Purpose
This study investigates the difference in whole‐body dose equivalent between 6 and 15 MV image‐guided radiotherapy (IGRT) for the treatment of a rhabdomyosarcoma in the prostate.
Methods
A ...previously developed model for stray radiation of the primary beam was improved and used to calculate the photon dose and photon energy in the out‐of‐field region for a radiotherapy patient. The dose calculated by the treatment planning system was fused with the model‐calculated out‐of‐field dose, resulting in a whole‐body photon dose distribution. The peripheral neutron dose equivalent was calculated using an analytical model from the literature. A daily cone beam CT dose was added to the neutron and photon dose equivalents. The calculated 3D dose distributions were compared to independent measurements conducted with thermoluminescence dosimeters and an anthropomorphic phantom. The dose contributions from the IGRT treatments of three different techniques applied with two nominal X‐ray energies were compared using dose equivalent volume histograms (DEVHs).
Results
The calculated and measured out‐of‐field whole‐body dose equivalents for the IGRT treatments agreed within (9 ± 10) % (mean and type A SD). The neutron dose equivalent was a minor contribution to the total out‐of‐field dose up to 50 cm from the isocenter. Further from the isocenter, head leakage was dominating inside the patient body, whereas the neutron dose equivalent contribution was important close to the surface. There were small differences between the whole‐body DEVHs of the 6 and 15 MV treatments applied with the same technique, although the single scatter contributions showed large differences. Independent of the beam energy, the out‐of‐field dose of the volumetric‐modulated arc therapy (VMAT) treatment was significantly lower than the dynamic intensity‐modulated radiation therapy (IMRT) treatment.
Conclusion
The calculated whole‐body dose helped to understand the importance of the dose contributions in different areas of the patient. Regarding radiation protection of the patient for IGRT treatments, the choice of beam energy is not important, whereas the treatment technique has a large influence on the out‐of‐field dose. If the patient is treated with intensity‐modulated beams, VMAT should be used instead of dynamic IMRT in terms of radiation protection of the patient. In general, the developed models for photon and neutron dose equivalent calculation can be used for any patient geometry, tumor location, and linear accelerator.
For the epidemiological evaluation of long-term side effects of radiotherapy patients, it is important to know the doses to organs and tissues everywhere in the patient. Computed tomography (CT) ...images of the patients which contain the anatomical information are sometimes available for each treated patient. However, the available CT scans usually cover only the treated volume of the patient including the target and surrounding anatomy. To overcome this limitation, in this work we describe the development of a software tool using the Varian Eclipse Scripting API for extending a partial-body CT to a whole-body representation in the treatment planning system for dose calculation. The whole-body representation is created by fusing the partial-body CT with a similarly sized whole-body computational phantom selected from a library containing 64 phantoms of different heights, weights, and genders. The out-of-field dose is calculated with analytical models from the literature and merged with the treatment planning system-calculated dose. To test the method, the out-of-field dose distributions on the computational phantoms were compared to dose calculations on whole-body patient CTs. The mean doses, D2% and D98% were compared in 26 organs and tissues for 14 different treatment plans in 5 patients using 3D-CRT, IMRT, VMAT, coplanar and non-coplanar techniques. From these comparisons we found that mean relative differences between organ doses ranged from −10% and +20% with standard deviations of up to 40%. The developed method will help epidemiologists and researchers estimate organ doses outside the treated volume when only limited treatment planning CT information is available.
The Delta4DVH Anatomy 3D quality assurance (QA) system (ScandiDos), which converts the measured detector dose into the dose distribution in the patient geometry was evaluated. It allows a direct ...comparison of the calculated 3D dose with the measured back‐projected dose. In total, 16 static and 16 volumetric‐modulated arc therapy (VMAT) fields were planned using four different energies. Isocenter dose was measured with a pinpoint chamber in homogeneous phantoms to investigate the dose prediction by the Delta4DVH Anatomy algorithm for static fields. Dose distributions of VMAT fields were measured using GAFCHROMIC film. Gravitational gantry errors up to 10° were introduced into all VMAT plans to study the potential of detecting errors. Additionally, 20 clinical treatment plans were verified. For static fields, the Delta4DVH Anatomy predicted the isocenter dose accurately, with a deviation to the measured phantom dose of 1.1%±0.6%. For VMAT fields the predicted Delta4DVH Anatomy dose in the isocenter plane corresponded to the measured dose in the phantom, with an average gamma agreement index (GAI) (3 mm/3%) of 96.9±0.4%. The Delta4DVH Anatomy detected the induced systematic gantry error of 10° with a relative GAI (3 mm/3%) change of 5.8%±1.6%. The conventional Delta4PT QA system detected a GAI change of 4.2%±2.0%. The conventional Delta4PT GAI (3 mm/3%) was 99.8%±0.4% for the clinical treatment plans. The mean body and PTV‐GAI (3 mm/5%) for the Delta4DVH Anatomy were 96.4%±2.0% and 97.7%±1.8%; however, this dropped to 90.8%±3.4% and 87.1%±4.1% for passing criteria of 3 mm/3%. The anatomy‐based patient specific quality assurance system predicts the dose distribution correctly for a homogeneous case. The limiting factor for the error detection is the large variability in the error‐free plans. The dose calculation algorithm is inferior to that used in the TPS (Eclipse).
PACS numbers: 87.56.Fc, 87.56.‐v
Long-term survivors of cancer who were treated with radiotherapy are at risk of a radiation-induced tumor. Hence, it is important to model the out-of-field dose resulting from a cancer treatment. ...These models have to be verified with measurements, due to the small size, the high sensitivity to ionizing radiation and the tissue-equivalent composition, LiF thermoluminescence dosimeters (TLD) are well-suited for out-of-field dose measurements. However, the photon energy variation of the stray dose leads to systematic dose errors caused by the variation in response with radiation energy of the TLDs. We present a dosimeter which automatically corrects for the energy variation of the measured photons by combining LiF:Mg,Ti (TLD100) and LiF:Mg,Cu,P (TLD100H) chips.
The response with radiation energy of TLD100 and TLD100H compared to 60Co was taken from the literature. For the measurement, a TLD100H was placed on top of a TLD100 chip. The dose ratio between the TLD100 and TLD100H, combined with the ratio of the response curves was used to determine the mean energy. With the energy, the individual correction factors for TLD100 and TLD100H could be found. The accuracy in determining the in- and out-of-field dose for a nominal beam energy of 6MV using the double-TLD unit was evaluated by an end-to-end measurement. Furthermore, published Monte Carlo (M.C.) simulations of the mean photon energy for brachytherapy sources, stray radiation of a treatment machine and cone beam CT (CBCT) were compared to the measured mean energies. Finally, the photon energy distribution in an Alderson phantom was measured for different treatment techniques applied with a linear accelerator. Additionally, a treatment plan was measured with a cobalt machine combined with an MRI.
For external radiotherapy, the presented double-TLD unit showed a relative type A uncertainty in doses of −1%±2% at the two standard deviation level compared to an ionization chamber. The type A uncertainty in dose was in agreement with the theoretically calculated type B uncertainty. The measured energies for brachytherapy sources, stray radiation of a treatment machine and CBCT imaging were in agreement with M.C. simulations. A shift in energy with increasing distance to the isocenter was noticed for the various treatment plans measured with the Alderson phantom. The calculated type B uncertainties in energy were in line with the experimentally evaluated type A uncertainties.
The double-TLD unit is able to predict the photon energy of scatter radiation in external radiotherapy, X-ray imagine and brachytherapy sources. For external radiotherapy, the individual energy correction factors enabled a more accurate dose determination compared to conventional TLD measurements.
Purpose
The use of X‐ray imaging in radiation therapy can give a substantial dose to the patient. A Cobalt machine combined with an magnetic resonance imaging (MRI) was recently introduced to ...clinical work. One positive aspect of using non‐ionizing imaging devices is the reduction of the patient exposure. The purpose of this study was to quantify the difference in out‐of‐field dose to the patient between the image guided radiation therapy (IGRT) treatment applied with a linear accelerator with cone beam CT (CBCT) equipment and a Cobalt machine combined with an MRI.
Methods
The treatment of a rhabdomyosarcoma in the prostate was planned and irradiated using different modalities and radiation therapy machines. The whole‐body dose was measured for a 3D‐conformal radiation therapy (3DCRT), an intensity‐modulated radiation therapy (IMRT), and a volumetric‐modulated arc therapy plan applied with a conventional linear accelerator operated at 6 MV beam energy. Additionally, the dose of an IMRT plan applied with a 60Co machine combined with an MRI was measured. Furthermore, the dose of one CBCT scan using the linear accelerator's on‐board imaging system was determined. The 3D dose measurements were performed in an anthropomorphic phantom containing 168 slots for thermoluminescence dosimeters (TLDs). A combination of LiF:Mg,Ti (TLD100) and LiF:Mg,Cu,P (TLD100H) was used to accurately determine the in‐ and out‐of‐field dose. The plans were rescaled to different fractionation schemes (2 Gy, 3 Gy, and 5 Gy fraction dose) and the dose of one CBCT scan was additionally added to the treatment dose per fraction applied with the linear accelerator. The resulting absorbed doses per fraction of the two machines were compared.
Results
In the target region, all measured treatment plans presented the same magnitude of dose, while the CBCT dose was a factor of 100 smaller. Close to the planned target volume (PTV), the dose from the 60Co machine was a factor of two higher compared with the 3DCRT + CBCT dose. Up to 45 cm from the PTV, the treatment applied with the 60Co‐sources showed an increased out‐of‐field dose compared to the linear accelerator + CBCT IGRT treatments. Further away from the PTV in the region where leakage from the gantry head is dominating, the out‐of‐field dose of the Cobalt machine was smaller compared to the linear accelerator + CBCT.
Conclusion
The peripheral dose of the 60Co machine combined with an MRI is larger up to 45 cm from the PTV and further away, it is lower than the dose from a linear accelerator + CBCT treatment. The presented fractionation schemes had a marginal impact on the results.
The use of X-ray imaging in radiation therapy can give a substantial dose to the patient. A Cobalt machine combined with an magnetic resonance imaging (MRI) was recently introduced to clinical work. ...One positive aspect of using non-ionizing imaging devices is the reduction of the patient exposure. The purpose of this study was to quantify the difference in out-of-field dose to the patient between the image guided radiation therapy (IGRT) treatment applied with a linear accelerator with cone beam CT (CBCT) equipment and a Cobalt machine combined with an MRI.
The treatment of a rhabdomyosarcoma in the prostate was planned and irradiated using different modalities and radiation therapy machines. The whole-body dose was measured for a 3D-conformal radiation therapy (3DCRT), an intensity-modulated radiation therapy (IMRT), and a volumetric-modulated arc therapy plan applied with a conventional linear accelerator operated at 6 MV beam energy. Additionally, the dose of an IMRT plan applied with a
Co machine combined with an MRI was measured. Furthermore, the dose of one CBCT scan using the linear accelerator's on-board imaging system was determined. The 3D dose measurements were performed in an anthropomorphic phantom containing 168 slots for thermoluminescence dosimeters (TLDs). A combination of LiF:Mg,Ti (TLD100) and LiF:Mg,Cu,P (TLD100H) was used to accurately determine the in- and out-of-field dose. The plans were rescaled to different fractionation schemes (2 Gy, 3 Gy, and 5 Gy fraction dose) and the dose of one CBCT scan was additionally added to the treatment dose per fraction applied with the linear accelerator. The resulting absorbed doses per fraction of the two machines were compared.
In the target region, all measured treatment plans presented the same magnitude of dose, while the CBCT dose was a factor of 100 smaller. Close to the planned target volume (PTV), the dose from the
Co machine was a factor of two higher compared with the 3DCRT + CBCT dose. Up to 45 cm from the PTV, the treatment applied with the
Co-sources showed an increased out-of-field dose compared to the linear accelerator + CBCT IGRT treatments. Further away from the PTV in the region where leakage from the gantry head is dominating, the out-of-field dose of the Cobalt machine was smaller compared to the linear accelerator + CBCT.
The peripheral dose of the
Co machine combined with an MRI is larger up to 45 cm from the PTV and further away, it is lower than the dose from a linear accelerator + CBCT treatment. The presented fractionation schemes had a marginal impact on the results.
Purpose:
There is an increasing number of cancer survivors who are at risk of developing late effects caused by ionizing radiation such as induction of second tumors. Hence, the determination of ...out-of-field dose for a particular treatment plan in the patient’s anatomy is of great importance. The purpose of this study was to analytically model the stray dose according to its three major components.
Methods:
For patient scatter, a mechanistic model was developed. For collimator scatter and head leakage, an empirical approach was used. The models utilize a nominal beam energy of 6 MeV to describe two linear accelerator types of a single vendor. The parameters of the models were adjusted using ionization chamber measurements registering total absorbed dose in simple geometries. Whole-body dose measurements using thermoluminescent dosimeters in an anthropomorphic phantom for static and intensity-modulated treatment plans were compared to the 3D out-of-field dose distributions calculated by a combined model.
Results:
The absolute mean difference between the whole-body predicted and the measured out-of-field dose of four different plans was 11% with a maximum difference below 44%. Computation time of 36 000 dose points for one field was around 30 s. By combining the model-calculated stray dose with the treatment planning system dose, the whole-body dose distribution can be viewed in the treatment planning system.
Conclusions:
The results suggest that the model is accurate, fast and can be used for a wide range of treatment modalities to calculate the whole-body dose distribution for clinical analysis. For similar energy spectra, the mechanistic patient scatter model can be used independently of treatment machine or beam orientation.
Purpose
To image the abdomen of a patient with a gantry mounted imaging system of a linear accelerator, different cone beam computed tomography (CBCT) protocols are available. The whole‐body dose of ...a full rotation abdomen CBCT and a half rotation CBCT was compared. In our clinic, both CBCT protocols are used in daily routine work.
Methods
With an adult anthropomorphic Alderson phantom, the whole‐body dose per CBCT scan was measured with thermoluminescence dosimeters. The half rotation CBCT was applied such that the gantry mounted X‐ray source rotated around the right side of the phantom. The 183 measurement locations covered all ICRP recommended critical organs (except the gonads). The effective dose was calculated with the mean organ dose and the corresponding tissue weighting factors. A point‐by‐point dose comparison of both protocols was conducted.
Results
The effective dose was 5.4 mSv ±5% and 5.0 mSv ±5% (estimated type B 1σ) for the full and the half rotation CBCT respectively. There was no significant difference (α = 0.05) in the effective dose within the precision of the measurement (1σ = 5%). The half rotation CBCT displayed an inhomogeneous dose distribution in a transversal phantom slice in contrast with the full rotation CBCT. In the imaging region, the mean dose was (20.5 ± 3.4) mGy and (19.2 ± 7.4) mGy (measured type A 1σ) for the full and the half rotation CBCT respectively.
Conclusion
The half compared to the full rotation CBCT displays a smaller field‐of‐view in a transversal slice and no significant difference in the effective dose. Hence, the full rotation CBCT is favorable compared to the half rotation CBCT. However, by using the half rotation protocol, critical volumes in the patient can be spared compared to the full rotation protocol.
Benzodiazepines and other sedative hypnotic drugs (BSHs) are frequently prescribed for sleep problems, but cause substantial adverse effects, particularly in older adults. Improving knowledge on ...barriers, facilitators and needs of primary care providers (PCPs) to BSH deprescribing could help reduce BSH use and thus negative effects.
We conducted a mixed methods study (February-May 2023) including a survey, semi-structured interviews and focus groups with PCPs in Switzerland. We assessed barriers, facilitators and needs of PCPs to BSH deprescribing. Quantitative data were analyzed descriptively, qualitative data deductively and inductively using the Theoretical Domain Framework (TDF). Quantitative and qualitative data were integrated using meta-interferences.
The survey was completed by 126 PCPs (53% female) and 16 PCPs participated to a focus group or individual interview. The main barriers to BSH deprescribing included patient and PCP lack of knowledge on BSH effects and side effects, lack of PCP education on treatment of sleep problems and BSH deprescribing, patient lack of motivation, PCP lack of time, limited access to cognitive behavioral therapy for insomnia and absence of public dialogue on BSHs. Facilitators included informing on side effects to motivate patients to discontinue BSHs and start of deprescribing during a hospitalization. Main PCP needs were practical recommendations for pharmacological and non-pharmacological treatment of sleep problems and deprescribing schemes. Patient brochures were wished by 69% of PCPs. PCPs suggested the brochures to contain explanations about risks and benefits of BSHs, sleep hygiene and sleep physiology, alternative treatments, discontinuation process and tapering schemes.
The barriers and facilitators as well as PCP needs and opinions on patient material we identified can be used to develop PCP training and material on BSH deprescribing, which could help reduce the inappropriate use of BSHs for sleep problems.
Abstract
Background
The burden and timeline of posttransplant infections are not comprehensively documented in the current era of immunosuppression and prophylaxis.
Methods
In this prospective study ...nested within the Swiss Transplant Cohort Study (STCS), all clinically relevant infections were identified by transplant–infectious diseases physicians in persons receiving solid organ transplant (SOT) between May 2008 and December 2014 with ≥12 months of follow-up.
Results
Among 3541 SOT recipients, 2761 (1612 kidney, 577 liver, 286 lung, 213 heart, and 73 kidney-pancreas) had ≥12 months of follow-up; 1520 patients (55%) suffered 3520 infections during the first year posttransplantation. Burden and timelines of clinically relevant infections differed between transplantations. Bacteria were responsible for 2202 infections (63%) prevailing throughout the year, with a predominance of Enterobacteriaceae (54%) as urinary pathogens in heart, lung, and kidney transplant recipients, and as digestive tract pathogens in liver transplant recipients. Enterococcus spp (20%) occurred as urinary tract pathogens in kidney transplant recipients and as digestive tract pathogens in liver transplant recipients, and Pseudomonas aeruginosa (9%) in lung transplant recipients. Among 1039 viral infections, herpesviruses predominated (51%) in kidney, liver, and heart transplant recipients. Among 263 fungal infections, Candida spp (60%) prevailed as digestive tract pathogens in liver transplant recipients. Opportunistic pathogens, including Aspergillus fumigatus (1.4%) and cytomegalovirus (6%), were rare, scattering over 12 months across all SOT recipients.
Conclusions
In the current era of immunosuppression and prophylaxis, SOT recipients experience a high burden of infections throughout the first year posttransplantation, with rare opportunistic pathogens and a predominance of bacteria.
Data on burden and timeline of infections following solid organ transplantation are currently lacking. This Swiss nationwide cohort study found a high burden of infections throughout the first year posttransplantation, with rare opportunistic pathogens and a predominance of bacteria.
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