Abstract: PurposeA joint Working Group of the American Association of Physicists in Medicine (AAPM), the European Society for Radiotherapy and Oncology (ESTRO), and the Australasian Brachytherapy Group (ABG) was created to aid in the transition from the AAPM TG-43 dose calculation formalism, the current standard, to model-based dose calculations. This work establishes the first test cases for low-energy photon-emitting brachytherapy using model-based dose calculation algorithms (MBDCAs).Acquisition and Validation MethodsFive test cases are developed: (1) a single model 6711 125I brachytherapy seed in water, 13 seeds (2) individually and (3) in combination in water, (4) the full Collaborative Ocular Melanoma Study (COMS) 16-mm eye plaque in water, and (5) the full plaque in a realistic eye phantom. Calculations are done with four Monte Carlo (MC) codes and a research version of a commercial treatment planning system (TPS). For all test cases, local agreement of MC codes was within & SIM;2.5% and global agreement was & SIM;2% (4% for test case 5). MC agreement was within expected uncertainties. Local agreement of TPS with MC was within 5% for test case 1 and & SIM;20% for test cases 4 and 5, and global agreement was within 0.4% for test case 1 and 10% for test cases 4 and 5.Data Format and Usage NotesDose distributions for each set of MC and TPS calculations are available online () along with input files and all other information necessary to repeat the calculations.Potential ApplicationsThese data can be used to support commissioning of MBDCAs for low-energy brachytherapy as recommended by TGs 186 and 221 and AAPM Report 372. This work additionally lays out a sample framework for the development of test cases that can be extended to other applications beyond eye plaque brachytherapy.

Abstract: Background Low-energy x-ray beams used in electronic brachytherapy (eBT) present significant dosimetric challenges due to their high depth-dose gradients, the dependence of detector response on materials, and the lack of standardized dose-to-water references. These challenges have driven the need for Monte Carlo (MC) simulations to ensure accurate dosimetry. However, discrepancies in the physics models used by different MC systems have raised concerns about their dosimetric consistency, particularly in modeling bremsstrahlung interactions. Purpose To assess the dosimetric impact of using different physics approaches in three state-of-the-art MC systems for eBT, focusing on the disagreements observed when different MC methods are used to evaluate bremsstrahlung interactions. Methods The MC studies of the Axxent S700, the Esteya, and the INTRABEAM eBT systems were performed using two EGSnrc applications (egsbrachy and egskerma), TOPAS, and PENELOPE-2018 (PEN18). The fluence spectra and depth doses were compared for simplified x-ray tube models, which maintain the target mode (transmission or reflection), the target material and thickness, and the surface applicators' source-to-surface distance. An extra simulation was made to evaluate the utility of the simplified models as proxies in predicting the most important characteristics of an accurate applicator's simulation (detailed model of INTRABEAM's 30 mm surface applicator). The EGSnrc applications and PEN18 utilized their default bremsstrahlung angular emission approaches. TOPAS used two physics lists: g4em-livermore (TOPAS(liv)) and g4em-penelope (TOPAS(pen)). Results The most significant differences between MC codes were observed for the transmission target mode. The bremsstrahlung component of the fluence spectra differed by about 15% on average, comparing PEN18, EGSnrc applications, and TOPAS(liv), with PEN18's fluences consistently lower. EGSnrc and PEN18 agreed within 3% for their characteristic spectrum components. However, PEN18's characteristic lines overreached TOPAS(liv)'s by 40%. Those spectral characteristics generated depth dose differences, where PEN18, on average, scored 9% lower than EGSnrc and TOPAS(liv). Considering TOPAS(pen) in the transmission mode, PEN18's fluence spectrum presented a lower bremsstrahlung (5%) but a higher characteristic component (10%); these spectral differences compensated, generating depth dose differences within 1% average. In the reflection target mode, EGSnrc and PEN18 agreed within 4% for the bremsstrahlung and characteristic components of the fluence spectra. With TOPAS(pen) in the reflection mode, PEN18 presents 12% lower fluences in the bremsstrahlung component but 6% higher characteristic lines. This spectral behavior diminished the depth dose differences up to 3%. Conclusion This work found considerable disagreements between three state-of-the-art MC systems commonly used in medical applications when simulating bremsstrahlung in eBT. The differences arose when the bremsstrahlung angular distribution and the atomic relaxation processes in the target became relevant. More theoretical and experimental studies are necessary to evaluate the impact of these differences on related calculations.

Abstract: We review our recent work about the stability of strange few-body systems containing N's, Lambda's, and Xi's. We make use of local central Yukawa-type Malfliet-Tjon interactions reproducing the low-energy parameters and phase shifts of the nucleon-nucleon system and the latest updates of the hyperon-nucleon and hyperon-hyperon ESCO8c Nijmegen potentials. We solve the three-and four-body bound-state problems by means of Faddeev equations and a generalized Gaussian variational method, respectively. The hypertriton, Lambda np(I)J(P) = (1/2)1/2(+), is bound by 144 keV; the recently discussed Lambda nn (I)J(P) = (1/2)1/2(+) system is unbound, as well as the Lambda Lambda nn (I)J(P) = (1)0(+) system, being just above threshold. Our results indicate that the Xi NN, Xi Xi N and Xi Xi NN systems with maximal isospin might be bound.