- Email: [email protected]
Dosimetric Implications of Abdominal Compression for Lung SBRT Treatment
S600
International Journal of Radiation Oncology Biology Physics
Results: Four hundred seventy-two PCI patients were matched to 1,888 non-PCI patients. Characteristics were balanced across groups, including race (p Z 1.00), gender (p Z 0.95), histology (p Z 1.00), stage (p Z 1.00), and surgery (p Z 0.81). The PCI group was younger, with a median age of 64 vs 68 years (p < 0.01). Median OS was 8 vs 10 months (p < 0.01) favoring the non-PCI group. OS in the PCI vs. non-PCI groups was 14% vs 28% at 2 years and 5% vs 12% at 5 years (p < 0.01). In Stage III patients (n Z 365) OS was 10% vs 21% at 2 years (p < 0.01). The decrement in OS with PCI was also observed when patients with bulky disease (T3 and above) and adenocarcinoma histology were examined separately. Median CSS was the same (9 months) in both groups. Conclusions: To date, four prospective trials examining PCI for NSCLC have been reported in full and demonstrated a significant reduction in the incidence of brain metastases, but the effect on overall survival is not clear. Here we demonstrate in the largest cohort study of PCI for NSCLC that there is a significant decrement in overall survival associated with PCI. While patients with limited stage small-cell lung cancer (SCLC) derive both an overall survival and brain metastasis-free survival benefit from PCI, there is a considerably higher likelihood for intracranial metastatic disease in SCLC than in NSCLC. Our results imply that there may be a propensity threshold for intracranial metastatic disease below which PCI is not warranted, and that future clinical trials investigating the role of PCI for NSCLC may not be justified. Author Disclosure: M.N. Corradetti: None. E. Xanthopolous: None. S. Cheng: None. D. Horowitz: None. A. Fernandes: None. A. Lusa: None. K. Chao: None. R. Rengan: None.
esophagus, increases in PET uptake were seen through treatment but these did not correlate with the onset or severity of RE symptoms. Author Disclosure: V.A. Ford: None. P. McCloskey: None. N. Becker: None. J. Bissonnette: None. K. Clarke: None. J. Higgins: None. C. Leavens: None. A. Hope: None. A. Bezjak: None. A. Sun: None.
3015 Role of FDG-PET as an Early Imaging Biomarker of Esophagitis and Pneumonitis During the Course of Radiation Therapy for Lung Cancer V.A. Ford, P. McCloskey, N. Becker, J. Bissonnette, K. Clarke, J. Higgins, C. Leavens, A. Hope, A. Bezjak, and A. Sun; Princess Margaret Hospital, Toronto, ON, Canada Purpose/Objective(s): To determine if FDG PET-CT during a course of radical chemoradiation therapy (CRT) correlates with development of esophagitis or pneumonitis. Materials/Methods: Patients were imaged serially with 4DCT and 4D FDG PET-CT at weeks 0, 2, 4, 7 during CRT and 3 months (3m) following RT. Patients were Stage II-III NSCLC and undergoing CRT receiving a dose of at least 60Gy. Fourteen patients were analyzed and chart review identified those who developed clinical radiation esophagitis (RE) or radiation pneumonitis (RP) and grade (CTCAE V4). Each serial 4DCT and 4D FDG PET-CT images were registered onto the clinical planning datasets (Pinnacle 9.0). Esophagus and non GTV lung (GTV from original clinical plan), were contoured on all serial exhale 4DCT datasets. The matching exhale PET dataset was examined for early indication of RE and RP. Contours were delineated using thresholding to match, in 10% increments, the 20 to 80% of the maximum SUV value on the 4DPET for lung and esophagus. The subsequent volumes were recorded for each patient for each week. Intensity Volume Histograms (IVH) were plotted using the volumes for % max SUV Contours (20-80) for each week, against the absolute SUV values. Changes in the SUV IVH from week to week were observed for each patient. Results: Four of 14 patients had grade 2 RP. The SUV uptake at 12 weeks increased for all these individuals. There was no significant uptake from week 0-7 for any patient. 10 of 13 patients had grade 2 RE, 2 of 13 had grade 3 RE. Of these, increases in SUV uptake were seen in the esophagus. The SUV peaked at variable times (week 7 in 5 patients, week 4 in 4 patients, week 2 in 3 patients). There was no correlation with grade or timing of peak esophagitis. Increased PET uptake was seen prior to RE in some individuals. Increase in SUV uptake from baseline was also seen in the patients who did not develop RE. Conclusions: In this series of patients, although PET uptake was seen to increase in normal lung tissue in those developing RP, there was no early increase to allow us to predict which individuals would be affected. For the
3016 The Influence of the Inhomogeneity Correction Factor on Dose Distributions in Lung Cancer Radiation Therapy Treatment Plans: A Retrospective Study R. Murphy, T. Hill, P. Rapley, L.S. Kandler, and K. Ramchandar; Thunder Bay Regional Health Sciences Centre, Thunder Bay, ON, Canada Purpose/Objective(s): The purpose of this retrospective study is to analyze the effect of the Convolution/Superposition Inhomogeneity Correction Factor (ICF) on the dose distribution when applied to lung cancer radiation therapy plans. The objective of this study is to better the delivery of care for patients with lung cancer by providing valuable information that can help determine what adaptations need to be made when moving from homogeneous planning to heterogeneous planning of lung cancer radiation treatments. Materials/Methods: The treatment plans of 38 patients prescribed radiation treatment for lung cancer planned within the last 3 years using homogeneous calculations were restored from archives. Included are 27 plans of patients treated for radical stage III non-small cell lung cancer (NSCLC), 9 plans of patients treated for radical T1N0 (NSCLC) and 7 plans of patients treated with palliative intent for lung cancer. Each homogeneous plan (plan A) was recalculated with the ICF applied (Plan B), and again with the ICF applied and the original number of monitor units restored (Plan C). Dose distributions of the inhomogeneity plans were compared with the original plan through comparison of dose to various points and volumes and statistical analysis was done with paired t-tests. Results: Because of a small population size, the results of this study yielded no significant results. However, the trends of the study suggests that when applying the ICF to the homogeneous plan, (Plan A vs. Plan B), a strongly correlated decrease (5%) was found in the number of monitor units needed to provide the prescribed dose to the ICRU reference point. Encouragingly, the results showed that even with a homogeneous plan, the estimations of the V95% coverage is consistent (0.2% difference) with what was shown to be actually delivered (Plan A vs. Plan C). The results do show that the homogeneous plan underestimates the dose to the lung tissue and according to the heterogeneous plan C, we are actually delivering on average 5-10% more dose to the lung (Plan A vs. Plan C). Conclusions: The results of this study show that by not taking into account the heterogeneity of the tissues in lung cancer radiation treatment plans, we are overdosing the patient and underestimating the dose to the lung. However the current homogeneous plans do provide acceptable coverage of the PTV in the V95%. Further investigations could be done with a larger population in order to provide statistically significant results, however even in this small patient population, trends can be seen that can help provide direction when beginning to plan using the Inhomogeneity Correction Factor to move from homogeneous to heterogeneous lung cancer radiation treatment planning. Author Disclosure: R. Murphy: None. T. Hill: None. P. Rapley: None. L.S. Kandler: None. K. Ramchandar: None.
3017 Dosimetric Implications of Abdominal Compression for Lung SBRT Treatment V. Sarkar, B. Wang, P. Rassiah-Szegedi, H. Zhao, J.Y. Huang, M.W. Szegedi, Y.J. Hitchcock, K.E. Kokeny, and B.J. Salter; Huntsman Cancer Hospital, Salt Lake City, UT Purpose/Objective(s): One of the methods to limit lung tumor motion stemming from respiration is through the use of abdominal compression devices. The purpose of this study is to evaluate how the use of such a device influences the dosimetry of the final plan in terms of normal lung
Volume 84 Number 3S Supplement 2012
Poster Viewing Abstracts S601
volumes covered by the 5Gy and 20Gy isodose lines (i.e. V5 and V20, respectively). Materials/Methods: Five patients with lower lobe tumors (greatest excursion due to respiratory motion) previously treated with SBRT at our institution were chosen for this study. A dynamic conformal arc technique was employed through the MM3 collimator on a linear accelerator. The PTV in the original plan had an average of 90.4cc (7.7 cc - 221.9cc). The original planned V20 averaged 4.1% (1%-11.6%) while V5 averaged 19.9% (6.7% - 37.5%) of normal lung volumes. Based on a survey of published data and the reported mean reductions in cranio-caudal ITV extent second to application of abdominal compression, we systematically reduced the ITV/PTV for each patient along the cranio-caudal (CC) direction by 6, 8 and 10 mm (i.e., 3, 4 and 5mm at each end). No change was made in the anterior-posterior or left-right directions. Plans were then created for each of the new PTVs using the same conformal arc extent as the original plan, and all plans were normalized such that 95% of the PTV received the prescription dose. In each case, the value of V5 and V20 for the new plan was compared with those from the original plan. Poster Viewing Abstract 3017; Table Effects of Decreasing ITV/PTV Size on the Values of V5 and V20 for the Lung ITV/PTV ITV/PTV ITV/PTV ITV/PTV ITV/PTV ITV/PTV shrunk by shrunk by shrunk by shrunk by shrunk by shrunk by 10 mm 10 mm 8 mm 8 mm 6 mm 6 mm
Average Minimum Maximum
Decrease in V5 (%)
Decrease in V20 (%)
Decrease in V5 (%)
Decrease in V20 (%)
Decrease in V5 (%)
Decrease in V20 (%)
1.7 0.9 3.1
0.4 0.0 1.1
2.6 1.3 4.7
1.0 0.3 2.0
3.5 2.0 5.9
1.1 0.4 2.5
Results: The Table shows the average, minimum and maximum decrease in V5 and V20 for each of the 3 scenarios investigated here. Conclusions: As expected, the value of V5 and V20 decreased when the PTV was reduced, with the magnitude of the decrease being larger the more the PTV size was decreased. However, the observed reduction of V5 and V20 was modest, even when the PTV was reduced by 10 mm, with the maximum drop in V5 and V20 being 5.9% and 2.5% respectively. This suggests that, for the conformal arc technique evaluated here, anticipation of significant reduction in V5 and V20 may not be a reasonable sole motivation for application of abdominal compression. Author Disclosure: V. Sarkar: None. B. Wang: None. P. Rassiah-Szegedi: None. H. Zhao: None. J.Y. Huang: None. M.W. Szegedi: None. Y.J. Hitchcock: None. K.E. Kokeny: None. B.J. Salter: None.
3018 Quantitative Evaluation of Impact Upon Tumor Control Probability (TCP) From Quality Assurance Criteria for Non-small Cell Lung Cancer From RTOG 1106 Study W. Chen,1 Y. Cui,1 F. Kong,2 M. Machtay,3 G. Videtic,4 B. Loo,5 E. Gore,6 J. Galvin,7 Y. Yan,1 and Y. Xiao7; 1Thomas Jefferson University Hospital, Philadelphia, PA, 2University of Michigan, Ann Arbor, MI, 3Case Medical Center, Cleveland, OH, 4Cleveland Clinic, Cleveland, OH, 5Department of Radiation Oncology and Stanford Cancer Institute, Stanford University, Stanford, CA, 6Medical College Wisconsin, Milwaukee, WI, 7Radiation Therapy Oncology Group, Philadelphia, PA Purpose/Objective(s): Adaptive radiation therapy (ART), which involves modifying the radiation plan for the target as it changes during therapy, is being explored for diseases such as lung cancer. Approximations are made in the protocol that organs-at-risk (OARs) remain constant in shape and relative location during ART. In this study, we investigate the accuracy of this assumption, volumetrically and dosimetrically. Materials/Methods: RTOG 1106 is a randomized Phase II Trial of Individualized Radiation therapy Using During-Treatment FDG-PET/CT (DurCT) and Modern Technology in Locally Advanced Non-Small Cell Lung Cancer (NSCLC). In the lead up to the study pre-clinical planning test
cases were given to several institutions to study feasibility and consistency in contouring the target and OARs, and to generate treatment plans meeting predefined criteria. After the initial plan of around 50Gy, a “highest achievable dose” adaptive plan was generated using the target defined on CT acquired during the course of the treatment (Dur-CT). Targets are re-defined but not the OARs. In this study, we generate OARs for the adaptive course by deforming OAR contours from the Pre-CT to Dur-CT with visual validation. These contours were then transferred back to Pre-CT for dosimetry assessments. Results: We evaluated dosimetric and volumetric parameters for three major OARs - cord, heart and lung from four institutions between pre-CT and dur-CT. There were significant volumetric variations: for cord, the volume difference ranged from 2.11% to 3.25% (2.51%0.45%). For heart, it ranged from 25.73% to 28.84% (26.82%1.34%). For lung, it ranges from 10.5% to 11.9% (11.06%0.53%). There were also significant dosimetric variations when we applied the adaptive plan to the deformed and non-deformed OARs. For cord, the mean dose percentage change ranged from 16.07% to 19.63% (17.65%1.53%); for heart, that ranged from 8.62% to 13.14% (9.78%2.02%); for lung, that ranged from 8.01% to 11.04% (10.53%0.44%). For cord, the max dose percentage change ranged from 6.04% to 16.14% (11.39%3.64%); for heart, that ranged from 0.36% to 3.15% (1.45%1.08%); for lung, that ranged from 0.59% to 2.86% (1.48%0.86%). Conclusions: Significant TCP variations were observed even from dosimetric variations meeting heuristic QA criteria. The target definition variation between clinicians is still a significant factor. The PTV expansion mitigates the dosimetric variations within QA tolerances. The solutions may be to require more stringent QA criteria and/or take these uncertainties into consideration explicitly in the PTV design. This work is supported by RTOG grant U10 CA21661 from the NCI and Pennsylvania Department of Health 2008 Formula Grant 4100047624. Author Disclosure: W. Chen: None. Y. Cui: None. F. Kong: None. M. Machtay: None. G. Videtic: None. B. Loo: None. E. Gore: None. J. Galvin: None. Y. Yan: None. Y. Xiao: None.
3019 Predictors of Rib Fracture and Nonfracture Chest Wall Pain After Lung Stereotactic Body Radiation Therapy (SBRT) J. Lee, K. Creach, A. Bierhals, T. DeWees, D. Mullen, P. Parikh, J. Bradley, and C. Robinson; Washington University, St Louis, MO Purpose/Objective(s): Rib fracture (fracture) and non-fracture related chest wall pain (CW pain) have been described after lung SBRT, but are typically combined for purposes of toxicity analysis despite having potentially different mechanisms for development. We sought to describe the natural history of fracture vs CW pain after lung SBRT, and identify patient, tumor, dosimetric and radiologic factors associated with their development. Materials/Methods: From an IRB approved institutional registry, we identified 123 lung lesions in 118 patients treated with SBRT to 54 Gy in 3 fractions from 2004-2009. Fracture and CW pain were identified by medical chart review. An independent radiologist verified fractures on chest CT and noted any findings of chest wall edema or rib radiation necrosis. Electronic treatment plans were available for 74 CWs, which were contoured as a 3 cm expansion from involved lung. Cox and Kaplan Meier (KM) log-rank uni/multivariate analyses evaluated patient (age, sex, Zubrod, diabetes, BMI, smoking, connective tissue disorder [CTD]), tumor (PTV volume and max dimension) and dosimetric factors (conformality index, gradient, max CW dose, absolute/relative CW V20 to 65Gy) for association with CW toxicity. Results: Median follow-up was 30.4 mo. CW pain occurred in 32 patients (27.7%) at a median of 8.2 mo. Of these, 22 had G1, 8 had G2 and 2 had G3 CW pain. Fractures occurred in 24 patients (20.3%) at a median of 14.5 mo. Nine had asymptomatic fractures, 10 had G1, 4 had G2 and 1 had G3 fracture pain. Of those with fractures, 20 (83.3%) had radiographic chest wall edema and 11 (45.8%) had rib radiation necrosis on chest CT. Chest wall edema predated fracture by a median of 6.9 mo. Rib radiation necrosis
International Journal of Radiation Oncology Biology Physics
Results: Four hundred seventy-two PCI patients were matched to 1,888 non-PCI patients. Characteristics were balanced across groups, including race (p Z 1.00), gender (p Z 0.95), histology (p Z 1.00), stage (p Z 1.00), and surgery (p Z 0.81). The PCI group was younger, with a median age of 64 vs 68 years (p < 0.01). Median OS was 8 vs 10 months (p < 0.01) favoring the non-PCI group. OS in the PCI vs. non-PCI groups was 14% vs 28% at 2 years and 5% vs 12% at 5 years (p < 0.01). In Stage III patients (n Z 365) OS was 10% vs 21% at 2 years (p < 0.01). The decrement in OS with PCI was also observed when patients with bulky disease (T3 and above) and adenocarcinoma histology were examined separately. Median CSS was the same (9 months) in both groups. Conclusions: To date, four prospective trials examining PCI for NSCLC have been reported in full and demonstrated a significant reduction in the incidence of brain metastases, but the effect on overall survival is not clear. Here we demonstrate in the largest cohort study of PCI for NSCLC that there is a significant decrement in overall survival associated with PCI. While patients with limited stage small-cell lung cancer (SCLC) derive both an overall survival and brain metastasis-free survival benefit from PCI, there is a considerably higher likelihood for intracranial metastatic disease in SCLC than in NSCLC. Our results imply that there may be a propensity threshold for intracranial metastatic disease below which PCI is not warranted, and that future clinical trials investigating the role of PCI for NSCLC may not be justified. Author Disclosure: M.N. Corradetti: None. E. Xanthopolous: None. S. Cheng: None. D. Horowitz: None. A. Fernandes: None. A. Lusa: None. K. Chao: None. R. Rengan: None.
esophagus, increases in PET uptake were seen through treatment but these did not correlate with the onset or severity of RE symptoms. Author Disclosure: V.A. Ford: None. P. McCloskey: None. N. Becker: None. J. Bissonnette: None. K. Clarke: None. J. Higgins: None. C. Leavens: None. A. Hope: None. A. Bezjak: None. A. Sun: None.
3015 Role of FDG-PET as an Early Imaging Biomarker of Esophagitis and Pneumonitis During the Course of Radiation Therapy for Lung Cancer V.A. Ford, P. McCloskey, N. Becker, J. Bissonnette, K. Clarke, J. Higgins, C. Leavens, A. Hope, A. Bezjak, and A. Sun; Princess Margaret Hospital, Toronto, ON, Canada Purpose/Objective(s): To determine if FDG PET-CT during a course of radical chemoradiation therapy (CRT) correlates with development of esophagitis or pneumonitis. Materials/Methods: Patients were imaged serially with 4DCT and 4D FDG PET-CT at weeks 0, 2, 4, 7 during CRT and 3 months (3m) following RT. Patients were Stage II-III NSCLC and undergoing CRT receiving a dose of at least 60Gy. Fourteen patients were analyzed and chart review identified those who developed clinical radiation esophagitis (RE) or radiation pneumonitis (RP) and grade (CTCAE V4). Each serial 4DCT and 4D FDG PET-CT images were registered onto the clinical planning datasets (Pinnacle 9.0). Esophagus and non GTV lung (GTV from original clinical plan), were contoured on all serial exhale 4DCT datasets. The matching exhale PET dataset was examined for early indication of RE and RP. Contours were delineated using thresholding to match, in 10% increments, the 20 to 80% of the maximum SUV value on the 4DPET for lung and esophagus. The subsequent volumes were recorded for each patient for each week. Intensity Volume Histograms (IVH) were plotted using the volumes for % max SUV Contours (20-80) for each week, against the absolute SUV values. Changes in the SUV IVH from week to week were observed for each patient. Results: Four of 14 patients had grade 2 RP. The SUV uptake at 12 weeks increased for all these individuals. There was no significant uptake from week 0-7 for any patient. 10 of 13 patients had grade 2 RE, 2 of 13 had grade 3 RE. Of these, increases in SUV uptake were seen in the esophagus. The SUV peaked at variable times (week 7 in 5 patients, week 4 in 4 patients, week 2 in 3 patients). There was no correlation with grade or timing of peak esophagitis. Increased PET uptake was seen prior to RE in some individuals. Increase in SUV uptake from baseline was also seen in the patients who did not develop RE. Conclusions: In this series of patients, although PET uptake was seen to increase in normal lung tissue in those developing RP, there was no early increase to allow us to predict which individuals would be affected. For the
3016 The Influence of the Inhomogeneity Correction Factor on Dose Distributions in Lung Cancer Radiation Therapy Treatment Plans: A Retrospective Study R. Murphy, T. Hill, P. Rapley, L.S. Kandler, and K. Ramchandar; Thunder Bay Regional Health Sciences Centre, Thunder Bay, ON, Canada Purpose/Objective(s): The purpose of this retrospective study is to analyze the effect of the Convolution/Superposition Inhomogeneity Correction Factor (ICF) on the dose distribution when applied to lung cancer radiation therapy plans. The objective of this study is to better the delivery of care for patients with lung cancer by providing valuable information that can help determine what adaptations need to be made when moving from homogeneous planning to heterogeneous planning of lung cancer radiation treatments. Materials/Methods: The treatment plans of 38 patients prescribed radiation treatment for lung cancer planned within the last 3 years using homogeneous calculations were restored from archives. Included are 27 plans of patients treated for radical stage III non-small cell lung cancer (NSCLC), 9 plans of patients treated for radical T1N0 (NSCLC) and 7 plans of patients treated with palliative intent for lung cancer. Each homogeneous plan (plan A) was recalculated with the ICF applied (Plan B), and again with the ICF applied and the original number of monitor units restored (Plan C). Dose distributions of the inhomogeneity plans were compared with the original plan through comparison of dose to various points and volumes and statistical analysis was done with paired t-tests. Results: Because of a small population size, the results of this study yielded no significant results. However, the trends of the study suggests that when applying the ICF to the homogeneous plan, (Plan A vs. Plan B), a strongly correlated decrease (5%) was found in the number of monitor units needed to provide the prescribed dose to the ICRU reference point. Encouragingly, the results showed that even with a homogeneous plan, the estimations of the V95% coverage is consistent (0.2% difference) with what was shown to be actually delivered (Plan A vs. Plan C). The results do show that the homogeneous plan underestimates the dose to the lung tissue and according to the heterogeneous plan C, we are actually delivering on average 5-10% more dose to the lung (Plan A vs. Plan C). Conclusions: The results of this study show that by not taking into account the heterogeneity of the tissues in lung cancer radiation treatment plans, we are overdosing the patient and underestimating the dose to the lung. However the current homogeneous plans do provide acceptable coverage of the PTV in the V95%. Further investigations could be done with a larger population in order to provide statistically significant results, however even in this small patient population, trends can be seen that can help provide direction when beginning to plan using the Inhomogeneity Correction Factor to move from homogeneous to heterogeneous lung cancer radiation treatment planning. Author Disclosure: R. Murphy: None. T. Hill: None. P. Rapley: None. L.S. Kandler: None. K. Ramchandar: None.
3017 Dosimetric Implications of Abdominal Compression for Lung SBRT Treatment V. Sarkar, B. Wang, P. Rassiah-Szegedi, H. Zhao, J.Y. Huang, M.W. Szegedi, Y.J. Hitchcock, K.E. Kokeny, and B.J. Salter; Huntsman Cancer Hospital, Salt Lake City, UT Purpose/Objective(s): One of the methods to limit lung tumor motion stemming from respiration is through the use of abdominal compression devices. The purpose of this study is to evaluate how the use of such a device influences the dosimetry of the final plan in terms of normal lung
Volume 84 Number 3S Supplement 2012
Poster Viewing Abstracts S601
volumes covered by the 5Gy and 20Gy isodose lines (i.e. V5 and V20, respectively). Materials/Methods: Five patients with lower lobe tumors (greatest excursion due to respiratory motion) previously treated with SBRT at our institution were chosen for this study. A dynamic conformal arc technique was employed through the MM3 collimator on a linear accelerator. The PTV in the original plan had an average of 90.4cc (7.7 cc - 221.9cc). The original planned V20 averaged 4.1% (1%-11.6%) while V5 averaged 19.9% (6.7% - 37.5%) of normal lung volumes. Based on a survey of published data and the reported mean reductions in cranio-caudal ITV extent second to application of abdominal compression, we systematically reduced the ITV/PTV for each patient along the cranio-caudal (CC) direction by 6, 8 and 10 mm (i.e., 3, 4 and 5mm at each end). No change was made in the anterior-posterior or left-right directions. Plans were then created for each of the new PTVs using the same conformal arc extent as the original plan, and all plans were normalized such that 95% of the PTV received the prescription dose. In each case, the value of V5 and V20 for the new plan was compared with those from the original plan. Poster Viewing Abstract 3017; Table Effects of Decreasing ITV/PTV Size on the Values of V5 and V20 for the Lung ITV/PTV ITV/PTV ITV/PTV ITV/PTV ITV/PTV ITV/PTV shrunk by shrunk by shrunk by shrunk by shrunk by shrunk by 10 mm 10 mm 8 mm 8 mm 6 mm 6 mm
Average Minimum Maximum
Decrease in V5 (%)
Decrease in V20 (%)
Decrease in V5 (%)
Decrease in V20 (%)
Decrease in V5 (%)
Decrease in V20 (%)
1.7 0.9 3.1
0.4 0.0 1.1
2.6 1.3 4.7
1.0 0.3 2.0
3.5 2.0 5.9
1.1 0.4 2.5
Results: The Table shows the average, minimum and maximum decrease in V5 and V20 for each of the 3 scenarios investigated here. Conclusions: As expected, the value of V5 and V20 decreased when the PTV was reduced, with the magnitude of the decrease being larger the more the PTV size was decreased. However, the observed reduction of V5 and V20 was modest, even when the PTV was reduced by 10 mm, with the maximum drop in V5 and V20 being 5.9% and 2.5% respectively. This suggests that, for the conformal arc technique evaluated here, anticipation of significant reduction in V5 and V20 may not be a reasonable sole motivation for application of abdominal compression. Author Disclosure: V. Sarkar: None. B. Wang: None. P. Rassiah-Szegedi: None. H. Zhao: None. J.Y. Huang: None. M.W. Szegedi: None. Y.J. Hitchcock: None. K.E. Kokeny: None. B.J. Salter: None.
3018 Quantitative Evaluation of Impact Upon Tumor Control Probability (TCP) From Quality Assurance Criteria for Non-small Cell Lung Cancer From RTOG 1106 Study W. Chen,1 Y. Cui,1 F. Kong,2 M. Machtay,3 G. Videtic,4 B. Loo,5 E. Gore,6 J. Galvin,7 Y. Yan,1 and Y. Xiao7; 1Thomas Jefferson University Hospital, Philadelphia, PA, 2University of Michigan, Ann Arbor, MI, 3Case Medical Center, Cleveland, OH, 4Cleveland Clinic, Cleveland, OH, 5Department of Radiation Oncology and Stanford Cancer Institute, Stanford University, Stanford, CA, 6Medical College Wisconsin, Milwaukee, WI, 7Radiation Therapy Oncology Group, Philadelphia, PA Purpose/Objective(s): Adaptive radiation therapy (ART), which involves modifying the radiation plan for the target as it changes during therapy, is being explored for diseases such as lung cancer. Approximations are made in the protocol that organs-at-risk (OARs) remain constant in shape and relative location during ART. In this study, we investigate the accuracy of this assumption, volumetrically and dosimetrically. Materials/Methods: RTOG 1106 is a randomized Phase II Trial of Individualized Radiation therapy Using During-Treatment FDG-PET/CT (DurCT) and Modern Technology in Locally Advanced Non-Small Cell Lung Cancer (NSCLC). In the lead up to the study pre-clinical planning test
cases were given to several institutions to study feasibility and consistency in contouring the target and OARs, and to generate treatment plans meeting predefined criteria. After the initial plan of around 50Gy, a “highest achievable dose” adaptive plan was generated using the target defined on CT acquired during the course of the treatment (Dur-CT). Targets are re-defined but not the OARs. In this study, we generate OARs for the adaptive course by deforming OAR contours from the Pre-CT to Dur-CT with visual validation. These contours were then transferred back to Pre-CT for dosimetry assessments. Results: We evaluated dosimetric and volumetric parameters for three major OARs - cord, heart and lung from four institutions between pre-CT and dur-CT. There were significant volumetric variations: for cord, the volume difference ranged from 2.11% to 3.25% (2.51%0.45%). For heart, it ranged from 25.73% to 28.84% (26.82%1.34%). For lung, it ranges from 10.5% to 11.9% (11.06%0.53%). There were also significant dosimetric variations when we applied the adaptive plan to the deformed and non-deformed OARs. For cord, the mean dose percentage change ranged from 16.07% to 19.63% (17.65%1.53%); for heart, that ranged from 8.62% to 13.14% (9.78%2.02%); for lung, that ranged from 8.01% to 11.04% (10.53%0.44%). For cord, the max dose percentage change ranged from 6.04% to 16.14% (11.39%3.64%); for heart, that ranged from 0.36% to 3.15% (1.45%1.08%); for lung, that ranged from 0.59% to 2.86% (1.48%0.86%). Conclusions: Significant TCP variations were observed even from dosimetric variations meeting heuristic QA criteria. The target definition variation between clinicians is still a significant factor. The PTV expansion mitigates the dosimetric variations within QA tolerances. The solutions may be to require more stringent QA criteria and/or take these uncertainties into consideration explicitly in the PTV design. This work is supported by RTOG grant U10 CA21661 from the NCI and Pennsylvania Department of Health 2008 Formula Grant 4100047624. Author Disclosure: W. Chen: None. Y. Cui: None. F. Kong: None. M. Machtay: None. G. Videtic: None. B. Loo: None. E. Gore: None. J. Galvin: None. Y. Yan: None. Y. Xiao: None.
3019 Predictors of Rib Fracture and Nonfracture Chest Wall Pain After Lung Stereotactic Body Radiation Therapy (SBRT) J. Lee, K. Creach, A. Bierhals, T. DeWees, D. Mullen, P. Parikh, J. Bradley, and C. Robinson; Washington University, St Louis, MO Purpose/Objective(s): Rib fracture (fracture) and non-fracture related chest wall pain (CW pain) have been described after lung SBRT, but are typically combined for purposes of toxicity analysis despite having potentially different mechanisms for development. We sought to describe the natural history of fracture vs CW pain after lung SBRT, and identify patient, tumor, dosimetric and radiologic factors associated with their development. Materials/Methods: From an IRB approved institutional registry, we identified 123 lung lesions in 118 patients treated with SBRT to 54 Gy in 3 fractions from 2004-2009. Fracture and CW pain were identified by medical chart review. An independent radiologist verified fractures on chest CT and noted any findings of chest wall edema or rib radiation necrosis. Electronic treatment plans were available for 74 CWs, which were contoured as a 3 cm expansion from involved lung. Cox and Kaplan Meier (KM) log-rank uni/multivariate analyses evaluated patient (age, sex, Zubrod, diabetes, BMI, smoking, connective tissue disorder [CTD]), tumor (PTV volume and max dimension) and dosimetric factors (conformality index, gradient, max CW dose, absolute/relative CW V20 to 65Gy) for association with CW toxicity. Results: Median follow-up was 30.4 mo. CW pain occurred in 32 patients (27.7%) at a median of 8.2 mo. Of these, 22 had G1, 8 had G2 and 2 had G3 CW pain. Fractures occurred in 24 patients (20.3%) at a median of 14.5 mo. Nine had asymptomatic fractures, 10 had G1, 4 had G2 and 1 had G3 fracture pain. Of those with fractures, 20 (83.3%) had radiographic chest wall edema and 11 (45.8%) had rib radiation necrosis on chest CT. Chest wall edema predated fracture by a median of 6.9 mo. Rib radiation necrosis