Implementation of a program for quality assurance on leaf positioning accuracy using Gafchromic ^® RTQA2 films

Abstract

In radiotherapy treatments the correct dose delivery to the target volume and the consequent conservation of healthy tissues is affected by multileaf collimator (MLC) leaf positioning accuracy and reproducibility, mostly in intensity-modulated radiation therapy (IMRT): For this reason a quality assurance (QA) program is necessary to ensure the best treatment possible to each patient. The aim of this study is the implementation of a method using Gafchromic® RTQA 2 films to perform routine QA on the MLC, both for qualitative and quantitative analysis. A flatbed document scanner (Epson 10000XL) was used in conjunction with radiochromic detector; a scanning protocol was firstly defined to improve readout accuracy. RTQA2 films were irradiated with 6 MV X-rays at different dose levels to obtain calibration curve. To evaluate the leaf positioning accuracy in different conditions, a rhomboidal shape and a field consisting in three rectangular segments were selected. The images quantitative analysis was handled with a program developed in MATLAB to evaluate the differences between expected and measured leaves positions. The reproducibility and global uncertainty of the method were estimated to be equal to 0.5% and 0.6 mm, respectively. Moreover, a qualitative test was performed: A garden picket fence field, consisting in multiple segments 2 × 22 cm2, was realized setting known leaves shifts to test the method sensitivity. The picket fence test shows that the method is able to detect displacements equal to 1 mm. The results suggest that Gafchromic® RTQA2 films represent a reliable tool to perform MLC routine QA.

Report of AAPM Task Group 235 Radiochromic Film Dosimetry: An Update to TG‐55

“…48,61,83,[181][182][183] RCF can be used for patient-specific QA (PSQA) in conformal radiation therapy 170 and routine machine mechanical QA tasks, including coincidence of the light/radiation field, flatness/symmetry of the radiation field, star pattern for gantry, collimator and couch rotations, and MLC leaf positioning accuracy (e.g., picket fence test). [184][185][186][187] The RTQA2 film with a flatbed scanner is also acceptable for measurement of beam dimensions, as in MLC offsets and secondary jaw calibrations within 0.5 mm accuracy. However, RTQA2 is not recommended for any application requiring good absolute calibration.…”

Calibration of Gafchromic XR-RV3 film under interventional radiology conditions

“…[2][3][4] The basis for this is the use of appropriate dosimetry systems and their proper calibration. Among the methods used for dose measurement in clinical practice, radiochromic films are commonly used in radiation therapy for dosimetric verification of treatment plans, [5][6][7]8 whereas in interventional radiology, they are used to assess the surface dose on the patient's skin(peak skin dose). 3,9 This kind of film is also used for instance to improve CT acquisition image processes 10 and to check the distributions of the laser-accelerated proton beams.…”

Evaluation of AutoCAL for electronic portal imaging device-based multi-leaf collimator quality assurance

“…Multiple studies describing different methods for assessing MLC performance have been published [3,[5][6][7][8].…”