Varian Medical Systems, A Siemens Healthineers Company Hagerstown, MARYLAND
K. Li; Varian Medical System, Hagerstown, MD; Mercy Cancer Center, Spingfield, MO
Purpose/Objective(s): In the NRC-GY020 protocol clinical trial, objectives have been developed to distinguish the Vaginal Brachytherapy with pelvic radiation with and without plus pembrolizumab (MK-3475), which is an intravenous immunotherapy. In clinical delivery setting, the density rate of MK-3475 and Iridium-192 high dose rate (HDR) source strength are both temporal variables, and the combination clinical effect could both affected by these two temporal factors, in this study, a variation sensitivity levels were computed to distinguish the temporal effect on the clinical trial case difference. Materials/
Methods: Five patients with same prescription were selected for this study. The selected HDR treatment dose prescription was 1200cGy delivered in two fractions. All the plans were computed with a treatment planning system. And the elapse days between fraction treatment date, source strength related fractionated delivery time, were collected for this study. Their difference was used to find the variation among these cases. And linear operation was applied to these two -fraction treatment modality. Results: The source strengths used for the first fraction of treatment in Ci were 6.4, 4.6, 7.6, 5.6, and 5.3; The difference to the average activity of the source in percentages were 9.6%, -22%, 29%, -5%, and -11% with standard deviation at 20%. Due to the non-linearity of decay characteristics of the radioactive source and target geometric variation, the delivery temporal difference to the average time in percentage were -23%, 28%, -20%, 31%, and -17% with standard deviation at 27%. Conclusion: The delivery source strength showed significant variation in the treatments of different patients, and these variations could be an important factor in optimal evaluation of clinical objective for the clinical trial. A further detailed analysis such as using the previous developed Dose Energy Density Distribution model should include the pembrolizumab delivery rate in better understanding of theoretical model in radiation therapy for this type of clinical trials.
