[Brachytherapy with pulsed dosage. General considerations. Radiobiological considerations. First clinical experience...

The pulsed dose rate (PDR) brachytherapy technique is analyzed and compared with the low and high dose rate (LDR and HDR, respectively) techniques relative to therapy and management, considering the advantages and pitfalls of each technique. From a radiobiological viewpoint, PDR optimization is aimed at obtaining the same therapeutic results as with LDR and HDR relative to both tumor cell killing and possible late damage. PDR permits to administer the same nominal dose rates as with LDR and HDR, but with very different pulse intervals and length. March, 1995, through March, 1996, forty-two patients were treated with microSelectron PDR at the radiotherapy Department of Umberto I Hospital in Mestre (Venice). Twenty-two patients were irradiated on the vaginal vault, 14 on the anal canal, 4 on the breast, one on the endometrium and one on the urethra (the latter patient was a man). Dose rates were 250-300 cGy/h in the vaginal vault and 90 cGy/h in the other sites. Source-dwell interval in the applicators was 2.5 mm, dwelling time for each position ranged 6.8-122 s, 3-73 pulses were applied lasting 167-1958 s. The unit was reliable and the only problem was the need to recalibrate it every 5-6 applications because of computer memory saturation. Because of the short minimum follow-up (3 months), only the early reactions to treatment have been assessed: no toxicity was found in the vaginal vault, endometrium and breast. Low-grade proctitis was observed in 11 of 14 treated anal canals and another patient complained of more severe symptoms for two weeks; the disease progressed in two anal canal patients, as in the urethra patient. In conclusion, PDR brachytherapy appears a reliable technique whose early clinical results are encouraging.