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Practical 4π Liver SBRT Using Eclipse Planning
Poster Viewing Session E587
Volume 93 Number 3S Supplement 2015 assembly that fits inside and concentric with the source carrier and a dynamically controlled patient support table. Two sets of 36 collimator holes are used to create beams of either 25mm or 15mm diameter and 36 tungsten rods block the sources when the system is in the beam-off state. The combination of 25mm and 15mm beams used in a treatment delivery is determined automatically by the inverse planning system. Once the sources are aligned with the collimator holes of a selected size, the source carrier and collimator assembly rotate together to form 36 non-coplanar, concentric, conical arcs focused at the isocenter. The breast is immobilized using a dual-layered breast cup applying a comfortable negative pressure between the two layers. The cup is embedded with fiducial markers that define a stereotactic coordinate system. An integrated patient loader transfers the patient from standing to prone position for treatment. Results: In APBI plan comparison examples, against four tangential linear accelerator beams, GammaPod reduces V50 by more than 40%. For a centrally located 6.4cm diameter target, the maximum dose to the heart and lung is 10% and V5 for the heart and lung is 6.5%, and 4.3%, respectively. In another comparison to various brachytherapy approaches, the skin dose was shown to be substantially reduced from 76-144% to 2123%, with substantially reduced dose heterogeneity. Conclusion: Using geometric beam focusing, dynamic treatment delivery and stereotactic localization, the GammaPod has shown its ability to deliver highly focused uniform dose distributions to breast targets with rapid dose fall-off. Author Disclosure: C.X. Yu: Partner; Xcision Medical Systems. Stock; Xcision Medical Systems. Y. Mutaf: None. W.F. Regine: Stock; Xcision Medical Systems. S.J. Feigenberg: None. E.M. Nichols: None. P.W. Hoban: Stock Options; Xcision Medical Systems.
and organs-at-risk (OAR) doses, liver volumes receiving <15 Gy, high dose spillage, and PTV homogeneity index, which was defined as D95/ D5, were compared. Results: Compared to the clinical plans, mean and maximum doses to OARs were either reduced (p<0.05) or unchanged (p>0.05) using 4p (Table 1). Significant reductions were found in the mean doses to the normal liver and stomach by 9.1% and 25.7%, and maximum doses to the normal liver, stomach, and spinal cord by 12.4%, 29.6%, and 35.5%, respectively. The mean liver volume receiving <15 Gy was increased by 61.71 cc (range -23 e 175 cc, pZ0.0061). The improved OAR sparing was achieved with slightly improved PTV dose coverage. The high dose spillage, R50, was also reduced by 25.55% (range -3.8% e 50.6%). The PTV homogeneity index was increased by 2.42% (range -5.3% e 8.4%). Conclusion: 4p radiation therapy implemented on a commercial planning system was able to significantly improve both PTV coverage and OAR sparing for liver SBRT compared to 2-arc VMAT plans created on the same planning system. The dosimetric gains are consistent with previously reported dosimetric gains achieved on an in-house 4p planning system. Therefore, this study further substantiates the practical gains using 4p radiation therapy for liver SBRT. Author Disclosure: A. Tran: Research Grant; Varian Medical Systems Inc. K. Woods: None. D. Nguyen: Research Grant; Varian Medical Systems Inc. V.Y. Yu: None. M. Cao: None. P. Lee: None. P.A. Kupelian: None. D. Low: None. K. Sheng: Research Grant; Varian Medical Systems Inc.
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Practical 4p Liver SBRT Using Eclipse Planning A. Tran, K. Woods, D. Nguyen, V.Y. Yu, M. Cao, P. Lee, P.A. Kupelian, D. Low, and K. Sheng; University of California, Los Angeles, Los Angeles, CA
Concurrent External Thermal Therapy (ETT) and Radiation Therapy (RT) Yields Increased Efficacy With Modest Toxicity: A SingleInstitution Experience J. Hyder,1 Z.H. Rana,2 J.W. Snider, III,3 P.P. Amin,1 and Z. Vujaskovic4; 1 Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, 2Virginia Hospital Center, Arlington, VA, 3 University of Maryland Medical Center, Baltimore, MD, 4University of Maryland School of Medicine, Baltimore, MD
Purpose/Objective(s): 4p radiation therapy extensively using automatically selected and optimized non-coplanar beams have been shown to significantly improve the liver stereotactic body radiation therapy (SBRT) normal organ sparing without compromising PTV coverage. To test if the dosimetric gains can be translated to a commercial planning system for clinical delivery, we create clinical 4p liver SBRT plans on a treatment planning system and then compare them against clinical plans. Materials/Methods: 4p radiation therapy was planned on 22 liver SBRT cases with prescription doses of 30-60 Gy to 95% of the planning target volume (PTV). The beam candidate pool consists of 1162 non-coplanar beams equally distributed throughout the 4p steradian. Beams causing collision between the couch, gantry, or patient were excluded by simulating all beam orientations using a computer assisted design model of the linear accelerator and human model. Using a column generation algorithm, 20 beams were selected with integrated fluence map optimization for intensity modulated radiation therapy (IMRT). The optimized beam angles were imported to the treatment planning system for dose recalculation to generate deliverable plans that can be directly compared to the clinical SBRT plans using 2 partial VMAT arcs entering from the body surface proximal to the tumor. PTV
Purpose/Objective(s): ETT has been coupled with external beam radiation therapy (EBRT) for its enhancement of radiation effect as a potent radiosensitizer. Improved techniques for ETT delivery and accurate monitoring have led to its increased use in the treatment of various tumors especially in the recurrent or hypoxic tumor settings. Concern has arisen that hyperthermia approaches might yield not only increased efficacy, but also substantially greater toxicity due to normal tissue sensitization. The aim of this study is to review the acute toxicity/ morbidity associated with concurrent ETT and RT delivered at our institution. Materials/Methods: We retrospectively reviewed the data of 28 patients treated at our institution from March 2013 to November 2014 who received ETT concurrent with at least 30 Gy of EBRT. Baseline characteristics gathered included race, age at diagnosis, BMI, site of disease, histology, TNM stage, previous therapy, RT dose, RT technique, ETT target temperatures, and duration of treatment. Outcomes recorded focused upon acute toxicities, radiographic response to treatment, local control, disease free survival, and overall survival. Toxicities were graded according to the Common Terminology Criteria for Adverse Events (CTCAE v4.0).
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Poster Viewing Abstracts 3472; Table 1
OAR and PTV dose changes from VMAT to 4p. *p<0.05 Dose Percent Differences
OAR
Normal Liver
Mean -9.15* Max -12.37* PTV Statistics D95 0.10
Stomach
Spinal Cord
-25.70* -29.63* D98 0.35
-21.47 -35.46* D99 0.52
L Kidney
R Kidney
-10.69 -27.19 mean -1.29*
Esophagus
4.47 -10.79 max -1.85*
Skin
-29.71 -36.76 R50 -25.55*
-0.68 -15.17 HI 2.42*
Volume 93 Number 3S Supplement 2015 assembly that fits inside and concentric with the source carrier and a dynamically controlled patient support table. Two sets of 36 collimator holes are used to create beams of either 25mm or 15mm diameter and 36 tungsten rods block the sources when the system is in the beam-off state. The combination of 25mm and 15mm beams used in a treatment delivery is determined automatically by the inverse planning system. Once the sources are aligned with the collimator holes of a selected size, the source carrier and collimator assembly rotate together to form 36 non-coplanar, concentric, conical arcs focused at the isocenter. The breast is immobilized using a dual-layered breast cup applying a comfortable negative pressure between the two layers. The cup is embedded with fiducial markers that define a stereotactic coordinate system. An integrated patient loader transfers the patient from standing to prone position for treatment. Results: In APBI plan comparison examples, against four tangential linear accelerator beams, GammaPod reduces V50 by more than 40%. For a centrally located 6.4cm diameter target, the maximum dose to the heart and lung is 10% and V5 for the heart and lung is 6.5%, and 4.3%, respectively. In another comparison to various brachytherapy approaches, the skin dose was shown to be substantially reduced from 76-144% to 2123%, with substantially reduced dose heterogeneity. Conclusion: Using geometric beam focusing, dynamic treatment delivery and stereotactic localization, the GammaPod has shown its ability to deliver highly focused uniform dose distributions to breast targets with rapid dose fall-off. Author Disclosure: C.X. Yu: Partner; Xcision Medical Systems. Stock; Xcision Medical Systems. Y. Mutaf: None. W.F. Regine: Stock; Xcision Medical Systems. S.J. Feigenberg: None. E.M. Nichols: None. P.W. Hoban: Stock Options; Xcision Medical Systems.
and organs-at-risk (OAR) doses, liver volumes receiving <15 Gy, high dose spillage, and PTV homogeneity index, which was defined as D95/ D5, were compared. Results: Compared to the clinical plans, mean and maximum doses to OARs were either reduced (p<0.05) or unchanged (p>0.05) using 4p (Table 1). Significant reductions were found in the mean doses to the normal liver and stomach by 9.1% and 25.7%, and maximum doses to the normal liver, stomach, and spinal cord by 12.4%, 29.6%, and 35.5%, respectively. The mean liver volume receiving <15 Gy was increased by 61.71 cc (range -23 e 175 cc, pZ0.0061). The improved OAR sparing was achieved with slightly improved PTV dose coverage. The high dose spillage, R50, was also reduced by 25.55% (range -3.8% e 50.6%). The PTV homogeneity index was increased by 2.42% (range -5.3% e 8.4%). Conclusion: 4p radiation therapy implemented on a commercial planning system was able to significantly improve both PTV coverage and OAR sparing for liver SBRT compared to 2-arc VMAT plans created on the same planning system. The dosimetric gains are consistent with previously reported dosimetric gains achieved on an in-house 4p planning system. Therefore, this study further substantiates the practical gains using 4p radiation therapy for liver SBRT. Author Disclosure: A. Tran: Research Grant; Varian Medical Systems Inc. K. Woods: None. D. Nguyen: Research Grant; Varian Medical Systems Inc. V.Y. Yu: None. M. Cao: None. P. Lee: None. P.A. Kupelian: None. D. Low: None. K. Sheng: Research Grant; Varian Medical Systems Inc.
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Practical 4p Liver SBRT Using Eclipse Planning A. Tran, K. Woods, D. Nguyen, V.Y. Yu, M. Cao, P. Lee, P.A. Kupelian, D. Low, and K. Sheng; University of California, Los Angeles, Los Angeles, CA
Concurrent External Thermal Therapy (ETT) and Radiation Therapy (RT) Yields Increased Efficacy With Modest Toxicity: A SingleInstitution Experience J. Hyder,1 Z.H. Rana,2 J.W. Snider, III,3 P.P. Amin,1 and Z. Vujaskovic4; 1 Department of Radiation Oncology, University of Maryland School of Medicine, Baltimore, MD, 2Virginia Hospital Center, Arlington, VA, 3 University of Maryland Medical Center, Baltimore, MD, 4University of Maryland School of Medicine, Baltimore, MD
Purpose/Objective(s): 4p radiation therapy extensively using automatically selected and optimized non-coplanar beams have been shown to significantly improve the liver stereotactic body radiation therapy (SBRT) normal organ sparing without compromising PTV coverage. To test if the dosimetric gains can be translated to a commercial planning system for clinical delivery, we create clinical 4p liver SBRT plans on a treatment planning system and then compare them against clinical plans. Materials/Methods: 4p radiation therapy was planned on 22 liver SBRT cases with prescription doses of 30-60 Gy to 95% of the planning target volume (PTV). The beam candidate pool consists of 1162 non-coplanar beams equally distributed throughout the 4p steradian. Beams causing collision between the couch, gantry, or patient were excluded by simulating all beam orientations using a computer assisted design model of the linear accelerator and human model. Using a column generation algorithm, 20 beams were selected with integrated fluence map optimization for intensity modulated radiation therapy (IMRT). The optimized beam angles were imported to the treatment planning system for dose recalculation to generate deliverable plans that can be directly compared to the clinical SBRT plans using 2 partial VMAT arcs entering from the body surface proximal to the tumor. PTV
Purpose/Objective(s): ETT has been coupled with external beam radiation therapy (EBRT) for its enhancement of radiation effect as a potent radiosensitizer. Improved techniques for ETT delivery and accurate monitoring have led to its increased use in the treatment of various tumors especially in the recurrent or hypoxic tumor settings. Concern has arisen that hyperthermia approaches might yield not only increased efficacy, but also substantially greater toxicity due to normal tissue sensitization. The aim of this study is to review the acute toxicity/ morbidity associated with concurrent ETT and RT delivered at our institution. Materials/Methods: We retrospectively reviewed the data of 28 patients treated at our institution from March 2013 to November 2014 who received ETT concurrent with at least 30 Gy of EBRT. Baseline characteristics gathered included race, age at diagnosis, BMI, site of disease, histology, TNM stage, previous therapy, RT dose, RT technique, ETT target temperatures, and duration of treatment. Outcomes recorded focused upon acute toxicities, radiographic response to treatment, local control, disease free survival, and overall survival. Toxicities were graded according to the Common Terminology Criteria for Adverse Events (CTCAE v4.0).
3472
Poster Viewing Abstracts 3472; Table 1
OAR and PTV dose changes from VMAT to 4p. *p<0.05 Dose Percent Differences
OAR
Normal Liver
Mean -9.15* Max -12.37* PTV Statistics D95 0.10
Stomach
Spinal Cord
-25.70* -29.63* D98 0.35
-21.47 -35.46* D99 0.52
L Kidney
R Kidney
-10.69 -27.19 mean -1.29*
Esophagus
4.47 -10.79 max -1.85*
Skin
-29.71 -36.76 R50 -25.55*
-0.68 -15.17 HI 2.42*