11. The analysis of doses in the tumour and in critical tissues in the brachytherapy of malignant melanoma localised in eyes

Abstract

Brachytherapy is known and used procedure in the treatment of tumours localised in eyes, especially recommended when avoiding of enucleation accompany the long term cure.

Aim

The aim of this paper was to compare the doses delivered to the tumour and critical tissues during the treatment of the group of patients treated with Ru-106 applicator.

Patients

Between 1994 and 2000, 67 patients (dgn. melanoma malignum in eye) underwent brachytherapy. At 51 patients the tumour was localized in the back of eye, at 15 equatorially and at one in the front section of the eyeball. The median of the patients’ age was 56.3 years. The CCB type applicator was applied for 56 patients, the COB for 7 and the ROA for 4 patients.

Method

Irradiation – Prescribed dose of 60 Gy was normalized to the top of the tumour, it decreased by 50%—10% per millimetre with the distance from applicator. The isotope producer determined the dose-rate accuracy for +/−30%. This caused that therapeutic dose had to be calculated taking account for the minimal dose-rate, while the doses in critical organs for maximal dose-rate possible.

Analysis

All patients were divided into three subgroups: 8 patients into 1^st, 19 into 2^nd and 40 into 3^rd. The inclusion criterion was size of tumour: up to 3 mm of height (1^st group), 3–5 mm (2^nd), and larger than 5 mm (3^rd) respectively.

Results

Table presents mean doses in the tumour, sclera and lens (calculated at it's middle) for each group of patients.[[tgroup cols="4"]][[colspec colname="col1"/]][[colspec colname="col2"/]][[colspec colname="col3"/]][[colspec colname="col4"/]][[tbody]][[row]][[entry morerows="1" rowsep="1" align="center"]]Tumour size [mm][[/entry]][[entry namest="col2" nameend="col4" rowsep="1" align="center"]]Doses [Gy][[/entry]][[/row]][[row]][[entry rowsep="1" align="center"]]Tumour[[/entry]][[entry rowsep="1" align="center"]]Sclera[[/entry]][[entry rowsep="1" align="center"]]lens[[/entry]][[/row]][[row]][[entry rowsep="1" align="center"]]<3[[/entry]][[entry rowsep="1" align="center"]]102.9[[/entry]][[entry rowsep="1" align="center"]]162.4[[/entry]][[entry rowsep="1" align="center"]]137.6[[/entry]][[/row]][[row]][[entry rowsep="1" align="center"]]3–5[[/entry]][[entry rowsep="1" align="center"]]186.2[[/entry]][[entry rowsep="1" align="center"]]463.5[[/entry]][[entry rowsep="1" align="center"]]396.2[[/entry]][[/row]][[row]][[entry align="center"]]>5[[/entry]][[entry align="center"]]268.2[[/entry]][[entry align="center"]]974.9[[/entry]][[entry align="center"]]840.6[[/entry]][[/row]][[/tbody]][[/tgroup]]

Conclusions

Mean doses in tumour varied from 102.9 Gy to 268.2 Gy depending on the tumour size. Doses in sclera and lens did not exceed the tolerance levels in all three groups of patients.