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OC-0483 A PLANNING COMPARISON OF INTENSITY-MODULATED RADIOTHERAPY TECHNIQUES FOR LEFT-SIDED BREAST CANCER
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ESTRO 31
and delivered the least amount of MU. For intermediate OAR doses, fIMRT and RA both had the advantage over h-IMRT, with f-IMRT being superior to RA, but it did deliver more than twice as many MU. Overall, h-IMRT was the preferable technique, but if it does not achieve enough sparing of heart and LAD, f-IMRT should be considered.
POSTER DISCUSSION: 10: MOTION MANAGEMENT
Conclusions: Preliminary results show that the IMRT BH technique results in a lower dose to the heart as well as to the LAD, while the dose in the lung and PTV trim is comparable. The mean number of monitor units is lower in the IMRT plans. Therefore, it seems preferable to use a breath hold IMRT technique in patients with radiation treatment for left sided breast conserving radiotherapy. OC-0483 A PLANNING COMPARISON OF INTENSITY-MODULATED RADIOTHERAPY TECHNIQUES FOR LEFT-SIDED BREAST CANCER M. Jeulink1, M. Dahele1, B.J. Slotman1, W.F.A.R. Verbakel1 1 VU University Medical Center, Radiotherapy, Amsterdam, The Netherlands Purpose/Objective: Irradiation of normal organs during breast radiotherapy may increase the risk of contra-lateral (CL) breast cancer and late cardiac toxicity, especially in left-sided breast irradiation with medially located boost. In this planning study we evaluated three IMRT techniques for their ability to deliver homogenous breast doses, a simultaneous integrated boost and organ at risk (OAR) sparing. Materials and Methods: Previously contoured CT scans (free-breathing 2,5mm slice thickness) from 7 patients with left-sided breast tumors, and a challenging, medially located boost volume were selected. Mean elective breast and boost PTV volumes were 728 (SD=554) and 83 (SD=52) cc, respectively. A dose of 15 fractions of 2.67 Gy was prescribed to the elective PTV (e-PTV) and 15x3.35 Gy to the boost PTV (b-PTV). Plans were normalized to deliver the elective prescription dose to 70% of e-PTV. The following plans (Eclipse, Varian Medical Systems) were created for each patient using 6MV photons at 600 MU/minute dose rate: (a) hybrid-IMRT (h-IMRT, 2 tangential open fields delivering 85% of breast dose and 4 IMRT fields: 2 tangential and 2 directed only at b-PTV), (b) full-IMRT (f-IMRT, 7 co-planar IMRT fields positioned approximately equidistant around the left breast from 300 to 140º), and (c) RapidArc (RA v10, 2 partial arcs, each irradiating between 290-305 and 160º). The same planning objectives and priorities were used for f-IMRT and RA plans. A range of OAR constraints (from high to low dose) were set on heart, CL breast, ipsilateral (IL) and CL lung. A maximum dose constraint was set on left anterior descending coronary artery (LAD) plus 3 mm. PTV and OAR metrics were compared. Results: For each technique the average of all 7 plans is presented in the table. For all three techniques, both PTV mean doses were comparable. Compared with f-IMRT, h-IMRT better spared LAD+3mm V20 in 2/7 patients. If h-IMRT could not adequately spare the LAD, fIMRT typically performed better than RA in terms of PTV coverage and OAR sparing. Metric e-PTV V95 (%) e-PTV V105 (%) b-PTV V95 (%) b-PTV V107 (%) Heart V20 (%) Heart V5 (%) LAD+3mm V30 (cc) IL-Lung V20 (%) IL-Lung V5 (%) CL-Lung Dmean (cGy) CL-Breast V5 (%) CL-Breast V2 (%) Monitor Units (MU)
h-IMRT 98,3 8 97,2 0 3,2 30,7 2,4 12,1 26,9 64,8 1,9 9,2 740
f-IMRT RA 96,5 93,2 22,8 21,8 94,7 88,3 0,6 4,6 2,1 1,9 33,4 37,1 0,2 0,4 7,1 9,5 35,2 40,4 131,1 178,4 4,5 7,1 23,1 49,8 1647 745
Conclusions: On average, h-IMRT provided the best coverage and homogeneity for elective and boost PTV, best low-dose OAR sparing,
PD-0484 INITIAL CLINICAL ASSESSMENT OF A GIMBALED LINAC TUMOR TRACKING SYSTEM IN A PATIENT SIMULATION STUDY T. Depuydt1, K. Poels1, B. Engels1, C. Haverbeke1, T. Gevaert1, G. Van Gompel2, N. Buls2, F. Vandenbroucke2, D. Verellen1, M. De Ridder1 1 UZ Brussel Vrije Universiteit Brussel, Radiotherapy department, Brussels, Belgium 2 UZ Brussel Vrije Universiteit Brussel, Radiology department, Brussels, Belgium Purpose/Objective: Recently the Vero SBRT system at UZ Brussels has been equipped with a first version of a clinical tumor tracking system. A simulation study was conducted on patients to evaluate the workflow and quantify the performance of the tracking system in clinical circumstances. Materials and Methods: The Vero system has an O-ring gantry equipped with a 6 MV linac. Two orthogonal gimbals hold the linacMLC assembly, allowing pan and tilt motions of the therapeutic beam. This mechanism enables tracking of moving tumors, decoupled from the DMLC intensity modulation of the dose. The maximum excursion of the beam axis is 4.4 cm in both directions. Two kV imaging systems are attached at ±45° from the MV beam allowing simultaneous orthogonal X-rays and fluoroscopy. Infra-red (IR) skin marker optical tracking is also integrated into the Vero system. To evaluate the dynamic tracking workflow and quantify its performance, a simulation study was conducted on 5 lung and liver patients. The procedure involved quantification of tumor motion based on stereoscopic fluoroscopy and automatic detection of a Visicoil gold marker implanted in the tumor. Additionally the entire tumor tracking workflow was executed involving patient positioning, synchronized acquisition of skin marker motion and X-ray fluoroscopy, fiducial marker detection, external-internal correlation model calculation, skin marker surrogate guided gimbals tracking and X-ray monitoring. The complete tracking workflow was carried out, except for switching on the 6 MV treatment beam. The tracking error was calculated from the gimbals log-files and the acquired monitoring X-rays during tracking. Additional imaging dose was measured with TLD on phantoms and on the patients. Results: The tumor motion ranged from 5.9 mm to 14.2 mm. Imaging skin dose was 0.08 mGy/image (SSD=900 mm, E=120 kVp, Itube=100 mA, tpulse=5 ms). Imaging for correlation model building required on average 220 monitoring X-ray stereo image pairs in 20 seconds, which resulted in 17.6 mGy skin dose. Taking the MU’s from a 3 x 20 Gy lung SBRT treatment, on average 3000 MU, and a dose rate of 500 MU/min, depending on the treatment fields orientation an additional maximal exposure of 28.8 mGy was estimated for acquiring 1 Hz X-ray monitoring during tracking. A mean absolute tracking error of 1.1 mm was measured, with a 90% percentile (E90%) of 2.1 mm. The time to set up a tracking treatment from the patient entering the room to the first MV beam-on was 9 min on average. From the acquisition of the modeling fluoroscopy sequence up to beam-on took 3 min. Conclusions: A clinical version of the Vero tumor tracking system has been installed, including automatic detection of fiducial markers implanted in the tumor. An initial assessment has shown that the tracking system is functional and its performance adequate to move forward to final commissioning and initiation of patient treatments.
ESTRO 31
and delivered the least amount of MU. For intermediate OAR doses, fIMRT and RA both had the advantage over h-IMRT, with f-IMRT being superior to RA, but it did deliver more than twice as many MU. Overall, h-IMRT was the preferable technique, but if it does not achieve enough sparing of heart and LAD, f-IMRT should be considered.
POSTER DISCUSSION: 10: MOTION MANAGEMENT
Conclusions: Preliminary results show that the IMRT BH technique results in a lower dose to the heart as well as to the LAD, while the dose in the lung and PTV trim is comparable. The mean number of monitor units is lower in the IMRT plans. Therefore, it seems preferable to use a breath hold IMRT technique in patients with radiation treatment for left sided breast conserving radiotherapy. OC-0483 A PLANNING COMPARISON OF INTENSITY-MODULATED RADIOTHERAPY TECHNIQUES FOR LEFT-SIDED BREAST CANCER M. Jeulink1, M. Dahele1, B.J. Slotman1, W.F.A.R. Verbakel1 1 VU University Medical Center, Radiotherapy, Amsterdam, The Netherlands Purpose/Objective: Irradiation of normal organs during breast radiotherapy may increase the risk of contra-lateral (CL) breast cancer and late cardiac toxicity, especially in left-sided breast irradiation with medially located boost. In this planning study we evaluated three IMRT techniques for their ability to deliver homogenous breast doses, a simultaneous integrated boost and organ at risk (OAR) sparing. Materials and Methods: Previously contoured CT scans (free-breathing 2,5mm slice thickness) from 7 patients with left-sided breast tumors, and a challenging, medially located boost volume were selected. Mean elective breast and boost PTV volumes were 728 (SD=554) and 83 (SD=52) cc, respectively. A dose of 15 fractions of 2.67 Gy was prescribed to the elective PTV (e-PTV) and 15x3.35 Gy to the boost PTV (b-PTV). Plans were normalized to deliver the elective prescription dose to 70% of e-PTV. The following plans (Eclipse, Varian Medical Systems) were created for each patient using 6MV photons at 600 MU/minute dose rate: (a) hybrid-IMRT (h-IMRT, 2 tangential open fields delivering 85% of breast dose and 4 IMRT fields: 2 tangential and 2 directed only at b-PTV), (b) full-IMRT (f-IMRT, 7 co-planar IMRT fields positioned approximately equidistant around the left breast from 300 to 140º), and (c) RapidArc (RA v10, 2 partial arcs, each irradiating between 290-305 and 160º). The same planning objectives and priorities were used for f-IMRT and RA plans. A range of OAR constraints (from high to low dose) were set on heart, CL breast, ipsilateral (IL) and CL lung. A maximum dose constraint was set on left anterior descending coronary artery (LAD) plus 3 mm. PTV and OAR metrics were compared. Results: For each technique the average of all 7 plans is presented in the table. For all three techniques, both PTV mean doses were comparable. Compared with f-IMRT, h-IMRT better spared LAD+3mm V20 in 2/7 patients. If h-IMRT could not adequately spare the LAD, fIMRT typically performed better than RA in terms of PTV coverage and OAR sparing. Metric e-PTV V95 (%) e-PTV V105 (%) b-PTV V95 (%) b-PTV V107 (%) Heart V20 (%) Heart V5 (%) LAD+3mm V30 (cc) IL-Lung V20 (%) IL-Lung V5 (%) CL-Lung Dmean (cGy) CL-Breast V5 (%) CL-Breast V2 (%) Monitor Units (MU)
h-IMRT 98,3 8 97,2 0 3,2 30,7 2,4 12,1 26,9 64,8 1,9 9,2 740
f-IMRT RA 96,5 93,2 22,8 21,8 94,7 88,3 0,6 4,6 2,1 1,9 33,4 37,1 0,2 0,4 7,1 9,5 35,2 40,4 131,1 178,4 4,5 7,1 23,1 49,8 1647 745
Conclusions: On average, h-IMRT provided the best coverage and homogeneity for elective and boost PTV, best low-dose OAR sparing,
PD-0484 INITIAL CLINICAL ASSESSMENT OF A GIMBALED LINAC TUMOR TRACKING SYSTEM IN A PATIENT SIMULATION STUDY T. Depuydt1, K. Poels1, B. Engels1, C. Haverbeke1, T. Gevaert1, G. Van Gompel2, N. Buls2, F. Vandenbroucke2, D. Verellen1, M. De Ridder1 1 UZ Brussel Vrije Universiteit Brussel, Radiotherapy department, Brussels, Belgium 2 UZ Brussel Vrije Universiteit Brussel, Radiology department, Brussels, Belgium Purpose/Objective: Recently the Vero SBRT system at UZ Brussels has been equipped with a first version of a clinical tumor tracking system. A simulation study was conducted on patients to evaluate the workflow and quantify the performance of the tracking system in clinical circumstances. Materials and Methods: The Vero system has an O-ring gantry equipped with a 6 MV linac. Two orthogonal gimbals hold the linacMLC assembly, allowing pan and tilt motions of the therapeutic beam. This mechanism enables tracking of moving tumors, decoupled from the DMLC intensity modulation of the dose. The maximum excursion of the beam axis is 4.4 cm in both directions. Two kV imaging systems are attached at ±45° from the MV beam allowing simultaneous orthogonal X-rays and fluoroscopy. Infra-red (IR) skin marker optical tracking is also integrated into the Vero system. To evaluate the dynamic tracking workflow and quantify its performance, a simulation study was conducted on 5 lung and liver patients. The procedure involved quantification of tumor motion based on stereoscopic fluoroscopy and automatic detection of a Visicoil gold marker implanted in the tumor. Additionally the entire tumor tracking workflow was executed involving patient positioning, synchronized acquisition of skin marker motion and X-ray fluoroscopy, fiducial marker detection, external-internal correlation model calculation, skin marker surrogate guided gimbals tracking and X-ray monitoring. The complete tracking workflow was carried out, except for switching on the 6 MV treatment beam. The tracking error was calculated from the gimbals log-files and the acquired monitoring X-rays during tracking. Additional imaging dose was measured with TLD on phantoms and on the patients. Results: The tumor motion ranged from 5.9 mm to 14.2 mm. Imaging skin dose was 0.08 mGy/image (SSD=900 mm, E=120 kVp, Itube=100 mA, tpulse=5 ms). Imaging for correlation model building required on average 220 monitoring X-ray stereo image pairs in 20 seconds, which resulted in 17.6 mGy skin dose. Taking the MU’s from a 3 x 20 Gy lung SBRT treatment, on average 3000 MU, and a dose rate of 500 MU/min, depending on the treatment fields orientation an additional maximal exposure of 28.8 mGy was estimated for acquiring 1 Hz X-ray monitoring during tracking. A mean absolute tracking error of 1.1 mm was measured, with a 90% percentile (E90%) of 2.1 mm. The time to set up a tracking treatment from the patient entering the room to the first MV beam-on was 9 min on average. From the acquisition of the modeling fluoroscopy sequence up to beam-on took 3 min. Conclusions: A clinical version of the Vero tumor tracking system has been installed, including automatic detection of fiducial markers implanted in the tumor. An initial assessment has shown that the tracking system is functional and its performance adequate to move forward to final commissioning and initiation of patient treatments.