Commissioning and Assessment of Radiation Field and Dose Inhomogeneity for a Dual X-Ray Tube Cabinet Irradiator: To Ensure Accurate Dosimetry in Radiation Biology Experiments

PURPOSE/OBJECTIVE(S)

Standardization of X-ray cabinet irradiators calibration and dose reporting is an ongoing process. Multi-tube designs have been introduced and provide theoretical benefit but have not been assessed for pre-clinical irradiation conditions. This study was to report our experience commissioning a dual x-ray tube cabinet irradiator and assess dose distribution for various conditions. Homogeneity and percent depth dose (PDD) of various tube designs in single-tube setting have been previously reported, however multi-tube designs can overcome field asymmetry caused by the heel effect and improve dose fall-off at depth.

MATERIALS/METHODS

Profile measurements and output calibration were performed with a calibrated ion chamber. We measured the percent-depth-dose (PDD) with film for each tube individually (PDDind) and both tubes simultaneously (PDDsim). To replicate conditions similar to petri dishes, we evaluated the range of attenuation and scatter under variable solid water thickness up to 9 mm with 3 mm build-up below (i.e., 1.2 cm total backscatter) under several geometries. The films were placed at a fixed position with variable amount of solid water placed above the film. We measured the output with variable water volumes with a 6 cm petri dish to simulate variable solution volumes that are frequently used during in vitro experiments. Film was also placed in a 3D printed mouse phantom with dimensions of (9.5 × 3.6 × 3.0 cm) and constructed to be roughly cylindrical.

RESULTS

The dose in the 20 × 20 cm2 tray was within 8.4% of the central axis dose with both tubes. Dose rates decreased at the furthest points on the tray, but remained within 5% within the 15 × 15 cm2 central area. PDDsim with total 7.9 cm backscatter shows that the output is within 95% of the maximum dose at 4 cm depth. PDDsim with 1.2 cm backscatter is also within 95% of the maximum. The PDDind was less than 90% at 1.8 cm, which is similar to other single-tube systems. Slight increase in dose was seen with increasing solution; however, the doses were within 7% of the measured max dose at 6.3 mm depth. This agrees well with the solid water measurements. The results for both solid water and petri dish with variable medium is shown in Table 1. The 3D printed mouse phantom profiles for each plane showed results consistent with the ion chamber measurements.

CONCLUSION

X-ray cell culture irradiation with dual-tube cabinet irradiation is robust when utilizing established dosimetric tools to confirm output and homogeneity. The conditions assumed for calibrations are often not maintained during experiments. We have confirmed that inhomogeneities are present for single tube use, however they are reduced with simultaneous tube use. Additional monitoring should be performed for each unique irradiation setup.

End-to-End Verification and Dosimetric Comparative Study of Brainlab Monte Carlo and Eclipse Acuros XB Photon Dose Calculation Algorithm for VMAT SRS Planning

PURPOSE/OBJECTIVE(S)

We commissioned the Brainlab Monte Carlo Dose Calculation Algorithm for VMAT SRS planning and verified it by measurements and comparisons with two other algorithms: Pencil beam and Eclipse Acuros. The end-to-end verification and dosimetric comparative study results are reported in this abstract.

MATERIALS/METHODS

Brainlab Elements Cranial SRS (v3.0) provides single lesion planning using VMAT optimization, thus allowing dose modulation with MLC leaf positioning, dose rate, and gantry speed. We commissioned and performed quality assurance for the available dose calculation algorithms, including Pencil Beam (PB) algorithm with only reference beam data (RBM PB) and PB with full beam data (Elements PB), and Monte Carlo (MC) algorithm XVMC. Calculation between the two were compared to each other and to Acuros XB dose calculation algorithm by Varian. Open field MLC, static cone, dynamic MLC, and conical cone plans were calculated with each algorithm. IBA CC01 ionization chamber was used for each measurement, and small field correction factors as determined in TRT-483 were applied. End-to-end tests were performed using an anthropomorphic stereotactic end-to-end verification (STEEV) phantom from CIRS and a phantom/diode array, StereoPHAN/SRSMapCHECK from SunNuclear. Each phantom was CT scanned with 0.5 mm slice thickness. Four clinical plans were optimized in Brainlab Elements Treatment Planning System (TPS). Each plan was calculated with the following algorithms: Elements PB, RBM PB, MC, and Acuros XB with 1 mm dose grid size. The delivered dose was measured with a SunNuclear SRSMapCHECK diode array detector. The calculated dose was compared with the measured dose by Gamma analysis with DTA 1%/1mm, 2%/1mm, and 3%/1mm.

RESULTS

The results of point dose measurements for field size larger than 1 × 1 cm2 among measured dose, dose calculated by pencil beam algorithms, and dose calculated by Monte Carlo algorithm were in excellent agreement (1.45% ± 0.7%). For the small rectangular field sizes (0.4 × 1, 0.2 × 1 cm2), Monte Carlo calculation showed superior accuracy and robustness to pencil beam algorithm when compared with measured dose, with percent dose difference 13% and -2.2%, respectively. Monte Carlo calculation have higher gamma results compared with pencil beam algorithm due more accurate calculations with heterogenous materials. Acuros XB showed comparable accuracy with MC in terms of gamma passing rate.

CONCLUSION

The SRS MapCHECK measurement agrees dosimetrically with the plans calculated by Pencil Beam algorithm and the Monte Carlo algorithm XVMC by Brainlab, as well as the Acuros XB dose calculation algorithm by Varian. Point dose calculation for small field dosimetry and gamma analysis using SRS MapCHECK both showed that Monte Carlo algorithm is more robust and is superior in regions of heterogenous materials. Therefore, we recommend that Monte Carlo algorithm for dose calculation be used in clinical SRS and SRT cases.

IAmHero: Preliminary Findings of an Experimental Study to Evaluate the Statistical Significance of an Intervention for ADHD Conducted through the Use of Serious Games in Virtual Reality

The use of new technologies, such as virtual reality (VR), represents a promising strategy in the rehabilitation of subjects with attention-deficit/hyperactivity disorder (ADHD). We present the results obtained by administering the IAmHero tool through VR to a cohort of subjects with ADHD between 5 and 12 years of age. The trial time was approximately 6 months. In order to assess the beneficial effects of the treatment, standardised tests assessing both ADHD symptoms and executive functions (e.g., Conners-3 scales) were administered both before and at the end of the sessions. Improvements were observed at the end of treatment in both ADHD symptoms (especially in the hyperactivity/impulsivity domain) and executive functions. One of the strengths of the VR approach is related above all to the acceptability of this tool and its flexibility. Unfortunately, to date, there are still few studies on this topic; therefore, future studies are essential to expand our knowledge on the utility and benefits of these technologies in the rehabilitation field.

CRISIS AFAR: an international collaborative study of the impact of the COVID-19 pandemic on mental health and service access in youth with autism and neurodevelopmental conditions

BACKGROUND

Heterogeneous mental health outcomes during the COVID-19 pandemic are documented in the general population. Such heterogeneity has not been systematically assessed in youth with autism spectrum disorder (ASD) and related neurodevelopmental disorders (NDD). To identify distinct patterns of the pandemic impact and their predictors in ASD/NDD youth, we focused on pandemic-related changes in symptoms and access to services.

METHODS

Using a naturalistic observational design, we assessed parent responses on the Coronavirus Health and Impact Survey Initiative (CRISIS) Adapted For Autism and Related neurodevelopmental conditions (AFAR). Cross-sectional AFAR data were aggregated across 14 European and North American sites yielding a clinically well-characterized sample of N = 1275 individuals with ASD/NDD (age = 11.0 ± 3.6 years; n females = 277). To identify subgroups with differential outcomes, we applied hierarchical clustering across eleven variables measuring changes in symptoms and access to services. Then, random forest classification assessed the importance of socio-demographics, pre-pandemic service rates, clinical severity of ASD-associated symptoms, and COVID-19 pandemic experiences/environments in predicting the outcome subgroups.

RESULTS

Clustering revealed four subgroups. One subgroup-broad symptom worsening only (20%)-included youth with worsening across a range of symptoms but with service disruptions similar to the average of the aggregate sample. The other three subgroups were, relatively, clinically stable but differed in service access: primarily modified services (23%), primarily lost services (6%), and average services/symptom changes (53%). Distinct combinations of a set of pre-pandemic services, pandemic environment (e.g., COVID-19 new cases, restrictions), experiences (e.g., COVID-19 Worries), and age predicted each outcome subgroup.

LIMITATIONS

Notable limitations of the study are its cross-sectional nature and focus on the first six months of the pandemic.

CONCLUSIONS

Concomitantly assessing variation in changes of symptoms and service access during the first phase of the pandemic revealed differential outcome profiles in ASD/NDD youth. Subgroups were characterized by distinct prediction patterns across a set of pre- and pandemic-related experiences/contexts. Results may inform recovery efforts and preparedness in future crises; they also underscore the critical value of international data-sharing and collaborations to address the needs of those most vulnerable in times of crisis.

Effect of initial levothyroxine dose on neurodevelopmental and growth outcomes in children with congenital hypothyroidism

OBJECTIVES

We designed a multicentre open prospective randomized trial to evaluate the risk-benefit profile of two different initial treatment schemes with levothyroxine (L-T4), 10-12.5 μg/kg/day vs 12.6-15 μg/kg/day, on growth and neurodevelopmental outcomes in children with congenital hypothyroidism (CH) detected by neonatal screening to identify the best range dose to achieve optimal neurocognitive development.

DESIGN PATIENTS AND METHODS

Children detected by neonatal screening were randomly assigned to receive an initial L-T4 dose of 10-12.5 μg/kg/day (Low) or 12.6-15 μg/kg/day (High). All patients underwent periodical clinical examination with measurement of growth parameters and measurement of TSH and FT4. Neurocognitive development was evaluated at the age of 24 months using Griffiths Mental Development Scales (GMDS) and cognitive and behavioral assessment was performed at 48 months of age using Wechsler Preschool and Primary scale of Intelligence (WIPPSI-III). The study was registered with clinicaltrials.gov (NCT05371262).

RESULTS

Treatment schemes below or above 12.5 μg/kg/day were both associated with rapid normalization of TSH and thyroid hormone levels in most patients with no differences in the risk of over- and under-treatment episodes in the first months of life. Growth parameters were normal and comparable between the two groups. Developmental quotients at 24 months of age were normal in both groups (Low 100.6 ± 15.5 vs High 96.9 ± 16.6). Likewise, at 4 years of age IQ and subtest scores were comparable between patients from Low and High (Total IQ 104.2 ± 11.4 vs 101.0 ± 20.3, Verbal IQ 103.9 ± 11.5 vs 98.7 ± 15.1, Performance IQ 105.3 ± 10.4 vs 100.3 ± 19.8). 6/45 CH patients (13.3%) showed a total IQ below 85 (73.7 ± 5.9) regardless of age at diagnosis, L-T4 starting dose, time of FT4 and TSH normalization and episodes of over and undertreatment. Worse socioeconomic status and delayed bone age at diagnosis were the only predictors of an increased risk of having suboptimal IQ at 24 and IQ at 48 months.

CONCLUSIONS

Our results indicate that initial treatment with L-T4, 10-12.5 μg/kg/day vs 12.6-15 μg/kg/day, are both associated with normal growth and neurodevelopmental outcomes in children with CH detected by neonatal screening. Further studies with a long-term follow-up on a larger number of patients are needed to confirm these results.

CLINICAL TRIAL REGISTRATION

https://clinicaltrials.gov/ct2/show/NCT05371262?term=NCT05371262&draw=2&rank=1 identifer NCT05371262.

Cognitive Function in Children With Idiopathic Subclinical Hypothyroidism: Effects of 2 Years of Levothyroxine Therapy

BACKGROUND

Long-term consequences of mild subclinical hypothyroidism (SH) in children are still unclear, and the need for levothyroxine (L-T4) supplementation remains controversial. We designed a 2-year, case-control, prospective study of a cohort of children with SH to evaluate the effects of L-T4 therapy on neurocognitive outcome.

METHODS

Thirty-four children, age 9.1 ± 2.6 years, with long-lasting, idiopathic, and mild SH, and 34 healthy matched controls, were enrolled. Twenty SH children underwent a 2-year L-T4 treatment (group A), whereas 14 refused treatment and were reevaluated after a 2-year-follow-up (group B). IQ and specific cognitive domains were evaluated in all children at study entry and after 2 years of therapy (group A) or observation (group B) in SH individuals.

RESULTS

In SH children baseline IQ scores were normal and comparable to controls (full-scale IQ [FSIQ] 100.4 ± 11.3 vs 101.8 ± 14.2, verbal IQ [VIQ] 99.7 ± 13.7 vs 98.3 ± 14.9 and performance IQ [PIQ] 101.2 ± 10.4 vs 105 ± 10.4).In group A, L-T4 treatment was associated with normalization of thyrotropin (6.3 ± 1.0 mIU/L at baseline vs 2.8 ± 1.4 mIU/L at 2 years, P < .001). However, 2-year L-T4 therapy was not associated with a change in IQ scores (FSIQ 104.4 ± 13.8 vs 102.7 ± 11.0; VIQ 101.8 ± 14.9 vs 102.3 ± 11.9; and PIQ 106.5 ± 13.9 vs 102.7 ± 10.7) or in verbal or performance subtest scores. No significant differences were found in IQ scores after 2 years of treatment in group A compared to group B after a 2-year follow-up.

CONCLUSIONS

Our data suggest neurocognitive function in children is not impaired by persistent, mild, untreated SH and is not significantly modified by 2-year L-T4 supplementation.

Linear growth and intellectual outcome in children with long-term idiopathic subclinical hypothyroidism

OBJECTIVE

The treatment of children with subclinical hypothyroidism (SH) is controversial for TSH values between 4.5 and 10 mU/l. The aim of this cross-sectional, controlled study was to evaluate growth and intellectual outcome in children with persistent SH who have never been treated with levothyroxine.

DESIGN AND METHODS

Clinical and auxological parameters, thyroid function, and intellectual outcome were evaluated in 36 children with persistent SH at the age of 9.7±0.6 (range 4-18.0) years. Children had been followed longitudinally for 3.3±0.3 (range 2.0-9.3) years, from first diagnosis of SH until enrollment in the study. Thirty-six age- and sex-matched children were enrolled in the study as controls.

RESULTS

At study entry, height (-0.8±0.2 SDS), bone age/chronological age (BA/CA ratio 0.92±0.6), and body mass index (BMI -0.1±0.2 SDS) in SH children were normal. Despite long-term duration of SH, none of these parameters showed a worsening with respect to height (-0.7±0.2 SDS), BA/CA (0.97±0.03), and BMI (-0.1±0.2) at the time of first SH detection. None of the children showed overt signs or symptoms of hypothyroidism during the follow-up. Verbal (99.1±2.2), performance (100.4±1.9), and full-scale (99.7±1.9) intelligence quotient (IQ) scores in SH children were normal and comparable to those of controls. No relationship was detected between IQ scores and the degree or duration of SH.

CONCLUSIONS

Persistent SH in children is not associated with alterations in growth, bone maturation, BMI, and cognitive function or other complaints that could be ascribed to SH even after several years without therapeutic intervention.

[Neurobehavioural testing in lead smelter workers]

Several recent meta-analyses, although some inconsistencies between studies, provide evidence for subtle deficits in neurobehavioural tests being associated with average blood levels (PbB) between 350 and 600 microg/l and for significant correlations between impairments in some test results and increasing indices present andlor cumulative exposure to inorganic lead. In this study we assessed the relationship between blood lead level (PbB) and results of some neurobehavioural tests derived from the SPES battery and from the WAIS-R among a sample of 94 lead smelter workers (median PbB: 302 microg/l; range: 60-690 microg/l). The stepwise multiple regression analysis shows that, even after adjusting for age, education level, score in the vocabulary test and for alcohol and cigarette consumption, the rise of PbB above 300 microg/l was significantly associated with the rise in the number of errors and in the response time of the Symbol Digit test. No significant relationship between PbB and results of the other tests was observed after adjusting for the main confounding factors. Despite the small size of this study and the few number of neurobehavioural tests applied, our results are suggestive for suble potential neurotoxic effects of inorganic lead even at the present exposure levels found in the studied sample of smelter workers and support the ACGIH BEI and the SCOEL recommendation for a biological limit of 300 microg/l of PbB.

[Study on mortality by specific cause among workers at a lead and zinc foundry in Sardinia]

The mortality of 918 Sardinian lead-smelter workers followed between 1972 and 2001 is reported. The assessment of individual exposure to inorganic lead was based on several environmental and blood lead measurements available, for each department and task, between 1985 and 2001. The mortality for all cancers was within the expected numbers (SMR 1.01, n 108). Even if not statistically significant, the mortality for gastric cancer (SMR 1.22, n 4), for lung cancer (SMR 1.21, n 18) and for lymphomas and leukaemias (SMR 1.82, n 6) was higher than that expected from the regional rates during the follow-up. Only for the lung cancer mortality a statistically significant upward trend with increasing categories of lead exposure was observed (SMR 1.96, 95% CI 1.02-3.68 for the highest exposure group). Our study, even if of small size, suggests an association between occupational exposure to inorganic lead and lung cancer risk.

[Mortality from lung cancer among workers of a Sardinian lead smelter [Follow-up: 1972-2001]]

The mortality of 918 Sardinian lead-smelter workers followed between 1972 and 2001 is reported. The assessment of individual exposure to inorganic lead was based on several environmental and blood lead measurements available, for each department and task, between 1985 and 2001. The mortality for all cancers was within the expected numbers (SMR 1.01, n 108). Even if not statistically significant, the mortality for gastric cancer (SMR 1.22, n 4), for lung cancer (SMR 1.21, n 18) and for lymphomas and leukaemias (SMR 1.82, n 6) was higher than that expected from the regional rates during the follow-up. Only for the lung cancer mortality a statistically significant upward trend with increasing categories of lead exposure was observed (SMR 1.96, 95% CI 1.02-3.68 for the highest exposure group). Our study, even if of small size, suggests an association between occupational exposure to inorganic lead and lung cancer risk.