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A Dosimetric Study of Volumetric Modulated Arc Therapy (VMAT) Versus Intensity Modulated Radiation Therapy (IMRT) in Locally-Advanced Nasopharyngeal Cancer Involving Base of Skull
Poster Viewing Abstracts S723
Volume 87 Number 2S Supplement 2013 results showed a significant speed up between the automated and manual planning process. Conclusions: Knowledge based system would transform the treatment planning process into a completely automated procedure. This work has the potential to be a promising platform for developing treatment plans and afford a powerful way to reliably automate the treatment planning process. It could have major predictive value to save clinical time in developing a cancer treatment plan. Author Disclosure: H. Wang: None. L. Xing: None.
3359 MRI-Based Radiation Therapy Planning of Prostate Cancer: Clinical Feasibility and Assessment of Dosimetric Accuracy for Different Treatment Techniques G. Perkins, M. McGarry, R.W. Hammoud, S. Divakar, M. Riyas, T. Torfeh, and N. Al Hammadi; Hamad Medical Corporation, DOHA, Qatar Purpose/Objective(s): MRI has been demonstrated to improve radiation therapy target volume delineation in prostate cancer, but has yet to seriously challenge CT as the primary modality for planning due to lack of image electron density information required for dose calculation, as well as potential geometric distortion in the images. To compare the clinical feasibility of MR only dose calculations based on manual segmentation of anatomical structures and bulk electron density assignment based on tissue classification. The dosimetric accuracy when compared to the reference CT dataset was also assessed for 4F, 6F CRT and VMAT planning techniques Materials/Methods: The registered CT-MR-SIM datasets of 10 prostate cancer patients were used in this retrospective study. For each patient, the CTV and PTV were copied from the reference CT onto each registered MR dataset. The external(body), bladder, rectum, small bowel, femoral heads and bone were segmented manually on MR. The addition of electrondensity information to MR images and dose calculation accuracy for 4F, 6F CRT and VMAT planning of the prostate was then quantified by comparing dose distributions created on the bulk-density assigned images with the original CT. Phantom measurements were performed to quantify geometric distortions after application of a gradient distortion correction algorithm for the FOV and the pulse sequence parameters used in this study (T1,T2 FSE, fat suppressed (FS) ‘hybrid’T2/PD FSE, and T1 LAVAFLEX). Results: Mean differences between dose calculation metrics for CT vs MRI were <1% for all three planning techniques and < 1.5% for bladder, rectum and small bowel (Table). For the PTV DVHs the normalized rootmean-square deviation which represents a percentage of similarity between the curves was found to range from 0.985-0.99 (full statistical data to be presented). Differences of up to 3.36% in max dose were seen for the femoral heads. From phantom studies, residual distortions were found to be < 1.0 mm within a 10 cm radius and < 1.5 mm within a 20 cm radius of the scan center for scan length of 15 cm for all sequences. The FS ‘hybrid’ PD/T2 sequence was found to be the most optimal for both organ and bone segmentation in MRI. Segmentation and electron density map creation added approx. 90 mins to the planning process for each study set. Conclusions: MR-alone bulk density planning appears feasible however, manual segmentation increases the time required for treatment planning. Author Disclosure: G. Perkins: None. M. McGarry: None. R.W. Hammoud: None. S. Divakar: None. M. Riyas: None. T. Torfeh: None. N. Al Hammadi: None.
Poster Viewing Abstract 3359; Table
3360 A Dosimetric Study of Volumetric Modulated Arc Therapy (VMAT) Versus Intensity Modulated Radiation Therapy (IMRT) in LocallyAdvanced Nasopharyngeal Cancer Involving Base of Skull C. Chakkabat, N. Tongtip, N. Amornwichet, and P. Alisanant; King Chulalongkorn Memorial Hospital, Faculty of Medicine Chulalongkorn University, Bangkok, Thailand Purpose/Objective(s): Intensity Modulated Radiation Therapy (IMRT) is widely accepted standard radiation therapy technique for nasopharyngeal cancer. However, IMRT in locally advanced nasopharyngeal cancer involving base of skull is challenging due to difficulty in treatment planning and treatment-related toxicities. Volumetric Modulated Arc Therapy (VMAT), the emerging technique, has been developed with potential benefit of shorter treatment time compared with conventional IMRT technique. The purpose of this study is to compare dosimetric parameters of VMAT versus IMRT focusing on dose to organs at risk and target coverage in nasopharyngeal cancer involving base of skull. Materials/Methods: Nine patients diagnosed locally advanced nasopharyngeal cancer involving base of skull were retrospectively planned using both IMRT (9 fields) and VMAT (3 arcs) techniques. Standard institutional guidelines on target design, plan optimization and critical organ tolerance were applied. Differences of dosimetric parameters between the two techniques were evaluated by paired t-test. Results: IMRT and VMAT techniques demonstrated comparable PTV coverage, each receiving >95% of the prescription dose. There were no significant differences in mean spinal cord maximum dose (43.20 Gy vs 42.59 Gy in IMRT and VMAT, respectively; p Z 0.178), mean optic nerves maximum dose (31.90 Gy vs 32.22 Gy, p Z 0.66) and mean parotid glands dose (Right parotid, 22.58 Gy vs 22.16 Gy; p Z 0.61) (Left parotid, 23.21 Gy vs 23.27 Gy; p Z 0.94) for the both techniques. IMRT showed significantly lower mean maximum brain stem dose (53.13 Gy vs 54.86 Gy, p Z 0.011). VMAT significantly reduced in treatment time (555.36 s VS 79.98 s, p < 0.001) and monitor units (2774.00 vs 799.78, p < 0.001). Conclusions: In locally advanced nasopharyngeal cancer involving base of skull, IMRT and VMAT techniques resulted in comparable outcomes in terms of dosimetry, target volume coverage and sparing organs at risk. Moreover, VMAT offered additional advantages in reduction of treatment time and monitor units. Author Disclosure: C. Chakkabat: None. N. Tongtip: None. N. Amornwichet: None. P. Alisanant: None.
3361 Clinical Impact and Utility of Acuros XB Dose Calculation Algorithm in Lung Stereotactic Body Radiation Therapy R. Clayton,1 H. Liu,1 H. Lau,1 P. Dunscombe,1 Z. Nugent,2 and R. Khan1; 1 Tom Baker Cancer Centre, Calgary, AB, Canada, 2Cancer Care Manitoba, Winnipeg, MB, Canada Purpose/Objective(s): To evaluate the clinical impact of using deterministic dose calculation algorithm, Acuros XB, for early stage lung cancer patients undergoing stereotactic body radiation therapy (SBRT). Materials/Methods: Seventy-seven patients who underwent lung SBRT from 2008 to 2012 at our cancer center were included in this study. All treatment plans were recalculated using anisotropic analytical algorithm (AAA) and Acuros XB algorithms with the same monitor units and beam arrangement as had been previously planned. The dose, dose distribution,
Mean differences in % dose: MR versus CT plan
Technique
PTV mean
PTV max
Bladder mean
Rectum mean
Rectum max
LT femoral head max
RT femoral head max
Small bowel max
4F 6F VMAT
0.53 0.44 0.82
0.56 0.85 0.95
1.27 1.53 1.16
1.04 0.74 1.42
0.66 0.74 0.69
1.73 1.11 1.24
1.36 3.11 3.36
1.26 0.87 1.09
Calculated MUs (CT vs MRI difference %) 1.79 0.23%
Volume 87 Number 2S Supplement 2013 results showed a significant speed up between the automated and manual planning process. Conclusions: Knowledge based system would transform the treatment planning process into a completely automated procedure. This work has the potential to be a promising platform for developing treatment plans and afford a powerful way to reliably automate the treatment planning process. It could have major predictive value to save clinical time in developing a cancer treatment plan. Author Disclosure: H. Wang: None. L. Xing: None.
3359 MRI-Based Radiation Therapy Planning of Prostate Cancer: Clinical Feasibility and Assessment of Dosimetric Accuracy for Different Treatment Techniques G. Perkins, M. McGarry, R.W. Hammoud, S. Divakar, M. Riyas, T. Torfeh, and N. Al Hammadi; Hamad Medical Corporation, DOHA, Qatar Purpose/Objective(s): MRI has been demonstrated to improve radiation therapy target volume delineation in prostate cancer, but has yet to seriously challenge CT as the primary modality for planning due to lack of image electron density information required for dose calculation, as well as potential geometric distortion in the images. To compare the clinical feasibility of MR only dose calculations based on manual segmentation of anatomical structures and bulk electron density assignment based on tissue classification. The dosimetric accuracy when compared to the reference CT dataset was also assessed for 4F, 6F CRT and VMAT planning techniques Materials/Methods: The registered CT-MR-SIM datasets of 10 prostate cancer patients were used in this retrospective study. For each patient, the CTV and PTV were copied from the reference CT onto each registered MR dataset. The external(body), bladder, rectum, small bowel, femoral heads and bone were segmented manually on MR. The addition of electrondensity information to MR images and dose calculation accuracy for 4F, 6F CRT and VMAT planning of the prostate was then quantified by comparing dose distributions created on the bulk-density assigned images with the original CT. Phantom measurements were performed to quantify geometric distortions after application of a gradient distortion correction algorithm for the FOV and the pulse sequence parameters used in this study (T1,T2 FSE, fat suppressed (FS) ‘hybrid’T2/PD FSE, and T1 LAVAFLEX). Results: Mean differences between dose calculation metrics for CT vs MRI were <1% for all three planning techniques and < 1.5% for bladder, rectum and small bowel (Table). For the PTV DVHs the normalized rootmean-square deviation which represents a percentage of similarity between the curves was found to range from 0.985-0.99 (full statistical data to be presented). Differences of up to 3.36% in max dose were seen for the femoral heads. From phantom studies, residual distortions were found to be < 1.0 mm within a 10 cm radius and < 1.5 mm within a 20 cm radius of the scan center for scan length of 15 cm for all sequences. The FS ‘hybrid’ PD/T2 sequence was found to be the most optimal for both organ and bone segmentation in MRI. Segmentation and electron density map creation added approx. 90 mins to the planning process for each study set. Conclusions: MR-alone bulk density planning appears feasible however, manual segmentation increases the time required for treatment planning. Author Disclosure: G. Perkins: None. M. McGarry: None. R.W. Hammoud: None. S. Divakar: None. M. Riyas: None. T. Torfeh: None. N. Al Hammadi: None.
Poster Viewing Abstract 3359; Table
3360 A Dosimetric Study of Volumetric Modulated Arc Therapy (VMAT) Versus Intensity Modulated Radiation Therapy (IMRT) in LocallyAdvanced Nasopharyngeal Cancer Involving Base of Skull C. Chakkabat, N. Tongtip, N. Amornwichet, and P. Alisanant; King Chulalongkorn Memorial Hospital, Faculty of Medicine Chulalongkorn University, Bangkok, Thailand Purpose/Objective(s): Intensity Modulated Radiation Therapy (IMRT) is widely accepted standard radiation therapy technique for nasopharyngeal cancer. However, IMRT in locally advanced nasopharyngeal cancer involving base of skull is challenging due to difficulty in treatment planning and treatment-related toxicities. Volumetric Modulated Arc Therapy (VMAT), the emerging technique, has been developed with potential benefit of shorter treatment time compared with conventional IMRT technique. The purpose of this study is to compare dosimetric parameters of VMAT versus IMRT focusing on dose to organs at risk and target coverage in nasopharyngeal cancer involving base of skull. Materials/Methods: Nine patients diagnosed locally advanced nasopharyngeal cancer involving base of skull were retrospectively planned using both IMRT (9 fields) and VMAT (3 arcs) techniques. Standard institutional guidelines on target design, plan optimization and critical organ tolerance were applied. Differences of dosimetric parameters between the two techniques were evaluated by paired t-test. Results: IMRT and VMAT techniques demonstrated comparable PTV coverage, each receiving >95% of the prescription dose. There were no significant differences in mean spinal cord maximum dose (43.20 Gy vs 42.59 Gy in IMRT and VMAT, respectively; p Z 0.178), mean optic nerves maximum dose (31.90 Gy vs 32.22 Gy, p Z 0.66) and mean parotid glands dose (Right parotid, 22.58 Gy vs 22.16 Gy; p Z 0.61) (Left parotid, 23.21 Gy vs 23.27 Gy; p Z 0.94) for the both techniques. IMRT showed significantly lower mean maximum brain stem dose (53.13 Gy vs 54.86 Gy, p Z 0.011). VMAT significantly reduced in treatment time (555.36 s VS 79.98 s, p < 0.001) and monitor units (2774.00 vs 799.78, p < 0.001). Conclusions: In locally advanced nasopharyngeal cancer involving base of skull, IMRT and VMAT techniques resulted in comparable outcomes in terms of dosimetry, target volume coverage and sparing organs at risk. Moreover, VMAT offered additional advantages in reduction of treatment time and monitor units. Author Disclosure: C. Chakkabat: None. N. Tongtip: None. N. Amornwichet: None. P. Alisanant: None.
3361 Clinical Impact and Utility of Acuros XB Dose Calculation Algorithm in Lung Stereotactic Body Radiation Therapy R. Clayton,1 H. Liu,1 H. Lau,1 P. Dunscombe,1 Z. Nugent,2 and R. Khan1; 1 Tom Baker Cancer Centre, Calgary, AB, Canada, 2Cancer Care Manitoba, Winnipeg, MB, Canada Purpose/Objective(s): To evaluate the clinical impact of using deterministic dose calculation algorithm, Acuros XB, for early stage lung cancer patients undergoing stereotactic body radiation therapy (SBRT). Materials/Methods: Seventy-seven patients who underwent lung SBRT from 2008 to 2012 at our cancer center were included in this study. All treatment plans were recalculated using anisotropic analytical algorithm (AAA) and Acuros XB algorithms with the same monitor units and beam arrangement as had been previously planned. The dose, dose distribution,
Mean differences in % dose: MR versus CT plan
Technique
PTV mean
PTV max
Bladder mean
Rectum mean
Rectum max
LT femoral head max
RT femoral head max
Small bowel max
4F 6F VMAT
0.53 0.44 0.82
0.56 0.85 0.95
1.27 1.53 1.16
1.04 0.74 1.42
0.66 0.74 0.69
1.73 1.11 1.24
1.36 3.11 3.36
1.26 0.87 1.09
Calculated MUs (CT vs MRI difference %) 1.79 0.23%