Comparison of IMRT planning with two-step and one-step optimization: a strategy for improving therapeutic gain and reducing the integral dose

Abstract

The aim of this study was to evaluate the effectiveness and efficiency in inverse IMRT planning of one-step optimization with the step-and-shoot (SS) technique as compared to traditional two-step optimization using the sliding windows (SW) technique. The Pinnacle IMRT TPS allows both one-step and two-step approaches. The same beam setup for five head-and-neck tumor patients and dose-volume constraints were applied for all optimization methods. Two-step plans were produced converting the ideal fluence with or without a smoothing filter into the SW sequence. One-step plans, based on direct machine parameter optimization (DMPO), had the maximum number of segments per beam set at 8, 10, 12, producing a directly deliverable sequence. Moreover, the plans were generated whether a split-beam was used or not. Total monitor units (MUs), overall treatment time, cost function and dose-volume histograms (DVHs) were estimated for each plan. PTV conformality and homogeneity indexes and normal tissue complication probability (NTCP) that are the basis for improving therapeutic gain, as well as non-tumor integral dose (NTID), were evaluated. A two-sided t-test was used to compare quantitative variables. All plans showed similar target coverage. Compared to two-step SW optimization, the DMPO-SS plans resulted in lower MUs (20%), NTID (4%) as well as NTCP values. Differences of about 15-20% in the treatment delivery time were registered. DMPO generates less complex plans with identical PTV coverage, providing lower NTCP and NTID, which is expected to reduce the risk of secondary cancer. It is an effective and efficient method and, if available, it should be favored over the two-step IMRT planning.

An integrated strategy of biological and physical constraints in biological optimization for cervical carcinoma

“…The optimization process was applied by two-step algorithm in the Eclipse planning system [19, 20]. All dose calculations were performed with the anisotropic analytical algorithm (AAA) with a calculation grid of 2.5 mm [21].…”

IsoBED: a tool for automatic calculation of biologically equivalent fractionation schedules in radiotherapy using IMRT with a simultaneous integrated boost (SIB) technique

“…The setup of the IMRT plan was calculated with Pinnacle 8.0 m TPS (Philips Medical Systems, Madison, WI) and based on seven 6 MV photon beam techniques (angles 35, 70, 130, 180, 230, 290 and 330 degrees) [13]. The acceptance criteria of the primary plan had to meet treatment goals (prescribed dose to >95% of the volumes) for all target while keeping the dose of the spinal cord, brain-stem, optic structures (optic nerves, chiasm and lens) and larynx under DV-constrains of sequential and SIB plans (Figure 2).…”

Motion as perturbation. II. Development of the method for dosimetric analysis of motion effects with fixed-gantry IMRT

“…29) structure sets and objectives for multitarget, mock prostate, mock head and neck, and C-shape cases. Direct machine parameter optimization 30 was used. Two plans (head and neck and C-shape) used 9 coplanar equally spaced beams, while the other two had 7 beams, to a total of 32 separate beams.…”