Reproducibility of the patient’s extremities positioning in the total marrow irradiation treatment
Simone Leopoldo Antonetti,
Italy
MO-0790
Abstract
Reproducibility of the patient’s extremities positioning in the total marrow irradiation treatment
Authors: Simone Leopoldo Antonetti1,2, Nicola Lambri1,3, Damiano Dei1,3, Giacomo Reggiori3, Ciro Franzese1,3, Stefano Tomatis3, Pierina Navarria3, Carmela Galdieri3, Marta Scorsetti1,3, Pietro Mancosu3
1Humanitas University, Department of Biomedical Sciences, Pieve Emanuele-Milan, Italy; 2Alessandria Hospital, Department of Oncologic Radiotherapy, Alessandria, Italy; 3IRCCS Humanitas Research Hospital, Radiotherapy and Radiosurgery Department, Rozzano-Milan, Italy
Show Affiliations
Hide Affiliations
Purpose or Objective
Total Marrow Irradiation (TMI) is an intensity modulated technique, evolution of TBI, aiming to irradiate the bones while sparing the neighboring healthy tissues. TMI delivery requires more time than standard RT treatments as the patient's entire body is treated. Therefore, the patient immobilization system is essential for an accurate position reproducibility, especially for the extremities, which, through the joints, could experience large movements. In this work, the reproducibility of TMI patients’ extremities was evaluated to find the best positioning and reduce unwanted movements which are not accounted for during treatment.
Material and Methods
88 TMI patients (2013-22) treated with VMAT were analyzed. Patients were positioned on a modular immobilization system with three thermoplastic masks (head-shoulders, thorax-abdomen, and lower-extremities). During treatment, a cone beam computed tomography (CBCT) was performed for each isocenter (7-9 to cover the whole body) to best reposition the patient. All CBCTs were evaluated considering: (i) the CBCT-CT shift that best matched the two series; (ii) the extremities residual shift which would still be needed after the online matching to reposition the patient’s extremities in the original simulated position; (iii) the CBCT-CT agreement on the extremities using a qualitative index (range 1-5). Patients were subdivided according to the extremities immobilization methods: (i) arms either leaning on the frame to maximize patient comfort, or above the body to minimize the lateral field of view and facilitate the plan optimization; (ii) lower extremities, w/ or w/o a personal cushion for feet positioning (cushions were used when discarded from other cranial treatments – figure 1). The Mann-Whitney test was considered (p<0.05 significant).
Results
685 CBCT were analyzed (>7000 features). The overall mean online shift was 5±3 mm. No significant differences were found between the qualitative assessment and the online shift. Four CBCT/CT cases were reported in figure 2. Only 1.4% of cases qualitatively ranked <3. The mean qualitative evaluation improved over the years, from 3.6 in 2013 to 4.5 in 2019-22. Only 0.6% of cases had part of bones outside the PTV (note that CTV-PTV margin was 10 mm for the bones within the extremities). Arms leaning on the frame showed significant better agreement than arms suspended (6±5 mm vs. 9±5 mm, p=0.04). The use of a personal cushion to fix the feet significantly improved the residual agreement than without cushions (4±4 mm vs. 8±5 mm, p<0.01).
Conclusion
The analysis of retrospective CBCTs allowed to evaluate which immobilization procedure is best suited for TMI patient setup and to optimize the procedure. Thanks to this study, all future patients will be positioned with arms leaning on the frame, and feet immobilized with a personal cushion. Thus, the role and experience of the RTT in TMI patient setup is fundamental.
This work was supported by grant GR-2019-12370739.