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PO-0784 ASSESSING SYSTEMATIC AND RANDOM COMPONENTS OF INTRAFRACTION MOTION DURING IGRT FOR PROSTATE CANCER
S304
ESTRO 31
Antero-Posterior
Supero-Inferior Lateral
PTV margin (mm) RANDO SYSTEMI M C ERROR Stroo Van σ ERROR Her (∑) m (σ) k (S) (VH) 3. WB 2.1 0.9 3.3 3.7 5 3. SKULL 2.2 1.1 3.7 4.3 5 MANDIBL 3. 2.5 1.5 4.8 5.5 E 7 3. C1-2 2.9 1.5 5 5.8 4 3. C3-5 2.6 1.8 5.4 6.3 4 7. C6-T1 3.3 2 6.3 7.3 3 4. HYOID 2.9 2 6 7 8
PTV
ROIs
∑
1 1. 3 1. 4 1. 4 1. 4 2. 4 2. 4
PTV σ
S
5
∑
VH
4.5 5 5.7
5.4 6.1 5.2 5.9 5.2 5.9
Rotatio n (degree )
1. 5 1. 7 1. 7 1. 8 1. 9 4. 9
9. 11. 9 1 8. 9.4 2 2
0. 6 1. 2 0. 9 0. 9 1. 6 0. 2 0. 9
σ S
VH
2. 3 3. 6
2. 6 4. 2 3. 4 3. 5 5. 3 8. 4 3. 7
3 3. 1 4. 5 7. 4 3. 2
∑
0.9 0.5 1.1 0.8 1.8 0.9 1.6 0.7 1.7 0.9 1.9 0.9 2.6 1.2
Conclusions: Due to feasibility of online corrections, margins are being reduced for patients of head neck cancer. However in absence of image guidance or unavailability of online correction margin of upto 5 mm may be adequate for tumors upto C2 regiond and 7-10 mm may be required for tumors of neck region. Better methods of immobilizing C6-T1 region and accounting for internal motion of hyoid needs to be addressed. PO-0784 ASSESSING SYSTEMATIC AND RANDOM COMPONENTS OF INTRAFRACTION MOTION DURING IGRT FOR PROSTATE CANCER 1 1 2 2 1 M. Källi , C. Italia , S. Andreoli , P. Colleoni , F. Filippone , M. Fortunato2, G. Gritti1, L. Maffioletti1, F. Piccoli1, C. Fiorino3 1 Ospedali Riuniti di Bergamo, Radioterapia Oncologica, Bergamo, Italy 2 Ospedali Riuniti di Bergamo, Fisica Sanitaria, Bergamo, Italy 3 IRCCS H. S.Raffaele, Fisica Sanitaria, Milano, Italy Purpose/Objective: To evaluate intrafraction prostate movements in IGRT prostate treatment using daily 'intrafield' shift measurements of implanted gold markers in order to define CTV-PTV margins. Materials and Methods: Forty prostate cancer patients underwent fiducial markers implant in prostate gland: three gold markers were implanted under transrectal ultrasound guidance. 3D-CRT imageguided radiation therapy (IGRT) was planned and delivered. All patients were treated with four 15 MV fields up to 78 Gy, in the supine position with a headrest, ankle and knee support. For daily position verification and correction, two orthogonal EPID images (0°90°) were taken to calculate couch shifts. For every patient, during three periods (1st to 5th, 21st to 25th and 33rd to 37th fractions), 'intrafield' movements were evaluated for all treatment fields by EPID in cine-acquisition modality (about 4 to 10 image-shots per field). The manual matching between the DRR and every image-shot EPID acquisition was performed offline by radiation oncologists. The shifts between the images taken during treatment and the initial set-up images were assessed: for each fraction and field, the mean deviation and its SD were calculated for each direction (right-left RL, anteriorposterior AP, cranial-caudal CC), assessing in this way systematic and random components of intra-fraction motion. The overall population mean set-up error (M), the population systematic (Σ) and random (σ) SDs of intrafraction motion were then assessed; Van Herk formula (2.5·Σ+0.7·σ) was finally applied to determine CTV-PTV margins for intrafraction uncertainties. The statistical correlation among the three periods of EPID 'intrafield' verification were also evaluated. Results: A summary of results is shown in the table. A total of 600 fractions, 2400 treatment fields and about 17000 image-shots were examined. The overall population mean set-up error proved less than 1 mm. Systematic and random errors were about 1.0 and 1.3 mm, respectively. Calculated CTV-PTV margins resulted 3.1 mm for R-L, 3.7 mm for A-P and 3.5 mm for C-C direction.
Conclusions: The impact of intrafraction prostate motion can be well described by repeated cine-EPID acquisition. In this way, systematic and random components may be assessed and reliable intrafraction margins can be estimated. Our results suggest that margins for intrafraction uncertainties around 3-4 mm should be appropriate. PO-0785 VARIABILITY OF MR BASED PROSTATE DELINEATION; A MULTI-CENTER,OBSERVER, AND -SCANNER STUDY T. Nyholm1, J. Jonsson1, C. Behrens2, P. Geertsen2, S. Hanvey3, A. Sadozye4, H. McCallum5, J. Frew6, G. Frykholm7, B. Zackrisson7 1 Umeå University, Radiation sciences, Umeå, Sweden 2 Herlev University Hospital, Department of Oncology, Herlev, Denmark 3 Beatson West of Scotland Cancer Centre, Department of Clinical Physics and Bioengineering, Glasgow, United Kingdom 4 Beatson West of Scotland Cancer Centre, Department of Clinical Oncology, Glasgow, United Kingdom 5 Newcastle General Hospital, Regional Medical Physics Department, Newcastle, United Kingdom 6 Newcastle General Hospital, ncct, Newcastle, United Kingdom 7 Karolinska University Hospital, Department of Oncology, Solna, Sweden Purpose/Objective: The use of MRI as part of the standard clinical workflow in radiotherapy is steadily increasing. The most common practice is to use MR information as compliment to CT in the target definition process, but it may also be possible to completely replace the CT for some diagnoses. The aim of the present multi-center study was to evaluate the variability of prostate and seminal vesicle delineations based on MR information, and its dependence on MR scanner and sequence. Materials and Methods: 5 clinics were part of the study, all already using or about to start using MR as a standard imaging modality for delineation. Each clinic contributed with MR data sets for 5 consecutive prostate patients, acquired with the standard clinical sequence used for target delineation at each site. Two physicians from each site, used to MRI information for target definition, delineated the prostate gland and the vesicles on all 25 patients. In total 250 delineations were analyzed, representing 25 patients, 5 radiotherapy clinics, 5 different imaging sequences, 3 different MR vendors, and 1, 1.5 and 3T scanners. The variability was analyzed in 8 directions: right, left, anterior, posterior, superior, inferior, right-posterior and left-posterior (fig 1), and in terms of volume. All distances were defined as the average distance over a 40 degree solid angle from the center of gravity to the border (fig 1). Results:
ESTRO 31
Antero-Posterior
Supero-Inferior Lateral
PTV margin (mm) RANDO SYSTEMI M C ERROR Stroo Van σ ERROR Her (∑) m (σ) k (S) (VH) 3. WB 2.1 0.9 3.3 3.7 5 3. SKULL 2.2 1.1 3.7 4.3 5 MANDIBL 3. 2.5 1.5 4.8 5.5 E 7 3. C1-2 2.9 1.5 5 5.8 4 3. C3-5 2.6 1.8 5.4 6.3 4 7. C6-T1 3.3 2 6.3 7.3 3 4. HYOID 2.9 2 6 7 8
PTV
ROIs
∑
1 1. 3 1. 4 1. 4 1. 4 2. 4 2. 4
PTV σ
S
5
∑
VH
4.5 5 5.7
5.4 6.1 5.2 5.9 5.2 5.9
Rotatio n (degree )
1. 5 1. 7 1. 7 1. 8 1. 9 4. 9
9. 11. 9 1 8. 9.4 2 2
0. 6 1. 2 0. 9 0. 9 1. 6 0. 2 0. 9
σ S
VH
2. 3 3. 6
2. 6 4. 2 3. 4 3. 5 5. 3 8. 4 3. 7
3 3. 1 4. 5 7. 4 3. 2
∑
0.9 0.5 1.1 0.8 1.8 0.9 1.6 0.7 1.7 0.9 1.9 0.9 2.6 1.2
Conclusions: Due to feasibility of online corrections, margins are being reduced for patients of head neck cancer. However in absence of image guidance or unavailability of online correction margin of upto 5 mm may be adequate for tumors upto C2 regiond and 7-10 mm may be required for tumors of neck region. Better methods of immobilizing C6-T1 region and accounting for internal motion of hyoid needs to be addressed. PO-0784 ASSESSING SYSTEMATIC AND RANDOM COMPONENTS OF INTRAFRACTION MOTION DURING IGRT FOR PROSTATE CANCER 1 1 2 2 1 M. Källi , C. Italia , S. Andreoli , P. Colleoni , F. Filippone , M. Fortunato2, G. Gritti1, L. Maffioletti1, F. Piccoli1, C. Fiorino3 1 Ospedali Riuniti di Bergamo, Radioterapia Oncologica, Bergamo, Italy 2 Ospedali Riuniti di Bergamo, Fisica Sanitaria, Bergamo, Italy 3 IRCCS H. S.Raffaele, Fisica Sanitaria, Milano, Italy Purpose/Objective: To evaluate intrafraction prostate movements in IGRT prostate treatment using daily 'intrafield' shift measurements of implanted gold markers in order to define CTV-PTV margins. Materials and Methods: Forty prostate cancer patients underwent fiducial markers implant in prostate gland: three gold markers were implanted under transrectal ultrasound guidance. 3D-CRT imageguided radiation therapy (IGRT) was planned and delivered. All patients were treated with four 15 MV fields up to 78 Gy, in the supine position with a headrest, ankle and knee support. For daily position verification and correction, two orthogonal EPID images (0°90°) were taken to calculate couch shifts. For every patient, during three periods (1st to 5th, 21st to 25th and 33rd to 37th fractions), 'intrafield' movements were evaluated for all treatment fields by EPID in cine-acquisition modality (about 4 to 10 image-shots per field). The manual matching between the DRR and every image-shot EPID acquisition was performed offline by radiation oncologists. The shifts between the images taken during treatment and the initial set-up images were assessed: for each fraction and field, the mean deviation and its SD were calculated for each direction (right-left RL, anteriorposterior AP, cranial-caudal CC), assessing in this way systematic and random components of intra-fraction motion. The overall population mean set-up error (M), the population systematic (Σ) and random (σ) SDs of intrafraction motion were then assessed; Van Herk formula (2.5·Σ+0.7·σ) was finally applied to determine CTV-PTV margins for intrafraction uncertainties. The statistical correlation among the three periods of EPID 'intrafield' verification were also evaluated. Results: A summary of results is shown in the table. A total of 600 fractions, 2400 treatment fields and about 17000 image-shots were examined. The overall population mean set-up error proved less than 1 mm. Systematic and random errors were about 1.0 and 1.3 mm, respectively. Calculated CTV-PTV margins resulted 3.1 mm for R-L, 3.7 mm for A-P and 3.5 mm for C-C direction.
Conclusions: The impact of intrafraction prostate motion can be well described by repeated cine-EPID acquisition. In this way, systematic and random components may be assessed and reliable intrafraction margins can be estimated. Our results suggest that margins for intrafraction uncertainties around 3-4 mm should be appropriate. PO-0785 VARIABILITY OF MR BASED PROSTATE DELINEATION; A MULTI-CENTER,OBSERVER, AND -SCANNER STUDY T. Nyholm1, J. Jonsson1, C. Behrens2, P. Geertsen2, S. Hanvey3, A. Sadozye4, H. McCallum5, J. Frew6, G. Frykholm7, B. Zackrisson7 1 Umeå University, Radiation sciences, Umeå, Sweden 2 Herlev University Hospital, Department of Oncology, Herlev, Denmark 3 Beatson West of Scotland Cancer Centre, Department of Clinical Physics and Bioengineering, Glasgow, United Kingdom 4 Beatson West of Scotland Cancer Centre, Department of Clinical Oncology, Glasgow, United Kingdom 5 Newcastle General Hospital, Regional Medical Physics Department, Newcastle, United Kingdom 6 Newcastle General Hospital, ncct, Newcastle, United Kingdom 7 Karolinska University Hospital, Department of Oncology, Solna, Sweden Purpose/Objective: The use of MRI as part of the standard clinical workflow in radiotherapy is steadily increasing. The most common practice is to use MR information as compliment to CT in the target definition process, but it may also be possible to completely replace the CT for some diagnoses. The aim of the present multi-center study was to evaluate the variability of prostate and seminal vesicle delineations based on MR information, and its dependence on MR scanner and sequence. Materials and Methods: 5 clinics were part of the study, all already using or about to start using MR as a standard imaging modality for delineation. Each clinic contributed with MR data sets for 5 consecutive prostate patients, acquired with the standard clinical sequence used for target delineation at each site. Two physicians from each site, used to MRI information for target definition, delineated the prostate gland and the vesicles on all 25 patients. In total 250 delineations were analyzed, representing 25 patients, 5 radiotherapy clinics, 5 different imaging sequences, 3 different MR vendors, and 1, 1.5 and 3T scanners. The variability was analyzed in 8 directions: right, left, anterior, posterior, superior, inferior, right-posterior and left-posterior (fig 1), and in terms of volume. All distances were defined as the average distance over a 40 degree solid angle from the center of gravity to the border (fig 1). Results: