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Zeitschrift Fur Medizinische Physik Nov 2023To employ the microDiamond and the microSilicon detector (mDD and mSD, both PTW-Freiburg, Germany) to determine the dose rate around a HDR Ir brachytherapy source (model... (Review)
Review
PURPOSE
To employ the microDiamond and the microSilicon detector (mDD and mSD, both PTW-Freiburg, Germany) to determine the dose rate around a HDR Ir brachytherapy source (model mHDR-v2r, Elekta AB, Sweden).
METHODS
The detectors were calibrated with a Co beam at the PTW Calibration Laboratory. Measurements around the Ir source were performed inside a PTW MP3 water phantom. The detectors were placed at selected points of measurement at radial distances r, ranging from 0.5 to 10 cm, keeping the polar angle θ = 90°. Additional measurements were performed with the mSD at fixed distances r = 1, 3 and 5 cm, with θ varying from 0 to 150°, 0 to 166°, and 0 to 168°, respectively. The corresponding mDD readings were already available from a previous work (Rossi et al., 2020). The beam quality correction factor of both detectors, as well as a phantom effect correction factor to account for the difference between the experimental geometry and that assumed in the TG-43 formalism, were determined using the Monte Carlo (MC) toolkit EGSnrc. The beam quality correction factor was factorized into energy dependence and volume-averaging correction factors. Using the abovementioned MC-based factors, the dose rate to water at the different points of measurement in TG-43 conditions was obtained from the measured readings, and was compared to the dose rate calculated according to the TG-43 formalism.
RESULTS
The beam quality correction factor was considerably closer to unity for the mDD than for the mSD. The energy dependence of the mDD showed a very weak radial dependence, similar to the previous findings showing a weak angular dependence as well (Rossi et al., 2020). Conversely, the energy dependence of the mSD decreased significantly with increasing distances, and also showed a considerably more pronounced angular dependence, especially for the smallest angles. The volume-averaging showed a similar radial dependence for both detectors: the correction had a maximal impact at 0.5 cm and then approached unity for larger distances, as expected. Concerning the angular dependence, the correction for the mSD was also similar to the one previously determined for the mDD (Rossi et al., 2020): a maximal impact was observed at θ = 0°, with values tending to unity for larger angles. In general, the volume-averaging was less pronounced for the mSD due to the smaller sensitive volume radius. After the application of the MC-based factors, differences between mDD dose rate measurements and TG-43 dose rate calculations ranged from -2.6% to +4.3%, with an absolute average difference of 1.0%. For the mSD, the differences ranged from -3.1% to +5.2%, with an absolute average difference of 1.0%. For both detectors, all differences but one were within the combined uncertainty (k = 2). The differences of the mSD from the mDD ranged from -3.9% to +2.6%, with the vast majority of them being within the combined uncertainty (k = 2). For θ ≠ 0°, the mDD was able to provide sufficiently accurate results even without the application of the MC-based beam quality correction factor, with differences to the TG-43 dose rate calculations from -1.9% to +3.4%, always within the combined uncertainty (k = 2).
CONCLUSION
The mDD and the mSD showed consistent results and appear to be well suitable for measuring the dose rate around HDR Ir brachytherapy sources. MC characterization of the detectors response is needed to determine the beam quality correction factor and to account for energy dependence and/or volume-averaging, especially for the mSD. Our findings support the employment of the mDD and mSD for source QA, TPS verification and TG-43 parameters determination.
Topics: Brachytherapy; Monte Carlo Method; Phantoms, Imaging; Water; Calibration; Radiometry
PubMed: 36038432
DOI: 10.1016/j.zemedi.2022.07.004 -
Clinical Efficacy and Openness to New Challenges of Low Dose Rate Brachytherapy for Prostate Cancer.Current Oncology (Toronto, Ont.) Nov 2023Over a century ago, low-dose-rate (LDR) brachytherapy was introduced to treat prostate cancer (PCa). Since then, it has been widely applied worldwide, including in East... (Review)
Review
Over a century ago, low-dose-rate (LDR) brachytherapy was introduced to treat prostate cancer (PCa). Since then, it has been widely applied worldwide, including in East Asia. LDR brachytherapy has been performed in 88 institutes in Japan. Beneficial clinical outcomes of LDR brachytherapy for intermediate-to-high-risk PCa have been demonstrated in large clinical trials. These clinical outcomes were achieved through advances in methods, such as urological precise needle puncture and seed placement, and the quantitative decision making regarding radiological parameters by radiation oncologists. The combined use of LDR brachytherapy with other therapeutic modalities, such as external beam radiation and androgen deprivation therapy, for the clinical risk classification of PCa has led to better anticancer treatment efficacy. In this study, we summarized basic LDR brachytherapy findings that should remain unchanged and be passed down in urology departments. We also discussed the applications of LDR brachytherapy for PCa in various clinical settings, including focal and salvage therapies. In addition, we highlighted technologies associated with brachytherapy that are under development.
Topics: Male; Humans; Prostatic Neoplasms; Brachytherapy; Androgen Antagonists; Radiotherapy Dosage; Treatment Outcome
PubMed: 37999133
DOI: 10.3390/curroncol30110713 -
Biomedical Physics & Engineering Express Sep 2023The combination of magnetic resonance (MR) imaging and linear accelerators (linacs) into MR-Linacs enables continuous MR imaging and advanced gated treatments of...
The combination of magnetic resonance (MR) imaging and linear accelerators (linacs) into MR-Linacs enables continuous MR imaging and advanced gated treatments of patients. Previously, a dose-rate transient (∼8% reduced dose rate during the initial 0.5 s of each beam) was identified for a Viewray MRIdian MR-Linac (Klavsen2022106759). Here, the dose-rate transient is studied in more detail at four linacs of the same type at different hospitals. The implications of dose-rate transients were examined for gated treatments. The dose-rate transients were investigated using dose-per pulse measurements with organic plastic scintillators in three experiments: (i) A gated treatment with the scintillator placed in a moving target in a dynamic phantom, (ii) a gated treatment with the same dynamic conditions but with the scintillator placed in a stationary target, and (iii) measurements in a water-equivalent material to examine beam quality deviations at a dose-per-pulse basis. Gated treatments (i) compared with non-gated treatments with a static target in the same setup showed a broadening of accumulated dose profiles due to motion (dose smearing). The linac with the largest dose-rate transient had a reduced accumulated dose of up to (3.1 ± 0.65) % in the center of the PTV due to the combined dose smearing and dose-rate transient effect. Dose-rate transients were found to vary between different machines. Two MR-Linacs showed initial dose-rate transients that could not be identified from conventional linearity tests. The source of the transients includes an initial change in photon fluence rate and an initial change in x-ray beam quality. For gated treatments, this caused a reduction of more than 1% dose delivered at the central part of the beam for the studied, cyclic-motion treatment plan. Quality assurance of this effect should be considered when gated treatment with the Viewray MRIdian is implemented clinically.
Topics: Humans; Heart Rate; Motion; Phantoms, Imaging; Photons; Plastics
PubMed: 37591227
DOI: 10.1088/2057-1976/acf138 -
Journal of Radiological Protection :... Sep 2023Here we investigate the annual effective dose rate obtained from gamma radiation emitted from radionuclides in construction materials in a model room with fixed...
Here we investigate the annual effective dose rate obtained from gamma radiation emitted from radionuclides in construction materials in a model room with fixed dimensions. The dose rate is calculated on the whole room area at half the room height. We focus our analyses on a comparison of the annual effective dose rate between the room centre and the room average at half the room height and provide wall-wise quadratic index equations for both. We find that the annual effective dose rate based on the room average is larger than for the room centre due to increased annual effective dose rates for positions in the room closer to the walls. Furthermore, we evaluate the annual effective dose rate under a non-equal distribution of radionuclides in the three wall types (floor and ceiling, long walls, short walls). When considering the room average of the annual effective dose rate, our analysis indicates that it appears advantageous to use construction materials with a higher radionuclide activity concentration for floor and ceiling and the material with a lower radionuclide content for long and short walls, if there is a choice in the construction process.
Topics: Construction Materials; Gamma Rays; Radioisotopes
PubMed: 37647869
DOI: 10.1088/1361-6498/acf505 -
Physics in Medicine and Biology Aug 2023. The objective of this study was to investigate the impact of mean and instantaneous dose rates on the production of reactive oxygen species (ROS) during ultra-high...
. The objective of this study was to investigate the impact of mean and instantaneous dose rates on the production of reactive oxygen species (ROS) during ultra-high dose rate (UHDR) radiotherapy. The study aimed to determine whether either dose rate type plays a role in driving the FLASH effect, a phenomenon where UHDR radiotherapy reduces damage to normal tissues while maintaining tumor control.. Assays of hydrogen peroxide (HO) production and oxygen consumption (ΔpO) were conducted using UHDR electron irradiation. Aqueous solutions of 4% albumin were utilized as the experimental medium. The study compared the effects of varying mean dose rates and instantaneous dose rates on ROS yields. Instantaneous dose rate was varied by changing the source-to-surface distance (SSD), resulting in instantaneous dose rates ranging from 10to 10Gy s. Mean dose rate was manipulated by altering the pulse frequency of the linear accelerator (linac) and by changing the SSD, ranging from 0.14 to 1500 Gy s.. The study found that both ΔHOand ΔpOdecreased as the mean dose rate increased. Multivariate analysis indicated that instantaneous dose rates also contributed to this effect. The variation in ΔpOwas dependent on the initial oxygen concentration in the solution. Based on the analysis of dose rate variation, the study estimated that 7.51 moles of HOwere produced for every mole of Oconsumed.. The results highlight the significance of mean dose rate as a predictor of ROS production during UHDR radiotherapy. As the mean dose rate increased, there was a decrease in oxygen consumption and in HOproduction. These findings have implications for understanding the FLASH effect and its potential optimization. The study sheds light on the role of dose rate parameters and their impact on radiochemical outcomes, contributing to the advancement of UHDR radiotherapy techniques.
Topics: Reactive Oxygen Species; Electrons; Hydrogen Peroxide; Oxygen; Heart Rate; Radiotherapy Dosage
PubMed: 37463588
DOI: 10.1088/1361-6560/ace877 -
Therapeutic Advances in Gastroenterology 2023A standard bismuth quadruple therapy, a fluoroquinolone-containing triple (or quadruple) therapy or a proton pump inhibitor (PPI)-amoxicillin high-dose dual therapy has... (Review)
Review
A standard bismuth quadruple therapy, a fluoroquinolone-containing triple (or quadruple) therapy or a proton pump inhibitor (PPI)-amoxicillin high-dose dual therapy has been recommended as a second-line treatment for infection by the Maastricht VI/Florence Consensus Report. The major shortcoming of levofloxacin-amoxicillin triple therapy is low cure rate for eradicating levofloxacin-resistant strains. With the rising prevalence of levofloxacin-resistant strains, levofloxacin-amoxicillin triple therapy cannot reliably achieve a high eradication rate for second-line treatment of infection in most countries now. The present article aims to review current second-line eradication regimens with a per-protocol eradication rate exceeding 85% in most geographic areas. Recently, a novel tetracycline-levofloxacin quadruple therapy consisting of a PPI, bismuth, tetracycline, and levofloxacin for rescue treatment of infection has been developed. The new therapy achieved a higher per-protocol eradication rate than levofloxacin-amoxicillin triple treatment in a randomized controlled trial (98% 69%). Additionally, the tetracycline-levofloxacin quadruple therapy also exhibits a higher eradication rate than amoxicillin-levofloxacin quadruple therapy. High-dose dual PPI-amoxicillin therapy is another novel second-line treatment for infection. The new therapy can achieve an eradication rate of 89% by per-protocol analysis for the second-line treatment in Taiwan. Recently, levofloxacin-based sequential quadruple therapy and potassium-competitive acid blocker have also been applied in the second-line treatment of infection. A meta-analysis revealed that a vonoprazan-based regimen has significant superiority over a PPI-based regimen for second-line eradication therapy. In conclusion, the eradication rate of levofloxacin-amoxicillin triple therapy is suboptimal in the second-line treatment of infection now. Currently, a standard bismuth quadruple therapy (tetracycline-metronidazole quadruple therapy), a tetracycline-levofloxacin quadruple therapy, an amoxicillin-levofloxacin quadruple therapy, a levofloxacin-based sequential quadruple therapy or a high-dose PPI-amoxicillin dual therapy is recommended for the second-line treatment of infection.
PubMed: 37675247
DOI: 10.1177/17562848231192750 -
Translational Oncology Oct 2023PD-1 inhibitor and chemotherapy demonstrated durable antitumor activity with a manageable safety profile as the first-line treatment in patients with advanced esophageal...
BACKGROUND
PD-1 inhibitor and chemotherapy demonstrated durable antitumor activity with a manageable safety profile as the first-line treatment in patients with advanced esophageal squamous cell carcinoma (ESCC). The present study aimed to evaluate the efficacy of PD-1 inhibitors plus different dose intensity neoadjuvant chemotherapy in the treatment of locally advanced ESCC.
METHODS
Patients with locally advanced but resectable thoracic ESCC, staged as T3 or T4a, N0-3, and M0 or M1 lymph node metastasis (confined to the supraclavicular lymph nodes), were enrolled in this study. The eligible patients received tislelizumab plus different dose intensity chemotherapy for a 21-day cycle with repeated 2-4 cycles before surgery. The primary endpoints are pathological complete response (pCR) and major pathological response (MPR), and the secondary endpoints are objective response rate (ORR), disease control rate (DCR), and disease-free survival (DFS).
RESULTS
From November 2019 to February 2022, 122 cases received at least two cycles neoadjuvant chemoimmunotherapy and were evaluated by imaging examination. Subsequently, 99 patients underwent surgery and were evaluated by pathological evaluation. According to chemotherapy dose intensity, the patients were divided into three cohorts: cohort 1 (<80% dose intensity), cohort 2 (80-90% dose intensity), cohort 3 (90-100% dose intensity). All surgery patients underwent minimally invasive esophagectomy (MIE). The average pCR was identified in 22.22%; 16% had pCR in cohort 1, 17.65% had pCR in cohort 2, and 30.00% had pCR in cohort 3. MPR was observed in 9 (36.00%) patients in cohort 1, 18 (52.94%) patients in cohort 2, 22 (55.00%) patients in cohort 3. In univariable and multivariable analysis, dose intensity was significantly associated with MPR (p = 0.048) in patients who underwent esophagectomy. For surviving patients, the median follow-up was 13.76 months after esophagectomy. Compared to cohort 1, cohorts 2 and 3 had better DFS (p = 0.056). In addition, the prognosis of patients with MPR was better than that of patients without MPR (p = 0.014).
CONCLUSIONS
The robust antitumor activity of neoadjuvant chemoimmunotherapy for locally advanced but resectable thoracic ESCC was confirmed. More than 80% of chemotherapy dose intensity combined with immunotherapy resulted in a high pCR rate and prolonged DFS.
PubMed: 37478670
DOI: 10.1016/j.tranon.2023.101736 -
Ophthalmology Science 2024To describe a pilot study on the use of single-session, high-dose-rate, Food and Drug Administration-cleared, yttrium-90 (Y) plaque brachytherapy for iris and...
PURPOSE
To describe a pilot study on the use of single-session, high-dose-rate, Food and Drug Administration-cleared, yttrium-90 (Y) plaque brachytherapy for iris and iridociliary melanoma.
DESIGN
A single-center, clinical case series.
PARTICIPANTS
Six consecutive patients were included in this study. Each was diagnosed with an iris or iridociliary melanoma based on clinical examination with or without biopsy.
METHODS
Each tumor was staged according to the American Joint Committee on Cancer criteria and received Y eye plaque brachytherapy. The main variables were tumor size, patient age, sex, and method of diagnosis (clinical or biopsy). Surgical techniques, treatment durations, and ocular side effects were recorded. Local control was defined as a lack of tumor growth or regression determined by clinical examinations, including slit-lamp and gonio photography, as well as high-frequency ultrasound measurements. Toxicity parameters included acute and short-term corneal/scleral change, anterior segment inflammation, and cataract progression.
MAIN OUTCOME MEASURES
Local and systemic cancer control, tumor regression, visual acuity, as well as radiation-related normal tissue toxicity.
RESULTS
High-dose-rate Y plaque brachytherapy was used to treat small (American Joint Committee on Cancer cT1) category melanomas. Single-surgery high-dose-rate irradiations were performed under anesthesia. Because of short treatment durations, high-dose-rate Y did not require the additional procedures used for low-dose-rate plaque (e.g., sutures, amniotic membrane epicorneal buffering, Gunderson flaps, and second surgeries for plaque removal). Only conjunctival recession was used to avoid normal tissue irradiation. High-dose-rate Y treatment durations averaged 8.8 minutes (median, 7.9; range, 5.8-12.9). High-dose-rate Y brachytherapy was associated with no periorbital, corneal (Descemet folds), or conjunctival edema. There was no acute or short-term anterior uveitis, secondary cataract, scleropathy, radiation retinopathy, maculopathy, or optic neuropathy. The follow-up was a mean of 16.0 (range 12-24) months. Evidence of local control included a lack of expansion of tumor borders ( = 6, 100%), darkening with or without atrophy of the tumor surface ( = 5/6, 83%), and a mean 24.5% reduction in ultrasonographically measured tumor thickness. There were no cases of metastatic disease.
CONCLUSIONS
High-dose-rate Y brachytherapy allowed for single-surgery, minimally invasive, outpatient irradiation of iris and iridociliary melanomas.
FINANCIAL DISCLOSURES
Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
PubMed: 38840779
DOI: 10.1016/j.xops.2024.100513 -
Journal of Veterinary Internal Medicine 2023Standard of care for dogs with high-grade lymphoma, multiagent chemotherapy, achieves good initial responses but long-term remissions are infrequent; previous studies...
BACKGROUND
Standard of care for dogs with high-grade lymphoma, multiagent chemotherapy, achieves good initial responses but long-term remissions are infrequent; previous studies using half-body irradiation suggest improved long-term outcomes.
HYPOTHESIS
The addition of low-dose rate half-body irradiation would improve outcomes in dogs with B-cell lymphoma.
ANIMALS
Client-owned dogs with stage III or higher, substage a, B-cell lymphoma that achieved complete remission after 4 doses of multiagent chemotherapy.
METHODS
A case-controlled design comparing 2-year remission and survival rates between dogs treated with CHOP-based chemotherapy and those treated with chemotherapy and sequential low-dose rate half-body irradiation.
RESULTS
Thirty-eight dogs were enrolled with 18 included in final analysis, 9 prospectively-enrolled dogs and 9 case-matched historical controls. The irradiation cohort's 2-year disease-free rate was 56% whereas median duration exceeded the 730-day study period compared with 0% and 261 days in the chemotherapy only group. Remission duration significantly differed between cohorts (P < .01), hazard ratio 0.218 (95% CI: 0.06-0.77). The irradiation cohort's 2-year survival rate was 78% with median overall survival duration exceeding the 730 day study period compared with 11% and 286 days in the chemotherapy only group. Overall survival time significantly differed between cohorts (P < .02), hazard ratio 0.173 (95% CI: 0.03-0.839).
CONCLUSIONS AND CLINICAL IMPORTANCE
The improved long-term outcome achieved by dogs administered sequential low-dose rate half-body irradiation in this study is similar to previous observational studies. Where long-term remission is sought in dogs with B-cell lymphoma low-dose rate half-body irradiation could be considered in addition to standard chemotherapy.
Topics: Animals; Dogs; Humans; Dog Diseases; Hemibody Irradiation; Lymphoma, B-Cell; Lymphoma, Non-Hodgkin; Case-Control Studies
PubMed: 37700548
DOI: 10.1111/jvim.16840 -
Current Issues in Molecular Biology Aug 2023The output constancy of the accelerator used for boron neutron capture therapy (BNCT) is essential to ensuring anti-tumor efficacy and safety. BNCT as currently...
The output constancy of the accelerator used for boron neutron capture therapy (BNCT) is essential to ensuring anti-tumor efficacy and safety. BNCT as currently practiced requires a wide variety of beam quality assessments to ensure that RBE dose errors are maintained within 5%. However, the necessity of maintaining a constant beam dose rate has not been fully discussed. We therefore clarified the effect of different physical dose rates of the accelerator BNCT on biological effects. SAS and A172 cells exposed to B-boronophenylalanine were irradiated using a neutron beam (normal operating current, 100 μA) at the Aomori Quantum Science Center. Thermal neutron flux was attenuated to 50.0 ± 0.96% under 50 μA irradiation compared to that under 100 μA irradiation. Cells were given physical doses of 1.67 and 3.36 Gy at 30 and 60 mC, respectively, and survival was significantly increased after 50 μA irradiation for both cell types ( = 0.0052 for SAS; = 0.046 for A172, for 60 mC). Differences in accelerator BNCT beam dose rates have non-negligible effects on biological effects. Dose rate fluctuations and differences should not be easily permitted to obtain consistent biological effects.
PubMed: 37754225
DOI: 10.3390/cimb45090441