Effects of interfractional motion and anatomic changes on proton therapy dose distribution in lung cancer.
OBJECTIVE
Proton doses are sensitive to intra- and interfractional anatomic changes. We analyzed the effects of interfractional anatomic changes in doses to lung tumors treated with proton therapy.


METHODS
Weekly four-dimensional computed tomography (4D-CT) scans were acquired for 8 patients with mobile Stage III non-small cell lung cancer who were actually treated with intensity-modulated photon radiotherapy. A conformal proton therapy passive scattering plan was designed for each patient. Dose distributions were recalculated at end-inspiration and end-expiration breathing phases on each weekly 4D-CT data set using the same plans with alignment based on bone registration.


RESULTS
Clinical target volume (CTV) coverage was compromised (from 99% to 90.9%) in 1 patient because of anatomic changes and motion pattern variation. For the rest of the patients, the mean CTV coverage on the repeated weekly 4D-CT data sets was 98.4%, compared with 99% for the original plans. For all 8 patients, however, a mean 4% increase in the volume of the contralateral lung receiving a dose of at least 5 Gy (V5) and a mean 4.4-Gy increase in the spinal cord maximum dose was observed in the repeated 4D-CT data sets. A strong correlation between the CTV density change resulting from tumor shrinkage or anatomic variations and mean contralateral lung dose was observed.


CONCLUSIONS
Adaptive re-planning during proton therapy may be indicated in selected patients with non-small cell lung cancer. For most patients, however, CTV coverage is adequate if tumor motion is taken into consideration in the original simulation and planning processes.
Hui
Zhouguang
Z
Department of Radiation Phyiscs, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA.
Zhang
Xiaodong
X
Starkschall
George
G
Li
Yupeng
Y
Mohan
Radhe
R
Komaki
Ritsuko
R
Cox
James D
JD
Chang
Joe Y
JY
D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy*; D017709:Fractals; D006801:Humans; D008168:Lung / Q000033:anatomy & histology / Q000528:radiation effects; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology* / Q000532:radiotherapy*; D009367:Neoplasm Staging; D061766:Proton Therapy; D012867:Skin / Q000528:radiation effects; D014057:Tomography, X-Ray Computed; D011522:Protons
D011522:Protons