Determination of CTV-to-ITV margin for free-breathing respiratory-gated treatments using 4DCT and the Novalis ExacTrac Gating System with implanted fiducials

The purpose of this project was to investigate the interplay between gating window characteristics and target margin required to compensate for residual motion during the gating window. This project investigated the accuracy of ExacTrac and 4DCT imaging localizing an implanted coil at various phases of respiration. Radiochromic film measured delivered dose patterns for selected gating intervals over a variety of respiratory patterns. In order to establish accurate dosimetry, this project implemented and tested an EBT radiochromic film dosimetry system. Film testing showed that the performance of a medical grade Vidar Dosimetry Pro radiographic film scanner and an Epson V700 Photo flatbed scanner were very similar. Both scanners showed nearly the same performance in terms of measurement repeatability, noise, vertical and horizontal uniformity over a range of doses from 11.5-511.9 cGy. The Vidar was selected for these studies due to clinical availability. Even at the greatest coil velocities observed, ExacTrac coil localization agreed with calculated coil motion to within 0.8 mm. 4DCT showed errors up to 5.5 mm resolving coil position during large respiratory-induced velocities. 4DCT accurately measured the coil length within 1 mm of actual coil length at end expiration/inhalation. 4DCT can provide an accurate representation of the phantom at end-respiration for treatment planning purposes, and ExacTrac can accurately localize the coil to determine target motion in all phases For patient treatments it is suggested that target margins should be set using the residual motion during gating. For patients without implanted coils, the residual motion can be computed based on the target motion measured from 4DCT and the size of the gating window. For patients with implanted coils, the ExacTrac system can be used to directly measure residual tumor motion during gating. The hypothesis of this work was that gated delivery combined with 4DCT could limit internal margins to less than 3 mm while maintaining 95% prescription dose coverage of moving targets. The hypothesis was found to be true for gating windows of 10% and 20% for target motions up to 25 mm and was true with gating windows up to 50% for smaller motions (5 & 10 mm)

Investigation of Respiratory Motion Management Techniques for Proton and Photon Radiotherapy of Lung Cancer

Protons as a source of therapeutic radiation can provide a substantial improvement over dose distributions that can be achieved with conventional sources of radiation such as high-energy photons. However, respiratory motion can significantly impact the delivered proton and photon dose distributions during lung cancer radiotherapy. The goals of this dissertation research were to evaluate the impact of respiratory motion and to estimate the benefit of respiratory gating for passively scattered proton therapy (PSPT) and intensity modulated photon therapy (IMRT). The first aim of this project was to determine the impact of respiratory motion in PSPT and IMRT. Four dimensional dose distributions were calculated in both modalities for a cohort of 20 patients. The mean changes in normal tissue dose-volume indices were indistinguishable except proton therapy had a greater increase in lung V5, heart V5 and spinal cord maximum dose. The effects of respiratory motion on the calculated dose were not correlated to the tumor motion. The second aim estimated the benefit of PSPT and IMRT respiratory gating by simulating end-exhale gated treatment plans. The results demonstrated that respiratory gating showed a benefit for a majority of proton and photon treatment plans. PSPT gating, compared to IMRT gating, allowed for larger reduction of all lung and intermediate esophagus dose-volume indices. The third aim attempted to correlate the benefit of respiratory gating to the extent of tumor motion. For the cohort, the benefit of respiratory gating in PSPT and IMRT cannot be predicted by the extent of tumor motion. This aim showed that the tumor motion was inadequate to predict the benefit of respiratory gating. In an additional fourth aim, we proposed a new metric to quantify respiratory motion in proton therapy: the water equivalent thickness (WET). The change in WET between the inhale and exhale phases of respiration (∆WET) was significantly correlated to the change in dose during respiration. Additionally, ∆WET analysis was used to create treatment plans that were more robust to respiratory motion. The use of ∆WET gives a powerful new tool, especially in proton therapy, to quantify the anatomical variations of all irradiated tissues along the beam path

Evaluation of the systematic error in using 3D dose calculation in scanning beam proton therapy for lung cancer

The objective of this study was to evaluate and understand the systematic error between the planned three-dimensional (3D) dose and the delivered dose to patient in scanning beam proton therapy for lung tumors. Single-field and multi-field optimized scanning beam proton therapy plans were generated for 10 patients with stage II–III lung cancer with a mix of tumor motion and size. 3D doses in CT data sets for different respiratory phases and the time weighted average CT, as well as the four-dimensional (4D) doses were computed for both plans. The 3D and 4D dose differences for the targets and different organs at risk were compared using dose volume histogram (DVH) and voxel-based techniques and correlated with the extent of tumor motion. The gross tumor volume (GTV) dose was maintained in all 3D and 4D doses using the internal GTV override technique. The DVH and voxel-based techniques are highly correlated. The mean dose error and the standard deviation of dose error for all target volumes were both less than 1.5% for all but one patient. However, the point dose difference between the 3D and 4D doses was up to 6% for the GTV and greater than 10% for the clinical and planning target volumes. Changes in the 4D and 3D doses were not correlated with tumor motion. The planning technique (single-field or multi-field optimized) did not affect the observed systematic error

In the bull's-eye of an echo

Environmental Writing and Great Lakes LiteratureAlgonquin Provincial Park in central Ontario contains thousands of lakes, moose, and bears. Located on 7,630 square kilometers of land in the Canadian Shield, the park is an area of transition between northern deciduous forests and southern coniferous forest. Car campers visit the edges of the forest, but the interior portions are completely cut off from civilization. In mid-July of 2006 the staff and campers of Camp Kennedy headed to Algonquin to spend six days canoeing its lakes and rivers. I was working on staff that summer and had been helping to prepare the campers for the trip since they arrived at Kennedy. It was a Jewish camp, and I was doing my best to conjure up that dormant part of myself in order to better connect with the campers. We were all very excited when we left the upper peninsula of Michigan in the camp’s green school bus. With Jeff, the director of the camp, at the wheel, we passed through the Sault, headed onto Canadian soil, and drove along the highway that runs north of the Huron’s Georgian Bay. Ten hours after leaving camp, we sleepily rolled into the northwestern portion of the Algonquin forest.http://deepblue.lib.umich.edu/bitstream/2027.42/61471/1/Matney_2008.pdfDescription of Matney_2008.pdf : Access restricted to on-site users at the U-M Biological Station