A GATE/Geant4 Monte Carlo toolkit for surface dose calculation in VMAT breast cancer radiotherapy

Evaluation of dose perturbations around iodine-125 seed sources in supplemental external beam prostate radiotherapy

We investigated dose perturbations caused by 125I seeds in patients undergoing supplemental external beam radiotherapy (EBRT) for prostate cancer. We examined two types of nonradioactive seed models: model 6711 and model STM1251. All experiments were performed using a water-equivalent phantom. Radiochromic film was used to measure the dose distributions adjacent to the seeds upstream and downstream of the external beam source. Single and clusters of multiple seeds were placed in slots in a solid water (SW) slab to measure dose perturbations with separate versus dense seed placement at beam energies of 6 or 10 MV. Monte Carlo simulations (MCSs) were also performed to include the theoretical basis against film dosimetry. Distinct patterns of dose enhancement (buildup [BU]) were upstream, and dose reduction (builddown [BD]) were downstream of the radiation source. Model 6711 with lower photon beam energies produced larger dose perturbations of BU and BD than the model STM1251. The results showed the same tendency with different seed placements and beam energies. However, these differences were not observed in the rotational irradiation measurement, which replicated a clinical plan. Dose perturbations around seeds result in dose enhancement and dose reduction with varying impact depending on the photon beam energy and seed type. This has the potential to cancel out these perturbations using multiple beam direction fields.

A GATE Monte Carlo framework for dosimetric evaluation in mammography in an Algerian hospital

A framework has been developed for dosimetric evaluation in mammography, using the GATE Monte Carlo (MC) platform, to simulate a MAMMOMAT 3000 Nova mammograph (Siemens) available at the University Hospital Center "1st November 1954" of Oran (EHU Oran 1er Novembre, 1954), Algeria. Calculated quantities such half-value layer (HVL), Entrance Surface Dose (ESD) and Mean Glandular Dose (MGD) have been compared to experimental data in order to validate the modeling of mammography examinations. Results are consistent with previous studies and show a good agreement between measurements and Monte Carlo calculations. By varying the tube voltage from 25 to 35 kV, we have estimated an increasing of a factor of 2.4 in ESD, and a factor of 2.75 for the MGD in a breast phantom. Furthermore, the current intensity of 100 mAs used for a beam quality combination (Mo/Mo) Anode/filter was found suitable for the tube voltages of 25-29 keV since the MGD does not exceed the limits set by the different quality insurance protocols. This GATE dose calculation framework thus provides a very useful tool for the optimization of mammography examinations at Oran hospital by allowing a better estimation of the dose delivered to patients according to the parameters of the examination.

Technical note: Simulation of lung counting applications using Geant4

A Geant4 simulation package has been developed to investigate and test detector configurations for lung counting applications. The objective of this study was to measure radiation emitted from the human body and to make a qualitative comparison of the results of the simulation with an experiment. Experimental data were measured from a plastic phantom with a set of lungs containing ²⁴¹Am activity. For comparison, simulations in which ²⁴¹Am activity was uniformly distributed inside the lungs of the ICRP adult reference computational phantom were made. The attenuation of photons by the chest wall was simulated and from this photopeak efficiency and photon transmission were calculated as a function of photon energy. The transmission of 59.5 keV gamma rays, characteristic of the decay of ²⁴¹Am, was determined from the computational phantom as a function of the angular position of the detector. It was found that the simulated detector response corresponds well with that from an experiment. The simulated count rate below 100 keV was 10.0(7) % greater compared to the experimental measurement. It was observed that 58.3(4) % of photons are attenuated for energies below 100 keV by the chest wall. In the simulation, the transmission of 59.5 keV gamma rays varied from 13.8(2) % to 38.0(4) % as a function of the angular position of the detector. The results obtained from the simulations show a satisfactory agreement with experimental data and the package can be used in the development of future body counting applications and enables optimization of the detection geometry.

Dose-volume constraints for head-and-neck cancer in carbon ion radiotherapy: A literature review

BACKGROUND

Carbon ion radiotherapy (CIRT) has been applied in cancer treatment for over 25 years. However, guidelines for dose-volume constraints have not been established yet. The aim of this review is to summarize the dose-volume constraints in CIRT for head-and-neck (HN) cancer that were determined through previous clinical studies based on the Japanese models for relative biological effectiveness (RBE).

METHODS

A literature review was conducted to identify all constraints determined for HN cancer CIRT that are based on the Japanese RBE models.

RESULTS

Dose-volume constraints are reported for 17 organs at risk (OARs), including the brainstem, ocular structures, masticatory muscles, and skin. Various treatment planning strategies are also presented for reducing the dose delivered to OARs.

CONCLUSIONS

The reported constraints will provide assistance during treatment planning to ensure that radiation to OARs is minimized, and thus adverse effects are reduced. Although the constraints are given based on the Japanese RBE models, applying the necessary conversion factors will potentially enable their application by institutions worldwide that use the local effect model for RBE.

The OpenGATE ecosystem for Monte Carlo simulation in medical physics

This paper reviews the ecosystem of GATE, an open-source Monte Carlo toolkit for medical physics. Based on the shoulders of Geant4, the principal modules (geometry, physics, scorers) are described with brief descriptions of some key concepts (Volume, Actors, Digitizer). The main source code repositories are detailed together with the automated compilation and tests processes (Continuous Integration). We then described how the OpenGATE collaboration managed the collaborative development of about one hundred developers during almost 20 years. The impact of GATE on medical physics and cancer research is then summarized, and examples of a few key applications are given. Finally, future development perspectives are indicated.

Skin Surface Dose for Whole Breast Radiotherapy Using Personalized Breast Holder: Comparison with Various Radiotherapy Techniques and Clinical Experiences

Purpose: Breast immobilization with personalized breast holder (PERSBRA) is a promising approach for normal organ protection during whole breast radiotherapy. The aim of this study is to evaluate the skin surface dose for breast radiotherapy with PERSBRA using different radiotherapy techniques. Materials and methods: We designed PERSBRA with three different mesh sizes (large, fine and solid) and applied them on an anthropomorphic(Rando) phantom. Treatment planning was generated using hybrid, intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques to deliver a prescribed dose of 5000 cGy in 25 fractions accordingly. Dose measurement with EBT3 film and TLD were taken on Rando phantom without PERSBRA, large mesh, fine mesh and solid PERSBRA for (a) tumor doses, (b) surface doses for medial field and lateral field irradiation undergoing hybrid, IMRT, VMAT techniques. Results: The tumor dose deviation was less than five percent between the measured doses of the EBT3 film and the TLD among the different techniques. The application of a PERSBRA was associated with a higher dose of the skin surface. A large mesh size of PERSBRA was associated with a lower surface dose. The findings were consistent among hybrid, IMRT, or VMAT techniques. Conclusions: Breast immobilization with PERSBRA can reduce heart toxicity but leads to a build-up of skin surface doses, which can be improved with a larger mesh design for common radiotherapy techniques.

Normal Tissue Complication Probability Model for Acute Radiation Dermatitis in Patients with Head and Neck Cancer Treated with Carbon Ion Radiotherapy

PURPOSE

This study aimed to explore the prognostic factors associated with acute radiation dermatitis (ARD). A normal tissue complication probability (NTCP) model for ARD in patients with head and neck cancer (HNC) treated with carbon ion radiotherapy (CIRT) was developed.

MATERIALS AND METHODS

A total of 187 patients were included in the analysis, and the endpoint was ≥grade 2 ARD. The biological and physical dose-surface parameters associated with ARD were used in the logistic regression model. The mean areas under the receiver operating characteristic curve (AUC) in the internal cross-validation and Akaike's corrected Information Criterion (AICc) were examined for model evaluation and selection. The multivariate logistic regression NTCP models were established based on factors with weak correlation.

RESULTS

Tumour volume, planning target volume to the skin, radiation technique and all dose-surface parameters were significantly associated with ARD (P < 0.05). Models with high performance for grade 2-3 ARD were constructed. The most significant prognostic predictors were S_{40 Gy (relative biological effectiveness, RBE)} and S_{20 Gy} [absolute surface area receiving RBE-weighted dose of 40 Gy (RBE) or physical dose of 20 Gy]. The internal cross-validation-based AUCs for models with S_{40 Gy (RBE)} and S_{20 Gy} were 0.78 and 0.77, respectively. The biological and physical dose-surface parameters had similar performance at various dose levels. However, the performance of the multivariate NTCP models based on two factors was not better than that of the univariate models.

CONCLUSIONS

NTCP models for ARD may provide a basis for the development of individualised treatment strategies and reduce the incidence of severe ARD in patients with HNC receiving CIRT. Furthermore, biological and physical dose-surface parameter-based models are comparable. However, further validation with more evaluation parameters is warranted.