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IMPACT OF AN OFF-LINE CORRECTION PROTOCOL ON SETUP UNCERTAINTY IN MODERN BREAST CANCER RADIATION THERAPY
IGRT: T REATMENT DELIVERY AND PATIENT POSITIONING
465 poster (Physics Track) IMPACT OF AN OFF-LINE CORRECTION PROTOCOL ON SETUP UNCERTAINTY IN MODERN BREAST CANCER RADIATION THERAPY M. Josipovic1 , S. Korreman1 , C. Zacharatou1 1
R IGSHOSPITALET, C OPENHAGEN U NIVERSITY H OSPITAL, Oncology, Copenhagen, Denmark
Radiation
Purpose: A NAL (no action level) off-line correction protocol was implemented for breast cancer patients at our clinic. An analysis of the setup position uncertainty was performed in order to evaluate the amount of improvement with NAL and calculate a possible impact on PTV margins. Materials: A total of 301 breast cancer patients entered the NAL off-line correction protocol from its implementation in April 2008 until January 2009. All patients were immobilised with vacuum cushions. Orthogonal images were taken (EPID or OBI) on the first three fractions. The systematic and random setup uncertainties (standard deviations) were calculated without the positioning corrections performed. Off-line corrections were implemented for deviations larger than 3 mm and remaining systematic set-up uncertainty was calculated. To see whether there was any learning curve in the process, the patients were divided in three subgroups chronologically according to their treatment start (each of 3 months duration). Since both gated and ungated breast cancer treatments entered the NAL protocol, the differences between these two subgroups were investigated as well. Furthermore we evaluated, whether NAL gives a possibility to reduce the PTV margins. Margins were calculated using van Herks formula (van Herk et al, IJROBP 2000), accounting for uncertainties in delineation (Struikmans et al, R&O 2005), respiration (own data) and setup. Results:
S 173
The random positioning uncertainty for our breast cancer patients was around 2 mm (1SD).The NAL protocol reduced the systematic positioning uncertainty from approximately 4 mm (1SD) to below 2 mm (1SD). There was no apparent learning curve between the three chronological subgroups. Gated and ungated treatments did not differ as far as positioning uncertainty is concerned. More details are presented in the table.The necessary margins ensuring 95% coverage of CTV in 90% of patients were found to be 16 mm in ML, 20 mm in CC and 17 mm in AP direction without NAL corrections. With NAL they can be reduced by 3 mm in ML and CC and 2 mm in AP direction. Conclusions: The results show a setup position uncertainty which is lower than known from the literature (Hurkmains et al, R&O 2005). Implementation of NAL reduced the systematic position uncertainty by approximately a factor 2. However, there might still be room for further improvement of systematic setup uncertainty and margins. As seen in the table, a small subgroup of patients immobilised with breast board demonstrated lower systematic uncertainty after the NAL protocol. Using extended NAL with weekly imaging and setup corrections may reduce the residual systematic setup uncertainty further and minimize the effect of possible time trends and transitions in patient setup. The inter- and intraobserver variability in image matching needs to be evaluated for possible impact on margins prior to a decision on their reduction. 466 poster (Physics Track) IMPLEMENTATION OF IMAGE GUIDED RADIATION THERAPY PERFORMED WITH MEGAVOLTAGE CONE BEAM CT T. Major1 , P. Agoston1 , C. Polgár1 1 N ATIONAL I NSTITUTE OF O NCOLOGY, Radiation Therapy, Budapest, Hungary
Purpose: To give an overview on the method of patient setup verification with megavoltage cone beam CT (MV-CBCT) and to present the initial patient setup data. Materials: Between December 2008 and March 2009 354 MV-CBCT studies of 64 patients were performed on an Artiste (Siemens) linear accelerator. The scans were performed before the first three fractions with 6 MV beam, field size of 27.4x27.4 cm, 200 degree gantry rotation and 15 MU. The treatment and planning CT images were automatically registered in 3D using the information of bony structures, and the isocenter shifts were determined. In the three cardinal directions the mean setup and random errors were calculated for each patient. Then, the mean systematic and random errors for the whole patient population were determined. Safety zone around CTV in lateral (LAT), longitudinal (LONG) and vertical (VERT) direction was calculated to correct the inaccuracies in patient setup. Results: Irradiation was performed for 47 pelvic patients, 9 for lung and 8 for head and neck (H&N) patients. The mean setup error for all scans were -0.1, 0.0 and 0.5 cm for LAT, LONG and VERT directions. At pelvic irradiation the errors were 0.0, 0.1, 0.5 cm, at lung -0.1, -0.1, 0.3 cm and at H&N -0.1, 0.0, 0.3 cm. The systematic and random errors for the whole patient population were 0.32, 0.39, 0.39 and 0.31, 0.31, 0.39 cm for LAT, LONG and VERT directions, respectively. The corresponding CTV-PTV safety zones calculated from the setup errors were 1.0, 1.2 and 1.3 cm. Conclusions: The MV-CBCT integrated into Artiste linear accelerator can be easily used for image-guided radiotherapy, but due to high energy the soft tissue registration is not possible. To evaluate its clinical role in improving patient setup and determination of the safety zone around CTV requires more subgroup analysis regarding tumor sites and patient immobilization technique. 467 poster (Physics Track) ONLINE DOSE-GUIDED CORRECTION PROTOCOL FOR HYPO FRACTIONATED LUNG RADIOTHERAPY C. Nagel1 , P. Remeijer1 , M. van Herk1 , J. J. Sonke1 1
NKI-AVL, Radiation Oncology, Amsterdam, Netherlands
Purpose: 4D-CBCT guidance allows high precision target localization. Tumor baseline variations, however, induce differential motion relative to organs at risk (OAR), potentially compromising the treatment planning dose limits for these organs when correctly positioning the target. Optimal couch corrections thus become a compromise between optimal target coverage and OAR sparing. Deriving patient specific geometric limits on the corrections during treatment planning is time consuming and suboptimal, making dose based decisions preferable. The purpose of this project was to develop an online dose-guided correction protocol. Materials: Five lung cancer patients that were treated with SBRT and that exhibited considerable baseline shifts (range of 0.5 to 2.5 cm) were selected for retrospective analysis. In current clinical practice, geometrical limits are derived from OAR expansions of 10 mm, 5 mm and 0 mm. The largest of these expansions that satisfies the OAR dose constraints is converted to additional orthogonal limits for residual OAR misalignment. Thus the allowed residual OAR misalignment will be 10 mm at most. For the online dose-guided protocol, planning CT, delineated structures, isocenter coordinates and dose distributions were exported from Pinnacle (v8.0h) using DICOM and imported
465 poster (Physics Track) IMPACT OF AN OFF-LINE CORRECTION PROTOCOL ON SETUP UNCERTAINTY IN MODERN BREAST CANCER RADIATION THERAPY M. Josipovic1 , S. Korreman1 , C. Zacharatou1 1
R IGSHOSPITALET, C OPENHAGEN U NIVERSITY H OSPITAL, Oncology, Copenhagen, Denmark
Radiation
Purpose: A NAL (no action level) off-line correction protocol was implemented for breast cancer patients at our clinic. An analysis of the setup position uncertainty was performed in order to evaluate the amount of improvement with NAL and calculate a possible impact on PTV margins. Materials: A total of 301 breast cancer patients entered the NAL off-line correction protocol from its implementation in April 2008 until January 2009. All patients were immobilised with vacuum cushions. Orthogonal images were taken (EPID or OBI) on the first three fractions. The systematic and random setup uncertainties (standard deviations) were calculated without the positioning corrections performed. Off-line corrections were implemented for deviations larger than 3 mm and remaining systematic set-up uncertainty was calculated. To see whether there was any learning curve in the process, the patients were divided in three subgroups chronologically according to their treatment start (each of 3 months duration). Since both gated and ungated breast cancer treatments entered the NAL protocol, the differences between these two subgroups were investigated as well. Furthermore we evaluated, whether NAL gives a possibility to reduce the PTV margins. Margins were calculated using van Herks formula (van Herk et al, IJROBP 2000), accounting for uncertainties in delineation (Struikmans et al, R&O 2005), respiration (own data) and setup. Results:
S 173
The random positioning uncertainty for our breast cancer patients was around 2 mm (1SD).The NAL protocol reduced the systematic positioning uncertainty from approximately 4 mm (1SD) to below 2 mm (1SD). There was no apparent learning curve between the three chronological subgroups. Gated and ungated treatments did not differ as far as positioning uncertainty is concerned. More details are presented in the table.The necessary margins ensuring 95% coverage of CTV in 90% of patients were found to be 16 mm in ML, 20 mm in CC and 17 mm in AP direction without NAL corrections. With NAL they can be reduced by 3 mm in ML and CC and 2 mm in AP direction. Conclusions: The results show a setup position uncertainty which is lower than known from the literature (Hurkmains et al, R&O 2005). Implementation of NAL reduced the systematic position uncertainty by approximately a factor 2. However, there might still be room for further improvement of systematic setup uncertainty and margins. As seen in the table, a small subgroup of patients immobilised with breast board demonstrated lower systematic uncertainty after the NAL protocol. Using extended NAL with weekly imaging and setup corrections may reduce the residual systematic setup uncertainty further and minimize the effect of possible time trends and transitions in patient setup. The inter- and intraobserver variability in image matching needs to be evaluated for possible impact on margins prior to a decision on their reduction. 466 poster (Physics Track) IMPLEMENTATION OF IMAGE GUIDED RADIATION THERAPY PERFORMED WITH MEGAVOLTAGE CONE BEAM CT T. Major1 , P. Agoston1 , C. Polgár1 1 N ATIONAL I NSTITUTE OF O NCOLOGY, Radiation Therapy, Budapest, Hungary
Purpose: To give an overview on the method of patient setup verification with megavoltage cone beam CT (MV-CBCT) and to present the initial patient setup data. Materials: Between December 2008 and March 2009 354 MV-CBCT studies of 64 patients were performed on an Artiste (Siemens) linear accelerator. The scans were performed before the first three fractions with 6 MV beam, field size of 27.4x27.4 cm, 200 degree gantry rotation and 15 MU. The treatment and planning CT images were automatically registered in 3D using the information of bony structures, and the isocenter shifts were determined. In the three cardinal directions the mean setup and random errors were calculated for each patient. Then, the mean systematic and random errors for the whole patient population were determined. Safety zone around CTV in lateral (LAT), longitudinal (LONG) and vertical (VERT) direction was calculated to correct the inaccuracies in patient setup. Results: Irradiation was performed for 47 pelvic patients, 9 for lung and 8 for head and neck (H&N) patients. The mean setup error for all scans were -0.1, 0.0 and 0.5 cm for LAT, LONG and VERT directions. At pelvic irradiation the errors were 0.0, 0.1, 0.5 cm, at lung -0.1, -0.1, 0.3 cm and at H&N -0.1, 0.0, 0.3 cm. The systematic and random errors for the whole patient population were 0.32, 0.39, 0.39 and 0.31, 0.31, 0.39 cm for LAT, LONG and VERT directions, respectively. The corresponding CTV-PTV safety zones calculated from the setup errors were 1.0, 1.2 and 1.3 cm. Conclusions: The MV-CBCT integrated into Artiste linear accelerator can be easily used for image-guided radiotherapy, but due to high energy the soft tissue registration is not possible. To evaluate its clinical role in improving patient setup and determination of the safety zone around CTV requires more subgroup analysis regarding tumor sites and patient immobilization technique. 467 poster (Physics Track) ONLINE DOSE-GUIDED CORRECTION PROTOCOL FOR HYPO FRACTIONATED LUNG RADIOTHERAPY C. Nagel1 , P. Remeijer1 , M. van Herk1 , J. J. Sonke1 1
NKI-AVL, Radiation Oncology, Amsterdam, Netherlands
Purpose: 4D-CBCT guidance allows high precision target localization. Tumor baseline variations, however, induce differential motion relative to organs at risk (OAR), potentially compromising the treatment planning dose limits for these organs when correctly positioning the target. Optimal couch corrections thus become a compromise between optimal target coverage and OAR sparing. Deriving patient specific geometric limits on the corrections during treatment planning is time consuming and suboptimal, making dose based decisions preferable. The purpose of this project was to develop an online dose-guided correction protocol. Materials: Five lung cancer patients that were treated with SBRT and that exhibited considerable baseline shifts (range of 0.5 to 2.5 cm) were selected for retrospective analysis. In current clinical practice, geometrical limits are derived from OAR expansions of 10 mm, 5 mm and 0 mm. The largest of these expansions that satisfies the OAR dose constraints is converted to additional orthogonal limits for residual OAR misalignment. Thus the allowed residual OAR misalignment will be 10 mm at most. For the online dose-guided protocol, planning CT, delineated structures, isocenter coordinates and dose distributions were exported from Pinnacle (v8.0h) using DICOM and imported