This study demonstrates that the algorithm can be effectively applied to IMRT scenarios to get fast and case specific beam angle configurations.

In static intensity‐modulated radiation therapy (IMRT), the fundamental factors that determine the quality of a plan are the number of beams and their angles. The objective of this study is to investigate the effect of beam angle optimization (BAO) on the beam number in IMRT. We used six head and neck cases to carry out the study. Basically the methodology uses a parameter called “Beam Intensity Profile Perturbation Score” (BIPPS) to determine the suitable beam angles in IMRT. We used two set of plans in which one set contains plans with equispaced beam configuration starting from beam numbers 3 to 18, and another set contains plans with optimal beam angles chosen using the in‐house BAO algorithm. We used quadratic dose‐based single criteria objective function as a measure of the quality of a plan. The objective function scores obtained for equispaced beam plans and optimal beam angle plans for six head and neck cases were plotted against the beam numbers in a single graphical plot for effective comparison. It is observed that the optimization of beam angles reduces the beam numbers required to produce clinically acceptable dose distribution in IMRT of head and neck tumors. Especially N0.1 (represents the beam number at which the objective function reaches a value of 0.1) is considerably reduced by beam angle optimization in almost all the cases included in the study. We believe that the experimental findings of this study will be helpful in understanding the interplay between beam angle optimization and beam number selection process in IMRT which, in turn, can be used to improve the performance of BAO algorithms and beam number selection process in IMRT.PACS number: 87.55.de

Purpose: A new algorithm for automated determination of Objective Function Parameters (OFPs) in inverse planning is proposed. Method and Materials: While in theory, optimization in inverse planning is a one‐step automatic process, in practice, planner intervention is often required to carry out a multiple trial‐and‐error process where several parameters are sequentially varied until an acceptable compromise is achieved. We propose an algorithm for automated determination of IMRT Objective Function Parameters (OFPs). The algorithm is based on a new approach called “Adapted Dose Prescription (ADP)” wherein the dose prescriptions are automatically tailored to the sensitivity of target and OARs, which immediately results in a treatment plan meeting the clinical goals. The sensitivity of a structure is estimated by calculating the difference between the expected and obtained dose values after the end of an optimization trial. We incorporated the proposed algorithm with Fast Simulated Annealing (FSA) scheme using MATLAB software package to generate Aperture‐based IMRT plans for various complex patient cases. The beam placements, aperture shaping and dose calculations were done using CMS XiO planning system in our clinic. Results: So far, three patients planned using the proposed algorithm has been treated in our clinic. Our observation is that the algorithm automatically fetches a set of OFPs that immediately results in a clinically acceptable dose distribution. This approach significantly reduces the time taken for optimization by reducing the no. of optimization trials, while providing dose distribution that is comparable to that of plans obtained using KonRad inverse planning system. Conclusion: The proposed algorithm facilitates the production of inverse solutions which, without the planner's intervention, precisely satisfy the specified constraints. Moreover, the results demonstrate that the proposed algorithm can be effectively used for clinical applications.

This article is available in open access under creative common attribution-Non-commercial-No Derivatives 4.0 International (cc BY-Nc-ND 4.0) license, allowing to download articles and share them with others as long as they credit the authors and the publisher, but without permission to change them in any way or use them commercially

Purpose: To dosimetrically evaluate beam matching procedure of two similar accelerators using gamma index. Method and Materials: The second accelerator was beam matched with first one using Vendor's acceptance test (ATP) protocol. Depth dose and inline‐crossline profiles were matched within ±1%. In order to quantify the level of agreement between the matched beams we performed a set of measurements including total scatter, collimator scatter, wedge transmission and absolute dose measurement. The ATP specifications are at particular points on the ionization curve for depth dose or profile. Gamma was used to compare planar dose distribution from EDR2 films exposed on both units. For 6MV photon we exposed a film for PDD (10×10cm), beam profile (5,10 and 20cm), a pyramid shape, to compare dosimetric and positional accuracy of MLC a pattern of strips with different MUs at different positions and a diamond shape was exposed. We also exposed a film at tray level to a segmented IMRT field to compare collimator scatter. To account for TPS calculations a film kept in axial plane was exposed to 3DCRT and IMRT plan with actual gantry angles. Absolute dose was measured simultaneously using point chamber. Results: Total scatter, collimator scatter and wedge transmission factors were within ±1%. The absolute dose for 3DCRT and IMRT plan was within ±1% of reference value and within ±3% of TPS value. EDR2 films exposed on both units were analyzed using OmniPro IMRT software. Gamma was calculated for different delta dose and delta distance. The analysis has shown that all these comparisons were in good agreement for delta dose of 2% and delta distance of 2mm. Conclusion: All these tests were done at the commissioning time. We are periodically checking few parameters like PDD, beam profile and MLC accuracy to assure the consistency in beam matching