CARDIAC TOXICITY AFTER RADIATION THERAPY FOR 52 PATIENTS WITH MALIGNANT THYMIC TUMORS

Objective: To analyze the influencing factors for radiation-induced heart disease (RIHD) in a panel of cases with malignant thymic tumors treated by radiotherapy. Methods: 52 consecutive patients were treated by radiotherapy for malignant thymic tumor (14 at Masaoka stage II, 23 at stage III and 15 at stage IV). Treatment included radical (in 20), postoperative (in 14), preoperative (in 2) and palliative (in 16) radiotherapy. The conventional two-dimension (2D) radiation therapy was performed in forty-seven patients and three-dimension (3D) conformal radiation therapy has been used in 5 patients since October 2000. The total tumor dose ranged from 10 Gy to 84.5 Gy (median of 55 Gy). Chemotherapy was given in twenty-five patients before or after radiotherapy. The results of following-up could be obtained from the database and updated where appropriated. The dose volume histogram (DVH) of heart in radiotherapy for all patients was analyzed for the effective volume dose of heart. Result: The median following-up was 14 months (ranged from 0.6 to 111.3 months) in the study. RIHD was observed in seven patients. Cardiac toxicity of these seven patients were evaluated as SOMA grade 1-3. The median two-third effective volume dose of heart was 47.2 Gy (ranged from 8.3 Gy to 70.1 Gy) for conventional 2D radiotherapy, which correlated with thymic tumor dose (P<0.0001). The median two-third effective volume dose of heart was 35.3 Gy (ranged from 13 Gy to 38.7 Gy) for 3D conformal radiotherapy. The effective volume doses of heart were decreased by using 3D conformal radiotherapy (P=0.048). A significant association between cardiac toxicity and effective volume dose of heart was found in this study (P<0.0001). Cardiac toxicity accounted for 10.4% and 4.1% of patients receiving and not receiving adjuvant chemotherapy, respectively, and occurred earlier in radiochemotherapy group (P=0.0528). Multivariate analysis suggested that cardiac toxicity was significantly influenced by the effective volume dose of heart and chemotherapy. Conclusion: the results indicate that decreasing the effective volume dose of heart and carefully using chemotherapy drugs that have significant cardiotoxicity may reduce the probability of radiation-induced heart disease.

A preliminary study of a new high-resolution detector matrix applied to three-dimensional dose verification in intensity-modulated radiotherapy

Objective:To test the basic dosimetry characteristics of a new high-resolution matrix and to perform a preliminary study on the three-dimensional(3D)dose verification of intensity-modulated treatment(IMRT).Methods:The dosimetry characteristics of the new matrix were investigated,including repeatability,dose-rate response,and dose linearity.Twenty cases of nasopharyngeal carcinoma(NPC)and 20 cases with lung cancer were randomly selected for IMRT plans,and the novel matrix was employed for 3D dose verification.The measured results were evaluated using the gamma passing rate(GPR)and dose volume histogram(DVH).The action limit(AL)and tolerance limit(TL)of the target volume and each organ at risk(OAR)were calculated with reference to the American Association of Physicists in Medicine(AAPM)TG218 report.Results:The matrix performed well for all dosimetry characteristic tests,with a deviation of<1%.The average GPRs of the body were(99.32±0.32)%,(98.36±0.59)%,and(96.27±1.20)%for NPC,and(99.17±0.74)%,(98.09±1.33)%,and(95.83±2.22)%for lung cancer at the gamma standards of 3%/3 mm,3%/2 mm,and 2%/2 mm.The average GPRs difference between the head-neck and thorax-abdomen plans were<1%for the same gamma standard.For both the target volumes and OARs,the average GPRs were>90%under the relatively strict standard of 2%/2 mm.The DVH showed that the measurement results of D_(98) and D_(95) for the target volumes were slightly lower and D_(2) were higher than those of treatment planning system(TPS)(P<0.01).In addition,with the same standard,there may be significant differences in the values of AL and TL between different structures for target volumes and OARs,especially small-volume OARs such as the chiasma and optic nerve-L.Conclusions:The new matrix showed good dosimetry characteristics and can be effectively applied to the treatment planning dose verification of the head-neck and lung cancer.Further research is needed to establish how to analyze the GPR and DVH of the target volume and OARs,and to determine more precise dose verification standards combined with the parameters of AL and TL to better guide 3D dose verification in clinic.