arXiv subjects

Mazen Moussallem

Publications and source records attributed to Mazen Moussallem.

3 recordsLinked to original sources

arXiv2026

Voxel-Based Conversion of Hypofractionated Radiotherapy Dose Distributions to 2 Gy-Equivalent OAR Constraints: Proof-of-Concept Demonstrating the Radiobiological Benefits of Hypofractionation in a Prostate Radiotherapy Case

Objectives: Existing voxel-based dose converters transform hypofractionated dose distributions into biologically effective dose (BED) or equivalent dose in 2 Gy fractions (EQD2), but they are not reliably applicable to organ-at-risk (OAR) dose constraints, particularly in low-dose regions, which may lead to dose misinterpretation. This study develops and demonstrates a voxel-based method to convert hypofractionated dose distributions into 2 Gy-equivalent OAR constraints. Methods: To2GyConstraints converter (www.healthy-innovations.com) was applied to a prostate cancer case. The method uses the Linear Quadratic (LQ) model for doses per fraction less than or equal to 7.5 Gy and the Linear Quadratic Linear (LQ-L) model for higher doses. For voxel fraction doses below a threshold defined as the mean between the prescribed hypofractionated fraction dose and 2 Gy, an equivalent number of fractions is calculated. The method then applies an EQDx-type conversion, rather than EQD2, using this calculated fraction number to better reproduce normofractionated dose behavior. Results: For doses above the defined threshold, unlike BED, the To2GyConstraints model produced results consistent with EQD2 and provided clinically realistic dose values comparable to standard dosimetric constraints, thereby offering a clearer demonstration of the radiobiological benefits of hypofractionation in prostate cancer. For doses below the threshold, unlike EQD2, the To2GyConstraints model showed behavior consistent with BED, yielding higher dose estimates when converted to a normofractionation scheme. Conclusions: To2GyConstraints converter shows promising results for radiobiological interpretation of hypofractionation. Further multicenter validation is required. Advances in knowledge: A voxel-based method enabling application of normofractionation OAR constraints to hypofractionated dosimetry after conversion.

physics.med-ph↗

arXiv2021

Dynamic radiological anthropomorphic thoracic phantom with a deformable chest wall

Purpose: Anthropomorphic phantoms can be used in radiotherapy to confirm dose distributions. In this work, a prototype phantom with a deformable chest wall was created based on real human. Methods: A technique similar to 3-dimensional printing was utilized, which involved collecting computed tomography (CT) images of a patient as a reference, contouring the organs, projecting them onto polystyrene panels, and pouring appropriate material into them. Balloons attached to a ventilator and an air compressor were used to periodically generate a breathing cycle. A silicone tumor was also implanted in the lower lobe of the right balloon to investigate its displacement during respiration. During silent and deep breathing, qualitative and quantitative tests were conducted, and the results were compared to research conducted on real humans. Results: The CT images and the shape of the phantom matches those of the real patient. However, few organs densities can be optimized. The air pressure in the ventilator was so weak that it could only create quiet breathing phantom motion on its own. However, deep breathing phantom motion was obtained manually by only using the air compressor. As a consequence, reproducibility and repeatability studies were done only for quiet breathing and results were acceptable. When compared to the real scenario, the phantom's motion amplitudes were appropriate, except in the lateral direction and abdomen section, near the diaphragm, they were negligible. In addition, the tumor displacement was predominant in the Anterior-Posterior direction rather than the Superior-Inferior direction as it should be. Conclusions: As a prototype, the work was successful, nevertheless, several improvements are required, such as optimization of the shape of the mediastinum and developing a mechanical diaphragm movement system synced with a high-pressure air pump.

physics.med-ph↗

arXiv2021

New dosimetry planning strategy based on continuous dose gradient used to reduce dose estimation errors due to respiratory motion in breast radiation therapy

A new strategy for radiation therapy dosimetry planning (RTDP) used to reduce dose estimation errors due to respiratory motion in breast treatment was illustrated and evaluated in this study. On CT data set acquired for breast treatment, six different RTDP tangential techniques were performed: (i) three-dimensional conformal radiotherapy (3DCRT) with physical wedge, (ii) 3DCRT with virtual wedge, (iii) motion management technique (MMT) with physical wedge, (iv) MMT with virtual wedge, (v) 3DCRT with field-in-field, and (vi) intensity-modulated radiation therapy (IMRT) with direct aperture optimization. These anti-motion techniques were considered to generate continuous dose degradation to avoid drastic changes in the delivered doses that involve the edge regions of the beams. A comparison was made between the delivered and simulated doses, with and without the presence of motions simulations. This study demonstrates that techniques without motion management can be affected by motions that can lead to a difference equal to 19 % between the delivered and the planned doses in a point located near to the beams collimators edges, and to a difference up to 3 % on multi-leaf collimators (MLCs) edges (gamma pass rates were 87.9 % for 3%/3mm). These differences were reduced to 11 % and to less than 3 % (gamma pass rates were 100 % for 3%/3mm) when MMT were used. As a conclusion, in tangential techniques motion can affect dose estimations on the MLCs and beams collimators edges. The proposed MMT reduce this effect to estimate the delivered dose accurately.

physics.med-ph↗