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4D Proton Treatment Planning for Liver Tumors
I. J. Radiation Oncology d Biology d Physics
S698
Volume 75, Number 3, Supplement, 2009
Results: The SBRT plans used a median of 10 non-coplanar beams (range 9-13), while all SBPT plans used 4 non-coplanar beams. The minimum planning target volume (PTV) coverage was equal in both SBRT and SBPT plans. The maximum PTV doses were 13.7% lower (median, with range 9.2-17.3%) in SBPT plans. Maximum chest wall doses were 11.9% lower (median, with range -17.5%-17.1%) in SBPT plans; however, the chest wall volume receiving greater than 50% of the prescription dose (V50%) was 22 cm3 greater (median, with range -5.9-63.1 cm3) in SBPT plans. Mean total lung doses were 64.9% lower (median, with range 30.498.4%) in SBPT plans. Mean liver doses were 72.5% lower (median, with range 25.2-100%) in SBPT plans. As an estimate of integral dose, mean body doses were 68.9% lower (median, with range 50.9-80.4%) in SBPT plans, with a corresponding reduction in body V50% of 38.6 cm3 (range 0-232.8 cm3). Mean doses to heart, kidneys, esophagus, spinal cord, and stomach were all reduced by 89-100% in SBPT plans. Conclusions: SBPT provides similar target coverage to that of SBRT but achieves substantial reductions in most OAR doses and in whole body dose. SBPT does not offer substantial reduction in chest wall doses with the techniques used in this study. These data suggest SBPT may offer advantages over SBRT if resources permit such treatment. Author Disclosure: J.G. Brabham, None; K. Shahnazi, None; C. Allgower, None; M.M. Fitzek, None; H.R. Cardenes, None; A.J. Fakiris, None; M.E. Ewing, None; I.J. Das, None.
3149
4D Proton Treatment Planning for Liver Tumors
1
G. Chen , T. S. Hong1, J. Hallman1, G. C. Sharp1, J. A. Wolfgang1, H. Lu1, S. Mori2 1
Massachusetts General Hospital, Boston, MA, 2National Institute of Radiological Sciences, Chiba, Japan
Purpose/Objective(s): We performed 4D dose calculations on 15 patients receiving proton beam treatment for liver tumors 1) to determine the robustness of proton treatment in irradiation of moving abdominal tumors and 2) to assess the gain from motion mitigation by gated proton treatment. Materials/Methods: For treatment, dose distributions are calculated on the T30 phase of a 4D CT scan. The compensator is smeared and aperture enlarged to account for organ motion and setup uncertainty. In this study, we recalculated the dose distribution using 4D treatment planning. The target volume defined at T30 is propagated to all other respiratory phases using deformable registration. Center of mass (COM) and bounding box motion of the CTV and other organs were quantified. The compensator was designed to deliver adequate treatment of the target in the presence of respiratory motion. In 4D planning, this compensator is applied to each respiratory phase, resulting in phase specific dose distributions. These dose distributions are warped onto the reference respiratory phase (T30) using deformable registration. In this reference phase, dose moves relative to static anatomy. This time varying dose distribution is integrated over time to yield the organ DVH. Results: Target volumes ranged from 16cc to 248cc, averaging 111 cc. Three patients had multiple (2-3) liver lesions. The average ungated liver COM motion along the SI axis was 10 mm peak to peak (pp) (range 4-24mm). The average ungated CTV COM motion was 11 mm pp (range 4-38mm). With a gating window of 40-60%, the average COM motion of the liver and CTV were \1 and 1.4mm pp respectively. Treatment fields typically included a right lateral field paired with an AP or PA field depending on lesion location. With anterior tumors, anterior oblique fields were used. One lesion was treated with 3 fields. Normal liver DVHs (Liver-CTV) were generated and were dependent on patient anatomy and field arrangement. By design, the target is covered by the prescribed dose during motion. Respiration can increase the volume of normal liver irradiated to low dose by 5-15%, depending on geometry. Isodose motion for gated and ungated treatment were visualized by generating movies in the room coordinate and reference phase frame. Lower value isodose lines can move by . 10mm, but the tight gradient around the target moved only a few mm. The increased volume of liver irradiated during respiration is a function of lesion location. Conclusions: Assuming respiratory motion at treatment and CT scan are similar, proton treatment of liver lesions adequately irradiate the target, with increased dose to normal liver if an ITV strategy is implemented. Gated treatment can significantly reduce the lower dose portion of the DVH, and decrease NTCP, particularly for central or medial tumors and those with significant CTV SI motion. Author Disclosure: G. Chen, None; T.S. Hong, None; J. Hallman, None; G.C. Sharp, None; J.A. Wolfgang, None; H. Lu, None; S. Mori, None.
3150
Feasibility Study of a Set of Quality Assurance Checks for Spot Scanning Proton Therapy Beams by using a 2-D Ion Chamber Array
N. Sahoo, X. R. Zhu, B. Arjomandy, G. Ciangaru, X. Ding, M. Gillin M.D. Anderson Cancer Center, Houston, TX Purpose/Objective(s): Spot scanned proton therapy beam is a relatively new modality and is in limited clinical use. Quality assurance (QA) tools and procedures for these beams are evolving. The purpose of this feasibility study was both to devise and to evaluate a number of QA procedures for checking the accuracy of delivered spot positions and the consistency of dose delivery of spot scanned proton therapy beams by using a 2-D ion chamber array. Materials/Methods: A 2-D ion chamber array (MatriXX) from Scanditronix/Wellhofer was used to carry out QA checks for the spot scanned proton beams of a Hitachi Pro-Beat machine. The geometric divergence of spot separation with the increase in source to surface distance (SSD), positioning accuracy of single and a line pattern of spots, and the accuracy of delivered planar dose from 3-D spot distributions were investigated by irradiating the MatriXX placed under plastic slab phantoms and a plastic step phantom that has different thickness for each of its steps. The expected planar dose distributions for the 3-D spot distributions were obtained from the Eclipse treatment planning system (TPS) using the CT images of the phantoms used in the measurement. Results: Deviations both in the distance between two spots due to beam divergence with the change of SSD and in the single spot position from their expected values can be detected with sub-millimeter accuracy. It is possible to detect deviations as small as 1 mm in the single spot position in a uniform line pattern by quantifiable differences seen between the expected uniform dose distribution and the one measured by the MatriXX. Consistency of the dose delivery by the 3-D spot distributions can be checked by
S698
Volume 75, Number 3, Supplement, 2009
Results: The SBRT plans used a median of 10 non-coplanar beams (range 9-13), while all SBPT plans used 4 non-coplanar beams. The minimum planning target volume (PTV) coverage was equal in both SBRT and SBPT plans. The maximum PTV doses were 13.7% lower (median, with range 9.2-17.3%) in SBPT plans. Maximum chest wall doses were 11.9% lower (median, with range -17.5%-17.1%) in SBPT plans; however, the chest wall volume receiving greater than 50% of the prescription dose (V50%) was 22 cm3 greater (median, with range -5.9-63.1 cm3) in SBPT plans. Mean total lung doses were 64.9% lower (median, with range 30.498.4%) in SBPT plans. Mean liver doses were 72.5% lower (median, with range 25.2-100%) in SBPT plans. As an estimate of integral dose, mean body doses were 68.9% lower (median, with range 50.9-80.4%) in SBPT plans, with a corresponding reduction in body V50% of 38.6 cm3 (range 0-232.8 cm3). Mean doses to heart, kidneys, esophagus, spinal cord, and stomach were all reduced by 89-100% in SBPT plans. Conclusions: SBPT provides similar target coverage to that of SBRT but achieves substantial reductions in most OAR doses and in whole body dose. SBPT does not offer substantial reduction in chest wall doses with the techniques used in this study. These data suggest SBPT may offer advantages over SBRT if resources permit such treatment. Author Disclosure: J.G. Brabham, None; K. Shahnazi, None; C. Allgower, None; M.M. Fitzek, None; H.R. Cardenes, None; A.J. Fakiris, None; M.E. Ewing, None; I.J. Das, None.
3149
4D Proton Treatment Planning for Liver Tumors
1
G. Chen , T. S. Hong1, J. Hallman1, G. C. Sharp1, J. A. Wolfgang1, H. Lu1, S. Mori2 1
Massachusetts General Hospital, Boston, MA, 2National Institute of Radiological Sciences, Chiba, Japan
Purpose/Objective(s): We performed 4D dose calculations on 15 patients receiving proton beam treatment for liver tumors 1) to determine the robustness of proton treatment in irradiation of moving abdominal tumors and 2) to assess the gain from motion mitigation by gated proton treatment. Materials/Methods: For treatment, dose distributions are calculated on the T30 phase of a 4D CT scan. The compensator is smeared and aperture enlarged to account for organ motion and setup uncertainty. In this study, we recalculated the dose distribution using 4D treatment planning. The target volume defined at T30 is propagated to all other respiratory phases using deformable registration. Center of mass (COM) and bounding box motion of the CTV and other organs were quantified. The compensator was designed to deliver adequate treatment of the target in the presence of respiratory motion. In 4D planning, this compensator is applied to each respiratory phase, resulting in phase specific dose distributions. These dose distributions are warped onto the reference respiratory phase (T30) using deformable registration. In this reference phase, dose moves relative to static anatomy. This time varying dose distribution is integrated over time to yield the organ DVH. Results: Target volumes ranged from 16cc to 248cc, averaging 111 cc. Three patients had multiple (2-3) liver lesions. The average ungated liver COM motion along the SI axis was 10 mm peak to peak (pp) (range 4-24mm). The average ungated CTV COM motion was 11 mm pp (range 4-38mm). With a gating window of 40-60%, the average COM motion of the liver and CTV were \1 and 1.4mm pp respectively. Treatment fields typically included a right lateral field paired with an AP or PA field depending on lesion location. With anterior tumors, anterior oblique fields were used. One lesion was treated with 3 fields. Normal liver DVHs (Liver-CTV) were generated and were dependent on patient anatomy and field arrangement. By design, the target is covered by the prescribed dose during motion. Respiration can increase the volume of normal liver irradiated to low dose by 5-15%, depending on geometry. Isodose motion for gated and ungated treatment were visualized by generating movies in the room coordinate and reference phase frame. Lower value isodose lines can move by . 10mm, but the tight gradient around the target moved only a few mm. The increased volume of liver irradiated during respiration is a function of lesion location. Conclusions: Assuming respiratory motion at treatment and CT scan are similar, proton treatment of liver lesions adequately irradiate the target, with increased dose to normal liver if an ITV strategy is implemented. Gated treatment can significantly reduce the lower dose portion of the DVH, and decrease NTCP, particularly for central or medial tumors and those with significant CTV SI motion. Author Disclosure: G. Chen, None; T.S. Hong, None; J. Hallman, None; G.C. Sharp, None; J.A. Wolfgang, None; H. Lu, None; S. Mori, None.
3150
Feasibility Study of a Set of Quality Assurance Checks for Spot Scanning Proton Therapy Beams by using a 2-D Ion Chamber Array
N. Sahoo, X. R. Zhu, B. Arjomandy, G. Ciangaru, X. Ding, M. Gillin M.D. Anderson Cancer Center, Houston, TX Purpose/Objective(s): Spot scanned proton therapy beam is a relatively new modality and is in limited clinical use. Quality assurance (QA) tools and procedures for these beams are evolving. The purpose of this feasibility study was both to devise and to evaluate a number of QA procedures for checking the accuracy of delivered spot positions and the consistency of dose delivery of spot scanned proton therapy beams by using a 2-D ion chamber array. Materials/Methods: A 2-D ion chamber array (MatriXX) from Scanditronix/Wellhofer was used to carry out QA checks for the spot scanned proton beams of a Hitachi Pro-Beat machine. The geometric divergence of spot separation with the increase in source to surface distance (SSD), positioning accuracy of single and a line pattern of spots, and the accuracy of delivered planar dose from 3-D spot distributions were investigated by irradiating the MatriXX placed under plastic slab phantoms and a plastic step phantom that has different thickness for each of its steps. The expected planar dose distributions for the 3-D spot distributions were obtained from the Eclipse treatment planning system (TPS) using the CT images of the phantoms used in the measurement. Results: Deviations both in the distance between two spots due to beam divergence with the change of SSD and in the single spot position from their expected values can be detected with sub-millimeter accuracy. It is possible to detect deviations as small as 1 mm in the single spot position in a uniform line pattern by quantifiable differences seen between the expected uniform dose distribution and the one measured by the MatriXX. Consistency of the dose delivery by the 3-D spot distributions can be checked by