Prdm15 acts upstream of Wnt4 signaling in anterior neural development of Xenopus laevis

Mutations in PRDM15 lead to a syndromic form of holoprosencephaly (HPE) known as the Galloway-Mowat syndrome (GAMOS). While a connection between PRDM15, a zinc finger transcription factor, and WNT/PCP signaling has been established, there is a critical need to delve deeper into their contributions to early development and GAMOS pathogenesis. We used the South African clawed frog Xenopus laevis as the vertebrate model organism and observed that prdm15 was enriched in the tissues and organs affected in GAMOS. Furthermore, we generated a morpholino oligonucleotide-mediated prdm15 knockdown model showing that the depletion of Prdm15 leads to abnormal eye, head, and brain development, effectively recapitulating the anterior neural features in GAMOS. An analysis of the underlying molecular basis revealed a reduced expression of key genes associated with eye, head, and brain development. Notably, this reduction could be rescued by the introduction of wnt4 RNA, particularly during the induction of the respective tissues. Mechanistically, our data demonstrate that Prdm15 acts upstream of both canonical and non-canonical Wnt4 signaling during anterior neural development. Our findings describe severe ocular and anterior neural abnormalities upon Prdm15 depletion and elucidate the role of Prdm15 in canonical and non-canonical Wnt4 signaling.

Internal Bremsstrahlung, the missing process in beta decay Monte Carlo simulation: The relevance in 32P Dose-Point-Kernel estimation

PURPOSE

In nuclear medicine, Dose Point Kernels (DPKs), representing the energy deposited all around a point isotropic source, are extensively used for dosimetry and are usually obtained by Monte Carlo (MC) simulations. For beta-decaying nuclides, DPK is usually estimated neglecting Internal Bremsstrahlung (IB) emission, a process always accompanying the beta decay and consisting in the emission of photons having a continuous spectral distribution. This work aims to study the significance of IB emission for DPK estimation in the case of ³²P and provide DPK values corrected for the IB photon contribution.

METHODS

DPK, in terms of the scaled absorbed dose fraction, F(R/X₉₀), was first estimated by GAMOS MC simulation using the standard beta decay spectrum of ³²P, F_β(R/X₉₀). Subsequently, an additional source term accounting for IB photons and their spectral distribution was defined and used for a further MC simulation, thus evaluating the contribution of IB emission to DPK values, F_β+IB(R/X₉₀). The relative percent difference, δ, between the DPKs obtained by the two approaches, F_β+IB vs. F_β, was studied as a function of the radial distance, R.

RESULTS

As far as the energy deposition is mainly due to the beta particles, IB photons does not significantly contribute to DPK; conversely, for larger R, F_β+IB values are higher by 30-40% than F_β.

CONCLUSIONS

The inclusion of IB emission in the MC simulations for DPK estimations is recommended, as well as the use of the DPK values corrected for IB photons, here provided.

Technical note: The contribution of internal bremsstrahlung to the 90 Y dose point kernel

BACKGROUND

Internal dosimetry has an increasing role in the planning and verification of nuclear medicine therapies with radiopharmaceuticals. Dose Point Kernels (DPKs), quantifying the energy deposition all around a point source, in a homogenous medium, are extensively used for 3D dosimetry and nowadays are mostly evaluated by Monte Carlo (MC) simulation. To our knowledge, DPK for beta emitters is estimated neglecting the continuous photon emission due to the Internal Bremsstrahlung (IB), whose contribution to the absorbed dose can be relevant beyond the maximum range of betas, as evidenced in recent works.

PURPOSE

Aim of this study was to investigate and quantify, by means of MC simulations, the contribution of IB photons to DPK calculated for ⁹⁰ Y and provide the updated ⁹⁰ Y DPK.

METHODS

The overall radiation due to the decay of a ⁹⁰ Y point source, placed at the centre of concentric water shells of increasing radii from 0.02 cm to 20 cm, was simulated with GAMOS, including the IB source term whose spectral distribution was described by an analytical model. Energy deposition was scored in the shells as a function of the distance from the source, R, and DPK was estimated in terms of the scaled absorbed dose fraction, F(R/X₉₀ ), where X₉₀ is the range within which the beta particles deposit 90% of their energy.

RESULTS

A comparison between the two simulated absorbed dose distributions, calculated with or without IB, clearly shows that the latter (incomplete) choice is consistent with the findings of other Authors and systematically underestimates the absorbed dose imparted to the tissue. ⁹⁰ Y DPK values currently used are underestimated by 20%-34% for R>2X₉₀ .

CONCLUSIONS

The revised values provided in this work suggest that the inclusion of IB emission in DPK evaluations is advisable for pure beta emitters.

An analytic model to calculate voxel s-values for177Lu

OBJECTIVE

¹⁷⁷Lu is one of the most employed isotopes in targeted radionuclide therapies and theranostics, and 3D internal dosimetry for such procedures has great importance. Voxel S-Values (VSVs) approach is widely used for this purpose, but VSVs are available for a limited number of voxel dimensions. The aim of this work is to develop an analytic model for the calculation of 177Lu-VSVs in any cubic voxelized geometry of practical interest.

APPROACH

Monte Carlo (MC) simulations were implemented with the toolkit GAMOS to evaluate VSVs in voxelized geometries of soft tissue from a source of¹⁷⁷Lu homogeneously distributed in the central voxel. Nine geometric setups, containing 15×15×15 cubic voxels of sideslranging from 2 mm to 6 mm, in steps of 0.5 mm, were considered. For eachl, the VSVs computed as a function of the "normalized radius",R_n= R/l(withR= distance from the center of the source voxel), were fitted with a parametric function. The dependencies of the parameters as a function oflwere then fitted with appropriate functions, in order to implement the model for deducing¹⁷⁷Lu-VSVs for anylwithin the aforementioned range.

MAIN RESULTS

The MC-derived VSVs were satisfactorily compared with literature data for validation, and the VSVs computed with the analytic model agree with the MC ones within 2% forR_n≤2 and within 6% forR_n>2.

SIGNIFICANCE

The proposed model enables the easy and fast calculation, with a simple spreadsheet, of¹⁷⁷Lu-VSVs in any cubic voxelized geometry of practical interest, avoiding the necessity of implementingad-hocMC simulations to estimate VSVs for specific voxel dimensions not available in literature data.

Enhancement of radiation exposure risk from β-emitter radionuclides due to Internal Bremsstrahlung effect: A Monte Carlo study of 90Y case

Employment of β-decaying radionuclides, used in many fields (industrial, clinical, research) requires a correct assessment of the operators' radiological exposure. Usually, in the dosimetric evaluation, the contribution coming from Internal Bremsstrahlung (IB) accompanying the β-decay is not kept into account; nevertheless, this negligibility does not always appear justified, at least for high-energy β-emitters. By means of Monte Carlo (MC) simulations, we showed how the contribution from IB photons is noteworthy for the evaluation of the overall radiation absorbed dose in the case of ⁹⁰Y source. We evaluated an increase of the absorbed doses, respectively for a point source and the considered receptacles, up to + 34% and + 60% or + 15% and + 28%, depending on the adopted model of IB spectrum. These results demonstrate the relevance of IB phenomenon in radiation protection estimations and suggest extending future theoretical and experimental studies to other β-decaying radionuclides.

Calculating equivalent dose received from a patient undergoing nuclear medicine procedure by merge phantoms tool and GAMOS/Geant4 6.0.0 software

PURPOSE

This report introduces a tool for merging two voxel phantoms to calculate the deposited dose that a person receives from a patient undergoing Nuclear medicine procedures.

MATERIALS AND METHODS

The phantoms must be converted to the text format used by GEANT4 to treat DICOM images via the GAMOS utilities. The Merge Phantoms Tool can merge two phantoms in two different cases: standing either side by side or opposite. The merged phantom is also in text format and is subsequently input back into GAMOS to calculate the equivalent dose that a person receives from a patient. The equivalent doses to the eyes of people in contact are calculated in a case where a patient was administered 185 MBq of 18F-FDG during a PET examination.

RESULTS

The corresponding doses when the two phantoms are standing opposite are greater than those when they are standing side by side and smaller than those from point and tube source calculated by Sumi Yokoyama at any distance.

CONCLUSIONS

The Merge phantoms tool and GAMOS software can be used to calculate the deposited dose that a person receives from a patient. An accurate dose calculation can be used for radiation protection, or deciding whether a patient can be released from isolation if the dose is small even in a close contact.