Ru106 Brachytherapy for Management of Choroidal Melanoma : Do we Need to Adjust Total dose According to the New NIST Calibration Measurement?

Abstract EN

Purpose: To detect the need of adjusting the apical total dose according to the new NIST calibration measurement introduced by BEBIG Isotopen und Medizintechnik GmbH for the treatment of choroidal melanoma.

As the total radiation dose should not be individualized depending on errors pf previous calibration but can be applicable if based on a radiosensitivity test that was able to predict the final response of tumor to radiation for each particular patient. Patients and Methods: Twenty patients with choroidal melanomas were treated between November 2002 and July 2004 at "Suzanne Mubarak Eye Tumor Centre", National Eye centre Rod-EL Farag, Cairo, Egypt.

The prescribed dose was calculated according to the new NISTcalibrated dosimetry introduced by BEBIG, but without dose modification by using a conversion factor F(type,z) from the ASMW calibrated measurement to the NIST calibrated measurement that have been calculated depending on the plaque type and the distance z from the inner concave plaque surface along the central axis.

For the treatment of choroidal melanoma in this study the apical dose ranged from 9000-10400cGy with a mean of 9855± 385. Results: After a follow up period from 12-28 months (median of 19 months) there was a local control rate of 100 % and the three years actuarial disease specific survival was 95% as only one patient died of liver metastases. Fourteen patients had a best corrected pre-treatment visual acuity of better than 6/60 in the affected eye.

At the last follow up available, useful visual acuity of >0.5 was preserved in 7 of the patients. Conclusion: Recalculation of the apical total dose (mostly increasing of the total dose) according to the conversion factor F(type,z), suggested by BEBIG after the new NIST calibration measurement, does not seem to have an effect on both local control and survival, in this study.