It has been clinically observed that log-file derived leaf positions can differ from their actual position by >1 mm, and therefore cannot be considered to be the actual leaf positions. This cautions the use of log-based methods for MLC or patient quality assurance without independent confirmation of log integrity. Frequent verification of MLC positions through independent means is a necessary precondition to trust log-file records. Intratreatment EPID imaging provides a method to capture departures from MLC planned positions.

The authors have successfully demonstrated that motion tracking of fiducial markers and the subsequent 4D reconstruction of CBCT and DTS are possible. Due to the significant reduction in motion-induced image blur, it is anticipated that such technology will be useful in image-guided liver SBRT treatments.

Purpose: To build, from grounds up, a novel dynamic modulated brachytherapy (DMBT) system for treating intracavitary tumors, such as rectal, breast, and vaginal cancers. The key component of the innovation is in enabling “dynamic” modulation (i.e., Ir‐192 source is highly collimated and dynamically moved during delivery) to create an unparalleled dose conformality compared with the currently available commercial systems/applicators. We show that our proposed prototype system (both soft‐ and hard‐ware) is extremely efficient in maximizing target volume coverage while minimizing dose to healthy tissues. Methods: Our system uses a 1.9‐cm diameter tungsten‐shield, with density of 18.5g/cc, to create a highly collimated Ir‐192 source radiation profiles. Various window openings in the shield have been simulated with the MCNP code for planning. The code itself was validated against TG43 parameters. The shield is controlled by an in‐house built, computer‐controlled, robotic arm which allows for 360° rotations and 1‐D translational motions. An in‐house coded planning system with the simulated annealing algorithm was used to design optimal plans on ideal rectal anatomies and patient cases. The optimal DMBT plans were then compared with the state‐of‐the‐art commercial Intracavitary Mold Applicator (ICMA)‐based plans. Results: The various simulations encompassing target sizes up to 5‐cm longitudinal and radial directions, with circumferential volumes from 45‐degree to 360‐degree were simulated. Results consistently show that the DMBT system yields broader shoulder past prescription dose in target DVH initially and drops off quicker at higher doses, compared with ICMA, which reflects better dose conformality. More spectacularly, however, up to 50% decrease in normal tissue dose across all dose range were observed. This will translate into clinically observable reduction in acute/late toxicities. Conclusions: Our preliminary results show that DMBT offers exceptional degrees of dynamics for achieving unparalleled dose conformality in brachytherapy. Further research is needed to validate our work in various clinical sites.

Understanding and mitigating against high heat loads at leading and blunt aerodynamic surfaces during hypersonic flight represents an ongoing technological challenge. Recent work has shown that the commercial software package, STAR CCM+, can provide reliable predictions of hypersonic aerothermodynamic flow and heating, under a wide range of complex, but common conditions. This chapter presents a preliminary experimental and numerical investigation of hypersonic flow over closed- and open-nose missile bodies, where the latter have been proposed as a means of reducing leading edge heat transfer. Four contributions are presented. First, a novel singular value decomposition (SVD)-based image processing technique is introduced, which significantly enhances the quality of raw schlieren images obtained in high-speed compressible flows. Second, numerically predicted hypersonic flow about a scale-model missile body, obtained using STAR-CCM+, is validated against experimental schlieren image data, an empirical correlation connecting bow shock stand-off distance and shock density ratio, and estimated drag forces. Third, scaling and physical arguments are presented as a means of choosing appropriate gas equations of state and for interpreting results of numerical simulations and experiments. Last, numerical experiments show that the forward facing cavity used in our wind tunnel experiments functions as a heat sink, reducing heat fluxes on the missile body downstream of the cavity.

Purpose: To develop a method to track lung tumors in rotational cone beam projections during rotational radiotherapy and cone beam CT scanning. Method and Materials: A multiple template based tracking algorithm was developed and used to track tumors in rotational cone beam projections. Templates were generated by creating DRRs of ten phases of 4DCT. These templates were generated for a sequential set of angles matching the projections of a CBCT scan. The position of the tumor in each template was derived from contours drawn on 4DCT. Shifting of the templates was used to allow for a greater tumor motion ranges. The mutual information between projections and templates was computed and used as one parameter in a probability function used to track tumor position. Tumor distance traveled and phase change between successive projections were also incorporated into the probability function. This output was compared to physician specified tumor locations on each cone beam projection. In addition to a patient study, the method was tested on a respiratory motion phantom programmed to exhibit sinusoidal motion in the SI direction. Results: In the phantom study, the SI motion of the tumor was tracked with a mean absolute error (MAE) ranging from 1.2mm to 1.6mm and a 95th percentile absolute error (P95) ranging from 3.2mm to 3.7mm. For the patient study, the SI motion was tracked with MAE ranging from 1.7mm to 1.9mm and P95 ranging from 3.4mm to 3.9mm. Conclusion: The algorithm has demonstrated the feasibility of tracking tumors in rotational x‐ray images. Further development is needed in order to achieve accuracy similar to that of fixed gantry fluoroscopic tracking.