Estrogen defines the dynamics and destination of transactivated EGF receptor in breast cancer cells: role of S1P₃ receptor and Cdc42

Sphingosine-1-phosphate (S1P) receptors mediate transactivation of epidermal growth factor receptor (EGFR) by estrogen (E2). Here we report that the amount of intracellular EGFR remains elevated after stimulation of MCF-7 cells with E2 and S1P, although membrane-localized EGFR and S1P3 receptors are quickly internalized. Co-localization of internalized EGFR and LAMP-2 was lower in cells treated with E2/S1P, suggesting that endosomal EGFR might be directed for recycling instead of degradation. In addition, we found that E2/S1P activated Cdc42 and that knockdown of Cdc42 restores fast EGFR degradation after E2/S1P stimulation. Inhibition of S1P3 receptors prevented E2-induced activation of Cdc42, supporting the important role of the S1P receptor in E2 signaling. This is a novel mechanism further defining the effect of E2/S1P on the EGFR transactivation in breast cancer cells.

SU-E-J-22: Effect of MLC Leaf Width on MLC Leaf Shifting Algorithm for Concurrent Treatment of Prostate and Pelvic Lymph Nodes

PURPOSE

Our previous study showed that adjusting selected MLC leaf pairsto follow prostate movement is an effective strategy to account for daily prostate displacement during concurrent treatment with pelvic lymph nodes. MLC leaf width affects the quality of MLC shifting plans for longitudinal prostate motion compensation. This study is to investigate the effect of the MLC leaf width in compensation of the prostate movement.

METHODS

Fifty-one daily CT on-rail scans from three patients were available for this study. On these CTs, the prostate, bladder and rectum were manually contoured, and the lymph nodes contours were transferred from the planning CT after rigid bony registration. For each patient, three different IMRT plans were created based on a planning CT using leaf width of 2.5, 5, and 10 mm, respectively. For each CT, the prostate displacement was determined by dual imaging registration and compensated by shifting MLC resulting in a total of 153 MLC shifted plans.

RESULTS

Among 51 daily CTs, the average prostate movement along the superior/inferior direction was 1.1±3.7 mm (range: -6 to 6.5 mm). The differences in D99 of the prostate between the dose of the day and dose of the plan were 2.3±3.3%, 1.3±2.0%, and 4.4±5.1% for 2.5, 5, and 10 mm leaf width plans, respectively (p<<0.05). The corresponding differences in D99 of the lymph nodes were 0.7±0.9%, 0.6±0.9%, and 1.4±0.8%. The mean differences in D50 were 0.8%, 1.6%, and 2.7% for the bladder, and 10.0%, 3.9%, and 5.7% for the rectum, respectively.

CONCLUSIONS

Using the MLC Shifting method to compensate for prostate movement in the longitudinal direction depends on the MLC leaf width and the magnitude of the prostate motion. The use of leaf width of 5 mm can provide sufficient tumor coverage without significantly affecting doses to the critical structures.

SU-E-J-104: Evaluation of Atlas-Based Auto-Segmentation on Daily In-Room CT for Prostate Cancer

PURPOSE

Anatomy delineation is a major time consuming task to correct for inter-fractional changes in anatomy. Atlas-based auto-segmentation (ABAS) was developed to expedite this process. This study aims to evaluate the performance of ABAS applying to high quality verification CT-imaging acquired using a CT-on-rail system for prostate cancer.

METHODS

The prostate, rectum and bladder were manually contoured for seven prostate cancer patients. For each patient, three patient specific atlases were generated consisting of one, four and seven prior image and contour sets. ABAS was applied using these atlases for the last seven daily CT images of each patient. The auto- and manual-contours were compared both geometrically and dosimetrically. The reproducibility of the observation was validated by an experienced radiation oncologist performing the same procedure. The performance of ABAS with patient and non-patient specific atlases were also evaluated on 21 image sets. P<0.05 was considered statistical significant for two-tailed paired student t-test.

RESULTS

Contours obtained from ABAS agreed well with the manual ones. With 1-image set atlas, the OI and DSC for the bladder were greater than 96% and 91%, respectively. Both indices were above 81% for rectum and prostate. The consistencies significantly improved by including 4 image sets in the atlas, while a further increase of atlas size to 7 did not show obvious benefits. Dose coverage for the auto- and manual-contours was similar for all organs. Similar results were obtained by the second observer. Compared with non-patient specific atlas, patient specific atlas yielded more accurate contours. The time for ABAS and manual contouring was ∼2 min and ∼20 min per image set, respectively.

CONCLUSIONS

With diagnostic quality verification images, ABAS can provide fast and accurate delineations for prostate cancer on a daily basis. The inclusion of more than one CT set in atlas improves the contouring results.

SU-E-T-486: Volume and Location Dependence on the Difference Between Monte Carlo and Pencil Beam Dose Calculations for Lung Stereotactic Body Radiation Therapy

PURPOSE

Stereotactic body radiotherapy has been an efficacious treatment modality for early stage non-small cell lung cancer. The accuracy of dose calculations is in question due to the presence of inhomogeneity. It was required in several clinical trials to calculate dose without heterogeneity correction. However, to better correlate the outcomes with the planned dose, accurate dose calculation with heterogeneity correction is highly desirable.

METHODS

We compared the recalculated dose with Monte Carlo (MC) algorithm to the original Pencil Beam (PB) calculations for clinical lung SBRT plans. Thirty-one clinical plans that followed protocol guidelines were retrospectively investigated. Dosimetric parameters D1, D95 and D99 for the PTV and D1 for organs at risk were compared. Correlations of mean lung dose and V20 of lungs between two calculations were investigated.

RESULTS

Compared to the PB calculations without heterogeneity correction in clinical plans, we found that in terms of D95 of PTV, (1) the two calculations resulted in similar D95 for edge tumors with volumes greater than 25.1cc; (2) an average overestimation of 5% in PB calculations for edge tumors with volumes less than 25.1cc; and (3) an average overestimation of 9% or underestimation of 3% in PB calculations for island tumors with volumes smaller or greater than 22.6 cc, respectively. With heterogeneity correction, the PB calculation resulted in an average reduction of 23.8% and 15.3% in D95 for island and edge lesions respectively compared to the MC calculation. For organs at risks, no clinical meaningful differences were found among all the comparisons. Excellent correlations for mean dose and V20 of lungs were observed between the two calculations.

CONCLUSIONS

Using a single scaling factor to account for the differences in using heterogeneity correction may not be sufficient. To understand dose-response relation in Lung SBRT, accurate dose calculation such as the Monte Carlo algorithms is highly recommended.

SU-E-J-30: Using Shifting Planned Dose Matrix to Evaluate Daily Dose Changes for IMRT Prostate Treatment

PURPOSE

Summation of daily DVH from KV-cone beam CT (KV-CBCT) to obtain a composite dose volume histogram (DVH) is challenging. Directly translating the planned dose matrix according to measured daily prostate displacements provided a common reference frame for a composite DVH from daily DVHs. The purpose of this study is to evaluate the shifting planned dose matrix method compared to the dose recalculation method using daily KV-CBCT.

METHODS

Six patients, who received concurrent IMRT treatment for prostate and pelvic lymph nodes with 124 daily CBCTs, were selected for this study. Contours for CBCT's were transferred from the planning CT after soft tissue registration for prostate and bony registration for pelvic lymph nodes. Using the same planning beam configurations, we re-calculated doses for these CBCTs after shifting to corrected treatment isocenters. The planned dose matrix translation was performed by an in-house program written in MATLAB and incorporated with Computational Environment for Radiotherapy Research (CERR) software. The corresponding daily DVH was obtained by shifting the planned dose matrix according to shifts of treatment iso-centers. To compare these two methods, selected endpoint doses for tumor targets and sensitive structures were extracted from DVHs.

RESULTS

For prostate displacement less then 1.5 cm, the dose matrix shifting method resulted in 93% and 98% fractions within 5% differences from the recalculation method for D95 of prostate and pelvic lymph nodes, respectively. These numbers decreased to 58% and 71% when 2% dose difference criterion was used.

CONCLUSIONS

Allowing 5% daily dose difference, shifting planned dose matrix provides effective means to evaluating daily dose changes for concurrent IMRT treatment for prostate and pelvic lymph nodes. The utility of this tool is to provide a common coordinate frame to obtain composite dose distributions.

Thalidomide attenuates graft arteriosclerosis of aortic transplant in a rat model

OBJECTIVE

The purpose of the current study was to evaluate the effects of thalidomide on graft arteriosclerosis.

MATERIALS AND METHODS

Male Lewis rats received abdominal aorta grafts from male Brown-Norway rats. The animals were divided into 4 groups: no treatment controls, a low-dose group that received thalidomide (50 mg/kg per day), a middle dose group that received thalidomide (100 mg/kg per day), and a high-dose group that received thalidomide (200 mg/kg per day) by daily intragastric administration. Rats were humanely killed at 60 days after surgery. The grafted aortas were analyzed by histology, immunohistochemistry, and Western blot analysis. The serum was analyzed by an enzyme-linked immunosorbent assay (ELISA).

RESULTS

The neointimal thickness of the thalidomide treated aortas was significantly thinner compared with that of no treatment aortas (P < .05). Vascular endothelial growth factor (VEGF), platelet-derived growth factor, and intracellular adhesian molecule (ICAM-1) protein expression in the treatment group were significantly lower than those in the control group (P < .05). Moreover, thalidomide significantly inhibited the production of VEGF and ICAM-1 in serum (P < .05).

CONCLUSION

Our data suggested that thalidomide can attenuate graft arteriosclerosis so as to protect aortic grafts.

FADD cleavage by NK cell granzyme M enhances its self-association to facilitate procaspase-8 recruitment for auto-processing leading to caspase cascade

Granzyme M (GzmM), an orphan Gzm, is constitutively and abundantly expressed in innate effector natural killer cells. We previously demonstrated that GzmM induces caspase (casp)-dependent apoptosis and cytochrome c release from mitochondria. We also resolved the crystal structure for GzmM and generated its specific inhibitor. However, how GzmM causes casp activation has not been defined. Here we found that casp-8 is an initiator caspase in GzmM-induced casp cascade, which causes other casp activation and Bid cleavage. GzmM does not directly cleave procaspase-3 and Bid, whose processing is casp dependent. Casp-8 knockdown or deficient cells attenuate or abolish GzmM-induced proteolysis of procaspase-3 and Bid. Extrinsic death receptor pathway adaptor Fas-associated protein with death domain (FADD) contributes to GzmM-induced casp-8 activation. GzmM specifically cleaves FADD after Met 196 to generate truncated FADD (tFADD) that enhances its self-association for oligomerization. The oligomerized tFADD facilitates procaspase-8 recruitment to promote its auto-processing leading to casp activation cascade. FADD-deficient cells abrogate GzmM-induced activation of casp-8 and apoptosis as well as significantly inhibit lymphokine-activated killer cell-mediated cytotoxicity. FADD processing by GzmM can potentiate killing efficacy against tumor cells and intracellular pathogens.