Comparison of Acuity Cone-Beam CT Based Image Guided HDR with the Conventional CT-Simulator Based Im

To investigate potential uncertainty and difference on planning of an HDR treatment using images from Acuity cone-beam CT and from conventional CT-simulator CT respectively. A 7-pound chicken bought from a grocery store was used as a phantom to mimic a patient for planning a tandem and ovoid HDR treatment. To start the experiment, a tandem and ovoid applicator was inserted firmly inside the chicken phantom. In order to measure the actual delivered dose and compare it with the calculated dose in the treatment plan, we placed NanoDot dosimeters at two reference points inside the phantom before inserting the tandem and ovoid applicator. Then 3-dimensional CT images were obtained by respectively scanning the phantom on the Varian Acuity Cone-Beam CT simulator in our brachytherapy suite and on the conventional CT-simulator that is generally used for external beam and brachytherapy treatment planning. Using these two sets of images with Varian's Brachy Vision treatment planning system we made two tandem and ovoid HDR treatment plans: one for Acuity CBCT based and the other for conventional CT based. A dose of 600 cGy/fraction was prescribed to the traditional defined “A” points in each plan. Source numbers, positions, and dwell times were set exactly the same for both plans. The plan based on the conventional CT images was delivered to treat the phantom. We compared the isodose distributions and the doses at “A” points in two plans as well as the doses between measured and calculated for the two reference points. No significant differences were found in terms of the doses at the “A” points (599.8 cGy to 596.6 cGy) and the isodose distributions between the two plans. The measured doses (1025 cGy, 1044 cGy) and the calculated doses (1015 cGy, 1046 cGy) at two reference points were consistent with each other within the accuracy of NanoDot dosimetry. Planning HDR gynecologic brachytherapy using images from Acuity cone-beam CT and from conventional CT and prescribing to geometrically determined prescription points -results in equivalent results. Using the Acuity cone-beam CT provides a more efficient process, reduces the chance for applicator shifting during movement of the patient, and improves patient comfort. Additional evaluations are ongoing to compare CT and cone-beam CT identification of tumor and normal tissue.