Accuracy of skin dose mapping in interventional cardiology: Comparison of 10 software products following a common protocol

PurposeOnline and offline software products can estimate the maximum skin dose (MSD) delivered to the patient during interventional cardiology procedures. The capabilities and accuracy of several skin dose mapping (SDM) software products were assessed on X-ray systems from the main manufacturers following a common protocol.MethodsSkin dose was measured on four X-ray systems following a protocol composed of nine fundamental irradiation set-ups and three set-ups simulating short, clinical procedures. Dosimeters/multimeters with semiconductor-based detectors, radiochromic films and thermoluminescent dosimeters were used. Results were compared with up to eight of 10 SDM products, depending on their compatibility.ResultsThe MSD estimates generally agreed with the measurements within ± 40% for fundamental irradiation set-ups and simulated procedures. Only three SDM products provided estimates within ± 40% for all tested configurations on at least one compatible X-ray system. No SDM product provided estimates within ± 40% for all combinations of configurations and compatible systems. The accuracy of the MSD estimate for lateral irradiations was variable and could be poor (up to 66% underestimation). Most SDM products produced maps which qualitatively represented the dimensions, the shape and the relative position of the MSD region. Some products, however, missed the MSD region when situated at the intersection of multiple fields, which is of radiation protection concern.ConclusionsIt is very challenging to establish a common protocol for quality control (QC) and acceptance testing because not all information necessary for accurate MSD calculation is available or standardised in the radiation dose structured reports (RDSRs).     

Validation of a dose tracking software for skin dose map calculation in interventional radiology

PurposeValidate the skin dose software within the radiation dose index monitoring system NEXO[DOSE]® (Bracco Injeneering S.A., Lausanne, Switzerland). It provides the skin dose distribution in interventional radiology (IR) procedures.MethodsTo determine the skin dose distribution and the Peak Skin Dose (PSD) in IR procedures, the software uses exposure and geometrical parameters taken from the radiation dose structured report and additional information specific to each angiographic system. To test the accuracy of the software, GafChromic® XR-RV3 films, wrapped under a cylindrical PMMA phantom, were irradiated with different setups. Calculations and films results are compared in terms of absolute dose and geometric accuracy, using two angiographic systems (Philips Integris Allura FD20, Siemens AXIOM-ArtisZeego).ResultsCalculated and film measured PSD values agree with an average difference of 7% ± 5%. The discrepancies in dose evaluation increase up to 33% in lower dose regions, because the algorithm does not consider the out-of-field scatter contribution of the neighboring fields, which is more significant in these areas. Regarding the geometric accuracy, the differences between the simulated dose spatial distributions and the measured ones are<3 mm (4%) in simple tests and 5 mm (5%) in setups closer to clinical practice. Moreover, similar results are obtained for the two studied angiographic system vendors.ConclusionsNEXO[DOSE]® provides an accurate skin dose distribution and PSD estimate. It will allow faster and more accurate monitoring of patient follow-up in the future.     

Quantification of residual dose estimation error on log file-based patient dose calculation

PurposeThe log file-based patient dose estimation includes a residual dose estimation error caused by leaf miscalibration, which cannot be reflected on the estimated dose. The purpose of this study is to determine this residual dose estimation error.Methods and materialsModified log files for seven head-and-neck and prostate volumetric modulated arc therapy (VMAT) plans simulating leaf miscalibration were generated by shifting both leaf banks (systematic leaf gap errors: ±2.0, ±1.0, and ±0.5 mm in opposite directions and systematic leaf shifts: ±1.0 mm in the same direction) using MATLAB-based (MathWorks, Natick, MA) in-house software. The generated modified and non-modified log files were imported back into the treatment planning system and recalculated. Subsequently, the generalized equivalent uniform dose (gEUD) was quantified for the definition of the planning target volume (PTV) and organs at risks.ResultsFor MLC leaves calibrated within ±0.5 mm, the quantified residual dose estimation errors that obtained from the slope of the linear regression of gEUD changes between non- and modified log file doses per leaf gap are in head-and-neck plans 1.32 ± 0.27% and 0.82 ± 0.17 Gy for PTV and spinal cord, respectively, and in prostate plans 1.22 ± 0.36%, 0.95 ± 0.14 Gy, and 0.45 ± 0.08 Gy for PTV, rectum, and bladder, respectively.ConclusionsIn this work, we determine the residual dose estimation errors for VMAT delivery using the log file-based patient dose calculation according to the MLC calibration accuracy.     

Validation of a method for “dose of the day” calculation in head-neck tomotherapy by using planning ct-to-MVCT deformable image registration

PurposeThe aim of this study was to test the feasibility and dosimetric accuracy of a method that employs planning CT-to-MVCT deformable image registration (DIR) for calculation of the daily dose for head and neck (HN) patients treated with Helical Tomotherapy (HT).MethodsFor each patient, the planning kVCT (CTplan) was deformably registered to the MVCT acquired at the 15th therapy session (MV15) with a B-Spline Free Form algorithm using Mattes mutual information (open-source software 3D Slicer), resulting in a deformed CT (CTdef). On the same day as MVCT15, a kVCT was acquired with the patient in the same treatment position (CT15). The original HT plans were recalculated both on CTdef and CT15, and the corresponding dose distributions were compared; local dose differences <2% of the prescribed dose (DD2%) and 2D/3D gamma-index values (2%-2 mm) were assessed respectively with Mapcheck SNC Patient software (Sun Nuclear) and with 3D-Slicer.ResultsOn average, 87.9% ± 1.2% of voxels were found for DD2% (on average 27 slices available for each patient) and 94.6% ± 0.8% of points passed the 2D gamma analysis test while the 3D gamma test was satisfied in 94.8% ± 0.8% of body’s voxels.ConclusionsThis study represents the first demonstration of the dosimetric accuracy of kVCT-to-MVCT DIR for dose of the day computations. The suggested method is sufficiently fast and reliable to be used for daily delivered dose evaluations in clinical strategies for adaptive Tomotherapy of HN cancer.     

Perturbation analysis of 4D dose distribution for scanned carbon-ion beam radiotherapy

PurposeTo evaluate the patients’ set-up error-induced perturbation effects on 4D dose distributions (4DDD) of range-adapted internal target volume-based (raITV) treatment plan using lung and liver 4DCT data sets.MethodsWe enrolled 20 patients with lung and liver cancer treated with respiratory-gated carbon-ion beam scanning therapy. PTVs were generated by adding a 2 mm range-adapted set-up margin on the raITVs. Set-up errors were simulated by shifting the beam isocenter in three translational directions of ±2 mm, ±4 mm, and ±6 mm. 4DDDs were calculated for both nominal and isocenter-shifted situations. Dose metrics of CTV dose coverage (D95) and normal tissue sparing were evaluated. Statistical significance with p < 0.01 was considered by Wilcoxon signed rank test.ResultsThe CTV dose coverage was more sensitive to set-up errors for lung cases than for liver cases, and more serious in superior-inferior direction. The sufficient CTV-D95 > 98% could be achieved with set-up errors less than ±2 mm in all shift directions both for lung and liver cases. With the increase of set-up error, the CTV dose coverage decreased gradually. The clinical criterial of CTV-D95 > 95% could not be fulfilled with set-up error reached to ±4 mm for lung cases, and ±6 mm for liver cases. OAR doses did not have a significant difference with each set-up error for both lung and liver cases.ConclusionsThe range-adapted set-up margin successfully prevented dose degradation of 4DDDs in the presence of the same magnitude of set-up error for raITV-based carbon-ion beam scanning therapy.     

Skin dose assessment in interventional radiology

For long, complex procedures in interventional radiology (IR) or in interventional cardiology (IC), the skin dose can be high and induce skin injuries. To improve patient follow-up, it is essential to measure and locate the peak skin dose (PSD). PSD can be measured using dosimeters or computed by skin dose calculation software solutions. Recently, a study was published (e.g. Malchair F et al Phys Med 2020; 80:75–83) listing all the software solutions developed and available and compared them in operation as regards accuracy of the calculated PSD and generated dose map. Similarities and differences exist between these different software packages, which are discussed here. The accuracy of PSD calculated on phantom studies with these software solutions are within ± 25% and poorer in patient studies. Improvements are therefore required for manufacturers of both software and IR systems. The medical physicists also have an important role to play in setting up and monitoring the dose in these software solutions to ensure the accuracy of the calculated PSD.     

Radiation dose in repeated CT guided radiofrequency ablations

ObjectiveTo calculate the cumulative effective and skin doses in patients that underwent repeated CT guided radiofrequency ablations (RFA).Materials and methodsFrom all patients that had undergone RFA during a five years period those which had three or more RFAs were selected. Using the CT images DICOM data, the dose length product (DLP), effective dose (E), skin dose profiles as well as the peak skin dose (PSD) were calculated, using appropriate methods and software developed for this purpose. For each patient, cumulative DLP and E were also calculated from the sum of the respective figures of each individual procedure. To calculate PSD, the skin dose profiles of each procedure were overlaid on the same Z-axis scale using anatomical landmarks for reference and the skin doses to each point were summed up.ResultsFive patients were studied; four had undergone 3 RFAs and one 10 RFAs. Cumulative DLP, E and PSD ranges were 5.6–22.3 Gy cm, 0.08–0.36 Sv and 0.8–3.4 Gy, respectively. Median E and PSD values per RFA were 35 mSv and 0.4 Gy, respectively. For comparison purposes it must be noted that in this CT department a routine abdomen-pelvis scan results to an E of about 10 mSv.ConclusionsPatients that undergo repeated RFAs are exposed to considerably high radiation exposure levels. When these patients are in the final stage of malignant diseases, stochastic effects may not be of major concern. However, optimization of the exposure factors and monitoring of these patients to avoid skin injuries are required.     

Patient doses and occupational exposure in a hybrid operating room

PurposeThis study aimed to characterize the radiation exposure to patients and workers in a new vascular hybrid operating room during X-ray-guided procedures.MethodsDuring one year, data from 260 interventions performed in a hybrid operating room equipped with a Siemens Artis Zeego angiography system were monitored. The patient doses were analysed using the following parameters: radiation time, kerma-area product, patient entrance reference point dose and peak skin dose. Staff radiation exposure and ambient dose equivalent were also measured using direct reading dosimeters and thermoluminescent dosimeters.ResultsThe radiation time, kerma-area product, patient entrance reference point dose and peak skin dose were, on average, 19:15 min, 67 Gy·cm², 0.41 Gy and 0.23 Gy, respectively. Although the contribution of the acquisition mode was smaller than 5% in terms of the radiation time, this mode accounted for more than 60% of the effective dose per patient. All of the worker dose measurements remained below the limits established by law.ConclusionsThe working conditions in the hybrid operating room HOR are safe in terms of patient and staff radiation protection. Nevertheless, doses are highly dependent on the workload; thus, further research is necessary to evaluate any possible radiological deviation of the daily working conditions in the HOR.     

A novel tool for assessing the correlation of internal/external markers during SGRT guided stereotactic ablative radiotherapy treatments

IntroductionAn in-house developed tool was implemented and validated to investigate the skin surface, hepatic dome, and target displacement for stereotactic ablative radiotherapy (SABR) of thoracic/abdominal lesions using a Surface Guided Radiation Therapy (SGRT) system combined with 4D- images.Materials and methodsFourteen consecutive patients with tumors near the hepatic dome undergoing SABR treatments were analyzed. For each patient, a planning 4D-CT and five 4D-CBCT images were acquired. The C-RAD technology was also used to register/monitor the position of the skin reference point (SRP) as an external marker representative of patient breathing. The 4D images were imported in the developed tool, and the absolute maximum height (P_max,dome) of the hepatic dome on the ten respiratory phases was semi-automatically detected. Similarly, the contour of the skin surface was extracted in correspondence with the SRP position. The tool has been validated using an ad hoc modified moving phantom with pre-selected amplitudes and numbers of cycles. The Pearson correlation coefficients and Bland-Altman plots were calculated.ResultsThere was a strong correlation between the skin motion amplitude based on 4D-CBCT and the C-RAD in all the patients (0.90 ± 0.08). Similarly, the mean ± SD of Pearson correlation coefficients of skin and P_max,dome movements registered by 4D-CT and 4D-CBCT were 0.90 ± 0.05 and 0.94 ± 0.05, respectively. The mean ± SD of Pearson correlation coefficients comparing the skin and P_max,dome displacements within each imaging modality were 0.88 ± 0.05 and 0.90 ± 0.05 for 4D-CT and 4D-CBCT, respectively. The SRP displacement during the set-up imaging and the treatment delivery were similar in all the investigated patients. Similar results were obtained for the ad hoc modified phantom in the preliminary validation phase.ConclusionThe strong correlation between the tumor/ hepatic dome and skin displacements confirms that the SGRT approach can be considered appropriate for intra- and inter-fraction motion management in SABR therapy.     

Infrared cameras overestimate skin temperature during rewarming from cold exposure

ObjectiveThe primary aim of this study was to assess the accuracy of an infrared camera and that of a skin thermistor, both commercially available. The study aimed to assess the agreement over a wide range of skin temperatures following cold exposure.MethodsFifty-two males placed their right hand in a thin plastic bag and immersed it in 8 °C water for 30 min whilst seated in an air temperature of 30 °C. Following hand immersion, participants removed the bag and rested their hand at heart level for 10 min. Index finger skin temperature (T_sk) was measured with a thermistor, affixed to the finger pad, and an infrared camera measured 1 cm distally to the thermistor. Agreement between the infrared camera and thermistor was assessed by mean difference (infrared camera minus thermistor) and 95% limits of agreement analysis, accounting for the repeated measures over time. The clinically significant threshold for T_sk differences was set at ±0.5 °C and limits of agreement ±1 °C.ResultsAs an average across all time points, the infrared camera recorded T_sk 1.80 (SD 1.16) °C warmer than the thermistor, with 95% limits of agreement ranging from −0.46 °C to 4.07 °C.ConclusionCollectively, the results show the infrared camera overestimated T_sk at every time point following local cooling. Further, measurement of finger T_sk from the infrared camera consistently fell outside the acceptable level of agreement (i.e. mean difference exceeding ±0.5 °C). Considering these results, infrared cameras may overestimate peripheral T_sk following cold exposure and clinicians and practitioners should, therefore, adjust their risk/withdrawal criteria accordingly.     

Implementation and evaluation of a transit dosimetry system for treatment verification

PurposeTo evaluate a formalism for transit dosimetry using a phantom study and prospectively evaluate the protocol on a patient population undergoing 3D conformal radiotherapy.MethodsAmorphous silicon EPIDs were calibrated for dose and used to acquire images of delivered fields. The measured EPID dose map was back-projected using the planning CT images to calculate dose at pre-specified points within the patient using commercially available software, EPIgray (DOSIsoft, France). This software compared computed back-projected dose with treatment planning system dose. A series of tests were performed on solid water phantoms (linearity, field size effects, off-axis effects). 37 patients were enrolled in the prospective study.ResultsThe EPID dose response was stable and linear with dose. For all tested field sizes the agreement was good between EPID-derived and treatment planning system dose in the central axis, with performance stability up to a measured depth of 18 cm (agreement within −0.5% at 10 cm depth on the central axis and within −1.4% at 2 cm off-axis). 126 transit images were analysed of 37 3D-conformal patients. Patient results demonstrated the potential of EPIgray with 91% of all delivered fields achieved the initial set tolerance level of Δ_D of 0 ± 5-cGy or %Δ_D of 0 ± 5%.ConclusionsThe in vivo dose verification method was simple to implement, with very few commissioning measurements needed. The system required no extra dose to the patient, and importantly was able to detect patient position errors that impacted on dose delivery in two of cases.     

Clinical application of MOSkin dosimeters to rectal wall in vivo dosimetry in gynecological HDR brachytherapy

PurposeThree MOSkins dosimeters were assembled over a rectal probe and used to perform in vivo dosimetry during HDR brachytherapy treatments of vaginal cancer. The purpose of this study was to verify the applicability of the developed tool to evaluate discrepancies between planned and measured doses to the rectal wall.Materials and methodsMOSkin dosimeters from the Centre for Medical Radiation Physics are particularly suitable for brachytherapy procedures for their ability to be easily incorporated into treatment instrumentation. In this study, 26 treatment sessions of HDR vaginal brachytherapy were monitored using three MOSkin mounted on a rectal probe. A total of 78 measurements were collected and compared to doses determined by the treatment planning system.ResultsMean dose discrepancy was determined as 2.2 ± 6.9%, with 44.6% of the measurements within ±5%, 89.2% within ±10% and 10.8% higher than ±10%. When dose discrepancies were grouped according to the time elapsed between imaging and treatment (i.e., group 1: ≤90 min; group 2: >90 min), mean discrepancies resulted in 4.7 ± 3.6% and 7.1 ± 5.0% for groups 1 and 2, respectively. Furthermore, the position of the dosimeter on the rectal catheter was found to affect uncertainty, where highest uncertainties were observed for the dosimeter furthest inside the rectum.ConclusionsThis study has verified MOSkin applicability to in-patient dose monitoring in gynecological brachytherapy procedures, demonstrating the dosimetric rectal probe setup as an accurate and convenient IVD instrument for rectal wall dose verification. Furthermore, the study demonstrates that the delivered dose discrepancy may be affected by the duration of treatment planning.     

Assessment of daily dose accumulation for robustly optimized intensity modulated proton therapy treatment of prostate cancer

PurposeTo implement a daily CBCT based dose accumulation technique in order to assess ideal robust optimization (RO) parameters for IMPT treatment of prostate cancer.MethodsTen prostate cancer patients previously treated with VMAT and having daily CBCT were included. First, RO-IMPT plans were created with ± 3 mm and ± 5 mm patient setup and ± 3% proton range uncertainties, respectively. Second, the planning CT (pCT) was deformably registered to the CBCT to create a synthetic CT (sCT). Both daily and weekly sampling strategies were employed to determine optimal dose accumulation frequency. Doses were recalculated on sCTs for both ± 3 mm/±3% and ± 5 mm/±3% uncertainties and were accumulated back to the pCT. Accumulated doses generated from ± 3 mm/±3% and ± 5 mm/±3% RO-IMPT plans were evaluated using the clinical dose volume constraints for CTV, bladder, and rectum.ResultsDaily accumulated dose based on both ± 3mm/±3% and ±5 mm/±3% uncertainties for RO-IMPT plans resulted in satisfactory CTV coverage (RO-IMPT_3mm/3% CTV_V95 = 99.01 ± 0.87% vs. RO-IMPT_5mm/3% CTV_V95 = 99.81 ± 0.2%, P = 0.002). However, the accumulated dose based on ± 3 mm/3% RO-IMPT plans consistently provided greater OAR sparing than ±5 mm/±3% RO-IMPT plans (RO-IMPT_3mm/3% rectum_V65Gy = 2.93 ± 2.39% vs. RO-IMPT_5mm/3% rectum_V65Gy = 4.38 ± 3%, P < 0.01; RO-IMPT_3mm/3% bladder_V65Gy = 5.2 ± 7.12% vs. RO-IMPT_5mm/3% bladder_V65Gy = 7.12 ± 9.59%, P < 0.01). The gamma analysis showed high dosimetric agreement between weekly and daily accumulated dose distributions.ConclusionsThis study demonstrated that for RO-IMPT optimization, ±3mm/±3% uncertainty is sufficient to create plans that meet desired CTV coverage while achieving superior sparing to OARs when compared with ± 5 mm/±3% uncertainty. Furthermore, weekly dose accumulation can accurately estimate the overall dose delivered to prostate cancer patients.     

A protocol for absolute dose verification of SBRT/SRS treatment plans using Gafchromic™ EBT-XD films

PurposeTo provide a practical protocol for absolute dose verification of stereotactic body radiotherapy (SBRT) and stereotactic radiosurgery (SRS) treatment plans, based on our clinical experience. It aims to be a concise summary of the main aspects to be considered when establishing an accurate film dosimetry system.MethodsProcedures for film calibration and conversion to dose are described for a dosimetry system composed of Gafchromic™ EBT-XD films and a flatbed document scanner. Factors that affect the film-scanner response are also reviewed and accounted for. The accuracy of the proposed methodology was assessed by taking a set of strips irradiated to known doses and its applicability is illustrated for ten SBRT/SRS treatment plans. The film response was converted to dose using red and triple channel dosimetry. The agreement between the planned and measured dose distributions was evaluated using global gamma analysis with criteria of 3%/2mm 10% threshold (TH), 2%/2mm 10% TH, and 2%/2mm 20% TH.ResultsThe differences between the expected and determined doses from the strips analysis were 0.9 ± 0.6% for the red channel and 1.1 ± 0.7% for the triple channel method. Regarding the SBRT/SRS plans verification, the mean gamma passing rates were 99.5 ± 1.0% vs 99.6 ± 1.0% (3%/2mm 10% TH), 96.9 ± 3.5% vs 99.1 ± 1.3% (2%/2mm 10% TH) and 98.4 ± 1.8% vs 98.8 ± 1.5% (2%/2mm 20% TH) for red and triple channel dosimetry, respectively.ConclusionsThe proposed protocol allows for accurate absolute dose verification of SBRT/SRS treatment plans, applying both single and triple channel methods. It may work as a guide for users that intend to implement a film dosimetry system.     

Dose to the skin in helical tomotherapy: Results of in vivo measurements with radiochromic films

PurposeThe aim of this study is to report results of measurements of dose to the skin in vivo with radiochromic EBT films in treatments with helical tomotherapy.Methods and materialsIn vivo measurements were performed by applying pieces of radiochromic films to the skin or to the inner side of thermoplastic mask before the treatment. The sites of treatment included scalp, brain, head and neck, cranio-spinal axis and lower limbs. Skin dosimetry was performed in a patient who experienced grade 3–4 acute side effects to the skin shortly after the first treatment sessions. For each patient we measured the setup errors using the daily MVCT acquired for image guidance of the treatment. EBT films were read with a flatbed Epson Expression scanner and images were processed with an in-house written routine.ResultsA total of 96 measurements of dose to the skin performed on 14 patients. The mean difference and standard error of the mean difference between measured and TPS-calculated dose was ?9.2% ± 2.6% for all treatments, ?6.6% ± 2.6% for head and neck treatments. These differences were statistically significant at the 0.05 significance level (t-Student test). Planned dose and dose range in the region of measurements were not correlated with dose discrepancy.ConclusionsRadiochromic EBT films are suitable detectors for surface dose measurements in tomotherapy treatments. Results show that TPS overestimates dose to the skin measured with EBT radiochromic films. In vivo skin measurements with EBT films are a useful tool for quality assurance of tomotherapy treatments, as the treatment planning system may not give accurate dose values at the surface.     

The influence of respiratory motion on dose distribution in accelerated partial breast irradiation using volumetric modulated arc therapy

PurposeAccelerated partial breast irradiation (APBI) is alternative treatment option for patients with early stage breast cancer. The interplay effect on volumetric modulated arc therapy APBI (VMAT-APBI) has not been clarified. This study aimed to evaluate the feasibility of VMAT-APBI for patients with small breasts and investigate the amplitude of respiratory motion during VMAT-APBI delivery that significantly affects dose distribution.MethodsThe VMAT-APBI plans were generated with 28.5 Gy in five fractions. We performed patient-specific quality assurance using Delta⁴ phantom under static conditions. We also measured point dose and dose distribution using the ionization chamber and radiochromic film under static and moving conditions of 2, 3 and 5 mm. We compared the measured and calculated point doses and dose distributions by dose difference and gamma passing rates.ResultsA total of 20 plans were generated; the dose distributions were consistent with those of previous reports. For all measurements under static conditions, the measured and calculated point doses and dose distributions showed good agreement. The dose differences for chamber measurement were within 3%, regardless of moving conditions. The mean gamma passing rates with 3%/2 mm criteria in the film measurement under static conditions and with 2 mm, 3 mm, and 5 mm of amplitude were 95.0 ± 2.0%, 93.3 ± 3.3%, 92.1 ± 6.2% and 84.8 ± 7.8%, respectively. The difference between 5 mm amplitude and other conditions was statistically significant.ConclusionsRespiratory management should be considered for the risk of unintended dose distribution if the respiratory amplitude is >5 mm.     

Dosimetric impact of 4DCT artifact in carbon-ion scanning beam treatment: Worst case analysis in lung and liver treatments

IntroductionWe evaluated the impact of 4DCT artifacts on carbon-ion pencil beam scanning dose distributions in lung and liver treatment.Methods & materials4DCT was performed in 20 liver and lung patients using area-detector CT (original 4DCT). 4DCT acquisition by multi-detector row CT was simulated using original 4DCT by selecting other phases randomly (plus/minus 20% phases). Since tumor position can move over the respiratory range in original 4DCT, mid-exhalation was set as reference phase. Total prescribed dose of 60 Gy (RBE) was delivered to the clinical target volume (CTV). Reference dose distribution was calculated with the original CT, and actual dose distributions were calculated with treatment planning parameters optimized using the simulated CT (simulated dose). Dose distribution was calculated by substituting these parameters into the original CT.ResultsFor liver cases, CTV-D95 and CTV-Dmin values for the reference dose were 97.6 ± 0.5% and 89.8 ± 0.6% of prescribed dose, respectively. Values for the simulated dose were significantly degraded, to 88.6 ± 14.0% and 46.3 ± 26.7%, respectively. Dose assessment results for lung cases were 84.8 ± 12.8% and 58.0 ± 24.5% for the simulated dose, showing significant degradation over the reference dose of 95.1 ± 1.5% and 87.0 ± 2.2%, respectively.Conclusions4DCT image quality should be closely checked to minimize degradation of dose conformation due to 4DCT artifacts. Medical staff should pay particular attention to checking the quality of 4DCT images as a function of respiratory phase, because it is difficult to recognize 4DCT artifact on a single phase in some cases     

Thermoregulation in premature infants: A mathematical model

PurposeIn 2010, approximately 14.9 million babies (11.1%) were born preterm. Because preterm infants suffer from an immature thermoregulatory system they have difficulty maintaining their core body temperature at a constant level. Therefore, it is essential to maintain their temperature at, ideally, around 37 °C. For this, mathematical models can provide detailed insight into heat transfer processes and body-environment interactions for clinical applications.MethodsA new multi-node mathematical model of the thermoregulatory system of newborn infants is presented. It comprises seven compartments, one spherical and six cylindrical, which represent the head, thorax, abdomen, arms and legs, respectively. The model is customizable, i.e. it meets individual characteristics of the neonate (e.g. gestational age, postnatal age, weight and length) which play an important role in heat transfer mechanisms. The model was validated during thermal neutrality and in a transient thermal environment.ResultsDuring thermal neutrality the model accurately predicted skin and core temperatures. The difference in mean core temperature between measurements and simulations averaged 0.25±0.21 °C and that of skin temperature averaged 0.36±0.36 °C. During transient thermal conditions, our approach simulated the thermoregulatory dynamics/responses. Here, for all infants, the mean absolute error between core temperatures averaged 0.12±0.11 °C and that of skin temperatures hovered around 0.30 °C.ConclusionsThe mathematical model appears able to predict core and skin temperatures during thermal neutrality and in case of a transient thermal conditions.     

A retrospective comparison of organ dose and effective dose in percutaneous vertebroplasty performed under CT guidance or using a fixed C-arm with a flat-panel detector

PurposeTo compare the organ-dose and effective-dose (E) delivered to the patient during percutaneous vertebroplasty (PVP) of one thoracic or lumbar vertebra performed under CT guidance or using a fixed C-arm.MethodsConsecutive adult patients undergoing PVP of one vertebra under CT-guidance, with optimized protocol and training of physicians, or using a fixed C-arm were retrospectively included from January 2016 to June 2017. Organ-doses were computed on 16 organs using CT Expo 2.4 software for the CT procedures and PCXMC 2.0 for the fixed C-arm procedures. E was also computed with both software. Dosimetric values per anatomic locations for all procedures were compared using the paired Mann-Whitney-Wilcoxon test.ResultsIn total, 73 patients were analysed (27 men and 46 women, mean age 78 ± 10 years) among whom 35 (48%) underwent PVP under CT guidance and 38 (52%) PVP using a fixed C-arm. The median E was 11.31 [6.54; 15.82] mSv for all PVPs performed under CT guidance and 5.58 [3.33; 8.71] mSv for fixed C-arm and the differences was significant (p<0.001). For lumbar PVP, the organ doses of stomach, liver and colon were significantly higher with CT-scan than with the fixed C-arm: 97% (p=0.02); 21% (p=0.099) and 375% (p=0.002), respectively. For thoracic PVP, the lung organ dose was significantly higher with CT-scan than with the fixed C-arm (127%; p<0.001) and the oesophagus organ doses were not significantly different (p = 0.626).ConclusionThis study showed that the E and the organ dose on directly exposed organs were both higher for PVP performed under CT-guidance than with the fixed C-arm.