K.C. Keum

The prognostic impact of the number of lymph nodes retrieved after neoadjuvant chemoradiotherapy with mesorectal excision for rectal cancer

We aimed to assess factors associated with the number of nodes retrieved and the impact of the number of lymph nodes in rectal cancer patients who underwent neoadjuvant chemoradiation with radical surgery.

Is elective nodal irradiation beneficial in patients with pathologically negative lymph nodes after neoadjuvant chemotherapy and breast-conserving surgery for clinical stage II–III breast cancer? A multicentre retrospective study (KROG 12-05)

Background:To evaluate the effects of elective nodal irradiation (ENI) in clinical stage II–III breast cancer patients with pathologically negative lymph nodes (LNs) (ypN0) after neoadjuvant chemotherapy (NAC) followed by breast-conserving surgery (BCS) and radiotherapy (RT).Methods:We retrospectively analysed 260 patients with ypN0 who received NAC followed by BCS and RT. Elective nodal irradiation was delivered to 136 (52.3%) patients. The effects of ENI on survival outcomes were evaluated.Results:After a median follow-up period of 66.2 months (range, 15.6–127.4 months), 26 patients (10.0%) developed disease recurrence. The 5-year locoregional recurrence-free survival and disease-free survival (DFS) for all patients were 95.5% and 90.5%, respectively. Pathologic T classification (0−is vs 1 vs 2–4) and the number of LNs sampled (<13 vs ⩾13) were associated with DFS (P=0.0086 and 0.0012, respectively). There was no significant difference in survival outcomes according to ENI. Elective nodal irradiation also did not affect survival outcomes in any of the subgroups according to pathologic T classification or the number of LNs sampled.Conclusions:ENI may be omitted in patients with ypN0 breast cancer after NAC and BCS. But until the results of the randomised trials are available, patients should be put on these trials.

The effect of respiratory motion on forward intensity modulated radiotherapy for breast cancer

This study evaluated the effect of respiratory movement on field-in-field (FIF) forward intensity-modulated radiotherapy (IMRT) for the treatment of breast cancer. FIF forward IMRT was performed on ten patients receiving radiotherapy to the whole breast after conservation surgery. Assuming that breast motion follows a sophisticated cyclic function, the changes in hot and cold region, dose homogeneity index (DHI), and skin dose were examined at different respiration amplitudes of 1 cm, 2 cm, and 3 cm. FIF forward IMRT significantly improved the hot region, DHI, and skin dose, but slightly worsened the cold region, compared to the two wedged tangential technique (TWT). Interestingly, we found that the respiration amplitude affected the DHI and cold region but had no effect on the hot region and skin dose. The DHI was slightly improved at 1 cm of amplitude probably due to the blurring effect, remained unchanged at 2 cm of amplitude, and was worsened at 3 cm of amplitude. FIF forward IMRT significantly increased the cold region at 2 cm and 3 cm of respiration amplitude compared to the TWT. At 3 cm of respiration amplitude, an average cold region of 3.27 cm3 was observed. In summary, our data indicate that during FIF forward IMRT, respiration movement has an important effect on various endpoints depending on the respiration amplitude of the patient.

SU-F-T-294: The Analysis of Gamma Criteria for Delta4 Dosimetry Using Statistical Process Control

PURPOSE To evaluate the sensitivity of gamma criteria for patient-specific volumetric modulated arc therapy(VMAT) quality assurance of the Delta4 dosimetry program using the statistical process control(SPC) methodology. METHODS The authors selected 20 patient-specific VMAT QA cases which were undertaken MapCHECK and ArcCHECK with gamma pass rate better than 97%. The QAs data were collected Delta4 Phantom+ and Elekta Agility six megavolts without using an angle incrementer. The gamma index(GI) were calculated in 2D planes with normalizing deviation to local dose(local gamma). The sensitivity of the GI methodology using criterion of 3%/3mm, 3%/2mm and 2%/3mm was analyzed with using process acceptability indices. We used local confidence(LC) level, the upper control limit(UCL) and lower control limit(LCL) of I-MR chart for process capability index(Cp) and a process acceptability index (Cpk). RESULTS The lower local confidence levels of 3%/3mm, 3%/2mm and 2%/3mm were 92.0%, 83.6% and 78.8% respectively. All of the calculated Cp and Cpk values that used LC level were under 1.0 in this study. The calculated LCLs of I-MR charts were 89.5%, 79.0% and 70.5% respectively. These values were higher than 1.0 which means good quality of QA. For the generally used lower limit of 90%, we acquired over 1.3 of Cp value for the gamma index of 3%/3mm and lower than 1.0 in the rest of GI. CONCLUSION We applied SPC methodology to evaluate the sensitivity of gamma criteria and could see the lower control limits of VMAT QA for the Delta 4 dosimetry and could see that Delta 4 phantom+ dosimetry more affected by the position error and the I-MR chart derived values are more suitable for establishing lower limits. Acknowledgement: This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education (No. 2015R1D1A1A01060463).

TU‐F‐CAMPUS‐I‐03: Enhancement of 4D CBCT Image Quality Using An Adaptive Prior Image Constrained Compressed Sensing

Purpose: To develop an iterative reconstruction algorithm using a compressed sensing with adaptive prior image constraints to solve 4D CBCT reconstruction problem. Methods: The images reconstructed by the FDK algorithm with a full set of unsorted projections are served as prior images for partial projections in each phase group and are utilized as an initial guess. Additionally, the prior images are clustered into several regions by applying intensity-based thresholding, which is referred to as the segmented prior images. The segmented prior images are employed to detect any possible mismatched areas compared with the target images generated by partial projection data. With these two prior images, our algorithm alternately performs the simultaneous algebraic reconstruction technique and anisotropic total variation regularization while adjusting a weighted relaxation map during the iterative reconstruction process. The weighted relaxation map depends on binary images created by the voxel-dependent comparison between the segmented prior and segmented target images. For the segmented target images, the k-means clustering with a geometric weighting is applied on the reconstruction images generated in each iteration step. The inverse values of the distance map converted from binary images are assigned to be the values of the relaxation map. Evaluations using Catphan504 phantom with a motion platform were carried out. Results: Qualitative and quantitative analyses showed that the method provides high-quality CBCT reconstruction images when compared with those generated by the FDK, CS, and PICCS algorithms, with higher contrast-to-noise ratio and faster convergence caused by minimizing data fidelity. Especially, the proposed method was superior to PICCS in the aspect of updating locally-mismatched region. Conclusion: The proposed method not only improves the image quality of 4D CBCT by adaptive updates during the reconstruction process, but also leads to a lower imaging dose and faster acquisition time by using a regular 3D CBCT scan.