Dosimetric comparison of 3DCRT and IMRT in radical chemoradiotherapy of squamous cell carcinoma esophagus.

BACKGROUND: Radical chemoradiation is the standard of treatment for locally advanced squamous cell carcinoma of esophagus and for patients with operable disease, but who are medically unfit or unwilling for surgery. As the esophagus is a central organ, the planning target volume (PTV) is central, lies close to the spinal cord and heart, and is surrounded by the lung, which is a radiosensitive organ. Irradiation of these critical structures is reduced by the use of three-dimensional conformal radiation therapy (3DCRT). Intensity-modulated radiation therapy (IMRT) has the potential to improve the uniformity of dose distribution to the tumor and reduce the dose received by surrounding normal tissues. AIM AND OBJECTIVES: 1. To compare the dose distribution, conformity, and homogeneity indices in radical radiotherapy of squamous cell carcinoma of esophagus using 3DCRT and IMRT techniques 2. To compare the doses received by critical structures such as heart, lung, spinal cord, and liver. MATERIALS AND METHODS: All cases of squamous cell carcinoma esophagus treated with radical chemoradiation to a dose of 50 Gy in 25 fractions using 3DCRT technique from January 2018 to July 2019 were included. IMRT plans were generated for these cases.The parameters that represent dose distribution to the target volume and the dose received by the organs at risk were obtained from the dose-volume histogram. The difference in the mean values of the parameters between the two techniques was calculated. The statistical significance of the difference was determined using Student's t-test and Wilcoxon signed-rank test. RESULTS: The volume of PTV receiving 105% and 107% of prescribed dose was significantly lower with IMRT (3.540% and 0.008%, respectively) compared to 3DCRT (7.654% and 0.623%). The homogeneity index was better with IMRT (0.088 vs. 0.107) than 3DCRT. Conformity index was found to be better with IMRT (1.149 vs. 1.573). Mean heart dose (18.216 vs. 24.591 Gy) and the volume of heart receiving 30 Gy were reduced with IMRT. The volume of lung receiving 20 Gy and the volume receiving 5 Gy were not significantly different between 3DCRT and IMRT. Maximum dose to spinal cord was similar with 3DCRT and IMRT. CONCLUSIONS: IMRT avoids areas of excessive irradiation within the PTV. IMRT improves dose conformity to the target volume and homogeneity of dose distribution within the PTV. The cardiac dose is significantly reduced with IMRT. The mean lung dose remains similar to 3DCRT. There is no significant increase in the volume of lung receiving low-dose radiation with IMRT.

Glutathione S-transferase M1, T1 and P1 polymorphisms: susceptibility and outcome in lung cancer patients.

The glutathione S-transferases (GSTs) are a superfamily of genes whose products are phase II enzymes, catalyzing the conjugation of reactive intermediates to soluble glutathione. Some of the GSTs are polymorphic and may play a role in lung cancer susceptibility. We investigated whether genetic polymorphisms of GSTM1, GSTP1 and GSTT1 genes modulated lung cancer risk and affect survival among lung cancer patients. We determined the GST genotypes in 422 study subjects, using polymerase chain reaction (PCR) and reverse PCR and restriction fragment length polymorphism (RFLP). Logistic Regression analysis was carried out to find the association of various polymorphisms and GSTs and lung cancer. The influence of the genetic polymorphisms on patient survival was estimated using the method of Kaplan-Meier survival function. Cox Proportional Hazard models were used to estimate hazard ratios (HR) for deaths. GSTT1 -/- genotype conferred a higher odds ratio of 2.9 (P = 0.001) compared to the GSTT1+/+. So also, the GSTP1 GG genotype too had higher risk compared to the GSTP1 AA genotype (OR = 2.3, P = 0.033). When the combined GST M1, GSTT1 and GSTP1 genotypes were examined, patients with the combinations GSTM1 null and GSTT1 null had a significant OR of 3.6. So also the combinations GSTT1-/- GSTP1 AA (P = 0.005) and GSTT1-/- GSTP1 AG/GG (P = 0.001) came out to be significant. There were some significant interactions between GST genotypes with tobacco smoking and also for clinicopathological factors. Regarding survival analysis, no association of GSTM1 or GSTP1 genes with survival was noted. The GSTT1 -/- genotype along with stage was significantly associated with overall survival and found to be an independent prognostic factors for shorter lung cancer survival.