PV QA 4 - Poster Viewing Q&A 4
TU_21_3526 - Radiobiological Plan Evaluation Parameters for the Fractionated High-Dose Rate GYN Brachytherapy
Tuesday, October 23
2:45 PM - 4:15 PM
Location: Innovation Hub, Exhibit Hall 3
Radiobiological Plan Evaluation Parameters for the Fractionated High-Dose Rate GYN Brachytherapy
M. Shojaei1, M. Rahman1, S. Pella2, and G. Kalantzis1; 1Florida Atlantic University, Boca Raton, FL, 2South Florida Radiation Oncology LLC, Boca Raton, FL
Purpose/Objective(s): Radiobiological plan evaluation parameters such as Equivalent Uniform Dose (EUD), Normal Tissue Complication Probability (NTCP), and Tumor Control Probability (TCP) are used as assessment methods of high-dose rate brachytherapy treatment plans in endometrial cancer. This retrospective study aims to calculate and evaluate the EUD and EUD-based NTCP for organs at risk, such as bladder and rectum using retrospective Dose Volume Histogram (DVH) data from repetitive CT scans during fractionated high-dose-rate brachytherapy treatments. A computer algorithm was employed to calculate Niemierko’s EUD-based NTCP model, and also a 3D point-cloud rigid registration method was utilized to calculate the applicator displacement.
Materials/Methods: The evaluations were performed for 118 HDR treatment plans for 30 patients by registration of the subsequent treatment plans into the initial CT-image guided plan. Dose fractionation regimens were varied from 4Gy to 7Gy per fraction and 1 or 2 fractions per week, depending on the cancer staging. Moreover, a computer algorithm based rigid registration method for 3D point-clouds was employed to determine rotation and translation of the implanted applicator precisely. For that purpose, Digital Imaging and Communications in Medicine files (DICOM) was imported in the Computational Environment for Radiotherapy Research (CERR) and the coordinates of the PTV voxels was exported to a text file in order to calculate the applicator displacement, rotation and translation. Knowing the displacements will assist to evaluate a possible correlation between the mean dose variations and the applicator displacement.
Results: For bladder, the average EUD value in optimized plan is 1.51Gy (SD = 0.51), while the number for registered plan is 2.16 Gy (SD = 1.64). The mean EUD difference is 0.43%. The average NTCP values of the bladder are calculated and both methods are 0.0000%. Likewise, for rectum, the average EUD value in optimized plan is 1.74Gy (SD = 0.67) and for registered plan is 2.89 Gy (SD = 4.59), which is inconsiderably higher than optimized plan. The mean EUD difference for rectum is 0.66%. Rectum average NTCP values for both optimized and registered methods are 0.0000%. In addition, the applicator rotations about Y and Z axis for the first fraction is compared with other fractions for each patient. 84% of applicators’ rotation about Z axis was less than five degrees, 7% five to ten, 6% 10 to 15, and only 3% applicators were rotated greater than 15 degrees. Besides, 94% of applicators rotated less than five degrees, and 6% had rotation about Y axis between 10 to 5 degrees.
Conclusion: our results demonstrated that no significant radiobiological impacts on organs at risks (OAR) are found from different fractions for 30 patients’ retrospective treatment plans. However, Immobilization devices need improvement in order to minimizing any applicator displacement and also to prevent any displacement during transportation and treatment delivery.
Author Disclosure: M. Shojaei: None. M. Rahman: None. S. Pella: Owner; Advanced Radiation Physics Inc. Professor; Florida Atlantic University. Stock; Etrade. Owner, CEO, Professor and consultalt; Advanced Radiation Physics Inc. CEO; Advanced Radiation Physics Inc. G. Kalantzis: None.