Investigation of dosimetric impact of organ motion in static and dynamic conditions for three stereotactic ablative body radiotherapy techniques: 3D conformal radiotherapy, intensity modulated radiation therapy, and volumetric modulated arc therapy by using presage 3D dosimeters.

AIM: To investigate the use of PRESAGE 3D dosimeters to quantify the dosimetric variation between the static and dynamic conditions of three stereotactic ablative body radiotherapy techniques. MATERIALS AND METHODS: An in-house custom-designed thorax dynamic phantom was designed to simulate the tumor motion in two directions (i.e., superior/inferior (Z-axis) and anterior/posterior (Y-axis)). The PRESAGE dosimeter was attached to the moving arm of the phantom and irradiated in two scenarios (static and dynamic) using three stereotactic ablative body radiotherapy (SABR) techniques: 3D conformal radiotherapy (3D CRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT). RESULTS: The highest differences in the mean volume measurements between the two conditions were noticed in IMRT (0.14 cm3) and 3D CRT (0.13 cm3). The mean volume measurements of the VMAT showed the lowest difference between the static and dynamic conditions of 0.10 cm3. The gamma analysis for 3%, 3-mm criterion showed passing rates of < 1 for 3D CRT, IMRT, and VMAT. CONCLUSION: This study quantify the dosimetric variations which are caused by the tumor motion in lung cases. In the SABR of the lung for QA purposes, this could help in identifying the prescription dose coverage due to tumor movement and correlate with the planned dose using 3D dosimeters like PRESAGE.

Evaluation of dose calculation algorithms using different density materials for in-field and out-of-field conditions.

AIM: The accuracy of the dose calculation is vital in the stereotactic ablative body radiotherapy (SABR) technique to achieve clinically effective dose distribution for better tumor control. Multiple commercial radiotherapy treatment planning systems (TPS) were implemented with different algorithms, such as Acuros XB in Eclipse and Superposition in XiO. The aim of this study is to investigate five different dose calculation algorithms, namely, pencil beam convolution (PBC), Acuros XB, AAA implemented in an Eclipse system, collapsed cone convolution (CCC) algorithm implemented in Mobius3D and superposition algorithms implemented in the XiO system, and then validate the results against measurements using an Institute of Physical Sciences in Medicine (IPSM) phantom with different density materials for in-field and out-of- field conditions. MATERIAL AND METHODS: The IPSM phantom was used to investigate the dose calculation algorithm performances in four different densities (water, lung, ribs, and dense bone) using different beam configurations, including small beam fields utilised in lung SABR. Five commercial algorithms implemented in two TPS (Eclipse and XiO) and one plan check (M3D) system were used for in-field and out-of-field measurement. RESULTS: In the in-field condition, the Acuros XB algorithm had lower mean differences than the measured dose by the IC ranging from -0.46 to 0.24 for all the densities. In the out-of-field condition, the results of eclipse system: AAA, PBC and Acuros XB algorithms demonstrated underdose point's measurements by -40% for all densities except for AAA calculations in lung density (overdosed by 40%). The measured points of the superposition algorithms were overestimated to the actual dose less than 30% in water, lung and dense bone. At the same densities, the CCC algorithms showed relatively the lowest differences in percentage compared to the superposition algorithms. CONCLUSION: Our results showed that the Acuros XB and superposition algorithms are closer to the actual measured dose than AAA, PBC and CCC for majority of the field conditions for water-equivalent, lung, rib and dense bone densities. The CCC algorithm resulted in a better agreement with the measurement of the out-of-field points compared with the other algorithms.