Conditioning regimens for allogeneic bone marrow transplantation

Total Body Irradiation Versus Chemotherapy Conditioning in Pediatric Acute Lymphoblastic Leukemia Patients Undergoing Hematopoietic Stem Cell Transplant: A Systematic Review and Meta-Analysis

Allogeneic hematopoietic stem cell transplant (HSCT) is indicated in pediatric patients with acute lymphoblastic leukemia (ALL) who have relapsed or are at a very high risk of relapse during first complete remission. Two types of myeloablative conditioning are employed before allogeneic HSCT: total body irradiation (TBI)-based regimens and chemotherapy (CHT) alone. This study compares the efficacy and safety of TBI-based regimens and CHT-based conditioning in pediatric, adolescent, and young adult patients with ALL (0-24 years old). TBI-based and CHT-conditioning regimens were evaluated in 4262 and 1367 patients, respectively, from 15 studies. Compared to CHT alone, TBI-based regimens were associated with better overall survival (OS), relative risk (RR) 1.21, better event-free survival (RR 1.34), and a reduced risk of relapse (RR 0.69). Both approaches had comparable risk of acute graft-versus-host disease (GVHD), grades 3 to 4 acute GVHD, chronic GVHD, and nonrelapse mortality (NRM). In the subgroup analysis for patients in first complete remission, TBI-based regimens and CHT alone had comparable OS and NRM. Our results demonstrate the superiority of TBI-based regimens compared to CHT alone in pediatric patients with ALL.

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.

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.

Space-time considerations for hematopoietic stem cell transplantation

The mammalian blood system contains a multitude of distinct mature cell lineages adapted to serving diverse functional roles. Mutations that abrogate the development or function of one or more of these lineages can lead to profound adverse consequences, such as immunodeficiency, autoimmunity, or anemia. Replacement of hematopoietic stem cells (HSC) that carry such mutations with HSC from a healthy donor can reverse such disorders, but because the risks associated with the procedure are often more serious than the blood disorders themselves, bone marrow transplantation is generally not used to treat a number of relatively common inherited blood diseases. Aside from a number of other problems, risks associated with cytoreductive treatments that create "space" for donor HSC, and the slow kinetics with which immune competence is restored following transplantation hamper progress. This review will focus on how recent studies using experimental model systems may direct future efforts to implement routine use of HSC transplantation to cure inherited blood disorders.

Dose response and factors related to interstitial pneumonitis after bone marrow transplant

PURPOSE

Total body irradiation (TBI) and chemotherapy are common components of conditioning regimens for bone marrow transplantation. Interstitial pneumonitis (IP) is a known regimen-related complication. Using published data of IP in a multivariate logistic regression, this study sought to identify the parameters in the bone marrow transplantation conditioning regimen that were significantly associated with IP and to establish a radiation dose-response function.

METHODS AND MATERIALS

A retrospective review was conducted of articles that reported IP incidence along with lung dose, fractionation, dose rate, and chemotherapy regimen. In the final analysis, 20 articles (n = 1090 patients), consisting of 26 distinct TBI/chemotherapy regimens, were included in the analysis. Multivariate logistic regression was performed to determine dosimetric and chemotherapeutic factors that influenced the incidence of IP.

RESULTS

A logistic model was generated from patients receiving daily fractions of radiation. In this model, lung dose, cyclophosphamide dose, and the addition of busulfan were significantly associated with IP. An incidence of 3%-4% with chemotherapy-only conditioning regimens is estimated from the models. The alpha/beta value of the linear-quadratic model was estimated to be 2.8 Gy. The dose eliciting a 50% incidence, D50, for IP after 120 mg/kg of cyclophosphamide was 8.8 Gy; in the absence of chemotherapy, the estimated D50 is 10.6 Gy. No dose rate effect was observed. The use of busulfan as a substitute for radiation is equivalent to treating with 14.8 Gy in 4 fractions with 50% transmission blocks shielding the lung. The logistic regression failed to find a model that adequately fit the multiple-fraction-per-day data.

CONCLUSIONS

Dose responses for both lung radiation dose and cyclophosphamide dose were identified. A conditioning regimen of 12 Gy TBI in 6 daily fractions induces an IP incidence of about 11% in the absence of lung shielding. Shielding the lung to receive 50% of this dose lowers the estimated incidence to about 2.3%. Because the lungs can be adequately shielded, we recommend against using busulfan as a substitute for fractionated TBI with cyclophosphamide.

High-dose therapy and blood or marrow transplantation for non-Hodgkin lymphoma with central nervous system involvement

The role of autologous or allogeneic blood or marrow transplantation (BMT) remains undefined in patients with central nervous system (CNS) involvement by lymphoma. The records of all adult and pediatric non-Hodgkin lymphoma patients receiving BMT at Johns Hopkins from 1980 to 2003 were reviewed, and 37 patients were identified who had CNS involvement that was treated into remission by the time of BMT. The chief histologies were diffuse large B-cell lymphoma and T-cell lymphoblastic lymphoma/leukemia. Twenty-four percent received intrathecal chemotherapy alone, and 70% received intrathecal chemotherapy and CNS irradiation before BMT. The main preparative regimens were cyclophosphamide/total body irradiation and busulfan/cyclophosphamide. Forty-one percent received an allogeneic transplant. Lymphoma relapsed after BMT in 14 patients (38%), and at least 5 had documented or suspected CNS relapse. In multivariate models, age > or =18 years at diagnosis, resistant systemic disease, busulfan/cyclophosphamide conditioning, and lack of intrathecal consolidation after BMT were statistically significant predictors of inferior survival. The 5-year actuarial event-free survival was 36%, and overall survival was 39%. After BMT, long-term survival is thus achievable in a subset of patients with a history of treated CNS involvement by non-Hodgkin lymphoma. The survival rates are not dissimilar to those typically seen in other high-risk lymphoma patients undergoing BMT. These data suggest that patients with lymphomatous involvement of the CNS who achieve CNS remission should be offered BMT if it is otherwise indicated.

Thiotepa, busulfan, and cyclophosphamide as a preparative regimen for allogeneic transplantation for advanced myelodysplastic syndrome and acute myelogenous leukemia

Sixty-two adults underwent marrow or blood stem cell transplantation from an HLA-matched related donor using high-dose thiotepa, busulfan, and cyclophosphamide (TBC) as the preparative regimen for treatment of advanced myelodysplastic syndrome (MDS) (refractory anemia with excess blasts with or without transformation) or acute myelogenous leukemia (AML) past first remission. All evaluable patients engrafted and had complete donor chimerism. A grade 3-4 regimen-related toxicity occurred in eight (13%) patients, and a diagnosis of MDS was the only independent risk factor for grade 3-4 regimen-related toxicity (hazard ratio 9.25, P = 0.01). Day-100 treatment-related mortality (TRM) was 19%. Poor-prognosis cytogenetics increased the risk of day-100 TRM (hazard ratio 11.4, P = 0.003), and use of tacrolimus for graft-versus-host disease prophylaxis reduced the risk of day-100 TRM (hazard ratio 0.13, P = 0.027). For all patients, the three-year relapse rate was 43% (95% CI, 28%-58%). Refractoriness to conventional induction chemotherapy prior to transplantation was an independent risk factor for relapse (hazard ratio 10.8, P = 0.02). Three-year survival was 26% (95% CI, 14%-37%); survival rates were 29% for those transplanted for AML in second remission, 31% transplanted for AML in relapse, and 17% with MDS, and there were no independent risk factors for survival. TBC is an active preparative regimen for advanced AML. Patients with advanced MDS appeared to have a higher risk of toxicity and early mortality, and alternative preparative regimens should be considered for these patients.

Aspects concerning busulfan pharmacokinetics and bioavailability

Busulfan as a high-dose therapy is an important component of many of the myeloablative regimens for both allogeneic and autologous bone marrow transplantation (BMT) in adults and children. During the last decade, several studies have shown a wide inter- and intra-patient variability of busulfan disposition in adults and children. Some of the factors affecting the interpatient-variability were identified as circadian rhythmicity, age, disease, drug interaction, alteration in hepatic function and recently busulfan bioavailability. In adults, pharmacodynamic studies have shown a positive correlation between high-systemic exposure of the drug and venocclusive disease (VOD). However, pharmacodynamic studies in children did not establish any correlation between the systemic exposure and VOD. Drug-monitoring and dose adjustment in adults were used successfully to decrease the occurrence of VOD and mortality. It was observed that about 20% of the busulfan dose crosses the blood brain barrier. The high amount of the drug which enters the brain can probably be involved in the CNS toxicities reported. In children, a low rate of toxicity combined with a high rate of engraftment failure were observed. Several investigators have expressed their concern about the dosage in children and many suggested higher doses based on the body surface area for young children. However, recently it was shown that busulfan bioavailability varied by 2-fold in adults (0.5-1.03) while in children a 6-fold variation was observed (0.22-1.20). The access to an intravenous form of busulfan and a deeper understanding of pharmacodynamics of the drug might be essential to optimize the treatment, reach a successful engraftment and lower the therapy related toxicities.

Simultaneous occurrence of osteosarcoma and osteochondroma following treatment of neuroblastoma with chemotherapy, radiotherapy, and bone marrow transplantation

Radiation-induced bone changes and second malignancies, as well as benign tumors, following bone marrow transplantation are being reported with increasing frequency. An osteosarcoma of the fourth right rib and an osteochondroma of the left scapula developed in a long-term survivor of abdominal neuroblastoma treated with chemotherapy, local radiation, and bone marrow transplantation. All these treatment modalities are known to induce neoplasia.