Effect of atelectasis changes on tissue mass and dose during lung radiotherapy

• Published in: Medical physics (Lancaster) Vol. 43; no. 11; pp. 6109 - 6117
• Main Authors: Guy, Christopher L., Weiss, Elisabeth, Jan, Nuzhat, Reshko, Leonid B., Christensen, Gary E., Hugo, Geoffrey D.
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-11-2016
• Subjects: atelectasis; Biological material, e.g. blood, urine; Haemocytometers; bone; cancer; Carcinoma, Non-Small-Cell Lung - complications; Carcinoma, Non-Small-Cell Lung - diagnostic imaging; Carcinoma, Non-Small-Cell Lung - pathology; Carcinoma, Non-Small-Cell Lung - radiotherapy; cellular biophysics; Computed tomography; Computerised tomographs; computerised tomography; Digital computing or data processing equipment or methods, specially adapted for specific applications; dosimetry; Dosimetry/exposure assessment; Heart; Humans; image analysis; Image data processing or generation, in general; Image registration; lung; lung cancer; Lung Neoplasms - complications; Lung Neoplasms - diagnostic imaging; Lung Neoplasms - pathology; Lung Neoplasms - radiotherapy; Lungs; medical image processing; Medical imaging; Organs at Risk - radiation effects; Pulmonary Atelectasis - complications; QUANTITATIVE IMAGING AND IMAGE PROCESSING; Radiation Dosage; radiation therapy; Radiotherapy Dosage; Radiotherapy Planning, Computer-Assisted; Therapeutic applications, including brachytherapy; tissue characterization; Tissues; Tomography, Spiral Computed; Tumor Burden - radiation effects; lung cancer; lung; tissue characterization; atelectasis; image analysis
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4965807

Purpose:
To characterize mass and density changes of lung parenchyma in
non-small cell lung
cancer
(NSCLC)
patients following midtreatment resolution of atelectasis and to quantify the
impact this large geometric change has on normal tissue
dose.
Methods:
Baseline and midtreatment CT
images and contours were obtained for 18 NSCLC patients with
atelectasis. Patients were classified based on atelectasis volume reduction
between the two scans as having either full, partial, or no resolution. Relative
mass and density changes from baseline to midtreatment were calculated based on
voxel intensity and volume for each lung lobe. Patients also had clinical treatment
plans available which were used to assess changes in normal tissue
dose
constraints from baseline to midtreatment. The midtreatment image was
rigidly aligned with the baseline scan in two ways: (1) bony anatomy and (2)
carina. Treatment parameters (beam apertures, weights, angles, monitor units,
etc.) were transferred to each image. Then, dose was recalculated.
Typical IMRT dose constraints were evaluated on all images, and the
changes from baseline to each midtreatment image were
investigated.
Results:
Atelectatic lobes experienced mean (stdev) mass changes of −2.8% (36.6%), −24.4%
(33.0%), and −9.2% (17.5%) and density changes of −66.0% (6.4%), −25.6% (13.6%),
and −17.0% (21.1%) for full, partial, and no resolution, respectively. Means
(stdev) of dose changes to spinal cord D
max,
esophagus D
mean, and lungs
D
mean were 0.67 (2.99), 0.99 (2.69), and 0.50 Gy (2.05
Gy), respectively, for bone alignment and 0.14 (1.80), 0.77 (2.95), and 0.06 Gy
(1.71 Gy) for carina alignment. Dose increases with bone alignment up to 10.93,
7.92, and 5.69 Gy were found for maximum spinal cord, mean esophagus, and mean
lung
doses,
respectively, with carina alignment yielding similar values. 44% and 22% of
patients had at least one metric change by at least 5 Gy (dose metrics) or 5%
(volume metrics) for bone and carina alignments, respectively. Investigation of
GTV coverage showed mean (stdev) changes in VRx
,
D
max, and D
min of −5.5%
(13.5%), 2.5% (4.2%), and 0.8% (8.9%), respectively, for bone alignment with
similar results for carina alignment.
Conclusions:
Resolution of atelectasis caused mass and density decreases, on average, and
introduced substantial changes in normal tissue
dose
metrics in a subset of the patient cohort.