Stereotactic Radiation Treatment Planning with Volumetric Modulated Arc Therapy (VMAT): Impact of...
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3309 Novel Treatment Planning Techniques for Treatment of Chest Wall Lesions using Stereotactic Body Radiotherapy K. Baker 1 , L. Santanam 2 , J. Bradley 3 1 Barnes-Jewish Hospital/Washington University, Saint Louis, MO, 2 Washington University/Siteman Cancer Center, Saint Louis, MO, 3 Washington University/Barnes-Jewish Hospital, Saint Louis, MO Purpose/Objective(s): Three distinct planning techniques were compared for the treatment of lung tumors using stereotactic body radiation therapy (SBRT). Materials/Methods: Ten patients with the target volumes attached or near to the chest wall were chosen for this study. Treatment plans using three different techniques were performed retrospectively. These three techniques included conventional 3D planning (3D), for- ward planning with manual optimization (Field in Field (FIF)) and segmented beams with inverse planning optimization (SIP). A 4D- CT simulation was performed using a Philips 16 slice CT scanner. All patients were simulated in the supine position with arms placed above their head and immobilized using a body frame or body fix. These 4D-CT images were fused with helical CT scans and were primarily used for target delineation. Note that all the treatment plans were performed on the free breathing helical CT scans. Plans involved anywhere between 7 -11 non- coplanar beams. 3D conformal plans were designed by manually creating all beam apertures using a uniform margin around the PTV and adjusting the block shape for avoiding critical structures. For FIF technique, 2-3 segments were created for each field. A segment was created by manually moving the MLC leaves into the aperture from the original block edge effectively blocking out an area where too much dose was being delivered. SIP technique uses the same beam angles as the two other techniques. Plans were optimized using direct machine parameter optimization, allowing 1-2 segments per beam. A minimum of 50 to 100 monitor units along with a minimum segment size of 5 to 10 cm 2 was used. Additional structures and optimization constraints were used for inverse planning. The following criteria were used for plan evaluation. All treatment plans had to adhere to the RTOG 0236 protocol. Volume of the PTV covering 90% prescription dose should be at least 99%. Conformality index (CI) was defined as the ratio of the volume of prescription isodose to the volume of PTV. Plans were evaluated for plan quality and time efficiency. Results: CI for all the three different techniques ranged from 1.1 -1.3. The volume of 105% prescription outside of the PTV was decreased on an average by 5% for the FIF and SIP techniques. The hotspot and the rib maximum doses were consistently lower for SIP and FIF compared to 3D. The planning times ranged from 2-3 hours for 3D, 4 -5 hours for FIF and 1- 2 hours for SIP. Conclusions: The SIP technique produced equal or better plans than 3D conformal and FIF techniques with better critical structure sparing. The high dose region near the chest wall reduced while utilizing inverse planning techniques thereby reducing the potential risk of rib fractures. Inverse planning techniques offers new hope for better optimized plans for SBRT. Author Disclosure: K. Baker, None; L. Santanam, None; J. Bradley, None. 3310 Interobserver Variability in NSCLC Target Delineation for Stereotactic Body Radiation Therapy: A Four-dimensional Analysis G. Bouilhol 1 , 2 , A. Arnaud 1 , J. Lesseur 1 , M. Ayadi 1 , D. Sarrut 1,2 , L. Claude 1 1 Centre Le ´on Be ´rard/Radiothe ´rapie, Lyon, France, 2 universite ´ De Lyon/Creatis-Lrmn, Villeurbanne, France Purpose/Objective(s): Nowadays target delineation is one of the main sources of uncertainties in tumor targeting. In lung Stereo- tactic Body Radiation Therapy (SBRT), three main strategies exist to define the Internal Target Volume (ITV). They are based either on basic 3DCT blurred acquisitions, on 4D-CT phases union or on 4D-CT Maximum Intensity Projection (MIP) reconstruc- tions. We investigated each of them to evaluate the interobserver variability in target delineation. Materials/Methods: Three physicians were asked to delineate Gross Tumor Volume (GTV) on three 4D-CT reconstructed phases (0, 40, 50%) and to delineate the ITV on the averaged blurred reconstruction and on the MIP 4D-CT one. The delineation work was realized using a lung window/level and was iterated for ten peripheral Non-Small Cell Lung Cancer (NSCLC) patients and for two 4D-CT acquisitions per patient, leading to a hundred contours per observer. The contours were then analyzed on a dedicated work- station, allowing to perform volumetric comparisons. Results: Preliminary results for five patients show GTV volumes ranging from 0.5 to 50.9 cc and tumor motion amplitudes ranging from 0.0 to 1.64 cm. Concerning the interobserver variability, we first focused on the Overlap Volume (OV) which is the ratio of the intersection volume to the union volume of all compared volumes. An OV of 0 corresponds to a complete disagreement between observers and a value of 1 reflects a perfect agreement. We observed a mean OV value of 0.559 (SD 0.141) on the GTV for the phases CT sets analysis, 0.540 (SD 0.149) for the averaged blurred CT sets analysis and 0.641 (SD 0.052) for the MIP CT sets analysis on the ITV. Full results will be presented at the congress. Conclusions: In spite of well-defined edges of lung peripheral tumors, the small tumor size in hypofractionated SBRT treatments can lead to significant interobserver variations in terms of OV. This explains why the interobserver agreement was found to be better for the MIP ITV than the phases GTV. Indeed, the ITV size, taking tumor motion into account, is higher than the GTV size. However, for the averaged reconstruction based volumes, the benefit induced by the ITV size is lost with the additional de- lineation uncertainty induced by the blur. Finally, delineation on 4D-CT MIP images to define the ITV seems to be a relevant strat- egy to reduce interobserver variability in lung SBRT. To confirm these observations, this study will be completed with a three- dimensional quantification of the associated delineation uncertainties. Author Disclosure: G. Bouilhol, None; A. Arnaud, None; J. Lesseur, None; M. Ayadi, None; D. Sarrut, None; L. Claude, None. 3311 Stereotactic Radiation Treatment Planning with Volumetric Modulated Arc Therapy (VMAT): Impact of Duodenal Sparing J. M. Herman, J. Kang, R. Tuli, C. Wolfgang, T. M. Pawlik, E. Tryggestad, K. Smith, T. L. DeWeese, J. Wong, E. C. Ford Johns Hopkins University, Baltimore, MD Purpose/Objective(s): Volumetric modulated arc therapy (VMAT) allows for intensity-modulated radiation delivery during gan- try rotation with dynamic MLC motion, variable dose rates and gantry speed modulation. The dose limiting structure for pancreatic S790 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010
Transcript of Stereotactic Radiation Treatment Planning with Volumetric Modulated Arc Therapy (VMAT): Impact of...
S790 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010
3309 Novel Treatment Planning Techniques for Treatment of Chest Wall Lesions using Stereotactic
Body RadiotherapyK. Baker1, L. Santanam2, J. Bradley3
1Barnes-Jewish Hospital/Washington University, Saint Louis, MO, 2Washington University/Siteman Cancer Center, Saint Louis,MO, 3Washington University/Barnes-Jewish Hospital, Saint Louis, MO
Purpose/Objective(s): Three distinct planning techniques were compared for the treatment of lung tumors using stereotactic bodyradiation therapy (SBRT).
Materials/Methods: Ten patients with the target volumes attached or near to the chest wall were chosen for this study. Treatment plansusing three different techniques were performed retrospectively. These three techniques included conventional 3D planning (3D), for-ward planning with manual optimization (Field in Field (FIF)) and segmented beams with inverse planning optimization (SIP). A 4D-CT simulation was performed using a Philips 16 slice CT scanner. All patients were simulated in the supine position with arms placedabove their head and immobilized using a body frame or body fix. These 4D-CT images were fused with helical CT scans and wereprimarily used for target delineation. Note that all the treatment plans were performed on the free breathing helical CT scans. Plansinvolved anywhere between 7 -11 non- coplanar beams. 3D conformal plans were designed by manually creating all beam aperturesusing a uniform margin around the PTV and adjusting the block shape for avoiding critical structures. For FIF technique, 2-3 segmentswere created for each field. A segment was created by manually moving the MLC leaves into the aperture from the original block edgeeffectively blocking out an area where too much dose was being delivered. SIP technique uses the same beam angles as the two othertechniques. Plans were optimized using direct machine parameter optimization, allowing 1-2 segments per beam. A minimum of 50 to100 monitor units along with a minimum segment size of 5 to 10 cm2 was used. Additional structures and optimization constraints wereused for inverse planning. The following criteria were used for plan evaluation. All treatment plans had to adhere to the RTOG 0236protocol. Volume of the PTV covering 90% prescription dose should be at least 99%. Conformality index (CI) was defined as the ratioof the volume of prescription isodose to the volume of PTV. Plans were evaluated for plan quality and time efficiency.
Results: CI for all the three different techniques ranged from 1.1 -1.3. The volume of 105% prescription outside of the PTV wasdecreased on an average by 5% for the FIF and SIP techniques. The hotspot and the rib maximum doses were consistently lower forSIP and FIF compared to 3D. The planning times ranged from 2-3 hours for 3D, 4 -5 hours for FIF and 1- 2 hours for SIP.
Conclusions: The SIP technique produced equal or better plans than 3D conformal and FIF techniques with better critical structuresparing. The high dose region near the chest wall reduced while utilizing inverse planning techniques thereby reducing the potentialrisk of rib fractures. Inverse planning techniques offers new hope for better optimized plans for SBRT.
Author Disclosure: K. Baker, None; L. Santanam, None; J. Bradley, None.
3310 Interobserver Variability in NSCLC Target Delineation for Stereotactic Body Radiation Therapy: A
Four-dimensional AnalysisG. Bouilhol1,2, A. Arnaud1, J. Lesseur1, M. Ayadi1, D. Sarrut1,2, L. Claude1
1Centre Leon Berard/Radiotherapie, Lyon, France, 2universite De Lyon/Creatis-Lrmn, Villeurbanne, France
Purpose/Objective(s): Nowadays target delineation is one of the main sources of uncertainties in tumor targeting. In lung Stereo-tactic Body Radiation Therapy (SBRT), three main strategies exist to define the Internal Target Volume (ITV). They are basedeither on basic 3DCT blurred acquisitions, on 4D-CT phases union or on 4D-CT Maximum Intensity Projection (MIP) reconstruc-tions. We investigated each of them to evaluate the interobserver variability in target delineation.
Materials/Methods: Three physicians were asked to delineate Gross Tumor Volume (GTV) on three 4D-CT reconstructed phases(0, 40, 50%) and to delineate the ITV on the averaged blurred reconstruction and on the MIP 4D-CT one. The delineation work wasrealized using a lung window/level and was iterated for ten peripheral Non-Small Cell Lung Cancer (NSCLC) patients and for two4D-CT acquisitions per patient, leading to a hundred contours per observer. The contours were then analyzed on a dedicated work-station, allowing to perform volumetric comparisons.
Results: Preliminary results for five patients show GTV volumes ranging from 0.5 to 50.9 cc and tumor motion amplitudes rangingfrom 0.0 to 1.64 cm. Concerning the interobserver variability, we first focused on the Overlap Volume (OV) which is the ratio of theintersection volume to the union volume of all compared volumes. An OV of 0 corresponds to a complete disagreement betweenobservers and a value of 1 reflects a perfect agreement. We observed a mean OV value of 0.559 (SD 0.141) on the GTV for thephases CT sets analysis, 0.540 (SD 0.149) for the averaged blurred CT sets analysis and 0.641 (SD 0.052) for the MIP CT setsanalysis on the ITV. Full results will be presented at the congress.
Conclusions: In spite of well-defined edges of lung peripheral tumors, the small tumor size in hypofractionated SBRT treatmentscan lead to significant interobserver variations in terms of OV. This explains why the interobserver agreement was found to bebetter for the MIP ITV than the phases GTV. Indeed, the ITV size, taking tumor motion into account, is higher than the GTVsize. However, for the averaged reconstruction based volumes, the benefit induced by the ITV size is lost with the additional de-lineation uncertainty induced by the blur. Finally, delineation on 4D-CT MIP images to define the ITV seems to be a relevant strat-egy to reduce interobserver variability in lung SBRT. To confirm these observations, this study will be completed with a three-dimensional quantification of the associated delineation uncertainties.
Author Disclosure: G. Bouilhol, None; A. Arnaud, None; J. Lesseur, None; M. Ayadi, None; D. Sarrut, None; L. Claude, None.
3311 Stereotactic Radiation Treatment Planning with Volumetric Modulated Arc Therapy (VMAT): Impact of
Duodenal SparingJ. M. Herman, J. Kang, R. Tuli, C. Wolfgang, T. M. Pawlik, E. Tryggestad, K. Smith, T. L. DeWeese, J. Wong, E. C. Ford
Johns Hopkins University, Baltimore, MD
Purpose/Objective(s): Volumetric modulated arc therapy (VMAT) allows for intensity-modulated radiation delivery during gan-try rotation with dynamic MLC motion, variable dose rates and gantry speed modulation. The dose limiting structure for pancreatic
Proceedings of the 52nd Annual ASTRO Meeting S791
stereotactic body radiation therapy (SBRT) is the duodenum. Herein we evaluate VMAT dose distribution, delivery times, anddetermine the effect of duodenal sparing (DS).
Materials/Methods: Plans from fifteen patients with unresectable pancreatic cancer (14 head/1 tail) were selected. VMAT treat-ment planning with the ‘‘SmartArc’’ function of Pinnacle v. 8.9 was used to plan a single fraction of 25 Gy to the PTV (GTV plusa 2 mm expansion). Two VMAT SBRT plans were conducted for each case; the first did not account for duodenal toxicity while thesecond did. In each case one 360� coplanar arc was used with 4 degree spacing between control points. Prescriptions were set for 25Gy in a single fraction normalized to the 80% isodose line. Constraints used during planning included: stomach/duodenum anypoint max\30 Gy (for DS plan), liver D50\5 Gy, ipsilateral kidney D25\5 Gy, cord Dmax\5 Gy and stomach D4\22.5 Gy.
Results: The pancreatic tumor volume ranged from 58.4cm3 to 320.3 cm3 and the average overlap volume between the PTV andthe duodenum was 8.4 cm3. In 10/15 original non-sparing plans the duodenal Dmax exceeded 30 Gy. With DS optimization, only 1/15 plans exceeded the 30 Gy threshold. These differences were statistically significant (p\0.001). Typical number of MU and de-livery times, as calculated by the planning software were: 5494 MU and 775 secs vs. 5296 MU and 703 secs for the DS and non-DSplans, respectively. Though the difference in delivery times was significant (p = 0.01), it averages only 1.2 minutes. In the initialnon DS plan, the average duodenal Dmax = 30.4Gy, and over 4% of the duodenum received at least 23.4 Gy. However, after addinga max dose objective for the duodenum, the average Dmax = 28.1Gy and 4% of the duodenum volume received less than 19.7 Gy(p\0.001). As expected VMAT plans with a larger proportion of overlap between the duodenum and PTV had a higher duodenalDmax.
Conclusions: This study demonstrates the feasibility of newly available VMAT for high-dose SBRT treatment of pancreatic can-cer. VMAT planning for pancreatic cancer should incorporate duodenal constraints in an attempt to limit the risk of duodenal tox-icity. Future studies will also evaluate whether VMAT with fractionated SBRT may result in improved duodenal sparing.
Author Disclosure: J.M. Herman, None; J. Kang, None; R. Tuli, None; C. Wolfgang, None; T.M. Pawlik, None; E. Tryggestad,None; K. Smith, None; T.L. DeWeese, None; J. Wong, None; E.C. Ford, None.
3312 Radiosurgery and Fractionated Radiotherapy for Multiple Cranial Tumors: Comparison between
Volumetric Modulated Arc Therapy, Dynamic Arc Therapy and IMRTC. Lee, N. Agazaryan, M. T. Selch, A. A. F. De Salles, P. E. Chow, S. E. Tenn, A. Gorgulho, P. Lee, M. L. Steinberg
University of California-Los Angeles, Los Angeles, CA
Purpose/Objective(s): This study compared single-isocenter VMAT (RapidArc) plans for multiple cranial tumors with DynamicArc and IMRT plans in terms of conformity and low dose spillage.
Materials/Methods: Six previously treated cranial radiosurgery and fractionated radiotherapy patients (three single-isocenterIMRT plans and three multiple-isocenter dynamic arc plans) were re-planned using single-isocenter VMAT to achieve clinicallycomparable PTV coverage and OAR sparing. All VMAT plans were normalized the same way as the initial IMRT and DynamicArc plans. The Paddick Conformity Index (CI) and low-dose spillage (V75, V50, V25 and V10) were calculated and comparedagainst those of the plans used in actual patient treatments.
Results: CI for three VMAT plans was consistently better than for IMRT plans (0.90, 0.86, 0.83 vs. 0.86, 0.83, 0.75 respectively).CI for other three RapidArc plans was also consistently better than Dynamic Arc plans (0.87, 0.67, 0.77 vs. 0.69, 0.66, 0.59 re-spectively). VMAT provided better results compared to IMRT in terms of achieving smaller V75, V50, and V25; however,VMAT was consistently worse compared to Dynamic Arc plans. VMAT provided larger V10 compared to all three IMRT cases,and similarly VMAT provides larger V10 compared to Dynamic Arc plans in two of three cases.
Conclusions: For equivalent target coverage, VMAT technique provided improvement in CI in all six test cases. Overall, VMATshowed improvement over IMRT in low dose spillage, and Dynamic Arc plans showed less low dose spillage than VMAT; how-ever, delivery time of single-isocenter VMAT for multiple tumors is significantly shorter compared to multiple-isocenter dynamicarc plan.
Author Disclosure: C. Lee, University of California Los Angeles, A. Employment; N. Agazaryan, University of California LosAngeles, A. Employment; Varian Medical Systems, B. Research Grant; Scientific Advisory Board, ViewRay, F. Consultant/Ad-visory Board; M.T. Selch, University of California Los Angeles, A. Employment; A.A.F. De Salles, University of California LosAngeles, A. Employment; P.E. Chow, University of California Los Angeles, A. Employment; S.E. Tenn, University of CaliforniaLos Angeles, A. Employment; A. Gorgulho, University of California Los Angeles, A. Employment; P. Lee, University of Califor-nia Los Angeles, A. Employment; M.L. Steinberg, University of California Los Angeles, A. Employment.
3313 High Dose Rate (HDR) Brachytherapy vs. Helical Tomotherapy in the Treatment of Cervical Cancer: A
Dosimetric ComparisonT. D. Schultz1, T. Kumar2, Q. Liu2, Z. Bharucha2, J. Burmeister2
1GLCI-McLaren, Flint, MI, 2Karmanos Cancer Institute, Detroit, MI
Purpose/Objective(s): The purpose of this study is to dosimetrically evaluate Tomotherapy (Hi-ART Tomotherapy� Madison,WI) boost vs. High Dose Rate (HDR) brachytherapy boost using a ring and tandem in the treatment of cervical cancer.
Materials/Methods: A Tomotherapy plan was generated in 5 patients that had previously undergone HDR treatment. For HDRplans the prescription dose was 30Gy to Pt. A in 6 fractions. The HDR DICOM data files were transferred to Eclipse planningsystem and the 100% isodose volumes were converted to structure contours and defined as the target structures for Tomotherapy.HDR isodose lines of 75%, 50%, and 30% were also converted to structure volumes for dosimetric comparison between the twomodalities. The planning goal for Tomotherapy was defined so that 98% of the target volume received 100% of the dose. Bladderand rectum were defined as organs at risk. The Tomotherapy planning system was set to use the fine calculation grid, 2.5 cm jawwidth, and a 0.172 pitch for all plans. Comparisons were performed between the two modalities in terms of dose-volume, targetcoverage, Conformity Index, Heterogeneity Index, and gEUD.
