ESTRO 38 Abstract book

S1104 ESTRO 38

data from protocol files, Monaco plan files, dicom image files, and the Mosaiq R&V system to confirm that settings are consistent and correct. The two parts proceed in parallel but take different times to complete. The end of phase 1 is declared when the plan is checked for possible errors by the C++ arm of the tool. The checker will also enter the results of manual checks such as checking the external contour. After succeeding in phase 1 of checking, the patient is re-imaged to confirm alignment while phase 2 of checking continues. The end of phase 2 is defined when the RayStation script has verified the plan parameters and the independent dose assessment has been checked. The plan is then approved in Monaco and transferred to Mosaiq. Finally the tool queries Mosaiq to confirm correct data transfer and a report is automatically added to the patient treatment record. Results The decision support tool is in routine clinical use for all treatments on the MR-Linac. It completes 56 separate tests on the plan parameters in phase 1 and 41 of those tests are duplicated in phase 2 (see table for example tests). Phase 1 of the checking process completes in an average of 3:38 (minutes:seconds) (+/- 0:57 sd) and phase 2 in an average of 6:59 (+/- 0:55 sd). As phase 2 of the checking process completes in parallel with re-imaging this does not limit the overall treatment time. The timing of the treatment is then extended by the time taken to complete phase 1 3:38 relative to a treatment without any checking procedure.

Purpose or Objective Reproducible patient positioning and image guidance are crucial aspects for effective particle therapy. Proper immobilization of patients with limb-extremities tumors can be challenging and existing guidelines on this topic are not univocal. The aim of this study is to analyze positional interfraction reproducibility of limb-extremities when multiple combinations of immobilization devices are used in particle therapy. Material and Methods Data of 12 patients treated at our institute between 2014 and 2017 were retrospectively recorded. Patient, treatment and setup data are enlisted in Table 1. Table 1. Patient characteristics, treatment data and details on patient setup and immobilization devices used. *NA= not available

All patients were immobilized using multiple combinations of immobilization devices: personalized AccuForm TM cushions, thermoplastic mask hooked on an indexed plate plus, when needed, either foot or ankle rest or head support. Tattoos setup points were drawn on patient skin to provide a reference for daily positioning. Before treatment, patients were first aligned according to the skin tattoos using localization laser. Daily orthogonal x-ray images were acquired prior irradiation and patient setup correction vectors were assessed by 2D-3D image registration. The correction of the set-up errors was performed using a 6-degree robotic positioning system. Sperman’s correlation coefficient was used to investigate correlation between patient data and correction vector. Analysis of variance (ANOVA) was performed to investigate the 3D correction vector across patients and treatment site (lower and upper limbs). Results A total of 156 treatment fractions were analyzed. The distribution of interfraction correction vectors is shown in Figure 1 for each patient (P1, P2, .., P12) and for the whole population. Median (interquartile range) correction vector over all patients was -0.6 (4.1) mm in latero-lateral direction, 1.2 (5.0) mm in cranio-caudal direction, -3.0 (4.8) mm in antero-posterior while rotations around the above mentioned axis were -0.2 (1.0)°, 0.0 (0.8)°, 0.0 (0.7)° respectively.

Conclusion Incorporating a decision support system into the clinical online adaptive workflow for MR Linac patients is feasible and effective. It adds confidence that the treatment is safe and optimal with a minimal increase in treatment time. EP-2015 Interfraction setup error using multiple immobilization devices for limb-extremity particle therapy R. Ricotti 1 , B. Tagaste 1 , A. Pella 2 , G. Fontana 3 , G. Elisei 1 , S. Tampellini 4 , M. Ciocca 5 , F. Valvo 6 , G. Baroni 7,8 1 Centro Nazionale di Adroterapia Oncologica CNAO, Clinical Department- Bioengineering Unit, Pavia, Italy ; 2 Centro Nazionale di Adroterapia Oncologica CNAO, Clinical Department- Bioenginnering Unit, Pavia, Italy ; 3 Centro Nazionale di Adroterapia Oncologica CNAO, Clinical Department- Bioengineering Unit, Pavia, Italy ; 4 Centro Nazionale di Adroterapia Oncologica CNAO, Clinical Department- RTTs Unit, Pavia, Italy ; 5 Centro Nazionale di Adroterapia Oncologica CNAO, Clinical Department- Medical Physics Unit, Pavia, Italy ; 6 Centro Nazionale di Adroterapia Oncologica CNAO, Clinical Department, Pavia, Italy ; 7 Centro Nazionale di Adroterapia Oncologica CNAO, Clinical Departmen- Bioengineering Unit, Pavia, Italy ; 8 Politecnico di Milano, Department of Electronics Information and Bioengineering, Milano, Italy