Portal dosimetry in radiotherapy repeatability evaluation

Abstract

The accuracy of radiotherapy is the subject of continuous discussion, and dosimetry methods, particularly in dynamic techniques, are being developed. At the same time, many oncology centers develop quality procedures, including pretreatment and online dose verification and proper patient tracking methods. This work aims to present the possibility of using portal dosimetry in the assessment of radiotherapy repeatability. The analysis was conducted on 74 cases treated with dynamic techniques. Transit dosimetry was made for each collision‐free radiation beam. It allowed the comparison of summary fluence maps, obtained for fractions with the corresponding summary maps from all other treatment fractions. For evaluation of the compatibility in the fluence map pairs (6798), the gamma coefficient was calculated. The results were considered in four groups, depending on the used radiotherapy technique: stereotactic fractionated radiotherapy, breath‐hold, free‐breathing, and conventionally fractionated other cases. The chi2 or Fisher's exact test was made depending on the size of the analyzed set and also Mann–Whitney U‐test was used to compare treatment repeatability of different techniques. The aim was to test whether the null hypothesis of error‐free therapy was met. The patient is treated repeatedly if the P‐value in all the fluence maps sets is higher than the level of 0.01. The best compatibility between treatment fractions was obtained for the stereotactic technique. The technique with breath‐holding gave the lowest percentage of compliance of the analyzed fluence pairs. The results indicate that the repeatability of the treatment is associated with the radiotherapy technique. Treated volume location is also an essential factor found in the evaluation of treatment accuracy. The EPID device is a useful tool in assessing the repeatability of radiotherapy. The proposed method of fluence maps comparison also allows us to assess in which therapeutic session the patient was treated differently from the other fractions.

Dose estimation in patients treated with radiotherapy for SARS-COVID disease based on EPID measurement

“…Publications show the possibilities of EPID in dose estimation [3,21]. Based on dynamic techniques [4,7,8], the comparison of fluence maps is an optimal way It can be seen that there are differences between the directional coefficients of the two straight lines and a greater dispersion of the measurement points in clinical conditions of assessing the calculated dose and its real distribution. This comparison is not about one point, but the matrix of points.…”

“…The fluence map obtained with EPID was tested to measure the dose in real time [3][4][5], repeated treatment [6][7][8][9], point dose measurement [10] and dose distribution [11][12][13][14]. Fluence maps were also used to verify the correct operation of the MLC [15][16][17][18] or compatibility with the planned dose distribution [19].…”

The application of gradient dose segmented analysis of in‐vivo EPID images for patients undergoing VMAT in a resource‐constrained environment

“…Although these are useful metrics to quantify the repeatability of treatment fractions, these methods do not provide DVH-specific statistics that relate the delivered dose to the planning target volume (PTV). 6,8,9,[12][13][14] To address this issue, a new analysis technique was introduced as a pre-treatment verification method in a doctoral dissertation that did not require recalculation of EPID-based data to patient dose, or analysis by means of the pass/fail gamma criteria. 15 Recently, Steers et al 16 published their work on applying the gradient dose segmented analysis (GDSA) technique to in-vivo EPID images for dose verification.…”

“…Other commercial approaches allow users to compare first‐fraction EPID transmission images to those of all subsequent fractions by means of applying the usual gamma‐analysis metric. Although these are useful metrics to quantify the repeatability of treatment fractions, these methods do not provide DVH‐specific statistics that relate the delivered dose to the planning target volume (PTV) 6,8,9,12–14 …”

Development of an Electronic Portal Imaging Device Dosimetry Method

“…An electronic portal imaging device (EPID) was originally used for patient setup verification. Due to its large imaging area, fast acquisition speed, high resolution, good linear response, long-term measurement stability, and being mounted on the linac, EPID has been extensively used in IMRT and VMAT quality assurance [ 2 , 3 , 4 , 5 , 6 , 7 ], including pretreatment and in-vivo dose verification. Pretreatment dose verification usually involves the following two approaches: first, the fluence generated by the treatment planning system (TPS) is convolved with the kernel to predict the EPID image; then, the predicted image is compared with the measured EPID image for verification [ 8 , 9 , 10 ].…”