Ayşe Koca

Results and complications of high dose rate and low dose rate brachytherapy in carcinoma of the cervix: Cerrahpaşa experience

PURPOSE To evaluate the results and complications of treatment with high dose rate (HDR) compared to low dose rate (LDR) brachytherapy in cervical carcinoma. METHODS Three hundred and seventy patients who were treated with external irradiation and intracavitary brachytherapy and followed for more than 2 years between 1978 and 1998 have been recently updated. The low dose rate group consisted of 77 cases treated between 1978 and 1982 and HDR group consisted of 293 cases treated between 1982 and 1998. All patients first received external irradiation with 60Co or 9-18 MV photons and a median dose of 54 Gy was given in 6 weeks. In the LDR group, intracavitary treatment was given with Manchester applicators loaded with radium (30 mg) in an intrauterine tube and 20 mg in vaginal ovoids. The dose delivered to point A was on average 32 Gy in one application. In the HDR group, a total dose of 24 Gy was given to point A in three insertions 1 week apart. The dose rate was 0.62 Gy at point A. RESULTS The 5-year pelvic control rate was found to be 73% in the HDR group, compared with 86% in the radium group for stage I cases. In stage IIB and IIIB cases, the rates were 68% and 45% for HDR and 65% and 53% for LDR, respectively. In all stages, there was no statistical difference in pelvic control and survival rates between the two groups. Overall incidence of late complications was found as 31.1% and 31.9% in HDR and LDR groups, respectively. The grade 2-4 late complication rate was 14% in the HDR group compared to 19% in the LDR group (P>0.05). CONCLUSION HDR brachytherapy in the management of the cervix appears to be a safe and efficacious approach. Pelvic control, survival and complications rates are quite similar when compared with LDR.

DETERMINATION OF SURFACE DOSE AND THE EFFECT OF BOLUS TO SURFACE DOSE IN ELECTRON BEAMS

When treating tumors from surface to a certain depth (<5 cm), electron beams are preferred in radiotherapy. To increase the surface doses of lower electron beams, tissue-equivalent bolus materials are often used. We observed that the surface doses increased with increasing field sizes and electron energies. At the same time, we also observed that all electron parameters were shifted toward the skin as much as the thickness of the bolus used. The effect of bolus to the surface doses was more significant at low electron energies than at higher electron energies. Rando phantom measurements at 6-, 7.5-, and 9-MeV were slightly lower than the solid phantom measurements, which could only be explained by the inverse square law effect and the Rando phantom contour irregularity.

THE INVESTIGATION OF FETAL DOSES IN MANTLE FIELD IRRADIATION

To determine clinically the fetal dose from irradiation of Hodgkins disease during pregnancy and to quantify the components of fetal dose using phantom measurements. The fetal dose was measured with phantom measurements using thermoluminescent dosemeters (TLDs). Phantom measurements were performed by simulating the treatment conditions on an anthropomorphic phantom. TLDs were placed on the phantom 41, 44, 46.5 and 49.5 cm from the centre of the treatment field. Two TLDs were placed on the surface of the phantom. The estimated total dose to all the TLDs ranged from 8.8 to 13.2 cGy for treatment with (60)Co and from 8.2 to 11.8 cGy for 4 MV photons. It was concluded that the doses in different sections were evaluated to investigate dose changes in different points and depths of fetal tissues in phantom. Precise planning and the use of supplemental fetal shielding may help reduce fetal exposure.

Depth Dose Characteristics of Electron Beams at Extended SSDS.

The purpec: of this study is to investigate the behaviour of the percent depth dose curves (%DD) and surface doses of electronbeams at extended Source-to Surface Distances (SSDS). A (GE) Saturne 42 linear accelerator was used in this study, which produces dual photon energies of 6 and 15 MV as well as eight electron energies ranging between 4.5 and 21 MeV. The % Depth Dose curves were geneated with water scanning equipment at 6, 9, and 15 MeV for 4x4 cm(2) and 20x20 cm(2) field sizes at SSDS of 100 cm, 108 cm, and 115 cm. According to the measurements from surface to the depth of dose maximum the surface dose increased for all of the electron energies studied at extended SSDS for small field sizes. On the other hand for larger field sizes the surface doses decreased at extended SSDS. It was also observed that the increase in the surface dose diminished as the field size approached to 10x10cm(2) then the surface dose started decreasing at extended SSDS as the field sizes increased. Extended SSDS have no observable effect on the tail portion of the depth dose curves.