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483 poster POSITIONING IN BREAST RADIOTHERAPY; SMALLER SETUP ERRORS IN SUPINE COMPARED TO PRONE POSITIONING
S 196
P OSTER
Young scientists ESTRO Poster Session: Radiation technologists
W EDNESDAY, M AY 11, 2011
corrections are applied. The consequence of the setup errors on HFS and HFP treatment plans will be presented.
482 poster TREATMENT DELIVERY FOR FRAMELESS INTRA-CRANIAL STEREOTACTIC PATIENTS: A FASTER AND MORE ACCURATE APPROACH A. Kuijpers1 , S. Lang1 , A. Walker1 , J. Hrbacek1 , C. Linsenmeier1 , O. Riesterer1 , C. Winter1 1 U NIVERSITY H OSPITAL Z ÜRICH, Zurich, Switzerland
Purpose: Since May 2010, twenty intra-cranial stereotactic patients have been treated with the Varian TrueBeam STx. This new platform of linear accelerators should allow easier, faster and more accurate patient set up and treatment delivery. We therefore performed time and accuracy studies to evaluate potential advantages of the TrueBeam. Materials: All twenty patients were immobilized using a BrainLAB mask system. Patients were treated either using a VMAT or an IMRT technique. For at least five fractions, image guidance was performed with a kV image pair followed by a CBCT. All positioning discrepancies were documented including pitch and roll. Translational and rotation errors were corrected daily. A post treatment CBCT was acquired to analyze intra-fractional patient stability. For each fraction the time needed for preparation, imaging and treatment was collected using a MatLab program. Results: Intra-fractional motion was found to be below 1.1mm for all patients for all treatments. The mean shift was 0.56 mm (2SD= 0.54 mm). Shifts during treatment in longitudinal and lateral direction were non-systematic, however we observed a systematic shift of -0.5 mm (2SD= 0.4 mm) in vertical direction, which is likely related to the sagging of the patient in the mask. Both pitch and roll were non-systematic and below 1.5◦ . Differences of up to 3 mm were observed between 2D-2D matching and 3D-3D matching. However when the cranial border of the skull was included on the 2D-2D matching better agreement was seen. Treatment delivery was reduced from 11 min on our former linac to 6.6 min for an IMRT plan and 2.99 min for Rapid Arc delivery. Conclusions: Less deviation was found between 2D-2D matching and 3D3D matching when the cranial border of the skull was included in the initial kV paired images. The minimal intra-fractional errors will enable us to further implement a non-invasive Radiosurgery program. The advanced clinical features of the Truebeam allowed us to significantly reduce our treatment delivery time. 483 poster POSITIONING IN BREAST RADIOTHERAPY; SMALLER SETUP ERRORS IN SUPINE COMPARED TO PRONE POSITIONING H. Jonker1 , W. Jansen2 , M. Jonker2 , A. Scholten2 , C. Marijnen2 1 L EIDEN U NIVERSITY M EDICAL C ENTER, Clinical Oncology, Leiden, Netherlands 2 L EIDEN U NIVERSITY M EDICAL C ENTER (LUMC), Leiden, Netherlands
Purpose: In radiotherapy a stable and reproducible treatment position allowing an efficient treatment plan for the desired target volume is instrumental. In view of this, the reproducibility of the two most widely used positions in breast cancer treatments were tested: head first supine (HFS) and head first prone (HFP). Materials: Thirty-one breast cancer patients got multiple CT-scans in both HFS and HFP position. In HFS patients were immobilized on an angled breast board with their ipsilateral arm abducted and externally rotated. A prone breast board (ClearVueTM Prone Position Breast Radiotherapy System) was used for HFP positioning. Patients were scanned in both HFS and HFP position on day 1 and again 3-4 days thereafter. To simulate actual treatment setup, fiducial markers at the isocenter were used to realign the patient.CTV’s were outlined by a single radiation oncologist. Volume matches between the first and second scan in each position were made with fusion in Pinnacle3 v8.0m. From this, data on rotation and translation could be extracted in X, Y and Z axes for each treatment position. The translation vector was calculated as the square root of X2 , Y2 and Z2 . Because the first and second scans were acquired on the same equipment, setup error can be interpreted as mainly random. Results: The average volume of the CTV was 780 cc for HFS and 870 cc for HFP respectively, but showed large individual differences (range 143-1992 cc for HFS and 143-2200 cc for HFP). Comparison on an individual base showed an average discrepancy of 11.5% (range <1-33%) between HFS and HFP. There was no significant difference in the rotation error between HFS and HFP (< 0.5). The average translations in X, Y, and Z direction were 3.9 mm, 4.1 mm and 5.5 mm for HFS and 4.6 mm, 3.6 mm and 6.7 mm for HFP, respectively. The average translation for HFP is 1 mm larger than for HFS in all directions (corresponding vector = 1.7mm). No correlation between CTV volume and required translation or rotation could be demonstrated. Figure 1 shows the translation vectors required for a match for each patient, ordered by magnitude. From this figure, it can be concluded that in HFS and HFP a vector of 1 cm is only sufficient for 50% of the patients if no further setup
Conclusions: In breast cancer patients, repeated CT-scans show equivalent rotation errors in HFS and HFP. However, translation vectors are smaller in HFS than in HFP. Hence, HFS has a smaller initial setup error than HFP. Both for HFS and HFP the setup error is shown to be independent of the breast volume. This indicates that CTV-PTV margins do not require adjustment with smaller or larger breast size. 484 poster AN INVESTIGATION OF THE SUITABILITY OF GE-DOPED OPTICAL FIBRES IN MAILED THERMOLUMINESCENCE DOSIMETRY AUDITS OF RADIOTHERAPY DOSE DELIVERY N. Mohd Noor1 , D. Bradley1 , A. Nisbet1 2 1 U NIVERSITY OF S URREY, Department of Physics, Guildford, United Kingdom 2 T HE R OYAL S URREY C OUNTY H OSPITAL NHS F OUNDATION T RUST, Department of Medical Physics, Guildford, United Kingdom
Purpose: The need for accuracy in radiotherapy is well established. One tool for ensuring consistency in dosimetry is the use of the intercomparison audit. This may range from use of lithium fluoride thermoluminescence dosimeter (TLD) audits, as organised by the IAEA, or on-site visits using ionisation chambers and appropriate phantoms. The complexity of parameters audited may cover basic reference dosimetry through to in vivo dosimetry or advanced radiotherapy techniques. The aim of the present investigation, using high energy photon beams, is to undertake a pilot audit aimed at establishing the potential of a mailed commercial Ge-doped optical fibre TLD system in measuring beam output under reference conditions. Prior to the audit, the Ge-doped fibres have first been screened to establish dosimetric characteristics of such TL media, including reproducibility, linearity, fading, energy-, dose rate-, angular-, and temperature-dependence. Fibres with suitable dosimetric characteristics were retained in groups of fifteen and loaded into plastic capsules for use in this pilot audit. The pilot audit irradiation was carried out using three different linear accelerators located in one UK radiotherapy centre. A total of 42 capsules of selected Ge-optical fibres were irradiated to an absorbed dose to water of 2 Gy using a purpose built holder, based on the IAEA TLD holder design, in a Qados water tank. In order to calculate absorbed dose to water the equation proposed by Izweska et al (2007) in the IAEA TLD audit system was applied. Subsequent to these irradiations a mailed audit of all Malaysian radiotherapy centres is ongoing. Materials: The silica-glass optical fibres used are single-mode INOCORP (Canada) Ge-doped optical fibres, core diameter 9 μm and cladding diameter 116 ± 0.1 μm. This medium has been determined to form an effective TL dosimeter, offering features such as good spatial resolution, high sensitivity, cost-effectiveness, small size and minimal fading. Prior to the audit excercise, a large collection of Ge-doped fibres were screened to establish individual performance using an ionisation chamber placed at the same depth as the TL-detector in a perspex phantom. Only fibres providing a response within ±5% of the batch mean and reproducibility of better than 5% were used in this audit. The fibres were also characterised for their individual sensitivity factor, linearity with dose, fading, dose-rate, energy, temperature and angular dependence to ensure the tightest possible control of influencing factors using nominal megavoltage energy photon beams of 6
P OSTER
Young scientists ESTRO Poster Session: Radiation technologists
W EDNESDAY, M AY 11, 2011
corrections are applied. The consequence of the setup errors on HFS and HFP treatment plans will be presented.
482 poster TREATMENT DELIVERY FOR FRAMELESS INTRA-CRANIAL STEREOTACTIC PATIENTS: A FASTER AND MORE ACCURATE APPROACH A. Kuijpers1 , S. Lang1 , A. Walker1 , J. Hrbacek1 , C. Linsenmeier1 , O. Riesterer1 , C. Winter1 1 U NIVERSITY H OSPITAL Z ÜRICH, Zurich, Switzerland
Purpose: Since May 2010, twenty intra-cranial stereotactic patients have been treated with the Varian TrueBeam STx. This new platform of linear accelerators should allow easier, faster and more accurate patient set up and treatment delivery. We therefore performed time and accuracy studies to evaluate potential advantages of the TrueBeam. Materials: All twenty patients were immobilized using a BrainLAB mask system. Patients were treated either using a VMAT or an IMRT technique. For at least five fractions, image guidance was performed with a kV image pair followed by a CBCT. All positioning discrepancies were documented including pitch and roll. Translational and rotation errors were corrected daily. A post treatment CBCT was acquired to analyze intra-fractional patient stability. For each fraction the time needed for preparation, imaging and treatment was collected using a MatLab program. Results: Intra-fractional motion was found to be below 1.1mm for all patients for all treatments. The mean shift was 0.56 mm (2SD= 0.54 mm). Shifts during treatment in longitudinal and lateral direction were non-systematic, however we observed a systematic shift of -0.5 mm (2SD= 0.4 mm) in vertical direction, which is likely related to the sagging of the patient in the mask. Both pitch and roll were non-systematic and below 1.5◦ . Differences of up to 3 mm were observed between 2D-2D matching and 3D-3D matching. However when the cranial border of the skull was included on the 2D-2D matching better agreement was seen. Treatment delivery was reduced from 11 min on our former linac to 6.6 min for an IMRT plan and 2.99 min for Rapid Arc delivery. Conclusions: Less deviation was found between 2D-2D matching and 3D3D matching when the cranial border of the skull was included in the initial kV paired images. The minimal intra-fractional errors will enable us to further implement a non-invasive Radiosurgery program. The advanced clinical features of the Truebeam allowed us to significantly reduce our treatment delivery time. 483 poster POSITIONING IN BREAST RADIOTHERAPY; SMALLER SETUP ERRORS IN SUPINE COMPARED TO PRONE POSITIONING H. Jonker1 , W. Jansen2 , M. Jonker2 , A. Scholten2 , C. Marijnen2 1 L EIDEN U NIVERSITY M EDICAL C ENTER, Clinical Oncology, Leiden, Netherlands 2 L EIDEN U NIVERSITY M EDICAL C ENTER (LUMC), Leiden, Netherlands
Purpose: In radiotherapy a stable and reproducible treatment position allowing an efficient treatment plan for the desired target volume is instrumental. In view of this, the reproducibility of the two most widely used positions in breast cancer treatments were tested: head first supine (HFS) and head first prone (HFP). Materials: Thirty-one breast cancer patients got multiple CT-scans in both HFS and HFP position. In HFS patients were immobilized on an angled breast board with their ipsilateral arm abducted and externally rotated. A prone breast board (ClearVueTM Prone Position Breast Radiotherapy System) was used for HFP positioning. Patients were scanned in both HFS and HFP position on day 1 and again 3-4 days thereafter. To simulate actual treatment setup, fiducial markers at the isocenter were used to realign the patient.CTV’s were outlined by a single radiation oncologist. Volume matches between the first and second scan in each position were made with fusion in Pinnacle3 v8.0m. From this, data on rotation and translation could be extracted in X, Y and Z axes for each treatment position. The translation vector was calculated as the square root of X2 , Y2 and Z2 . Because the first and second scans were acquired on the same equipment, setup error can be interpreted as mainly random. Results: The average volume of the CTV was 780 cc for HFS and 870 cc for HFP respectively, but showed large individual differences (range 143-1992 cc for HFS and 143-2200 cc for HFP). Comparison on an individual base showed an average discrepancy of 11.5% (range <1-33%) between HFS and HFP. There was no significant difference in the rotation error between HFS and HFP (< 0.5). The average translations in X, Y, and Z direction were 3.9 mm, 4.1 mm and 5.5 mm for HFS and 4.6 mm, 3.6 mm and 6.7 mm for HFP, respectively. The average translation for HFP is 1 mm larger than for HFS in all directions (corresponding vector = 1.7mm). No correlation between CTV volume and required translation or rotation could be demonstrated. Figure 1 shows the translation vectors required for a match for each patient, ordered by magnitude. From this figure, it can be concluded that in HFS and HFP a vector of 1 cm is only sufficient for 50% of the patients if no further setup
Conclusions: In breast cancer patients, repeated CT-scans show equivalent rotation errors in HFS and HFP. However, translation vectors are smaller in HFS than in HFP. Hence, HFS has a smaller initial setup error than HFP. Both for HFS and HFP the setup error is shown to be independent of the breast volume. This indicates that CTV-PTV margins do not require adjustment with smaller or larger breast size. 484 poster AN INVESTIGATION OF THE SUITABILITY OF GE-DOPED OPTICAL FIBRES IN MAILED THERMOLUMINESCENCE DOSIMETRY AUDITS OF RADIOTHERAPY DOSE DELIVERY N. Mohd Noor1 , D. Bradley1 , A. Nisbet1 2 1 U NIVERSITY OF S URREY, Department of Physics, Guildford, United Kingdom 2 T HE R OYAL S URREY C OUNTY H OSPITAL NHS F OUNDATION T RUST, Department of Medical Physics, Guildford, United Kingdom
Purpose: The need for accuracy in radiotherapy is well established. One tool for ensuring consistency in dosimetry is the use of the intercomparison audit. This may range from use of lithium fluoride thermoluminescence dosimeter (TLD) audits, as organised by the IAEA, or on-site visits using ionisation chambers and appropriate phantoms. The complexity of parameters audited may cover basic reference dosimetry through to in vivo dosimetry or advanced radiotherapy techniques. The aim of the present investigation, using high energy photon beams, is to undertake a pilot audit aimed at establishing the potential of a mailed commercial Ge-doped optical fibre TLD system in measuring beam output under reference conditions. Prior to the audit, the Ge-doped fibres have first been screened to establish dosimetric characteristics of such TL media, including reproducibility, linearity, fading, energy-, dose rate-, angular-, and temperature-dependence. Fibres with suitable dosimetric characteristics were retained in groups of fifteen and loaded into plastic capsules for use in this pilot audit. The pilot audit irradiation was carried out using three different linear accelerators located in one UK radiotherapy centre. A total of 42 capsules of selected Ge-optical fibres were irradiated to an absorbed dose to water of 2 Gy using a purpose built holder, based on the IAEA TLD holder design, in a Qados water tank. In order to calculate absorbed dose to water the equation proposed by Izweska et al (2007) in the IAEA TLD audit system was applied. Subsequent to these irradiations a mailed audit of all Malaysian radiotherapy centres is ongoing. Materials: The silica-glass optical fibres used are single-mode INOCORP (Canada) Ge-doped optical fibres, core diameter 9 μm and cladding diameter 116 ± 0.1 μm. This medium has been determined to form an effective TL dosimeter, offering features such as good spatial resolution, high sensitivity, cost-effectiveness, small size and minimal fading. Prior to the audit excercise, a large collection of Ge-doped fibres were screened to establish individual performance using an ionisation chamber placed at the same depth as the TL-detector in a perspex phantom. Only fibres providing a response within ±5% of the batch mean and reproducibility of better than 5% were used in this audit. The fibres were also characterised for their individual sensitivity factor, linearity with dose, fading, dose-rate, energy, temperature and angular dependence to ensure the tightest possible control of influencing factors using nominal megavoltage energy photon beams of 6