Comparing the dosimetric characteristics of the electron beam from dedicated intraoperative and conventional radiotherapy accelerators.

Mohammad Esmail Akbari,Seyed Rabi Mahdavi,Hamid Reza Mirzaei,Seyed Mahmoud Reza Aghamiri,Hamid Reza Baghani

doi:10.1120/jacmp.v16i2.5017

Abstract

The specific design of the mobile dedicated intraoperative radiotherapy (IORT) accelerators and different electron beam collimation system can change the dosimetric characteristics of electron beam with respect to the conventional accelerators. The aim of this study is to measure and compare the dosimetric characteristics of electron beam produced by intraoperative and conventional radiotherapy accelerators. To this end, percentage depth dose along clinical axis (PDD), transverse dose profile (TDP), and output factor of LIAC IORT and Varian 2100C/D conventional radiotherapy accelerators were measured and compared. TDPs were recorded at depth of maximum dose. The results of this work showed that depths of maximum dose, R90,R50, and RP for LIAC beam are lower than those of Varian beam. Furthermore, for all energies, surface doses related to the LIAC beam are substantially higher than those of Varian beam. The symmetry and flatness of LIAC beam profiles are more desirable compared to the Varian ones. Contrary to Varian accelerator, output factor of LIAC beam substantially increases with a decrease in the size of the applicator. Dosimetric characteristics of beveled IORT applicators along clinical axis were different from those of the flat ones. From these results, it can be concluded that dosimetric characteristics of intraoperative electron beam are substantially different from those of conventional clinical electron beam. The dosimetric characteristics of the LIAC electron beam make it a useful tool for intraoperative radiotherapy purposes.PACS number: 87.56.‐v, 87.56.bd

Highlights

Intraoperative radiation therapy (IORT) is designed to deliver a high single fraction of radiation dose to the patient after surgery and under anesthesia.[1,2,3] There are three different methods to perform this kind of radiotherapy: IOERT, HDR-IORT, and Low KV IORT,(4,5) of which, IOERT is the most popular, because of the desired dose distribution,(6) limited penetration of the electron beam, and treatment time
The presence of high dose per pulse electron beam causes some degree of uncertainty in determination of recombination correction factor of ions formed in the chamber sensitive volume.[12,13,14] This uncertainty is due to the fact that the free electron fraction created in the chamber sensitive volume is not taken into account during determination of recombination correction factor[15] using the two voltage analysis (TVA) method presented by the IAEA TRS-398 and AAPM TG-51 protocols.[16,17] the extended Boag theory and Laitano or Di Martino formalism[18,19]
Two types of collimation systems are employed to collimate the electron beam produced by these mobile radiotherapy machines, namely hard and soft docking system.[5,11] In the first one, the IORT applicator is connected to the machine head, while in the second one, the applicator is fixed to the surgical bed as well as being in contact with the patient, while there is no connection to the accelerator.[20,21] Using this type of applicators and collimation systems can change the physical characteristics of the electron beam

Summary

Introduction

Intraoperative radiation therapy (IORT) is designed to deliver a high single fraction of radiation dose to the patient after surgery and under anesthesia.[1,2,3] There are three different methods to perform this kind of radiotherapy: IOERT, HDR-IORT, and Low KV IORT,(4,5) of which, IOERT is the most popular, because of the desired dose distribution,(6) limited penetration of the electron beam, and treatment time. The most important differences between these mobile dedicated and conventional accelerators are the electron beam collimation system and the type of the applicator used with each of them. The aim of this study is to measure and compare the dosimetric characteristics of the electron beam from IORT and conventional radiotherapy accelerators. To this end, percentage depth dose along clinical axis (PDD), transverse dose profile (TDP), and output factor related to the LIAC (12 MeV model) mobile dedicated accelerator (Sordina SpA, Vicenza, Italy) and the Varian 2100C/D conventional accelerator (Varian Medical Systems, Palo Alto, CA) were measured and compared

Objectives

Methods

Results

Conclusion