Dosimetric and qualitative analysis of kinetic properties of millennium 80 multileaf collimator system for dynamic intensity modulated radiotherapy treatments.

The aim of this paper is to analyze the positional accuracy, kinetic properties of the dynamic multileaf collimator (MLC) and dosimetric evaluation of fractional dose delivery for the intensity modulated radiotherapy (IMRT) for step and shoot and sliding window (dynamic) techniques of Varian multileaf collimator millennium 80. Various quality assurance tests such as accuracy in leaf positioning and speed, stability of dynamic MLC output, inter and intra leaf transmission, dosimetric leaf separation and multiple carriage field verification were performed. Evaluation of standard field patterns as pyramid, peaks, wedge, chair, garden fence test, picket fence test and sweeping gap output was done. Patient dose quality assurance procedure consists of an absolute dose measurement for all fields at 5 cm depth on solid water phantom using 0.6 cc water proof ion chamber and relative dose verification using Kodak EDR-2 films for all treatment fields along transverse and coronal direction using IMRT phantom. The relative dose verification was performed using Omni Pro IMRT film verification software. The tests performed showed acceptable results for commissioning the millennium 80 MLC and Clinac DHX for dynamic and step and shoot IMRT treatments.

Analytical approach to estimate normal tissue complication probability using best fit of normal tissue tolerance doses into the NTCP equation of the linear quadratic model.

AIMS AND OBJECTIVES: Aims and objectives of this study are to get the best fit of the normal tissue tolerance doses to the NTCP model of the linear quadratic model. METHODS AND MATERIALS: To compute the NTCP, the modified form of the Poisson cell kill model of NTCP, based on linear-quadratic model, is used. The model has been applied to compute the parameters of the NTCP model using clinical tolerance doses of various normal tissues / organs extracted from published reports of various authors. The normal tissue tolerance doses are calculated for partial volumes of the organs using the values of above-said parameters for published data on normal tissue tolerance doses. In this article, a graphical representation of the computed NTCP for bladder, brain, heart and rectum is presented. RESULTS AND CONCLUSION: A fairly good correspondence is found between the curves of 2 sets of data for brain, heart and rectum. Hence the model may, therefore, be used to interpolate clinical data to provide an estimate of NTCP for these organs for any altered fractionated treatment schedule.