Lung Cancer.pdf

144 R. Komaki
morbid conditions prevent aggressive treatment. Adjuvant chemotherapy
in addition to radiation therapy in this population has not been shown to
improve outcomes because patients’ comorbid conditions interfere with
long-term assessment of treatment efficacy.
Radiation therapy is usually delivered with 6- to 18-MV photons. Since
these patients have very poor lung function, the margins around the gross
tumor volume (GTV) should be minimal to avoid pulmonary complications
after completion of radiation therapy. After treatment planning with contrast
material and respiratory gating, the contour of the GTV is drawn. The
clinical target volume (CTV) is drawn at 5 mm outside the GTV for squamous
cell carcinoma and at 8 mm outside the GTV for adenocarcinoma to
ensure coverage of subclinical disease extension. The gating for respiration
motion reduces the planning target volume (PTV), which encompasses the
CTV plus a margin around it. Usually respiratory gating reduces the PTV
from 15 to 20 mm beyond the CTV down to about 5 mm beyond the CTV. If
a lesion is attached to the vertebral body or located at the apex of the lung,
gating is not necessary since the lesion usually does not move beyond 10 mm
with respiration (Figure 8–1). Dose and volume constraints differ depending
on the normal organ tissue surrounding the tumor. If respiratory gating is not
done because of unpredictable respiration patterns, the motion of the tumor
has to be checked under fluoroscopy, and we must take much larger mar-
Figure 8–1. Radiation therapy target volumes in an 80-year-old man with a T1 lesion
in the right lower lobe, severe asthma, and chronic obstructive pulmonary
disease with FEV 1 of 35%. GTV, gross tumor volume; CTV, clinical target volume;
PTV, planning target volume. No respiratory gating was used.