comparison study of radiation dose received during cone beam computerized tomography and portal imaging techniques

Although widely varied in modality and method, all radiographic guidance techniques have one thing in common; they can give a significant radiation dose to the patient; which may have a late radiation stochastic effect on normal body tissues. To quantify and compare radiation doses to the tumour and the surrounding critical organs resulting from the orthogonal pair portal and megavoltage cone beam computarized tomography [MV CBCT] imaging techniques. The dose to the patient resulting from the orthogonal pair and the MV CBCT imaging techniques, has been calculated based on a 6 MV Oncor linear accelerator equipped with an amorphous silicon flat panel. All calculations were done on Eclipse 3D treatment planning system. 18 patients representing three different treatment sites [head and neck, thorax, and pelvis] were analysed. Data from 6 patients for each treatment site were used to calculate the mean doses. Calculations were done for: The integral dose, maximum dose to the patient, dose at the isocenter, and mean dose to the tumour and each critical organ. The absolute dose measured as integral dose, maximum dose to the patient, dose at the isocenter, and mean dose to the tumour and each critical organ was higher for MV CBCT as compared to orthogonal pair technique for all treatment sites. For both techniques, the absolute dose was higher for head and neck and thorax as compared to pelvis. The difference of maximum dose to the patient showed greater variation for head and neck, but not for thorax and pelvis. There are relatively high dose regions generated by MV CBCT that occur inside critical organs as well treatment area and tend to be larger than those generated by the orthogonal pair technique

3D-CRT techniques for simultaneously integrated boost in breast conserving radiation therapy

To evaluate the dosimetric outcomes of two different three dimensional conformal radiation therapy [3D-CRT] of concomitant boost delivery to the intact breast. Ten patients were evaluated using two standard opposed tangents conformal to the whole breast PTV, plus a pair of wedged fields conformal to the boost PTV; all fields have the same isocenter, placed in the whole breast planning target volume [PTV] [WBI] or located in the boost [BI] PTV. Dose Volume Histograms were calculated and analysed for the difference in maximum and minimum doses; also mean doses and volumes receiving 90% and 107% of the prescribed dose. Lung irradiation was analysed in terms of maximum and mean doses. For breast PTV coverage, significant differences were observed only in the maximum doses [62.3Gy Vs. 61Gy, p=0.003] and higher Dose Homogeneity Index DHI [0.66 Vs. 0.64, p=0.003] in favour WBI. For boost PTV coverage, a significant difference between the two techniques with maximum dose [62.6 versus 60.87, p=0.003] as well the DHI [0.97 Vs. 0.94, p=0.002] in favour of WBI. The Conformity Index CI was significantly better in WBI [0.87 Vs. 0.64, p=0.001]. Dose to lung or healthy tissue was not statistically significant difference between the two methods. This study shows a dosimetrical superiority of using the whole breast isocenter technique over boost isocenter technique in whole breast PTV coverage, dose homogeneity index and boost PTV coverage. The clinical significance of this difference needs further clinical studies