Journal of Medical Physics最新文献

Background: Advanced radiotherapy techniques are widely used for the treatment of breast cancer. Breast cancer treatment often involves acute and late radiation effects on the skin. Quantification of surface dose is crucial due to its impact on skin toxicity, cosmetic outcomes, and local tumor control.

Aims: In this study, the feasibility of using unlaminated Gafchromic EBT3 film (Ashland Advanced Materials, Bridgewater, NJ, USA) for quantification of surface dose during breast radiotherapy was explored.

Materials and methods: The dosimetric properties of this film, such as dose response, dose rate dependence, orientation dependence, and Ultraviolet-spectrum analysis, were also studied. A CIRS thorax phantom (CIRS Inc. Norfolk, Virginia) with a removable breast attachment was used for surface dose measurement. Tangential beam three-dimensional-conformal radiotherapy (3D-CRT) and 7-field intensity-modulated radiotherapy (IMRT) treatment plans were generated on the computed tomography images of the CIRS thorax phantom. The unlaminated EBT3 films were positioned on the breast attachment, at medial and lateral positions, and the treatment was delivered using 6 megavoltage X-rays generated by a TrueBeam medical electron linear accelerator (Varian Medical Systems, Palo Alto, USA). The exposed films were scanned with an EPSON 10000XL flatbed scanner, and the percentage surface dose was determined by taking the ratio of the measured dose and prescribed dose.

Results: The average percentage surface doses for 3D-CRT and IMRT techniques were found to be 43.11% and 34.78%, respectively.

Conclusion: This study demonstrated the feasibility of using unlaminated EBT3 Gafchromic film for surface dose evaluation in breast radiotherapy, providing valuable insights to optimize treatment strategies and enhance patient outcomes.

Objective: The quality of positron emission tomography/computed tomography (PET/CT) and PET/magnetic resonance (MR) images is a critical factor affecting the diagnostic reliability of clinical studies. An image quality (IQ) phantom is used to evaluate PET IQ. This study aims to acquire PET IQ phantom images on PET/CT and PET/MR systems and investigate the effects of attenuation correction on IQ.

Materials and methods: The PET IQ phantom was filled with F-18 fluorodeoxyglucose to achieve a lesion/background ratio of 4/1. The phantom was imaged separately on two different PET/CT scanners and one PET/MR scanner. Region of interest (ROIs) was drawn on both raw and attenuation-corrected images. Contrast and contrast-to-noise ratios (CNRs) were calculated from ROI counts.

Results: For the smallest lesion with a diameter of 10 mm without attenuation correction, the contrast values in PET/CT and PET/MR images were found to be 1.32, 1.68, and 1.76, respectively. In attenuation-corrected images of the same lesion, the contrast values were 1.55, 1.89, and 2.22, respectively. The CNR values for the attenuation-corrected 10 cm lesion were 13.92, 12.05, and 13.36, respectively.

Conclusion: Attenuation correction significantly improved IQ, with attenuation-corrected images demonstrating higher contrast and CNR values.

Purpose: This study investigates the preclinical dosimetry of Lutetium-177 in targeted radionuclide therapy for cancer treatment, focusing on the radiopharmaceutical [¹⁷⁷Lu] Lu-DOTATATE.

Materials and methods: Subcutaneous HT-29 xenografts were established in nu/nu mice and administered [¹⁷⁷Lu] Lu-DOTATATE intravenously. Tumor uptake was quantified by radiometry, and absorbed doses were calculated using MIRD formalism and a linear-quadratic model to determine cell death probability.

Results: Using HT-29 tumor cell xenografts in nude mice, the research evaluated the absorbed doses in tumor cell nuclei, considering both self-radiation and cross-radiation from neighboring cells. A mathematical model of a spherical cell cluster (radius = 280 µm) was developed to simulate dose distribution, accounting for beta-particle range and linear energy transfer.

Conclusions: Results indicate that the absorbed dose varies with cell position within the cluster, ranging from 3.2 Gy at the surface to 8.4 Gy at the center. The study also calculates cell survival probabilities using a linear-quadratic model, revealing a relative biological effectiveness (RBE) of up to 2 for [¹⁷⁷Lu] Lu-DOTATATE compared to gamma irradiation. These findings underscore the therapeutic potential of [¹⁷⁷Lu] Lu-DOTATATE in inducing tumor regression.

Background: In July 2024, a major failure in our magnetic resonance-guided linear accelerator (MR-linac) led to a 2-week treatment interruption for four patients.

Objective: To evaluate the clinical outcomes and toxicities at the end of the treatment, and up to 6 months after dose compensation for treatment interruption.

Materials and methods: Following the guidelines of the Royal College of Radiologists, we hypo fractionated the treatments. The dose per fraction and number of fractions were recalculated using the linear-quadratic model.

Results: Despite the treatment delay, the adapted dose had minimal impact on the oncological outcomes in the follow-up up to 6 months posttreatment. All patients demonstrated adequate tolerance to toxicity with no disease progression. Two patients achieved complete responses, while two showed partial responses.

Conclusion: Hypofractionation proved to be a feasible strategy for managing treatment interruptions in MR-linac adaptive radiotherapy, ensuring treatment continuity without compromising safety and efficacy. The biological approach maintained tumor control while minimizing toxicity, demonstrating its potential for broader applications in similar clinical scenarios.

Purpose: The purpose of this study was to implement and evaluate an end-to-end (E2E) test using an anthropomorphic head-and-neck (H and N) phantom across different radiotherapy modality platforms for photon and proton.

Materials and methods: The CIRS SHANE anthropomorphic phantom was used for the E2E test across multiple modalities, including Varian Clinac iX, four Varian TrueBeam systems, two Varian Halcyon systems, one Varian ETHOS system, and one ProBeam system. The volumetric modulated arc therapy plans were independently optimized for each photon machine while the intensity modulated proton therapy was planned for proton. Dosimetric measurements were taken using a 0.125 cc semiflex ionization chamber at three planning target volumes (PTVs) and one spinal cord point.

Results: The Kruskal-Wallis test revealed no significant differences in dose/volume parameters across the different modalities (P = 0.976). However, the Varian TrueBeam system showed a higher percentage dose difference compared to the other modalities, with the largest deviation of -3.7%. The O-ring gantry systems, Varian Halcyon and Varian ETHOS, demonstrated smaller dose differences and deviations compared to the C-based gantry systems. The Varian ETHOS delivered the highest number of monitor units at 641.6, while the Clinac iX delivered the lowest at 407.0. The ProBeam system showed good results for PTV and spinal cord.

Conclusions: The implementation of the E2E test using an anthropomorphic H and N phantom has proven feasible across multiple radiotherapy modalities in both photon and proton machines. This approach offers a valuable tool for center with advanced radiotherapy technologies, particularly those without a national dosimetry audit program.

Introduction: Breast cancer is the most common cancer in females worldwide. Radiation therapy has occupied a very important role in the treatment of women with breast cancer in early as well as in advanced stage. Various modern states of art radiotherapy techniques are being used for the treatment of breast cancer.

Objectives: The main objective of the study was to compare three different radiotherapy treatment planning techniques, namely three-dimensional conformal radiotherapy (3DCRT), field-in-field forward planned intensity modulated radiotherapy (FIF-FP-IMRT), and inversely planned IMRT (IP-IMRT) in terms of various dosimetric parameters.

Materials and methods: The present study involved 150 postmastectomy breast cancer patients. Treatment plans with three different planning techniques were generated for each patient and were compared for various dosimetric parameters of tumor and normal structures.

Results: Statistically significant differences (P < 0.05) were observed for most of the dosimetric parameters on comparing three planning techniques.

Conclusion: Most of the parameters were found in favor of IP-IMRT. FIF-FP-IMRT and IP-IMRT has been found better than 3DCRT.

Aim: Ultrasound shear wave elastography (USWE) is a noninvasive imaging technique developed in the last two decades for clinical diagnosis. Commercialized tools of USWE perform imaging by measuring tissue elasticity. Consequently, pathological diagnosis can be ineffective owing to a lack of viscosity. Accurately imaging complete viscoelasticity is challenging for USWE because it induces high underdetermination level of the inverse problem. We seek to develop a time steps expandable inverse model to facilitate viscoelasticity imaging for USWE.

Materials and methods: Tissue displacements induced by ultrasound shear waves are simulated by an in-house forward model. Then, the time steps expandable inverse model is used as a regularization method for USWE imaging.

Results: By applying the proposed time steps expandable inverse model, our numerical results demonstrate that the underdetermination level of the system can be reduced, and USWE is able to image complete viscoelasticity.

Conclusions: The proposed inverse model enables USWE to image complete viscoelasticity. It possesses advantages to reduce memory storage and to accelerate computational speed during inversion. The proposed model is helpful to enable wider clinical diagnosis for the state-of-the-art USWE technology.

The application of ISORAD diode detectors in treatments like total body irradiation (TBI), where small fractions of potentially lethal doses are delivered, lacks comprehensive clarity and requires further investigation. The study evaluates the feasibility of using ISORAD diode detectors as in vivo dosimeter for extended source to surface distance (SSD) treatments like TBI, despite a 250 cm limit in the manufacturer's specifications. Four identical ISORAD-1163 n-type cylindrical diode detectors manufactured by Sun Nuclear Corporation were studied for their operational characteristics and compared with 0.6cc Farmer chamber. The performance evaluation involved assessing reproducibility, linearity, field size dependence, and dose rate dependence at an SSD of 100 cm, extending up to 400 cm. Postirradiation signal drift, short-term reproducibility, and Signal Stability were monitored at extended SSDs. Directional dependence was evaluated in both the axial plane and transverse plane at 100 cm SSD. A diode was then used as an in vivo dosimeter for the bilateral TBI technique at 380 cm SSD. Acceptable dose rate effect (<0.91%), linearity (<0.99%), and reproducibility (<0.19%) with minimum deviations in postirradiation signal drift (<0.09%) and signal consistency (<0.09%) were observed up to 400 cm SSD for all diodes. Significant directional dependence of more than 1.1% was observed beyond ± 30° in the transverse plane of the detector, while it was insignificant in the axial plane. In vivo measurements of TBI patients with diodes at head, neck, umbilicus, chest, ankle, and shoulder showed that the maximum dose difference in the calculated and actual diode readings did not exceed 8.5%. Operational characteristics of in vivo diodes revealed to be consistent up to 400 cm SSD, supporting their applicability for in vivo measurements in TBI patients.

This study presents a comparative dosimetric and efficiency analysis of volumetric modulated arc therapy (VMAT) for large planning target volumes (PTVs) (≥1000 cm³), contrasting plans from a flattening filter-free (FFF) Halcyon system with a conventional flattened filter (FF) Clinac iX. Retrospective plans for 11 rectal cancer patients were evaluated for key dosimetric parameters, monitor unit (MU) requirements, and treatment times. While all plans achieved comparable PTV coverage, FF plans demonstrated marginally superior dose homogeneity. Conversely, Halcyon's FFF plans yielded superior organ-at-risk (OAR) sparing, demonstrating a statistically significant reduction in mean OAR doses. Despite necessitating a substantial MU increase, the 3-arc VMAT treatment time was reduced by approximately 62% versus the conventional FF platform. In conclusion, for large-volume PTVs, Halcyon-based FFF VMAT offers equivalent target coverage with enhanced OAR sparing and markedly accelerated delivery, establishing it as a highly efficient and clinically valuable modality.

Aim: This study aims to evaluate and compare the impact of dosimetric parameters on lungs, heart, and associated normal tissue complication probability (NTCP) values among three different right (RT) prescription doses in patients with synchronous bilateral breast cancer (SBBC).

Materials and methods: For retrospectively selected five patients diagnosed with SBBC, volumetric-modulated arc therapy treatment plans were developed across three different fractionation schedules: ultra-hypofractionated (UHF) (26 Gy/5#), hypofractionated (HF) (40.05 Gy/15#), and conventional fractionation (CF) (50 Gy/25#). The dosimetric parameters, including conformity index (CI), coverage index, homogeneity index, D95%, and V105%, along with the doses to organ at risk (OAR) (lung, heart, left anterior descending artery), were assessed. NTCP models were used to estimate the risks of complications.

Results: The dose-volume parameters for OAR exhibited a parabolic trend (χ²) with the prescribed dose, showing significant statistical differences across various fractionation schedules (P = 0.985, P < 0.001). NTCP models indicated a reduction in risks with UHF compared to CF and HF, with probabilities of grade ≥2 radiation pneumonitis ranging from 2.69% to 6.80% and symptomatic fibrosis probabilities from 22.45% to 38.91%, both of which increased from UHF to CF. The calculations for biological effective dose and equivalent dose in 2 Gy fractions showed greater biological effectiveness for late-responding tissues in CF, while the impact on tumor control remained more uniform across different fractionation schemes.

Conclusion: This study provides evidence in favor of hypofractionation for breast cancer radiotherapy, showing promise in minimizing normal tissue side effects.