Adaptive Proton Therapy of Pediatric Head and Neck Cases Using MRI-Based Synthetic CTs: Initial Experience of the Prospective KiAPT Study.

BACKGROUND AND PURPOSE: Interfractional anatomical changes might affect the outcome of proton therapy (PT). We aimed to prospectively evaluate the role of Magnetic Resonance Imaging (MRI) based adaptive PT for children with tumors of the head and neck and base of skull. METHODS: MRI verification images were acquired at half of the treatment course. A synthetic computed tomography (CT) image was created using this MRI and a deformable image registration (DIR) to the reference MRI. The methodology was verified with in-silico phantoms and validated using a clinical case with a shrinking cystic hygroma on the basis of dosimetric quantities of contoured structures. The dose distributions on the verification X-ray CT and on the synthetic CT were compared with a gamma-index test using global 2 mm/2% criteria. RESULTS: Regarding the clinical validation case, the gamma-index pass rate was 98.3%. Eleven patients were included in the clinical study. The most common diagnosis was rhabdomyosarcoma (73%). Craniofacial tumor site was predominant in 64% of patients, followed by base of skull (18%). For one individual case the synthetic CT showed an increase in the median D2 and Dmax dose on the spinal cord from 20.5 GyRBE to 24.8 GyRBE and 14.7 GyRBE to 25.1 GyRBE, respectively. Otherwise, doses received by OARs remained relatively stable. Similarly, the target volume coverage seen by D95% and V95% remained unchanged. CONCLUSIONS: The method of transferring anatomical changes from MRIs to a synthetic CTs was successfully implemented and validated with simple, commonly available tools. In the frame of our early results on a small cohort, no clinical relevant deterioration for neither PTV coverage nor an increased dose burden to OARs occurred. However, the study will be continued to identify a pediatric patient cohort, which benefits from adaptive treatment planning.

On a phase-field approach to model fracture of small intestine walls.

We address anisotropic elasticity and fracture in small intestine walls (SIWs) with both experimental and computational methods. Uniaxial tension experiments are performed on porcine SIW samples with varying alignments and quantify their nonlinear elastic anisotropic behavior. Fracture experiments on notched SIW strips reveal a high sensitivity of the crack propagation direction and the failure stress on the tissue orientation. From a modeling point of view, the observed anisotropic elastic response is studied with a continuum mechanical model stemming from a strain energy density with a neo-Hookean component and an anisotropic component with four families of fibers. Fracture is addressed with the phase-field approach, featuring two-fold anisotropy in the fracture toughness. Elastic and fracture model parameters are calibrated based on the experimental data, using the maximum and minimum limits of the experimental stress-stretch data set. A very good agreement between experimental data and computational results is obtained, the role of anisotropy being effectively captured by the proposed model in both the elastic and the fracture behavior. STATEMENT OF SIGNIFICANCE: This article reports a comprehensive experimental data set on the mechanical failure behavior of small intestinal tissue, and presents the corresponding protocols for preparing and testing the samples. On the one hand, the results of this study contribute to the understanding of small intestine mechanics and thus to understanding of load transfer mechanisms inside the tissue. On the other hand, these results are used as input for a phase-field modelling approach, presented in this article. The presented model can reproduce the mechanical failure behavior of the small intestine in an excellent way and is thus a promising tool for the future mechanical description of diseased small intestinal tissue.

Trismus in head and neck cancer patients treated by telecobalt and effect of early rehabilitation measures.

CONTEXT: Trismus is one of the common late side effects of radiotherapy (RT) of head and neck cancers. It occurs in about 30% of patients treated by telecobalt. It, in turn, leads to significant morbidity, including malnutrition, difficulty in speaking, and compromised oral hygiene with severe psychosocial, and economic impacts. AIMS: To determine the prevalence of trismus and its progression in patients who have received radical concurrent chemoradiation for head and neck cancer by telecobalt at our institution. To note the effect of early rehabilitative measures on the severity of trismus and to assess its impact on the quality of life (QOL). SUBJECTS AND METHODS: A total of 47 evaluable patients of head and neck cancer patients treated by telecobalt with radical intent between January 2012 and December 2013 were analyzed and baseline maximal inter-incisal opening (MIO) and MIO at the completion of RT, after 3 months, 6 months, and 1 year, after completion of RT were noted. Grading of trismus was done using Modified Common Toxicity Criteria (CTCAE Version 3.0). QOL assessment was done using European Organization for Research and Treatment of Cancer QLQ-HN35. The time when the rehabilitative measures were started were also noted. STATISTICAL ANALYSIS USED: Chi-square test with Fisher exact probability test and Students t-test. RESULTS: Radiation-induced trismus (RIT) was seen in 31.9%, 34.04%, and 38.39% of cases at 3, 6, and 12 months after completion of RT. Grade II and III trismus accounted for 17.02% and 6.38% at the end of 1 year. Patients who started regular rehabilitative exercises soon, after completion of RT had a better mean MIO as compared to those who were not compliant (32 mm vs. 24 mm at 1 year), and there was a trend toward delayed progression in them. Trismus was also seen to adversely affect QOL of the patients. CONCLUSIONS: RIT is a major cause for late morbidity in patients treated with conventional RT leading to poor QOL. Early rehabilitative measures are useful in preventing progression of trismus.