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Is It Necessary to Account for Organs at Risk Respiratory Induced Motion Effects in Radiotherapy Planning with Tumor Tracking?
M Gilles1*, H Fayad2 , N Boussion3 , O Pradier4 , D Visvikis5 , (1) INSERM UMR 1101 - LaTIM, Brest, France (2) INSERM UMR 1101 - LaTIM, UBO, Brest, France (3) INSERM UMR 1101 - LaTIM, Brest, France (4) CHRU Morvan, Radiotherapy, Brest, France (5) INSERM UMR 1101 - LaTIM, Brest, France
Presentations
SU-E-J-268 Sunday 3:00PM - 6:00PM Room: Exhibit HallPurpose: The objective of this study was to evaluate the necessity to account for the organs at risk (OARs) respiratory induced motion in addition to the tumor displacement when planning a radiotherapy treatment that accounts for tumor motion.
Methods: For 18 lung cancer patients, conformational radiotherapy treatment plans were generated using 3 different CT volumes: the two extreme respiratory phases corresponding to either the full inspiration (plan 1) or expiration (plan 3), as well as a manually deformed phase consisting in full inspiration combined with the full expiration tumor location (plan 2) simulating a tumor tracking plan without addressing OARs motion. Treatment plans were initially created on plan 1 and then transferred to plan 2 and 3 which represent respectively the tumor displacement only and the whole anatomic variations due to breathing. The dose coverage and the dose delivered to the OARs were compared using conformational indexes and generalized equivalent uniform dose.
Results: The worst conformational indexes were obtained for plans with all anatomic deformations (Table 1) with an underestimation of the 95% isodose spreading on healthy tissue compared to plans considering the tumor displacement only. Furthermore, mean doses to the OARs when accounting for all the anatomic changes were always higher than those associated with the tumor displacement only: the mean difference between these two plans was 1±1.37 Gy (maximum of 3.8 Gy) for the heart and 1.4±1.42 Gy (maximum of 4.1 Gy) for the lung in which the tumor was located (Figure 1).
Conclusion: OARs deformations due to breathing motion should be included in the treatment planning in order to avoid unnecessary OARs dose and/or allow for a tumor dose escalation. This is even more important for treatments like stereotactic radiation therapy which necessitates a high precision ballistic and dose control.
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