In previous works, we showed that incorporating individual airways as organs-at-risk (OARs) in the treatment of lung stereotactic ablative radiotherapy (SAbR) patients potentially mitigates post-SAbR ...radiation injury. However, the performance of common clinical dose calculation algorithms in airways has not been thoroughly studied. Airways are of particular concern because their small size and the density differences they create have the potential to hinder dose calculation accuracy. To address this gap in knowledge, here we investigate dosimetric accuracy in airways of two commonly used dose calculation algorithms, the anisotropic analytical algorithm (AAA) and Acuros-XB (AXB), recreating clinical treatment plans on a cohort of four SAbR patients. A virtual bronchoscopy software was used to delineate 856 airways on a high-resolution breath-hold CT (BHCT) image acquired for each patient. The planning target volumes (PTVs) and standard thoracic OARs were contoured on an average CT (AVG) image over the breathing cycle. Conformal and intensity-modulated radiation therapy plans were recreated on the BHCT image and on the AVG image, for a total of four plan types per patient. Dose calculations were performed using AAA and AXB, and the differences in maximum and mean dose in each structure were calculated. The median differences in maximum dose among all airways were ≤0.3Gy in magnitude for all four plan types. With airways grouped by dose-to-structure or diameter, median dose differences were still ≤0.5Gy in magnitude, with no clear dependence on airway size. These results, along with our previous airway radiosensitivity works, suggest that dose differences between AAA and AXB correspond to an airway collapse variation ≤0.7% in magnitude. This variation in airway injury risk can be considered as not clinically relevant, and the use of either AAA or AXB is therefore appropriate when including patient airways as individual OARs so as to reduce risk of radiation-induced lung toxicity.
Background: As screening central nervous system (CNS) imaging is not routinely performed, the incidence and clinical relevance of occult CNS metastases in advanced breast cancer is unknown. Patients ...and methods: All patients screened for participation in one of four clinical trials were included; each of the trials excluded patients with known CNS involvement and required screening CNS imaging. A cohort of breast cancer patients with symptomatic CNS metastases was identified from the IU Cancer Center Tumor Registry for comparison. Results: From November 1998 to August 2001, 155 screening imaging studies were performed. Twenty-three patients (14.8%) had occult CNS metastases. HER-2 overexpression (P = 0.02) and number of metastatic sites (P = 0.03) were predictive of CNS involvement by multivariate analysis. Median survival from time of metastasis (1.78 versus 2.76 years; P <0.0001) and from screening (4.67 versus 10.4 months; P = 0.0013) was shorter in patients with than without occult CNS metastasis. Survival among patients with occult CNS metastasis was similar to patients with symptomatic CNS disease. Conclusions: Patients with CNS involvement, whether occult or symptomatic, have an impaired survival. Occult CNS metastasis is relatively common, but impact on survival of treating occult CNS disease in patients with progressive systemic metastases is questionable.
Purpose: To evaluate the use of the CyberKnife delivery platform and Multiplan treatment planning system (TPS) to achieve acceptable target coverage and normal tissue sparing for dose escalation when ...treating the involved hemi‐larynx and at risk paraglottic space for early‐stage laryngeal cancer. Methods: Specialized anthropomorphic phantoms containing a hollow larynx were constructed based upon patient CT images with earlystage glottic cancer. Contours of the hemi‐larynx clinical target volume (CTV) as well as the thyroid gland, arytenoids, contralateral vocal cord, and anterior commissure were created in the Multiplan TPS. Treatment plans were created using the ray‐tracing algorithm and were re‐calculated using the Monte Carlo algorithm. Radiochromic EBT2 film was sandwiched in the phantom at the level of the vocal cords to determine the dose delivered to the target and critical structures. Phantoms were irradiated with multiple fractionation schemes including 50 Gy in 15 fractions, 45 Gy in 10 fractions, and 42.5 Gy in 5 fractions using 6 MV photons. Film dose distributions were compared with that predicted by the TPS. Results: For plans generated using the Monte Carlo algorithm, greater than 95% PTV coverage by the prescription dose was achieved with conformality indices ranging from 1.4 to 1.5. Mean dose to the contralateral vocal cord and arytenoids was less than 40% and 25% of the prescription dose, respectively. A gamma passing rate of 90% was seen using a 3%/3mm criteria when comparing the Monte Carlo algorithm with film, while a 79% passing rate was seen when comparing the ray‐tracing algorithm with film. Conclusion: Adequate dose delivery with significant sparing of uninvolved normal tissue is feasible and practical with CyberKnife radiotherapy when using the Monte Carlo dose calculation algorithm. This technique has the potential to allow hypofractionation for the purpose of improving local control, voice quality outcome, and patient convenience.
Purpose: To determine the optimal prescription isodose line that minimizes normal tissue irradiation for stereotactic radiation therapy comparing conventional linear accelerator and robotic delivery. ...Methods: A computer based digital torso phantom which has the capability to simulate respiratory and cardiac motion were used in this study. Spherical targets were constructed in lung and liver, with diameter of 20mm, 30mm, and 40mm. Two concentric 5mm shells, from the target surface extending 5mm radially and from 5mm to 10mm, were identified/contoured. Non‐coplanar, non‐ opposing 3D conformal beams were designed for linac planning. Variable prescription isodose lines were achieved by varying the block margin. 4D dose calculation was used for moving target and surrounding tissue. After linac planning, the CT images and contours were transferred for Cyberknife® planning. Variable prescription isodose lines were achieved by inverse planning technique. Doses of 60Gy in 3 fractions were prescribed to cover exactly 95% of target tumor with each technology. gEUD (generalized effective uniform dose) with different formulations for parallel and serial tissues was used for comparison between different plans. Results: For linac plans, the optimal prescription isodose line yielding maximum normal tissue sparing occurs between 50% and 70% for the lung tumor and 60% and 90% for liver tumor. The gEUD difference between plans with optimum and arbitrarily chosen prescription isodose line may be up to 20% of prescription dose. For Cyberknife plans, the optimal prescription isodose line is approximately 50% for tissues displaying either parallel or serial behavior. These results are similar for different tumor sizes. Conclusions: Both conventional linac and Cyberknife® delivery can provide conformal tumor coverage with normal tissue sparing. By carefully choosing the optimal prescription isodose line, the gEUD of the surrounding normal tissue can be reduced by up to 20% of prescription dose.
Background
The utilization of three-dimensional printing has grown rapidly within the field of surgery over recent years. Within the subspecialty of colorectal surgery, the technology has been used ...to create personalized anatomical models for preoperative planning, models for surgical training, and occasionally customized implantable devices and surgical instruments. We aim to provide a systematic review of the current literature discussing clinical applications of three-dimensional printing in colorectal surgery.
Methods
Full-text studies published in English which described the application of 3D printing in pre-surgical planning, advanced surgical planning, and patient education within the field of colorectal surgery were included. Exclusion criteria were duplicate articles, review papers, studies exclusively dealing with surgical training and/or education, studies which used only virtual models, and studies which described colorectal cancer only as it pertained to other organs.
Results
Eighteen studies were included in this review. There were two randomized controlled trials, one retrospective outcomes study, five case reports/series, one animal model, and nine technical notes/feasibility studies. There were three studies on advanced surgical planning/device manufacturing, six on pre-surgical planning, two on pelvic anatomy modeling, eight on various types of anatomy modeling, and one on patient education.
Conclusions
While more studies with a higher level of evidence are needed, the findings of this review suggest many promising applications of three-dimensional printing within the field of colorectal surgery with the potential to improve patient outcomes and experiences.
Kitaev's toric code Hamiltonian in dimension D=2 has been extensively studied for its topological properties, including its quantum error correction capabilities.
While the Hamiltonian is quantum, it ...lies within the class of models that admits a D+1-dimensional classical representation.
In these notes, we provide details of a Suzuki-Trotter expansion of the partition function of the toric code Hamiltonian in the presence of
an external magnetic field.
By coupling additional degrees of freedom in the form of a matter field that can subsequently be gauged away,
we explicitly derive a classical Hamiltonian on a cubic lattice which takes the form of a non-isotropic
3D Ising gauge theory.
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