Dosimetric evaluation of a three-dimensional treatment planning system

Abstract

The computerized treatment planning system plays a major role in radiation therapy in delivering correct radiation dose to the patients within ±5% as recommended by the ICRU. To evaluate the dosimetric performance of the Treatment Planning system (TPS) with three-dimensional dose calculation algorithm using the basic beam data measured for 6 MV X-rays. Eleven numbers of test cases were created according to the Technical Report Series-430 (TRS 430) and are used to evaluate the TPS in a homogeneous water phantom. These cases involve simple field arrangements as well as the presence of a low-density material in the beam to resemble an air in-homogeneity. Absolute dose measurements were performed for the each case with the MU calculation given by the TPS, and the measured dose is compared with the corresponding TPS calculated dose values. The result yields a percentage difference maximum of 2.38% for all simple test cases. For complex test cases in the presence of in-homogeneity, beam modifiers or beam modifiers with asymmetric fields a maximum percentage difference of 5.94% was observed. This study ensures that the dosimetric calculations performed by the TPS are within the accuracy of ±5% which is very much warranted in patient dose delivery. The test procedures are simple, not only during the installation of TPS, but also repeated at periodic intervals.

Evaluation collapsed cone convolution/superposition (CCCS) algorithms in prowess treatment planning system for calculating symmetric and asymmetric field size

“…The comparison between measured and calculated dose made by gamma index method showed that the average difference for asymmetric fields is less than 3%. Except for field size 4 cm × 4 cm, our data compared with previous data from Birgani et al 18 , El-Attar et al 9 , Chegeni and Birgani 19,20 , and Murugan et al 21 Asymmetric collimation dose lead to significant errors (up to approximately 7%) in dose calculations if changes in primary beam intensity and beam quality. 22 It is obvious that the most difference in the isodose curves was found in buildup region and the penumbra region.…”

An institutional experience of quality assurance of a treatment planning system on photon beam

“…Hence, it was decided that for patients involving (skin tumors) build-up region dose calculation, smaller grid size should be used. 20 In the study of the TRS 430 report 1 used by Murugan et al 22 , the result yields were declared to find a max. deviation of 2.38% (tolerance: 2%) for all simple tests and 5.94% (tolerance: 5%) for complex tests in the presence of inhomogeneity, beam modifiers or beam modifiers with asymmetric field.…”

“…A number of authors [20][21][22][23] have implemented dosimetric and non-dosimetric tests of QA procedure into TPS with the guidance of the IAEA TRS 430 report. These authors have reported that the most critical difference occurred for oblique incidence, oblique incidence-off axis, shaped fields and off axis-wedged.…”

Treatment planning validation for symmetric and asymmetric motorized wedged fields

“…The beam profile for the scanned fields were measured at depths of dmax, 5, 10, 20 cm with source to surface distance (SSD) of 100 cm as shown in Figure 1 for field size 20 × 20. Calculations were performed in a phantom created by Elekta precise 3D planning a homogeneous density of 1 g/cm 3 . The dose was calculated for 6 and 15 MV photon beams at each depth.…”

“…1 The radiation dose must be delivered within ±5% of the prescribed dose. 2,3 In computerized treatment planning system TPS, the most important software component is the dose calculation algorithm which is responsible for the precise delivery of dose to target volume, and it may be linked to the calculation of monitor units (MUs). Three-dimensional conformal radiotherapy (3D-CRT) uses certain beam shaping devices in order to confirm the shape of beam to the target area of the patient.…”