Effects of Interfractional Motion and Anatomic Changes on Proton Therapy Dose Distribution in Lung Cancer

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 endinspiration 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.

Advances in radiotherapy techniques and delivery for non-small cell lung cancer: benefits of intensity-modulated radiation therapy, proton therapy, and stereotactic body radiation therapy

“…These uncertainties are highlighted in lung cancers (101)(102)(103)(104). In particular, several studies have demonstrated the heightened sensitivity of IMPT to changes in heterogeneity and motion interplay effects as compared with PS-PT (105)(106)(107)(108)(109).…”

Adaptive Radiotherapy for Lung Cancer Using Uniform Scanning Proton Beams

“…Hui et al found that the effects of inter-fractional motion and anatomic change could lead to a result of up to 8% reduction of the CTV coverage, a mean 4% dose increase of the volume of the contralateral lung receiving at least 5 CGE, and a mean 4.4 CGE increase in spinal cord maximum dose [20]. Koey et al reported that without adaptive planning, target coverage could be dropped to below 60% compared with adaptive planning for some lung cancer case undergoing proton therapy [21].…”

Quantitative assessment of anatomical change using a virtual proton depth radiograph for adaptive head and neck proton therapy

“…Some examples of these changes include patient weight change, tumor response, patient setup variations, and variations in normal tissue filling and location. The impact on dose distribution arising from anatomic changes may be more pronounced in proton therapy compared to photon therapy, (1) thus it is necessary to find a quick way to identify and quantify these changes and integrate them into the image guidance or adaptive therapy workflow during proton therapy.…”