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Adaptive Proton Radiation Therapy for Base of Skull Tumors
Poster Viewing Abstracts S803
Volume 84 Number 3S Supplement 2012 Poster Viewing Abstract 3553; Table
Population systematic and random errors
Systematic error (cm)
CBCT US Manual bony match Automatic bony match
Random error (cm)
SI
AP
LR
SI
AP
LR
0.32 0.30 0.18 0.41
0.35 0.42 0.22 0.21
0.31 0.32 0.31 0.30
0.26 0.29 0.21 0.28
0.35 0.35 0.21 0.23
0.21 0.26 0.20 0.21
Conclusion: Our study demonstrates that anatomic change during proton radiation therapy for base of skull tumor, especially tumor shrinkage in the sinuses, can occur. Increased heterogeneity of tissue densities within the GTV can result in hot spots. The results of six additional cases will be presented at the meeting. Author Disclosure: N. Shusharina: None. A.W. Chan: None. J. Adams: None. G.T. Chen: None. G.C. Sharp: None.
3555 directions were 1.0cm, 1.1cm and 0.9cm respectively using CBCT soft tissue matching, 1.0cm, 1.3cm and 1.0cm using US, 1.2cm, 0.7cm and 0.9cm using automatic bony matching and 0.6cm, 0.7cm and 0.9cm using manual bony matching. Conclusions: This study has shown that random and systematic errors and margins were similar between CBCT and US soft tissue matching, suggesting a similar level of accuracy. As has been noted in other studies, however, larger systematic errors were observed, and thus larger margins were required, in the AP direction using US, which may be explained by probe pressure effects. This study, however, did not evaluate intrafraction motion which might give more information regarding appropriate margins when daily online correction is used. Author Disclosure: L. Murray: None. J. Conway: None. D. Siddall: None. D. Redding: None. P. Kirkbride: None. O.S. Din: None.
3554 Adaptive Proton Radiation Therapy for Base of Skull Tumors N. Shusharina, A.W. Chan, J. Adams, G.T. Chen, and G.C. Sharp; Massachusetts General Hospital, Boston, MA Purpose/Objective(s): Proton therapy offers additional sparing of critical organs for head and neck tumors compared to IMRT. However, proton beams are sensitive to changes in tissue densities, and anatomic change during the course of treatment may affect the proton dose distribution. This study investigates whether adaptive replanning is needed to compensate for anatomic change during therapy. Materials/Methods: Six patients, three with nasopharyngeal carcinoma and three with paranasal sinus cancer, treated with definitive or postoperative proton radiation therapy were analyzed retrospectively. A replanning CT scan was acquired during mid-late course at a median dose of 53 Gy. The scans were registered rigidly to bony structures of the skull to remove the setup error. A deformable B-spline based registration was then performed to transfer structure contours from the planning CT to the replanning CT. The original treatment plan was applied to the re-planning CT, and proton dose was re-calculated. Anatomic differences between the two CT scans were analyzed interactively, and dose distributions were evaluated by comparing isodose lines and distance-to-agreement analysis. Dose-volume histograms were compared using transferred contours on the re-planning CT and original contours on the pre-treatment CT. Results: Autotransferred contours for critical organs were evaluated, and found to be satisfactory for critical structures. Target structures were redelineated manually. Anatomic changes were observed in all six cases. The most significant change in the re-planning CT was the decrease in GTV volume with a median change of -12% (range, 0-36%). As a result of the increase in air in the sinuses, the average density within GTV was decreased from 93 +/- 11 Hounsfield unit (HU) to 37 +/- 36 HU (median, 43 HU). Of the 6 studied cases, the median change in the mean GTV dose was +1% (range, 0 - +1%). Hot spots larger than 1 cm3 within the GTV with dose increase of 6% and 7% were observed in 2 cases. The median GTV volume that received > 110% of the prescribed dose increased from 0.4% to 2.37%. The median of the maximum dose to the GTV nearly unchanged (79.28 vs. 79.44 Gy). There is no significant change in the CTV dose in all the studied cases. The median dose change to the Dmax of brainstem was +8% (range, 0 - +15%). The median dose change to the mean of the brainstem dose was +1.5% (range, -6% - +3%). The median dose change to the Dmax of optic chiasm and optic nerve (left or right), were -3% (range, -11% - 0) and -0.5% (range, -4.5% - +11%), respectively.
Feasibility of MR-alone-based Brachytherapy Treatment Planning Using a Titanium Tandem and Ring Applicator for Cervical Cancer J. Cai, J. Chino, Y. Qin, T.R. De Oliveira, J. Adamson, B. Steffey, and O. Craciunescu; Duke University Medical Center, Durham, NC Purpose/Objective(s): To characterize a CT/MR compatible HDR titanium tandem and ring (T&R) applicator and to test the feasibility of MRalone-based treatment planning using this applicator. Methods: A stabilized and gel-embedded CT/MR compatible T&R applicator was imaged with a high-resolution CT (slice thickness Z 1.25 mm) on a 1.5 T GE clinical scanner using 9 different MR sequences: T2-w frFSE (scanned for transverse, sagittal, coronal, oblique-axial, obliquecoronal, oblique-sagittal views), 3D-fGRE, axial T2-w FSE-xl, and axialSE. The imaging was performed with and without 2 Alatus balloons (20cc saline) attached to the applicator, to mimic clinical use. Image artifacts were evaluated for all MR image sets. The CT and MR image sets were registered and the applicator was geometrically characterized on both sets. In this study we used 4 cm, 45/60 degree tandems, and black/white ring caps. To test the feasibility of MR-alone-based treatment planning, a total of 23 fractions, from 5 patients were retrospectively planned. The T&R applicators were delineated on the MR image set, using characterizations obtained from the phantom study. The MR-alone-based plans (Plan1) were compared to the clinical MR-CT-hybrid plans (Plan2) to determine the following dosimetric metrics: D100 and D90 for the high risk CTV (HRCTV), D2cc of Bladder, Bowel, Rectum, and Sigmoid. Statistical significance was tested using paired t-test. Results: Three-dimensional-fGRE MR was found to have the least image artifacts of the T&R applicator at 1.5 T. The black-band artifacts observed in 3D-fGRE MR resulted in minimally greater dimensions of the tandem and the ring caps, as compared to those in CT. The tip of the tandem matched between MR and CT (tip to first dwell position Z 0.5 cm in both). Distal point of the ring is 0.6 cm away from the neck of the ring, which can be identified as an air dent adjacent to the balloon in the MR. There is a consistent spherical black-band artifact with a width of about 4 mm at the tip of the tandem. There is a small lateral shift (0.5 mm) for the tandem in the sagittal view of the applicator. In patient study, small but significant differences were found in Bladder D2cc (4.010.63Gy EQD2 and 4.170.69Gy EQD2 in Plan1 and Plan2 respectively; p Z 0.007) and Sigmoid D2cc (3.450.59Gy EQD2 and 3.310.58Gy EQD2 in Plan1 and Plan2 respectively, p Z 0.001). No significant differences were found in other metrics (p-value range: 0.13 to 0.44). Conclusions: Among the evaluated MR techniques, the 3D-fGRE 1.5T MR showed the least image artifacts of the applicator. MR-alone-based planning revealed small but significant differences in D2cc of Bladder and Sigmoid, as compared to the clinical MR-CT-hybrid planning. Cautions should be taken when MR images are used alone for T&R HDR brachytherapy treatment planning. Author Disclosure: J. Cai: None. J. Chino: None. Y. Qin: None. T.R. De Oliveira: None. J. Adamson: None. B. Steffey: None. O. Craciunescu: None.
3556 Quantitative Analysis of Head Scatter and Jaw Transmission Correction Factor for Enhanced Dynamic Wedge Fields Using a 2-dimensional Diode Array E. Parsai, E.C. Dickerson, and D. Shvydka; University of Toledo Health Science Campus, Toledo, OH
Volume 84 Number 3S Supplement 2012 Poster Viewing Abstract 3553; Table
Population systematic and random errors
Systematic error (cm)
CBCT US Manual bony match Automatic bony match
Random error (cm)
SI
AP
LR
SI
AP
LR
0.32 0.30 0.18 0.41
0.35 0.42 0.22 0.21
0.31 0.32 0.31 0.30
0.26 0.29 0.21 0.28
0.35 0.35 0.21 0.23
0.21 0.26 0.20 0.21
Conclusion: Our study demonstrates that anatomic change during proton radiation therapy for base of skull tumor, especially tumor shrinkage in the sinuses, can occur. Increased heterogeneity of tissue densities within the GTV can result in hot spots. The results of six additional cases will be presented at the meeting. Author Disclosure: N. Shusharina: None. A.W. Chan: None. J. Adams: None. G.T. Chen: None. G.C. Sharp: None.
3555 directions were 1.0cm, 1.1cm and 0.9cm respectively using CBCT soft tissue matching, 1.0cm, 1.3cm and 1.0cm using US, 1.2cm, 0.7cm and 0.9cm using automatic bony matching and 0.6cm, 0.7cm and 0.9cm using manual bony matching. Conclusions: This study has shown that random and systematic errors and margins were similar between CBCT and US soft tissue matching, suggesting a similar level of accuracy. As has been noted in other studies, however, larger systematic errors were observed, and thus larger margins were required, in the AP direction using US, which may be explained by probe pressure effects. This study, however, did not evaluate intrafraction motion which might give more information regarding appropriate margins when daily online correction is used. Author Disclosure: L. Murray: None. J. Conway: None. D. Siddall: None. D. Redding: None. P. Kirkbride: None. O.S. Din: None.
3554 Adaptive Proton Radiation Therapy for Base of Skull Tumors N. Shusharina, A.W. Chan, J. Adams, G.T. Chen, and G.C. Sharp; Massachusetts General Hospital, Boston, MA Purpose/Objective(s): Proton therapy offers additional sparing of critical organs for head and neck tumors compared to IMRT. However, proton beams are sensitive to changes in tissue densities, and anatomic change during the course of treatment may affect the proton dose distribution. This study investigates whether adaptive replanning is needed to compensate for anatomic change during therapy. Materials/Methods: Six patients, three with nasopharyngeal carcinoma and three with paranasal sinus cancer, treated with definitive or postoperative proton radiation therapy were analyzed retrospectively. A replanning CT scan was acquired during mid-late course at a median dose of 53 Gy. The scans were registered rigidly to bony structures of the skull to remove the setup error. A deformable B-spline based registration was then performed to transfer structure contours from the planning CT to the replanning CT. The original treatment plan was applied to the re-planning CT, and proton dose was re-calculated. Anatomic differences between the two CT scans were analyzed interactively, and dose distributions were evaluated by comparing isodose lines and distance-to-agreement analysis. Dose-volume histograms were compared using transferred contours on the re-planning CT and original contours on the pre-treatment CT. Results: Autotransferred contours for critical organs were evaluated, and found to be satisfactory for critical structures. Target structures were redelineated manually. Anatomic changes were observed in all six cases. The most significant change in the re-planning CT was the decrease in GTV volume with a median change of -12% (range, 0-36%). As a result of the increase in air in the sinuses, the average density within GTV was decreased from 93 +/- 11 Hounsfield unit (HU) to 37 +/- 36 HU (median, 43 HU). Of the 6 studied cases, the median change in the mean GTV dose was +1% (range, 0 - +1%). Hot spots larger than 1 cm3 within the GTV with dose increase of 6% and 7% were observed in 2 cases. The median GTV volume that received > 110% of the prescribed dose increased from 0.4% to 2.37%. The median of the maximum dose to the GTV nearly unchanged (79.28 vs. 79.44 Gy). There is no significant change in the CTV dose in all the studied cases. The median dose change to the Dmax of brainstem was +8% (range, 0 - +15%). The median dose change to the mean of the brainstem dose was +1.5% (range, -6% - +3%). The median dose change to the Dmax of optic chiasm and optic nerve (left or right), were -3% (range, -11% - 0) and -0.5% (range, -4.5% - +11%), respectively.
Feasibility of MR-alone-based Brachytherapy Treatment Planning Using a Titanium Tandem and Ring Applicator for Cervical Cancer J. Cai, J. Chino, Y. Qin, T.R. De Oliveira, J. Adamson, B. Steffey, and O. Craciunescu; Duke University Medical Center, Durham, NC Purpose/Objective(s): To characterize a CT/MR compatible HDR titanium tandem and ring (T&R) applicator and to test the feasibility of MRalone-based treatment planning using this applicator. Methods: A stabilized and gel-embedded CT/MR compatible T&R applicator was imaged with a high-resolution CT (slice thickness Z 1.25 mm) on a 1.5 T GE clinical scanner using 9 different MR sequences: T2-w frFSE (scanned for transverse, sagittal, coronal, oblique-axial, obliquecoronal, oblique-sagittal views), 3D-fGRE, axial T2-w FSE-xl, and axialSE. The imaging was performed with and without 2 Alatus balloons (20cc saline) attached to the applicator, to mimic clinical use. Image artifacts were evaluated for all MR image sets. The CT and MR image sets were registered and the applicator was geometrically characterized on both sets. In this study we used 4 cm, 45/60 degree tandems, and black/white ring caps. To test the feasibility of MR-alone-based treatment planning, a total of 23 fractions, from 5 patients were retrospectively planned. The T&R applicators were delineated on the MR image set, using characterizations obtained from the phantom study. The MR-alone-based plans (Plan1) were compared to the clinical MR-CT-hybrid plans (Plan2) to determine the following dosimetric metrics: D100 and D90 for the high risk CTV (HRCTV), D2cc of Bladder, Bowel, Rectum, and Sigmoid. Statistical significance was tested using paired t-test. Results: Three-dimensional-fGRE MR was found to have the least image artifacts of the T&R applicator at 1.5 T. The black-band artifacts observed in 3D-fGRE MR resulted in minimally greater dimensions of the tandem and the ring caps, as compared to those in CT. The tip of the tandem matched between MR and CT (tip to first dwell position Z 0.5 cm in both). Distal point of the ring is 0.6 cm away from the neck of the ring, which can be identified as an air dent adjacent to the balloon in the MR. There is a consistent spherical black-band artifact with a width of about 4 mm at the tip of the tandem. There is a small lateral shift (0.5 mm) for the tandem in the sagittal view of the applicator. In patient study, small but significant differences were found in Bladder D2cc (4.010.63Gy EQD2 and 4.170.69Gy EQD2 in Plan1 and Plan2 respectively; p Z 0.007) and Sigmoid D2cc (3.450.59Gy EQD2 and 3.310.58Gy EQD2 in Plan1 and Plan2 respectively, p Z 0.001). No significant differences were found in other metrics (p-value range: 0.13 to 0.44). Conclusions: Among the evaluated MR techniques, the 3D-fGRE 1.5T MR showed the least image artifacts of the applicator. MR-alone-based planning revealed small but significant differences in D2cc of Bladder and Sigmoid, as compared to the clinical MR-CT-hybrid planning. Cautions should be taken when MR images are used alone for T&R HDR brachytherapy treatment planning. Author Disclosure: J. Cai: None. J. Chino: None. Y. Qin: None. T.R. De Oliveira: None. J. Adamson: None. B. Steffey: None. O. Craciunescu: None.
3556 Quantitative Analysis of Head Scatter and Jaw Transmission Correction Factor for Enhanced Dynamic Wedge Fields Using a 2-dimensional Diode Array E. Parsai, E.C. Dickerson, and D. Shvydka; University of Toledo Health Science Campus, Toledo, OH