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Safety and Efficacy of Second Stereotactic Body Radiation Therapy (SBRT) for Local Recurrence of Non-small Cell Lung Cancer (NSCLC) or Lung Metastasis Previously Treated With SBRT
Volume 84 Number 3S Supplement 2012 Syracuse, NY, 2University of Rochester, Rochester, NY, 3Albany Medical College, Albany, NY Purpose/Objective(s): Obtaining a tissue diagnosis has traditionally been standard of care prior to initiating therapy for early stage NSCLC. In several recent studies from Europe and Asia, a substantial proportion of patients have received stereotactic body radiation therapy (SBRT) based only on the imaging characteristics of the suspicious lesion. The underlying assumption is that the risk of percutaneous needle biopsy may outweigh the benefits in a population that generally has underlying pulmonary dysfunction and other medical co-morbidity. Nevertheless, there is limited information regarding biopsy related complication rates in high-risk patients with early stage NSCLC who are treated with SBRT. Methods: Retrospective review of outcomes following biopsy in patients treated with stereotactic body radiation therapy. Complications of percutaneous biopsy (i.e. pneumothorax, chest tube placement) were analyzed in relation to patient and tumor characteristics. Each biopsy event was analyzed independently for patients with multiple biopsies. Statistical calculations and multivariate regression using a logistic model were performed using R software. Results: A total of 112 percutaneous biopsies were performed in 103 patients. Pneumothorax of any degree was observed in 40 (35%) patients (95% CI 27%-45%), while 12 patients (10.7%) had a clinically significant pneumothorax requiring chest tube placement, 95% CI (6%-18%). Eighteen patients (16%) required overnight hospitalization, 95% CI (10%24%). Reasons for hospitalization other than chest tube placement included: pain control (1 patient), systemic disease workup (2 patients), close observation due to prior pneumonectomy (1 patient), history of previous pneumothorax from previous biopsy (1 patient), observation for pneumothorax not requiring chest tube (1 patient). Grade 2 bleeding was not observed and no patient developed post-biopsy infection. Eight out of 61 (13%) patients with a history of COPD required chest tube placement, compared with 4 out of 50 who did not have a diagnosis of COPD (8%). On multivariate analysis, age, performance status, smoking history, pack years of smoking, or COPD history were not statistically significantly associated with chest tube placement. Conclusions: CT guided-needle biopsy in a primarily medically inoperable patient population is safe with an acceptable degree of complications. Author Disclosure: V. Chowdhry: None. A.K. Chowdhry: None. N. Goldman: None. E.M. Scalzetti: None. R.A. Grage: None. J.A. Bogart: None.
2933 Analysis of Prognostic Factors Affecting Local and Distant Recurrence Following Surgery for Non-small Cell Lung Cancer: A Recursive Partitioning Analysis C.R. Kelsey,1 K. Higgins,2 B. Peterson,1 L.B. Marks,3 D. Tandberg,1 J. Chino,1 M. DeCamp,4 and J. Varlotto5; 1Duke University, Durham, NC, 2 Emory University, Atlanta, GA, 3University of North Carolina, Chapel Hill, NC, 4Northwestern University, Chicago, IL, 5Pennsylvania State University, Hershey, PA Purpose/Objective(s): The risk of local/regional recurrence (LRR) and distant recurrence (DR) after surgery for early-stage NSCLC depends largely on surgical and pathological prognostic factors. While multiple risk factors for both LRR and DR have been identified using multivariate modeling, estimating the aggregate risk in an individual patient, or population, based on the presence or absence of multiple factors is a challenge. We sought to define subgroups at high risk of LRR and DR using a recursive partitioning analysis (RPA), within both a primary and validation dataset. Materials/Methods: This IRB-approved study included patients who underwent upfront surgery for I-IIIA NSCLC between 1995-2008 at multiple other institutions (validation set). Patients were excluded if they had positive surgical margins, received postoperative radiation therapy or died in the postoperative period. Disease recurrence at the surgical margin, ipsilateral hilum, and/or mediastinum was considered a LRR. Other sites of recurrence were scored as DR. Recursive partitioning was used to build regression trees for the prediction of time to LRR and time to DR for both
Poster Viewing Abstracts S569 datasets separately using standard clinical and pathological factors. Recursive partitioning was done with the rcart function of R’s statistical software. LRR and DR were scored as independent events with patients censored at the time of death with actuarial 5-year rates of recurrence estimated using the Kaplan-Meier method. Results: A total of 1411 patients comprised the primary set with 5-year actuarial rates of LRR and DR of 23% and 30%, respectively. Eight hundred eighty-seven patients comprised the validation set with 5-year actuarial rates of LRR and DR of 24% and 32%, respectively. For LRR, the primary RPA identified three groups based on stage and histology to best segregate patients into risk groups with the following 5-year recurrence risks: stage I/adenocarcinoma 13%; Stage I/squamous or large cell 28%; Stage II-IIIA 38%. For LRR, the validation RPA identified three groups based on lymphovascular invasion (LVI) and stage: no LVI/stage IA 19%; no LVI/stage IB-IIIA 27%; LVI 42%. For DR, the primary RPA identified three groups based on stage and LVI with the following 5-year recurrence risks: stage I/no LVI 19%; stage I/LVI 39%; stage II-IIIA 54%. For DR, the validation RPA identified three groups, also based on stage and LVI: stage I-IIA/no LVI 28%; stage I-IIA/LVI 52%; stage IIB-IIIA 57%. Conclusions: For LRR, there is discordance between the two data sets with regard to the parameters that best segregate patients into risk groups. Nevertheless, both data sets implicated stage as being a major predictive factor. Pathological stage and LVI were the key determinant of DR in both datasets. RPA is able to define subgroups at variable risk of LRR and DR. Author Disclosure: C.R. Kelsey: E. Research Grant; Varian Medical Systems. K. Higgins: None. B. Peterson: None. L.B. Marks: None. D. Tandberg: None. J. Chino: None. M. DeCamp: None. J. Varlotto: None.
2934 Safety and Efficacy of Second Stereotactic Body Radiation Therapy (SBRT) for Local Recurrence of Non-small Cell Lung Cancer (NSCLC) or Lung Metastasis Previously Treated With SBRT K. Kosaki,1 Y. Shibamoto,1 A. Miyakawa,1 K. Uchiyama,2 C. Hashizume,3 H. Ogino,1 R. Murata,1 and Y. Mori1; 1Nagoya City University Graduate School of Medical Sciences, Department of Radiology, Nagoya, Japan, 2 Aichi Cancer Center Aichi Hospital, Okazaki, Japan, 3Nagoya Radiosurgery Center, Nagoya, Japan Purpose/Objective(s): SBRT is establishing its role in the treatment of stage I NSCLC and solitary lung metastasis in patients who are not suitable for or refuse surgery. Considerably high local control rates of 70-85% have been reported, but still local recurrence is one of major patterns of failure after SBRT. In such cases, salvage surgery is difficult, and patients are generally not indicated for it nor wish it. As a salvage treatment of local recurrence after SBRT, we have attempted to use second SBRT. The purpose of this study was to evaluate the safety and efficacy of stereotactic re-irradiation after local in-field relapse of NSCLC or solitary lung metastasis previously treated with SBRT. Materials/Methods: From July 2004 to January 2011, 14 patients with local relapse of NSCLC (nZ9) or lung metastasis (nZ5) were retreated with SBRT. Median patient age at second SBRT was 78 years (range, 5884), and 9 were men and 5 were women. These patients had grade 1 or 2 radiation pneumonitis after first SBRT. Local recurrence was first suspected on contrast-enhanced CT images showing an increasing mass-like shadow within the area of once consolidated radiation fibrosis. To support the diagnosis of local recurrence, FDG-PET was performed and a standardized uptake ratio was 3 or higher in all cases. Biopsy of the mass was performed whenever necessary. The median interval between first and second SBRT was 12 months (range, 5-78). First SBRT doses were 36 Gy in 2 fractions (fr) or 48, 50 or 52 Gy in 4 fr according to the institutional protocols. Second SBRT doses were 48 Gy in 4-6 fr (nZ7), 50 Gy in 4 fr (nZ2), 52 Gy in 4fr (nZ4) or 55 Gy in 10 fr (nZ1). The prescribed doses were determined considering the tumor size and the distance between the tumor and organs at risk. Results: Nine patients are alive (median, 18.5 months). Four patients died of cancer and one committed suicide. Overall survival and local control rates were 79% and 42%, respectively, at 2 years. The longest survival was
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71 months; he had a histologically-confirmed recurrence and is now alive with no evidence of disease. All but two patients had grade 1 or 2 radiation pneumonitis after second SBRT. Grade 3 radiation pneumonitis occurred in two patients who had severe emphysema; domiciliary oxygen therapy became necessary for them eventually. The other adverse events were rib fracture in two and pain around the treatment volume in one. Conclusions: Second SBRT was relatively safe. Local control and survival rates were higher than expected. SBRT should be an important treatment option for local recurrence of NSCLC or lung metastasis in patients who did not show grade 3 or higher radiation pneumonitis after first SBRT. Author Disclosure: K. Kosaki: None. Y. Shibamoto: None. A. Miyakawa: None. K. Uchiyama: None. C. Hashizume: None. H. Ogino: None. R. Murata: None. Y. Mori: None.
Purpose/Objective(s): To evaluate the prognostic value of F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) in patients with T1-2N0M0 non-small cell lung cancer (NSCLC) treated with hypofractionated radiation therapy. Methods and Materials: Thirty-two (20 T1N0M0, 12 T2N0M0) medically inoperable patients from November 2006 to October 2011 were retrospectively analyzed. All the lung tumors were pathologically proved and the patients were treated with Cyber knife. Before hypofractionated radiation therapy, patients were undergoing the first FDG PET/CT scan. All patients were followed up with the second FDG PET/CT scan in about a month after radiation therapy. A total dose of 45-60 Gy was delivered to the PTV in 3 to 8 equal fractions in one week or less than two weeks. Median calculated biological effective dose (BED) was 136.8Gy (range, 76.8 -180 Gy). Standardized uptake values (SUVs) at the two times (pre-SUVmax and post-SUVmax) and the decreased ratio of these SUVmax (post-SUVmax/pre-SUVmax) were calculated. Cox proportional hazard regression analyses were performed to search prognostic factors for local recurrence, distant metastasis, overall survival (OS) and disease free survival (DFS) rates. The independent valuables consisted of pre-SUVmax, post-SUVmax, decreased SUVmax ratio, age, gender, Karnofsky performance status, histology and maximum tumor diameter were analysis. Results: The median follow-up time was 33 months (range, 4-62 months). At the end of follow-up, twelve patients were still alive with the OS was 31.816.8m and the PFS was 22.415.9m. Two-year local control, PFS and OS were 95.8%, 56.0% and 82.2%, respectively. The pre-SUVmax and post-SUVmax did not significantly affect local recurrence, distant metastases or OS. On univariate analysis, the only predictor for PFS was preSUV (max) ([95% confidence interval, 22.487-38.622], pZ0. 041). Interestingly, HRs of post-SUVmax for local recurrence were low (0.662) while early pre-SUVmax were relatively high (0.910) though there is no significant correlation. Conclusions: The SUVmax of pre-treatment FDG PET/CT scan may be an important predict factor for PFS in stage I NSCLC patients treated with hypofractionated radiation therapy. Author Disclosure: P. Wang: None. N. Liu: None. C. Qu: None. L. Zhu: None. B. Wang: None. Q. Pang: None. Z. Yuan: None. L. Zhao: None.
2935 A MCNP5 Comparison of the Dose Distribution from 169-Ytterbium LDR Brachytherapy Sources Within Heterogeneous Tissue to TG-43 Guidelines B. Currier, D.C. Medich, and J.J. Munro; University of Massachusetts Lowell, Lowell, MA Purpose/Objective(s): Lung cancer is the leading cause of cancer death in the United States with an estimated 2226, 160 new cases and 160, 340 deaths in 2011 . One growing method used for treatment is brachytherapy, which is superior to external beam because of the limited absorbed dose to normal tissue. In clinical brachytherapy, absorbed dose treatment calculations historically have been based on AAPM Task Group No. 43 (TG-43) recommendations, which assume the body is a semi-infinite water medium. While this method is the only AAPM treatment planning technique for brachytherapy, it does not accurately account for heterogeneous tissue compositions such as lung tissue. Based on ICRU 44, the density of healthy tissue (r Z 1.06 g cm^-3) is over five times greater than lung tissue (r Z 0.20 g cm^-3) and has effects on the radial dose function of the radioactive implant. This study compares typical treatment plans using a 169-Yb brachytherapy implant within two phantom types: a lung phantom accounting for differences in tissue compositions and a TG-43 phantom containing a homogeneous water medium. Materials/Methods: Using MCNP5, a Source Production and Equipment Co (SPEC) Model M-31 169-Ytterbium source with a photon spectrum was modeled on the outside of two phantoms: a modified ORNL lung and a TG-43 homogeneous water medium. The ORNL phantom was modified through the addition of a 2cm section of compressed lung tissue (r Z 0.35 g cm^-3), accounting for the area stapled during the source implant surgery. The dose distribution, defined by TG-43, D(r,q), was measured at 1cm increments through the prescribed treatment volume and 2cm outside the treatment volume. Results: Our preliminary results demonstrate that by inaccurately accounting for lung tissue compositions in 169-Yb brachytherapy, there is a significant under estimation in the dose to healthy tissue. Complete results are expected to be obtained within the next two months. Conclusions: From this study, it was concluded that the current methods of determining brachytherapy absorbed dose for 169-Ytterbium sources underestimates the dose to bone and healthy tissue. By inaccurately accounting for lung tissue compositions in the absorbed dose to cortical bone surrounding the lungs could be under estimated by as much as 7.2%. Author Disclosure: B. Currier: None. D.C. Medich: None. J.J. Munro: None.
2936 Prognostic Value of Serial FDG-PET/CT Scanning in Stage I Non-small Cell Lung Cancer Patients Treated With Hypofractionated Radiation Therapy P. Wang,1 N. Liu,1 C. Qu,2 L. Zhu,3 B. Wang,2 Q. Pang,1 Z. Yuan,2 and L. Zhao1; 1Department of Radiation Oncology, Tianjin Cancer Institute and Hospital, Tianjin, China, 2Cyber Knife Center, Tianjin Cancer Institute and Hospital, Tianjin, China, 3PET-CT Center, Tianjin Cancer Institute and Hospital, Tianjin, China
2937 Dosimetric Effect of Patient Weight Change on VMAT Lung Treatments C. Knill, J. Maier, S. Miller, and A. Konski; Karmanos Cancer Institute, Detroit, MI Purpose/Objective(s): The goal of this study was to determine how variations in patient body thickness, caused by patient weight change throughout the course of a VMAT lung treatment, affect the dose delivered to the Internal Target Volume (ITV) and critical structures (spinal cord, total lung). Material/Methods: Twenty-two weekly cone beam CTs (CBCTs) of lungtumor patients, treated using VMAT, were imported into the Eclipse treatment planning software. The CBCTs were registered to their original planning CTs using a rigid bony-anatomy match. The external body contour of the original planning CTs were modified to match the weekly CBCTs, by adding and subtracting fatty tissue (-100 Hounsfield Units) from the surface of the patients. The changes in tissue were used to calculate the average change in patient thickness for each modified planning CT. Only the surface tissue located in the same axial slice as the ITV contour was included in this calculation. The original VMAT plans were recalculated on the modified CTs and the changes in dose to 95% of ITV(ITV-95%), maximum dose to 1cc of the spinal cord(Cord D1cc), and the total lung volume receiving at least 20GY(Lung V20) and 5GY(Lung V5) were recorded. Pearson r-correlation coefficients (r-values) comparing the changes in patient thickness and the changes in dose were calculated. Results: The r-values for ITV-95%, Cord D1cc, Lung V20, and Lung V5 were 0.872, 0.368, 0.860, and 0.930 respectively. The largest [negative / positive] change in dose for ITV-95%, Cord D1cc, Lung V20, and Lung
2933 Analysis of Prognostic Factors Affecting Local and Distant Recurrence Following Surgery for Non-small Cell Lung Cancer: A Recursive Partitioning Analysis C.R. Kelsey,1 K. Higgins,2 B. Peterson,1 L.B. Marks,3 D. Tandberg,1 J. Chino,1 M. DeCamp,4 and J. Varlotto5; 1Duke University, Durham, NC, 2 Emory University, Atlanta, GA, 3University of North Carolina, Chapel Hill, NC, 4Northwestern University, Chicago, IL, 5Pennsylvania State University, Hershey, PA Purpose/Objective(s): The risk of local/regional recurrence (LRR) and distant recurrence (DR) after surgery for early-stage NSCLC depends largely on surgical and pathological prognostic factors. While multiple risk factors for both LRR and DR have been identified using multivariate modeling, estimating the aggregate risk in an individual patient, or population, based on the presence or absence of multiple factors is a challenge. We sought to define subgroups at high risk of LRR and DR using a recursive partitioning analysis (RPA), within both a primary and validation dataset. Materials/Methods: This IRB-approved study included patients who underwent upfront surgery for I-IIIA NSCLC between 1995-2008 at multiple other institutions (validation set). Patients were excluded if they had positive surgical margins, received postoperative radiation therapy or died in the postoperative period. Disease recurrence at the surgical margin, ipsilateral hilum, and/or mediastinum was considered a LRR. Other sites of recurrence were scored as DR. Recursive partitioning was used to build regression trees for the prediction of time to LRR and time to DR for both
Poster Viewing Abstracts S569 datasets separately using standard clinical and pathological factors. Recursive partitioning was done with the rcart function of R’s statistical software. LRR and DR were scored as independent events with patients censored at the time of death with actuarial 5-year rates of recurrence estimated using the Kaplan-Meier method. Results: A total of 1411 patients comprised the primary set with 5-year actuarial rates of LRR and DR of 23% and 30%, respectively. Eight hundred eighty-seven patients comprised the validation set with 5-year actuarial rates of LRR and DR of 24% and 32%, respectively. For LRR, the primary RPA identified three groups based on stage and histology to best segregate patients into risk groups with the following 5-year recurrence risks: stage I/adenocarcinoma 13%; Stage I/squamous or large cell 28%; Stage II-IIIA 38%. For LRR, the validation RPA identified three groups based on lymphovascular invasion (LVI) and stage: no LVI/stage IA 19%; no LVI/stage IB-IIIA 27%; LVI 42%. For DR, the primary RPA identified three groups based on stage and LVI with the following 5-year recurrence risks: stage I/no LVI 19%; stage I/LVI 39%; stage II-IIIA 54%. For DR, the validation RPA identified three groups, also based on stage and LVI: stage I-IIA/no LVI 28%; stage I-IIA/LVI 52%; stage IIB-IIIA 57%. Conclusions: For LRR, there is discordance between the two data sets with regard to the parameters that best segregate patients into risk groups. Nevertheless, both data sets implicated stage as being a major predictive factor. Pathological stage and LVI were the key determinant of DR in both datasets. RPA is able to define subgroups at variable risk of LRR and DR. Author Disclosure: C.R. Kelsey: E. Research Grant; Varian Medical Systems. K. Higgins: None. B. Peterson: None. L.B. Marks: None. D. Tandberg: None. J. Chino: None. M. DeCamp: None. J. Varlotto: None.
2934 Safety and Efficacy of Second Stereotactic Body Radiation Therapy (SBRT) for Local Recurrence of Non-small Cell Lung Cancer (NSCLC) or Lung Metastasis Previously Treated With SBRT K. Kosaki,1 Y. Shibamoto,1 A. Miyakawa,1 K. Uchiyama,2 C. Hashizume,3 H. Ogino,1 R. Murata,1 and Y. Mori1; 1Nagoya City University Graduate School of Medical Sciences, Department of Radiology, Nagoya, Japan, 2 Aichi Cancer Center Aichi Hospital, Okazaki, Japan, 3Nagoya Radiosurgery Center, Nagoya, Japan Purpose/Objective(s): SBRT is establishing its role in the treatment of stage I NSCLC and solitary lung metastasis in patients who are not suitable for or refuse surgery. Considerably high local control rates of 70-85% have been reported, but still local recurrence is one of major patterns of failure after SBRT. In such cases, salvage surgery is difficult, and patients are generally not indicated for it nor wish it. As a salvage treatment of local recurrence after SBRT, we have attempted to use second SBRT. The purpose of this study was to evaluate the safety and efficacy of stereotactic re-irradiation after local in-field relapse of NSCLC or solitary lung metastasis previously treated with SBRT. Materials/Methods: From July 2004 to January 2011, 14 patients with local relapse of NSCLC (nZ9) or lung metastasis (nZ5) were retreated with SBRT. Median patient age at second SBRT was 78 years (range, 5884), and 9 were men and 5 were women. These patients had grade 1 or 2 radiation pneumonitis after first SBRT. Local recurrence was first suspected on contrast-enhanced CT images showing an increasing mass-like shadow within the area of once consolidated radiation fibrosis. To support the diagnosis of local recurrence, FDG-PET was performed and a standardized uptake ratio was 3 or higher in all cases. Biopsy of the mass was performed whenever necessary. The median interval between first and second SBRT was 12 months (range, 5-78). First SBRT doses were 36 Gy in 2 fractions (fr) or 48, 50 or 52 Gy in 4 fr according to the institutional protocols. Second SBRT doses were 48 Gy in 4-6 fr (nZ7), 50 Gy in 4 fr (nZ2), 52 Gy in 4fr (nZ4) or 55 Gy in 10 fr (nZ1). The prescribed doses were determined considering the tumor size and the distance between the tumor and organs at risk. Results: Nine patients are alive (median, 18.5 months). Four patients died of cancer and one committed suicide. Overall survival and local control rates were 79% and 42%, respectively, at 2 years. The longest survival was
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71 months; he had a histologically-confirmed recurrence and is now alive with no evidence of disease. All but two patients had grade 1 or 2 radiation pneumonitis after second SBRT. Grade 3 radiation pneumonitis occurred in two patients who had severe emphysema; domiciliary oxygen therapy became necessary for them eventually. The other adverse events were rib fracture in two and pain around the treatment volume in one. Conclusions: Second SBRT was relatively safe. Local control and survival rates were higher than expected. SBRT should be an important treatment option for local recurrence of NSCLC or lung metastasis in patients who did not show grade 3 or higher radiation pneumonitis after first SBRT. Author Disclosure: K. Kosaki: None. Y. Shibamoto: None. A. Miyakawa: None. K. Uchiyama: None. C. Hashizume: None. H. Ogino: None. R. Murata: None. Y. Mori: None.
Purpose/Objective(s): To evaluate the prognostic value of F-18 fluorodeoxyglucose positron emission tomography (FDG-PET) in patients with T1-2N0M0 non-small cell lung cancer (NSCLC) treated with hypofractionated radiation therapy. Methods and Materials: Thirty-two (20 T1N0M0, 12 T2N0M0) medically inoperable patients from November 2006 to October 2011 were retrospectively analyzed. All the lung tumors were pathologically proved and the patients were treated with Cyber knife. Before hypofractionated radiation therapy, patients were undergoing the first FDG PET/CT scan. All patients were followed up with the second FDG PET/CT scan in about a month after radiation therapy. A total dose of 45-60 Gy was delivered to the PTV in 3 to 8 equal fractions in one week or less than two weeks. Median calculated biological effective dose (BED) was 136.8Gy (range, 76.8 -180 Gy). Standardized uptake values (SUVs) at the two times (pre-SUVmax and post-SUVmax) and the decreased ratio of these SUVmax (post-SUVmax/pre-SUVmax) were calculated. Cox proportional hazard regression analyses were performed to search prognostic factors for local recurrence, distant metastasis, overall survival (OS) and disease free survival (DFS) rates. The independent valuables consisted of pre-SUVmax, post-SUVmax, decreased SUVmax ratio, age, gender, Karnofsky performance status, histology and maximum tumor diameter were analysis. Results: The median follow-up time was 33 months (range, 4-62 months). At the end of follow-up, twelve patients were still alive with the OS was 31.816.8m and the PFS was 22.415.9m. Two-year local control, PFS and OS were 95.8%, 56.0% and 82.2%, respectively. The pre-SUVmax and post-SUVmax did not significantly affect local recurrence, distant metastases or OS. On univariate analysis, the only predictor for PFS was preSUV (max) ([95% confidence interval, 22.487-38.622], pZ0. 041). Interestingly, HRs of post-SUVmax for local recurrence were low (0.662) while early pre-SUVmax were relatively high (0.910) though there is no significant correlation. Conclusions: The SUVmax of pre-treatment FDG PET/CT scan may be an important predict factor for PFS in stage I NSCLC patients treated with hypofractionated radiation therapy. Author Disclosure: P. Wang: None. N. Liu: None. C. Qu: None. L. Zhu: None. B. Wang: None. Q. Pang: None. Z. Yuan: None. L. Zhao: None.
2935 A MCNP5 Comparison of the Dose Distribution from 169-Ytterbium LDR Brachytherapy Sources Within Heterogeneous Tissue to TG-43 Guidelines B. Currier, D.C. Medich, and J.J. Munro; University of Massachusetts Lowell, Lowell, MA Purpose/Objective(s): Lung cancer is the leading cause of cancer death in the United States with an estimated 2226, 160 new cases and 160, 340 deaths in 2011 . One growing method used for treatment is brachytherapy, which is superior to external beam because of the limited absorbed dose to normal tissue. In clinical brachytherapy, absorbed dose treatment calculations historically have been based on AAPM Task Group No. 43 (TG-43) recommendations, which assume the body is a semi-infinite water medium. While this method is the only AAPM treatment planning technique for brachytherapy, it does not accurately account for heterogeneous tissue compositions such as lung tissue. Based on ICRU 44, the density of healthy tissue (r Z 1.06 g cm^-3) is over five times greater than lung tissue (r Z 0.20 g cm^-3) and has effects on the radial dose function of the radioactive implant. This study compares typical treatment plans using a 169-Yb brachytherapy implant within two phantom types: a lung phantom accounting for differences in tissue compositions and a TG-43 phantom containing a homogeneous water medium. Materials/Methods: Using MCNP5, a Source Production and Equipment Co (SPEC) Model M-31 169-Ytterbium source with a photon spectrum was modeled on the outside of two phantoms: a modified ORNL lung and a TG-43 homogeneous water medium. The ORNL phantom was modified through the addition of a 2cm section of compressed lung tissue (r Z 0.35 g cm^-3), accounting for the area stapled during the source implant surgery. The dose distribution, defined by TG-43, D(r,q), was measured at 1cm increments through the prescribed treatment volume and 2cm outside the treatment volume. Results: Our preliminary results demonstrate that by inaccurately accounting for lung tissue compositions in 169-Yb brachytherapy, there is a significant under estimation in the dose to healthy tissue. Complete results are expected to be obtained within the next two months. Conclusions: From this study, it was concluded that the current methods of determining brachytherapy absorbed dose for 169-Ytterbium sources underestimates the dose to bone and healthy tissue. By inaccurately accounting for lung tissue compositions in the absorbed dose to cortical bone surrounding the lungs could be under estimated by as much as 7.2%. Author Disclosure: B. Currier: None. D.C. Medich: None. J.J. Munro: None.
2936 Prognostic Value of Serial FDG-PET/CT Scanning in Stage I Non-small Cell Lung Cancer Patients Treated With Hypofractionated Radiation Therapy P. Wang,1 N. Liu,1 C. Qu,2 L. Zhu,3 B. Wang,2 Q. Pang,1 Z. Yuan,2 and L. Zhao1; 1Department of Radiation Oncology, Tianjin Cancer Institute and Hospital, Tianjin, China, 2Cyber Knife Center, Tianjin Cancer Institute and Hospital, Tianjin, China, 3PET-CT Center, Tianjin Cancer Institute and Hospital, Tianjin, China
2937 Dosimetric Effect of Patient Weight Change on VMAT Lung Treatments C. Knill, J. Maier, S. Miller, and A. Konski; Karmanos Cancer Institute, Detroit, MI Purpose/Objective(s): The goal of this study was to determine how variations in patient body thickness, caused by patient weight change throughout the course of a VMAT lung treatment, affect the dose delivered to the Internal Target Volume (ITV) and critical structures (spinal cord, total lung). Material/Methods: Twenty-two weekly cone beam CTs (CBCTs) of lungtumor patients, treated using VMAT, were imported into the Eclipse treatment planning software. The CBCTs were registered to their original planning CTs using a rigid bony-anatomy match. The external body contour of the original planning CTs were modified to match the weekly CBCTs, by adding and subtracting fatty tissue (-100 Hounsfield Units) from the surface of the patients. The changes in tissue were used to calculate the average change in patient thickness for each modified planning CT. Only the surface tissue located in the same axial slice as the ITV contour was included in this calculation. The original VMAT plans were recalculated on the modified CTs and the changes in dose to 95% of ITV(ITV-95%), maximum dose to 1cc of the spinal cord(Cord D1cc), and the total lung volume receiving at least 20GY(Lung V20) and 5GY(Lung V5) were recorded. Pearson r-correlation coefficients (r-values) comparing the changes in patient thickness and the changes in dose were calculated. Results: The r-values for ITV-95%, Cord D1cc, Lung V20, and Lung V5 were 0.872, 0.368, 0.860, and 0.930 respectively. The largest [negative / positive] change in dose for ITV-95%, Cord D1cc, Lung V20, and Lung