Jung Suk Shin

The first private-hospital based proton therapy center in Korea; status of the Proton Therapy Center at Samsung Medical Center

Purpose The purpose of this report is to describe the proton therapy system at Samsung Medical Center (SMC-PTS) including the proton beam generator, irradiation system, patient positioning system, patient position verification system, respiratory gating system, and operating and safety control system, and review the current status of the SMC-PTS. Materials and Methods The SMC-PTS has a cyclotron (230 MeV) and two treatment rooms: one treatment room is equipped with a multi-purpose nozzle and the other treatment room is equipped with a dedicated pencil beam scanning nozzle. The proton beam generator including the cyclotron and the energy selection system can lower the energy of protons down to 70 MeV from the maximum 230 MeV. Results The multi-purpose nozzle can deliver both wobbling proton beam and active scanning proton beam, and a multi-leaf collimator has been installed in the downstream of the nozzle. The dedicated scanning nozzle can deliver active scanning proton beam with a helium gas filled pipe minimizing unnecessary interactions with the air in the beam path. The equipment was provided by Sumitomo Heavy Industries Ltd., RayStation from RaySearch Laboratories AB is the selected treatment planning system, and data management will be handled by the MOSAIQ system from Elekta AB. Conclusion The SMC-PTS located in Seoul, Korea, is scheduled to begin treating cancer patients in 2015.

Comparison of film dosimetry techniques used for quality assurance of intensity modulated radiation therapy

PURPOSE Accurate dosimetry is essential to ensure the quality of advanced radiation treatments, such as intensity modulated radiation therapy (IMRT). Therefore, a comparison study was conducted to assess the accuracy of various film dosimetry techniques that are widely used in clinics. METHODS A simulated IMRT plan that produced an inverse pyramid dose distribution in a perpendicular plane of the beam axis was designed with 6 MV x rays to characterize the large contribution of scattered photons to low dose regions. Three film dosimetry techniques, EDR2, EDR2 with low-energy photon absorption lead filters (EDR2 WF), and GafChromic® EBT, were compared to ionization chamber measurements as well as Monte Carlo (MC) simulations. The accuracy of these techniques was evaluated against the ionization chamber data. Two-dimensional comparisons with MC simulation results were made by computing the gamma index (γ) with criteria ranging from 2% of dose difference or 2 mm of distance to agreement (2%/2 mm) to 4%/4 mm on the central vertical plane (20×20cm2) of a square solid water phantom. Depth doses and lateral profiles at depths of 5, 10, and 15 cm were examined to characterize the deviation of film measurements and MC predictions from ionization chamber measurements. RESULTS In depth dose comparisons, the deviation between the EDR2 films was 9% in the low dose region and 5% in high dose region, on average. With lead filters, the average deviation was reduced to -1.3% and -0.3% in the low dose and high dose regions, respectively. EBT film results agreed within 1.5% difference on average with ionization chamber measurements in low and high dose regions. In two-dimensional comparisons with MC simulation, EDR2 films passed gamma tests with a 2%/2 mm criterion only in the high dose region (γ⩽1, total of 63.06% of the tested region). In the low dose region, EDR2 films passed gamma tests with 3%/3 mm criterion (γ⩽1, total of 98.4% of the tested region). For EDR2 WF and GafChromic® EBT films, gamma tests with a 2% /2 mm criterion (γ⩽1) in the tested area was 97.3% and 96.8% of the tested region, respectively. CONCLUSIONS The EDR2 film WF and GafChromic® EBT film achieved an average accuracy level of 1.5% against an ionization chamber. These two techniques agreed with the MC prediction in 2%/2mm criteria evaluated by the gamma index, whereas EDR2 without filters achieved an accuracy level of 3%/3 mm with the decision criteria of agreement greater than 95% of the tested region. The overall results will provide a useful quantitative reference for IMRT verifications.

Different effects of bladder distention on point A-based and 3D-conformal intracavitary brachytherapy planning for cervical cancer

This study sought to evaluate the differential effects of bladder distention on point A-based (AICBT) and three-dimensional conformal intracavitary brachytherapy (3D-ICBT) planning for cervical cancer. Two sets of CT scans were obtained for ten patients to evaluate the effect of bladder distention. After the first CT scan, with an empty bladder, a second set of CT scans was obtained with the bladder filled. The clinical target volume (CTV), bladder, rectum, and small bowel were delineated on each image set. The AICBT and 3D-ICBT plans were generated, and we compared the different planning techniques with respect to the dose characteristics of CTV and organs at risk. As a result of bladder distention, the mean dose (D50) was decreased significantly and geometrical variations were observed in the bladder and small bowel, with acceptable minor changes in the CTV and rectum. The average D2 cm3and D1 cm3showed a significant change in the bladder and small bowel with AICBT; however, no change was detected with the 3D-ICBT planning. No significant dose change in the CTV or rectum was observed with either the AICBT or the 3D-ICBT plan. The effect of bladder distention on dosimetrical change in 3D-ICBT planning appears to be minimal, in comparison with AICBT planning.

Development of a video‐guided real‐time patient motion monitoring system

PURPOSE The authors developed a video image-guided real-time patient motion monitoring (VGRPM) system using PC-cams, and its clinical utility was evaluated using a motion phantom. METHODS The VGRPM system has three components: (1) an image acquisition device consisting of two PC-cams, (2) a main control computer with a radiation signal controller and warning system, and (3) patient motion analysis software developed in-house. The intelligent patient motion monitoring system was designed for synchronization with a beam on/off trigger signal in order to limit operation to during treatment time only and to enable system automation. During each treatment session, an initial image of the patient is acquired as soon as radiation starts and is compared with subsequent live images, which can be acquired at up to 30 fps by the real-time frame difference-based analysis software. When the error range exceeds the set criteria (δ(movement)) due to patient movement, a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.1, 0.2, 0.3, 0.5, and 1.0 cm for 1 and 2 s, respectively, was used to evaluate the system performance. The authors measured optimal δ(movement) for clinical use, the minimum distance that can be detected with this system, and the response time of the whole system using a video analysis technique. The stability of the system in a linear accelerator unit was evaluated for a period of 6 months. RESULTS As a result of the moving phantom test, the δ(movement) for detection of all simulated phantom motion except the 0.1 cm movement was determined to be 0.2% of total number of pixels in the initial image. The system can detect phantom motion as small as 0.2 cm. The measured response time from the detection of phantom movement to generation of the warning signal was 0.1 s. No significant functional disorder of the system was observed during the testing period. CONCLUSIONS The VGRPM system has a convenient design, which synchronizes initiation of the analysis with a beam on/off signal from the treatment machine and may contribute to a reduction in treatment error due to patient motion and increase the accuracy of treatment dose delivery.

Effect of Radiation Therapy Techniques on Outcome in N3-positive IIIB Non-small Cell Lung Cancer Treated with Concurrent Chemoradiotherapy

Purpose This study was conducted to evaluate clinical outcomes following definitive concurrent chemoradiotherapy (CCRT) for patients with N3-positive stage IIIB (N3-IIIB) non-small cell lung cancer (NSCLC), with a focus on radiation therapy (RT) techniques. Materials and Methods From May 2010 to November 2012, 77 patients with N3-IIIB NSCLC received definitive CCRT (median, 66 Gy). RT techniques were selected individually based on estimated lung toxicity, with 3-dimensional conformal RT (3D-CRT) and intensity-modulated RT (IMRT) delivered to 48 (62.3%) and 29 (37.7%) patients, respectively. Weekly docetaxel/paclitaxel plus cisplatin (67, 87.0%) was the most common concurrent chemotherapy regimen. Results The median age and clinical target volume (CTV) were 60 years and 288.0 cm3, respectively. Patients receiving IMRT had greater disease extent in terms of supraclavicular lymph node (SCN) involvement and CTV ≥ 300 cm3. The median follow-up time was 21.7 months. Fortyfive patients (58.4%) experienced disease progression, most frequently distant metastasis (39, 50.6%). In-field locoregional control, progression-free survival (PFS), and overall survival (OS) rates at 2 years were 87.9%, 38.7%, and 75.2%, respectively. Although locoregional control was similar between RT techniques, patients receiving IMRT had worse PFS and OS, and SCN metastases from the lower lobe primary tumor and CTV ≥ 300 cm3were associated with worse OS. The incidence and severity of toxicities did not differ significantly between RT techniques. Conclusion IMRT could lead to similar locoregional control and toxicity, while encompassing a greater disease extent than 3D-CRT. The decision to apply IMRT should be made carefully after considering oncologic outcomes associated with greater disease extent and cost.

SU‐E‐J‐172: Development of a Video Guided Real‐Time Patient Motion Monitoring System for Helical Tomotherpay

PURPOSE We developed a video image-guided real-time patient motion monitoring system for helical Tomotherapy (VGRPM-Tomo), and its clinical utility was evaluated using a motion phantom. METHODS The VGRPM-Tomo consisted of three components: an image acquisition device consisting of two PC-cams, a main control computer with a radiation signal controller and warning system, and patient motion analysis software, which was developed in house. The system was designed for synchronization with a beam on/off trigger signal to limit operation during treatment time only and to enable system automation. In order to detect the patient motion while the couch is moving into the gantry, a reference image, which continuously updated its background by exponential weighting filter (EWF), is compared with subsequent live images using the real-time frame difference-based analysis software. When the error range exceeds the set criteria (δ_movement) due to patient movement, a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.1, 0.2, 0.5, and 1.0 cm for 1 and 2 sec, respectively, was used to evaluate the system performance at maximum couch speed (0.196 cm/sec) in a Helical Tomotherapy (HD, Hi-art, Tomotherapy, USA). We measured the optimal EWF factor (a) and δ_movement, which is the minimum distance that can be detected with this system, and the response time of the whole system. RESULTS The optimal a for clinical use ranged from 0.85 to 0.9. The system was able to detect phantom motion as small as 0.2 cm with tight δ_movement, 0.1% total number of pixels in the reference image. The measured response time of the whole system was 0.1 sec. CONCLUSIONS The VGRPM-tomo can contribute to reduction of treatment error caused by the motion of patients and increase the accuracy of treatment dose delivery in HD. This work was supported by the Technology Innovation Program, 10040362, Development of an integrated management solution for radiation therapy funded by the Ministry of Knowledge Economy (MKE, Korea). This idea is protected by a Korean patent (patent no. 10-1007367).

SU-E-T-438: Motion Induced Dose Artifact of Multi-Fractional Tomotheapy

Purpose: Treating moving oragan has been an issue due to the dynamic nature of Tomotheapy. Non of study has investigated throughly the multi‐ fractional effects of treatments. Therefore, we designed a study to evaluate the cumulative error in moving target and nearby normal tissues. Methods: A moving phantom whose motion pattern could be rogrammed by a user was produced. Four plans which used different jaw width (1.05 cm, 2.5 cm), pitch (0.660, 0,287) and modulation factor (1.5, 2.5) to deliver 1.49 Gy to 95% of PTV in each fraction were made. For each plan, 5 different motions ( amplitude 1–3cm, Period 3–5sec) and irregular motion were tested. Film measurements for accumulated dose were made with Gafchromic@EBT films from 1 to 5 fractions. Dose distribution on each film was compared with that measured in static phantom. Profile shapes, DoseArea Histogram (DAH)s and gamma index were used for comparison Results: The dose distortion increased up to 3rd fractions and, after 3rd fractions dose distributions in the target and OAR converged to some constant distribution. The distortion level inside the target was affected by motion parameters; larger motion amplitude and larger motion period resulted in increased dose. However dose at the center of the critical organ was rather affected by the motion amplitude than the motion period . The irregularity of the motion was not thought to cause large dose artifact. More complicated plan with larger modulation factor (2.5) resulted in larger dose distortin than the plan with modulation factor 1.5. The observed phenomena is thought to be reproducible since 3 different measurements of accumulated 5 fraction of treatments showed very similar dose distributions Conclusions: When treating moving organ in small number of fractions, verifying the dose artifact is necessary. (This work was supported by Korea Government (MEST, Grant No2010‐0011771)

PIXEL-BASED CORRECTION METHOD FOR GAFCHROMIC ® EBT FILM DOSIMETRY

In this paper, a new approach using a pixel-based correction method was developed to fix the non-uniform responses of flat-bed type scanners used for radiochromic film dosimetry. In order to validate the method’s performance, two cases were tested: the first consisted of simple dose distributions delivered by a single port; the second was a complicated dose distribution composed of multiple beams. In the case of the simple individual dose condition, ten different doses, from 8.3 cGy to 307.1 cGy, were measured, horizontal profiles were analyzed using the pixel-based correcton method and compared with results measured by an ionization chamber and results corrected using the existing correction method. A complicated inverse pyramid dose distribution was made by piling up four different field shapes, which were measured with GAFCHROMIC ® EBT film and compared with the Monte Carlo calculation; as well as the dose distribution corrected using a conventional method. The results showed that a pixel-based correction method reduced dose difference from the reference measurement down to 1% in the flat dose distribution region or 2 mm in a steep dose gradient region compared to the reference data, which were ionization chamber measurement data for simple cases and the MC computed data for the complicated case, with an exception for very low doses of less than about 10 cGy in the simple case. Therefore, the pixel-based scanner correction method is expected to enhance the accuracy of GAFCHROMIC ® EBT film dosimetry, which is a widely used tool for two-dimensional dosimetry.

Is higher dose always the right answer in stereotactic body radiation therapy for small hepatocellular carcinoma

Purpose This study was conducted to compare clinical outcomes and treatment-related toxicities after stereotactic body radiation therapy (SBRT) with two different dose regimens for small hepatocellular carcinomas (HCC) ≤3 cm in size. Materials and Methods We retrospectively reviewed 44 patients with liver-confined HCC treated between 2009 and 2014 with SBRT. Total doses of 45 Gy (n = 10) or 60 Gy (n = 34) in 3 fractions were prescribed to the 95% isodose line covering 95% of the planning target volume. Rates of local control (LC), intrahepatic failure-free survival (IHFFS), distant metastasis-free survival (DMFS), and overall survival (OS) were calculated using the Kaplan-Meier method. Results Median follow-up was 29 months (range, 8 to 64 months). Rates at 1 and 3 years were 97.7% and 95.0% for LC, 97.7% and 80.7% for OS, 76% and 40.5% for IHFFS, and 87.3% and 79.5% for DMFS. Five patients (11.4%) experienced degradation of albumin-bilirubin grade, 2 (4.5%) degradation of Child-Pugh score, and 4 (9.1%) grade 3 or greater laboratory abnormalities within 3 months after SBRT. No significant difference was seen in any oncological outcomes or treatment-related toxicities between the two dose regimens. conclusions SBRT was highly effective for local control without severe toxicities in patients with HCC smaller than 3 cm. The regimen of a total dose of 45 Gy in 3 fractions was comparable to 60 Gy in efficacy and safety of SBRT for small HCC.

SU-E-T-292: Dosimetric Advantage of Prone Breast Radiotherapy for Korean Left-Sided Breast Cancer Patients

Purpose: To evaluate the dosimetric benefit of prone breast radiotherapy for Korean left-sided early-stage breast cancer patients who have relatively small breast Methods: From April to June, 2014, 10 left-sided breast cancer patients received the whole breast irradiation in prone position after partial mastectomy with sentinel lymph node biopsy or axillary lymph node dissection. All patients were pTmi-2N0-1mi. Each patient underwent two computed tomoradiography (CT) simulations in supine and prone positions. The whole breast, ipsilateral lung, heart, and left anterior descending coronary artery (LAD) were contoured on each simulation CT images, and then tangential-fields treatment plan in each position was designed for the whole breast irradiation with the total dose of 50 Gy in 2 Gy fractions. Dose-volume histograms of two setups were compared for target coverage and radiation dose to normal organs with Wilcoxon signed rank tests. Results: The median age of patients was 47 years (range, 37 to 53). The median chest size was 82.5 cm (range, 75 to 90) and bra cup size was A in 4, B in 4, and C in 2 patients. The radiation dose to the whole breast was similar when comparing mean dose (Dmean) and dose covering 95% of the breast volume, but maximum dose (Dmax) of breast was higher in supine (median 52.3 vs. 52.7 Gy, p=0.013). Prone position reduced significantly the radiation dose in ipsilateral lung, heart, and LAD by median 5.7, 1.1, and 6.9 Gy of Dmean (p=0.005, 0.007, and 0.005) and 28.2, 18.8, and 35.0 Gy of Dmax (p=0.005, 0.005, and 0.007), respectively. Conclusion: Prone breast radiotherapy could be beneficial for Korean breast cancer patients since it substantially spared normal organs while achieving adequate coverage of the breast tissue. Further prospective study is required to validate the potential benefit of prone breast radiotherapy.