Sophie C. Huijskens

Quantification of renal and diaphragmatic interfractional motion in pediatric image-guided radiation therapy: A multicenter study

BACKGROUND AND PURPOSE To quantify renal and diaphragmatic interfractional motion in order to estimate systematic and random errors, and to investigate the correlation between interfractional motion and patient-specific factors. MATERIAL AND METHODS We used 527 retrospective abdominal-thoracic cone beam CT scans of 39 childhood cancer patients (<18 years) to quantify renal motion relative to bony anatomy in the left-right (LR), cranio-caudal (CC) and anterior-posterior (AP) directions, and diaphragmatic motion in the CC direction only. Interfractional motion was quantified by distributions of systematic and random errors in each direction (standard deviations Σ and σ, respectively). Also, correlation between organ motion and height was analyzed. RESULTS Inter-patient organ motion varied widely, with the largest movements in the CC direction. Values of Σ in LR, CC, and AP directions were 1.1, 3.8, 2.1 mm for the right, and 1.3, 3.0, 1.5 mm for the left kidney, respectively. The σ in these three directions was 1.1, 3.1, 1.7 mm for the right, and 1.2, 2.9, 2.1 mm for the left kidney, respectively. For the diaphragm we estimated Σ=5.2 mm and σ=4.0 mm. No correlations were found between organ motion and height. CONCLUSIONS The large inter-patient organ motion variations and the lack of correlation between motion and patient-related factors, suggest that individualized margin approaches might be required.

Magnitude and variability of respiratory-induced diaphragm motion in children during image-guided radiotherapy

BACKGROUND AND PURPOSE To analyse the variability of respiratory motion during image-guided radiotherapy in paediatric cancer patients and to investigate possible relationships thereof with patient-specific factors. MATERIAL AND METHODS Respiratory-induced diaphragm motion was retrospectively analysed on 480 cone beam CTs acquired during the treatment course of 45 children (<18years). The cranial-caudal positions of the top of the right diaphragm in exhale and inhale phases were manually selected in the projection images. The difference in position between both phases defines the amplitude. The cycle time equalled inspiratory plus expiratory time. We analysed the variability of the intra- and interfractional respiratory motion and studied possible correlations between respiratory-induced diaphragm motion and age, height, and weight. RESULTS Over all patients, mean amplitude and cycle time were 10.7mm (range 4.1-17.4mm) and 2.9s (range 2.1-3.9s). Intrafractional variability was larger than interfractional variability (2.4mmvs. 1.4mm and 0.5svs. 0.4s for amplitude and cycle time, respectively). Correlations between mean amplitude and patient-specific factors were significant but weak (p<0.05, ρ≤0.45). CONCLUSIONS Large ranges of amplitude and cycle time and weak correlations confirm that respiratory motion is patient-specific and requires an individualized approach to account for. Since interfractional variability was small, we suggest that a pre-treatment 4DCT in children could be sufficiently predictive to quantify the respiratory motion.

Interfractional renal and diaphragmatic position variation during radiotherapy in children and adults: is there a difference?

Abstract Background: Pediatric safety margins are generally based on data from adult studies; however, adult-based margins might be too large for children. The aim of this study was to quantify and compare interfractional organ position variation in children and adults. Material and methods: For 35 children and 35 adults treated with thoracic/abdominal irradiation, 850 (range 5–30 per patient) retrospectively collected cone beam CT images were registered to the reference CT that was used for radiation treatment planning purposes. Renal position variation was assessed in three orthogonal directions and summarized as 3D vector lengths. Diaphragmatic position variation was assessed in the cranio-caudal (CC) direction only. We calculated means and SDs to estimate group systematic (Σ) and random errors (σ) of organ position variation. Finally, we investigated possible correlations between organ position variation and patients’ height. Results: Interfractional organ position variation was different in children and adults. Median 3D right and left kidney vector lengths were significantly smaller in children than in adults (2.8, 2.9 mm vs. 5.6, 5.2 mm, respectively; p < .05). Generally, the pediatric Σ and σ were significantly smaller than in adults (p < .007). Overall and within both subgroups, organ position variation and patients’ height were only negligibly correlated. Conclusions: Interfractional renal and diaphragmatic position variation in children is smaller than in adults indicating that pediatric margins should be defined differently from adult margins. Underlying mechanisms and other components of geometrical uncertainties need further investigation to explain differences and to appropriately define pediatric safety margins.

OC-0161: Renal and diaphragmatic interfractional motion in children and adults: is there a difference?

Conclusion: Within the limitations of a retrospective study, our results show that the growth and shift of brain metastasis over time can be significant and may vary over patient groups. Given the typical steep dose gradient in SRS treatments (>10%/mm), tumour growths and shifts may have a significant impact on the tumour dose. Therefore, this phenomenon must be considered if the workup and treatment of SRS for brain metastasis is encompassing multiple days.

Heart volume reduction during radiotherapy involving the thoracic region in children: An unexplained phenomenon

BACKGROUND AND PURPOSE Radiotherapy involving the thoracic region is associated with cardiotoxicity in long-term childhood cancer survivors. We quantified heart volume changes during radiotherapy in children (<18 years) and investigated correlations with patient and treatment related characteristics. MATERIAL AND METHODS Between 2010 and 2016, 34 children received radiotherapy involving the thoracic region. We delineated heart contours and measured heart volumes on 114 CBCTs. Relative volume changes were quantified with respect to the volume on the first CBCT (i.e., 100%). Cardiac radiation dose parameters expressed as 2 Gy/fraction equivalent doses were calculated from DVHs. Chemotherapy was categorized as treatment with anthracyclines, alkylating agents, vinca-alkaloids, and other. RESULTS The overall median heart volume reduction from the first to the last CBCT was 5.5% (interquartile range1.6-9.7%; p < 0.001). Heart volumes decreased significantly between the baseline measurement and the first week (Bonferronis adjusted p = 0.002); volume changes were not significant during the following weeks. Univariate analysis showed a significant correlation between heart volume reduction and alkylating agents; however, no multivariate analyses could be done to further confirm this. CONCLUSIONS We found a significant heart volume reduction in children during radiotherapy. Elucidation of underlying mechanisms, clinical relevance, and possible long-term consequences of early heart volume reduction require a prospective follow-up study.