FIRST EXPERIENCES WITH SUPERFRACTIONATED SKIN IRRADIATIONS USING LARGE AFTERLOADING MOLDS

Purpose: Radiotherapy of cutaneous metastases of breast cancer require s large radiation fields and high doses, This report examines the effe ctiveness and sequelae of superfractionated irradiation of cutaneous m etastases of breast cancer with afterloading molds on preirradiated an d nonirradiated skin, Methods and Materials: A flexible reusable skin mold was developed for use with a pulsed (PDR) afterloader. An array o f 18 parallel catheters was sewn between two foam rubber slabs 5 mm in thickness to provide a defined constant distance to the skin, By sele ction of appropriate dwell positions, arbitrarily shaped skin areas ca n be irradiated up to a maximal field size of 17 x 23.5 cm(2). Irradia tions are performed with a nominal 37 GBq Ir-192 stepping source in pu lses of 1 Gy/h at the skin surface, The dose distribution is geometric ally optimized, The 80 and 50% dose levels lie 5 and 27 mm below the s kin surface, Sixteen patients suffering from metastases at the thoraci c wall were treated with 18 fields (78-798 cm(2)) and total doses of 4 0-50 Gy applying two PDR split courses with a pause of 4-6 weeks, Elev en of the fields had been previously irradiated with external beam the rapy to doses of 50-60 Gy at 7-22 months in advance. Results: For prei rradiated fields (n = 10) the results were as follows: follow-up 4.5-2 8.5 months (median 17); local control (LC): 8 of 10; acute skin reacti ons: Grade 2 (moist desquamation) 2 of 10; intermediate/late skin reac tions after minimum follow-up of 3 months: Grade 1 (atrophy/pigmentati on): 2 of 10, Grade 2-3a (minimal/ marked teleangiectasia): 7 of 10, G rade 4 (ulcer): 1 of 10; recurrencies: 2 of 10, For newly irradiated f ields (n = 7) results were: follow-up: 2-20 months (median 5); LC: 6 o f 7; acute reactions: Grade 1: 4 of 7, Grade 2: 3 of 7; intermediate/l ate skin reactions after minimum follow-up of 3 months (II = 5): Grade 2-3a: 2 of 5; recurrencies: 0 of 7, Local control could be achieved i n 82% of the mold fields, Geometric optimization was mandatory to achi eve a homogeneous dose distribution on the skin. Conclusion: Superfrac tionated 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 e xternal beam therapy, which would require several weeks. At the curved chest wail, 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 t olerance even in previously unirradiated fields.