Integration of the M6 Cyberknife in the Moderato Monte Carlo platform and prediction of beam parameters using machine learning

PURPOSE

This work describes the integration of the M6 Cyberknife in the Moderato Monte Carlo platform, and introduces a machine learning method to accelerate the modelling of a linac.

METHODS

The MLC-equipped M6 Cyberknife was modelled and integrated in Moderato, our in-house platform offering independent verification of radiotherapy dose distributions. The model was validated by comparing TPS dose distributions with Moderato and by film measurements. Using this model, a machine learning algorithm was trained to find electron beam parameters for other M6 devices, by simulating dose curves with varying spot size and energy. The algorithm was optimized using cross-validation and tested with measurements from other institutions equipped with a M6 Cyberknife.

RESULTS

Optimal agreement in the Monte Carlo model was reached for a monoenergetic electron beam of 6.75 MeV with Gaussian spatial distribution of 2.4 mm FWHM. Clinical plan dose distributions from Moderato agreed within 2% with the TPS, and film measurements confirmed the accuracy of the model. Cross-validation of the prediction algorithm produced mean absolute errors of 0.1 MeV and 0.3 mm for beam energy and spot size respectively. Prediction-based simulated dose curves for other centres agreed within 3% with measurements, except for one device where differences up to 6% were detected.

CONCLUSIONS

The M6 Cyberknife was integrated in Moderato and validated through dose re-calculations and film measurements. The prediction algorithm was successfully applied to obtain electron beam parameters for other M6 devices. This method would prove useful to speed up modelling of new machines in Monte Carlo systems.

Growth Failure in Children with Systemic Juvenile Idiopathic Arthritis and Prolonged Inflammation despite Treatment with Biologicals: Late Normalization of Height by Combined Hormonal Therapies

BACKGROUND

Biologicals targeting the interleukin (IL)-1β or IL-6 pathway are becoming prime choices for the treatment of children with systemic juvenile idiopathic arthritis (sJIA). Up to 1 in 3 sJIA children receiving such treatment continues to have inflammatory activity and to require supra-physiological glucocorticoid doses which may reduce growth velocity for years and may lead to an extremely short stature for age, if not for life. Currently, there is no long-term proposal to normalize the adult height of these children with sJIA.

METHODS AND RESULTS

We present long-term (up to 10 years), proof-of-concept evidence that the adult stature and adipose body composition of short sJIA children can be normalized with a hormonal combination strategy: (i) pubertal onset is postponed with a gonadotropin-releasing hormone analog (triptorelin) until a minimum height is reached, or until prepubertal growth is exhausted, and (ii) height gain is promoted with growth hormone (≈50 μg/kg/day), once inflammation is under control and high glucocorticoid doses are no longer needed. The latter treatment takes advantage of the window of relative glucocorticoid deficiency, which is known to open after prolonged glucocorticoid administration, and to be uniquely favorable to height gain.

CONCLUSION

A long-term combination of biological and hormonal treatments for short sJIA children can be guided by a simple concept that involves (i) postponement of pubertal development and (ii) growth-promoting therapy after the episodes of major inflammation and high-dose glucocorticoid treatment. Limited long-term experience in short sJIA children suggests that this strategy leads consistently - albeit late - to a normal adult stature.

Evolution of body mass index in children with type 1 diabetes mellitus

The prevalence of childhood overweight and obesity has risen during the last 30 years, not only in children with type 2 diabetes, but also those with type 1 (T1D) and this is linked with an increased cardiovascular risk. A better understanding of weight patterns in the years after diagnosis of T1D is important to identify those children with a risk for excess weight gain and strategies to decrease this. We retrospectively analyzed data of all children with T1D followed at the department of Pediatric Endocrinology Leuven and diagnosed between 1991 and 2015. Data as age, sex, BMI, and Tanner score were extracted in 390 subjects. Standardized BMI (BMI SDS) in this study group using all data was 0.26. An increase in BMI SDS was seen as a function of time since diagnosis and age, both being independent predictors. Data comparison showed a significant stronger relation between BMI SDS and both time since diagnosis and age in girls. Children diagnosed after puberty showed a higher increase in BMI SDS.Conclusion: These longitudinal data suggest an important increase in BMI in children with T1D, both as a function of time since diagnosis and age, especially in girls. What is Known: • The prevalence of childhood overweight and obesity is risen during the last 30 years, in children with type 2 diabetes, but also those with type 1 diabetes. What is New: • Our study demonstrates with longitudinal data an increase in BMI in children with type 1 diabetes, especially girls. The increase in BMI SDS is seen as a function of time since diagnosis and age, both being independent predictors. Given the increased risk of metabolic syndrome and other complications in overweight children, special attention is needed to prevent this evolution.

Adult Height after Growth Hormone Treatment at Pubertal Onset in Short Adolescents Born Small for Gestational Age: Results from a Belgian Registry-Based Study

OBJECTIVES

Information on the efficacy of GH treatment in short SGA children starting their treatment in adolescence is limited. Therefore, adult height (AH), total height gain, and pubertal height gain were evaluated in short SGA children who started GH treatment at pubertal onset.

PATIENT AND METHODS

Growth data of 47 short SGA adolescents (22 boys) who started GH treatment at pubertal onset (PUB group) were compared with results from 27 short SGA patients (11 boys) who started GH therapy at least 1 year before pubertal onset (PrePUB group).

RESULTS

The PUB group achieved a mean (±SD) total height gain of 0.8 ± 0.7 SDS and an AH of -2.5 ± 0.7 SDS after 4.1 ± 1.1 years of GH treatment with a dosage of 41.8 ± 8.4 μg/kg/day. These results were comparable with those in the PrePUB group, which was treated for a longer duration (5.8 ± 2.1 years), resulting in a total height gain of 1.1 ± 0.7 SDS and an AH of -2.1 ± 1.0 SDS. Multiple regression analysis showed a significantly lower height gain in pubertal patients, females, and patients weighing less at start of GH treatment. An AH above -2 SDS and above the parent-specific lower limit of height was, respectively, reached in 28% and 70% of PUB and 44% and 67% of PrePUB patients (NS). AH SDS was positively correlated with the height SDS at start of GH.

CONCLUSIONS

Short SGA adolescents starting GH therapy at an early pubertal stage have a modest and variable height gain. A normal AH can be expected in one third of the patients, especially in those with a smaller height deficit at onset of GH treatment.

Use of an in-house Monte Carlo platform to assess the clinical impact of algorithm-related dose differences on DVH constraints

PURPOSE

The aim of the present work is to evaluate a semi-automatic prescription and validation system of treatment plans for complex delivery techniques, integrated in a Monte Carlo platform, and to investigate the clinical impact of dose differences due to the calculation algorithms, by assessing the changes in DVH constraints.

METHODS

A new prescription module was implemented into the Moderato system, an in-house Monte Carlo platform, with corresponding dose constraints generated depending on the anatomical region and fractionation scheme considered. The platform was tested on 83 cases treated with Cyberknife and Tomotherapy machines, to assess whether dose variations between the re-calculated dose and the Treatment Planning System might impact the dose constraints on the sensitive structures.

RESULTS

Dose differences were small (within 3%) between calculation algorithms in most of the thoracic, pelvic and abdominal cases, both for the Cyberknife and Tomotherapy machines. On the other hand, spinal and head and neck treatments presented a few significant dose deviations for constraints on small volumes, such as the optic pathways and the spinal cord. These differences range from -11% to +6%, inducing constraint violations of up to 8% over the dose limit.

CONCLUSIONS

The Moderato platform offers an interesting tool for plan quality validation, with a prescription module highlighting crucial features in the structures list, and a Monte Carlo dose re-calculation for complex modern techniques. Due to the high number of warnings appearing in some situations, display optimization is required in practice.

Expanding the CHARGE Geno-Phenotype: A Girl with Novel CHD7 Deletion, Hypogonadotropic Hypogonadism, and Agenesis of Uterus and Ovaries

BACKGROUND

CHARGE syndrome is a variable entity. Clinical diagnosis is based on the Blake-Verloes criteria and can be confirmed by identifying a mutation or deletion in the CHD7 gene. Hypoplasia of the male genitalia and lack or incomplete secondary sexual development in both sexes is a common feature, and is most often attributable to hypogonadotropic hypogonadism which is described in >80% of the CHARGE patients. Other genital anomalies in CHARGE patients are rare.

METHODS AND RESULTS

We describe the case of a girl with a novel heterozygous deletion in exon 15 of the CHD7 gene and combined agenesis of uterus and ovaries, besides gonadotropin deficiency, thus expanding the geno-phenotype of CHARGE syndrome.

CONCLUSION

In case of persistent primary amenorrhea, despite estrogen replacement, this unusual combination should be considered in girls with CHARGE syndrome.

Short Stature in KBG Syndrome: First Responses to Growth Hormone Treatment

BACKGROUND

KBG syndrome is a rare disorder characterized by intellectual disability and associated with macrodontia of the upper central incisors, specific craniofacial findings, short stature and skeletal anomalies. Genetic corroboration of a clinical diagnosis has been possible since 2011, upon identification of heterozygous mutations in or a deletion of the ANKRD11 gene.

METHODS

We summarized the height data of 14 adults and 18 children (age range 2-16 years) with a genetically confirmed diagnosis of KBG syndrome. Two of these children were treated with growth hormones.

RESULTS

Stature below the 3rd centile or -1.88 standard deviation score (SDS) was observed in 72% of KBG children and in 57% of KBG adults. Height below -2.50 SDS was observed in 62% of KBG children and in 36% of KBG adults. The mean SDS of height in KBG children was -2.56 and in KBG adults -2.17. Two KBG children on growth hormone therapy increased their height by 0.6 and 1 SDS within 1 year, respectively. The former also received a gonadotropin-releasing hormone agonist due to medical necessity.

CONCLUSION

Short stature is prevalent in KBG syndrome, and spontaneous catch-up growth beyond childhood appears limited. Growth hormone intervention in short KBG children is perceived as promising.