ESTRO 2023 - Abstract Book

S1431

Digital Posters

ESTRO 2023

Cyberknife plans with the RayStation (RS) 12A TPS for all collimator and tracking mode combinations (static and dynamic with respiratory) and to compare the results to results from the Accuray Precision TPS v3.3.1.0. Materials and Methods E2E plans were prepared in RS and Precision according to the Cyberknife manufacturer’s guidelines. The same reference images of dedicated phantoms containing EBT3 Gafchromic films were used to prepare the plans in the two TPS. In Precision, an isocentric technique was used for all collimators (manufacturer recommendation), and in RS an isocentric technique was used for MLC plans and a non-isocentric technique for cones and iris (isocentric technique not available for cones and iris in RS). Plans consisted of a concentric dose distribution around a ball target (centered on the films in the phantom) with prescribed dose 4.2 Gy to the 70 % (+/- 5%) isodose line. In Precision, final dose was calculated with the Ray Tracing algorithm for iris and cone collimators, and with finite- pencil beam with lateral scaling for MLC. In RS, final dose was calculated using the collapsed cone algorithm for all collimators. Treatment was delivered to the phantom with the appropriate tracking mode after setup using the imaging system. Tests were performed at the same time for the plans from both TPS. Films were analyzed using the Accuray E2E film analysis software v4.0 with the threshold for the analysis set to the isodose line surrounding the ball (70% +/- 5%). The targeting error on each axis and the radial total error were reported. Results For all combinations of collimators and tracking modes, the RS results were within the manufacturer’s recommended tolerance (< 0.95 mm for static targets; < 1.5 mm for moving targets). Precision and RS E2E test results were equivalent within the uncertainty of the method (uncertainty 0.30 mm, see Table 1).

Conclusion This study shows that RS can be used to generate E2E plans for Cyberknife with equivalent results to plans from the Precision TPS. An important outcome of this work is that E2E test results from RS plans can be used as input for the DeltaMan correction that is used to fine-tune the robotic targeting accuracy, and which must be done during Cyberknife commissioning and after robot remastering. For both TPS, the plans used for E2E tests must be prepared according to the manufacturer’s guidelines.

PO-1717 Increased clinical utility of MC secondary dose calculation vs state-of-the-art analytical algorithm

M. Linaa 1 , D. Sloth Møller 1 , M. Alber 2 , S. Nyberg Thomsen 3 , L. Hoffmann 1

1 Aarhus University Hospital, Department of Oncology, Aarhus, Denmark; 2 Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany, Germany; 3 Aarhus University, Dept. of Clinical Medicine, Faculty of Health Science, Aarhus, Denmark Purpose or Objective Independent secondary dose calculation (ISDC) is becoming an essential element of patient-specific QA. Here, we explore the question whether the increased accuracy of a Monte-Carlo based system with customized beam models translates into a clinical benefit compared to a Convolution-Superposition algorithm with generic beam models. Materials and Methods For a set of 95 consecutive patients grouped into 19 case classes, treatment plans were re-calculated with SciMoCa v1.5.2 (Radialogica, St. Louis, USA) and Mobius v3.1(Varian, Sunnyvale, USA) and subsequently analysed with various Gamma and DVH criteria. The treatment planning system was Eclipse v15.6 (Varian, Sunnyvale, USA) using the Acuros algorithm. In order to increase sensitivity of ISDC, the strictest criteria that still produced acceptable levels of false positives were identified. Failing treatment plans were analysed by various modulation complexity measures and for other sources of disagreement to the TPS.

Results