Gross tumor volume dependency on phase sorting methods of four-dimensional computed tomography images for lung cancer

PURPOSE: To see the gross tumor volume (GTV) dependency according to the phase selection and reconstruction methods, we measured and analyzed the changes of tumor volume and motion at each phase in 20 cases with lung cancer patients who underwent image-guided radiotherapy. MATERIALS AND METHODS: We retrospectively analyzed four-dimensional computed tomography (4D-CT) images in 20 cases of 19 patients who underwent image-guided radiotherapy. The 4D-CT images were reconstructed by the maximum intensity projection (MIP) and the minimum intensity projection (Min-IP) method after sorting phase as 40%–60%, 30%–70%, and 0%–90%. We analyzed the relationship between the range of motion and the change of GTV according to the reconstruction method. RESULTS: The motion ranges of GTVs are statistically significant only for the tumor motion in craniocaudal direction. The discrepancies of GTV volume and motion between MIP and Min-IP increased rapidly as the wider ranges of duty cycles are selected. CONCLUSION: As narrow as possible duty cycle such as 40%–60% and MIP reconstruction was suitable for lung cancer if the respiration was stable. Selecting the reconstruction methods and duty cycle is important for small size and for large motion range tumors.

Gross tumor volume dependency on phase sorting methods of four-dimensional computed tomography images for lung cancer

PURPOSE: To see the gross tumor volume (GTV) dependency according to the phase selection and reconstruction methods, we measured and analyzed the changes of tumor volume and motion at each phase in 20 cases with lung cancer patients who underwent image-guided radiotherapy. MATERIALS AND METHODS: We retrospectively analyzed four-dimensional computed tomography (4D-CT) images in 20 cases of 19 patients who underwent image-guided radiotherapy. The 4D-CT images were reconstructed by the maximum intensity projection (MIP) and the minimum intensity projection (Min-IP) method after sorting phase as 40%–60%, 30%–70%, and 0%–90%. We analyzed the relationship between the range of motion and the change of GTV according to the reconstruction method. RESULTS: The motion ranges of GTVs are statistically significant only for the tumor motion in craniocaudal direction. The discrepancies of GTV volume and motion between MIP and Min-IP increased rapidly as the wider ranges of duty cycles are selected. CONCLUSION: As narrow as possible duty cycle such as 40%–60% and MIP reconstruction was suitable for lung cancer if the respiration was stable. Selecting the reconstruction methods and duty cycle is important for small size and for large motion range tumors.

Variation of organ position and dose for cervical cancer patients treated with helical tomotherapy / 中华放射医学与防护杂志

Objective To observe the interfractional variation and actual dose for cervical cancer patients treated with tomotherapy.Methods Five patients who received tomotherapy were chosen from Aug 2013 to Feb 2014.A megavohage computed tomography (MVCT) scan was performed before treatment and then registered with the planning CT images.Dose distributions were recalculated and targets were contoured on the MVCT images.The differences between the actual radiation and planning were analyzed.Results In the patients received external radiotherapy, the decline in cervix volume and maximum diameter was 68.90％ and 26.91％ , respectively (t =5.21, 8.39, P ＜0.05).Cervix, uterus and CTV movement in left-right, anteroposterior, superoinferior were 1.43,-7.72, 0.02,-0.40,-1.24, -6.51,-0.43,-1.68and-0.22mm.The medianCTV V95％ was 99.40％ (95.96％-100％), and missing volume was 6.94 cm3 (0-32.30 cm3).Conclusions During radiotherapy for cervical cancer patients, the volume, position and doses are different between initial plan and actual radiation.Based on image guided radiation therapy (IGRT), missing targets are limited.

Estimated radiation dose to cardiac substructures and their corresponding planning risk volumes / 中国肿瘤临床

Objective:To investigate the role of planning risk volume (PRV) in estimating the radiation dose for various cardiac substructures (CS). Methods:The CS of 23 patients with left-sided breast cancer who underwent postoperative intensity-modulated ra-diotherapy (IMRT) was delineated. PRV was expanded from CS with an additional margin determined by the mean amplitude of cardi-ac motion. Two IMRT plans were designed. The volume, mean dose, maximal dose (D2%), and standard deviation of CS and its PRV were calculated. Results:In comparison to the volume of CS, the PRV of the heart, specifically the left ventricle, increased by 50%to 80%, whereas the PRV of the main coronary arteries and sub-branches increased by 18.7 times to 42.6 times. In the two IMRT plans, the mean dose to the heart, anterior myocardial territory, anterior descending artery, and their corresponding PRVs ranged from 9.4 Gy to 11.4 Gy, 11.0 Gy to 17.5 Gy, and 22.6 Gy to 27.8 Gy, respectively. The D2%to CS and its PRV was 24.5 Gy to 36.2 Gy, 28.2 Gy to 38.8Gy, and 36 Gy to 45 Gy. The mean dose and D2%to the coronary arteries, including both left and right main coronary arteries, right marginal artery, and left circumflex artery, were 8.6 Gy to 14.9 Gy and 12.5 Gy to 23.7 Gy, respectively. The difference of the mean dose and D2%to CS and its corresponding PRVs was 2.5%to 12.5%and 8.0%to 43.1%, respectively. Compared with the stan-dard deviation of the radiation dose to CS, majority of the standard deviation to PRVs increased significantly. Conclusion:The radia-tion dose difference between CS and its corresponding PRVs is<12%.

Application of CT image-guided technology in radiotherapy of the mid-and upper-thoracic esophageal carcinoma / 中华放射医学与防护杂志

Objective To compare the clinical target volume (CTV) expanding margins in the mid-and upper-thoracic esophageal carcinoma during radiotherapy measured with and without online image guidance technique by CT on rail.Methods 100 patients with mid-and upper-thoracic esophageal carcinoma undergoing intensity modulated radiotherapy received CT scanning.Image registration was conducted between the scanning results and the planned CT images,thus set-up error data were acquired and got on-line correction.Fifty patients were randomly selected to undergo additional post-treatment CT scanningso as to analyze the revised residuals,displacement during treatment,and infra-fraction GTV shifts.Results Compared to the radiotherapy without CT-based image guidance,the CTV expanding margins obtained with CT-based image guidance was reduced significantly from 9.1,8.8 and 6.1 mm to 4.1,4.5 and 4.3 mm in the left-right,head-feet,and belly-back directions respectively.Conclusions The on-line image-guided technology significantly improves the accuracy of target and reduces the CTV expanding margins.

Development of an Offline Based Internal Organ Motion Verification System during Treatment Using Sequential Cine EPID Images / 의학물리

Verification of internal organ motion during treatment and its feedback is essential to accurate dose delivery to the moving target. We developed an offline based internal organ motion verification system (IMVS) using cine EPID images and evaluated its accuracy and availability through phantom study. For verification of organ motion using live cine EPID images, a pattern matching algorithm using an internal surrogate, which is very distinguishable and represents organ motion in the treatment field, like diaphragm, was employed in the self-developed analysis software. For the system performance test, we developed a linear motion phantom, which consists of a human body shaped phantom with a fake tumor in the lung, linear motion cart, and control software. The phantom was operated with a motion of 2 cm at 4 sec per cycle and cine EPID images were obtained at a rate of 3.3 and 6.6 frames per sec (2 MU/frame) with 1,024x768 pixel counts in a linear accelerator (10 MVX). Organ motion of the target was tracked using self-developed analysis software. Results were compared with planned data of the motion phantom and data from the video image based tracking system (RPM, Varian, USA) using an external surrogate in order to evaluate its accuracy. For quantitative analysis, we analyzed correlation between two data sets in terms of average cycle (peak to peak), amplitude, and pattern (RMS, root mean square) of motion. Averages for the cycle of motion from IMVS and RPM system were 3.98+/-0.11 (IMVS 3.3 fps), 4.005+/-0.001 (IMVS 6.6 fps), and 3.95+/-0.02 (RPM), respectively, and showed good agreement on real value (4 sec/cycle). Average of the amplitude of motion tracked by our system showed 1.85+/-0.02 cm (3.3 fps) and 1.94+/-0.02 cm (6.6 fps) as showed a slightly different value, 0.15 (7.5% error) and 0.06 (3% error) cm, respectively, compared with the actual value (2 cm), due to time resolution for image acquisition. In analysis of pattern of motion, the value of the RMS from the cine EPID image in 3.3 fps (0.1044) grew slightly compared with data from 6.6 fps (0.0480). The organ motion verification system using sequential cine EPID images with an internal surrogate showed good representation of its motion within 3% error in a preliminary phantom study. The system can be implemented for clinical purposes, which include organ motion verification during treatment, compared with 4D treatment planning data, and its feedback for accurate dose delivery to the moving target.

Estimation of Internal Motion for Quantitative Improvement of Lung Tumor in Small Animal / 의학물리

The purpose of this study was to estimate internal motion using molecular sieve for quantitative improvement of lung tumor and to localize lung tumor in the small animal PET image by evaluated data. Internal motion has been demonstrated in small animal lung region by molecular sieve contained radioactive substance. Molecular sieve for internal lung motion target was contained approximately 37 kBq Cu-64. The small animal PET images were obtained from Siemens Inveon scanner using external trigger system (BioVet). SD-Rat PET images were obtained at 60 min post injection of FDG 37 MBq/0.2 mL via tail vein for 20 min. Each line of response in the list-mode data was converted to sinogram gated frames (2~16 bin) by trigger signal obtained from BioVet. The sinogram data was reconstructed using OSEM 2D with 4 iterations. PET images were evaluated with count, SNR, FWHM from ROI drawn in the target region for quantitative tumor analysis. The size of molecular sieve motion target was 1.59x2.50 mm. The reference motion target FWHM of vertical and horizontal was 2.91 mm and 1.43 mm, respectively. The vertical FWHM of static, 4 bin and 8 bin was 3.90 mm, 3.74 mm, and 3.16 mm, respectively. The horizontal FWHM of static, 4 bin and 8 bin was 2.21 mm, 2.06 mm, and 1.60 mm, respectively. Count of static, 4 bin, 8 bin, 12 bin and 16 bin was 4.10, 4.83, 5.59, 5.38, and 5.31, respectively. The SNR of static, 4 bin, 8 bin, 12 bin and 16 bin was 4.18, 4.05, 4.22, 3.89, and 3.58, respectively. The FWHM were improved in accordance with gate number increase. The count and SNR were not proportionately improve with gate number, but shown the highest value in specific bin number. We measured the optimal gate number what minimize the SNR loss and gain improved count when imaging lung tumor in small animal. The internal motion estimation provide localized tumor image and will be a useful method for organ motion prediction modeling without external motion monitoring system.

Comparison of dosimetry distribution between three-dimension conformal and intensity modulated plan integrated with breath motion in postoperative radiation of gastric cancer / 中华放射肿瘤学杂志

Objective To compare the dose distribution of the target and normal tissues in gastric cancers between three-dimension conformal radiation therapy (3DCRT) and intensity modulated radiation therapy (IMRT) plan when respiratory motion factors integrated in the plan. Methods From January 2005to November 2006, 10 patients with post-operatively radiation of gastric cancer were enrolled in this study.Planning CT were acquired conventionally with free-breath mode and the static treatment plans of the 3DCRT and IMRT were designed respectively. Probability distribution functions (PDF) were generated and convoluted with the static dose distributions from 3DCRT and IMRT plans to obtain the integrated plans. The dose distributions of the target and normal tissues were compared between 3DCRT and IMRT integration treatment plans, such as V45 of clinical target volume, V4o of liver and V15, V18 of left and right kidney.Results In the respiratory integrated treatment planning, the target volume coverage and homogeneity with IMRT are superior to those with 3DCRT ( ( V45 98%∶ 87% (t = -3. 35 ,P =0. 010) ,mean dose 46. 81 Gy ±0. 75 Gy∶45.99 Gy ± 1.12 Gy (t = -0. 31 ,P=0. 020) ). The V40 of teh liver in IMRT are smaller than those in 3DCRT ( 12%∶ 16% ;t=3.75,P=0.010). For the left kidney, the V15 and V18 in IMRT are smaller than those in 3DCRT ( (34%∶ 50% (t = 2. 17 ,P = 0. 050) and 27%∶46% (t = 3. 11 ,P = 0. 020) ),but for the right kidney, V15 and V18 in 3DCRT are smaller than those in IMRT ( ( 15%∶ 21% (t = - 2. 42,P=0.040) and 11%∶15% (t= -2.71,P=0.030)). Conclusions When respiratory motion factor integrated in the treatment plan, IMRT showed advantage both in target coverage and normal tissue sparing in the high dose region of liver and left kidney.

An Effect of Time Gating Threshold (TGT) on the Delivered Dose at Internal Organ with Movement due to Respiration / 의학물리

In this study, we investigated the effect of time gating threshold on the delivered dose at a organ with internal motion by respiration. Generally, the internal organs have minimum motion at exhalation during normal breathing. Therefore to compare the dose distribution time gating threshold, in this paper, was determined as the moving region of target during 1 sec at the initial position of exhalation. The irradiated fields were then delivered under three conditions; 1) non-moving target 2) existence of the moving target in the region of threshold (1sec), 3) existence of the moving target region out of threshold (1.4 sec, 2 sec). And each of conditions was described by the moving phantom system. It was compared with the dose distributions of three conditions using film dosimetry. Although the treatment time increased when the dose distributions was obtained by the internal motion to consider the TGT, it could be obtained more exact dose distribution than in the treatment field that didn't consider the internal motion. And it could be reduced the unnecessary dose at the penumbra region. When we set up 1.4 sec of threshold, to reduce the treatment time, it could not be obtained less effective dose distribution than 1 sec of threshold. Namely, although the treatment time reduce, the much dose was distributed out of the treatment region. Actually when it is treated the moving organ, it would rather measure internal motion and external motion of the moving organ than mathematical method. If it could be analyzed the correlation of the internal and external motion, the treatment scores would be improved.

Set-up errors in radiation therapy for pelvic tumor patients of different somatotypes / 医学研究生学报

Objective: The purpose of this study was to quantitatively assess the systematic and random errors in radiation therapy for pelvic tumor patients of different somatotypes and seek an individualized mathematic basis for defining the planning target volume(PTV) and planning organ at risk volume(PRV) in 3 dimensional space.Methods: Thirty patients with pelvic tumor were immobilized by thermoplastic body mask in a spine position and divided into four somatotypes according to their body mass indexes(BMI).CT simulations were performed and digitally reconstructed radiographs(DRR) were generated as the reference image.To define the appropriate PTV-and PRV-margins for intensity modulation radiated therapy(IMRT),inter-fractional set-up errors and intra-fractional organ motions were quantitatively evaluated in the right-left(R-L),anterior-posterior(A-P) and cranial-caudal(C-C) directions.And the frequency of shift in the three directions were observed.Results: For the pelvic tumor patients with different BMIs,the inter-fractional set-up errors of the emaciated,moderate,overweight and obese somatotypes were 1.8,1.8,2.2 and 2.7 mm in the R-L direction,2.2,1.8,3.6 and 2.8 mm in the A-P direction,and 2.4,2.1,2.7 and 2.6 mm in the C-C direction.The intra-fractional organ motions of the four somatotypes were 1.9,1.9,2.3 and 2.5 mm in the R-L,2.1,2.2,2.9 and 3.0 mm in the A-P,and 1.8,1.9,2.2 and 2.5 mm in the C-C direction.Conclusion: In the pelvic irradiation,the definition of PTV and PRV should be individualized.

Development of Conformal Radiotherapy with Respiratory Gate Device / 대한방사선종양학회지

PURPOSE: 3D conformal radiotherapy, the optimum dose delivered to the tumor and provided the risk of normal tissue unless marginal miss, was restricted by organ motion. For tumors in the thorax and abdomen, the planning target volume (PTV) is decided including the margin for movement of tumor volumes during treatment due to patients breathing. We designed the respiratory gating radiotherapy device (RGRD) for using during CT simulation, dose planning and beam delivery at identical breathing period conditions. Using RGRD, reducing the treatment margin for organ (thorax or abdomen) motion due to breathing and improve dose distribution for 3D conformal radiotherapy. MATERIALS AND METHODS: The internal organ motion data for lung cancer patients were obtained by examining the diaphragm in the supine position to find the position dependency. We made a respiratory gating radiotherapy device (RGRD) that is composed of a strip band, drug sensor, micro switch, and a connected on-off switch in a LINAC control box. During same breathing period by RGRD, spiral CT scan, virtual simulation, and 3D dose planing for lung cancer patients were performed, without an extended PTV margin for free breathing, and then the dose was delivered at the same positions. We calculated effective volumes and normal tissue complication probabilities (NTCP) using dose volume histograms for normal lung, and analyzed changes in doses associated with selected NTCP levels and tumor control probabilities (TCP) at these new dose levels. The effects of 3D conformal radiotherapy by RGRD were evaluated with DVH (Dose Volume Histogram), TCP, NTCP and dose statistics. RESULTS: The average movement of a diaphragm was 1.5 cm in the supine position when patients breathed freely. Depending on the location of the tumor, the magnitude of the PTV margin needs to be extended from 1 cm to 3 cm, which can greatly increase normal tissue irradiation, and hence, results in increase of the normal tissue complications probability. Simple and precise RGRD is very easy to setup on patients and is sensitive to length variation (+2 mm), it also delivers on-off information to patients and the LINAC machine. We evaluated the treatment plans of patients who had received conformal partial organ lung irradiation for the treatment of thorax malignancies. Using RGRD, the PTV margin by free breathing can be reduced about 2 cm for moving organs by breathing. TCP values are almost the same values (4-5% increased) for lung cancer regardless of increasing the PTV margin to 2.0 cm but NTCP values are rapidly increased (60-70% increased) for upon extending PTV margins by 2.0 cm. CONCLUSION: Internal organ motion due to breathing can be reduced effectively using our simple RGRD. This method can be used in clinical treatments to reduce organ motion induced margin, thereby reducing normal tissue irradiation. Using treatment planning software, the dose to normal tissues was analyzed by comparing dose statistics with and without RGRD. Potential benefits of radiotherapy derived from reduction or elimination of planning target volume (PTV) margins associated with patient breathing through the evaluation of the lung cancer patients treated with 3D conformal radiotherapy.