Pretreatment dose verification in volumetric modulated arc therapy using liquid ionization chamber

Abstract

Purpose: The purpose of the present study was to evaluate the practicability of liquid ionization chamber (LIC) for pretreatment dose verification of the advanced radiotherapy techniques such as volumetric modulated arc therapy (VMAT). Materials and Methods: The dosimetric characteristics of LIC such as repeatability, sensitivity, monitor unit linearity, dose rate dependence, angular dependence, voltage-current response, and output factors were investigated in 6 MV therapeutic X-ray beams. The LIC was cross-calibrated against 0.125-cc air-filled thimble ionization chamber. A dedicated dosimetry insert made up of Perspex to incorporate the LIC at proper location in the intensity-modulated radiation therapy thorax phantom was locally fabricated. The collection efficiency and ion recombination correction factor was determined using the two-dose rate method. Pretreatment dose verification measurement of VMAT treatment plans were carried out using the liquid ionization chamber as well as small volume (0.125 cc) air-filled thimble ionization chamber. The measured dose values by the two dosimeters and TPS calculated dose at a given point were compared. Results: The relative percentage differences between the TPS calculated and measured doses were within ± 1.57% for LIC and ± 2.21% for 0.125 cc ionization chamber, respectively. Conclusions: The measured dose values by the two dosimeters and TPS calculated dose at a given point were found comparable suggesting that the LIC could be a good choice of dosimeter for pretreatment dose verification in VMAT.

Dosimetry audit in advanced radiotherapy using in-house developed anthropomorphic head & neck phantom

“…Radiotherapy is one of the major modalities for cancer treatment, along with surgery and chemotherapy. Advanced radiotherapy techniques, such as Intensity Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT), offer the remarkable ability to precisely deliver concentrated doses to tumors while minimizing radiation exposure to critical organs at risk (OARs) and normal tissue [1]. This attribute proves particularly valuable in treating complex clinical sites like the head and neck (H&N), where sensitive structures like parotid glands, spinal cord, and eyes are situated in close proximity to the tumor [2].…”

“…The materials used for fabrication must closely resemble human tissue in terms of scattering and attenuation. Although air-filled ionization chambers, electronic portal imaging devices, ion chamber arrays, and liquid ion chambers are commonly employed for pre-treatment dose verification [10], remote dosimetry QAu programs typically favor passive dosimeters such as thermoluminescent dosimeters (TLDs) and radiochromic films [11]. Thus, the phantom should be designed to accommodate these dosimeters within the planning target volume (PTV) and OARs.…”