Generally, three-dimensional conformal radiotherapy treatment planning is based on CT images; however, the information provided by CT data often cannot meet the requirements of target volume delineation . In recent years, PET-CT has been increasingly used in clinical practice to delineate the target volumes for radiotherapy of lung cancer. PET-CT has an accuracy superior to that of conventional CT and other imaging modalities. Deniaud-Alexandre et al.  delineated the GTV in 92 NSCLC patients by PET-CT and found that the GTVPET-CT was reduced in 23% of the patients and increased in 26% of cases compared to GTVCT, and 21 patients had a GTV change of ≥ 25%. In this study, we found that all 30 patients had varying degrees of changes in the GTVPET-CT and GTVCT, including 12 (40%) patients who had a change over 25%. This result is consistent with those reported by Deniaud-Alexandre et al. and Ceresoli et al. .
Although it is important to meet the requirements of target dose distribution, serious complications of radiation therapy caused by too large irradiated volume or too high dose to OARs should also be avoided. A given radiation treatment plan in which the target irradiation volume and the PTV fit well and the dose is evenly distributed is still unacceptable when the dose to OARs exceeds the tolerable dose of the organ or the irradiated volume of OARs is too large, because the implementation of this treatment plan will cause great damage to normal tissue and serious radiotherapy complications. Bradley et al.  contoured the GTV from the CT and PET-CT data sets in 26 NSCLC patients and found that, in three patients with atelectasis, the GTV and PTV obtained from PET-CT images were significantly reduced compared to those obtained from CT images, the MLD decreased from 14.83 Gy to 12.93 Gy, and lung V20 decreased from 25.33% to 21.33%. They also discovered that the MLD and mean esophageal dose increased with the increase in the GTV in 11 patients whose target volumes increased as a result of additional detection of metastatic lymph nodes. Van Der Wel et al.  contoured the target volumes by PET-CT and found that the GTV of the lymph nodes, lung V20, MLD, esophageal V45 and V55 decreased. At the same level of radiation toxicity, radiation dose and tumor control rate were improved. As a result, the efficacy of radiation therapy was enhanced. In the present study, we found that PlanPET-CT parameters showed varying degrees of change compared to PlanCT parameters. The changes in lung V20, V30, esophageal V50 and V55 were statistically significant (Ps< 0.05 for all), while the differences in MLD, lung V5, V10, V15, heart V30, MHD, esophageal Dmax, and spinal cord Dmax were not significant (Ps> 0.05 for all).
Acute radiation-induced lung injury is a kind of lymphocytic alveolar inflammation caused by direct radiation damage and body’s immune response. The severity of lung functional injury after radiotherapy is closely related to the irradiated volume. The dose-volume histogram (DVH) offers a range of physical parameters for the evaluation of radiotherapy-induced lung injury in lung cancer patients after three-dimensional conformal radiotherapy. The V20 is currently the most widely used parameter for clinical evaluation of treatment plans. However, the results obtained on factors associated with acute radiation-induced lung injury are different among different studies. In a study involving 99 NSCLC patients performed by Graham et al. , univariate analysis showed that the V20 and MLD were closely associated with the development of acute radiation-induced lung injury (grade 2 or higher), and multivariate analysis showed that the V20 was the only independent predictive factor for acute radiation-induced lung injury. This result is consistent with that obtained by Tsujino et al. . In a study conducted by Zhang et al. , univariate analysis indicated that the MLD, mean dose to the affected lung, and V20 were factors associated with the development of acute radiation-induced lung injury, and multivariate analysis indicated that only the mean dose to the affected lung is the independent risk factor. Studies performed by Hernando et al. , Claude et al. , and Kim et al.  demonstrated that the V30 was a factor associated with the development of acute radiation-induced lung injury. A recent study by Wang et al.  showed that the V5 is also associated with the development of acute radiation-induced lung injury, suggesting that V5 as a dose-volume constraint should be fully taken into account in designing radiation treatment plans. In our study, all PlanPET-CT parameters had varying degrees of decrease compared to PlanCT parameters, indicating that delineation of the target volumes for radiotherapy by PET-CT can help reduce the incidence of acute radiation-induced lung injury in NSCLC patients.
Acute radiation-induced esophageal injury usually occurs about two weeks after the start of radiotherapy. In recent years, there have been more and more studies investigating factors associated with the development of esophageal injury in patients undergoing three-dimensional conformal radiotherapy for NSCLC, although the parameters used and the conclusions drawn varied among different studies. Kim et al.  suggested that the V60 was an important parameter to predict acute radiation esophagitis (grade 3 or higher). Algara et al.  found that the V50 was the most valuable predictor. Topkan et al.  indicated that the V55 was the only relevant dosimetric parameter. More studies indicated that the V55 was likely to be the most valuable parameter for predicting acute radiation-induced esophageal injury. Our results indicated that the decrease in esophageal V55 obtained using PlanPET-CT was statistically significant (p < 0.05) compared to that obtained using PlanCT, suggesting that delineation of the target volumes for radiotherapy by PET-CT can help reduce the incidence of acute radiation-induced esophageal injury in NSCLC patients.
Radiation myelitis is a myelopathy that develops following spinal cord exposure to therapeutic radiation . Due to the combined effects of a variety of factors, neuronal degeneration and necrosis occur. The development of radiation myelitis is associated with exposure of normal spinal cord tissue to high-dose radiation [23, 24]. In our study, spinal cord Dmax obtained using PlanPET-CT decreased compared to that obtained using PlanCT, but the difference was not statistically significant. More emphasis should be put on the prevention of radioactive myelitis, and radiation dose to the spinal cord must be strictly controlled during radiotherapy.
Radiation damage to the heart is mainly manifested as ECG abnormalities, especially ischemic ST-T changes. The incidence of heart injury will significantly increase if 1/3 of the heart volume receives 70 Gy, 2/3 of the heart volume receives 55 Gy, or the whole heart receives 50 Gy. Our study suggests that PET-CT can help protect from cardiac injury to a certain extent, although the difference was not obvious between the two groups.