Screening and identification of peritoneal metastasis-related genes of gastric adenocarcinoma using a cDNA microarray

With the aim of identifying peritoneal metastasis-related genes in gastric cancer, we performed a broad analysis of differential gene expression between the parental cell line GC9811 and its highly metastatic peritoneal counterpart, cell line GC9811-P. Two fluorescent cDNA probes, labeled with Cy3 and Cy5 dyes, were prepared from GC9811 and GC9811-P mRNA samples by the reverse transcription method. The two color probes were then mixed and hybridized to a cDNA chip constructed with double-dots from 11,901 human genes; this was scanned at two wavelengths. The experiment was repeated twice. In GC9811-P cells, 218 genes were upregulated and 30 genes were downregulated compared with the parental cell lines. Some selected genes were confirmed by RT-PCR and Western blot; we found that S100A4 and CTNNB1 were upregulated and PTEN was downregulated in GC9811-P cells. Identification of these differentially expressed genes could contribute to disclose the molecular mechanisms involved and provide new targets for therapeutic intervention to avoid peritoneal dissemination of gastric adenocarcinoma.

SU-E-T-104: Commissioning and Dosimetric Characteristics of TrueBeam System: Composite Data of Three TrueBeam Machines

INTRODUCTION

A TrueBeam linear accelerator (TB-LINAC) is designed to deliver standard flattened and flattening-filter-free (FFF) beams. In our institute, three TB-LINAC units are installed. In this work, composite data of the three units and multi-unit comparison are presented.

METHODS

Each TB-LINAC can deliver photon beams from 4MV to 15MV, electron beams from 6MeV to 22MeV, and 6MV-FFF and 10MV-FFF. Dosimetric characteristics are systematically measured for commissioning including percent depth dose (PDD), beam profile, relative scatter factor, dynamic leaf shift, output factor and MLC leakage. Critic considerations of Pion of FFF photon beams and dosimetric penumbra are investigated.

RESULTS

All measured PDDs and profiles of photon and electron matched well across the three machines. Beam data were quantitatively compared and combined through average to yield composite beam data. The discrepancies among the machines were quantified using standard deviation (SD). For example, the mean SD of the PDDs among the three units is 0.12%, and the mean SD of the profiles is 0.40% for 10MV-FFF open fields. The variations of Pion of the chamber CC13 is 1.2±0.1% under 6MV-FFF and 2.0±0.5% from dmax to the 18cm-off-axis point at 35cm depth under 40×40cm² . The measured relative output factors range from 0.866 to 1.141 with the mean discrepancy of 0.06±0.04% among the three units. The measured wedge factors range from 0.863 to 1.254 with the mean overall discrepancy of 0.04±0.04%. The mean MLC transmission and dynamic leaf shift were measured from 1.0% to 1.5% and from 0.77mm to 0.96 mm from 4MV to 15MV. The mean penumbra of various photon beams are measured from 5.88±0.09mm to 5.99±0.13mm from 4MV to 15MV at 10cm depth of 10×10 cm² .

CONCLUSIONS

Dosimetric data demonstrated that the three units could and had been matched well. The systematically measured data might be useful for future reference.

MO-D-BRB-10: Modeling Inter-Patient Variation of Organ-At-Risk Sparing in IMRT Plans: An Evidence-Based Plan Quality Evaluation

PURPOSE

To develop a predictive model to assess the quality of critical organ dose sparing in IMRT plans by providing patient specific dose sparing references, based on an array of patient anatomical features and prior planning experience.

METHODS

Contributions of various patient anatomical features to the inter-patient OAR dose sparing variation in IMRT planning were systematically studied using machine learning method based on high quality prior plans. The dependence of anatomical factor on OAR dosimetric parameters is formulated into predictive models. The OAR dosimetric parameters generated by these predictive models represent the "best feasible" clinical outcomes based on past planning experiences. IMRT plans of 88 prostate, 106 head-and-neck (HN) and 21 spine SBRT treatments were used to train the models. The final models were tested by additional 24 prostate and 48 HN plans. The model for spine SBRT was tested by the leave-one-out method.

RESULTS

For HN and prostate planning, the significant patient anatomical features that affect OAR sparing are: the distance between OAR and PTV, the portion of OAR volume within an OAR specific distance range, the overlap volume between OAR and PTV, and the portion of OAR volume outside the primary treatment field. For spine SBRT planning, the most significant patient anatomical feature that affects cord sparing is the tightness of the geometric enclosure of PTV surrounding the cord and the homogeneity of PTV dose coverage. The dosimetric parameters predicted for the test patient cases using the models were in agreement with those from the clinical plans in more than 75% of the cases.

CONCLUSIONS

The developed predictive models indicated substantial correlation between some important patient anatomical features and OAR dose sparing based on expert experiences. These models can be used as effective tools for evaluating the quality of treatment plans customized to individual patient's anatomy. Partially supported by a master research agreement with Varian Medical System, Inc.

SU-E-J-209: A Simple Method to Minimize Uncertainty in ITV Delineation: Phantom Verification

PURPOSE

Irregular breathing causes variation in delineation of internal target volume (ITV), which is typically generated in the maximum intensity projection (MIP) images [1]. Previous studies have shown that MIP-based ITV can underestimate true tumor range [2]. This study examines a simple method to reduce such errors by combining the GTV of 3D-CT with the ITV of MIP.

METHODS

The Computerized Imaging Reference Systems (CIRS) Dynamic Thorax Phantom Model 008A (CIRS, Norfolk, VA) with CIRS motion control software was used to model 4 irregular patient respiratory profiles and one regular respiratory profile (sine wave). A 3 cm tumor insert was used as target. For each breathing profile, a 3D-CT and 3 repeated 4D-CT scans with random intervals within the breathing profile were performed on a 4-slice clinical scanner (Lightspeed, GE, WI). The RPM system (Varian, Palo Alto, CA) was used to track the respiratory profiles. GTV was contoured on 3D-CT, and ITV was contoured on each MIP (ITVMIP) using a consistent lung window by the same person. The new method of creating ITV was to combine the GTV and ITVMIP, namely ITVCOMB. To evaluate which ITV is more accurate, ITVCOMB and ITVMIP were compared to a 'ground truth' ITV (ITVGT) which was generated by combining the three ITVMIPs.

RESULTS

For the regular profile, both ITVMIP (27.25 cm³ ) and ITVCOMB (28.12 cm³ ) were comparable to ITVGT (27.25 cm³ ). For irregular profiles, the mean absolute difference between ITVCOMB and ITVGT (6.3%±4.9) was significantly (p-value=0.0078) smaller than that between ITVMIP and ITVGT (18.1%±12.3).

CONCLUSIONS

The results suggest that combining GTV of the 3D-CT with the ITV of the MIP is more accurate than the ITV of the MIP alone, and thus would be a simple method to reduce breathing irregularity induced errors in ITV delineation for treatment planning of lung cancer.

SU-E-T-626: Individualized Trade-Off of Dose Coverage and Sparing in IMRT Planning

PURPOSE

We present an evidence-based approach to quantifying the dose sparing trade-offs between different Organs-at-risk (OARs) and the trade-off between OAR dose sparing and target dose coverage in IMRT plans.

METHODS

The interaction between dose sparing of different OARs and between target dose coverage and OAR dose sparing are modeled using high-quality prior IMRT plans of prostate, head-and-neck (HN), and spine SBRT cases. The dose sparing for each OAR is modeled separately at first based on their own anatomical features and then the contributions from other OARs or PTV are added into the model to account for the possible trade-off effects in plans whose modeled OAR DVH deviates from that of actual plans.

RESULTS

The most significant OAR dose sparing trade-off is between bladder and rectum in prostate plans and between the left and the right parotids in HN plans. Trade-off is most apparent when the parotid on one side has very large overlap with the PTV. In most of these plans (83%), the planer chooses to loosen the dose constraint for that parotid in exchange for lower contra-lateral parotid median dose. The interaction between OAR dose sparing and PTV dose coverage is most significant in spine SBRT plans, (R2=0.37). Another important factor is the tightness of the geometric enclosure of PTV around OAR (R2=0.38).

CONCLUSIONS

The dosimetric trade-off between multiple OARs and between PTV and OAR in IMRT planning is quantified by studying prior plans. These findings will help physicians and planners obtain better OAR dose sparing by exploring different trade-off options for individual patient cases. Partially supported by a master research agreement with Varian Medical Systems, Inc.