Comparison and characterization of pretreatment verification systems for small fields (SBRT and HSRT)
Radiation therapy involves delivering a high dose (energy of absorbed radiation per unit mass) to a target volume within the patient. Ionizing radiation is used for penetrating the tumor tissue, causing its the death and eliminating also the cancerous cells surrounding the target. When per- formed,...
| Autor: | |
|---|---|
| Tipo de recurso: | tesis de maestría |
| Fecha de publicación: | 2024 |
| País: | España |
| Institución: | Universitat Politècnica de Catalunya (UPC) |
| Repositorio: | UPCommons. Portal del coneixement obert de la UPC |
| Idioma: | inglés |
| OAI Identifier: | oai:upcommons.upc.edu:2117/412322 |
| Acceso en línea: | https://hdl.handle.net/2117/412322 |
| Access Level: | acceso abierto |
| Palabra clave: | Radiation--Dosage Radiotherapy Radiació--Dosificació Radioteràpia Àrees temàtiques de la UPC::Ciències de la salut::Medicina |
| Sumario: | Radiation therapy involves delivering a high dose (energy of absorbed radiation per unit mass) to a target volume within the patient. Ionizing radiation is used for penetrating the tumor tissue, causing its the death and eliminating also the cancerous cells surrounding the target. When per- formed, the aim is to minimize the impact on healthy organs by reducing the absorbed doses in their tissues. In the case of external radiation therapy, this is achieved using particle accelerators that target the affected area and direct the radiation using collimators. Before radiation therapy treatment can be administered to the patient, a specific quality control process must be conducted to ensure that the accelerator behaves appropriately according to a designed plan, from which the dose distribution to be administered to the patient’s tissues has been calculated. In addition to verifying critical design parameters of the radiotherapy plan for the accelerator, measurements are taken on phantoms with detectors to verify that the admin- istered dose distribution is within acceptable tolerances. When tumors are small, the volumes that need to receive high doses are small as well, thus requiring the use of radiation beams with very small open collimator apertures. This results in the formation of small radiation fields, which present challenges for measurement, as precision dose delivery to the target is desired and they exhibit dose profiles with very abrupt changes. Therefore, detectors of small volume concentrated in a very small region are required. In this master’s thesis, the behavior of two measurement devices, the SRS MapCHECK and the ArcCHECK (both from Sun Nuclear), has been studied. These devices feature semiconductor detectors and have been specifically designed to perform dose distribution measurements in pre-treatment verifications. The study was conducted by evaluating the gamma passing rates in three scenarios using the SRS MapCHECK and GAFChromic EBT-XD radiographic films (to validate the former) in the StereoPHAN phantom, as well as the ArcCHECK. Initially, square static fields ranging from 0.5 to 4 cm were irradiated using 6MV, 6MV FFF, and 10MV FFF beam energies. Subsequently, pre-treatment verifications were conducted for lung (SBRT) and brain (HSRT) stereotactic plans with target volumes having equivalent spherical diameters ranging from 3 to 1 cm. The VMAT technique was employed to deliver the radiation, which involves modulating the collimator throughout the continuous rotation of the accelerator arm. Unlike the SBRT plans, the HSRT plans were highly modulated and involved significant couch rotations. Finally, sensitivity was tested using the SEAFARER [1] methodology in a spinal SBRT plan. The results showed that the SRS MapCHECK was capable of accurately measuring fields uti- lizing VMAT techniques over volumes with equivalent diameters equal to or greater than 1.0 cm. However, the ArcCHECK encountered greater challenges in measuring all fields, showing lower sensitivity in detecting errors in radiotherapy machines with small fields. Additionally, it did not precisely measured dose distributions for equivalent diameters less than 2.0 cm, or 3.0 cm if the field was highly modulated. |
|---|