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Evidence regarding radiation-induced lymphopenia and its negative impact on oncological outcome is incrementing. Therefore, the aim of this study is to evaluate the feasibility of lymphocyte-rich organs at risk (LOAR) sparing in pelvic irradiation for localized prostate cancer and to estimate its impact on the effective dose to circulating immune cells (EDIC).Twenty patients with pelvic nodal and prostate or prostate bed irradiation were included. The following bone marrow (BM) structures were delineated as LOARs using semi-automatic segmentation: lumbosacral spine (Ls-BM), ilium (Il-BM), lower pelvis (Lp-BM), and the combined whole-pelvis (Wp-BM). Twenty new lymphocyte sparing treatment plans (LS plans) were calculated, optimizing doses to LOARs while maintaining strict coverage of the targets and respecting standard OARs dose constraints. Finally, we elaborated an EDIC calculation model for pelvic irradiation.LS plans showed a statistically significant dose decrease for LOAR compared to standard of care plans without compromising target coverage nor classic OAR dose constraints: in prostate plans, the V40Gy for Ls-BM, Il-BM, and Lp-BM was decreased by 23 %, 36 %, 52 % respectively. For prostate bed plans, the V40Gy for Ls-BM, Il-BM, and Lp-BM was decreased by 25 %, 59 %, 56 %, respectively. For Wp-BM, the V10Gy, V20Gy, and Dmean have been decreased by 3 %, 14 %, 15 %, and by 5 %, 15 %, 17 %, respectively for prostate and prostate bed plans. A statistically significant decrease in EDIC was seen for LS plans in both groups.We successfully demonstrated the feasability of lympocyte-sparing treatment planning in pelvic irradiation, also proposing a model for EDIC calculation.

The study aims to investigate qualitatively how Radiation Therapist IGRT specialists (RTT spIGRTs) experience their role and whether they have an impact on the treatment delivery.Eleven RTTs, i.e. six RTT spIGRTs and five RTTs not specialised in IGRT (RTTs noIGRT) were interviewed during October and November 2020. RTTs noIGRT having knowledge of the daily practice before and after the creation of this RTT spIGRT role, served as control group capable of weighing its impact on the work environment. A qualitative method using face-to-face semi-structured questionnaires was used. Interviews lasted approximately 10-20 min, and were after coded and analysed for thematic content.Five themes and twelve sub-themes were drawn from the analysis. RTT spIGRTs experience their role positively, despite the limited role perception and different work experiences. The implemented role increased autonomy and facilitated decision-making and Radiotherapy (RT) treatment delivery.Interviewees considered the new role useful to very useful. The raised concerns are related to a bigger role involvement and improvement, with focus on visibility, regular meetings and training. Interviewees considered the RTT spIGRT role to have an influence on the treatment delivery when properly carried out.RTT spIGRTs experience their role positively. Their knowledge confidence seems to rely on the training received. The RTT spIGRT role is perceived to have a positive influence on the treatment delivery. Continuous follow up and training were amongst the suggested solutions to improve the RTT spIGRT's role. This study stresses the urgent need for a legal framework to provide formal RTT training and continuous education in order to increase RT treatment quality.