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Interfraction Regional Variation of Tumor Breathing Motion in Lung Stereotactic Body Radiation Therapy (SBRT)
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International Journal of Radiation Oncology Biology Physics
in the sagittal plane with the following parameters: TE/TR/Flip/Matrix-size/ Slices of 1.29 ms/2.57 ms/60/176 x 256/5. In-plane spatial resolution was w1.95 mm, and slice thickness ranged from 9-16 mm. Dynamic imaging was carried out for w8 min for each session, acquiring w200 image frames with 5 slices each. The center slice that contained the tumor was selected from each dataset to create a series of w200 frames with a temporal resolution of w2.5 s. An automated tumor tracking techniqueetemplate matchingewas used to estimate the tumor position frame-by-frame. For each session, an average position across all frames was used as the reference. Subsequently, the tumor movement on each frame was calculated relative to this reference in both the AP and SI directions. We calculated the amount of time as a percentage of the total acquisition time when centroids of the tumor moved more than 5 mm for each session. Results: For the 5 patients in the study, the 5 mm margin is sufficient to cover the tumor motion in the AP direction for w99% of the time. However, tumor motion in the SI direction was larger than 5 mm for 1 patient (tumor size w450 mL) in all 3 sessions with the percentage of time spent outside the 5 mm margin being 13%, 5%, and 11% respectively. In contrast, tumor movement in the SI direction was less than 5 mm w99% of the time when the tumor size is no greater than 100 mL. Conclusions: The overall outcome of radiation treatment highly relies on the characterization of PTV, which depends on the choice of the margin. In this study, motion of tumors of various sizes in lung cancer patients determined with an automatic tumor tracking technique was compared to the conventionally chosen margin size of 5 mm based on the original definition of the internal target using 4DCT. Results from the study indicate that the decision of margin size, especially in the SI direction, made using 4DCT can underestimate the tumor motion especially for large tumors. Author Disclosure: X. Shi: None. S. Chen: None. W.D. D’Souza: E. Research Grant; Varian Medical Systems. N.N. Mistry: None.
r Z +0.58, p Z 0.038) and cumulative dose in the ipsilateral normal lung (lung minus PTV) (r Z +0.72, p Z 0.0059) are each directly correlated to the inter-fraction volume range. The average enlargement of squamous cell carcinomas was greater than adenocarcinomas; however, the difference was not statistically significant. The observed CBCT volume changes during treatment had minimal effect on treatment planning dose coverage. Conclusions: Our preliminary data suggest that for ablative SBRT doses significant changes in inter-fraction tumor volume exist that are correlated to age, cumulative radiation dose in lung tissue and average PTV dose. The frequently observed increase followed by decrease in tumor volume suggests the presence of competing physiological processes during ablative radiation, and may be related to acute vascular injury, edema and inflammation, as well as tumor cell death and normal tissue effects of radiation. Author Disclosure: S. Salamekh: None. Y. Rong: None. V. Diavolitsis: None. T. Williams: None. N. Mayr: None. A.S. Ayan: None. M.X. Welliver: None.
164 Interfraction Tumor Volume Changes During Lung Stereotactic Body Radiation Therapy S. Salamekh, Y. Rong, V. Diavolitsis, T. Williams, N. Mayr, A.S. Ayan, and M.X. Welliver; The Ohio State University Comprehensive Cancer Center, Columbus, OH Purpose/Objectives(s): To analyze the inter-fraction tumor volume changes during Stereotactic Body Radiation Therapy (SBRT) of early stage non-small cell lung cancer (NSCLC) with respect to deposited doses and patient characteristics. Materials/Methods: Tumor volumes of 15 consecutive patients (age 5786) treated with SBRT at our institution between November 1, 2011 and June 1, 2012 were retrospectively analyzed. Patients were treated with a total dose of 45-54 Gy in 3-5 fractions. Kilovoltage cone-beam CT (CBCT) images obtained immediately prior to each administered dose were used to delineate gross tumor volume (GTV) resulting in 84 sets of contours from 18 tumors. The sum of the differential dose-volume histogram (DVH) of structures contoured prior to treatment was used to determine the average dose and cumulative radiation delivered. Pearson’s r and Spearman’s r correlation as well as partial correlation analysis were performed to study tumor volume changes with respect to patient and tumor characteristics as well as radiation delivered. Results: Relative to their original volume, most tumors increased in size and then decreased during the treatment course. The baseline CBCT tumor volume during the first treatment was between 0.41 and 43.9 mL. An average maximum increase of 15% relative to the baseline volume and regression of 11% were observed in tumor size, corresponding to a 26% average inter-fraction tumor volume range. The PTV size was inversely correlated to inter-fraction tumor volume changes (r Z 0.59, p Z 0.013 and r Z 0.62, p Z 0.0090), whereas age was proportional to the interval between the first treatment and the time point when the largest volume increase was observed (r Z +0.52, p Z 0.031 and r Z +0.63, p Z 0.0062). Partial correlation between radiation dose and inter-fraction volume revealed that the average PTV dose (r Z +0.60, p Z 0.031 and
165 Interfraction Regional Variation of Tumor Breathing Motion in Lung Stereotactic Body Radiation Therapy (SBRT) K. Atkins, A. Varchani, T.L. Nam, M. Fuss, and J.A. Tanyi; Oregon Health and Science University, Portland, OR Purpose/Objective(s): Narrow PTV margins and steep dose gradients underscore the importance of evaluating breathing-associated tumor motion for lung SBRT. However, the extent to which interfraction variation in tumor breathing motion correlates with anatomic tumor location has not been studied. Materials/Methods: Nineteen patients who received a 5-fraction course of SBRT underwent standard free-breathing 4DCT simulation and daily image-guidance 4DCTs using an identical in-room installed CT scanner. Tumors selected for analysis were located in the upper lobe (UL, n Z 9) or lower lobe (LL, n Z 10). Gross tumor volumes (GTV) for each of the 10 respiratory phases were delineated semi-automatically using a thresholdbased contouring technique. Centroid values from each respiratory phase were used to determine absolute tumor motion amplitude in the mediolateral (ML), anterior-posterior (AP), and superior-inferior (SI) directions. Results: A total of 65 simulation and daily 4DCTs from 19 patients were analyzed. In general, both UL and LL tumors showed limited breathing motion in the ML and AP directions (mean < 2.5 mm). Expectedly, LL tumors showed markedly larger centroid motion along the SI direction compared to UL tumors (10.8 5.2 mm vs 1.9 1.4 mm, p < 0.001). The mean variance in interfraction tumor motion amplitude in the ML and AP directions was < 1.5 mm for all tumors. In the SI direction, however, tumors in the LL showed a mean variance in interfraction motion amplitude of 5.1 7.0 mm vs 0.8 0.8 mm in the UL (p Z 0.01), with an overall mean variance in breathing motion amplitude of 2.8 5.2 mm for both UL and LL tumors combined. To note, these values represent the mean variance in interfraction tumor motion amplitude both beyond and within the maximum excursion observed in the reference (simulation) 4DCT. In LL tumors, 20% (n Z 2) had a mean variance in interfraction tumor motion amplitude along the SI direction 15 mm beyond the maximum excursion observed in the reference 4DCT, while the remaining 80% (n Z 8) did not exceed 5 mm. No UL tumors had a variance in interfraction tumor motion amplitude along the SI direction > 4 mm and 89% (n Z 8) were < 2.5 mm. Conclusions: While interfraction variances in tumor breathing motion along the SI direction were within our standard PTV margins (a uniform 5 mm beyond the ITV) for the vast majority of the tumors in this study, changes in interfraction breathing motion exceeded PTV margins in 20% of LL tumors. These results suggest that while day-to-day changes in tumor breathing motion are mostly small, typical ITV-based PTV margins may be insufficient for a subset of LL lesions. Thus, daily breathing motion re-assessment and adaptive re-planning may benefit patients with tumors in the LL.
Volume 87 Number 2S Supplement 2013 Author Disclosure: K. Atkins: None. A. Varchani: None. T.L. Nam: None. M. Fuss: E. Research Grant; Brainlab, Varian Medical. F. Honoraria; Brainlab, Varian Medical. G. Consultant; Brainlab, Varian Medical, Philips. J.A. Tanyi: F. Honoraria; Brainlab.
166 Novel Method of Cardiac Sparing With Deep-Inspiration BreathHold Utilizing Surface Electromagnetic Transponders in Women With Left-Sided Breast Cancer L. Fang,1,2 J. Kim,1,2 D. Kaurin,3 K. Holloway,2 M. Lavilla,2 and L. Sweeney3; 1University of Washington, Seattle, WA, 2Seattle Cancer Care Alliance, Seattle, WA, 3Northwest Medical Physics Center, Lynnwood, WA Purpose/Objective(s): Deep-inspiration breath hold (DIBH) for radiation therapy of the breast is an established technique that has been shown to minimize heart dose. A method for intrafraction motion management with DIBH technique was developed utilizing electromagnetic transponders placed on the skin. This retrospective study is the first report on the pilot experience of this novel method. Materials/Methods: Between January 1 and October 1, 2012, 40 patients with left-sided breast cancer underwent CT simulation and were treated with DIBH using surface electromagnetic transponders. Simulation CT scans were obtained in both free-breathing (FB) and DIBH positions in all patients. Treatment planning was performed on the DIBH CT scan with fusion of the FB scan. The heart was contoured and dose volume histograms computed. To reproduce the DIBH from the simulation and for intrafraction motion management, two methods of monitoring were simultaneously employed in all patients: 1) surface electromagnetic transponder system with real-time tracking and 2) lasers aligned to DIBH skin marks with continuous video surveillance during entire beam-on time. Results: Median age was 50 years (range, 31-70), 27.5% (11/40) DCIS, 45% (18/40) stage I, 20% (8/40) stage II, 7.5% (3/40) stage III. Eighty percent (32/40) of patients received 45-50.4 Gy in standard fractionation and 20% (8/40) received 42.5 Gy in 16 fractions to the left whole breast. Seventy-five percent (30/40) were treated to the left breast, one patient to the chest wall, one patient to a chest wall with tissue expander, three patients to the breast and supraclavicular field (SCF) and five patients to the chest wall with tissue expander plus SCF. The average mean heart dose was 78.9 c Gy with DIBH compared with 290.2 c Gy in FB (p-value < 0.0001). The mean heart V5 was 0.96% with DIBH and 12.7% with FB, mean V10 was 0.28% with DIBH versus 7.5% with FB, mean heart V15 was 0.014% with DIBH versus 5.2% with FB (p-value < 0.0001). The average transponder to laser difference for the first consecutive 535 fractions was 0.09 cm in the superior-inferior direction (SD 0.23), 0.09 cm in the anterior-posterior direction (SD 0.32) and 0.03 cm in the right-left direction (SD 0.29). Conclusions: An initial cohort of women with left-sided breast cancer has been successfully treated with DIBH technique using a novel method of skin surface electromagnetic transponders. This method was found to be feasible, accurate and well-tolerated by patients. There was a significant reduction in cardiac dose with DIBH. A prospective registry trial using the surface electromagnetic transponder system with DIBH is being initiated to confirm these findings. Author Disclosure: L. Fang: None. J. Kim: F. Honoraria; Varian. D. Kaurin: G. Consultant; Varian. K. Holloway: None. M. Lavilla: None. L. Sweeney: G. Consultant; Varian.
167 Intrafraction Variability and Deformation Quantification for Accelerated Partial-Breast Irradiation (APBI) C.K. Glide-Hurst, M. Shah, I. Aref, I.J. Chetty, B. Movsas, and E.M. Walker; Henry Ford Health System, Detroit, MI Purpose/Objective(s): While IGRT reduces setup error for linac-based APBI, IGRT cannot fully account for deformations arising from intrafraction motion. This study sought to evaluate intra-fraction variability and
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local deformations of the lumpectomy cavity (LC), breast, and nearby organs at risk. Materials/Methods: Sixteen early-stage (T0-T2N0M0) left-sided postlumpectomy breast cancer cases and 1 bilateral case with discernible LCs were retrospectively evaluated on an IRB-approved study. During simulation, each patient underwent a free-breathing CT and 10-phase 4DCT. For each patient, treated breast, heart, lungs, and LC were delineated on the end-inhale (EI) 4DCT phase. B-spline multi-resolution deformable image registration was employed to propagate contours to all phases. For the entire population, respiration-induced motion was calculated via centroid analysis. To quantify deformation, displacement vector fields (DVFs) were analyzed between EI and end-exhale (EE) datasets for the breast and LC volumes by classifying the vector magnitudes as < 2 mm, 2-4 mm, and > 4 mm. Results: For the patient population, LC intra-fraction motion was 0.7 0.7 mm, 1.1 0.7 mm, and 1.8 1.2 mm in lateral (LAT), anteriorposterior (A-P), and superior-inferior (S-I) directions, respectively. Similar intra-fraction motion results were obtained for the treated breast: 0.4 0.3 mm, 0.9 0.5 mm, and 1.6 0.9 mm LAT, A-P, and S-I directions, respectively. In the most extreme case, LC and breast excursions of w2 mm and w3 mm were observed in the A-P and S-I directions, respectively. Respiration-induced motion was dominant S-I for the heart (3.8 1.7 mm) and lungs (3.6 2.0 mm). Over all patients, DVF analysis revealed that 51.2 20.3% (range, 9.6 - 82.6%) of the treated breast volume deformed between 2-4 mm, whereas 11.3 12.7% deformed > 4 mm (range, 0 to 36.7%). The majority of LC volumes (60.7 37.6%) deformed 2-4 mm. However, a small subset demonstrated > 4 mm deformation (6.8 14.6%). The patient with the largest deformation (w45% of the LC volume deformed > 4 mm) also demonstrated the largest intra-fraction cavity and breast excursions. Conclusions: Overall, LC and breast demonstrated < 3 mm intra-fraction centroid motion, whereas heart and lung were slightly more mobile. Deformation characterization of the LC and breast revealed large variability among patients, suggesting value in patient-specific margins for APBI. A subset of volumes showed substantial deformation (> 4 mm), which, if unaccounted for, could potentially impact dose distribution. Further work is needed to resolve dominant regions of deformation. Coupling these results with inter-fraction setup analysis will likely yield better margin design, and potentially support the need for image-guided adaptive radiation therapy for APBI. Author Disclosure: C.K. Glide-Hurst: E. Research Grant; Philips Medical Systems, Varian Medical Systems. M. Shah: None. I. Aref: None. I.J. Chetty: E. Research Grant; Varian Medical Systems. B. Movsas: E. Research Grant; Varian Medical Systems. E.M. Walker: None.
168 Long-term Toxicities of a Prospective Trial Delivering Limited Margin 3DCRT/IMRT in Children With Rhabdomyosarcoma M. Krasin, C. Hua, L.E. Kun, A. Pappo, A. Pai Panandiker, M. Brown, A. Davidoff, B. Shulkin, B. McCarville, and T.E. Merchant; St. Jude Children’s Research Hospital, Memphis, TN Purpose/Objective(s): To evaluate the long term toxicity profile of 3DCRT/IMRT used to treat children with rhabdomyosarcoma (RMS). Materials/Methods: Sixty-six patients with a diagnosis of RMS (median age 6.7) were enrolled on a prospective IRB approved institutional trial of limited margin 3DCRT/IMRT integrating MR based anatomically constrained targeting. The GTV included the tumor bed (group II patients) or the residual MR based tumor plus surfaces of tissues initially in contact with tumor. The CTV included a 1 cm margin constrained to tissues tumor may have infiltrated (excluding pushing borders). A 3-5 mm PTV was then added. Prescribed doses were 36 Gy to the CTV (and its PTV) and 50.4 Gy to the GTV. Patients were scored routinely for general acute and late toxicities (CTCv2.0) as well as site specific toxicities. All related toxicities grade 3 were scored. Results: Forty-three of 66 patients remain disease free at a median followup of 72 months (range, 10-114 mos). The 5-year LC rate is 91%. The 5
International Journal of Radiation Oncology Biology Physics
in the sagittal plane with the following parameters: TE/TR/Flip/Matrix-size/ Slices of 1.29 ms/2.57 ms/60/176 x 256/5. In-plane spatial resolution was w1.95 mm, and slice thickness ranged from 9-16 mm. Dynamic imaging was carried out for w8 min for each session, acquiring w200 image frames with 5 slices each. The center slice that contained the tumor was selected from each dataset to create a series of w200 frames with a temporal resolution of w2.5 s. An automated tumor tracking techniqueetemplate matchingewas used to estimate the tumor position frame-by-frame. For each session, an average position across all frames was used as the reference. Subsequently, the tumor movement on each frame was calculated relative to this reference in both the AP and SI directions. We calculated the amount of time as a percentage of the total acquisition time when centroids of the tumor moved more than 5 mm for each session. Results: For the 5 patients in the study, the 5 mm margin is sufficient to cover the tumor motion in the AP direction for w99% of the time. However, tumor motion in the SI direction was larger than 5 mm for 1 patient (tumor size w450 mL) in all 3 sessions with the percentage of time spent outside the 5 mm margin being 13%, 5%, and 11% respectively. In contrast, tumor movement in the SI direction was less than 5 mm w99% of the time when the tumor size is no greater than 100 mL. Conclusions: The overall outcome of radiation treatment highly relies on the characterization of PTV, which depends on the choice of the margin. In this study, motion of tumors of various sizes in lung cancer patients determined with an automatic tumor tracking technique was compared to the conventionally chosen margin size of 5 mm based on the original definition of the internal target using 4DCT. Results from the study indicate that the decision of margin size, especially in the SI direction, made using 4DCT can underestimate the tumor motion especially for large tumors. Author Disclosure: X. Shi: None. S. Chen: None. W.D. D’Souza: E. Research Grant; Varian Medical Systems. N.N. Mistry: None.
r Z +0.58, p Z 0.038) and cumulative dose in the ipsilateral normal lung (lung minus PTV) (r Z +0.72, p Z 0.0059) are each directly correlated to the inter-fraction volume range. The average enlargement of squamous cell carcinomas was greater than adenocarcinomas; however, the difference was not statistically significant. The observed CBCT volume changes during treatment had minimal effect on treatment planning dose coverage. Conclusions: Our preliminary data suggest that for ablative SBRT doses significant changes in inter-fraction tumor volume exist that are correlated to age, cumulative radiation dose in lung tissue and average PTV dose. The frequently observed increase followed by decrease in tumor volume suggests the presence of competing physiological processes during ablative radiation, and may be related to acute vascular injury, edema and inflammation, as well as tumor cell death and normal tissue effects of radiation. Author Disclosure: S. Salamekh: None. Y. Rong: None. V. Diavolitsis: None. T. Williams: None. N. Mayr: None. A.S. Ayan: None. M.X. Welliver: None.
164 Interfraction Tumor Volume Changes During Lung Stereotactic Body Radiation Therapy S. Salamekh, Y. Rong, V. Diavolitsis, T. Williams, N. Mayr, A.S. Ayan, and M.X. Welliver; The Ohio State University Comprehensive Cancer Center, Columbus, OH Purpose/Objectives(s): To analyze the inter-fraction tumor volume changes during Stereotactic Body Radiation Therapy (SBRT) of early stage non-small cell lung cancer (NSCLC) with respect to deposited doses and patient characteristics. Materials/Methods: Tumor volumes of 15 consecutive patients (age 5786) treated with SBRT at our institution between November 1, 2011 and June 1, 2012 were retrospectively analyzed. Patients were treated with a total dose of 45-54 Gy in 3-5 fractions. Kilovoltage cone-beam CT (CBCT) images obtained immediately prior to each administered dose were used to delineate gross tumor volume (GTV) resulting in 84 sets of contours from 18 tumors. The sum of the differential dose-volume histogram (DVH) of structures contoured prior to treatment was used to determine the average dose and cumulative radiation delivered. Pearson’s r and Spearman’s r correlation as well as partial correlation analysis were performed to study tumor volume changes with respect to patient and tumor characteristics as well as radiation delivered. Results: Relative to their original volume, most tumors increased in size and then decreased during the treatment course. The baseline CBCT tumor volume during the first treatment was between 0.41 and 43.9 mL. An average maximum increase of 15% relative to the baseline volume and regression of 11% were observed in tumor size, corresponding to a 26% average inter-fraction tumor volume range. The PTV size was inversely correlated to inter-fraction tumor volume changes (r Z 0.59, p Z 0.013 and r Z 0.62, p Z 0.0090), whereas age was proportional to the interval between the first treatment and the time point when the largest volume increase was observed (r Z +0.52, p Z 0.031 and r Z +0.63, p Z 0.0062). Partial correlation between radiation dose and inter-fraction volume revealed that the average PTV dose (r Z +0.60, p Z 0.031 and
165 Interfraction Regional Variation of Tumor Breathing Motion in Lung Stereotactic Body Radiation Therapy (SBRT) K. Atkins, A. Varchani, T.L. Nam, M. Fuss, and J.A. Tanyi; Oregon Health and Science University, Portland, OR Purpose/Objective(s): Narrow PTV margins and steep dose gradients underscore the importance of evaluating breathing-associated tumor motion for lung SBRT. However, the extent to which interfraction variation in tumor breathing motion correlates with anatomic tumor location has not been studied. Materials/Methods: Nineteen patients who received a 5-fraction course of SBRT underwent standard free-breathing 4DCT simulation and daily image-guidance 4DCTs using an identical in-room installed CT scanner. Tumors selected for analysis were located in the upper lobe (UL, n Z 9) or lower lobe (LL, n Z 10). Gross tumor volumes (GTV) for each of the 10 respiratory phases were delineated semi-automatically using a thresholdbased contouring technique. Centroid values from each respiratory phase were used to determine absolute tumor motion amplitude in the mediolateral (ML), anterior-posterior (AP), and superior-inferior (SI) directions. Results: A total of 65 simulation and daily 4DCTs from 19 patients were analyzed. In general, both UL and LL tumors showed limited breathing motion in the ML and AP directions (mean < 2.5 mm). Expectedly, LL tumors showed markedly larger centroid motion along the SI direction compared to UL tumors (10.8 5.2 mm vs 1.9 1.4 mm, p < 0.001). The mean variance in interfraction tumor motion amplitude in the ML and AP directions was < 1.5 mm for all tumors. In the SI direction, however, tumors in the LL showed a mean variance in interfraction motion amplitude of 5.1 7.0 mm vs 0.8 0.8 mm in the UL (p Z 0.01), with an overall mean variance in breathing motion amplitude of 2.8 5.2 mm for both UL and LL tumors combined. To note, these values represent the mean variance in interfraction tumor motion amplitude both beyond and within the maximum excursion observed in the reference (simulation) 4DCT. In LL tumors, 20% (n Z 2) had a mean variance in interfraction tumor motion amplitude along the SI direction 15 mm beyond the maximum excursion observed in the reference 4DCT, while the remaining 80% (n Z 8) did not exceed 5 mm. No UL tumors had a variance in interfraction tumor motion amplitude along the SI direction > 4 mm and 89% (n Z 8) were < 2.5 mm. Conclusions: While interfraction variances in tumor breathing motion along the SI direction were within our standard PTV margins (a uniform 5 mm beyond the ITV) for the vast majority of the tumors in this study, changes in interfraction breathing motion exceeded PTV margins in 20% of LL tumors. These results suggest that while day-to-day changes in tumor breathing motion are mostly small, typical ITV-based PTV margins may be insufficient for a subset of LL lesions. Thus, daily breathing motion re-assessment and adaptive re-planning may benefit patients with tumors in the LL.
Volume 87 Number 2S Supplement 2013 Author Disclosure: K. Atkins: None. A. Varchani: None. T.L. Nam: None. M. Fuss: E. Research Grant; Brainlab, Varian Medical. F. Honoraria; Brainlab, Varian Medical. G. Consultant; Brainlab, Varian Medical, Philips. J.A. Tanyi: F. Honoraria; Brainlab.
166 Novel Method of Cardiac Sparing With Deep-Inspiration BreathHold Utilizing Surface Electromagnetic Transponders in Women With Left-Sided Breast Cancer L. Fang,1,2 J. Kim,1,2 D. Kaurin,3 K. Holloway,2 M. Lavilla,2 and L. Sweeney3; 1University of Washington, Seattle, WA, 2Seattle Cancer Care Alliance, Seattle, WA, 3Northwest Medical Physics Center, Lynnwood, WA Purpose/Objective(s): Deep-inspiration breath hold (DIBH) for radiation therapy of the breast is an established technique that has been shown to minimize heart dose. A method for intrafraction motion management with DIBH technique was developed utilizing electromagnetic transponders placed on the skin. This retrospective study is the first report on the pilot experience of this novel method. Materials/Methods: Between January 1 and October 1, 2012, 40 patients with left-sided breast cancer underwent CT simulation and were treated with DIBH using surface electromagnetic transponders. Simulation CT scans were obtained in both free-breathing (FB) and DIBH positions in all patients. Treatment planning was performed on the DIBH CT scan with fusion of the FB scan. The heart was contoured and dose volume histograms computed. To reproduce the DIBH from the simulation and for intrafraction motion management, two methods of monitoring were simultaneously employed in all patients: 1) surface electromagnetic transponder system with real-time tracking and 2) lasers aligned to DIBH skin marks with continuous video surveillance during entire beam-on time. Results: Median age was 50 years (range, 31-70), 27.5% (11/40) DCIS, 45% (18/40) stage I, 20% (8/40) stage II, 7.5% (3/40) stage III. Eighty percent (32/40) of patients received 45-50.4 Gy in standard fractionation and 20% (8/40) received 42.5 Gy in 16 fractions to the left whole breast. Seventy-five percent (30/40) were treated to the left breast, one patient to the chest wall, one patient to a chest wall with tissue expander, three patients to the breast and supraclavicular field (SCF) and five patients to the chest wall with tissue expander plus SCF. The average mean heart dose was 78.9 c Gy with DIBH compared with 290.2 c Gy in FB (p-value < 0.0001). The mean heart V5 was 0.96% with DIBH and 12.7% with FB, mean V10 was 0.28% with DIBH versus 7.5% with FB, mean heart V15 was 0.014% with DIBH versus 5.2% with FB (p-value < 0.0001). The average transponder to laser difference for the first consecutive 535 fractions was 0.09 cm in the superior-inferior direction (SD 0.23), 0.09 cm in the anterior-posterior direction (SD 0.32) and 0.03 cm in the right-left direction (SD 0.29). Conclusions: An initial cohort of women with left-sided breast cancer has been successfully treated with DIBH technique using a novel method of skin surface electromagnetic transponders. This method was found to be feasible, accurate and well-tolerated by patients. There was a significant reduction in cardiac dose with DIBH. A prospective registry trial using the surface electromagnetic transponder system with DIBH is being initiated to confirm these findings. Author Disclosure: L. Fang: None. J. Kim: F. Honoraria; Varian. D. Kaurin: G. Consultant; Varian. K. Holloway: None. M. Lavilla: None. L. Sweeney: G. Consultant; Varian.
167 Intrafraction Variability and Deformation Quantification for Accelerated Partial-Breast Irradiation (APBI) C.K. Glide-Hurst, M. Shah, I. Aref, I.J. Chetty, B. Movsas, and E.M. Walker; Henry Ford Health System, Detroit, MI Purpose/Objective(s): While IGRT reduces setup error for linac-based APBI, IGRT cannot fully account for deformations arising from intrafraction motion. This study sought to evaluate intra-fraction variability and
Oral Scientific Sessions
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local deformations of the lumpectomy cavity (LC), breast, and nearby organs at risk. Materials/Methods: Sixteen early-stage (T0-T2N0M0) left-sided postlumpectomy breast cancer cases and 1 bilateral case with discernible LCs were retrospectively evaluated on an IRB-approved study. During simulation, each patient underwent a free-breathing CT and 10-phase 4DCT. For each patient, treated breast, heart, lungs, and LC were delineated on the end-inhale (EI) 4DCT phase. B-spline multi-resolution deformable image registration was employed to propagate contours to all phases. For the entire population, respiration-induced motion was calculated via centroid analysis. To quantify deformation, displacement vector fields (DVFs) were analyzed between EI and end-exhale (EE) datasets for the breast and LC volumes by classifying the vector magnitudes as < 2 mm, 2-4 mm, and > 4 mm. Results: For the patient population, LC intra-fraction motion was 0.7 0.7 mm, 1.1 0.7 mm, and 1.8 1.2 mm in lateral (LAT), anteriorposterior (A-P), and superior-inferior (S-I) directions, respectively. Similar intra-fraction motion results were obtained for the treated breast: 0.4 0.3 mm, 0.9 0.5 mm, and 1.6 0.9 mm LAT, A-P, and S-I directions, respectively. In the most extreme case, LC and breast excursions of w2 mm and w3 mm were observed in the A-P and S-I directions, respectively. Respiration-induced motion was dominant S-I for the heart (3.8 1.7 mm) and lungs (3.6 2.0 mm). Over all patients, DVF analysis revealed that 51.2 20.3% (range, 9.6 - 82.6%) of the treated breast volume deformed between 2-4 mm, whereas 11.3 12.7% deformed > 4 mm (range, 0 to 36.7%). The majority of LC volumes (60.7 37.6%) deformed 2-4 mm. However, a small subset demonstrated > 4 mm deformation (6.8 14.6%). The patient with the largest deformation (w45% of the LC volume deformed > 4 mm) also demonstrated the largest intra-fraction cavity and breast excursions. Conclusions: Overall, LC and breast demonstrated < 3 mm intra-fraction centroid motion, whereas heart and lung were slightly more mobile. Deformation characterization of the LC and breast revealed large variability among patients, suggesting value in patient-specific margins for APBI. A subset of volumes showed substantial deformation (> 4 mm), which, if unaccounted for, could potentially impact dose distribution. Further work is needed to resolve dominant regions of deformation. Coupling these results with inter-fraction setup analysis will likely yield better margin design, and potentially support the need for image-guided adaptive radiation therapy for APBI. Author Disclosure: C.K. Glide-Hurst: E. Research Grant; Philips Medical Systems, Varian Medical Systems. M. Shah: None. I. Aref: None. I.J. Chetty: E. Research Grant; Varian Medical Systems. B. Movsas: E. Research Grant; Varian Medical Systems. E.M. Walker: None.
168 Long-term Toxicities of a Prospective Trial Delivering Limited Margin 3DCRT/IMRT in Children With Rhabdomyosarcoma M. Krasin, C. Hua, L.E. Kun, A. Pappo, A. Pai Panandiker, M. Brown, A. Davidoff, B. Shulkin, B. McCarville, and T.E. Merchant; St. Jude Children’s Research Hospital, Memphis, TN Purpose/Objective(s): To evaluate the long term toxicity profile of 3DCRT/IMRT used to treat children with rhabdomyosarcoma (RMS). Materials/Methods: Sixty-six patients with a diagnosis of RMS (median age 6.7) were enrolled on a prospective IRB approved institutional trial of limited margin 3DCRT/IMRT integrating MR based anatomically constrained targeting. The GTV included the tumor bed (group II patients) or the residual MR based tumor plus surfaces of tissues initially in contact with tumor. The CTV included a 1 cm margin constrained to tissues tumor may have infiltrated (excluding pushing borders). A 3-5 mm PTV was then added. Prescribed doses were 36 Gy to the CTV (and its PTV) and 50.4 Gy to the GTV. Patients were scored routinely for general acute and late toxicities (CTCv2.0) as well as site specific toxicities. All related toxicities grade 3 were scored. Results: Forty-three of 66 patients remain disease free at a median followup of 72 months (range, 10-114 mos). The 5-year LC rate is 91%. The 5