Accuracy of Acuros XB and AAA dose calculation for small fields with reference to RapidArc® stereotactic treatments

• Published in: Medical physics (Lancaster) 2011-11, Vol.38 (11), p.6228-6237
• Main Authors: Fogliata, Antonella, Nicolini, Giorgia, Clivio, Alessandro, Vanetti, Eugenio, Cozzi, Luca
• Format: Article
• Language: English
• Subjects: ACCURACY; ALGORITHMS; ANISOTROPY; cancer; COLLIMATORS; CONFIGURATION; Diamond; DISTANCE; DOSIMETRY; Dosimetry/exposure assessment; Field size; JAW; Linear accelerators; Lungs; Medical treatment planning; MODULATION; Multileaf collimators; NEOPLASMS; Particle beam detectors; PHANTOMS; PHOTON BEAMS; PHOTONS; Photons - therapeutic use; Position sensitive detectors; Radiation Dosage; RADIATION DOSES; RADIATION PROTECTION AND DOSIMETRY; radiation therapy; RADIOLOGY AND NUCLEAR MEDICINE; Radiosurgery - methods; RADIOTHERAPY; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted - methods; SENSITIVITY; Stereotactic radiosurgery; Therapeutic applications, including brachytherapy; TRANSMISSION; WATER
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.3654739

Purpose : To assess the accuracy against measurements of two photon dose calculation algorithms (Acuros XB and the Anisotropic Analytical algorithm AAA) for small fields usable in stereotactic treatments with particular focus on RapidArc®. Methods : Acuros XB and AAA were configured for stereotactic use. Baseline accuracy was assessed on small jaw-collimated open fields for different values for the spot sizes parameter in the beam data: 0.0, 0.5, 1, and 2 mm. Data were calculated with a grid of 1 × 1 mm2. Investigated fields were: 3 × 3, 2 × 2, 1 × 1, and 0.8 × 0.8 cm2 with a 6 MV photon beam generated from a Clinac2100iX (Varian, Palo Alto, CA). Profiles, PDD, and output factors were measured in water with a PTW diamond detector (detector size: 4 mm2, thickness 0.4 mm) and compared to calculations. Four RapidArc test plans were optimized, calculated and delivered with jaw settings J3 × 3, J2 × 2, and J1 × 1 cm2, the last was optimized twice to generate high (H) and low (L) modulation patterns. Each plan consisted of one partial arc (gantry 110° to 250°), and collimator 45°. Dose to isocenter was measured in a PTW Octavius phantom and compared to calculations. 2D measurements were performed by means of portal dosimetry with the GLAaS method developed at authors’ institute. Analysis was performed with gamma pass–fail test with 3% dose difference and 2 mm distance to agreement thresholds. Results : Open square fields: penumbrae from open field profiles were in good agreement with diamond measurements for 1 mm spot size setting for Acuros XB, and between 0.5 and 1 mm for AAA. Maximum MU difference between calculations and measurements was 1.7% for Acuros XB (0.2% for fields greater than 1 × 1 cm2) with 0.5 or 1 mm spot size. Agreement for AAA was within 0.7% (2.8%) for 0.5 (1 mm) spot size. RapidArc plans: doses were evaluated in a 4 mm diameter structure at isocenter and computed values differed from measurements by 0.0, −0.2, 5.5, and −3.4% for Acuros XB calculations (1 mm spot size), and of −0.1, 0.3, 6.7, and −1.2% for AAA, respectively for J3 × 3, J2 × 2, J1 × 1H, J1 × 1L RapidArc plans. Gamma Agreement Index from 2D dose analysis was higher than 95% for J3 × 3 and J2 × 2 plans, being around 80% for J1 × 1 maps. Sensitivity with respect to the dosimetric leaf gap and transmission factor MLC parameters was evaluated in the four RapidArc plans, showing the need to properly set the dosimetric leaf gap for accurate calculations. Conclusions : Acuros XB and A