The effect of total body irradiation dose and chronic graft-versus-host disease on leukaemic relapse after allogeneic bone marrow transplantation

ESTRO ACROP and SIOPE recommendations for myeloablative Total Body Irradiation in children

BACKGROUND AND PURPOSE

Myeloablative Total Body Irradiation (TBI) is an important modality in conditioning for allogeneic hematopoietic stem cell transplantation (HSCT), especially in children with high-risk acute lymphoblastic leukemia (ALL). TBI practices are heterogeneous and institution-specific. Since TBI is associated with multiple late adverse effects, recommendations may help to standardize practices and improve the outcome versus toxicity ratio for children.

MATERIAL AND METHODS

The European Society for Paediatric Oncology (SIOPE) Radiotherapy TBI Working Group together with ESTRO experts conducted a literature search and evaluation regarding myeloablative TBI techniques and toxicities in children. Findings were discussed in bimonthly virtual meetings and consensus recommendations were established.

RESULTS

Myeloablative TBI in HSCT conditioning is mostly performed for high-risk ALL patients or patients with recurring hematologic malignancies. TBI is discouraged in children <3-4 years old because of increased toxicity risk. Publications regarding TBI are mostly retrospective studies with level III-IV evidence. Preferential TBI dose in children is 12-14.4 Gy in 1.6-2 Gy fractions b.i.d. Dose reduction should be considered for the lungs to <8 Gy, for the kidneys to ≤10 Gy, and for the lenses to <12 Gy, for dose rates ≥6 cGy/min. Highly conformal techniques i.e. TomoTherapy and VMAT TBI or Total Marrow (and/or Lymphoid) Irradiation as implemented in several centers, improve dose homogeneity and organ sparing, and should be evaluated in studies.

CONCLUSIONS

These ESTRO ACROP SIOPE recommendations provide expert consensus for conventional and highly conformal myeloablative TBI in children, as well as a supporting literature overview of TBI techniques and toxicities.

Optimized Conformal Total Body Irradiation methods with Helical TomoTherapy and Elekta VMAT: Implementation, Imaging, Planning and Dose Delivery for Pediatric Patients

Optimized conformal total body irradiation (OC-TBI) is a highly conformal image guided method for irradiating the whole human body while sparing the selected organs at risk (OARs) (lungs, kidneys, lens). This study investigated the safety and feasibility of pediatric OC-TBI with the helical TomoTherapy (TomoTherapy) and volumetric modulated arc (VMAT) modalities and their implementation in routine clinical practice. This is the first study comparing the TomoTherapy and VMAT modalities in terms of treatment planning, dose delivery accuracy, and toxicity for OC-TBI in a single-center setting. The OC-TBI method with standardized dosimetric criteria was developed and implemented with TomoTherapy. The same OC-TBI approach was applied for VMAT. Standardized treatment steps, namely, positioning and immobilization, contouring, treatment planning strategy, plan evaluation, quality assurance, visualization and treatment delivery procedure were implemented for 157 patients treated with TomoTherapy and 52 patients treated with VMAT. Both modalities showed acceptable quality of the planned target volume dose coverage with simultaneous OARs sparing. The homogeneity of target irradiation was superior for TomoTherapy. Overall assessment of the OC-TBI dose delivery was performed for 30 patients treated with VMAT and 30 patients treated with TomoTherapy. The planned and delivered (sum of doses for all fractions) doses were compared for the two modalities in groups of patients with different heights. The near maximum dose values of the lungs and kidneys showed the most significant variation between the planned and delivered doses for both modalities. Differences in the patient size did not result in statistically significant differences for most of the investigated parameters in either the TomoTherapy or VMAT modality. TomoTherapy-based OC-TBI showed lower variations between planned and delivered doses, was less time-consuming and was easier to implement in routine practice than VMAT. We did not observe significant differences in acute and subacute toxicity between TomoTherapy and VMAT groups. The late toxicity from kidneys and lungs was not found during the 2.3 years follow up period. The study demonstrates that both modalities are feasible, safe and show acceptable toxicity. The standardized approaches allowed us to implement pediatric OC-TBI in routine clinical practice.

Total Body Irradiation in Haematopoietic Stem Cell Transplantation for Paediatric Acute Lymphoblastic Leukaemia: Review of the Literature and Future Directions

Total body irradiation (TBI) has been a pivotal component of the conditioning regimen for allogeneic myeloablative haematopoietic stem cell transplantation (HSCT) in very-high-risk acute lymphoblastic leukaemia (ALL) for decades, especially in children and young adults. The myeloablative conditioning regimen has two aims: (1) to eradicate leukaemic cells, and (2) to prevent rejection of the graft through suppression of the recipient's immune system. Radiotherapy has the advantage of achieving an adequate dose effect in sanctuary sites and in areas with poor blood supply. However, radiotherapy is subject to radiobiological trade-offs between ALL cell destruction, immune and haematopoietic stem cell survival, and various adverse effects in normal tissue. To diminish toxicity, a shift from single-fraction to fractionated TBI has taken place. However, HSCT and TBI are still associated with multiple late sequelae, leaving room for improvement. This review discusses the past developments of TBI and considerations for dose, fractionation and dose-rate, as well as issues regarding TBI setup performance, limitations and possibilities for improvement. TBI is typically delivered using conventional irradiation techniques and centres have locally developed heterogeneous treatment methods and ways to achieve reduced doses in several organs. There are, however, limitations in options to shield organs at risk without compromising the anti-leukaemic and immunosuppressive effects of conventional TBI. Technological improvements in radiotherapy planning and delivery with highly conformal TBI or total marrow irradiation (TMI), and total marrow and lymphoid irradiation (TMLI) have opened the way to investigate the potential reduction of radiotherapy-related toxicities without jeopardising efficacy. The demonstration of the superiority of TBI compared with chemotherapy-only conditioning regimens for event-free and overall survival in the randomised For Omitting Radiation Under Majority age (FORUM) trial in children with high-risk ALL makes exploration of the optimal use of TBI delivery mandatory. Standardisation and comprehensive reporting of conventional TBI techniques as well as cooperation between radiotherapy centres may help to increase the ratio between treatment outcomes and toxicity, and future studies must determine potential added benefit of innovative conformal techniques to ultimately improve quality of life for paediatric ALL patients receiving TBI-conditioned HSCT.

Improved outcome in young adults with de novo acute myeloid leukemia in first remission, undergoing an allogeneic bone marrow transplant

We assessed the outcome of 170 patients with AML in first complete remission, aged 1-47 years (median 29), who had undergone an allogeneic BMT before or after 1990 (n=80 and n=90, respectively); all patients were prepared with cyclophosphamide and TBI; the median follow-up for surviving patients was 13 years. The donor was an HLA-identical sibling in 164 patients. Transplant-related mortality (TRM) was 30% before and 7% after 1990 (P<0.001); relapse-related death (RRD) was 26 and 11% (P=0.002); and actuarial 10-year survival was 42 and 79% (P<0.00001). Patients transplanted after 1990 were older, had a shorter interval diagnosis-BMT, had less FAB-M3 cases, received a higher dose of TBI, a higher marrow cell dose and combined (cyclosporine+methotrexate) GVHD prophylaxis. Patients relapsing after transplant had an actuarial survival of 0 vs 31% if grafted before or after 1990 (P=0.01), and their median follow-up exceeds 10 years. In conclusion, the overall survival of first remission AML undergoing an allogeneic BMT has almost doubled in the past two decades, despite older age and fewer M3 cases. Improvement has come not only from changes in transplant procedures, but also from effective rescue of patients relapsing after transplant.

Conditioning with 8-Gy total body irradiation and fludarabine for allogeneic hematopoietic stem cell transplantation in acute myeloid leukemia

Seventy-one patients with acute myeloid leukemia (AML), most of them (63/71) considered ineligible for conventional allogeneic hematopoietic stem cell transplantation (HSCT), were enrolled into a phase 2 study on reduced-intensity myeloablative conditioning with fractionated 8-Gy total body irradiation (TBI) and fludarabine (120 mg/m2). Patients received mobilized peripheral blood stem cells (n = 68) or bone marrow (n = 3) from siblings (n = 39) or unrelated donors (n = 32). Thirty-six patients received a transplant in complete remission (CR) and 35 had untreated or refractory disease (non-CR). Median patient age was 51 years (range, 20-66 years). Sustained engraftment was attained in all evaluable patients. With a median follow-up of 25.9 months (range, 3.7-61.2 months) in surviving patients, probabilities of overall survival for patients who received a transplant in CR and non-CR were 81% and 21% at 2 years, respectively. Relapse-free survival rates were 78% and 16%. The cumulative incidence of nonrelapse mortality (NRM) in CR patients was 8% at 2 years and beyond but amounted to 37% at 2 years in non-CR patients. Outcome data in this poor-risk population indicate that allogeneic HSCT from related or unrelated donors with 8-Gy TBI/fludarabine conditioning is feasible with low NRM and preserved antileukemic activity in AML patients in first or later CR.

Low-dose fractionated total body irradiation (TBI) adversely affects prognosis of patients with leukemia receiving an HLA-matched allogeneic bone marrow transplant from an unrelated donor (UD-BMT)

The optimal total body irradiation (TBI) regimen for unrelated donor bone marrow transplant (UD-BMT) is unknown. In the present study we analyze the outcomes of two different TBI regimens used in our center for patients with leukemia undergoing an UD-BMT. Between January 1994 and August 2001, 99 consecutive UD-BMT patients entered this comparative study. The conditioning regimen consisted of cyclophosphamide, 120 mg/kg followed by TBI on days -3, -2 and -1. Forty-six patients received TBI 12 Gy (2 Gy, twice a day) in six fractions (HF-TBI) and 53 patients received TBI 9.90 Gy (3.30 Gy per day) fractionated over 3 days (F-TBI). End-points were transplanted-related mortality (TRM), leukemia relapse rate (LRR) and overall survival (OS). At median follow-up of 22 months (58 months for HF-TBI and 17 for F-TBI, respectively), 60 patients were alive (32 in HF-TBI sub-group and 28 in F-TBI one). The actuarial 5-year TRM was 31% for HF-TBI and 41% for F-TBI (P = 0.1), whereas the 5-year LRR was 13% for HF-TBI and 31% for F-TBI (P = 0.04). The actuarial 5-year OS was 68% for patients treated with HF-TBI and 51% for those treated with F-TBI (P = 0.02). At multivariate analysis F-TBI schedule emerged as an adverse predictor for OS (P = 0.04) and LRR (P = 0.03). These data indicate that a lower total dose of TBI appears significantly less effective in leukemia eradication and associated with worse overall survival when compared with a higher dose of radiation.

Relevance of bone marrow cell dose on allogeneic transplantation outcomes for patients with acute myeloid leukemia in first complete remission: results of a European survey

PURPOSE

Many attempts have been made to improve the results of allogeneic bone marrow transplantation (alloBMT) for patients with acute myeloid leukemia (AML) in first complete remission (CR1). Bone marrow cell dose has been reported to be an important factor in alloBMT; however, its true impact on relapse incidence (RI), leukemia-free survival (LFS), and nonrelapse mortality (NRM) in a large cohort of patients is unknown.

PATIENTS AND METHODS

From January 1992 to December 1999, 572 bone marrow transplantation recipients reported to the European Blood and Marrow Transplantation (EBMT) registry underwent allografting from an HLA-identical sibling donor with an unmanipulated bone marrow for AML in CR1.

RESULTS

The median number of nucleated cells (NCs) infused was 2.6 x 10(8)/kg. Estimated 5-year NRM, LFS, and RI for patients receiving more or less than 2.6 x 10(8) NCs/kg were, respectively, 18% +/- 5% v 30% +/- 5% (P =.001), 68% +/- 3% v 46% +/- 3% (P <.00001), and 14% +/- 4% v 24% +/- 5% (P =.004). The association of cell dose with the above outcomes was confirmed in multivariate analyses for NRM (relative risk [RR], 0.53; P =.0007), for LFS (RR, 0.53; P =.00008), and for RI (RR, 0.57; P =.02). The cell dose was also an important factor for neutrophil (RR, 0.76; P =.009) and platelet (RR, 0.77; P =.03) recoveries; however, it did not statistically influence the incidence of acute graft-versus-host disease.

CONCLUSION

This study shows that marrow cell dose is one of the most important factors influencing relapse, NRM, and LFS after alloBMT for patients with AML in CR1. Therefore, increasing the marrow cell dose should substantially improve the survival of these patients.

The combined effect of total body irradiation (TBI) and cyclosporin A (CyA) on the risk of relapse in patients with acute myeloid leukaemia undergoing allogeneic bone marrow transplantation

One hundred and fifty acute myeloid leukaemia (AML) patients in first remission received an allogeneic bone marrow transplant (BMT), after conditioning with cyclophosphamide 120 mg/kg and total body irradiation (TBI) 3.3 Gy x 3 (total nominal dose 9.9). The received dose, as recorded by thermoluminescent dosimeters, ranged between 7. 83 and 12.25 Gy. Patients who received TBI < 9.9 Gy (n = 34) had a significantly higher relapse rate when compared with patients receiving >/= 9.9 Gy (n = 116) (43% vs. 19%; P = 0.002). Graft versus host disease (GvHD) prophylaxis consisted of cyclosporin A (CyA) with or without methotrexate (MTX). The dose of CyA was either 1 or 5 mg/kg/day i.v. from day -1 to + 20, then 10 mg/kg/day orally until day + 365. Patients receiving 5 mg/kg CyA (n = 40) had a higher risk of relapse (49% vs. 15%; P = 0.0001). Thus, low-dose TBI (< 9.9 Gy) and high-dose CyA (5 mg/kg) were significant predictors of leukaemia relapse. Patients were then divided into three groups: those who had both negative predictors (< 9.9 Gy TBI and 5 mg/kg CyA; n = 26); those who had only one (either < 9.9 Gy TBI or 5 mg/kg CyA; n = 22); and those who had neither (>/= 9.9 Gy TBI and 1 mg/kg CyA; n = 102). The three groups were comparable for FAB subtype, interval diagnosis transplant and age. The 5-year actuarial relapse rate for these three groups of patients was 49%, 41% and 15%, with no difference between the first two and a significant difference when compared with the latter (P < 0.01). These data indicate that acute myeloid leukaemia can be cured with allogeneic bone marrow transplantation given an intensive conditioning regimen and low-dose immunosuppression post-graft. Either alone is insufficient to produce long-term disease-free survival. These results may be relevant for programmes of reduced intensity conditioning designed for patients with acute leukaemia.

Total body irradiation correlates with chronic graft versus host disease and affects prognosis of patients with acute lymphoblastic leukemia receiving an HLA identical allogeneic bone marrow transplant

PURPOSE

To investigate whether different procedure variables involved in the delivery of fractionated total body irradiation (TBI) impact on prognosis of patients affected by acute lymphoblastic leukemia (ALL) receiving allogeneic bone marrow transplant (BMT).

METHODS AND MATERIALS

Ninety-three consecutive patients with ALL receiving a human leukocyte antigen (HLA) identical allogeneic BMT between 1 August 1983 and 30 September 1995 were conditioned with the same protocol consisting of cyclophosphamide and fractionated TBI. The planned total dose of TBI was 12 Gy (2 Gy, twice a day for 3 days). Along the 12-year period, variations in delivering TBI schedule occurred with regard to used radiation source, instantaneous dose rate, technical setting, and actual total dose received by the patient. We tested these different TBI variables as well as factors related to patient, state of disease, and transplant-induced disease to investigate their influence on transplant-related mortality, leukemia relapse, and survival.

RESULTS

At median follow-up of 7 years (range 3-15 years) the probabilities of leukemia-free survival (LFS) and overall survival (OS) for the 93 patients were 60% and 41%, respectively. At univariate analysis, chronic graft versus host disease (cGvHd) (p = 0.0005), age (p = 0.01), and state of disease (p = 0.03) were factors affecting LFS whereas chronic GvHd (p = 0.0005), acute GvHd (p = 0.03), age (p = 0.0001), and GvHd prophylaxis (p = 0.01) were factors affecting overall survival. The occurrence of chronic GvHd was correlated with actually delivered TBI dose (p = 0.04). Combined stratification of prognostic factors showed that patients who received the planned total dose of TBI (12 Gy) and were affected by chronic GvHd had higher probabilities of LFS (p = 0.01) and OS (p = n.s.) than patients receiving less than 12 Gy and/or without occurrence of chronic GvHd. Moreover, TBI dose had a significant impact on LFS in patients transplanted in first remission (p = 0.05). At multivariate analysis, TBI dose was an independent factor affecting overall survival (p = 0.05) as well as chronic GvHd (p = 0.001) and age (p = 0.04).

CONCLUSIONS

This retrospective analysis showed that different variables involved in TBI delivery may influence the occurrence of cGvHd and affect prognosis of patients with ALL receiving allogeneic BMT. The total dose of 12 Gy, administered in six fractions over 3 days, appears to be an effective and low toxic regimen for ALL patients transplanted in first remission.

Low Transplant Mortality in Allogeneic Bone Marrow Transplantation for Acute Myeloid Leukemia: A Randomized Study of Low-Dose Cyclosporin Versus Low-Dose Cyclosporin and Low-Dose Methotrexate

Sixty patients undergoing allogeneic bone marrow transplant for acute myeloid leukemia (AML) in first remission (CR1; n = 49) or more advanced phase (n = 11) were entered in a prospective trial of graft-versus-host disease (GvHD) prophylaxis: low-dose cyclosporin A (IdCSA; 1 mg/kg/d from day −1 to +20 day; n = 28) or IdCSA plus low-dose methotrexate (IdMTX; 10 mg/m2 for day +1, 8 mg/m2 for days +3, +6, and +11; n = 32). Primary end points were acute GvHD (aGvHD) and transplant-related mortality (TRM); secondary end points were relapse and survival. The conditioning regimen consisted of cyclophosphamide (120 mg/kg) and fractionated total body irradiation (3.3 Gy/d for 3 consecutive days). The actuarial risk of developing aGvHD grade II-III was 61% for IdCSA alone and 34% for IdCSA + IdMTX (P = .02). The actuarial risk of TRM at 1 year was 11% versus 13%, respectively, and older patients (≧29 years) had higher TRM than younger patients (22% v 5%,P = .01). The age effect was significant in the IdCSA group (P = .04) but not in the IdCSA + IdMTX group (P = .1). The median follow-up is 4.4 years, with an overall actuarial survival of 78% for CR1 patients and 36% for patients with advanced disease. For patients in CR1 the outcome of the two regimens was as follows: survival 77% versus 80% (P = .6), relapse 20% versus 9% (P = .1), and TRM 13% versus 17% (P = .6). This study suggests that TRM can be reduced in AML patients undergoing allogeneic marrow transplants with a mild conditioning regimen and low-dose immunosuppression, and this translates in a 78% 5-year survival for CR1 patients. Beyond CR1 the major obstacle remains leukemia relapse, which is not prevented by low-dose in vivo immunosuppression.

Low Transplant Mortality in Allogeneic Bone Marrow Transplantation for Acute Myeloid Leukemia: A Randomized Study of Low-Dose Cyclosporin Versus Low-Dose Cyclosporin and Low-Dose Methotrexate

Sixty patients undergoing allogeneic bone marrow transplant for acute myeloid leukemia (AML) in first remission (CR1; n = 49) or more advanced phase (n = 11) were entered in a prospective trial of graft-versus-host disease (GvHD) prophylaxis: low-dose cyclosporin A (IdCSA; 1 mg/kg/d from day −1 to +20 day; n = 28) or IdCSA plus low-dose methotrexate (IdMTX; 10 mg/m2 for day +1, 8 mg/m2 for days +3, +6, and +11; n = 32). Primary end points were acute GvHD (aGvHD) and transplant-related mortality (TRM); secondary end points were relapse and survival. The conditioning regimen consisted of cyclophosphamide (120 mg/kg) and fractionated total body irradiation (3.3 Gy/d for 3 consecutive days). The actuarial risk of developing aGvHD grade II-III was 61% for IdCSA alone and 34% for IdCSA + IdMTX (P = .02). The actuarial risk of TRM at 1 year was 11% versus 13%, respectively, and older patients (≧29 years) had higher TRM than younger patients (22% v 5%,P = .01). The age effect was significant in the IdCSA group (P = .04) but not in the IdCSA + IdMTX group (P = .1). The median follow-up is 4.4 years, with an overall actuarial survival of 78% for CR1 patients and 36% for patients with advanced disease. For patients in CR1 the outcome of the two regimens was as follows: survival 77% versus 80% (P = .6), relapse 20% versus 9% (P = .1), and TRM 13% versus 17% (P = .6). This study suggests that TRM can be reduced in AML patients undergoing allogeneic marrow transplants with a mild conditioning regimen and low-dose immunosuppression, and this translates in a 78% 5-year survival for CR1 patients. Beyond CR1 the major obstacle remains leukemia relapse, which is not prevented by low-dose in vivo immunosuppression.

Cytotoxic T-lymphocyte (CTL) responses against acute or chronic myeloid leukemia

In addition to chemotherapy and irradiation, in the context of allogeneic stem cell transplantation (SCT), the donor cell-mediated antileukemic effect can lead to sustained complete remissions, also in cases of a large tumor load. This phenomenon appears to be an immunologically mediated response, possibly due to various effector cell populations. Cytotoxic T-lymphocyte (CTL) responses against minor histocompatibility antigens with restricted tissue distribution, in particular restricted to some or all hematopoietic cells, may be highly efficient in inducing anti-leukemic responses for adoptive immunotherapy. Specific CTL responses against leukemia-associated antigens may be generated using leukemic cells modified to coexpress costimulatory molecules identical to professional antigen-presenting cells. Donor-derived T cells recognizing such antigens may be used in the context of allogeneic SCT to induce complete and sustained remissions, also in patients with leukemia refractory to chemotherapy. In these circumstances, the primary objective of allogeneic SCT may be not to diminish the number of malignant cells by the chemotherapy and irradiation as part of the conditioning regimen, but to allow immunotherapy against leukemic cells using donor lymphocyte populations.

Recognition of clonogenic leukemic cells, remission bone marrow and HLA-identical donor bone marrow by CD8+ or CD4+ minor histocompatibility antigen-specific cytotoxic T lymphocytes

We investigated whether minor histocompatibility (mH) antigen-specific cytotoxic T lymphocytes (CTL) can discriminate between leukemic hematopoietic progenitor cells (leukemic-HPC) from AML or CML patients, the HPC from their remission bone marrow (remission-HPC), and normal HPC from their HLA-identical sibling bone marrow donor (donor-HPC). Specific lysis by CD8+ CTL clones was observed not only of the leukemic-HPC but also of the donor-HPC in 3/4 patient/donor combinations expressing mH antigen HA-1, 3/5 combinations expressing mH antigen HA-2, 2/3 combinations expressing mH antigen HA-3, and 2/2 combinations expressing mH antigen HY-A1. In four patient/donor combinations the recognition of the donor-HPC was clearly less than of the leukemic-HPC, indicating differential susceptibility to lysis by these mH CTL clones. In addition, differential recognition of leukemic-HPC and remission-HPC within seven patients was analyzed. In one patient expressing the HA-2 antigen on the leukemic cells the recognition of the remission-HPC was clearly less than of the leukemic-HPC. One CD4+ CTL clone showed specific lysis of the leukemic-HPC from an AML patient and a CML patient as well as of normal remission-HPC and donor-HPC. These results illustrate that in general CD8+ and CD4+ mH antigen specific CTL clones do not differentially recognize leukemic-HPC and normal-HPC. However, differences in susceptibility to lysis of malignant versus normal cells may contribute to a differential GVL effect.

Single dose versus fractionated total body irradiation before bone marrow transplantation: radiobiological and clinical considerations

PURPOSE

This present review is intended to evaluate the specific influence of fractionation of total body irradiation on the outcome of a subsequent bone marrow transplantation.

METHODS AND MATERIALS

Available experimental and clinical data on the influence of fractionation on leukemia cell killing, immunosuppression, and sparing of normal tissues were analyzed.

RESULTS

Review of available data shows: (a) The role of fractionation on leukemia cell killing may vary with the leukemia type. For acute nonlymphoblastic leukemia, a few experimental and several clinical studies show no or little fractionation effect; a 12-13 Gy fractionated scheme could, therefore, be more efficient than a conventional 10 Gy single dose total body irradiation. For chronic myelogenous leukemia, some sensitivity to fractionation is suggested, so that an increase in total or fractional dose may be necessary in fractionated schemes to equate the efficacy of a 10 Gy single dose. For acute lymphoblastic leukemia, a high fractionation sensitivity was observed for some leukemic cell lines in vitro, without undisputable clinical confirmation for the moment. (b) Numerous experimental studies have demonstrated that the immunosuppressive effect of total body irradiation, a major determinant of engraftment, is highly fractionation sensitive. In humans, high rates of graft failures have been reported when T-cell depletion of the graft was associated to fractionated total body irradiation schedules. (c) A large amount of radiobiological and clinical data have demonstrated that late radiation-induced injuries to normal tissues and organs are highly fractionation sensitive. However, in a context of total body irradiation for bone marrow transplantation, the number of other determinants of normal tissue damage makes it difficult to demonstrate a clear-cut advantage of fractionated over single dose scheme, with a possible exception for children.

CONCLUSIONS

In 1994, available data suggest that very cautious attempts could be made to adapt total body irradiation schedules to the potential normal tissue toxicity, T-cell depletion, and to the type of leukemia.

Risk factors for early mortality in allogeneic bone marrow transplantation. A multivariate analysis on 174 leukaemia patients

Allogeneic bone marrow transplantation in patients with leukaemia is an aggressive therapeutic procedure which implies high early mortality. Current opinion trends attribute the greater part of the procedure toxicity to the preparative regimen. The results of a multivariate analysis on data of 174 leukaemia patients conditioned with total body irradiation (TBI), 10-12 Gy, single dose or fractionated, and lung shielding at 8 Gy, plus chemotherapy: cyclophosphamide 120 mg/kg, before or after TBI, are presented. The variables statistically related with early mortality are age, Karnofsky index (KI) and acute graft-versus-host disease (GvHD). No variable depending on radiotherapy reached the significance level. The relative risk of early mortality for patients older than 26 years, in bad general condition (KI < 90%), or developing acute severe (grades II-IV)GvHD, is 3.99, 5.68, and 6.71, respectively. We conclude that in the range of TBI schedules analysed, radiation therapy is not an important factor in early death, but acute severe GvHD, or recipient's bad general condition are factors to be improved by bone marrow transplantation teams if they want to improve the therapeutic index of the procedure.

Eradication of leukaemic marrow and prevention of leukaemia relapse with total body irradiation and bone marrow transplantation

A series of studies was carried out to determine the effect of allogeneic bone marrow transplantation (BMT) on leukaemia. The study aimed at two different, but strictly linked issues: (1) identification of the eradication capability of BMT, and (2) evaluation of the effect of BMT, both in preventing relapse and in producing long-term disease-free survival. Fifty-four patients allografted for leukaemia were evaluated at various intervals, after bone marrow transplantation, for the presence of host haemopoiesis using red-blood-cell and cytogenetic markers. Among 40 patients in remission, 10 showed functional host and donor haemopoiesis (mixed chimerism), while in 30, host haemopoiesis was never detected (complete chimerism). Seven of the 14 evaluable patients who relapsed showed the reappearance of host haemopoiesis at the time of relapse. The records of received doses of TBI indicate that patients who achieved mixed chimerism, either relapsing or not, received significantly lower doses than complete chimeras. However, some patients with complete chimerism received a TBI dose equivalent to the dose received by those with mixed chimerism, suggesting that the TBI dose is not the only factor determining the reappearance of host haemopoiesis. The data on chimerism and relapse suggest that there is heterogeneity in radiosensitivity between normal marrow cells and leukaemic cells, and further, within the different types of leukaemia. The incidence/severity of acute and chronic graft-vs-host disease (GvHD) was significantly higher in complete chimeras than in mixed chimeras suggesting that mixed chimerism may play a role in the development of tolerance; however, it could be the tolerance (i.e. absence of GvHD) which is responsible for the persistence of host haemopoietic cells. One-hundred-and-sixty-eight patients undergoing allogeneic bone marrow transplantation (BMT) for acute myeloid leukaemia (AML) and chronic myeloid leukaemia were analyzed for risk factor associated with relapse. All patients received marrow from an HLA identical sibling after preparation with cyclophosphamide 120 mg/kg and total body irradiation (TBI) of 330 cGy on days -3, -2, -1. There was a difference of +/- 18% between the nominal total dose of 990 cGy and the actual received dose as indicated by dosimetric recordings. While interstitial pneumonitis had minimal impact on survival there was a considerable difference in the incidence of relapses. The incidence of relapse was higher in patients receiving less, than in patients receiving more than 1000 cGy respectively and this had a major impact on survival. However, transplant-related mortality was slightly higher in the group of patients receiving higher doses of TBI.(ABSTRACT TRUNCATED AT 400 WORDS)