Single or multi-CT simulation for high dose rate brachytherapy and dosimetric verification : is replanning necessary prior to each fraction?

• Κύριος συγγραφέας: Δουβάρα, Αγγελική
• Άλλοι συγγραφείς: Douvara, Angeliki
• Γλώσσα: English
• Έκδοση: 2022
• Θέματα: Post-operative gynecological high-dose-rate brachytherapy; Single versus multi-CT simulation; Dosimetric evaluation; Dosimetric verification; Μετεγχειρητική γυναικολογική βραχυθεραπεία υψηλού ρυθμού δόσης; Προσομοίωση μονής έναντι πολλαπλής αξονικής τομογραφίας; Δοσιμετρική αξιολόγηση; Δοσιμετρική επαλήθευση

The aim of this study was the comparison, analysis and dosimetric evaluation of single versus multi computed tomography (CT)–simulation-based treatment plans for post-operative gynecological intracavitary high-dose-rate brachytherapy, and dosimetric verification. Materials and methods: Eighty (80) patients were enrolled, each of them receiving three fractions of 7 Gy (one fraction/week). Firstly, a CT-simulation was performed prior to each fraction (3 CTs, 3 original plans). For all the CT- simulations organs at risk (OARs) and clinical target volume (CTV) were delineated. The doses for 2cc and 1cc volumes of the rectum, the sigmoid, the bladder, and for 1cc of the rectal wall were evaluated, as well as the doses for the 90% and 100% CTV volume. Secondly, for the single CT-simulation method, the 2nd and 3rd fraction were decay corrected from the 1st treatment plan dwell times and implemented on the aforementioned 2nd and 3rd CT (revised plans). A dosimetric comparison of the results was performed. Finally, in order to verify the doses for the rectum calculated by the treatment planning system (TPS), thermoluminescent dosimeters (TLDs) were used. Statistical analysis with the software package SPSS was performed. Results: The dosimetric differences between original and revised plans for the rectum, the bladder, the sigmoid, the rectal wall, and the CTV were not statistically significant (p>0.05). However, in some cases of single CT method the dose of the rectum exceeded the dose constraints. That dose increase ranged from 0.86% to 18.75%. Finally, statistically significant rectal dose difference between TLD measured and TPS calculated dose (p<0.05), was observed. This difference ranged from -53.3% to 142.7%. Conclusion: Although the dosimetric differences for the OARs and the CTV were not statistically significant, the increased dose of rectum in some cases may be significant in clinical practice. Thus, the use of single or multi-CT-simulation is a medical/clinical decision, depending upon several factors. The process that was followed for dosimetric verification with TLDs was considered unsuitable for the rectum, due to position uncertainties.