Journal of Medical Physics最新文献

Radiation dosimeters play a crucial role in radiation oncology by accurately measuring radiation dose, ensuring precise and safe radiation therapy. This study presents the design and development of a low-cost printed circuit board (PCB) dosimeter and an integrated electrometer with sensitivity optimized for dose rates intended for use in megavoltage radiation therapy. The PCB dosimeter was designed in KiCad, and it uses a low-cost S5MC-13F general-purpose 1 kV 5A power diode as a radiation detector. The dosimeter is calibrated against a known dose derived from an ionization chamber and tested for dose linearity, dose rate dependence, field size dependence, and detector orientation dependence. The observed average dose differences between the delivered and measured doses for most measurements were found to be < 1.1%; the dose rate linearity between 100 MU/min and 1400 MU/min was found to be within 1.3%. This low-cost architecture could successfully be adapted further for a scalable, cost-effective dosimetry solution through firmware or circuit design.

Introduction: Although medical physics as a profession is recognized as part of the health-care professional workforce by the International Labor Organization, in the Mexican context, the figure of the medical physicist (MP) is often inappropriately associated solely with technical work, leading to perception, recognition, and salary implications. The aim of this study was to explore the perception of medical specialists regarding the role and responsibilities of MPs in clinical practice in Mexico.

Methods: A national survey was answered by medical personnel, ranging from residents to qualified specialists in November 2019. The questionnaire consisted of ten questions related to perception of MPs. The survey was open to all medical specialists regardless of their involvement in the use of ionizing radiations or otherwise.

Results: It was shown that approximately two-thirds of specialists know and recognize the medical physics profession in hospitals and the roles and responsibilities of MPs. However, 19% of medical specialists considered the standard of service as inadequate.

Conclusion: MPs must exert greater efforts to promote their status and enhance the recognition of their contribution to health care. The low level of recognition in diagnostic and interventional radiology and in nuclear medicine in Mexico might be related to nonexistent or unclear documentation and inadequate regulations, policies, or directives promoted by the health-care authorities.

Aim: The Mobius3D software addresses limitations lacking in measurement-based methods in patient-specific quality assurance (QA). The objective of this study was to validate its dosimetric performance against conventionally used portal dose measurements using gamma analysis and confidence limits.

Materials and methods: A total of 240 patient-specific QA plans for the Varian Halcyon linear accelerator were collected. The Mobius3D software was commissioned through beam data and plan verification. All plans underwent QA through the electronic portal imaging device, coupled with the Portal Dosimetry software, and the Mobius3D. Data were assessed using >95% gamma pass. Portal measurements were evaluated using 3%/2 mm and 3%/3 mm criteria, whereas Mobius3D was analyzed at 3%/3 mm and 5%/3 mm, at the 10% threshold.

Results: Mobius 5%/3 mm mean gamma passes were 99.89% for volumetric-modulated arc therapy (VMAT) and 99.31% for intensity-modulated radiotherapy (IMRT), and correspondingly, the data for portal 3%/2 mm were 99.99% and 99.96%. The Mobius3D at 5%/3 mm can perform like Portal 3%/2 mm for VMAT plans at 0.1% difference, especially for head/neck and pelvic/abdominal cases. In IMRT-based treatments, at 0.7% difference in Mobius3D 5%/3 mm and Portal 3%/2 mm, the performance and error identification in IMRT plans should be applied more carefully due to the amount of failed plans, particularly the chest region. The confidence limits for VMAT plans for Portal 3%/2 mm and Mobius 5%/3 mm are 99.93% and 99.42%, respectively, while for IMRT plans are 99.69% and 97.43%, respectively.

Conclusions: At a 5%/3 mm criterion, the Mobius3D may yield percentage gamma pass rates like measurements obtained by Portal Dosimetry 3%/3 mm and Portal Dosimetry 3%/2 mm. As the software is largely dependent on commissioned data, rigorous commissioning and a comprehensive QA program should be implemented.

This article aims to identify, through a literature review, the best intensity-modulated technique (IMRT)/volumetric-modulated arc therapy (VMAT) for the breast/chest wall (Br/CW) as a function of the treatment planning system (TPS) and present the institutional dosimetric data for the same. A PubMed search was conducted following intensity-modulated irradiation techniques (IMRT) presented in the study: field-in-field (FiF), tangential IMRT (t-IMRT), multi-field IMRT, tangential VMAT (t-VMAT), half-arc VMAT (HA-VMAT), and large arc VMAT (LA-VMAT). The literature with at least one arm VMAT is included in this study. A total of 370 articles were identified between 2010 and 2022, out of which 19 articles were found to be unique. These articles were classified in terms of the TPS used: Eclipse (9), Monaco (6), RayStation (2), Pinnacle (1), and one unidentified TPS. Based on the literature review, dosimetric attributes, and second cancer risk analysis (SCRA), t-IMRT was found to be the most preferable technique in Eclipse, Pinnacle, and RayStation TPS. However, for Monaco TPS, t-VMAT (approximately 30° tangential arc) offers better dose coverage with lower organ-at-risk (OAR) doses. In terms of OAR doses and SCRA, LA-VMAT (≥210°) and HA-VMAT (180°) are avoidable techniques in any TPS, and FiF should be preferred over these two techniques. In our present institution, which uses the Eclipse TPS, data for 300 patients treated with t-IMRT were collected. The data included beam angle, monitor unit [MU], target coverage (D95% and V105% [cc]), and analysis of the maximum (%), and mean dose (%) of the OAR. t-IMRT utilizes two medial and three lateral tangential beams placed at a spread of approximately 10° and 20°, respectively. The results showed a D95% of 96.3 ± 1.2% and a V105% of 4.9 ± 7.0 cc. The mean doses to the heart and ipsilateral lung were 10.1 ± 20.9% and 11.4 ± 10.2%, respectively. The mean MU was 1282.7 ± 453.4. Based on the findings, the most preferred intensity-modulated technique for Eclipse, Pinnacle, and RayStation is t-IMRT, while for Monaco, it is t-VMAT. The data from the Eclipse planning system demonstrate a satisfactory dosimetric outcome for t-IMRT. However, the use of VMAT techniques employing an arc angle between 180° and 210° or higher is strongly discouraged.

Aim: The aim of the study was to develop a simple prediction model based on previous treatment plans for head-and-neck cancer (HNC).

Materials and methods: This study was conducted on 95 patients who underwent volumetric-modulated arc therapy (VMAT) with curative intent for HNC at our institute between January 2016 and December 2022 with intact bilateral parotid glands. Two simple prediction models were used: one linear regression model and one exponential model. Both models use fractional overlapping parotid volume with planning target volume (PTV) as a predictor of mean parotid dose. The fractional overlapping volume was calculated as the difference between the volume of the parotid gland minus the volume of the parotid gland outside the PTV plus a 2 mm margin, divided by the volume of the parotid gland. Statistical calculations were done using data analysis tools and Solver in Microsoft Excel (Microsoft Office 2013, Redmond, WA, USA). To enhance the accuracy of the results, outliers were excluded with residuals >2 standard deviations below and above the residuals. R² and root-mean-square error were calculated for both models to evaluate the quality of the predictions. The normality of both models' residuals was validated using the Shapiro-Wilk test.

Results: Both linear and exponential prediction models exhibited strong correlation statistics, with r² = 0.85 and 0.82, respectively. The authors found a fractional overlap of 16.4% and 18.9% in linear and exponential models that predict parotid mean dose 26 Gy. The implementation was carried out on a cohort of 12 prospective patients, demonstrating a remarkable improvement in minimizing the dose to the parotid glands.

Conclusion: In this single-institutional study, the authors successfully developed a prediction model for mean parotid dose in HNC patients undergoing radiotherapy. The model showed promising accuracy and has the potential to assist planners in optimizing treatment plans and minimizing radiation-related toxicity. It is possible to avoid under sparing the organs at risks in some cases and wasting time or effort on physically impossible goals in others using this prediction model. As a result, planning resources can be used much more efficiently. Future studies should focus on validating the model's performance using external datasets and exploring its integration into clinical practice.

Aim: This article aimed to present the salient features of the in-house developed Java program for the determination of inflection point and dosimetric parameters of flattening filter-free (FFF) photon beam. Reference levels for the dosimetric parameters of the FFF photon beams were also presented.

Materials and methods: Beam profiles of 6 MV FFF and 10 MV FFF photon beams for a collimator setting of 20 cm × 20 cm measured at 10 cm depth in an isocentric setup acquired from various institutions were analyzed using an in-house developed Java program and manual method. The values of reference dose value (RDV), field size, penumbra, and degree of un-flatness (defined as the lateral separation between 90% [X_90%], 75% [X_75%], and 60% [X_60%] dose points on the profile) were calculated and compared. The reference values of field size, penumbra, and degree of un-flatness were also determined for Varian and Elekta medical electron linear accelerators (LINACs).

Results: The maximum differences for RDV determined using the Java method and manual method are 2.4% and 2.7% for 6 and 10 MV FFF photon beams, respectively. The maximum difference between the values of field size, penumbra, and degree of un-flatness determined using Java and manual methods is within 1.3 mm. The reference values of field size and penumbra for Varian LINACs are 19.94 ± 0.10 cm and 0.83 ± 0.08 cm (6 MV FFF) and 19.95 ± 0.10 cm and 0.83 ± 0.08 cm (10 MV FFF). Similarly, the reference values of field size and penumbra for Elekta LINACs are 20.02 ± 0.09 cm and 0.94 ± 0.12 cm (6 MV FFF) and 20.03 ± 0.11 cm and 0.97 ± 0.16 cm (10 MV FFF).

Conclusions: A software program was developed in Java for analyzing the beam profiles of FFF photon beams. The results of Java-derived values of dosimetric parameters of FFF photon beams were found in good agreement with the values determined using the manual method. The reference values of these parameters were also derived and quoted using a large cohort of the data.

Aims: Analysis of colonoscopy images is an important diagnostic procedure in the identification of colorectal cancer. It has been observed that owing to advancements in technology, numerous machine-learning models now excel in the analysis of colorectal polyps classification. This work focused on developing a framework that can classify polyps using images during colonoscopy.

Materials and methods: First, the images were corrected by removing their spectral reflection. Second, feature pools were obtained by applying Radon transform (θ=45, 90, 135, and 180). From the Radon transform, fractal dimension was calculated as a feature vector combined with Zernike moment obtained from the Zernike features. Finally, Extreme Gradient Boosting (XGBoost) algorithm was applied for the classification and to compare it with state-of-the-art methods.

Results: The experimental results obtained with the proposed framework have been reported, cross-validated, and discussed. The proposed method gives a classification accuracy of 93% for light XGBoost and 92% for XGBoost.

Conclusion: This study shows that by applying scale invariant features over a small dataset, XGBoost outperforms state-of-the-art methods when it comes to polyp classification.

Purpose: The purpose of the study was to investigate the dosimetric characteristics of radiophotoluminescent glass dosimeters (RGDs) for pencil beam scanning proton therapy. The RGD's end-to-end testing of intensity-modulated proton therapy (IMPT) plans was also evaluated.

Materials and methods: The dosimetric characteristics of the GD-302M type glass dosimeter were studied in terms of uniformity, short-term and long-term reproducibility, stability of the magazine position readout, dose linearity in the range from 0.2 to 20 Gy, energy response in 70-220 MeV, and fading effect. The reference conditions of the spot scanning beam from the Varian ProBeam Compact system were operation at 160 MeV, a 2 cm water-equivalent depth in a solid water phantom, a 10 cm × 10 cm field size at the isocenter, and 2 Gy dose delivery. End-to-end testing of IMPT plans for the head, abdomen, and pelvis was verified using the Alderson Rando phantom. The overall uncertainty analysis was confirmed in this study.

Results: The relative response of RGDs for the uniformity test was within 0.95-1.05. The percentages of the coefficients of variation for short-term and long-term reproducibility were 1.16% and 1.50%, respectively. The dose ACE glass dosimetry reader FGD-1000 showed a stable magazine position readout. The dose was found to be linear with R² = 0.9988. The energy response relative to 160 MeV was approximately within 4.0%. The fading effect was within 2.4%. For the end-to-end test, the difference between the treatment plan and RGD measurement was within 1.0%. The overall uncertainty of the RGD measurement for the proton beam was 4.6%, which covered all energy ranges in this study.

Conclusion: The experimental study indicates that the RGDs have the potential to be used in the dosimetry of therapeutic proton beams, including end-to-end dosimetry.

Aim: In this study, a 6MV flattening filter (FF) and 6MV FF Free (FFF) photon beam small-field output factors (OF) were measured with various collimators using different detectors. The corrected OFs were compared with the treatment planning system (TPS) calculated OFs.

Materials and methods: OF measurements were performed with four different types of collimators: Varian Millennium multi-leaf collimator (MLC), Elekta Agility MLC, Apex micro-MLC (mMLC) and a stereotactic cone. Ten detectors (four ionization chambers and six diodes) were used to perform the OF measurements at a depth of 10 cm with a source-to-surface distance of 90 cm. The corrected OF was calculated from the measurements. The corrected OFs were compared with existing TPS-generated OFs.

Results: The use of detector-specific output correction factor (OCF) in the PTW diode P detector reduced the OF uncertainty by <4.1% for 1 cm × 1 cm S_clin. The corrected OF was compared with TPS calculated OF; the maximum variation with the IBA CC01 chamber was 3.75%, 3.72%, 1.16%, and 0.90% for 5 mm stereotactic cone, 0.49 cm × 0.49 cm Apex mMLC, 1 cm × 1 cm Agility MLC, and 1 cm × 1 cm Millennium MLC, respectively.

Conclusion: The technical report series-483 protocol recommends that detector-specific OCF should be used to calculate the corrected OF from the measured OF. The implementation of OCF in the TPS commissioning will reduce the small-field OF variation by <3% for any type of detector.