Graduate Degree Type
Medical Dosimetry (M.S.)
The majority of prostate cancers are detected in men ages 65 and older, resulting in an increased probability that these patients have prosthetic devices. Hip prostheses can pose a challenge when creating a radiation therapy treatment plan for prostate cancer patients. The purpose of this study is to compare two planning techniques that treat the target volume while avoiding irradiation through these prostheses.
This retrospective study obtained previously treated patient data from the center’s treatment planning system. Patients who were treated for prostate cancer and had one or two hip prostheses were included in this study. Two plans were created for each patient, one which utilized avoidance sectors around the prostheses, and one which utilized Varian’s Eclipse tool “avoidance structures in optimization”. Prescriptions and optimization parameters were kept constant between the two plans in an effort to observe the potential dosimetric differences between the two planning techniques.
It is observed that the mean bladder and rectum doses were decreased by using the avoidance structure technique as compared to the avoidance sector optimization. The average difference in mean rectum doses between the two plans was 497.3 cGy. For the mean bladder doses, the average difference was 128.9 cGy. Additionally, the global maximum dose was observed to be lower on average for the avoidance sector plans when compared to the alternative plan. An average decrease of 2.23% was calculated. Tests on the conformity index of the treatment plans yielded no significant difference between the two planning strategies.
The results of this study indicate that there is a dosimetric benefit to the use of avoidance structures compare to avoidance sectors with respect to the mean bladder, mean rectum, and global maximum doses. Additional studies with a larger data set that also takes into account organ at risk volumes are required to further assess the impact of the new Varian Eclipse optimization technique.
Bowhall, Grace E., "A Dosimetric Comparison Using Avoidance Sectors vs Avoidance Structures for Hip Prostheses in Cancer Patients Receiving Pelvic Irradiation" (2022). Culminating Experience Projects. 165.