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International Journal of Urology :... Jan 2020The history of prostate brachytherapy has passed one century. In 1983, modern low-dose-rate prostate brachytherapy using a transrectal ultrasound-guided procedure was... (Review)
Review
The history of prostate brachytherapy has passed one century. In 1983, modern low-dose-rate prostate brachytherapy using a transrectal ultrasound-guided procedure was introduced. In the early 1990s, low-dose-rate brachytherapy was introduced and rapidly spread across the USA due to its excellent oncological control, cost-effectiveness and technically easy procedure. Since low-dose-rate brachytherapy was introduced in Japan (2003), over 15 years have passed. More than 43 000 patients have undergone low-dose-rate brachytherapy. Japanese urologists and radiation oncologists are on course with leading brachytherapists in the USA. A nationwide prospective cohort study, J-POPS, was initiated in 2005. The J-POPS group also provides educational programs including an annual novel training course in low-dose-rate brachytherapy to familiarize urologists, radiation oncologists and pathologists with the procedure. Important information on Japanese patients has accumulated, especially by the J-POPS study group. The Japanese investigators reported excellent oncological outcomes of low-dose-rate brachytherapy, showing equivalent or superior efficacy to surgery in low- to intermediate-risk patients, and superior efficacy in high-risk patients using the surgery biochemical recurrence definition (prostate-specific antigen cut-off value of 0.2 ng/mL). Two randomized controlled studies (SHIP study: intermediate risk, and TRIP study: high risk) carried out by the J-POPS group are ongoing, and an additional follow-up study (J-POPS 2 study) has been started to evaluate survival outcomes over longer follow-up periods. Low-dose-rate brachytherapy is expected to provide a survival benefit, which must be confirmed by further studies with longer follow-up periods in the future.
Topics: Brachytherapy; Humans; Japan; Male; Prostatic Neoplasms; Radiotherapy Dosage; Time Factors; Treatment Outcome
PubMed: 31549770
DOI: 10.1111/iju.14098 -
International Journal of Radiation... Oct 2017In 2011, the International Commission on Radiological Protection reduced the threshold for the lens effects of low linear energy transfer (LET) radiation. On one hand,... (Review)
Review
PURPOSE
In 2011, the International Commission on Radiological Protection reduced the threshold for the lens effects of low linear energy transfer (LET) radiation. On one hand, the revised threshold of 0.5 Gy is much lower than previously recommended thresholds, but mechanisms behind high radiosensitivity remain incompletely understood. On the other hand, such a threshold is independent of dose rate, in contrast to previously recommended separate thresholds each for single and fractionated/protracted exposures. Such a change was made predicated on epidemiological evidence suggesting that a threshold for fractionated/protracted exposures is not higher than an acute threshold, and that a chronic threshold is uncertain. Thus, the dose rate dependence is still unclear. This paper therefore reviews the current knowledge on the radiosensitivity of the lens and the dose rate dependence of radiation cataractogenesis, and discusses its mechanisms.
CONCLUSIONS
Mounting biological evidence indicates that the lens cells are not necessarily radiosensitive to cell killing, and the high radiosensitivity of the lens thus appears to be attributable to other mechanisms (e.g., excessive proliferation, abnormal differentiation, a slow repair of DNA double-strand breaks, telomere, senescence, crystallin changes, non-targeted effects and inflammation). Both biological and epidemiological evidence generally supports the lack of dose rate effects. However, there is also biological evidence for the tissue sparing dose rate (or fractionation) effect of low-LET radiation and an enhancing inverse dose fractionation effect of high-LET radiation at a limited range of LET. Emerging epidemiological evidence in chronically exposed individuals implies the inverse dose rate effect. Further biological and epidemiological studies are warranted to gain deeper knowledge on the radiosensitivity of the lens and dose rate dependence of radiation cataractogenesis.
Topics: Animals; Cataract; Dose-Response Relationship, Radiation; Humans; Lens, Crystalline; Radiation Tolerance
PubMed: 27899034
DOI: 10.1080/09553002.2016.1266407 -
The Science of the Total Environment Jul 2021After the 2011 Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident, wild populations of animals and plants living in the evacuation zone received additional...
After the 2011 Fukushima Dai-ichi Nuclear Power Station (FDNPS) accident, wild populations of animals and plants living in the evacuation zone received additional ionizing radiation of both internal and external radiation doses. Morphological abnormalities of pine and fir trees near the FDNPS were reported. In order to evaluate dose-effect relationships, it is necessary to quantify the radiation doses to trees and plants. In this study, the internal and external dose rates to Japanese cedar and plants collected at three sites in Okuma, approximately 4 km southwest of FDNPS were estimated applying the ERICA Assessment Tool. The activity concentrations of Cs and Cs in soils, cedar trunks, and plants were determined. The total dose rates to cedar ranged from 2.2 ± 1.2 to 6.1 ± 2.2 μGy h. These rates were within the derived consideration reference levels (DCRLs) reported by ICRP 108 as 4-40 μGy h for pine trees. The highest estimate for plants was 7.1 ± 2.7 μGy h, much smaller than the DCRLs reported for grasses and herbs (40-400 μGy h). On average, the internal radiation dose rates to cedars at the two sites accounted for 5% and 29% of the external dose rates, respectively, while the value in another site was only 0.4% for cedar. This was attributed to differences in the crown area between the three sites. The trunk diameter of cedars shows a positive correlation with the ratio of internal to external radiation dose rates. It indicates that the total dose rate to cedars is easily estimated with the soil radiocaesium inventory and trunk diameter. The internal radiation dose rate to the plant varied depending on the plant species. This variation was considerably large in plants due to the presence of two species, including Solidago altissima and Artemisia indica var. maximowiczii.
Topics: Animals; Cesium Radioisotopes; Cryptomeria; Fukushima Nuclear Accident; Japan; Nuclear Power Plants; Radiation Dosage; Radiation Monitoring; Soil Pollutants, Radioactive
PubMed: 33744576
DOI: 10.1016/j.scitotenv.2021.146350 -
Radiation Protection Dosimetry Sep 2022Radiation response differs depending on the dose and dose rate in intestinal stem cells; however, the underlying mechanisms are not clear. To understand the effects of...
Radiation response differs depending on the dose and dose rate in intestinal stem cells; however, the underlying mechanisms are not clear. To understand the effects of low-dose and low-dose-rate radiation, the authors established an organoid system that mimics the in vivo environment and sporadic low-dose-rate irradiation conditions in vitro. Organoid-forming potential and the number of stem cells in the organoids derived from 1 Gy-irradiated cells were lower than those from non-irradiated cells; however, the difference was not significant, although 1 Gy-irradiated stem cells exhibited significant growth disadvantage in the mixed-organoid with non-irradiated and irradiated stem cells. Furthermore, the authors irradiated a cell with X-ray microbeams and performed time-lapse observations and found that irradiated cells did not remain in the organoid. These results suggest that radiation-induced stem cell competition can occur in intestinal organoids and contribute to a low risk of cancers at low-dose-rate exposures.
Topics: Organoids; Stem Cells; X-Rays
PubMed: 36083761
DOI: 10.1093/rpd/ncac068 -
Biomedical Physics & Engineering Express Nov 2021The dose rate distributions delivered to 55 prostate and head & neck (H&N) cancer patients treated with a helical TomoTherapy (HT) system were resolved and assessed with...
The dose rate distributions delivered to 55 prostate and head & neck (H&N) cancer patients treated with a helical TomoTherapy (HT) system were resolved and assessed with regard to pitch and field width defined during treatment planning. Statistical analysis of the studied cases showed that the median treatment delivery time was 4.4 min and 6.3 min for the prostate and H&N cases, respectively. Dose rate volume histogram data for the studied cases showed that the 25% and 12% of the volume of the planning target volumes of the prostate and H&N cases are irradiated with a dose rate of greater or equal to 1 Gy min. Quartile dose rate (QDR) data confirmed that in HT, where the target is irradiated in slices, most of the dose is delivered to each voxel of the target when it travels within the beam. Analysis of the planning data from all cases showed that this lasts for 68 s (median value). QDRs results showed that using the 2.5 cm field width, 75% of the prescribed dose is delivered to target voxels with a median dose rate of at least 3.2 Gy minand 4.5 Gy min, for the prostate and H&N cases, respectively. Systematically higher dose rates were observed for the H&N cases due to the shallower depths of the lesions in this anatomical site. Delivered dose rates were also found to increase with field width and pitch setting, due to the higher output of the system which, in general, results in accordingly decreased total treatment time. The biological effect of the dose rate findings of this work needs to be further investigated using in-vitro studies and clinical treatment data.
Topics: Head and Neck Neoplasms; Humans; Male; Prostate; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Radiotherapy, Intensity-Modulated
PubMed: 34755680
DOI: 10.1088/2057-1976/ac37cb -
Clinical Oncology (Royal College of... May 2022Following adoption of moderately hypofractionated radiotherapy as a standard for localised prostate cancer, ultrahypofractioned radiotherapy delivered in five to seven... (Review)
Review
Following adoption of moderately hypofractionated radiotherapy as a standard for localised prostate cancer, ultrahypofractioned radiotherapy delivered in five to seven fractions is rapidly being embraced by clinical practice and international guidelines. However, the question remains: how low can we go? Can radiotherapy for prostate cancer be delivered in fewer than five fractions? The current review summarises the evidence that radiotherapy for localised prostate cancer can be safely and effectively delivered in fewer than five fractions using high dose rate brachytherapy or stereotactic body radiotherapy. We also discuss important lessons learned from the single-fraction high dose rate brachytherapy experience.
Topics: Brachytherapy; Humans; Male; Prostatic Neoplasms; Radiation Dose Hypofractionation; Radiosurgery
PubMed: 34961659
DOI: 10.1016/j.clon.2021.12.006 -
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 -
Medical Physics Dec 2022The combined use of Bragg peak (BP) and shoot-through (ST) beams has previously been shown to increase the normal tissue volume receiving FLASH dose rates while...
PURPOSE
The combined use of Bragg peak (BP) and shoot-through (ST) beams has previously been shown to increase the normal tissue volume receiving FLASH dose rates while maintaining dose conformality compared to conventional intensity-modulated proton therapy (IMPT) methods. However, the fixed beam optimization method has not considered the effects of beam orientation on the dose and dose rates. To maximize the proton FLASH effect, here, we incorporate dose rate objectives into our beam orientation optimization framework.
METHODS
From our previously developed group-sparsity dose objectives, we add upper and lower dose rate terms using a surrogate dose-averaged dose rate definition and solve using the fast-iterative shrinking threshold algorithm. We compare the dosimetry for three head-and-neck cases between four techniques: (1) spread-out BP IMPT (BP), (2) dose rate optimization using BP beams only (BP-DR), (3) dose rate optimization using ST beams only (ST-DR), and (4) dose rate optimization using combined BP and ST (BPST-DR), with the goal of sparing organs at risk without loss of tumor coverage and maintaining high dose rate within a 10 mm region of interest (ROI) surrounding the clinical target volume (CTV).
RESULTS
For BP, BP-DR, ST-DR, and BPST-DR, CTV homogeneity index and Dmax were found to be on average 0.886, 0.867, 0.687, and 0.936 and 107%, 109%, 135%, and 101% of prescription, respectively. Although ST-DR plans were not able to meet dosimetric standards, BPST-DR was able to match or improve either maximum or mean dose in the right submandibular gland, left and right parotids, constrictors, larynx, and spinal cord compared to BP plans. Volume of ROIs receiving greater than 40 Gy/s ( was 51.0%, 91.4%, 95.5%, and 92.1% on average.
CONCLUSIONS
The dose rate techniques, particularly BPST-DR, were able to significantly increase dose rate without compromising physical dose compared with BP. Our algorithm efficiently selects beams that are optimal for both dose and dose rate.
Topics: Humans; Proton Therapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Neoplasms; Protons; Radiotherapy, Intensity-Modulated; Organs at Risk
PubMed: 36222217
DOI: 10.1002/mp.16009 -
Journal of Radiological Protection :... Nov 2021In the event of an accidental release of radioactive elements from a nuclear power plant, it has been shown that the radionuclides contributing the most to long-term...
In the event of an accidental release of radioactive elements from a nuclear power plant, it has been shown that the radionuclides contributing the most to long-term exposure areCs andCs. In the case of nuclear power plant fallout, with subsequent intake of radionuclides through the food chain, the internal absorbed dose to target tissues from protracted intake of radionuclides needs to be estimated. Internal contamination from food consumption is not caused by a single intake event; hence, the committed equivalent dose, calculated by a dose coefficient or dose per content function, cannot be easily used to calculate the cumulative absorbed dose to relevant target tissues in the body. In this study, we calculated updated absorbed dose rate coefficients forCs andCs based on data from the International Commission on Radiological Protection (ICRP) on specific absorbed fractions. The absorbed dose rate coefficients are provided for male and female adult reference phantoms, respectively, assuming a steady-state distribution of Cs that we calculated from the ICRP biokinetic model for Cs. With these coefficients, the absorbed dose to the listed target tissues, separately and to the total body, are related to the number of nuclear transitions (time-integrated activity) in each listed source region. Our new absorbed dose rate coefficients are given for the complete set of target tissues and have not been presented before. They are also provided for aggregated categories of organs to facilitate epidemiological studies.
Topics: Adult; Female; Human Body; Humans; Male; Nuclear Power Plants; Phantoms, Imaging; Radiation Dosage; Radiation Protection
PubMed: 34634780
DOI: 10.1088/1361-6498/ac2ec4 -
Physics in Medicine and Biology Jul 2023This work aims at investigating the response of various thermally stimulated luminescence detectors (TLDs) and optically stimulated luminescence detectors (OSLDs) for...
This work aims at investigating the response of various thermally stimulated luminescence detectors (TLDs) and optically stimulated luminescence detectors (OSLDs) for dosimetry of ultra-high dose rate electron beams. The study was driven by the challenges of dosimetry at ultra-high dose rates and the importance of dosimetry for FLASH radiotherapy and radiobiology experiments.Three types of TLDs (LiF:Mg,Ti; LiF:Mg,Cu,P; CaF:Tm) and one type of OSLD (AlO:C) were irradiated in a 15 MeV electron beam with instantaneous dose rates in the (1-324) kGy srange. Reference dosimetry was carried out with an integrating current transformer, which was calibrated in absorbed dose to water against a reference ionization chamber. Additionally, dose rate independent BeO OSLDs were employed as a reference. Beam non-uniformity was addressed using a matrix of TLDs/OSLDs.The investigated TLDs were shown to be dose rate independent within the experimental uncertainties, which take into account the uncertainty of the dosimetry protocol and the irradiation uncertainty. The relative deviation between the TLDs and the reference dose was lower than 4 % for all dose rates. A decreasing response with the dose rate was observed for AlO:C OSLDs, but still within 10 % from the reference dose.The precision of the investigated luminescence detectors make them suitable for dosimetry of ultra-high dose rate electron beams. Specifically, the dose rate independence of the TLDs can support the investigation of the beam uniformity as a function of the dose rate, which is one of the challenges of the employed beam. AlO:C OSLDs provided high precision measurements, but the decreasing response with the dose rate needs to be confirmed by additional experiments.
Topics: Electrons; Radiometry; Luminescence; Water
PubMed: 37336230
DOI: 10.1088/1361-6560/acdfb2