- Email: [email protected]
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S674
I. J. Radiation Oncology
● Biology ● Physics
Volume 66, Number 3, Supplement, 2006
Materials/Methods: The University of Florida optimized radiation therapy (UFORT) in-house treatment-planning system was commissioned with measured data from Cobalt-60, 6MV, and 18MV beamlets. A total of 25 IMRT cases were studied, including 5 H & N, 5 prostate, 5 lung, and 5 breast, and 5 CNS. Treatment plans using a Cobalt-60 gamma-ray based source were compared with 6MV and 18MV linear-accelerator plans. The IMRT treatment plans were optimized with a convex optimization model that can be solved to optimality without the possibility of trapping in local minima. Plans were generated for all cases with 5, 7, 9, 11, 17, 35 and 71 equispaced cone beams. Helical tomotherapy plans with a pitch of 0.5 were also investigated for the 5 H & N cases. Dose volume histograms (DVH) were used to assess the plan quality using standard clinical dose volume constraints. Results: The same target coverage could be achieved for plans with 5 through 71 beams for all cases. Small variations between the three beam qualities were observed when evaluating plans with standard clinical dose volume constraints on critical structures for all cases studied. Dose to unspecified tissue in the range of 5 to 40 Gy was always lower by 2–7% volume for more penetrating linac beams. Improvements in organ sparing with increasing equidistant beam number were observed for increasing beam number up to 11 beams but yielded marginal improvements for more than 11 beams. Improved tissue sparing at low doses was always observed for prostate cases with increased beam number; however, standard dose volume constraints for targets and critical structures were well below tolerance for all investigated beam numbers. Conclusions: Gamma-ray IMRT produces high quality IMRT treatment plans for integration with on-board real-time MRI. Beam quality and beam number did not have a significant impact on treatment plan quality as assessed by standard clinical dose volume constraints. Author Disclosure: C. Fox, None; D. Aleman, None; H.E. Romeijn, None; J.G. Li, None; J.F. Dempsey, ViewRay, Inc., A. Employment; ViewRay, Inc., E. Ownership Interest.
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IMRT in the Treatment of Anal Cancer: A Dosimetric Comparison of Conventional 3D, IMRT, and IMRT With Integrated Boost
A. Hsu, W. Hara, T. Pawlicki, J. Bazan, A. Koong, K. Goodman Stanford University, Stanford, CA Purpose/Objective(s): We report a dosimetric analysis of IMRT compared to conventional 3D conformal treatment plans for patients with anal cancer. We also explore the feasibility of integrated boost IMRT plans to deliver a higher dose per fraction to the anal canal and lower dose to the pelvic and inguinal nodes. Materials/Methods: 5 patients with T2N0 –1 squamous cell carcinoma of the anal canal were treated with definitive chemoradiotherapy using IMRT plans. Doses ranged from 50 to 55.8Gy, in 25 -31 fractions over 32– 46 days, with most patients receiving 5FU and mitomycin C (1 patient received cisplatin/FU). All patients underwent CT simulation with custom immobilization and IV contrast. Target volumes were standardized for all patients with PTV defined as the CTV with 1.5cm margin. For each patient, an AP/PA with inguinal electrons, 4-field, 7-field IMRT, and 7-field IMRT integrated boost (IB) plan were created using the Eclipse treatment planning system. 54Gy was prescribed to the primary, and the nodes were prescribed 45Gy (integrated boost: PTV 50Gy/25 fractions and nodes 45Gy/25 fractions). We created an IMRT template using 7 equally spaced co-planar 15MV beams, with each plan then individually optimized. Dose constraints were femoral heads V45⬍1%, bladder V40⬍50%, and bowel V45⬍5%. The IMRT plans were normalized to D95, and all 3D plans were normalized to the isocenter. Results: The IMRT plans improved the dose conformality around the PTV and pelvic lymph nodes, keeping Dmax within the PTV and was particularly helpful for inguinal lymph nodes coverage with a ⬎25% improvement. IMRT plans greatly improved tissue sparing for critical normal structures including the bladder, femoral heads and bowel. Mean bladder dose decreased 59 – 65%, femoral head dose by 3–22%, and bowel dose by 27–38%. The low dose to bone marrow was similar for the different plans. PTV coverage and tissue sparing appeared to be equivalent between standard and integrated boost plans. Conclusions: IMRT is better than 3D conformal for the treatment of patients with anal cancer undergoing definitive chemoradiotherapy with marked improvements in inguinal lymph node coverage as well as normal tissue sparing. The integrated boost technique for anal cancer allows normal tissue sparing while minimizing treatment duration and may translate to increased biologic effectiveness. Further study is necessary to determine if improvements in dose delivery translate to improved clinical outcome and decreased acute and late morbidity. Table 1: Dose volume results for critical structures Volume Below the Prescription Dose* Goal (Gy) PTV Pelvic LN Inguinal LN Dmax (Gy) Bladder Femoral Heads Bowel Bone Marrow
AP/PA (%)
4 Field (%)
54 (50 IB) 1.8 ⫾ 3.4 4.4 ⫾ 1.3 45 23.7 ⫾ 3.2 17.4 ⫾ 3.5 45 36.3 ⫾ 32.2 27.0⫾10.1 Global Maxium Dose for each plan 61.09 ⫾ 0.87 57.66 ⫾ 0.69 Volume Above the Dose Constraint Goal 40 100.0 ⫾ 0.0 99.2 ⫾ 0.0 45 3.1 ⫾ 4.7 22.4 ⫾ 13.2 45 39.1 ⫾ 15.8 30.8 ⫾ 16.5 20 65.4 ⫾ 3.5 67.2 ⫾ 24.0
IMRT 7 field (%)
IMRT IB (%)
4.3 ⫾ 0.1 20.5 ⫾ 4.3 0.8 ⫾ 0.8
5.1 ⫾ 0.1 8.8 ⫾ 3.2 2.0 ⫾ 0.6
57.11 ⫾ 0.43
52.73 ⫾ 0.35
40.6 ⫾ 10.5 0.0 ⫾ 0.0 1.0 ⫾ 2.1 77.2 ⫾ 0.3
35.3 ⫾ 2.1 0.0 ⫾ 0.0 3.5 ⫾ 3.9 77.1 ⫾ 1.4
*Mean ⫾ Standard Deviation, IB ⫽ Integrated Boost.
Author Disclosure: A. Hsu, None; W. Hara, None; T. Pawlicki, None; J. Bazan, None; A. Koong, None; K. Goodman, None.
I. J. Radiation Oncology
● Biology ● Physics
Volume 66, Number 3, Supplement, 2006
Materials/Methods: The University of Florida optimized radiation therapy (UFORT) in-house treatment-planning system was commissioned with measured data from Cobalt-60, 6MV, and 18MV beamlets. A total of 25 IMRT cases were studied, including 5 H & N, 5 prostate, 5 lung, and 5 breast, and 5 CNS. Treatment plans using a Cobalt-60 gamma-ray based source were compared with 6MV and 18MV linear-accelerator plans. The IMRT treatment plans were optimized with a convex optimization model that can be solved to optimality without the possibility of trapping in local minima. Plans were generated for all cases with 5, 7, 9, 11, 17, 35 and 71 equispaced cone beams. Helical tomotherapy plans with a pitch of 0.5 were also investigated for the 5 H & N cases. Dose volume histograms (DVH) were used to assess the plan quality using standard clinical dose volume constraints. Results: The same target coverage could be achieved for plans with 5 through 71 beams for all cases. Small variations between the three beam qualities were observed when evaluating plans with standard clinical dose volume constraints on critical structures for all cases studied. Dose to unspecified tissue in the range of 5 to 40 Gy was always lower by 2–7% volume for more penetrating linac beams. Improvements in organ sparing with increasing equidistant beam number were observed for increasing beam number up to 11 beams but yielded marginal improvements for more than 11 beams. Improved tissue sparing at low doses was always observed for prostate cases with increased beam number; however, standard dose volume constraints for targets and critical structures were well below tolerance for all investigated beam numbers. Conclusions: Gamma-ray IMRT produces high quality IMRT treatment plans for integration with on-board real-time MRI. Beam quality and beam number did not have a significant impact on treatment plan quality as assessed by standard clinical dose volume constraints. Author Disclosure: C. Fox, None; D. Aleman, None; H.E. Romeijn, None; J.G. Li, None; J.F. Dempsey, ViewRay, Inc., A. Employment; ViewRay, Inc., E. Ownership Interest.
2826
IMRT in the Treatment of Anal Cancer: A Dosimetric Comparison of Conventional 3D, IMRT, and IMRT With Integrated Boost
A. Hsu, W. Hara, T. Pawlicki, J. Bazan, A. Koong, K. Goodman Stanford University, Stanford, CA Purpose/Objective(s): We report a dosimetric analysis of IMRT compared to conventional 3D conformal treatment plans for patients with anal cancer. We also explore the feasibility of integrated boost IMRT plans to deliver a higher dose per fraction to the anal canal and lower dose to the pelvic and inguinal nodes. Materials/Methods: 5 patients with T2N0 –1 squamous cell carcinoma of the anal canal were treated with definitive chemoradiotherapy using IMRT plans. Doses ranged from 50 to 55.8Gy, in 25 -31 fractions over 32– 46 days, with most patients receiving 5FU and mitomycin C (1 patient received cisplatin/FU). All patients underwent CT simulation with custom immobilization and IV contrast. Target volumes were standardized for all patients with PTV defined as the CTV with 1.5cm margin. For each patient, an AP/PA with inguinal electrons, 4-field, 7-field IMRT, and 7-field IMRT integrated boost (IB) plan were created using the Eclipse treatment planning system. 54Gy was prescribed to the primary, and the nodes were prescribed 45Gy (integrated boost: PTV 50Gy/25 fractions and nodes 45Gy/25 fractions). We created an IMRT template using 7 equally spaced co-planar 15MV beams, with each plan then individually optimized. Dose constraints were femoral heads V45⬍1%, bladder V40⬍50%, and bowel V45⬍5%. The IMRT plans were normalized to D95, and all 3D plans were normalized to the isocenter. Results: The IMRT plans improved the dose conformality around the PTV and pelvic lymph nodes, keeping Dmax within the PTV and was particularly helpful for inguinal lymph nodes coverage with a ⬎25% improvement. IMRT plans greatly improved tissue sparing for critical normal structures including the bladder, femoral heads and bowel. Mean bladder dose decreased 59 – 65%, femoral head dose by 3–22%, and bowel dose by 27–38%. The low dose to bone marrow was similar for the different plans. PTV coverage and tissue sparing appeared to be equivalent between standard and integrated boost plans. Conclusions: IMRT is better than 3D conformal for the treatment of patients with anal cancer undergoing definitive chemoradiotherapy with marked improvements in inguinal lymph node coverage as well as normal tissue sparing. The integrated boost technique for anal cancer allows normal tissue sparing while minimizing treatment duration and may translate to increased biologic effectiveness. Further study is necessary to determine if improvements in dose delivery translate to improved clinical outcome and decreased acute and late morbidity. Table 1: Dose volume results for critical structures Volume Below the Prescription Dose* Goal (Gy) PTV Pelvic LN Inguinal LN Dmax (Gy) Bladder Femoral Heads Bowel Bone Marrow
AP/PA (%)
4 Field (%)
54 (50 IB) 1.8 ⫾ 3.4 4.4 ⫾ 1.3 45 23.7 ⫾ 3.2 17.4 ⫾ 3.5 45 36.3 ⫾ 32.2 27.0⫾10.1 Global Maxium Dose for each plan 61.09 ⫾ 0.87 57.66 ⫾ 0.69 Volume Above the Dose Constraint Goal 40 100.0 ⫾ 0.0 99.2 ⫾ 0.0 45 3.1 ⫾ 4.7 22.4 ⫾ 13.2 45 39.1 ⫾ 15.8 30.8 ⫾ 16.5 20 65.4 ⫾ 3.5 67.2 ⫾ 24.0
IMRT 7 field (%)
IMRT IB (%)
4.3 ⫾ 0.1 20.5 ⫾ 4.3 0.8 ⫾ 0.8
5.1 ⫾ 0.1 8.8 ⫾ 3.2 2.0 ⫾ 0.6
57.11 ⫾ 0.43
52.73 ⫾ 0.35
40.6 ⫾ 10.5 0.0 ⫾ 0.0 1.0 ⫾ 2.1 77.2 ⫾ 0.3
35.3 ⫾ 2.1 0.0 ⫾ 0.0 3.5 ⫾ 3.9 77.1 ⫾ 1.4
*Mean ⫾ Standard Deviation, IB ⫽ Integrated Boost.
Author Disclosure: A. Hsu, None; W. Hara, None; T. Pawlicki, None; J. Bazan, None; A. Koong, None; K. Goodman, None.