Investigation of the dosimetric effect of respiratory motion using four-dimensional weighted radiotherapy

Abstract

We have developed a four-dimensional weighted radiotherapy (4DW-RT) technique. This method involves designing the motion of the linear accelerator beam to coincide with the tumour motion determined from 4D-CT imaging while including a weighting factor to account for irregular motion and limitations of the delivery system. Experiments were conducted with a moving phantom to assess limitations of the delivery system when applying this method. Although the multi-leaf collimator motion remains within the tolerance of the linear accelerator, the extent of motion was less than 1 mm larger than the designed one, and there was a net system latency of approximately 0.2 s. The dose distributions were measured and simulated using different weighting factors and motion scenarios. The breathing characteristics (period, extent of motion, drift and standard deviations) of 32 patients were evaluated using the Varian RPM system. Breathing variability was assessed by plotting the average breathing motion as a function of the breathing phase. Simulations were carried out to determine the optimal weighting factor based on typical patient breathing characteristics. These results establish that the 4DW-RT method demonstrates potential for dose escalation without increasing exposure to healthy tissue.

Gated Radiotherapy Development and its Expansion

“…In spite of these remarkable advancements in dynamic delivery of therapeutic doses [98], such as Dynamic Multi Leaf Collimators (DMLCs), robotic accelerators and robotic couches, all of these technologies suffer from a time lag in conformity of moving tumor location with therapeutic beam. As a result of this time lag, there is a lapse between adaptations of planned and delivered dose and this adaptation can be affected adversely by increasing the system time lag and latency [99][100][101][102][103]. Therefore, implementation of dynamic tumor tracking techniques due to the technological restrictions as well as unpredictable and complex respiratory motions, which have been shown for lung tumors, are more challenging than accomplishment of breath-hold and respiratory gating techniques [16,90].…”

High performance computing for deformable image registration: Towards a new paradigm in adaptive radiotherapy

“…Extensive research has been carried out in inter-and intrafraction patient movement/organ deformation for lung and prostate radiotherapy, including strategies for measuring this motion during treatment, and its effect on the actual versus computed dose volume histograms ͑DVHs͒. [1][2][3][4][5][6][7] In order for this plethora of time series imaging to be clinically relevant, it is imperative to implement fast and automated algorithms that do not significantly increase the workload of the radiation oncologist. This requires fast near real-time online deformable image registration ͑DIR͒ if one is to use time series volumetric imaging data as part of adaptive radiotherapy ͑ART͒.…”

“…Beyond radiation therapy, DIR is also used in other areas of medical imaging, including motion corrected image reconstruction. 6,[16][17][18][19][20] The conventional approach in medical imaging to reduce the computation time has been to use higher performance CPUs ͑i.e., higher clock speed and dual core architecture͒ and multiprocessor systems. Other highly promising approaches being pursued include utilizing the cell broadband engine, 21 field-programmable gate array ͑FPGA͒, [22][23][24] and graphics processing unit ͑GPU͒.…”