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Dose calculation accuracy for photon small fields in treatment planning systems with comparison by Monte Carlo simulations

Abazarfard Mojtaba, Azadeh Payam, Mostaar Ahmad

Polish Journal of Medical Physics and Engineering

2021

Vol. 27, Iss. 3

181--190

Purpose: Advanced radiation therapy techniques use small fields in treatment planning and delivery. Small fields have the advantage of more accurate dose delivery, but with the cost of some complications in dosimetry. Different dose calculation algorithms imported in various treatment planning systems (TPSs) which each of them has different accuracy. Monte Carlo (MC) simulation has been reported as one of the accurate methods for calculating dose distribution in radiation therapy. The aim of this study was the evaluation of TPS dose calculation algorithms in small fields against 2 MC codes. Methods: A linac head was simulated in 2 MC codes, MCNPX, and GATE. Then three small fields (0.5×0.5, 1×1 and 1.5×1.5 cm2) were simulated with 2 MC codes, and also these fields were planned with different dose calculation algorithms in Isogray and Monaco TPS. PDDs and lateral dose profiles were extracted and compared between MC simulations and dose calculation algorithms. Results: For 0.5×0.5 cm2 field mean differences in PDDs with MCNPX were 2.28, 4.6, 5.3, and 7.4% and with GATE were -0.29, 2.3, 3 and 5% for CCC, superposition, FFT and Clarkson algorithms respectively. For 1×1 cm2 field mean differences in PDDs with MCNPX were 1.58, 0.6, 1.1 and 1.4% and with GATE were 0.77, 0.1, 0.6 and 0.9% for CCC, superposition, FFT and Clarkson algorithms respectively. For 1.5×1.5 cm2 field mean differences in PDDs with MCNPX were 0.82, 0.4, 0.6 and -0.4% and with GATE were 2.38, 2.5, 2.7 and 1.7% for CCC, superposition, FFT and Clarkson algorithms respectively. Conclusions: Different dose calculation algorithms were evaluated and compared with MC simulation in small fields. Mean differences with MC simulation decreased with the increase of field sizes for all algorithms.

Dozymetria małych pól fotonowych – suplement

Dąbrowski R.

Inżynier i Fizyk Medyczny

2015

Vol. 4, nr 5

279-281

W artykule omówiono nowe fakty w dziedzinie pomiarów dozymetrycznych małych pól. Szczególny nacisk położono na problem perturbacji sygnału w przypadku detektorów półprzewodnikowych. Sformułowano też sugestie dotyczące optymalnej, w chwili obecnej, metody pomiaru wydajności małych pól fotonowych.

The present work provides information on signal perturbation in the case of silicon diodes. Some suggestions are given concerning the optimal methods of output factor measurements for small photon beams.