Author: Nobukazu Fuwa, Masato Horita, Takahiro Kato, Ryo Tanokura, Yuki Tominaga 👨🔬
Affiliation: Medical Co. Hakuhokai, Osaka Proton Therapy Clinic, Central Japan International Medical Center, Department of Radiological Sciences, School of Health Sciences, Fukushima Medical University 🌍
Purpose:
We have installed a new type of scanned proton therapy system (Varian ProBeam 360°TM). This study aimed to evaluate the four different dose calculation algorithms.
Methods:
Sixteen box plans were created using the Eclipse ver. 16.1 and RayStation 10A treatment planning systems, both of which were equipped with and without a 5 cm range shifter (RS). Target volumes were set up 3×3×4, 5×5×6, 10×10×10, and 15×15×10 cm³ at depths of 10, 15, and 20 cm, respectively.Additional plans with RS were created with dimensions of 3×3×5 and 10×10×5 cm³ at depth of 5 cm and 3×3×10 and 10×10×10 cm³ at depth of 10 cm. To validate heterogeneous phantom plan, a 9×9×4 cm3 box plan was created with a cheese phantom with rods of four different materials.Treatment plans were optimized using Eclipse’s Non-Linear Universal Proton Optimizer algorithm, and dose distributions were calculated using Eclipse’s Pencil Beam Convolution (PCS) and AcurosPT (AXPT), as well as RayStation’s Pencil Beam Algorithm (PBA) and Monte Carlo (MC).Dose distributions were measured with 2D-array detector in a solid phantom. Evaluation employed gamma index analysis at 3%/3 mm criteria.
Results:
The average gamma pass rates (γ-passing) of box plans were 100±0.1%, 97.7±3.5%, 85.1±12.5% and 99.85±0.3% for the PCS, AXPT, PBA, and MC, respectively. The γ-passing of heterogeneous phantom plans were 87.6%, 100%, 81.1% and 99.6%. Box plans became over 90% γ-passing except for the PBA because it has arisen deterioration of calculation accuracy due to the nuclear halo. AXPT and MC algorithms were shown more accurate for dose calculations in heterogeneous tissues.
Conclusion:
All algorithm calculations corresponded with the measurements except for the PBA. However, in the case of heterogeneous tissues, deterioration in calculation accuracy was confirmed in PCS.