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First experiences with superfractionated skin irradiations using large afterloading molds.

PURPOSE: Radiotherapy of cutaneous metastases of breast cancer requires large radiation fields and high doses. This report examines the effectiveness and sequelae of superfractionated irradiation of cutaneous metastases of breast cancer with afterloading molds on preirradiated and nonirradiated skin. METHODS AND MATERIALS: A flexible reusable skin mold was developed for use with a pulsed ( PDR) afterloader. An array of 18 parallel catheters was sewn between two foam rubber slabs 5 mm in thickness to provide a defined constant distance to the skin. By selection of appropriate dwell positions, arbitrarily shaped skin areas can be irradiated up to a maximal field size of 17 x 23.5 cm2. Irradiations are performed with a nominal 37 GBq 192Ir stepping source in pulses of 1 Gy/h at the skin surface. The dose distribution is geometrically optimized. The 80 and 50% dose levels lie 5 and 27 mm below the skin surface. Sixteen patients suffering from metastases at the thoracic wall were treated with 18 fields (78-798 cm2) and total doses of 40-50 Gy applying two PDR split courses with a pause of 4-6 weeks. Eleven of the fields had been previously irradiated with external beam therapy to doses of 50-60 Gy at 7-22 months in advance. RESULTS: For preirradiated fields (n = 10) the results were as follows: follow-up 4.5-28.5 months (median 17); local control (LC): 8 of 10; acute skin reactions: Grade 2 (moist desquamation) 2 of 10; intermediate/late skin reactions after minimum follow-up of 3 months: Grade 1 (atrophy/pigmentation): 2 of 10, Grade 2-3a (minimal/marked teleangiectasia): 7 of 10, Grade 4 (ulcer): 1 of 10; recurrencies: 2 of 10. For newly irradiated fields (n = 7) results were: follow-up: 2-20 months (median 5); LC: 6 of 7; acute reactions: Grade 1: 4 of 7, Grade 2: 3 of 7; intermediate/late skin reactions after minimum follow-up of 3 months (n = 5): Grade 2-3a: 2 of 5; recurrencies: 0 of 7. Local control could be achieved in 82% of the mold fields. Geometric optimization was mandatory to achieve a homogeneous dose distribution on the skin. CONCLUSION: Superfractionated brachytherapy with skin molds is an effective alternative for the treatment of skin metastases of breast cancer even if the skin is preirradiated. This method is economically advantageous compared to external beam therapy, which would require several weeks. At the curved chest wall, optimized molds can provide better dose homogeneity than abutted electron fields. Skin reactions are comparable to the sequelae of orthovolt irradiation. In preirradiated areas, PDR doses should be restricted to 40-45 Gy. PDR doses of 50 Gy seem to be the limit for tolerance even in previously unirradiated fields.[1]

References

  1. First experiences with superfractionated skin irradiations using large afterloading molds. Fritz, P., Hensley, F.W., Berns, C., Schraube, P., Wannenmacher, M. Int. J. Radiat. Oncol. Biol. Phys. (1996) [Pubmed]
 
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