Abstract
Purpose: 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 and Materials: 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.
Original language | English (US) |
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Pages (from-to) | 1385-1395 |
Number of pages | 11 |
Journal | International Journal of Radiation Oncology Biology Physics |
Volume | 72 |
Issue number | 5 |
DOIs | |
State | Published - Dec 1 2008 |
Keywords
- 4D CT
- Adaptive radiotherapy
- Intensity-modulated radiation therapy
- Lung cancer
- Proton therapy
ASJC Scopus subject areas
- Radiation
- Oncology
- Radiology Nuclear Medicine and imaging
- Cancer Research