Room: AAPM ePoster Library
Purpose: the relatively short half-life of radiation source used for high-dose-rate (HDR) afterloading brachytherapy, the varieties of dose rate can be quite large amongst different patients or consecutive fractions of the same patient, especially for those treated with both old and new sources in the same course. It is unclear but clinically desirable to understand the impact of radiation source activity on the biological effects such as short-term outcomes of cervical carcinoma (CC) patients.
Methods: retrospective analysis was performed on 700 CC patients treated with HDR afterloading brachytherapy using Ir-192 source, 104 of which experienced a source change (SC group) during their treatment course. The remaining patients were divided into high activity (HA, n=190) and low activity (LA, n=406) groups according to their mean dose rate of all fractions (19/30/361/254/35/1 patients received 2/3/4/5/6/7 fractions respectively). The cutoff was set as the average of the maximum and minimum air kerma strength, i.e. 25403.4 cG*cm2/h. The 1-month and 3-month follow-up results were marked by complete response (CR), partial response (PR), stable disease (SD), and progressive disease (PD), per response evaluation criteria in solid tumors 1.1. To reduce patient selection bias, pairs of propensity-score-matched (PSM) were generated based on clinical information. Results were compared using Pearson's Chi-squared test.
Results: SC, HA and LA groups, short-term follow-up results showed no significant difference (P>0.05). The CR/PR/SD/PD results and the corresponding p-values were 73-85/74-59/1-4/0-0 for HA-LA 1-month, p=0.111; 120-128/26-17/0-2/2-0 for HA-LA 3-month, p=0.105; 32-43/45-36/4-2/0-0 for SC-No SC (HA and LA) 1-month, p=0.194; and 66-66/13-13/0-1/2-0 for SC-No SC 3-month, p=0.393 respectively.
Conclusion: preliminary PSM study observed no significant impact of radiation source activity on biological effects in terms of short-term outcomes of cervical carcinoma patients treated with brachytherapy. Studies based on larger patient volume and long-term follow-up surveys are being performed.
Funding Support, Disclosures, and Conflict of Interest: Capital's Funds for Health Improvement and Research[2018-4-1027]; Fundamental Research Funds for the Central Universities/Peking University Clinical Medicine Plus X - Young Scholars Project(PKU2020LCXQ019); National Key R&D Program of China(2019YFF01014405); Ministry of Education Science and Technology Development Center[2018A01019]; National Natural Science Foundation of China[11505012,11905150].Corresponding author: Yibao Zhang, firstname.lastname@example.org
Source Strength, Brachytherapy, Ir-192 Source