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Colorectal cancer patients are treated at our hospital with 192Ir high dose rate (HDR) brachytherapy using an applicator that allows the introduction of a lead or tungsten shielding rod to reduce the dose to healthy tissue. The clinical dose planning calculations are, however, currently performed without taking the shielding into account. To study the dose distributions in shielded cases, three techniques were employed. The first technique was to adapt a shielding algorithm which is part of the Nucletron PLATO HDR treatment planning system. The isodose pattern exhibited unexpected features but was found to be a reasonable approximation. The second technique employed a ray tracing algorithm that assigns a constant dose ratio with/without shielding behind the shielding along a radial line originating from the source. The dose calculation results were similar to the results from the first technique but with improved accuracy. The third and most accurate technique used a dose-matrix-superposition algorithm, based on Monte Carlo calculations. The results from the latter technique showed quantitatively that the dose to healthy tissue is reduced significantly in the presence of shielding. However, it was also found that the dose to the tumor may be affected by the presence of shielding; for about a quarter of the patients treated the volume covered by the 100% isodose lines was reduced by more than 5%, leading to potential tumor cold spots. Use of any of the three shielding algorithms results in improved dose estimates to healthy tissue and the tumor. [ABSTRACT FROM AUTHOR]

Between January 1978 and December 1982 successful sequential chromosome analyses were carried out on bone marrow cells of five patients previously treated for Hodgkin's lymphoma (HL) presenting unexplained cytopenia or pancytopenia during follow-up. All patients had concurrent morphological examination of bone marrow specimens showing signs of dysplasia and/or hypoplasia, without leukaemic infiltrate. Six other patients treated for HL who had normal haematological parameters served as controls. All the patients with unexplained cytopenias had clonal chromosome abnormalities; monosomy for chromosome No. 5 was the most frequent. No abnormalities were detected in the control group. Two patients have evolved to resistant leukaemia, one died of sepsis before leukaemic conversion while severely neutropenic, and two are in full marrow and cytogenetic recovery after aggressive anti-leukaemic treatment in the pre-leukaemic phase. Our data suggest that cytogenetic studies may be of crucial value in detecting therapy-induced preleukaemia (t-PL) at an early stage of its evolution and in planning appropriate therapy before the establishment of overt leukaemia.