Dosimetric verification of advanced radiotherapy techniques using thermoluminescent dosimeters - TLD

Postgraduate Thesis uoadl:2880665 298 Read counter

Unit:
Κατεύθυνση Ιατρική Φυσική-Ακτινοφυσική
Library of the School of Health Sciences
Deposit date:
2019-09-12
Year:
2019
Author:
Tsimpoukas Dimitrios
Supervisors info:
Καραΐσκος Παντελής, Καθηγητής, Ιατρική , ΕΚΠΑ
Παπαγιάννης Παναγιώτης, Αναπληρωτής Καθηγητής, Ιατρική, ΕΚΠΑ
Λουκάς Κωνσταντίνος, Επίκουρος Καθηγητής , Ιατρική , ΕΚΠΑ
Original Title:
Δοσιμετρική επιβεβαίωση εξελιγμένων τεχνικών ακτινοθεραπείας με χρήση δοσιμέτρων θερμοφωταύγειας – TLD
Languages:
Greek
Translated title:
Dosimetric verification of advanced radiotherapy techniques using thermoluminescent dosimeters - TLD
Summary:
Radiotherapy is, after the surgery, the most widely used method of treating cancer and has the highest succession rates. It is applied to more than 50% of cancer sufferers today, as well as in many cases of benign tumors. For this reason it is imperative to accurately plan the best possible treatment plan and confirm it. This work focuses on the confirmation of radiotherapy techniques using thermoluminescence dosimeters (TLDs). Initially, a theoretical approach was made to the different dosimeters used in radiotherapy as well as the methods for comparing the measured and studied dose distributions.
In the experimental part of the present study, two different treatment plans were experimentally confirmed in four total irradiations and the differences of these plans were compared with each other, after the necessary calibration of the TLDs and the TLD reader was performed. In summary, the irradiations involved a simulation of irradiation of multiple (five) metastases using two treatment plans with one and two isocenters each of which were applied 2 times with and without positioning correction using VMAT technique with a 6MV energy beam. For this purpose, a batch 95 TLD of 1mm3 size was initially calibrated, which was then used to confirm the dose distributions of the respective plan after being placed on a special dummy model. The dummy model with the dosimeters was subjected to the whole chain of a radiotherapy application (CT, treatment plan, placement, CT scan incorporated in the linear accelerator, position correction, and irradiation). The results of the TLD measurements were initially compared to their respective point-to-point dosing rates by the TPS and dosing maps were constructed at the measurement points as well as using g-index maps
The final evaluation of these results showed a good agreement between experimental and theoretical dose distributions. Several dose difference and distance difference criteria ranging from 7% / 2mm to 3% / 1mm were selected in the g-index evaluation, the results of which for all 4 irradiations were quite satisfactory especially in the case of the global g-index, in which, in most cases, passing rates of more than 80% were observed even for g-index values of 3% / 1mm. However, when the local dose difference was used as the acceptance criterion in the g-index method, the irradiations for which not only the positioning but also the shifts were corrected before irradiation showed clearly improved agreement between the TLD measurements and the TPS calculations.
When comparing the results, correlations were also found between the measured and calculated dose difference and the expected dose value with the differences being increased at low doses. A similar correlation was observed between the measured and calculated dose difference and the distance from the isocenter, with the differences increasing at longer distances.
Main subject category:
Health Sciences
Keywords:
TLD dosimetry, Calibration TLD-reader, VMAT, Point to point comparison, G-index
Index:
No
Number of index pages:
0
Contains images:
Yes
Number of references:
32
Number of pages:
103
File:
File access is restricted only to the intranet of UoA.

Tsimpoukas Dimitrios Master.pdf
4 MB
File access is restricted only to the intranet of UoA.