Supervisors info:
Καλλιόπη Πλατώνη, Επίκουρη Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Ευστάθιος Ευσταθόπουλος, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Βασίλειος Κουλουλίας, Καθηγητής, Ιατρική Σχολή, ΕΚΠΑ
Summary:
Purpose: The purpose of this study isthe comparison and the dosimetric evaluation of treatment plans optimization methods for intracavitary high-dose-rate (HDR) brachytherapy for post-operative gynecological cancer and dosimetric verification.
Materials and Methods: This study includes 100 patients with gynecological cancer, who underwent intracavitary high-dose-rate (HDR) brachytherapy at the University General Hospital “Attikon”. The patients had previously undergone surgery, while a proportion had also received chemotherapy and external beam radiotherapy EBRT. The prescribed dose during brachytherapy was 21Gy divided in three fractions of 7 Gy per fraction. The Single-channel Vaginal Cylinder (SVC) applicator was used. Initially, the pelvic area was imaged through computed tomography (CT). Contouring and treatment planning were performed using Oncentra Brachy Image Guided 3D Treatment Planning system (version 4.3, Elekta). The radiation oncologist delineated the clinical target volume CTV and Organs at Risk (OARs) (rectum, bladder, sigmoid, urethra) according to GEC-ESTRO guidelines. Then the treatment planning was performed using Graphical Optimization (GO) as an optimization method. A recalculation of the plan was followed using alternative optimization methods such as the Dose Point Optimization (DPO) and IPSA as well. Five evaluation indices to evaluate HDR brachytherapy plans. The Coverage Index (CI), the Homogeneity Index (HI), the Overdose Volume Index (OI), the Dose Non-uniformity Ratio (DNR) and the Conformity Index (COIN), were calculated. Finally, in order to verify the doses calculated by the treatment planning system (TPS), GAFCHROMIC EBT3 Films were used.
Results: Coverage Index (CI) with GO plan (0.809), DPO plan (0.79) and IPSA algorithm (0.803) did not present a statistically significant difference (p=0.21). Dose Homogeneity Index (DHI) with GO (0.465 p<0.001) plan and IPSA algorithm (0.459 p=0.031) was significantly higher as compared with DPO plan (0.45). The Overdose Volume Index (OI), for GO plans (0.392), DPO plans (0.381), and IPSA (0.385) did not present a statistically significant difference (p=0.302) as well as, Dose Non-uniformity ratio, DNR, (p=0.128) for GO (0.576), DPO (0.573), IPSA (0.576). However, GO resulted in high conformity with Conformity Index, COIN, of 0.649 as compared with 0.623 (p=0.028) for DPO plans. IPSA resulted COIN 0.636 with no statistical significance (p=0.581) as compared with GO plan. The dosimetric verification with GAFCHROMIC EBT3 film for Graphical Optimization and IPSA, led to dose differences of 16% and 13%, respectively.
Conclusion: Graphical Optimization and IPSA resulted higher Dose Homogeneity Index (DHI) and Conformity Index (COIN) than Dose Point Optimization. However, the differences for Coverage Index (CI), Overdose Volume Index (OI), Dose Non-uniformity ratio (DNR), it were not statistically significant. The dosimetric verification with GAFCHROMIC EBT3 film presented differences within the limits of radiochromic film dosimetry uncertainty.
Keywords:
Post-operative gynecological high-dose-rate HDR brachytherapy, Optimization methods, Dosimetric evaluation, Dosimetric verification
