Biomedical subjects

Di Yan

Publications and source records attributed to Di Yan.

29 records · Page 2Linked to original sources

PubMed2004

The validity of surgical clips as a radiographic surrogate for the lumpectomy cavity in image-guided accelerated partial breast irradiation.

PURPOSE: We hypothesize that surgical clips placed in the biopsy cavity during lumpectomy can be used as radiographic markers to facilitate image-guided external beam accelerated partial breast irradiation. METHODS AND MATERIALS: We evaluated 28 patients with surgically placed clips in the lumpectomy cavity and two CT scans on different days. To establish whether the clips remain predictive of the lumpectomy cavity throughout therapy, we analyzed the motion of both cavities with repeat volumetric CT scans. The three-dimensional (3D) locations of each lumpectomy cavity and the associated clips were defined as individual regions of interest (ROIs). A single point of interest (POI) was defined for each ROI. The calculated movements of the lumpectomy cavity POIs between different scans were compared to those of the clip POIs. The second CT data set was then moved in accordance to the calculated clip POI's movement. The volume of the (second) lumpectomy cavity associated with the second scan outside of the (first) cavity of the first scan was measured. In addition, the required amount of a radial margin expansion around the first lumpectomy cavity to ensure coverage of the second lumpectomy cavity both before and after moving the second lumpectomy according to the clip POI movement was calculated. RESULTS: The two CT scans were obtained on average 27 days apart, and the mean lumpectomy size decreased from 35 to 16 cc. The clip and lumpectomy cavity POIs moved a mean of 3 mm along the three principal Cartesian axes. In moving the second lumpectomy cavity according to the clip POI displacement from its original position, the volume of the second lumpectomy cavity outside of the volume of the first decreased from 2.6 cc to 1.0 cc after correction, and the required radial margin on the first lumpectomy cavity to include the second lumpectomy cavity decreased from 5.5 mm vs. 3.8 mm. CONCLUSION: The surgically placed clips after lumpectomy are strong radiographic surrogates for the biopsy cavity. If the clips were used to guide accelerated partial breast irradiation, a planning target volume margin of the order of 5 mm could be used, significantly smaller than the 10-mm margin currently employed.

Breast Neoplasms↗

PubMed2004

Impact of breathing motion on whole breast radiotherapy: a dosimetric analysis using active breathing control.

PURPOSE: The active breathing control (ABC) apparatus was used to quantify the effect of breathing motion on whole breast radiotherapy (RT) with standard wedges and intensity-modulated RT (IMRT). METHODS AND MATERIALS: Ten patients with early-stage breast cancer underwent routine free-breathing (FB) CT simulations for whole breast RT. An ABC apparatus was used to obtain two additional CT scans with the breath held at the end of normal inhalation and normal exhalation. The FB scan was used to develop both a standard treatment plan using wedged coplanar tangents and an IMRT plan using multiple static multileaf collimator segments. To simulate breathing, each plan was copied and applied to the normal inhalation and normal exhalation CT scans. RESULTS: The medial field border (defined by a radiopaque catheter) for the normal inhalation and normal exhalation scans moved an average of 0.6 cm anteriorly and 0.3 cm posteriorly compared with the FB position, respectively. The corresponding movement of the lateral field border was an average of 0.4 cm anteriorly and 0.2 cm posteriorly compared with the FB position. For both the wedged and the IMRT techniques, the dose delivered to breast tissue, biopsy cavity, and ipsilateral lung was similar for each of the three CT scan positions. However, the internal mammary node dose varied significantly with breathing. CONCLUSIONS: The dose delivered to breast using standard wedges or step-and-shoot IMRT is relatively insensitive to the effects of breast motion during normal breathing. However, an appreciable portion of the internal mammary nodes are irradiated during normal inhalation, contributing to the uncertainty in the analysis of the efficacy of internal mammary nodal RT in breast treatment.

Breast Neoplasms↗

PubMed2004

The influence of small bowel motion on both a conventional three-field and intensity modulated radiation therapy (IMRT) for rectal cancer.

PURPOSE: To investigate the reduction of irradiated small bowel volume with intensity modulated radiation therapy (IMRT) planning in rectal cancer and to asses the variability of the irradiated small bowel in the conventional planning as in the IMRT planning (IMPlan) by obtaining weekly CT scans. PATIENTS AND MATERIALS: Twelve patients with rectal cancer had treatment planning CT scans of the pelvis with small bowel contrast obtained for planning and once a week during treatment (65 CT scans total). The scans were registered using the bony structures. The clinical target volume (CTV), small bowel, large bowel and bladder were outlined on each slice. The first CT scan was used for IMPlan and conventional three-field planning (ConPlan), which were then applied to the CT scans obtained during therapy. RESULTS: The median value among patients of the mean volume over a patient's scan of small bowel irradiated > or =95% was 112 cm3 (standard deviation (SD): 31 cm3) for the ConPlan and 42 cm3 (SD: 17 cm3) for the IMPlan. The median total bladder volume was 148 cm3 (SD: 130 cm3). There was a good correlation between the volume of irradiated small bowel and the bladder volume for IMPlan with <50 cm3 irradiated small bowel and ConPlan with <150 cm3 (p = 0.002). CONCLUSION: The use of IMRT led to a potentially clinically meaningful reduction in the volume of small bowel irradiated, even when accounting for small bowel motion. A full bladder was of greatest benefit in individuals with the smallest volume of small bowel in the treatment field.

Contrast Media↗

PubMed2004

Evaluation of a 2D diode array for IMRT quality assurance.

BACKGROUND AND PURPOSE: The QA of intensity modulated radiotherapy (IMRT) dosimetry is a laborious task. The goal of this work is to evaluate the dosimetric characteristics of a new 2D diode array (MapCheck from Sun Nuclear Corporation, Melbourne, Florida) and assess the role it can play in routine IMRT QA. MATERIAL AND METHODS: Fundamental properties of the MapCheck such as reproducibility, linearity and temperature dependence are studied for high-energy photon beams. The accuracy of the correction for difference of diode sensitivity is also assessed. The diode array is benchmarked against film and ion chambers for conventional and IMRT treatments. The MapCheck sensitivity to multileaf collimator position errors is determined. RESULTS: The diode array response is linear with dose up to 295 cGy. All diodes are calibrated to within +/-1% of each other, and mostly within +/-0.5%. The MapCheck readings are reproducible to within a maximum SD of +/-0.15%. A temperature dependence of 0.57%/ degrees C was noted and should be taken into account for absolute dosimetric measurement. Clinical performance of the MapCheck for relative and absolute dosimetry is demonstrated with seven beam (6 MV) head and neck IMRT plans, and compares well with film and ion chamber measurements. Comparison to calculated dose maps demonstrates that the planning system model underestimates the dose gradients in the penumbra region. CONCLUSIONS: The MapCheck offers the dosimetric characteristics required for performing both relative and absolute dose measurements. Its use in the clinic can simplify and reduce the IMRT QA workload.

Dose-Response Relationship, Radiation↗

PubMed2003

Three-dimensional evaluation of intra- and interfraction immobilization of lung and chest wall using active breathing control: a reproducibility study with breast cancer patients.

PURPOSE: A CT-based three-dimensional (3D) method was used to analyze the intra- and interfraction reproducibility of lung immobilization during moderate deep inspiration breath hold (mDIBH), defined as 75% of the maximal inspiration using an active breathing control (ABC) apparatus. METHODS AND MATERIALS: The ABC apparatus was used to immobilize the breathing motion with a computer-controlled valve. Immobilization of the lungs in breast cancer patients was used as a model to evaluate the reproducibility of mDIBH using the ABC apparatus. CT scans were acquired twice at mDIBH in the same session for 30 breast cancer patients. Twenty-three of them were immobilized with an alpha-cradle, of which 14 had a repeat scan at mDIBH 1-4 weeks later. Twelve of those patients received intensity-modulated radiotherapy to the left breast at mDIBH to displace the heart from the beam. The remaining patients were treated at free breathing, with either intensity-modulated irradiation to the whole breast or conformal partial breast irradiation. To remove the component of setup error, mDIBH scans were registered with respect to the vertebrae. The lungs and carina were auto-contoured to form 3D surfaces for each data set. The closest distance-to-agreement (DTA) for each point between the 3D surfaces of the corresponding CT scans was displayed on a 3D surface map. For analysis, each lung was divided along its inferior to superior extent into six regions, from the basal 10%, the next four consecutive 20% sections in height, to the last apical 10%. Likewise, the carina was divided into regions of the trachea and bifurcation. The mean and standard deviation (SD) of the DTA for each of these regions was computed. RESULTS: With the patient positioned in an alpha-cradle, the mean +/- SD intrafraction DTA was 1.5 +/- 1.4 mm for the left lung and 1.0 +/- 1.4 mm for the right lung. The corresponding values without the use of an alpha-cradle were significantly greater, with 1.9 +/- 2.1 mm and 2.2 +/- 2.2 mm for the left and right lung, respectively (p <0.005 for the SD of the left lung and p <0.0003 for the SD of the right lung). The interfraction DTA for the left and right lungs was 1.4 +/- 1.7 mm and 1.4 +/- 1.6 mm, respectively. The regional analysis demonstrated better immobilization for the upper two-thirds of the chest wall compared with that for the lung base. The DTA values obtained for the tracheal bifurcation were 0.9 +/- 0.8 mm for intrafraction and 1.4 +/- 1.0 mm for interfraction. CONCLUSION: The ABC device can be used to reduce respiratory motion at mDIBH in breast cancer patients or those patients who can perform the maneuver. This device demonstrated excellent intra- and interfraction reproducibility of chest wall and carina immobilization, especially when combined with alpha-cradle immobilization. Internal margins for suspended breathing can be extrapolated from these data for various anatomic regions within the lung and chest wall.

Breast Neoplasms↗

PubMed2003

Potential for reduced toxicity and dose escalation in the treatment of inoperable non-small-cell lung cancer: a comparison of intensity-modulated radiation therapy (IMRT), 3D conformal radiation, and elective nodal irradiation.

PURPOSE: To systematically evaluate four different techniques of radiation therapy (RT) used to treat non-small-cell lung cancer and to determine their efficacy in meeting multiple normal-tissue constraints while maximizing tumor coverage and achieving dose escalation. METHODS AND MATERIALS: Treatment planning was performed for 18 patients with Stage I to IIIB inoperable non-small-cell lung cancer using four different RT techniques to treat the primary lung tumor +/- the hilar/mediastinal lymph nodes: (1) Intensity-modulated radiation therapy (IMRT), (2) Optimized three-dimensional conformal RT (3D-CRT) using multiple beam angles, (3) Limited 3D-CRT using only 2 to 3 beams, and (4) Traditional RT using elective nodal irradiation (ENI) to treat the mediastinum. All patients underwent virtual simulation, including a CT scan and (18)fluorodeoxyglucose positron emission tomography scan, fused to the CT to create a composite tumor volume. For IMRT and 3D-CRT, the target included the primary tumor and regional nodes either > or =1.0 cm in short-axis dimension on CT or with increased uptake on PET. For ENI, the target included the primary tumor plus the ipsilateral hilum and mediastinum from the inferior head of the clavicle to at least 5.0 cm below the carina. The goal was to deliver 70 Gy to > or =99% of the planning target volume (PTV) in 35 daily fractions (46 Gy to electively treated mediastinum) while meeting multiple normal-tissue dose constraints. Heterogeneity correction was applied to all dose calculations (maximum allowable heterogeneity within PTV 30%). Pulmonary and esophageal constraints were as follows: lung V(20) < or =25%, mean lung dose < or =15 Gy, esophagus V(50) < or =25%, mean esophageal dose < or =25 Gy. At the completion of all planning, the four techniques were contrasted for their ability to achieve the set dose constraints and deliver tumoricidal RT doses. RESULTS: Requiring a minimum dose of 70 Gy within the PTV, we found that IMRT was associated with a greater degree of heterogeneity within the target and, correspondingly, higher mean doses and tumor control probabilities (TCPs), 7%-8% greater than 3D-CRT and 14%-16% greater than ENI. Comparing the treatment techniques in this manner, we found only minor differences between 3D-CRT and IMRT, but clearly greater risks of pulmonary and esophageal toxicity with ENI. The mean lung V(20) was 36% with ENI vs. 23%-25% with the three other techniques, whereas the average mean lung dose was approximately 21.5 Gy (ENI) vs. 15.5 Gy (others). Similarly, the mean esophagus V(50) was doubled with ENI, to 34% rather than 15%-18%. To account for differences in heterogeneity, we also compared the techniques giving each plan a tumor control probability equivalent to that of the optimized 3D-CRT plan delivering 70 Gy. Using this method, IMRT and 3D-CRT offered similar results in node-negative cases (mean lung and esophageal normal-tissue complication probability [NTCP] of approximately 10% and 2%-7%, respectively), but ENI was distinctly worse (mean NTCPs of 29% and 20%). In node-positive cases, however, IMRT reduced the lung V(20) and mean dose by approximately 15% and lung NTCP by 30%, compared to 3D-CRT. Compared to ENI, the reductions were 50% and >100%. Again, for node-positive cases, especially where the gross tumor volume was close to the esophagus, IMRT reduced the mean esophagus V(50) by 40% (vs. 3D-CRT) to 145% (vs. ENI). The esophageal NTCP was at least doubled converting from IMRT to 3D-CRT and tripled converting from IMRT to ENI. Finally, the total number of fractions for each plan was increased or decreased until all outlined normal-tissue constraints were reached/satisfied. While meeting all constraints, IMRT or 3D-CRT increased the deliverable dose in node-negative patients by >200% over ENI. In node-positive patients, IMRT increased the deliverable dose 25%-30% over 3D-CRT and 130%-140% over ENI. The use of 3D-CRT without IMRT increased the deliverable RT dose >80% over ENI. Using a limited number of 3D-CRT beams decreased the lung V(20), mean dose, and NTCP in node-positive patients. CONCLUSION: The use of 3D-CRT, particul mean dose, and NTCP in node-positive patients. The use of 3D-CRT, particularly with only 3 to 4 beam angles, has the ability to reduce normal-tissue toxicity, but has limited potential for dose escalation beyond the current standard in node-positive patients. IMRT is of limited additional value (compared to 3D-CRT) in node-negative cases, but is beneficial in node-positive cases and in cases with target volumes close to the esophagus. When meeting all normal-tissue constraints in node-positive patients, IMRT can deliver RT doses 25%-30% greater than 3D-CRT and 130%-140% greater than ENI. Whereas the possibility of dose escalation is severely limited with ENI, the potential for pulmonary and esophageal toxicity is clearly increased.

Carcinoma, Non-Small-Cell Lung↗

PubMed2002

Treatment of prostate cancer with radiotherapy: should the entire seminal vesicles be included in the clinical target volume?

PURPOSE: When treating high-risk prostate cancer with radiation therapy, inclusion of the seminal vesicles (SVs) within the clinical target volume (CTV) can dramatically increase the volume of radiated normal tissues and hinder dose escalation. Because cancer may involve only the proximal portion of the frequently lengthy SVs, we performed a complete pathology review of prostatectomy specimens to determine the appropriate length of SV to include within the CTV when SV treatment is indicated. METHODS AND MATERIALS: A detailed pathologic analysis was performed for 344 radical prostatectomy specimens (1987-2000). All slides from each case were reviewed by a single pathologist (N.S.G.). Factors recorded for each case included length of each SV (cm), length of cancer involvement in each SV (cm) measured from the prostate-SV junction, and percentage of SV length involved. RESULTS: Fifty-one patients (15%) demonstrated SV involvement in 81 SVs (21 unilateral, 30 bilateral SV involvement). The median SV length was 3.5 cm (range: 0.7-8.5 cm). Factors associated with SV involvement included the pretreatment PSA level, biopsy Gleason score, and clinical T classification. The commonly used risk group stratification was very effective at predicting SV positivity. Only 1% of low-risk patients (PSA <10 ng/mL, Gleason or=10 ng/mL, biopsy Gleason >or=7, or clinical T stage >or=T2b). When treating the SV for prostate cancer, only the proximal 2.0-2.5 cm (approximately 60%) of the SV should be included within the CTV.

Aged↗

PubMed2002

A model to simulate day-to-day variations in rectum shape.

PURPOSE: To develop a model that predicts possible rectum configurations that can occur during radiotherapy of prostate cancer on the basis of a planning CT scan and patient group data. MATERIALS AND METHODS: We used a stochastic shape description model with a limited number of parameters (area, area difference, and curvature) on a slice-by-slice basis to simulate rectum motion. The probability distributions of the chosen parameters were obtained from a group of 9 reference patients, who each received 15-17 repeat CT scans. We used a Monte Carlo technique to generate different rectum configurations from the probability distributions. We verified the model by comparing dose-wall histograms (DWHs) of the originally delineated rectal contours and simulated rectums for a three-field treatment technique with a prescription dose of 78 Gy. The 15-17 sets of rectal contours of each patient are regarded as the golden standard and provide a good estimate of the actual dose received during the treatment. We determined the equivalent uniform dose (EUD) for a quantitative comparison between the actual dose, the dose predicted on the basis of the simulations, and the dose predicted on the basis of a single planning CT scan. RESULTS: The simulated rectum configurations yield a better estimate of the actual dose in the rectal wall than the rectum in the planning CT scan alone. The differences between the EUD based on the planning CT scan and the actual EUD ranged between -1.1 Gy and 2.1 Gy, with respect to a mean actual EUD of 69.8 Gy. This range is smaller for the EUD based on the simulated rectums, namely -0.4 Gy to 0.6 Gy. Furthermore, the simulation generates a set of rectum configurations that provides an estimate of the variation in DWHs during the course of the treatment. This estimate can be used in addition to the DWH of the planning CT scan in the analysis of gastrointestinal toxicity. CONCLUSIONS: To simulate rectum shapes, we have developed a model that can be used in addition to the information available in the planning CT scan in the analysis of the received dose to the rectal wall during radiotherapy of prostate cancer.

Algorithms↗

PubMed2002

The variability of the clinical target volume for rectal cancer due to internal organ motion during adjuvant treatment.

PURPOSE: This study defined the clinical target volume (CTV) for the adjuvant treatment of rectal cancer and applied this definition to multiple CT scans obtained during the typical 5-week course of treatment to measure the modification to the CTV due to internal organ motion that would be needed to define the planning target volume (PTV). METHODS AND MATERIALS: Ten patients with rectal cancer had weekly treatment planning CT scans during adjuvant radiation therapy. All patients were given oral contrast, placed prone on a rigid foam cradle with a depressed area for small bowel exclusion, and instructed to have a full bladder. The CT scans were registered according to the bones of the pelvis, and the CTV was outlined on each CT slice. Movement of the CTV in all dimensions was measured. The CT scan with the lowest and highest bladder volume for each patient was used to calculate the CTV movement due to bladder filling. RESULTS: The largest difference in the CTV occurred 10 cm caudal to the anus, with a standard deviation of 1 cm. Bladder filling displaced the anterior border of the CTV an average of 7 mm over a cranial to caudal length of 2.5 cm. Other borders of the CTV were based on muscle, bone, or major blood vessels and were stable. CONCLUSION: Modification of the CTV to design a PTV can be unequal, with the largest change at the anterior border of the inferior pelvis.

Female↗

PubMed2002

The dose-volume relationship of acute small bowel toxicity from concurrent 5-FU-based chemotherapy and radiation therapy for rectal cancer.

PURPOSE: A direct relationship between the volume of small bowel irradiated and the degree of acute small bowel toxicity experienced during concurrent 5-fluorouracil (5-FU)-based chemoradiotherapy for rectal carcinoma is well recognized but poorly quantified. This study uses three-dimensional treatment-planning tools to more precisely quantify this dose-volume relationship. METHODS AND MATERIALS: Forty patients receiving concurrent 5-FU-based chemotherapy and pelvic irradiation for rectal carcinoma had treatment-planning CT scans with small bowel contrast. A median isocentric dose of 50.4 Gy was delivered using a posterior-anterior and opposed lateral field arrangement. Bowel exclusion techniques were routinely used, including prone treatment position on a vacuum bag cradle to allow anterior displacement of the abdominal contents and bladder distension. Individual loops of small bowel were contoured on each slice of the planning CT scan, and a small bowel dose-volume histogram was generated for the initial pelvis field receiving 45 Gy. The volume of small bowel receiving each dose between 5 and 40 Gy was recorded at 5-Gy intervals. RESULTS: Ten patients (25%) experienced Common Toxicity Criteria Grade 3+ acute small bowel toxicity. A highly statistically significant association between the development of Grade 3+ acute small bowel toxicity and the volume of small bowel irradiated was found at each dose level. Specific dose-volume threshold levels were found, below which no Grade 3+ toxicity occurred and above which 50-60% of patients developed Grade 3+ toxicity. The volume of small bowel receiving at least 15 Gy (V15) was strongly associated with the degree of toxicity. Univariate analysis of patient and treatment-related factors revealed no other significant predictors of severe toxicity. CONCLUSIONS: A strong dose-volume relationship exists for the development of Grade 3+ acute small bowel toxicity in patients receiving concurrent 5-FU-based chemoradiotherapy for rectal carcinoma.

Acute Disease↗

PubMed2002

Methodological issues in radiation dose-volume outcome analyses: summary of a joint AAPM/NIH workshop.

This report represents a summary of presentations at a joint workshop of the National Institutes of Health and the American Association of Physicists in Medicine (AAPM). Current methodological issues in dose-volume modeling are addressed here from several different perspectives. Areas of emphasis include (a) basic modeling issues including the equivalent uniform dose framework and the bootstrap method, (b) issues in the valid use of statistics, including the need for meta-analysis, (c) issues in dealing with organ deformation and its effects on treatment response, (d) evidence for volume effects for rectal complications, (e) the use of volume effect data in liver and lung as a basis for dose escalation studies, and (f) implications of uncertainties in volume effect knowledge on optimized treatment planning. Taken together, these approaches to studying volume effects describe many implications for the development and use of this information in radiation oncology practice. Areas of significant interest for further research include the meta-analysis of clinical data; interinstitutional pooled data analyses of volume effects; analyses of the uncertainties in outcome prediction models, minimal parameter number outcome models for ranking treatment plans (e.g., equivalent uniform dose); incorporation of the effect of motion in the outcome prediction; dose-escalation/isorisk protocols based on outcome models; the use of functional imaging to study radioresponse; and the need for further small animal tumor control probability/normal tissue complication probability studies.

Clinical Trials as Topic↗