Abstract ID: 89 Investigation of conformal arc therapy utilizing Cobalt 60 beams

Purpose The trend today in modern radiation therapy is toward conformal therapy with segmented or moving field techniques. Generally, this requires multifield irradiation or the use of arc/rotation therapy. Many authors have pointed out in literature that if the Co-60 machines were modernized with state of the art devices, it may be able to provide similar quality of radiation therapy as provided by linacs. Co-60 units will have the advantage of having more simple and robust design, and minimal maintenance and technical expertise to operate the machine as compared to the technologically complex linacs. Thus, in this work we conduct a dosimetric comparison between conformal arc utilizing Co-60 beams and that utilizing 6MV beam energy. Material and methods CT scans was unarchived for patient previously treated by SBRT in our department. We selected lung, breast, and head and neck cases. All of these cases were previously planned on Eclipse planning system (Varian, Palo Alto, Medical Systems). We regenerated treatment plans using conformal arcs with the arc being modeled by delivery of multiple conformal beams. Dose distributions for all plans were calculated using Monte Carlo simulation for both 6MV and Co-60 beam energies. Results As the number of fields increases, advantage of higher energies over lower radiation energies decreases. In all studied cases, conformal arc plans utilizing Co-60 beam was achieving almost same conformity when compared to the 6Mv plans. Isodose distributions were tailored similarly around the PTV. On reviewing the minimum and maximum dose reaching all targets, it was shown that both Co-60 and 6Mv plans was achieving our clinical acceptation criteria for the target coverage. The DVH of Co-60 plans were showing slightly lower dose to critical structures however the difference was small in most cases. Conclusion Our results have shown the potential for newly designed Co-60 machines as a modality that could treat a good fraction of cancer patients. The overall performance seen in the conformal arcs using Co-60 beams was encouraging as being compared to the 6MV conformal arcs. There was no significant superiority detected for the 6MV plans over the Co-60 plans for SBRT cases.