Unit:
Κατεύθυνση Ιατρική Φυσική-ΑκτινοφυσικήLibrary of the School of Health Sciences
Author:
Vitoraki Stamatia
Supervisors info:
Παντελής Καραΐσκος Καθηγητής, Ιατρική, ΕΚΠΑ
Παναγιώτης Παπαγιάννης, Αναπληρωτής Καθηγητής, Ιατρική, ΕΚΠΑ
Κωνσταντίνος Λουκάς, Επίκουρος Καθηγητής, Ιατρική ,ΕΚΠΑ
Original Title:
Μελέτη ρυθμού εναπόθεσης δόσης σε εξελιγμένες τεχνικές ακτινοθεραπείας με έμφαση σε στερεοτακτικές εφαρμογές
Translated title:
Analysis of dose rate delivery in advanced radiotherapy techniques focusing on stereotactic applications
Summary:
In stereotactic radiotherapy a high dose fraction is prescribed and delivered in 2-5 sessions or in a single session (Stereoractic Radiosurgery-SRS). Stereotactic radiotherapy is used in small tumors and aims to deliver maximum dose to the tumor and also minimum dose to the organs at risk. It includes techniques such as γ-knife, cyberknife and linear accelerator (linacs) based systems such as IMRT and VMAT. In IMRT and VMAT techniques, intensity modulated radiation fields are used, since the dose rate changes during a session.
It is observed that in biological response of human tissues, not only the value of the dose delivered is important, but also the dose rate. For dose rates below 1 Gy/min the dose response begins to change (tissue sparing effect) and has a different impact in different tissue types. So it is important, to investigate the dose rate for treatment plans in which it may change.
In this essay, the delivery of dose rates in applications of stereotactic radiotherapy such as γ-knife, IMRT and VMAT was studied.
In the beginning, the dose rate in γ-knife plans of 84 acoustic neuroma cases was studied. The results showed that the dose rate varies in many cases and also that in some cases, an important percentage of dose is delivered with dose rates below 1Gy/min. Furthermore, a correlation test was made, and a statistically significant correlation was found between the percentage change of the tumor volume 4 years after radiotherapy treatment and the percentage dose delivered with dose rate below 1Gy/min (r=0.459 p=0.000). Also a statistically significant correlation was found between the percentage change of the tumor volume 4 years after radiotherapy treatment and the weighted average dose rate (r= -0.390 p=0.000).
Finally, different dose rates were further studied in IMRT and VMAT treatment plans (FF and FFF mode). The study was focused on 3 patients’ plans of a) acoustic neuroma b) prostate cancer c) head and neck cancer. The results showed that dose rates are high and the percentage dose which is delivered with dose rate below 1Gy/min inside the PTV is low, when IMRT and VMAT techniques are used. A significant difference between FF and FFF mode was also observed in this study.
Main subject category:
Health Sciences
Keywords:
Stereotactic radiosurgery, Stereotactic radiotherapy, Dose rate
File:
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Διπλωματική-ΠΜΣ_PK.pdf
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