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Feasibility and Efficacy of Stereotactic Body Radiation Therapy Using Robotic Radiosurgery as Curative Treatment for Metastatic Thyroid Carcinoma
S900
International Journal of Radiation Oncology Biology Physics
3751
Purpose/Objective(s): To report the dosimetric results of the first 32 patients randomized in a prospective multicenter phase II trial of urethrasparing stereotactic body radiation therapy (SBRT) for localized prostate cancer. Materials/Methods: Dosimetric data of 32 patients randomized between 2012 and 2013 in 8 different centers were analyzed. The SBRT protocol consisted of 36.25 Gy in 5 fractions of 7.25 Gy to the planning target volume (PTV Z prostate with (n Z 15) or without (n Z 17) seminal vesicles (SV) with a 5-mm anisotropic expansion, except 3-mm posteriorly) (NTD2Gy of 90 and 74 Gy, for a/b ratio Z 1.5 and 3 Gy, respectively) over two alternative time schedules: either over 9 days (study A), or over 28 days once-a-week, the same week-day (study B). The prostatic urethra with an additional margin of 3 mm (urethral planning risk volume, uPRV) received simultaneously 5 x 6.5 Gy Z 32.5 Gy (NTD2Gy of 74 and 62 Gy for a/b ratio Z 1.5 and 3 Gy, respectively). All but 3 patients were simulated and treated with a 100cc endorectal balloon and the plans were generated using a volumetric arc therapy (VMAT, n Z 21) or intensitymodulated radiation therapy (IMRT, n Z 11) technique. All plans were optimized until the dose prescription parameters and organs at risk (OAR) dose-volume constraints were obtained. Mean doses SD to the PTV, uPRV and the other OAR were analyzed. The PTV homogeneity index (HI) and the dice similarity coefficient (DSC) were analyzed. Results: For the PTV, the D98% and D2% were 34.60.4Gy (95.41.1%) and 38.30.5 Gy (105.61.5%), respectively. Dose constraints were respected for all OAR: the V100, V90 and V80 for the rectal wall were 2.31.6% (ref. <5%), 10.93.3% (ref. <10-15%) and 15.63.9% (ref. <20-25%); for the bladder wall, the V100, V90 and V50 were 7.33.2% (ref. <10-15%), 13.24.1% (ref. <20%) and 3010.3% (ref. <50%). The D98% and D2% for the uPRV were 310.8 Gy (95.42.4%) and 34.50.7 Gy (106.12%), respectively. The HI and DSC values were 0.090.02 and 0.760.13, respectively. The mean number of MU delivered per fraction was 2637727. As compared to IMRT plans, VMAT required a lower number of MU (2191 vs. 3490, p Z .0001) and resulted in a better HI (0.08 vs. 0.1, p Z .001) and uPRV coverage (D98% 31.3 vs. 30.4 Gy, p Z .0001). Inclusion of the SV in the PTV resulted in a higher V90 (12.3 vs. 9.6%, p Z .009) and V80 (17.2 vs. 14.2%, p Z .014) for the rectal wall as compared to patients treated to the prostate only. Conclusions: For all participating centers, urethra-sparing SBRT plans met all the dosimetric endpoints in terms of PTV coverage as well as OAR sparing, irrespectively of the technique used. Compared with IMRT, VMAT plans resulted in more homogeneous dose distribution, reduced number of MU and better uPRV coverage. Tolerance, quality of life and outcome results of this urethra-sparing SBRT approach are warranted. Author Disclosure: T. Zilli: None. L. Tsvang: None. Z. Symon: None. U. Abacıoglu: None. A. Bruynzeel: None. M. Rouzaud: None. A. Dubouloz: None. S. Pampallona: None. A. Oliveira: None. H. Minn: None. Z. Ozen: None. J. Pe´rez-Moreno: None. E. Sa´nchez Saugar: None. S. Jorcano: None. L. Escude´: None. R. Miralbell: None.
Duty Cycle Selection of Gating in Lung SBRT With Flatting Filtere Free Beams J. Wu,1 J. Ye,2 F. Chen,1 G. Hill,1 J. Spiegel,1 and V. Mehta1; 1Swedish Cancer Institute, Seattle, WA, 2Swedish Medical Center-Tumor Institute, Seattle, WA Purpose/Objective(s): We investigated the dosimetric benefits of gated plans with various duty cycles over the non-gated plans for lung SBRT. We also compared the delivery efficiency for those plans delivered on various Linacs. Materials/Methods: VMAT plans were created to deliver 48Gy to the target in 4 fractions. Those plans were categorized into four types. In the first category, plans were generated on the average intensity projection CTs, where -the ITVs were delineated on the maximum intensity projection CTs. Those plans represented the scenario where patients were treated with free-breathing. The other three types of plans were for the gated treatments delivered with duty cycles of 50%, 30% and 10% respectively. The gated plans were generated on the 50% CT. The corresponding ITVs were the combination of the 30% to 70% GTVs, combination of 40% to 60% GTVs, and 50% GTV only. To investigate delivery efficiency, we created three plans in each category using the following Linacs: Linac1 with 1 cm leave at maximal dose rate of 450 MU/min, Linac2 with 0.5 cm leave at maximal dose rate of 620MU/min, and Linac3 with 0.5 cm leave in FFF mode at a maximal dose rate of 1230 MU/min. The three plans were matched in DVHs on ITV, PTV, and organs at risk. At treatment delivery, beam-on times were recorded. The treatment time for each plan was estimated as the beam-on time divided by its duty cycles. Results: Plan quality across the four categories was compared. The averaged Conformity Index of the PTVs for plans with free-breathing and gating with 50%, 30%, 10% duty cycles was 1.0000.000, 0.9990.001, 1.0000.001 and 1.0000.001 respectively. The corresponding Heterogeneity Index was 1.0570.033, 1.0530.019, 1.0500.020 and 1.0570.033. The difference in PTV dose coverage is insignificant. The corresponding averaged lung V20 was 8.294.20%, 6.352.37%, 6.272.44% and 6.252.33%. Treatment MUs of plans using different machines were also compared. The averaged MU for the three linacs was 2237.8347.2, 1991.3176.3 and 2183.3112.4, respectively. The mean treatment times for free-breathing plans delivered on the three machines were 5.410.44, 3.470.09 and 1.720.12 minutes. The treatment times for gating plans delivered on the three machines were 11.862.69, 6.970.58, 3.720.15 min for 50% duty cycle, 17.412.08, 11.431.01, 6.130.23 min for 30% duty cycle, and 47.002.92, 33.721.44, 18.500.73 min for 10% duty cycle, respectively. Conclusions: Compared with non-gated therapy, gating improved plan quality. The differences in lung dose for gating with various duty cycles were clinically insignificant. FFF mode offers a dose rate much higher than the conventional dose rate. The significant reduction in treatment time in FFF mode makes it feasible to gate the SBRT with a small gating window. Author Disclosure: J. Wu: None. J. Ye: None. F. Chen: None. G. Hill: None. J. Spiegel: None. V. Mehta: None.
3752 Urethra-Sparing Stereotactic Body Radiation Therapy for Localized Prostate Cancer: Dosimetric Results From a Prospective Multicenter Randomized Phase 2 Trial T. Zilli,1 L. Tsvang,2 Z. Symon,2 U. Abacıoglu,3 A. Bruynzeel,4 M. Rouzaud,1 A. Dubouloz,1 S. Pampallona,1 A. Oliveira,5 H. Minn,6 Z. Ozen,3 J. Pe´rez-Moreno,7 E. Sa´nchez Saugar,7 S. Jorcano,8 L. Escude´,8 and R. Miralbell1,8; 1Geneva University Hospital, Geneva, Switzerland, 2 Chaim Sheba Medical Center, Tel Hashomer, Israel, 3Neolife Medical Center, Istanbul, Turkey, 4VU University Medical Center, Amsterdam, Netherlands, 5Portuguese Institut of Oncology, Porto, Portugal, 6 University Hospital Turku, Turku, Finland, 7Hospital Universitario Sanchinarro, Madrid, Spain, 8Teknon Oncologic Institute, Barcelona, Spain
3753 Feasibility and Efficacy of Stereotactic Body Radiation Therapy Using Robotic Radiosurgery as Curative Treatment for Metastatic Thyroid Carcinoma H. Wang, M. Meng, C. Jiang, D. Qian, L. Zhao, Z. Yuan, and P. Wang; Tianjin Medical University Cancer Hospital & Institute, Tianjin, China Purpose/Objective(s): There was no consensus existing on the optimal treatment strategy for metastatic thyroid carcinoma currently. This case series was to investigate the feasibility and efficacy of stereotactic body radiation therapy (SBRT) using robotic radiosurgery as curative treatment for metastases from thyroid carcinoma. Materials/Methods: Between October 2006 and July 2013, cases with metastatic thyroid carcinoma were enrolled and treated with SBRT using robotic radiosurgery at our institution. Age, pathology of thyroid carcinoma, site of metastases, symptoms at metastases, the tracking model, volume of planning target volume (PTV), dose/fractionation, isodose line
Volume 90 Number 1S Supplement 2014
Poster Viewing Abstracts S901
of SBRT, disappearance of symptoms, response of SBRT, and patient’s status and toxicities were evaluated. Results: There were 13 cases with metastatic thyroid carcinoma including 6 men and 7 women with a mean age of 46.85 years (range, 23-73 years) treated with SBRT. The papillary was the most common histologic type in 11 patients. The metastases of 5 patients were located in the cervical vertebra, 3 patients in lymph node, 3 patients in the skull and brain, 1 patient in the lung, as well as 1 patient in the ventricle, respectively. The most common symptom at metastases was pain, which was present in 5 patients with cervical vertebra metastases. The tracking models contained vertebral spine tracking system (7 patients), skull tracking system (4 patients), fiducial tracking system (1 patient), and synchrony tracking system (1 patient), respectively. The median PTVof SBRTwas 8.05 cc (range, 2.50-72.66 cc). The patients received a median five fractions (range, one to five fractions) with a median dose of 8 Gy per fraction (range, 6-23Gy). The median biologically equivalent dose (BED) was 59.5 Gy (range, 26.4-150 Gy). The dose was prescribed to the median 80% isodose line (range, 70-81%), which encompassed 95% of the PTV. To the end of the following-up, the metastatic sites of all patients were controlled, and the symptoms related to the metastases had relieved about one week after SBRT. There were 10 patients (76.9%) were alive without evidence of recurrence, and 3 patients (23.1%) died due to other reasons. In addition, no adverse events were observed. Conclusions: With excellent in-field local control and symptoms relieved without severe toxicities, SBRT for metastatic thyroid carcinoma seems to be feasible and safe for appropriately selected patients. Further research is warranted for more accurate selection of patients suitable for SBRT. Author Disclosure: H. Wang: None. M. Meng: None. C. Jiang: None. D. Qian: None. L. Zhao: None. Z. Yuan: None. P. Wang: None.
3754 A Planning Comparison of 3D Conformal Multiple Static Field, Conformal Arc, and Volumetric Modulated Arc Therapy for the Delivery of Stereotactic Body Radiation Therapy for Lung Cancer Z. Gabos,1 M.J. Dickey,2 S. Drodge,1 B. Murray,2 S. Ghosh,2 R. Scrimger,2 and W. Roa1; 1University of Alberta, Edmonton, AB, Canada, 2Cross Cancer Institute, Edmonton, AB, Canada Purpose/Objective(s): Utilization of Stereotactic Body Radiation Therapy (SBRT) for early stage non-small cell lung cancer (NSCLC) has increased. A number of different treatment delivery techniques are clinically utilized. The primary objective of this study was to compare treatment time, monitor units and dosimetric non-inferiority of 3D conformal multiple static field (MSF) to conformal arc (CA) and volumetric modulated arc therapy (VMAT) plans. Materials/Methods: This retrospective study identified 23 NSCLC patients previously treated with SBRT using a MSF technique. Plans consisted of 9-11 static coplanar and non-coplanar fields. Each patient was replanned using CA and VMAT techniques. The ratio of the prescription isodose volume to PTV volume (R100%), the maximum dose 2cm away
Scientific Abstract 3755; Table
Shots/MU Beam-on (min) 1400 (P < .0001) Target max (Gy) (P Z .0004) Brainstem max (Gy) (P Z .4255) Cochlea mean (Gy) (P < .0001) Brain V6 (Gy) (P Z .8101) Brain V12 (Gy) (P Z .9604) Conformity Index (< 2 cc) (P Z .5403) Conformity Index ( 2 cc) (P Z .01)
from the PTV (D2cm), percentage of lung receiving 20Gy or more (V20Gy), van’t Riet conformity number (CN), total monitor units (MU) and treatment time were evaluated. Non-inferiority comparisons to detect significance were performed using a two-tailed paired t-test. A p-value of 0.017 (0.05/3) was used to adjust for multiple hypothesis testing. Results: The VMAT plans had significantly lower R100% than either the MSF or CA, and the CA plans were significantly better than MSF plans [mean difference: MSF-v-CA Z 0.07 (p<0.0001); MSF-v-VMAT Z 0.15 (p<0.0001); CA-vVMAT Z 0.08 (p<0.0001)]. Looking at D2cm, the VMAT plans had significantly lower values than either the MSF or CA, and the CA plans were significantly better than MSF plans [mean difference (percentage of total dose): MSFv-CA Z 2.73 (p Z 0.005); MSF-v-VMAT Z 4.80 (p<0.0001); CA-v-VMAT Z 2.08 (p Z 0.006)]. Comparing the van’t Riet conformity numbers, the higher VMAT values were significantly better than either CA or MSF plans, while again the CA plans were better than MSF plans [mean difference: MSF-v-CA Z -0.5 (p<0.0001); MSF-v-VMAT Z -0.11 (p<0.0001); CA-v-VMAT Z -0.06 (p<0.0001)]. Total monitor units for the plans revealed that VMAT had the highest MUs, and CA had the lowest, with significant differences between all three techniques [mean MUs: 2687, 2164 and 2072 (p<0.0001)]. Evaluation of treatment times (not including imaging) demonstrated that conformal arcs were the quickest to deliver, significantly faster than VMAT or MSF [mean treatment time: 3.91 min, 4.73 min and 8.56 min respectively (p<0.0001)]. Conclusions: This study supports the use of CA for lung SBRT in eligible patients with significant dosimetric advantages over multiple static fields. VMAT demonstrated additional gains except increased monitor units and treatment time. Considering the additional optimization time during planning, treatment delivery verification, dedicated machine requirements and conflicting reports on the safe use of hypofractionated VMAT in the thorax, conformal arcs provide an adequate alternative to MSF for delivering SBRT. Author Disclosure: Z. Gabos: None. M.J. Dickey: None. S. Drodge: None. B. Murray: None. S. Ghosh: None. R. Scrimger: None. W. Roa: None.
3755 Dosimetric Comparison of Gamma Knife and VMAT Radiosurgery for Vestibular Schwannoma H. Kim, P. Potrebko, H. Liu, H.B. Eldredge-Hindy, V. Gunn, M. WernerWasik, D.W. Andrews, J.J. Evans, C.J. Farrell, K. Judy, and W. Shi; Thomas Jefferson University Hospital, Philadelphia, PA Purpose/Objective(s): Stereotactic radiosurgery (SRS) is a common treatment option for vestibular schwannoma (acoustic neuroma). Gamma Knife (GK) SRS is traditionally the technique of choice. With the increasing availability of volumetric modulated arc therapy (VMAT), LINAC SRS is an appealing alternative with the potential to avoid invasive frame based setup and shorten treatment time. We hypothesized that VMAT SRS for vestibular schwannoma can deliver comparable dosimetric outcomes to GK plans with potentially reduced treatment times.
Dosimetric comparison of VMAT and GK SRS plans. *Statistically significant difference to GK. Gamma Knife
VMAT 1 arc
VMAT 3 non-coplanar arcs
VMAT 5 non-coplanar arcs
10 3 20.5 8.0
4986 848 3.6 0.7*
5138 930 3.7 0.7*
5627 1061 4.0 0.9*
20.4 2.5*
21.5 2.8*
21.0 2.4*
10.3 4.7
9.6 4.8
9.1 4.7
6.2 1.4*
6.0 1.6*
24.0 10.6 5.7 6.8 1.7
7.7 1.4*
9.8 8.0
12.0 9.0
9.4 6.7
8.6 6.0
2.9 2.4
2.8 2.2
2.7 2.1
2.5 1.9
1.61 0.12
1.97 0.61
1.89 0.45
1.86 0.47
1.48 0.08
1.37 0.07
1.31 0.05*
1.24 0.11*
International Journal of Radiation Oncology Biology Physics
3751
Purpose/Objective(s): To report the dosimetric results of the first 32 patients randomized in a prospective multicenter phase II trial of urethrasparing stereotactic body radiation therapy (SBRT) for localized prostate cancer. Materials/Methods: Dosimetric data of 32 patients randomized between 2012 and 2013 in 8 different centers were analyzed. The SBRT protocol consisted of 36.25 Gy in 5 fractions of 7.25 Gy to the planning target volume (PTV Z prostate with (n Z 15) or without (n Z 17) seminal vesicles (SV) with a 5-mm anisotropic expansion, except 3-mm posteriorly) (NTD2Gy of 90 and 74 Gy, for a/b ratio Z 1.5 and 3 Gy, respectively) over two alternative time schedules: either over 9 days (study A), or over 28 days once-a-week, the same week-day (study B). The prostatic urethra with an additional margin of 3 mm (urethral planning risk volume, uPRV) received simultaneously 5 x 6.5 Gy Z 32.5 Gy (NTD2Gy of 74 and 62 Gy for a/b ratio Z 1.5 and 3 Gy, respectively). All but 3 patients were simulated and treated with a 100cc endorectal balloon and the plans were generated using a volumetric arc therapy (VMAT, n Z 21) or intensitymodulated radiation therapy (IMRT, n Z 11) technique. All plans were optimized until the dose prescription parameters and organs at risk (OAR) dose-volume constraints were obtained. Mean doses SD to the PTV, uPRV and the other OAR were analyzed. The PTV homogeneity index (HI) and the dice similarity coefficient (DSC) were analyzed. Results: For the PTV, the D98% and D2% were 34.60.4Gy (95.41.1%) and 38.30.5 Gy (105.61.5%), respectively. Dose constraints were respected for all OAR: the V100, V90 and V80 for the rectal wall were 2.31.6% (ref. <5%), 10.93.3% (ref. <10-15%) and 15.63.9% (ref. <20-25%); for the bladder wall, the V100, V90 and V50 were 7.33.2% (ref. <10-15%), 13.24.1% (ref. <20%) and 3010.3% (ref. <50%). The D98% and D2% for the uPRV were 310.8 Gy (95.42.4%) and 34.50.7 Gy (106.12%), respectively. The HI and DSC values were 0.090.02 and 0.760.13, respectively. The mean number of MU delivered per fraction was 2637727. As compared to IMRT plans, VMAT required a lower number of MU (2191 vs. 3490, p Z .0001) and resulted in a better HI (0.08 vs. 0.1, p Z .001) and uPRV coverage (D98% 31.3 vs. 30.4 Gy, p Z .0001). Inclusion of the SV in the PTV resulted in a higher V90 (12.3 vs. 9.6%, p Z .009) and V80 (17.2 vs. 14.2%, p Z .014) for the rectal wall as compared to patients treated to the prostate only. Conclusions: For all participating centers, urethra-sparing SBRT plans met all the dosimetric endpoints in terms of PTV coverage as well as OAR sparing, irrespectively of the technique used. Compared with IMRT, VMAT plans resulted in more homogeneous dose distribution, reduced number of MU and better uPRV coverage. Tolerance, quality of life and outcome results of this urethra-sparing SBRT approach are warranted. Author Disclosure: T. Zilli: None. L. Tsvang: None. Z. Symon: None. U. Abacıoglu: None. A. Bruynzeel: None. M. Rouzaud: None. A. Dubouloz: None. S. Pampallona: None. A. Oliveira: None. H. Minn: None. Z. Ozen: None. J. Pe´rez-Moreno: None. E. Sa´nchez Saugar: None. S. Jorcano: None. L. Escude´: None. R. Miralbell: None.
Duty Cycle Selection of Gating in Lung SBRT With Flatting Filtere Free Beams J. Wu,1 J. Ye,2 F. Chen,1 G. Hill,1 J. Spiegel,1 and V. Mehta1; 1Swedish Cancer Institute, Seattle, WA, 2Swedish Medical Center-Tumor Institute, Seattle, WA Purpose/Objective(s): We investigated the dosimetric benefits of gated plans with various duty cycles over the non-gated plans for lung SBRT. We also compared the delivery efficiency for those plans delivered on various Linacs. Materials/Methods: VMAT plans were created to deliver 48Gy to the target in 4 fractions. Those plans were categorized into four types. In the first category, plans were generated on the average intensity projection CTs, where -the ITVs were delineated on the maximum intensity projection CTs. Those plans represented the scenario where patients were treated with free-breathing. The other three types of plans were for the gated treatments delivered with duty cycles of 50%, 30% and 10% respectively. The gated plans were generated on the 50% CT. The corresponding ITVs were the combination of the 30% to 70% GTVs, combination of 40% to 60% GTVs, and 50% GTV only. To investigate delivery efficiency, we created three plans in each category using the following Linacs: Linac1 with 1 cm leave at maximal dose rate of 450 MU/min, Linac2 with 0.5 cm leave at maximal dose rate of 620MU/min, and Linac3 with 0.5 cm leave in FFF mode at a maximal dose rate of 1230 MU/min. The three plans were matched in DVHs on ITV, PTV, and organs at risk. At treatment delivery, beam-on times were recorded. The treatment time for each plan was estimated as the beam-on time divided by its duty cycles. Results: Plan quality across the four categories was compared. The averaged Conformity Index of the PTVs for plans with free-breathing and gating with 50%, 30%, 10% duty cycles was 1.0000.000, 0.9990.001, 1.0000.001 and 1.0000.001 respectively. The corresponding Heterogeneity Index was 1.0570.033, 1.0530.019, 1.0500.020 and 1.0570.033. The difference in PTV dose coverage is insignificant. The corresponding averaged lung V20 was 8.294.20%, 6.352.37%, 6.272.44% and 6.252.33%. Treatment MUs of plans using different machines were also compared. The averaged MU for the three linacs was 2237.8347.2, 1991.3176.3 and 2183.3112.4, respectively. The mean treatment times for free-breathing plans delivered on the three machines were 5.410.44, 3.470.09 and 1.720.12 minutes. The treatment times for gating plans delivered on the three machines were 11.862.69, 6.970.58, 3.720.15 min for 50% duty cycle, 17.412.08, 11.431.01, 6.130.23 min for 30% duty cycle, and 47.002.92, 33.721.44, 18.500.73 min for 10% duty cycle, respectively. Conclusions: Compared with non-gated therapy, gating improved plan quality. The differences in lung dose for gating with various duty cycles were clinically insignificant. FFF mode offers a dose rate much higher than the conventional dose rate. The significant reduction in treatment time in FFF mode makes it feasible to gate the SBRT with a small gating window. Author Disclosure: J. Wu: None. J. Ye: None. F. Chen: None. G. Hill: None. J. Spiegel: None. V. Mehta: None.
3752 Urethra-Sparing Stereotactic Body Radiation Therapy for Localized Prostate Cancer: Dosimetric Results From a Prospective Multicenter Randomized Phase 2 Trial T. Zilli,1 L. Tsvang,2 Z. Symon,2 U. Abacıoglu,3 A. Bruynzeel,4 M. Rouzaud,1 A. Dubouloz,1 S. Pampallona,1 A. Oliveira,5 H. Minn,6 Z. Ozen,3 J. Pe´rez-Moreno,7 E. Sa´nchez Saugar,7 S. Jorcano,8 L. Escude´,8 and R. Miralbell1,8; 1Geneva University Hospital, Geneva, Switzerland, 2 Chaim Sheba Medical Center, Tel Hashomer, Israel, 3Neolife Medical Center, Istanbul, Turkey, 4VU University Medical Center, Amsterdam, Netherlands, 5Portuguese Institut of Oncology, Porto, Portugal, 6 University Hospital Turku, Turku, Finland, 7Hospital Universitario Sanchinarro, Madrid, Spain, 8Teknon Oncologic Institute, Barcelona, Spain
3753 Feasibility and Efficacy of Stereotactic Body Radiation Therapy Using Robotic Radiosurgery as Curative Treatment for Metastatic Thyroid Carcinoma H. Wang, M. Meng, C. Jiang, D. Qian, L. Zhao, Z. Yuan, and P. Wang; Tianjin Medical University Cancer Hospital & Institute, Tianjin, China Purpose/Objective(s): There was no consensus existing on the optimal treatment strategy for metastatic thyroid carcinoma currently. This case series was to investigate the feasibility and efficacy of stereotactic body radiation therapy (SBRT) using robotic radiosurgery as curative treatment for metastases from thyroid carcinoma. Materials/Methods: Between October 2006 and July 2013, cases with metastatic thyroid carcinoma were enrolled and treated with SBRT using robotic radiosurgery at our institution. Age, pathology of thyroid carcinoma, site of metastases, symptoms at metastases, the tracking model, volume of planning target volume (PTV), dose/fractionation, isodose line
Volume 90 Number 1S Supplement 2014
Poster Viewing Abstracts S901
of SBRT, disappearance of symptoms, response of SBRT, and patient’s status and toxicities were evaluated. Results: There were 13 cases with metastatic thyroid carcinoma including 6 men and 7 women with a mean age of 46.85 years (range, 23-73 years) treated with SBRT. The papillary was the most common histologic type in 11 patients. The metastases of 5 patients were located in the cervical vertebra, 3 patients in lymph node, 3 patients in the skull and brain, 1 patient in the lung, as well as 1 patient in the ventricle, respectively. The most common symptom at metastases was pain, which was present in 5 patients with cervical vertebra metastases. The tracking models contained vertebral spine tracking system (7 patients), skull tracking system (4 patients), fiducial tracking system (1 patient), and synchrony tracking system (1 patient), respectively. The median PTVof SBRTwas 8.05 cc (range, 2.50-72.66 cc). The patients received a median five fractions (range, one to five fractions) with a median dose of 8 Gy per fraction (range, 6-23Gy). The median biologically equivalent dose (BED) was 59.5 Gy (range, 26.4-150 Gy). The dose was prescribed to the median 80% isodose line (range, 70-81%), which encompassed 95% of the PTV. To the end of the following-up, the metastatic sites of all patients were controlled, and the symptoms related to the metastases had relieved about one week after SBRT. There were 10 patients (76.9%) were alive without evidence of recurrence, and 3 patients (23.1%) died due to other reasons. In addition, no adverse events were observed. Conclusions: With excellent in-field local control and symptoms relieved without severe toxicities, SBRT for metastatic thyroid carcinoma seems to be feasible and safe for appropriately selected patients. Further research is warranted for more accurate selection of patients suitable for SBRT. Author Disclosure: H. Wang: None. M. Meng: None. C. Jiang: None. D. Qian: None. L. Zhao: None. Z. Yuan: None. P. Wang: None.
3754 A Planning Comparison of 3D Conformal Multiple Static Field, Conformal Arc, and Volumetric Modulated Arc Therapy for the Delivery of Stereotactic Body Radiation Therapy for Lung Cancer Z. Gabos,1 M.J. Dickey,2 S. Drodge,1 B. Murray,2 S. Ghosh,2 R. Scrimger,2 and W. Roa1; 1University of Alberta, Edmonton, AB, Canada, 2Cross Cancer Institute, Edmonton, AB, Canada Purpose/Objective(s): Utilization of Stereotactic Body Radiation Therapy (SBRT) for early stage non-small cell lung cancer (NSCLC) has increased. A number of different treatment delivery techniques are clinically utilized. The primary objective of this study was to compare treatment time, monitor units and dosimetric non-inferiority of 3D conformal multiple static field (MSF) to conformal arc (CA) and volumetric modulated arc therapy (VMAT) plans. Materials/Methods: This retrospective study identified 23 NSCLC patients previously treated with SBRT using a MSF technique. Plans consisted of 9-11 static coplanar and non-coplanar fields. Each patient was replanned using CA and VMAT techniques. The ratio of the prescription isodose volume to PTV volume (R100%), the maximum dose 2cm away
Scientific Abstract 3755; Table
Shots/MU Beam-on (min) 1400 (P < .0001) Target max (Gy) (P Z .0004) Brainstem max (Gy) (P Z .4255) Cochlea mean (Gy) (P < .0001) Brain V6 (Gy) (P Z .8101) Brain V12 (Gy) (P Z .9604) Conformity Index (< 2 cc) (P Z .5403) Conformity Index ( 2 cc) (P Z .01)
from the PTV (D2cm), percentage of lung receiving 20Gy or more (V20Gy), van’t Riet conformity number (CN), total monitor units (MU) and treatment time were evaluated. Non-inferiority comparisons to detect significance were performed using a two-tailed paired t-test. A p-value of 0.017 (0.05/3) was used to adjust for multiple hypothesis testing. Results: The VMAT plans had significantly lower R100% than either the MSF or CA, and the CA plans were significantly better than MSF plans [mean difference: MSF-v-CA Z 0.07 (p<0.0001); MSF-v-VMAT Z 0.15 (p<0.0001); CA-vVMAT Z 0.08 (p<0.0001)]. Looking at D2cm, the VMAT plans had significantly lower values than either the MSF or CA, and the CA plans were significantly better than MSF plans [mean difference (percentage of total dose): MSFv-CA Z 2.73 (p Z 0.005); MSF-v-VMAT Z 4.80 (p<0.0001); CA-v-VMAT Z 2.08 (p Z 0.006)]. Comparing the van’t Riet conformity numbers, the higher VMAT values were significantly better than either CA or MSF plans, while again the CA plans were better than MSF plans [mean difference: MSF-v-CA Z -0.5 (p<0.0001); MSF-v-VMAT Z -0.11 (p<0.0001); CA-v-VMAT Z -0.06 (p<0.0001)]. Total monitor units for the plans revealed that VMAT had the highest MUs, and CA had the lowest, with significant differences between all three techniques [mean MUs: 2687, 2164 and 2072 (p<0.0001)]. Evaluation of treatment times (not including imaging) demonstrated that conformal arcs were the quickest to deliver, significantly faster than VMAT or MSF [mean treatment time: 3.91 min, 4.73 min and 8.56 min respectively (p<0.0001)]. Conclusions: This study supports the use of CA for lung SBRT in eligible patients with significant dosimetric advantages over multiple static fields. VMAT demonstrated additional gains except increased monitor units and treatment time. Considering the additional optimization time during planning, treatment delivery verification, dedicated machine requirements and conflicting reports on the safe use of hypofractionated VMAT in the thorax, conformal arcs provide an adequate alternative to MSF for delivering SBRT. Author Disclosure: Z. Gabos: None. M.J. Dickey: None. S. Drodge: None. B. Murray: None. S. Ghosh: None. R. Scrimger: None. W. Roa: None.
3755 Dosimetric Comparison of Gamma Knife and VMAT Radiosurgery for Vestibular Schwannoma H. Kim, P. Potrebko, H. Liu, H.B. Eldredge-Hindy, V. Gunn, M. WernerWasik, D.W. Andrews, J.J. Evans, C.J. Farrell, K. Judy, and W. Shi; Thomas Jefferson University Hospital, Philadelphia, PA Purpose/Objective(s): Stereotactic radiosurgery (SRS) is a common treatment option for vestibular schwannoma (acoustic neuroma). Gamma Knife (GK) SRS is traditionally the technique of choice. With the increasing availability of volumetric modulated arc therapy (VMAT), LINAC SRS is an appealing alternative with the potential to avoid invasive frame based setup and shorten treatment time. We hypothesized that VMAT SRS for vestibular schwannoma can deliver comparable dosimetric outcomes to GK plans with potentially reduced treatment times.
Dosimetric comparison of VMAT and GK SRS plans. *Statistically significant difference to GK. Gamma Knife
VMAT 1 arc
VMAT 3 non-coplanar arcs
VMAT 5 non-coplanar arcs
10 3 20.5 8.0
4986 848 3.6 0.7*
5138 930 3.7 0.7*
5627 1061 4.0 0.9*
20.4 2.5*
21.5 2.8*
21.0 2.4*
10.3 4.7
9.6 4.8
9.1 4.7
6.2 1.4*
6.0 1.6*
24.0 10.6 5.7 6.8 1.7
7.7 1.4*
9.8 8.0
12.0 9.0
9.4 6.7
8.6 6.0
2.9 2.4
2.8 2.2
2.7 2.1
2.5 1.9
1.61 0.12
1.97 0.61
1.89 0.45
1.86 0.47
1.48 0.08
1.37 0.07
1.31 0.05*
1.24 0.11*