Clinical indications and biological mechanisms of splenic irradiation in chronic leukaemias and myeloproliferative disorders.

Splenic irradiation (SI) was the first efficient treatment for chronic leukaemia, but with the emergence of effective drugs its use has been more and more restricted to advanced cases presenting with splenomegaly. But in selected patients who are not responsive or not suitable to drug treatment, SI may offer still an effective, low toxic and cost-effective palliative modality. Eight studies of SI in chronic lymphatic leukaemia (CLL) including 198 patients, six reports about SI in prolymphocytic leukaemia (PLL), including 18 patients, one study and six case reports about SI in hairy cell leukaemia (HCL) and nine studies about SI in myeloproliferative disorders has been analyzed. In CLL, symptoms of splenomegaly have been improved in 50-87% of all patients with overall doses between 4 and 10 Gy in mostly 1-Gy fractions. PLL seems to be more resistant to SI with a median response rate of 66%. Casuistic reports described also efficacy of SI in HCL patients using similar radiation schedules. Symptomatic relief is also provided by SI in myeloproliferative disorders using lower overall doses between 1 and 9 Gy with small single fractions of 0.25 Gy (median). Acute toxicity was low in lymphoid disorders, but higher in myeloproliferative disorders with severe cytopenia in 10-30% of all cases, indicating the need for a cautious fractionation schedule. Interestingly, even complete systemic remissions after SI in all types of lymphoproliferative disorders have been described. Different mechanisms underlying SI such as direct cell kill, immune modulation via changes in lymphocyte subsets or cytokine induction or "radiotherapeutic" splenectomy with high doses are discussed.