Kyoung Ju Kim

Dosimetric characteristics of linear accelerator photon beams with small monitor unit settings

Several studies on the effect of tumor cell killing by dose rate variation have implied that the use of a shorter treatment time is more favorable for intensity modulated radiation therapy (IMRT). Aiming at step-and-shoot IMRT with higher dose rates, the stabilities of beam output and profiles with small monitor unit (MU) settings were investigated for various dose rates. With the use of a Varian 21EX (Varian Medical Systems Inc., Palo Alto, CA), static and step-and-shoot IMRT beam output along with profiles were measured by use of an ion chamber and a two-dimensional diode array detector as a function of monitor units and dose rates. For a static case, as the MU approached 1, the beam output increased up to 2% for 300 MU/min and 4.5% for 600 MU/min, showing a larger overdose as the dose rate increased. Deterioration of the beam symmetry and flatness were also observed as the MU decreased to 1 monitor unit. For the step-and-shoot IMRT case, a large dosimetric error of more than 10% was also detected with the use of a small MU segment. However, no definite correlation with the dose rate was observed due to the combined beam start-up effects by the grid pulse and finite communication time between the machine console and multileaf collimator (MLC) controller. For step-and-shoot IMRT with higher dose rates, beam output and beam profile stability with small MU needs to be checked, and adequate MU limitation where segments are not allowed need to be reflected in the step-and-shoot IMRT planning.

Systemic chemotherapy after cranial irradiation in patients with brain metastases from non-small cell lung cancer : A retrospective study

BACKGROUND Brain metastases (BMs) are found in about 10% of patients with newly diagnosed non-small cell lung cancer (NSCLC). This retrospective study was conducted to assess the clinical outcomes and prognostic factors of patients who received chemotherapy after cranial irradiation for NSCLC with synchronous BMs. MATERIALS AND METHODS From January 2000 through July 2007, we reviewed the medical records of patients who received systemic chemotherapy following cranial irradiation for BMs from newly diagnosed NSCLC. RESULTS A total of 40 patients were included in this review. As the first-line chemotherapy, a total of 114 cycles were administered, for a median number of 2 cycles per patient (range, 0.5-8 cycles). Thirty-four patients (85%) received platinum-based combination regimen and the remaining 6 received chemotherapy with a single agent. Sixteen (40%) patients, 11 of whom had ECOG of 2, only received 1 cycle or less of chemotherapy due to early death, rapid progression, clinical impairment, or toxicity. For 28 patients who were evaluable for response, the extracranial overall response rate was 43%. The median overall survival for all patients was 7 months (range, 0.9-25.3 months) and an estimated 1-year survival rate was 23%. Multivariate analysis revealed that ECOG status (P=0.018) and number of BM (P=0.038) were independent prognostic factors. CONCLUSION Our results suggest that chemotherapy can be used to increase survival of patients treated with cranial irradiation for newly diagnosed NSCLC with synchronous BM. However, systemic chemotherapy should be carefully considered according to the patients prognostic condition. Especially, patients with good performance status and limited number of BM may be good candidates for systemic chemotherapy after cranial irradiation.

Clinical features and treatment outcomes of skin cancer arising from burn scar: a single-institution experience.

Aims and Background This study was conducted to investigate the clinicopathological features and long-term outcomes of patients with skin cancer arising from burn scar (SCBS). Patients and Methods We retrospectively reviewed the medical records of patients diagnosed with SCBS between January 2000 and May 2012. A total of 44 patients were enrolled in this study. Results The median latent period between burn injury and development of SCBS was 32 years (range, 8–78 years). The most frequent sites of SCBS were the lower limbs (68.2%) followed by the upper limbs (15.9%) and trunk (11.4%). Most patients (95.4%) had squamous cell carcinoma. Of 34 patients with localized disease at the time of diagnosis, 33 patients are alive with no evidence of recurrence. Of 10 patients with regional lymph node metastasis (referred to as locally advanced disease), 4 died of disease progression and 5 are alive with metastatic disease in the lymph nodes, bone or lung. Patients with localized disease survived longer than patients with locally advanced disease (P = 0.000). In patients with locally advanced disease, the median overall survival time was 16 months (95% CI, 2.88–29.4 months). Conclusions While localized SCBS is a potentially curable disease, locally advanced SCBS has a poor prognosis in spite of aggressive treatment. These results suggest that early recognition and aggressive treatment are essential to improve the outcomes of SCBS.

Enhancement of megavoltage electronic portal images for markerless tumor tracking

Abstract Purpose The poor quality of megavoltage (MV) images from electronic portal imaging device (EPID) hinders visual verification of tumor targeting accuracy particularly during markerless tumor tracking. The aim of this study was to investigate the effect of a few representative image processing treatments on visual verification and detection capability of tumors under auto tracking. Methods Images of QC‐3 quality phantom, a single patients setup image, and cine images of two‐lung cancer patients were acquired. Three image processing methods were individually employed to the same original images. For each deblurring, contrast enhancement, and denoising, a total variation deconvolution, contrast‐limited adaptive histogram equalization (CLAHE), and median filter were adopted, respectively. To study the effect of image enhancement on tumor auto‐detection, a tumor tracking algorithm was adopted in which the tumor position was determined as the minimum point of the mean of the sum of squared pixel differences (MSSD) between two images. The detectability and accuracy were compared. Results Deblurring of a quality phantom image yielded sharper edges, while the contrast‐enhanced image was more readable with improved structural differentiation. Meanwhile, the denoising operation resulted in noise reduction, however, at the cost of sharpness. Based on comparison of pixel value profiles, contrast enhancement outperformed others in image perception. During the tracking experiment, only contrast enhancement resulted in tumor detection in all images using our tracking algorithm. Deblurring failed to determine the target position in two frames out of a total of 75 images. For original and denoised set, target location was not determined for the same five images. Meanwhile, deblurred image showed increased detection accuracy compared with the original set. The denoised image resulted in decreased accuracy. In the case of contrast‐improved set, the tracking accuracy was nearly maintained as that of the original image. Conclusions Considering the effect of each processing on tumor tracking and the visual perception in a limited time, contrast enhancement would be the first consideration to visually verify the tracking accuracy of tumors on MV EPID without sacrificing tumor detectability and detection accuracy.

Tumor response assessment by the single-lesion measurement per organ in small cell lung cancer.

Background: The criterion of two target lesions per organ in the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1 is an arbitrary one, being supported by no objective evidence. The optimal number of target lesions per organ still needs to be investigated. We compared tumor responses using the RECIST 1.1 (measuring two target lesions per organ) and modified RECIST 1.1 (measuring the single largest lesion in each organ) in patients with small cell lung cancer (SCLC). Methods: We reviewed medical records of patients with SCLC who received first-line treatment between January 2004 and December 2014 and compared tumor responses according to the two criteria using computed tomography. Results: There were a total of 34 patients who had at least two target lesions in any organ according to the RECIST 1.1 during the study period. The differences in the percentage changes of the sum of tumor measurements between RECIST 1.1 and modified RECIST 1.1 were all within 13%. Seven patients showed complete response and fourteen showed partial response according to the RECIST 1.1. The overall response rate was 61.8%. When assessing with the modified RECIST 1.1 instead of the RECIST 1.1, tumor responses showed perfect concordance between the two criteria (k=1.0). Conclusions: The modified RECIST 1.1 showed perfect agreement with the original RECIST 1.1 in the assessment of tumor response of SCLC. Our result suggests that it may be enough to measure the single largest target lesion per organ for evaluating tumor response.

Electron dose distributions caused by the contact-type metallic eye shield: Studies using Monte Carlo and pencil beam algorithms

A metallic contact eye shield has sometimes been used for eyelid treatment, but dose distribution has never been reported for a patient case. This study aimed to show the shield-incorporated CT-based dose distribution using the Pinnacle system and Monte Carlo (MC) calculation for 3 patient cases. For the artifact-free CT scan, an acrylic shield machined as the same size as that of the tungsten shield was used. For the MC calculation, BEAMnrc and DOSXYZnrc were used for the 6-MeV electron beam of the Varian 21EX, in which information for the tungsten, stainless steel, and aluminum material for the eye shield was used. The same plan was generated on the Pinnacle system and both were compared. The use of the acrylic shield produced clear CT images, enabling delineation of the regions of interest, and yielded CT-based dose calculation for the metallic shield. Both the MC and the Pinnacle systems showed a similar dose distribution downstream of the eye shield, reflecting the blocking effect of the metallic eye shield. The major difference between the MC and the Pinnacle results was the target eyelid dose upstream of the shield such that the Pinnacle system underestimated the dose by 19 to 28% and 11 to 18% for the maximum and the mean doses, respectively. The pattern of dose difference between the MC and the Pinnacle systems was similar to that in the previous phantom study. In conclusion, the metallic eye shield was successfully incorporated into the CT-based planning, and the accurate dose calculation requires MC simulation.

Electron arc planning on the commercial radiation treatment planning system

A commercial radiation treatment planning system, Pinnacle3, has been prepared for the electron arc treatment with a Varian machine. For this purpose, a new physics machine was commissioned for the exclusive electron arc therapy. The electron arc plan was made with multiple static beams with fixed interval. The phantom measurements were executed with a MOSFET and EBT films. The resulting plan shows an impressive dose distribution, however, in-vivo dosimetry for a few representative points should be proceeded before treatment to be sure of the calculation accuracy.