Journal of Medical Physics最新文献

Purpose: The purpose of this study was to systematically examine the normal tissue objective (NTO) function by comparing its variations for planning solitary brain metastasis with intensity-modulated and volumetric-modulated arc radiosurgery techniques.

Materials and methods: Twenty-two cases were retrospectively planned with two NTO parameter sets named A and B using intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) techniques. The Type A set used slope, k = 0.4 mm^-1 plus end dose, D_e = 20%, whereas the Type B set used k = 1.0 mm^-1 plus D_e = 10%. The resulting four plan types were assessed using mean dose to 5 mm exterior ring, normal brain receiving 12 Gy (V12), 5 Gy total brain dose volume (V5), gradient index (R50%), focal index (FI), Paddick conformity index (PCI), prescription isodose surface (PIDS), and MU/Gy.

Results: Brain doses were significantly lower for VMAT than for IMRT. R50% was more favorable for VMAT than for IMRT for each planning target volume (PTV). The mean FI was comparable between the corresponding IMRT and VMAT plan types. PCI was better for the IMRT_A plan type. PIDS was significantly lower for Type B plans than Type A for both techniques. For PTVs <3 cm³, IMRT plans showed poor dosimetry and required NTO settings stricter than Type B.

Conclusions: The application of NTO variations demonstrated varied dosimetry for IMRT and VMAT techniques. The NTO parameter variations produced field size and/or beamlet size/shape variations. The strict NTO parameter set generated more conformal beam apertures to reduce the brain dose. VMAT plan types showed significantly lower brain doses and better dosimetry for all target sizes.

The utilization of actinium-225 (²²⁵Ac) radionuclides in targeted alpha therapy for cancer was initially outlined in 1993. Over the past two decades, substantial research has been conducted, encompassing the establishment of ²²⁵Ac production methods, various preclinical investigations, and several clinical studies. Currently, there is a growing number of compounds labeled with ²²⁵Ac that are being developed and tested in clinical trials. In response to the increasing demand for this nuclide, production facilities are either being built or have already been established. This article offers a concise summary of the present state of clinical advancements in compounds labeled with ²²⁵Ac. It outlines various processes involved in the production and purification of ²²⁵Ac to cater to the growing demand for this radionuclide. The article examines the merits and drawbacks of different procedures, delves into preclinical trials, and discusses ongoing clinical trials.

Aim: This study aimed to perform dosimetry in patients with metastatic prostate cancer treated with ¹⁷⁷Lutetium (Lu) prostate-specific membrane antigen (PSMA)-617 radiopharmaceutical, calculating organ blood clearance and consequently determining the maximum tolerable treatment activity.

Materials and methods: Eighteen patients with metastatic prostate cancer were enrolled in the study. Patients were administered 5.55 gigabecquerel (GBq) of ¹⁷⁷Lu-PSMA-617 radiopharmaceutical per treatment cycle through infusion. Blood samples (2 mL each) were collected at 2, 4, 6, 8, 18, 24, 36, and 44 h postinjection to assess the bone marrow absorbed dose. Organ doses were calculated using the OLINDA/EXM software based on scintigraphic images of the 18 patients who received ¹⁷⁷Lu-PSMA-617.

Results: The blood clearance of ¹⁷⁷Lu-PSMA-617 radiopharmaceutical was determined to be bi-exponential. The mean absorbed doses for the parotid glands, kidneys, bone marrow, and liver were found to be 1.18 ± 0.27, 1.05 ± 0.3, 0.07 ± 0.05, and 0.31 ± 0.2 Gy/GBq, respectively. The radiation dose to the bone marrow was significantly lower than that to the kidneys and parotid glands. No dose limitations were necessary for kidneys and bone marrow in any of the patients.

Conclusions: Our dosimetry results indicate that ¹⁷⁷Lu-PSMA-617 therapy is safe in terms of radiation toxicity.

Purpose: The current study provides insights into the challenges of safely operating a magnetic resonance imaging (MRI)-guided focused ultrasound (MRgFUS) robotic system in a high-field MRI scanner in terms of robotic motion accuracy.

Materials and methods: Grid sonications were carried out in phantoms and excised porcine tissue in a 3T MRI scanner using an existing MRgFUS robotic system. Fast low-angle shot-based magnetic resonance thermometry was employed for the intraprocedural monitoring of thermal distribution.

Results: Strong shifting of the heated spots from the intended points was observed owing to electromagnetic interference (EMI)-induced malfunctions in system's operation. Increasing the slice thickness of the thermometry sequence to at least 8 mm was proven an efficient method for preserving the robotic motion accuracy.

Conclusions: These findings raise awareness about EMI effects on the motion accuracy of MRgFUS robotic devices and how they can be mitigated by employing suitable thermometry parameters.

Purpose and aim: Modern generation linear accelerator (linac) either generates X-rays with a flattening filter (WFF beam) or without flattening filter free (FFF beam). The FFF beams are associated with a significantly higher dose per pulse compared to WFF beams due to the absence of a flattening filter and the corresponding attenuation caused by it. This results in increased ion recombination and a larger saturation correction factor (k_s). In accordance with the IAEA TRS 398 dosimetry protocol, k_s is necessary for the accurate measurement of absorbed dose at a point in water. The objective of this study was to evaluate the k_s for the indigenous FAR 65-GB ion chamber (IC) for the FFF X-rays.

Materials and methods: The study was carried out on TrueBeam linac (Varian, A Siemens Healthineers company) which offers 6 MV WFF, 6 MV FFF, 10 MV WFF and 10 MV FFF beams. The two-voltage method was employed to measure k_s in a solid water phantom at a depth of 10 cm for a FAR 65-GB and SNC 600c and 0.6cc PTW 30013 Farmer chambers at 100 cm and 150 cm source-to-chamber distances for a 10 cm × 10 cm field size.

Results: The k_s values for the FAR 65-GB, PTW 30,013, and SNC 600c were 1.0055 (1.0113), 1.0051 (1.0071), and 1.0033 (1.0066) for the 6 MV WFF (FFF) beams, respectively, and 1.0066 (1.0178), 1.0061 (1.0137), and 1.0035 (1.0119) for the 10MV WFF (FFF) beams, respectively. The k_s values calculated by two-voltage method matches with k_s values obtained from Jaffe's plot. The chamber exhibited a linear dose-response up to 3000 cGy, beyond which a saturation effect was observed.

Conclusions: Our study reveals that this chamber is suitable for the reference dosimetry for the FFF beams.

Purpose: This study aims to minimize monitor units (MUs) of intensity-modulated treatments in the Monaco treatment planning system while preserving plan quality by optimizing the "Minimum Segment Width" (MSW) and "Fluence Smoothing" parameters.

Materials and methods: We retrospectively analyzed 30 prostate, 30 gynecological, 15 breast cancer, 10 head and neck tumor, 11 radiosurgery, and 10 hypo-fractionated plans. Original prostate plans employed "Fluence Smoothing" = Off and were reoptimized with Low, Medium, and High settings. The remaining pathologies initially used MSW = 0.5 cm and were reoptimized with MSW = 1.0 cm. Plan quality, including total MU, delivery time, and dosimetric constraints, was statistically analyzed with a paired t-test.

Results: Prostate plans exhibited the highest MU variation when changing "Fluence Smoothing" from Off to High (average ΔMU = -5.1%; P < 0.001). However, a High setting may increase overall MU when MSW = 0.5 cm. Gynecological plans changed substantially when MSW increased from 0.5 cm to 1.0 cm (average ΔMU = -29%; P < 0.001). Organs at risk sparing and planning target volumes remained within 1.2% differences. Replanning other pathologies with MSW = 1.0 cm affected breast and head and neck tumor plans (average ΔMU = -168.38, average Δt = -11.74 s, and average ΔMU = -256.56, average Δt = -15.05 s, respectively; all with P < 0.004). Radiosurgery and hypofractioned highly modulated plans did not yield statistically significant results.

Conclusions: In breast, pelvis, head and neck, and prostate plans, starting with MSW = 1.0 cm optimally reduces MU and treatment time without compromising plan quality. MSW has a greater impact on MU than the "Fluence Smoothing" parameter. Plans with high modulation might present divergent behavior, requiring a case-specific analysis with MSW values higher than 0.5 cm.

Purpose: This paper explores different machine learning (ML) algorithms for analyzing diffusion nuclear magnetic resonance imaging (dMRI) models when analytical fitting shows restrictions. It reviews various ML techniques for dMRI analysis and evaluates their performance on different b-values range datasets, comparing them with analytical methods.

Materials and methods: After standard fitting for reference, four sets of diffusion-weighted nuclear magnetic resonance images were used to train/test various ML algorithms for prediction of diffusion coefficient (D), pseudo-diffusion coefficient (D*), perfusion fraction (f), and kurtosis (K). ML classification algorithms, including extra-tree classifier (ETC), logistic regression, C-support vector, extra-gradient boost, and multilayer perceptron (MLP), were used to determine the existence of diffusion parameters (D, D*, f, and K) within single voxels. Regression algorithms, including linear regression, polynomial regression, ridge, lasso, random forest (RF), elastic-net, and support-vector machines, were used to estimate the value of the diffusion parameters. Performance was evaluated using accuracy (ACC), area under the curve (AUC) tests, and cross-validation root mean square error (RMSE_CV). Computational timing was also assessed.

Results: ETC and MLP were the best classifiers, with 94.1% and 91.7%, respectively, for the ACC test and 98.7% and 96.3% for the AUC test. For parameter estimation, RF algorithm yielded the most accurate results The RMSE_CV percentages were: 8.39% for D, 3.57% for D*, 4.52% for f, and 3.53% for K. After the training phase, the ML methods demonstrated a substantial decrease in computational time, being approximately 232 times faster than the conventional methods.

Conclusions: The findings suggest that ML algorithms can enhance the efficiency of dMRI model analysis and offer new perspectives on the microstructural and functional organization of biological tissues. This paper also discusses the limitations and future directions of ML-based dMRI analysis.

Aim: This study aims to validate the Razor Nano Chamber (RNC) and Razor Chamber (RC) dosimetric characteristics in a small field. The dosimetric parameters of the two chambers were compared.

Materials and methods: The chamber characteristics of leakage (pre and post), stability, energy dependency, dose linearity, dose rate effect, stem effect, angular dependency, ion recombination effect, and polarity effect were studied. Relative dose measurements of the percentage depth dose, profile measurement, and output factor (OF) measurements were performed for small fields. All measurements were performed in a Theratron 780E telecobalt unit and an Elekta Versa HD™ Linear Accelerator.

Results and discussion: The measured pre- and postirradiation leakage and energy dependency were within 0.5% of the acceptable limit. In the stability check, the standard error and standard error of mean were 0.047% and 0.068%, respectively, for both RNC and RC. The deviation in the angular responses of the RNC and RC ion chambers was negligible. In the ion recombination measurements, both the RNC and RC were overestimated for the 10 flattening filter-free photon beam. In small fields, there were no significant differences in the k_pol values for either chamber. The RNC showed good agreement in the relative dose measurements compared to the RC.

Conclusion: RNC and RC showed good agreement in small-field dosimetry. The RNC angular dependency and OF showed a superior response compared to the RC because of the small volume spherical shape and high spatial resolution, which gives a reduced penumbra and no volume averaging effect.

Purpose: The present article deals with investigating the effects of tissue heterogeneity consideration on the dose distribution of ¹⁹²Ir and ⁶⁰Co sources in high-dose-rate brachytherapy (HDR-BT).

Materials and methods: A Monte Carlo N-Particle 5 (MCNP5) code was developed for the simulation of the dose distribution in homogeneous and heterogeneous phantoms for cervical cancer patients. The phantoms represented water-equivalent and human body-equivalent tissues. Treatment data for a patient undergoing HDR-BT with a ¹⁹²Ir source were used as a reference for validation, and for ⁶⁰Co, AAPM Task Group 43 methodology was also applied. The dose values were calculated for both source types in the phantoms.

Results: The results showed a good agreement between the calculated dose in the homogeneous phantom and the real patient's treatment data, with a relative difference of less than 5% for both sources. However, when comparing the absorbed doses at critical points such as Point A right, Point A left, Point B right, Point B left, bladder International Commission on Radiation Units and Measurement (ICRU) point, and recto-vaginal ICRU point, the study revealed significant percentage differences (approximately 5.85% to 12.02%) between the homogeneous and heterogeneous setups for both ¹⁹²Ir and ⁶⁰Co sources. The analysis of dose-volume histograms (DVH) indicated that organs at risk, notably the rectum and bladder, still received doses within recommended limits.

Conclusions: The study concludes that ⁶⁰Co and ¹⁹²Ir sources can be effectively used in HDR-BT, provided that careful consideration is given to tissue heterogeneity effects during treatment planning to ensure optimal therapeutic outcomes.

Purpose: To show the workflow for the commissioning of a MRlinac, and some proposed tests; off-axis targets, output factors for small fields, dose in inhomogeneities, and multileaf collimator quality assurance (MLC QA).

Methods: The tests were performed based on TG-142, TG-119, ICRU 97, TRS-398, and TRS-483 recommendations as well as national regulations for radiation protection and safety.

Results: The imaging tests are in agreement with the protocols. The radiation isocenter was 0.34 mm, and for off-axis targets location was up to 0.88 mm. The dose profiles measured and calculated in treatment planning system (TPS) passed in all cases the gamma analysis of 2%/2 mm (global dose differences). The output factors of fields larger than 2 cm × 2 cm are in agreement with the model of the MRlinac in the TPS. However, for smaller fields, their differences are higher than 10%. Picket fence test for different gantry angles showed a maximum leaf deviation up to 0.2 mm. Displacements observed in treatment couch adding weight (50 kg) are lower than 1 mm. Cryostat, bridge, and couch attenuation was up to 1.2%, 10%, and 24%, respectively.

Conclusion: The implemented tests confirm that the studied MRlinac agrees with the standards reported in the literature and that the strict tolerances established as a baseline should allow a smoother implementation of stereotactic treatments in this machine.