Helical tomotherapy for total lymphoid irradiation

Tomotherapy Applied Total Lymphoid Irradiation and Allogeneic Hematopoietic Cell Transplantation Generates Mixed Chimerism in the Rhesus Macaque Model

Development of a new methodology to induce immunological chimerism after allogeneic hematopoietic cell (HC) transplantation in a rhesus macaque model is described. The chimeric state was achieved using a non-myeloablative, helical tomotherapy-based total lymphoid irradiation (TomoTLI) conditioning regimen followed by donor HC infusions between 1-haplotype matched donor/recipient pairs. The technique was tested as a feasibility study in an experimental group of seven rhesus macaques that received the novel TomoTLI tolerance protocol and HC allo-transplants. Two tomotherapy protocols were compared: TomoTLI (n = 5) and TomoTLI/total-body irradiation (TBI) (n = 2). Five of seven animals developed mixed chimerism. Three of five animals given the TomoTLI protocol generated transient mixed chimerism with no graft-versus-host disease (GVHD) with survival of 33, 152 and >180 days. However, the inclusion of belatacept in addition to a single fraction of TBI resulted in total chimerism and fatal GVHD in both animals, indicating an unacceptable conditioning regimen.

First Multimodal, Three-Dimensional, Image-Guided Total Marrow Irradiation Model for Preclinical Bone Marrow Transplantation Studies

PURPOSE

Total marrow irradiation (TMI) has significantly advanced radiation conditioning for hematopoietic cell transplantation in hematologic malignancies by reducing conditioning-induced toxicities and improving survival outcomes in relapsed/refractory patients. However, the relapse rate remains high, and the lack of a preclinical TMI model has hindered scientific advancements. To accelerate TMI translation to the clinic, we developed a TMI delivery system in preclinical models.

METHODS AND MATERIALS

A Precision X-RAD SmART irradiator was used for TMI model development. Images acquired with whole-body contrast-enhanced computed tomography (CT) were used to reconstruct and delineate targets and vital organs for each mouse. Multiple beam and CT-guided Monte Carlo-based plans were performed to optimize doses to the targets and to vary doses to the vital organs. Long-term engraftment and reconstitution potential were evaluated by a congenic bone marrow transplantation (BMT) model and serial secondary BMT, respectively. Donor cell engraftment was measured using noninvasive bioluminescence imaging and flow cytometry.

RESULTS

Multimodal imaging enabled identification of targets (skeleton and spleen) and vital organs (eg, lungs, gut, liver). In contrast to total body irradiation (TBI), TMI treatment allowed variation of radiation dose exposure to organs relative to the target dose. Dose reduction mirrored that in clinical TMI studies. Similar to TBI, mice treated with different TMI regimens showed full long-term donor engraftment in primary BMT and second serial BMT. The TBI-treated mice showed acute gut damage, which was minimized in mice treated with TMI.

CONCLUSIONS

A novel multimodal image guided preclinical TMI model is reported here. TMI conditioning maintained long-term engraftment with reconstitution potential and reduced organ damage. Therefore, this TMI model provides a unique opportunity to study the therapeutic benefit of reduced organ damage and BM dose escalation to optimize treatment regimens in BMT and hematologic malignancies.

The role of radiotherapy in Hodgkin's lymphoma: what has been achieved during the last 50 years?

Currently, Hodgkin's lymphoma (HL) has an excellent clinical outcome, with overall survival of approximately 90% in early stages of the disease. Based on young age of the majority of patients at the time of diagnosis and their long survival time, increased attention has been focused on long-term toxicity of therapy. While novel, directly targeting antitumor agents, with an excellent safety profile, have been developed for HL treatment, the role of radiotherapy is still debated. Radiotherapy may induce cardiovascular disease and impairment of thyroid or pulmonary function and, most importantly, may lead to development of secondary cancers. As a consequence, the current radiation therapy planning paradigm is mainly focused on a reduction of field size. As it was investigated in clinical trials regional therapy is as effective as extended field radiotherapy, but less toxic. Although chemotherapy is the mainstay of HL treatment, consolidative involved field radiation therapy is still considered to be the standard of care in both early and advanced stages. Recently, further field reduction has been investigated to further decrease the late radiation-induced toxicity. In this paper we describe the role and safety profile of radiotherapy in the past and present and hope for the novel techniques in the future.

Applications of new irradiation modalities in patients with lymphoma: Promises and uncertainties

New highly conformal irradiation modalities have emerged for treatment of Hodgkin lymphoma. Helical tomotherapy offers both intensity-modulated irradiation and accurate patient positioning and was shown to significantly decrease radiation doses to the critical organs. Here we review some of the most promising applications of helical tomotherapy in Hodgkin disease. By decreasing doses to the heart or the breast, helical tomotherapy might decrease the risk of long-term cardiac toxicity or secondary breast cancers, which are major concerns in patients receiving chest radiotherapy. Other strategies, such as debulking radiotherapy prior to stem cell transplantation or total lymphoid irradiation may be clinically relevant. However, helical tomotherapy may also increase the volume of tissues that receive lower doses, which has been implicated in the carcinogenesis process. Prospective assessments of these new irradiation modalities of helical tomotherapy are required to confirm the potential benefits of highly conformal therapies applied to hematological malignancies.

Comparison of CT and integrated PET-CT based radiation therapy planning in patients with malignant pleural mesothelioma

Background

When combined with adequate tumoricidal doses, accurate target volume delineation remains to be the one of the most important predictive factors for radiotherapy (RT) success in locally advanced or medically inoperable malignant pleural mesothelioma (MPM) patients. Recently, 18-fluorodeoxyglucose positron emission tomography (PET) has demonstrated significant improvements in diagnosis and accurate staging of MPM. However, role of additional PET data has not been studied in RT planning (RTP) of patients with inoperable MPM or in those who refuse surgery. Therefore, we planned to compare CT with co-registered PET-CT as the basis for delineating target volumes in these patients group.

Methods

Retrospectively, the CT and co-registered PET-CT data of 13 patients with histologically proven MPM were utilized to delineate target volumes separately. For each patient, target volumes (gross tumor volume [GTV], clinical target volume [CTV], and planning target volume [PTV]) were defined using the CT and PET-CT fusion data sets. The PTV was measured in two ways: PTV1 was CTV plus a 1-cm margin, and PTV2 was GTV plus a 1-cm margin. We analyzed differences in target volumes.

Results

In 12 of 13 patients, compared to CT-based delineation, PET-CT-based delineation resulted in a statistically significant decrease in the mean GTV, CTV, PTV1, and PTV2. In these 12 patients, mean GTV decreased by 47.1% ± 28.4%, mean CTV decreased by 38.7% ± 24.7%, mean PTV1 decreased by 31.1% ± 23.1%, and mean PTV2 decreased by 40.0% ± 24.0%. In 4 of 13 patients, hilar lymph nodes were identified by PET-CT that was not identified by CT alone, changing the nodal status of tumor staging in those patients.

Conclusion

This study demonstrated the usefulness of PET-CT-based target volume delineation in patients with MPM. Co-registration of PET and CT information reduces the likelihood of geographic misses, and additionally, significant reductions observed in target volumes may potentially allow escalation of RT dose beyond conventional limits potential clinical benefits in tumor control rates, which needs to be tested in future studies.