SU-E-T-132: Investigation of Photon and Proton Overlapping Fields in PRESAGE- Dosimeters

PURPOSE

To evaluate the effects of overlapping dose volumes for varying field arrangements in two formulations of PRESAGE®: one intended for, and irradiated with, proton beams and the other photon beams.

METHODS

For each treatment modality (photon, proton), three overlapping field setups were performed. These included a stationary dosimeter irradiated over six fractions, a dosimeter shifted laterally to the field to deliver a dose plateau in two fractions, and a dosimeter rotated on its axis to deliver a two-field (for protons) and four-field (for photons) box treatment overlapping in the center of the dosimeter. All subsequent fractions were given within ten minutes and never less than one minute apart. Two cylindrical PRESAGE® dosimeters approximately 7.5 cm in length by 7.5 cm in diameter were irradiated for each setup. The dosimeters were paired, with one dosimeter given total dose by a single fraction while the other followed one of the overlapping field setups. The dosimeters were analyzed using an optical CT scanner and exported to the CERR environment where the doses were compared between paired dosimeters.

RESULTS

Dose profile comparisons showed relative dose agreement between paired dosimeters within 5% along the SOBP region of the proton formulation. In the case of the fractionated proton irradiation, there was an over-response while other setups resulted in under-responses. Dose agreement between the photon dosimeter treated with six fractions showed a dose under-response within 11% and never less than 5%. Future measurements will include the remaining field setups.

CONCLUSIONS

The proton formulation of PRESAGE® showed good dose agreement between single and multiple field irradiations. While the photon formulation had slightly less agreement, additional field setup comparisons may show improved results. These results will aid future measurements of overlapping field treatment plans delivered to PRESAGE® for treatment verification for proton and photon 3D dosimetry.

BCR-ABL: a multi-faceted promoter of DNA mutation in chronic myelogeneous leukemia

The role of the BCR-ABL oncogene in the progression of chronic myeloid leukemia (CML) to blast crisis (BC) is unknown. The appearance of chromosomal aberrations in patients with CML BC has led to many attempts to elucidate a mechanism whereby BCR-ABL affects DNA damage and repair. BCR-ABL-expressing cells have been found to accumulate genetic abnormalities, but the mechanism leading to this genomic instability is controversial. In this study, we review the effects of BCR-ABL on DNA repair mechanisms, centrosomes, checkpoint activation and apoptosis. BCR-ABL has diverse effects on these mechanisms, but which of these effects are necessary for the progression of CML to BC is still unresolved.

A robust xenotransplantation model for acute myeloid leukemia

Xenotransplantation of human acute myeloid leukemia (AML) in immunocompromised animals has been critical for defining leukemic stem cells. However, existing immunodeficient strains of mice have short life spans and low levels of AML cell engraftment, hindering long-term evaluation of primary human AML biology. A recent study suggested that NOD/LtSz-scid IL2Rgammac null (NSG) mice have enhanced AML cell engraftment, but this relied on technically challenging neonatal injections. Here, we performed extensive analysis of AML engraftment in adult NSG mice using tail vein injection. Of the 35 AML samples analyzed, 66% showed bone marrow engraftment over 0.1%. Further, 37% showed high levels of engraftment (>10%), with some as high as 95%. A 2-44-fold expansion of AML cells was often seen. Secondary and tertiary recipients showed consistent engraftment, with most showing further AML cell expansion. Engraftment did not correlate with French-American-British subtype or cytogenetic abnormalities. However, samples with FLT3 mutations showed a higher probability of engraftment than FLT3 wild type. Importantly, animals developed organomegaly and a wasting illness consistent with advanced leukemia. We conclude that the NSG xenotransplantation model is a robust model for human AML cell engraftment, which will allow better characterization of AML biology and testing of new therapies.

Tanespimycin plus bortezomib in patients with relapsed and refractory multiple myeloma: Final results of a phase I/II study

8503

Background: Tanespimycin (Tan) disrupts HSP90, a key molecular chaperone for signal transduction proteins critical to myeloma (MM) growth, survival and drug resistance. Preclinical data show anti-tumor synergy between Tan and bortezomib (Bz) and suggest Tan may be neuroprotective, including reversibility of Bz-induced peripheral neuropathy (PN). A phase I study of single agent Tan in advanced MM showed favorable tolerability and modest activity. Methods: 72 patients (pts) with relapsed/refractory MM received 0.7 - 1.3 mg/m2 Bz as IVB followed by 1-hr infusion of 100 -340 mg/m2 Tan on days 1, 4, 8,11 q 21d, with 42 pts receiving the highest dose of both drugs as part of a phase II expansion. Toxicities were assessed by CTCAE v3 and response by modified EBMT criteria. Results: Of 72 pts, 72% had IgG subtype with a median age of 60 yo. Median time since MM diagnosis was 50 mos with median of 5 (1–15) prior regimens. Prior treatments included stem cell transplant (69%), thalidomide (74%), Bz (69%), lenalidomide (28%) and Hsp90 inhibitors (13%). 58 pts with measurable disease were treated at 1 or 1.3 mg/m2 Bz. Response rates (≥ MR) were 41%, 20% and 14% in the Bz-naive, -pretreated and -refractory pts respectively. In the subgroup with 1–3 prior therapies and who were Bz-naive, the response rate was 56%. Median duration of response (DOR) for all pts with response (n=14) was 10.7 mos, including 3 Bz-refractory pts who had durable PR through mos 12, 22 and 28. 3 other pts remain in response through 24 mos. Of the 72 pts, the most frequent AEs were diarrhea (60%), nausea (49%), fatigue (49%), thrombocytopenia (40%) and AST elevation (28%), which proved manageable with dose reduction and supportive care. Most frequent G3–4 AEs included thrombocytopenia (25%), diarrhea, anemia and fatigue (7% each), as well as back pain and AST elevation (4% each). Only 21% of pts had G1–2 PN; no G3–4 PN was seen. Conclusions: Tan + Bz is active and well tolerated in relapsed/refractory MM, with durable responses in Bz-naive, -pretreated and -refractory pts. Median DOR for the combination compares favorably to Bz monotherapy. Final PFS data will be presented. No severe PN has been observed, consistent with Tan's neuroprotective effect in pre-clinical models. A phase III study of Tan + Bz vs Bz is ongoing.

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Trends of elevated blood pressure among children and adolescents: data from the National Health and Nutrition Examination Survey1988-2006

BACKGROUND

Elevated blood pressure (EBP) in children and adolescents increases future risk of cardiovascular disease. Among children and adolescents, increased weight is associated with EBP.

METHODS

National cross-sectional data for children and adolescents aged 8-17 years from the National Health and Nutrition Examination Surveys (NHANESs): 1988-1994, 1999-2002, and 2003-2006. The main outcome measures were EBP and pre-EBP estimates.

RESULTS

Overweight boys (odds ratio (OR) 1.54, confidence interval (CI) 1.11-2.13) and both obese boys and girls were significantly more likely to be classified as pre-EBP (boys, OR 2.81, CI 2.13-3.71; girls, OR 2.55, CI 1.75-3.73) and having EBP (boys aged 8-12 years, OR 6.06, CI 2.73-13.44, boys aged 13-17, OR 9.62 CI 4.86-19.06; girls, OR 2.33, CI 1.31-4.13) when compared to the reference weight and controlling for all other covariates.During 2003-2006, 13.6% (s.e. = 1.2) of boys aged 8-17 years and 5.7% (s.e. = 0.7) of the girls aged 8-17 years were classified as pre-EBP and 2.6% (s.e. = 0.5) of the boys aged 8-17 and 3.4% (s.e. = 0.7) of the girls aged 8-17 were having EBP. After controlling for age, race/ethnicity, and body mass index (BMI), girls only were significantly more likely to have EBP during 2003-2006 than during 1988-1994 (OR 2.17, CI 1.05-4.49). In contrast, adolescent boys aged 13-17 years were significantly less likely to be having EBP during 2003-2006 than during 1988-1994 (OR 0.32, CI 0.13-0.81).

CONCLUSIONS

Obesity is strongly, positively, and independently associated with EBP and pre-EBP among youths. However, controlling for all covariates including BMI, EBP has increased among girls but decreased among adolescent boys aged 13-17, during 2003-2006 when compared with 1988-1994.

BCR/ABL induces chromosomal instability after genotoxic stress and alters the cell death threshold

Earlier reports have suggested that the BCR/ABL oncogene, associated with chronic myeloid leukemia, induces a mutator phenotype; however, it is unclear whether this leads to long-term changes in chromosomes and whether the phenotype is found in primary chronic myelogeneous leukemia (CML) cells. We have addressed both these issues. BCR/ABL-expressing cell lines show an increase in DNA breaks after treatment with etoposide as compared to control cells. However, although BCR/ABL-expressing cell lines have an equivalent cell survival, they have an increase in chromosomal translocations after DNA repair as compared to control cells. This demonstrates that BCR/ABL expression decreases the fidelity of DNA repair. To see whether this is true in primary CML samples, normal CD34+ progenitor cells and CML progenitor cells were treated with etoposide. CML progenitor cells have equivalent survival but have an increase in DNA double-strand breaks (DSBs). Spectral karyotyping demonstrates new chromosomal translocations in CML cells, but not normal progenitor cells, consistent with error-prone DNA repair. Taken together, these data demonstrate that BCR/ABL enhances the accumulation of DSBs and alters the apoptotic threshold in CML leading to error-prone DNA repair.