Improvement in IMRT dose calculation with penumbral corrected AAA algorithm using film dosimetry

Arvind K. Shukla; Sanjeev Kumar; I.S. Sandhu; Arun S. Oinam; Gaurav Trivedi

Volume : II, Issue : XII, December - 2013

Improvement in IMRT dose calculation with penumbral corrected AAA algorithm using film dosimetry

Arvind K. Shukla, Sanjeev Kumar, I. S. Sandhu, Arun S. Oinam, Gaurav Trivedi

Abstract :

Background. ?e accuracy of dose calculation by any treatment planning system for linear accelerator based intensity modulated radiation therapy (IMRT) has always been a concern in radiotherapy. ?e commissioning data taken with standard ion chamber oaden the measured beam penumae leads to inaccuracy in IMRT planning. To achieve good results, a radiation detector with small volume and high spatial resolution has to be used for penuma measurements. Materials and methods. ?e penuma measurements at several depth and field sizes were performed in water phantom and solid water phantom with 0.13cc ionization chamber and radiographic films, respectively. ?e IMRT dose calculations were done with an anisotropic analytical algorithm (AAA) using commissioning data taken with and without the use of film dosimetry. ?e accuracy of these calculations was investigated from the two highly modulated test patterns constructed using Eclipse treatment planning system. Results. ?e widths of 80%–20% penumae showed increasing trend with increase in the depth of phantom and nearly independent from field sizes except for smaller fields. ?e highly modulated test patterns exhibit good agreement between the AAA–Film model calculated and measured dose at both 10 cm and 20 cm depths. However, AAA–IC model calculated are significantly lower than measurements at local maxima and higher than measurements at local minima. Conclusions. ?ese results clearly affirms that accurately measuring of beam penumae improves the accuracy of dose distributions calculated by treatment planning system and it is important when commissioning the IMRT.