximately 35% at 1 cm distance from the needle behind the platinum shield, as compared to the unshielded side. Additionally, when using the same dose volume histogram (DVH) planning criteria as the original plan, the DMBT plan reduced the maximum urethral dose at the pre-apical region by 16% and 28% for 0 mm and 2 mm planning organ at risk (PRV) margins, respectively, while maintaining equivalent V100 and D90 target coverage. The novel DMBT needle design offers a promising solution for reducing the dose to the pre-apical region of the urethra without compromising target coverage, increasing the dose to other organs-at-risk, or increasing the treatment time.

Treatment of Recurrent Orbital Rhabdomyosarcoma with Exenteration and HDR Brachytherapy in a Custom Mold

Rhabdomyosarcoma (RMS) is the most frequent cancer affecting the orbit in children. The orbit is classified as a favorable site for RMS as treatment with chemotherapy and radiation is effective. Local failure for patients with RMS of the orbit has ranged from 2-16% on IRS and COG protocols. In the event of local recurrence, survival is poor, and management is difficult. We report four patients with local recurrence of orbital RMS managed with orbital exenteration followed by high dose rate (HDR) brachytherapy. Four patients were treated from 2016-2022. HDR brachytherapy with Ir-192 was delivered in a custom mold of the orbit made after the orbital exenteration procedure. Brachytherapy was given in 6-7 twice daily (BID) fractions starting 1 week after the orbital exenteration. At the time of brachytherapy, patient ages were 3, 1, 7, and 7 years. Three patients had embryonal histology and underwent initial systemic therapy with ARST0331 regimen A. The fourth patient had alveolar, FOXO1 fusion positive RMS and was initially treated as per COG D9803 regimen A. All patients had received proton radiotherapy as part of initial treatment. Three received 50.40 Gy and one received 45 Gy. Patients developed biopsy-proven, recurrent disease an average of 56 weeks (range 38-77) after initial diagnosis. All patients received salvage chemotherapy before undergoing orbital exenteration at an average of 12 weeks after recurrence (range 5-16). Three patients received 30 Gy in 6 BID fractions, and one patient received 28 Gy in 7 fractions with HDR brachytherapy using an Ir-192 source. All four patients are alive without evidence of disease at an average of 27 months (range 6-70) from recurrence and 39 months (range 21-78) from initial diagnosis. All patients have acceptable orbit healing. Two patients have asymptomatic evidence of frontal lobe edema (and in one case possible necrosis) extending 1-2 cm above the orbit. This appears to be beyond the range of the brachytherapy dosimetry, but the combination of proton beam and brachytherapy are implicated. No other toxicities have occurred. Orbital RMS has a favorable prognosis, but local failure after initial combined modality therapy can be fatal. Options for successful local salvage are limited. Orbital exenteration with HDR brachytherapy in a custom mold is an effective and safe procedure for local control in these difficult cases.

Development of Novel Focal Irradiation Tool for High-Precision Irradiation Using Clinical Brachytherapy System

Several small animals, including mice, are used to conduct research on state-of-the-art radiation therapy techniques or treatment-related toxicity. However, it is difficult to conduct the focal irradiation to a shallow depth on small animals, because irradiation using LINAC has limitations in energy and field size. The purpose of this paper was to develop a focal irradiation tool for high-precision irradiation and to evaluate beam characteristics. We designed the collimator of 1 mm diameter consisting of tungsten material for high-precision irradiation applied to the clinical brachytherapy system and the percent depth dose and horizontal profile were measured. We compared the depth dose and horizontal profile with 4 mm diameter SRS cone for 6 MV in LINAC. We measured the PDD and horizontal profile using EBT3 film for high-precision irradiation of 1 mm diameter using Ir-192 source. In case of 4 mm diameter, the beam was measured using edge detector. In addition, all measurements were compared with the results of planning tool simulation. In case of focal irradiation tool, the maximum dose showed at the surface for both measurement and simulation, and 26% and 32% doses at 1 mm depth, respectively. In addition, FWHM at a 1 mm depth showed that high-precision irradiation was possible with measurement and simulation results of 1.86 and 1.28 mm. In case of LINAC, the maximum dose was showed at a depth of 1 cm and 0.8 cm in the measurement and simulation, respectively. Even if the smallest cone is used, the FWHM at a dmax depth was 4.0 mm in both simulation and measurement. We overcame the limitation for energy and field size through the focal irradiation tool for high-precision irradiation. The focal irradiation tool enables high dose delivery to the shallow depth. In addition, small FWHM reduced dose delivery to the periphery at a specific depth and enabled accurate dose delivery. These results mean that the focal irradiation tool can be useful in small animal experiments that require accurate doses near the shallow depth.

Development of a hybrid line dosimeter using lead (II) iodide and Gd2O2S:Tb for dose monitoring in brachytherapy

In brachytherapy, a radiation source is injected into the human body, and accurate evaluation of the source location is critical for patient safety. However, identification of the source location each time is difficult. Therefore, in this study, a PbI2-based hybrid line dosimeter that can reduce drift current while measuring dose in real time was fabricated by adding Gd2O2S:Tb (0–20 wt%), and the sensitivity of the hybrid line sensor was characterized using an 192Ir source. Before creating the line dosimeter, a unit-cell sensor was fabricated to define the optimal addition of Gd2O2S:Tb. The results showed that a dosimeter with 20 wt% Gd2O2S:Tb yielded the lowest drift current, which was 92% lower than that with PbI2alone (relative standard deviation [RSD], 0.73%) to allow the most stable signal output. Evaluation of the line dosimeter showed that the signal output was stable with RSD ≤ 1.5% and R 2 ≥ 0.9990 for all 25 pixels except one. The sensitivity was high at the pixel closest to the source location, and the accuracy of the source location was as high as ±2 mm. The PbI2-based hybrid line dosimeter with Gd2O2S:Tb fabricated in this study was shown to be applicable as a dosimeter to determine the source location accurately in brachytherapy.

PP03 Presentation Time: 3:48 PM: Realtime Ir-192 Source Localization Employing Spatio-Temporal Sensing along Brachytherapy Catheter

PP03 Presentation Time: 3:48 PM: Realtime Ir-192 Source Localization Employing Spatio-Temporal Sensing along Brachytherapy Catheter

PO61: Can Current Monotherapy High-Dose-Rate Prostate Brachytherapy Prescriptions Overcome Intrafractional DNA Damage Repair and 192Ir Source Decay?

PO61: Can Current Monotherapy High-Dose-Rate Prostate Brachytherapy Prescriptions Overcome Intrafractional DNA Damage Repair and 192Ir Source Decay?

Energy and exergy-based threshold setting for the auxiliary heating source of a hybrid solar/IR drying system

In special case of spirulina drying, the energy and exergy investigations were performed for a pure solar dryer and a hybrid solar/infrared (IR) drying system. For three drying temperatures 40, 50 and 60 °C, the specific energy consumption (SEC) and energy utility ratio (EUR) were evaluated and it was found that the maximum contribution of IR to the drying process was at 40 °C, in which SEC was reduced by 12.18 % and EUR was increases by 14.4 %. But at higher temperatures, negligible contribution of auxiliary heat source was found and less fraction of supplied power was used for removing the water content of the samples. The variation of exergy efficiency was also evaluated at different temperatures, and it was noted that the hybrid dryer had the best performance at 40 °C, while the conventional solar dryer showed better exergy efficiencies at 50 °C and 60 °C. As a result, a convenient criterion was established for optimum use of IR source in a hybrid system. Uncertainty analysis was performed.

Low level detection of acetone vapor by improvised design of high “Q” tunable frequency Helmholtz photoacoustic cell using UV, mid- IR and THz sources

The paper reports the designing and fabrication aspects of a high “Q = 492.3” Helmholtz photoacoustic (PA) cell employed for the trace level detection of acetone, a biomarker by using 266 nm- UV, Mid-IR (5.4–10.6 micron) and 0.11 Terahertz (THz) sources. The designed Helmholtz PA cell is made of Aluminum and possesses a natural frequency tunable between 1.4 to 4.4 kHz range using a movable piston arrangement of the microphone sensor. Numerous types of disorders, including diabetes, asthma, lung cancer, etc., can be diagnosed using the acetone concentration obtained through breath analysis. The comparative study is related to the response of different types of excitation mechanisms contributed by electronics, vibrational and rotational modes of acetone. The low-level detection (LoD) limit for acetone is of the order of 5.06 & 7.92 ppbV, and 15.3 pptV, respectively, in UV, Mid-IR, and THz region. This study contributes to the development of a highly sensitive, non-invasive acetone detection and quantification modality.

Retrospective Analysis of Treatment Time Calculation Agreement Between TPS and Manual Method and Source Strength Verification for 13 HDR Ir-192 Sources In Flexitron Brachytherapy Unit: A Single Institute Experience

Introduction: Source strength measurement and verification during every source exchange in high dose rate (HDR) Brachytherapy 192Ir is primary part of quality assurance program as recommended by national regulatory body Atomic Energy Regulatory Board, Mumbai, India. The purpose of this study was to evaluate RAKR (in-house measurement) of 192Ir using re-entrant well-type ionization chamber with stated RAKR values as provided by the manufacturer in source certificate and to check the accuracy of the Oncentra treatment planning system calculation with manual method of computation at different intervals for 13 HDR Ir-192 sources. Materials And Methods: We have retrospectively evaluate the in-house measured RAKR with the calibrated Standard Imaging HDR 1000 PLUS Well chamber /electrometer CDX 2000B for 13 HDR Ir192 sources with stated RAKR and the treatment time calculation accuracy of Oncentra TPS verified by manual method of computation using TG-43 formalism. Results: The study shows, that the measured RAKR and stated RAKR were well within the tolerance limits set by the national and international recommendations i.e. ±3 % for 13 HDR Ir192 sources. The verification of TPS treatment time calculation with manual calculation for single source as well as for multi-source lies within ±2%. Conclusions: There is good agreement between in-house measured and vendor quoted values of RAKR which shows that the chamber has been stable to better than ±3 % and manual calculations shows agreement with the TPS outcome within ±2% for 13 HDR Ir192 sources. The manual method of computation works reliably and reassures the TPS functioning.

Attenuation properties of 3D-printed materials for an Ir-192 high dose rate source using Valencia skin applicators

ObjectiveTo evaluate the physical properties of commonly used 3D-printed materials and the dose attenuation around a high-dose-rate 192Ir source, in order to provide a reference for selecting appropriate 3D-printed materials for brachytherapy. MethodsFifteen 3D-printed materials (12 non-metallic material and 3 metallic material) were assessed. Each material was fabricated into a wafer with a diameter of 30 ​mm and thickness of 3 ​mm using 3D printing. The CT number of each material was measured, and attenuation measurements were conducted with a Valencia skin applicator and well-type ionization chamber. 192Ir was used as the radioactive source, and the attenuated ionization charges were normalized against that obtained in the presence of a solid water phantom at the same depth. ResultsThe CT number of nylon was (−7.78 ​± ​3.36) HU, closest to water among all materials. The CT numbers of the other 11 non-metallic materials were below 300 HU. Moreover, the CT number of the Al alloy was (1,350.89 ​± ​374.55) HU, while the CT numbers of the Ti alloy and stainless steel exceeded 2,976 HU, reaching the upper limit of the CT number range. The results of the attenuation measurements were normalized with the solid water phantom. The average attenuation coefficients of a polyamide, epoxy resin, photosensitive resin, carbon fiber, silica gel, Al alloy, Ti alloy, and stainless steel were 1.003, 0.994, 0.992, 0.995, 0.995, 0.967, 0.939, and 0.866, respectively. ConclusionsAmong the common 3D-printed materials with a density similar to that of water, nylon exhibited the best performance, while the metallic materials caused significant dose attenuation and exhibited CT number distortion. As a result, care should be taken when metallic materials are used as 3D-printed materials for brachytherapy.

A novel direction modulated brachytherapy technique for urethra sparing in high-dose-rate brachytherapy of prostate cancer

PurposeImage-guided high-dose-rate (HDR) prostate brachytherapy is a safe and effective treatment option for prostate cancer patients; however, some patients still experience acute and late genitourinary (GU) toxicity. Studies have shown that urethral dose is associated with the incidence and severity of GU toxicity. Therefore, a technique that can further spare the urethra while ensuring adequate target coverage is highly desirable. Intensity modulated brachytherapy (IMBT) designs, such as rotating shield brachytherapy (RSBT), offer ideal dosimetry theoretically but are challenging to implement clinically due to the need for high precision in moving the treatment delivery mechanisms synchronized with the source loading. In this study, we propose a novel relatively easy-to-implement solution based on the direction modulated brachytherapy (DMBT) design concept, which does not involve moving parts and works effectively with the ubiquitous 192Ir source. Materials and MethodsThe popular Varian VS2000 (VS) and GammaMedPlus (GMP) 192Ir sources, with outer diameters of 0.6 mm and 0.9 mm, respectively, were simulated using the GEANT4 Monte Carlo (MC) simulation code. The novel DMBT needle concept consists of a 14-gauge nitinol needle, which houses a platinum shield inside. A single groove, consistent with the outer diameter of each source, was incorporated inside the platinum shield to accommodate the HDR source. The maximum thickness of the shield was 1.1 mm (0.8 mm) for the VS (GMP) source. To evaluate the effectiveness of the DMBT needle concept in reducing urethral dose, 6 patient cases were studied and DMBT plans were created by replacing two needles close to the urethra with the DMBT needles. The dosimetric comparisons between the DMBT and reference clinical plans were done by assessing the dose-volume histogram (DVH) planning criteria for the target coverage and organs-at-risk. ResultsThe MC results showed that the use of the novel DMBT needle design with the VS source (GMP source) could reduce the dose by 49.6% (39.2%) at 1 cm from the needle behind the platinum shield, as compared to the unshielded side. Additionally, when using the same DVH planning criteria as the original plan, the DMBT plan with the VS (GMP) source reduced the maximum urethral dose by 10.3% ± 5.6% (8.1% ± 5.0%) and 17.7% ± 14.2% (16.6% ± 13.3%) for 0 mm and 2 mm margins, respectively, while maintaining equivalent V90% and D100 target coverage. ConclusionThe novel DMBT technique offers a promising clinically implementable solution for sparing urethra, particularly in pre-apical region, without compromising the target coverage or increasing treatment time.

Suitability Assessment of CsPbI_3 Dosimeter with ^192Ir Source for Brachytherapy Quality Assurance

In brachytherapy, quality assurance (QA) is a prerequisite to minimize the dose irradiation to the healthy tissues in patients during treatment, as it evaluates the accuracy of the dose applied to the patients as well as the accuracy of the position of the irradiation. Therefore, a strong emphasis has been placed on brachytherapy QA in clinical practice. This study assessed the suitability of a CsPbI3 dosimeter for the brachytherapy QA system. To verify the reliability of the unit cell sensor fabricated with CsPbI3, the electrical parameters were evaluated, after which the position dependence of the sensor was analyzed. A high level of reliability (R 2 > 0.99) and reproducibility (relative standard deviation < 1.5%) were observed. The maximal value measured at the isocenter of the sensor as the distance of the dosimeter from the irradiation source was gradually decreased. When the optimal angle was assessed, the variation was as high as 5.01 nC depending on the form of the 192Ir source. Therefore, the CsPbI3 dosimeter fabricated in this study is a suitable substitute for the conventional QA dosimeter.

Discovering New B[e] Supergiants and Candidate Luminous Blue Variables in Nearby Galaxies

Mass loss is one of the key parameters that determine stellar evolution. Despite the progress we have achieved over the last decades we still cannot match the observational derived values with theoretical predictions. Even worse, there are certain phases, such as the B[e] supergiants (B[e]SGs) and the Luminous Blue Variables (LBVs), where significant mass is lost through episodic or outburst activity. This leads to various structures forming around them that permit dust formation, making these objects bright IR sources. The ASSESS project aims to determine the role of episodic mass in the evolution of massive stars, by examining large numbers of cool and hot objects (such as B[e]SGs/LBVs). For this purpose, we initiated a large observation campaign to obtain spectroscopic data for ∼1000 IR-selected sources in 27 nearby galaxies. Within this project we successfully identified seven B[e] supergiants (one candidate) and four Luminous Blue Variables of which six and two, respectively, are new discoveries. We used spectroscopic, photometric, and light curve information to better constrain the nature of the reported objects. We particularly noted the presence of B[e]SGs at metallicity environments as low as 0.14 Z⊙.

Gadolinium dose enhancement determination by unlaminated EBT3 films irradiated with 192Ir brachytherapy source

In this work, Gafchromic® EBT3 films were carefully delaminated and resealed with a thin mylar film of 12 μm for implementing accuracy measurements of Gd dose enhancement by a192Ir brachytherapy source. The intervened dosimeters were previously characterized in terms of their quality intervention (mechanical damage and dosimetry modification). The dose enhancement measurements were implemented in a phantom formed by a set of acrylic slabs of 30 × 30 × 0.5 cm3 machined to contain in the central axis 2 vials of 1.25 × 1.25 × 4.5 cm3 which were filled with a 20 mg/ml solution of Gd agents and with water simulating a tumoral phantom doped and undoped with Gd. In the center of the phantom, a machined acrylic slab was placed to introduce the 2.5 mm flexible guide of GammaMedplus iX equipment to position the source. Fragments of delaminated and resealed EBT3 of 0.9 × 4 cm2 were placed inside the second vial and 0.5 cm away from it, at 1.95 cm and 3.55 cm from the radioactive source respectively, to measure simultaneously the tumor dose enhancement and the radiation shielding produced at a proximal zone. CT images of the phantom were taken to prescribe 5 Gy to 1.95 cm (EBT3 film position) using a Varian BrachyVision™ planning system. Films were read out by a flatbed scanner Epson V750 PRO, 48 h after irradiation. The measurements in both tumor and healthy tissue were repeated ten times in each condition to analyze the uncertainties of the complete experimental realization. The results showed variations in the response of the intervened dosimeters, less than 1.7% for the range of interest and average fluctuations in the readout of 4.6%. The implemented dosimeter showed the feasibility of measuring dose enhancement by 192Ir source of 13 ± 7% for the concentration studied. Additionally, radiation shielding up to 6% was obtained, consistent with what has been reported in the literature.

Development of quality assurance dosimeter for brachytherapy based on CsPbBr3 and evaluation of applicability

In brachytherapy, since a radioactive source is inserted into the human body to kill tumor tissue, it is important to accurately determine the positional accuracy of the source. In this study, we aimed to develop a dosimeter that can be used for brachytherapy using CsPbBr3. This material can replace existing materials for radiation detectors because it is cheaper than others and has a simple manufacturing process. In addition, the basic performance of the dosimeter was evaluated by analyzing reproducibility, linearity, position (distance) dependence, and angular dependence with the 192Ir source. As a result of the reproducibility evaluation, the relative standard deviation (RSD) was 1.07%, which satisfied the standard deviation criteria of 1.50%. As a result of the linearity evaluation by linear regression analysis, the R 2 value was 0.9991, which was higher than the standard criterion of an R 2 value of 0.9990. As a result of the position (distance) dependence evaluation, the signal value decreased exponentially and uniformly according to the inverse square law of the distance up to 3 cm. As a result of angular dependence evaluation, the signal value of the dosimeter 10 cm away from the front of the source was 5.64 μC, and the signal values of the dosimeter 10 cm away from the sides of the source were 8.49 μC on the left and 8.91 μC on the right. From these four results of reproducibility, linearity, position (distance) dependence, and angular dependence, we anticipate that the manufactured CsPbBr3 dosimeter with performance outcomes beyond the standards can be used as a dosimeter for brachytherapy.

The role of image-guided volume-adapted high-dose-rate endorectal brachytherapy boost in total neoadjuvant treatment of distal locally advanced rectal cancer.

3611 Background: Endorectal brachytherapy has been used as palliative or preoperative treatment for advanced or locally advanced rectal cancer, with moderate radiation induced toxicity. This study aimed to explore the efficacy of high-dose-rate 192Ir brachytherapy combined with external beam radiotherapy (EBRT) in total neoajuvant treatment (TNT) of distal rectal cancer. Methods: From January 2017 to December 2022, eligible rectal adenocarcinoma patients were assessed as clinical stage II -III, with primary tumor located in distal rectum (≤5 cm from anal verge). The local staging was determined using endorectal ultrasound and magnetic resonance imaging (MRI). In addition, cases included in this study underwent preoperative semiweekly endorectal brachytherapy of 8-12Gy/2-3F/1-1.5w, followed by EBRT of 45-50.4Gy/25-28F, fluorouracil-based concurrent and consolidation chemotherapy. The brachytherapy was image-guided volume-adapted, and delivered by multi-channel 192Ir source applicators with different diameters. Radiation proctitis was graded from 0 to 4 using Radiation Therapy Oncology Group (RTOG) criteria. Results: A total of 40 cases were enrolled in this retrospective study, biopsy-proven and diagnosed as clinical stage II (n = 8), stage III (n = 32). The rates of T4 and positive circumferential resection margin (CRM) were 35% and 87.5% respectively. The median value of the interval from completion of radiotherapy to operation was 86 days (interquartile range: 75-98 days). After neoadjuvant treatment, 2 cases were undergoing the watch-and-wait strategy with sustained clinical complete response (cCR), 38 patients received operation and R0 resection rate was 97.4%. The pathological complete response (pCR) rate was 28.9%, and major pathological regression rate was 67.5%. The theoretical rate of anus preservation was 62.5%, including 6 of 21 cases underwent abdominoperineal resection but achieved pCR, 17 cases underwent low anterior resection or intersphincteric resection, and 2 cases with sustained cCR. After a median follow-up of 37 months (range 12-68 months), the 3-year disease-free survival, local-regional reccurence-free survival and overall survival was 81.1% (95%CI: 64.3%-91.2%), 94.9% (95%CI: 80.6%-98.5%) and 96.9% (95%CI: 82.1%-99.4%), respectively. No patients experienced Grade ≥3 radiation proctitis. The median Wexner fecal incontinence score of anus-preserving cases was 1 (range 0-8). Subgroup analysis showed that the complete response rate (pCR or sustained cCR) was lower in cases received 2 fractions brachytherapy than those received 3 fractions (27.8% vs 36.4%). Conclusions: The addition of image-guided volume-adapted high-dose-rate 192Ir endorectal brachytherapy boost to TNT could improve the pathological tumor response and anus preservation rate in distal locally advanced rectal cancer.

Development of a Primary Iridium Solution Standard Traceable to the International System of Units.

The purpose of this work was to develop a primary solution standard for iridium (Ir) that is directly traceable to the International System of Units (SI). The candidate starting material was ammonium hexachloroiridate hydrate, ((NH4)3IrCl6·3H2O), the Ir salt. The SI traceability of the Ir salt was established by the gravimetric reduction (GR) of the salt to the metal under H2. GR traces the results of the analysis directly to the SI base unit of mass, the kg. The GR was also performed on high-purity Ir metal powder, an independent source of Ir, used as a comparison material for the salt. A method for dissolving the Ir metal was developed by modifying information found in the literature. Trace metallic impurities (TMI) analysis was performed on the Ir salt using ICP-OES and ICP-MS. Inert gas fusion (IGF) analysis provided data for the O, N, and H content of the gravimetrically reduced and unreduced Ir metals. The combined results of the TMI and IGF analyses provided the purity data, a required component for the claim to SI traceability. Solution standards were gravimetrically prepared from the candidate SI traceable Ir salt. Solution standards for comparison were prepared from the dissolved, unreduced high-purity Ir metal powder. These solutions were compared by a high-precision ICP-OES method. Agreement in the results between these Ir solutions, with uncertainty estimates calculated by error budget analysis, confirmed the accuracy of the Ir assay in the candidate SI traceable Ir salt, (NH4)3IrCl6·3H2O, thus confirming the concentrations and uncertainties for the primary SI traceable Ir solution standards made from the (NH4)3IrCl6·3H2O.