Determination of 3D dose distribution from intracavitary brachytherapy of cervical cancer by MRI of irradiated ferrous sulphate gel.

BACKGROUND AND PURPOSE: MRI ferrous sulphate gel dosimetry has proven to be a valuable method for assessment of dose delivered in teletherapy. The intention of this study was to investigate ferrous sulphate gel as a possible dosimeter for intracavitary brachytherapy applications. MATERIALS AND METHODS: A plastic duplicate of a cervix ring applicator set was submerged in Fe2(+)-infused gelatin gel. The gel was subsequently irradiated by a stepwise moving 192Ir source, using automatic afterloading equipment (Microselectron, Nucletron-Oldelft International BV, Veenendaal, The Netherlands). A 3D dose distribution was reconstructed from MR images of the gel. RESULTS: The gel dose measurements were found to be of the same accuracy as TLD measurements. Isodose curves based on gel dosimetry and isodose curves computed by a dose planning system were generally less than 2 mm apart. MR images showing the position of the applicator set in a patient during treatment were used to obtain images describing patient anatomy in the sagittal and ring planes of the applicator set. Isodose curves computed from the gel measurements were then superimposed on these images, illustrating one possible way of linking dosimetrical and anatomical data. CONCLUSIONS: Our study shows that MRI ferrous sulphate gel dosimetry is a useful tool for studies of dose distributions in brachytherapy and their relation to critical organs. Possible improvements of the gel dosimeter lie in reducing the diffusion of ferric ions and increasing the radiation sensitivity of the gel.

Computed tomography/magnetic resonance based volume changes of the primary tumour in patients with prostate cancer with or without androgen deprivation.

BACKGROUND AND PURPOSE: To evaluate changes of the volume of the cancerous prostatic gland during androgen deprivation (AD) started immediately after diagnosis (IAD). Hypothetically, these data would assist the radiotherapist to determine the appropriate duration of pre-radiotherapy downsizing neoadjuvant luteinizing hormone releasing hormone (LHRH) treatment. A second aim was to assess any increase of the prostatic volume during the 1st year of diagnosis in patients who were allocated to a deferred treatment policy (DAD). METHODS AND MATERIALS Thirteen patients in the IAD cohort and 13 patients in the DAD group, all with T1-3pN1-2M0 prostate cancer, had regular computed tomography/magnetic resonance (CT/MR) examinations during the 1st year after randomization within the EORTC-GU trial 30846. Pre-treatment prostate specific antigen (PSA) values were available in only 12 patients. RESULTS: In the IAD group the prostate gland decreased with significant difference as compared with the DAD patients (P=0.033). As compared with the pre-treatment situation the prostate gland in the IAD group was reduced in size by 18, 35, and 46% at 1, 6, and 12 months, respectively. In four of six evaluable IAD patients the prostatic volume continued to shrink after achievement of the nadir PSA level (at 3 months). In three of the 13 DAD patients the prostate volume increased by >25% during the 1st 3 months after randomization. CONCLUSION: If neoadjuvant androgen deprivation is applied before local treatment to downsize the volume of the cancerous prostate gland, our limited data suggest that such treatment should last at least 6 months in order to achieve a maximal effect in the majority of patients. In about 1/4 of untreated patients an increase in the prostate volume by >25% may occur within 3 months of diagnosis. If no AD is given, radiotherapy should start within this period.