Lung dose for minimally moving thoracic lesions treated with respiration gating.
OBJECTIVE
To evaluate incidental doses to benign lung tissue for patients with minimally moving lung lesions treated with respiratory gating.


METHODS
Seventeen lung patient plans were studied retrospectively. Tumor motion was less than 5 mm in all cases. For each patient, mid-ventilation (MidVen) and mid-inhalation (MidInh) breathing phases were reconstructed. The MidInh phase was centered on the end-of-inhale (EOI) phase within a 30% gating window. Planning target volumes, heart, and spinal cord were delineated on the MidVen phase and transferred to the MidInh phase. Lungs were contoured separately on each phase. Intensity-modulated radiotherapy plans were generated on the MidVen phases. The plans were transferred to the MidInh phase, and doses were recomputed. The evaluation metric was based on dose indices, volume indices, generalized equivalent uniform doses, and mass indices for targets and critical structures. Statistical tests were used to establish the significance of the differences between the reference (MidVen) and compared (MidInh) dose distributions.


RESULTS
Statistical tests demonstrated that the indices evaluated for targets, cord, and heart differed by within 2.3%. The index differences in the lungs, however, are in excess of 6%, indicating the potentially achievable lung sparing and/or dose escalation.


CONCLUSIONS
Respiratory gating is a clinical option for patients with minimally moving lung lesions treated at EOI. Gating will be more beneficial for larger tumors, since dose escalation in those cases will result in a larger increase in the tumor control probability.
Mihaylov
Ivaylo B
IB
Department of Radiation Oncology, University of Arkansas for Medical Sciences, Little Rock, Arkansas 72205, USA. ibmihaylov@uams.edu
Fatyga
Mirek
M
Moros
Eduardo G
EG
Penagaricano
Jose
J
Lerma
Fritz A
FA
D045853:Exhalation; D056973:Four-Dimensional Computed Tomography / Q000379:methods; D006321:Heart / Q000528:radiation effects; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000528:radiation effects; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D009068:Movement; D011832:Radiation Injuries / Q000517:prevention & control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*; D012189:Retrospective Studies; D013116:Spinal Cord / Q000528:radiation effects