Introduction/Background 3D brachytherapy (BRT) planning, based on magnetic resonance (MR) imaging, has become a standard approach in cervical cancer radiotherapy treatment in many radiotherapy centres. T2W MR images give us precise visualization of the tumor tissue volume and tumor changes during the treatment. Adequate BRT dose coverage of the target volumes, presented through D90 and D100 dose parameters, has a primary role in achieving local control of the disease.
The goal is to estimate the initial tumor volume impact on the registered target volume dose parameters.
Methodology The curative chemoradiation was applied to 30 patients with advanced cervical cancer. Brachytherapy was performed in a high-dose rate regimen, in 4–5 weekly applications, with a dose of 7Gy per application, starting after 15 external beam fractions, endocavitary without interstitial catheters. For each patient a 3D T2W MR imaging was performed, initially prior treatment and at the time of the first and the fourth BRT application. MR images were used for tumor volume assessment and for 3D BRT planning, obtaining that way the target dose-volume parameters. Initial tumor volume influence on the registered HR-CTV dose parameters (clinically the most important target volume dose parameter) was then investigated.
Results MR based assessment of tumor volumes initially, at the time of the first and the fourth BRT application, were as follows: (49.9±33.3 ccm, 11.3–124.2 ccm), (17.3±19.2 ccm, 1.7–78.4ccm) and (7.0±10.9ccm, 0.8–58.5ccm) respectively. Registered EQD2 HR-CTV doses for the whole group of patients were D90 (107.15±22.06Gy), and D100 (80.66±14.58Gy). Initial tumor volume showed a strong negative, statistically significant correlation with registered HR-CTV D90 dose at the time of the first BRT application (rho= -0.8). ROC analysis confirmed the discriminative influence of initial tumor volume on achieving recommended HR-CTV dose, with the best initial tumor volume cut-off value of 47.87ccm, with high sensitivity 89.4%, and specificity 90.9%. A statistically significant difference between two groups of patients (regarding the identified tumor volume cut-off value of 47.87ccm) was found for the EQD2 HR-CTV doses: D90 (120.4±14.6Gy vs 87.33±15.48Gy, p=6.9*10–7) and D100 (101.8±13.39 vs 75.85±11.93Gy, p=9*10–5).
Conclusion The initial volume of the cervical tumor has a great influence on achieving the recommended values of HR-CTV D90 and D100 doses. Tumors with initial volume greater than 47.87 ccm cause a statistically significant lower total EQD2 dose at the HR-CTV volume, leading to poor local disease control.
Disclosures The results are part of my paper published recently in J BUON.
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