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EP-1363 COMPARISON OF BEAM CHARACTERISTICS AT LOW MONITOR UNITS BETWEEN TWO DIFFERENT LINAC WORKING MODES
ESTRO 31
S517
E (MV) PDD at depth Depth of max dose Penumbra width 10 cm (mm) 80%-20% (mm)
Mean energy (MeV)
6
53.31
11
2.8
1.26
5
5.37
10
2.7
1.06
4
47.64
9
2.6
0.91
3
44.09
7
2.5
0.75
2
39.70
5
2.4
0.58
Table I. Dosimetric characteristics of photon beams of different maximum energy. Conclusions: Our study shows the radiological penumbra decreases by using low energy megavoltage photon beams, while there is still adequate penetration and skin sparing particularly for multiple beam treatments.
Conclusions: The procedure presented in this work allows an easy estimation of the secondary cancer risk due to the neutron component for any patient as a function of the treatment MU. It will provide very valuable information when selecting the optimal treatment for a patient and it could be useful for retrospective evaluation as it can be applied for patients already treated. Finally, the implementation of the algorithm has been performed for Pinnacle3 (Philips Medical Systems). References: [1] Gómez F et al. Phys. Med. Biol. 2010;55:1025-1039.[2] Sánchez-Doblado F et al. Radioter. Oncol. 2010;96:S475. [3] ICRP. Publication 103 2007. [4] Expósito M R et al. Radioter. Oncol. 2010;96:S473. EP-1362 IMPROVEMENT OF RADIOLOGICAL PENUMBRA USING LOW MEGAVOLTAGE PHOTON BEAMS FOR SMALL RADIOSURGICAL FIELD SIZES M. Yarahmadi1, M. Allahverdi1, H.A. Nedaie1, S.A. Vaezzadeh1, O.A. Sauer2 1 Tehran University of Medical Sciences, Medical physics, Tehran, Iran Islamic Republic of 2 University of Würzburg, Klinik und Poliklinik für Strahlentherapie, Würzburg, Germany Purpose/Objective: In stereotactic radiosurgery, sharp photon beam edges have clear advantages for normal tissue prevention because they require a smaller beam aperture margin. In general, the dose gradient is a limiting factor in minimizing dose to nearby critical structures for clinical cases. Therefore the penumbral width should be diminished in order to achieve a steep dose gradient. Materials and Methods: In this work The Varian Clinac 2100 linear accelerator equipped with in-house designed radiosurgical collimators was modeled using the EGSnrc / BEAMnrc Monte Carlo code. The calculation results were compared with measured values. The 0.015 cm3 PTW PinPoint chamber was used to measure the 6 MV photon beam characteristics. Additional to the 6 MV photon beam, 5, 4, 3 and 2 MV beams were simulated. Percent depth dose (PDD) and off-axis dose profiles were calculated for a small field size of 10 mm diameter with DOSXYZnrc. The mean energy and photon fluence at the water surface were calculated with BEAMDP for all beams. Results: Radiological penumbra widths (80%-20%) and (90%-10%) at the depth of 5 cm were reduced 14 % and 18 % respectively when a 6 MV beam was replaced with a 2 MV beam. The respective mean energies of photon energy spectra, the depths of maximum dose and the PDD at depth of 10 cm are shown in Table I.
EP-1363 COMPARISON OF BEAM CHARACTERISTICS AT LOW MONITOR UNITS BETWEEN TWO DIFFERENT LINAC WORKING MODES J. Cortes Rodicio1, O. Ripol Valentín2, A. García Romero1, P. Ortega Pardina1, V. Laliena Bielsa1, A. Hernández Vitoria1, E. Millán Cebrián1, M. Canellas Anoz1 1 Hospital Clinico Universitario Lozano Blesa, Fisica y Protección Radiologica, Zaragoza, Spain 2 Hospital Universitari Arnau de Vilanova, Radiofisica Hospitalaria, Lerida, Spain Purpose/Objective: When the LINAC Mevatron Oncor™ Expression is working in IMRT mode the beam is not completely turned off between segments. It uses a PAUSE control which desynchronizes the injection current trigger but high voltage or any other previous systems are still on. When the next segment is ready this trigger is synchronized. This working mode makes the beam, in principle, faster and more stable. The aim of this work is to investigate the beam characteristics, linearity and dose delivery at low monitor unit comparing them in two different LINAC working situations: IMRT delivery and standard delivery. Materials and Methods: Five IMRT treatments have been prepared, each of them with segments 10cm x 10cm with different MU (1, 2, 4, 7 10MU). The same fields were prepared not in the IMRT mode but in the standard LINAC working mode. The LINAC is a Mevatron Oncor™ Expression (Siemens Medical Solutions, Concord, California). An amorphous silicon based EPID (OptiVue™ 1000 ST) has been used as portal dosimeter using a homemade software that converts the EPID images into dose distributions at the isocentre plane. The dose at the centre of each segment of the IMRT treatment has been investigated as well as other parameters like flatness, symmetry and reproducibility using commercial software (OmniPro-I'mRT version 1.7. by IBA Dosimetry) and comparing them with those in the standard LINAC working mode. Results: The analysis of the linearity at low MU showed that there is no difference between both LINAC working modes reaching values of R2 of 0.9999. Differences in the dose at the centre of the fields have been observed: at low MU (1MU and 2MU) the dose delivered working in the standard LINAC mode is higher than that delivered in the IMRT mode, changing this trend at higher MU. Some lacks of reproducibility of the flatness have been detected for both the segments of the IMRT treatments and the fields of the standard treatments (Figure). These problems increase as the MU decrease, particularly below 4MU.
S518
Conclusions: The beam characteristics, linearity and dose delivery at low monitor unit have been studied comparing two different LINAC working modes. Differences in the dose delivery and problems in the reproducibility of the flatness have been found. Anyway, these results do not have clinical implications. EP-1364 EVALUATION OF DOSE CONTROL SYSTEM IMPLEMENTATION IN A TOMOTHERAPY HI-ART UNIT J.A. Ramos Pacho1, S. Garcia Repiso1, J. Hernandez Rodriguez1, C. Martin Rincon1, J.M. Verde Velasco1, E. De Sena Espinel1, M.E. Perez Alvarez1, J.M. Delgado Aparicio1 1 Hospital Universitario, Medical Physics and Radiation Protection, Salamanca, Spain Purpose/Objective: Tomotherapy Hi-Art radiation unit consists of a linear accelerator that can rotate around the treatment couch while it is moving at constant speed, i.e., it works like a CT unit but with a treatment aim. This unit has a binary MLC of 64 leaves moving continuously during irradiation time. These and other characteristics allow a helical IMRT treatment. This kind of units had not a feedback loop between the dose monitor chambers and the magnetron, so it can’t be assured that the dose rate output is constant during treatment. We observed a drift in the dose rate of about 2% down for large treatment times. To solve this problem, Tomotherapy Inc. is installing a dose servo namely DCS (Dose Control System), which controls the magnetron current to adjust the dose rate output automatically. Our hospital is the second institution in Europe in which the DCS has been installed. In this paper measurements performed before and after the implementation of dose servo are compared. Materials and Methods: To evaluate the dose rate drift, a rotational plan of 510 seconds long has been developed. This time is a usual treatment time and long enough to ensure a complete observation of this effect. The plan has a period of 17 seconds, in which the MLC leaves are fully open and the treatment couch is stationary. Charge measurements have been performed with Exradín A1SL Slimline Miniature Shonka IC (Standard Imaging) of 0.056 cm3, placed into the closest to the center hole of the Cheese Phantom and connected to the TomoElectrometer. Using the TomoElectrometer software (TEMS) we obtain a plot of charge collected every second vs time. These data have been processed, plotting the cycle-integrated charge vs time to avoid dose rate oscillations due to rotation of the gantry. Results:
The graph shows that the dose rate is more stable after the dose servo implementation. Conclusions: The dose servo installation allows a more accurate dose delivering during the irradiation and a improvement of treatment quality. EP-1365 VERIFICATION OF THE 3D DOSE DISTRIBUTION IN SPINAL RADIOSURGERY BY USING AGEL DOSIMETER D. Lee1, H. Chung2 1 Inje University IlsanPaik Hospital, Neurosurgery, Goyang, Korea Republic of 2 Seoul National University, Neurosurgery, Seoul, Korea Republic of
ESTRO 31
Purpose/Objective: The aim of this study was to compare the 3D relative dose distribution between the commercially available BANG3gel dosimeter(MGS Research Inc., CT,USA) and clinical plan dosimetry applied to spinal tumor patients, as well as to compare gel dosimetry and film dosimetry of the axial plane of the isocenter. To validate polymer gel dosimetry for IMRS dose distribution verification are compared the dose maps with the dose maps obtained from calculated dosimetry with the treatment planning system Materials and Methods: BANG3gel dosimeter and Gafchromic EBT film (ISP, NJ, USA) were used to compare the dose distribution between gel and planned dosimetry of the axial plane at the isocenter. The BANG3gel was designed for use in our study in the dose range of 0 – 20 Gy by using a response modifier. To obtain a polymer gel dosimeter calibration curve, 8 test vials containing the gel were irradiated at dose levels of 1, 2, 3, 5, 7, 10, 15, and 20 Gy. We performed radiosurgery treatment on the gel and film by delivering the radiation to the target as a marginal dose and saving the spinal cord as an OAR. Results: We measured both the gel and the film dosimeter in the axial plane. Quantitative evaluation of these results is expressed as DTA. The results show good agreement between the 2 methods at the selected plane. The DTA values of the 80% and 50% isodose lines were within 1.0 mm and 3.0 mm, respectively. The DTA value of the OAR profile was within 1.0 mm in both gel and film dosimetry. In the coronal direction between the gel and the treatment planning calculations with 1 plane passing through the isocenter. The DTA values of the 80% and 50% isodose lines were within 1.0 mm and 3.0 mm, respectively. In the sagittal direction from the gel and the treatment planning calculations with 1 plane passing through the isocenter plane. The DTA values of the 80% and 50% isodose lines were within 1.1 mm and 2.0 mm, respectively. Conclusions: The data shown in this study support the conclusion that gel dosimetry can produce 3D dose mapping of sufficient quality for dosimetry verification. We observed good agreement between the measured and the calculated dose distribution, within 1 mm in the high-dose gradient region. In addition to sufficiently verifying the 3D dose distributions, we found that the gel dosimeter was a useful tool for preclinical dosimetry before performing radiosurgery treatment. Therefore, use of gel dosimetry is sufficient for verifying complex dose distributions in the field of radiosurgery. EP-1366 TO EVALUATE THE DELIVERY EFFICIENCY OF SLIDING-WINDOW VERSUS STEP AND SHOOT TECHNIQUES USING PORTAL DOSIMETRY V. Fusco1, R. Caivano2, M. Cozzolino2, G. Califano2, A. Fiorentino1, C. Chiumento1, S. Clemente2 1 IRCCS CROB, Radiotherapy, Rionero in Vulture, Italy 2 IRCCS CROB, Medical Physics, Rionero in Vulture, Italy Purpose/Objective: To evaluate the delivery efficiency of dynamic (DMLC) and segmental (SMLC, also known as ''step-and-shoot'') Intensity Modulated Radiation Therapy (IMRT) techniques, using Portal Dosimetry (PD) in Treatment Planning System Eclipse (8.6 version). Materials and Methods: 7 Head and Neck (HN) patients treated in our Institute with IMRT DMLC technique were retrospectively selected for the study. Plans were also re-calculated with SMLC at 5, 10 and 20 levels of intensity. A total of 107 fields/sub fields were analyzed. The dosimetric verification was performed with Portal Dosimetry system into Eclipse, the agreement between calculated and measured fluence was evaluated using the gamma index (maximum γmax, average γavg, percentage of points with γ%≤1). The images were acquired at a source-detector distance (SDD) of 100 cm, in integrated mode with 30 frames per second (fps), projecting each field on the EPID at gantry 0°. Measures, keeping the real clinical gantry angles, were also carried out to assess the effect of gantry rotation on the dosimetric results. Results: For all techniques measurements are well within the acceptable criteria γavg< 0.5, γ% ≤ 1 greater than 95% (99.8%, 99.7%, 99.4%, 99.0% for DMLC and SMLC 20,10,5 respectively). γmax improves (+19.5%) increasing the numbers of intensity levels from 5 to 20 and using DMLC (+34%). Delivery efficiency for all tecniques was affected by gantry angles and leaves traveling direction, improvements for SMLC compared to DMLC were observed increasing the number of intensity levels. Conclusions: A good agreement between calculated and measured fluence was obtained for both DMLC and SMLC techniques and levels. The effect of gantry rotation as well as leaves traveling direction opposite to the gravitational force influence results for all techniques in particular for SMLC at low intensity levels.
S517
E (MV) PDD at depth Depth of max dose Penumbra width 10 cm (mm) 80%-20% (mm)
Mean energy (MeV)
6
53.31
11
2.8
1.26
5
5.37
10
2.7
1.06
4
47.64
9
2.6
0.91
3
44.09
7
2.5
0.75
2
39.70
5
2.4
0.58
Table I. Dosimetric characteristics of photon beams of different maximum energy. Conclusions: Our study shows the radiological penumbra decreases by using low energy megavoltage photon beams, while there is still adequate penetration and skin sparing particularly for multiple beam treatments.
Conclusions: The procedure presented in this work allows an easy estimation of the secondary cancer risk due to the neutron component for any patient as a function of the treatment MU. It will provide very valuable information when selecting the optimal treatment for a patient and it could be useful for retrospective evaluation as it can be applied for patients already treated. Finally, the implementation of the algorithm has been performed for Pinnacle3 (Philips Medical Systems). References: [1] Gómez F et al. Phys. Med. Biol. 2010;55:1025-1039.[2] Sánchez-Doblado F et al. Radioter. Oncol. 2010;96:S475. [3] ICRP. Publication 103 2007. [4] Expósito M R et al. Radioter. Oncol. 2010;96:S473. EP-1362 IMPROVEMENT OF RADIOLOGICAL PENUMBRA USING LOW MEGAVOLTAGE PHOTON BEAMS FOR SMALL RADIOSURGICAL FIELD SIZES M. Yarahmadi1, M. Allahverdi1, H.A. Nedaie1, S.A. Vaezzadeh1, O.A. Sauer2 1 Tehran University of Medical Sciences, Medical physics, Tehran, Iran Islamic Republic of 2 University of Würzburg, Klinik und Poliklinik für Strahlentherapie, Würzburg, Germany Purpose/Objective: In stereotactic radiosurgery, sharp photon beam edges have clear advantages for normal tissue prevention because they require a smaller beam aperture margin. In general, the dose gradient is a limiting factor in minimizing dose to nearby critical structures for clinical cases. Therefore the penumbral width should be diminished in order to achieve a steep dose gradient. Materials and Methods: In this work The Varian Clinac 2100 linear accelerator equipped with in-house designed radiosurgical collimators was modeled using the EGSnrc / BEAMnrc Monte Carlo code. The calculation results were compared with measured values. The 0.015 cm3 PTW PinPoint chamber was used to measure the 6 MV photon beam characteristics. Additional to the 6 MV photon beam, 5, 4, 3 and 2 MV beams were simulated. Percent depth dose (PDD) and off-axis dose profiles were calculated for a small field size of 10 mm diameter with DOSXYZnrc. The mean energy and photon fluence at the water surface were calculated with BEAMDP for all beams. Results: Radiological penumbra widths (80%-20%) and (90%-10%) at the depth of 5 cm were reduced 14 % and 18 % respectively when a 6 MV beam was replaced with a 2 MV beam. The respective mean energies of photon energy spectra, the depths of maximum dose and the PDD at depth of 10 cm are shown in Table I.
EP-1363 COMPARISON OF BEAM CHARACTERISTICS AT LOW MONITOR UNITS BETWEEN TWO DIFFERENT LINAC WORKING MODES J. Cortes Rodicio1, O. Ripol Valentín2, A. García Romero1, P. Ortega Pardina1, V. Laliena Bielsa1, A. Hernández Vitoria1, E. Millán Cebrián1, M. Canellas Anoz1 1 Hospital Clinico Universitario Lozano Blesa, Fisica y Protección Radiologica, Zaragoza, Spain 2 Hospital Universitari Arnau de Vilanova, Radiofisica Hospitalaria, Lerida, Spain Purpose/Objective: When the LINAC Mevatron Oncor™ Expression is working in IMRT mode the beam is not completely turned off between segments. It uses a PAUSE control which desynchronizes the injection current trigger but high voltage or any other previous systems are still on. When the next segment is ready this trigger is synchronized. This working mode makes the beam, in principle, faster and more stable. The aim of this work is to investigate the beam characteristics, linearity and dose delivery at low monitor unit comparing them in two different LINAC working situations: IMRT delivery and standard delivery. Materials and Methods: Five IMRT treatments have been prepared, each of them with segments 10cm x 10cm with different MU (1, 2, 4, 7 10MU). The same fields were prepared not in the IMRT mode but in the standard LINAC working mode. The LINAC is a Mevatron Oncor™ Expression (Siemens Medical Solutions, Concord, California). An amorphous silicon based EPID (OptiVue™ 1000 ST) has been used as portal dosimeter using a homemade software that converts the EPID images into dose distributions at the isocentre plane. The dose at the centre of each segment of the IMRT treatment has been investigated as well as other parameters like flatness, symmetry and reproducibility using commercial software (OmniPro-I'mRT version 1.7. by IBA Dosimetry) and comparing them with those in the standard LINAC working mode. Results: The analysis of the linearity at low MU showed that there is no difference between both LINAC working modes reaching values of R2 of 0.9999. Differences in the dose at the centre of the fields have been observed: at low MU (1MU and 2MU) the dose delivered working in the standard LINAC mode is higher than that delivered in the IMRT mode, changing this trend at higher MU. Some lacks of reproducibility of the flatness have been detected for both the segments of the IMRT treatments and the fields of the standard treatments (Figure). These problems increase as the MU decrease, particularly below 4MU.
S518
Conclusions: The beam characteristics, linearity and dose delivery at low monitor unit have been studied comparing two different LINAC working modes. Differences in the dose delivery and problems in the reproducibility of the flatness have been found. Anyway, these results do not have clinical implications. EP-1364 EVALUATION OF DOSE CONTROL SYSTEM IMPLEMENTATION IN A TOMOTHERAPY HI-ART UNIT J.A. Ramos Pacho1, S. Garcia Repiso1, J. Hernandez Rodriguez1, C. Martin Rincon1, J.M. Verde Velasco1, E. De Sena Espinel1, M.E. Perez Alvarez1, J.M. Delgado Aparicio1 1 Hospital Universitario, Medical Physics and Radiation Protection, Salamanca, Spain Purpose/Objective: Tomotherapy Hi-Art radiation unit consists of a linear accelerator that can rotate around the treatment couch while it is moving at constant speed, i.e., it works like a CT unit but with a treatment aim. This unit has a binary MLC of 64 leaves moving continuously during irradiation time. These and other characteristics allow a helical IMRT treatment. This kind of units had not a feedback loop between the dose monitor chambers and the magnetron, so it can’t be assured that the dose rate output is constant during treatment. We observed a drift in the dose rate of about 2% down for large treatment times. To solve this problem, Tomotherapy Inc. is installing a dose servo namely DCS (Dose Control System), which controls the magnetron current to adjust the dose rate output automatically. Our hospital is the second institution in Europe in which the DCS has been installed. In this paper measurements performed before and after the implementation of dose servo are compared. Materials and Methods: To evaluate the dose rate drift, a rotational plan of 510 seconds long has been developed. This time is a usual treatment time and long enough to ensure a complete observation of this effect. The plan has a period of 17 seconds, in which the MLC leaves are fully open and the treatment couch is stationary. Charge measurements have been performed with Exradín A1SL Slimline Miniature Shonka IC (Standard Imaging) of 0.056 cm3, placed into the closest to the center hole of the Cheese Phantom and connected to the TomoElectrometer. Using the TomoElectrometer software (TEMS) we obtain a plot of charge collected every second vs time. These data have been processed, plotting the cycle-integrated charge vs time to avoid dose rate oscillations due to rotation of the gantry. Results:
The graph shows that the dose rate is more stable after the dose servo implementation. Conclusions: The dose servo installation allows a more accurate dose delivering during the irradiation and a improvement of treatment quality. EP-1365 VERIFICATION OF THE 3D DOSE DISTRIBUTION IN SPINAL RADIOSURGERY BY USING AGEL DOSIMETER D. Lee1, H. Chung2 1 Inje University IlsanPaik Hospital, Neurosurgery, Goyang, Korea Republic of 2 Seoul National University, Neurosurgery, Seoul, Korea Republic of
ESTRO 31
Purpose/Objective: The aim of this study was to compare the 3D relative dose distribution between the commercially available BANG3gel dosimeter(MGS Research Inc., CT,USA) and clinical plan dosimetry applied to spinal tumor patients, as well as to compare gel dosimetry and film dosimetry of the axial plane of the isocenter. To validate polymer gel dosimetry for IMRS dose distribution verification are compared the dose maps with the dose maps obtained from calculated dosimetry with the treatment planning system Materials and Methods: BANG3gel dosimeter and Gafchromic EBT film (ISP, NJ, USA) were used to compare the dose distribution between gel and planned dosimetry of the axial plane at the isocenter. The BANG3gel was designed for use in our study in the dose range of 0 – 20 Gy by using a response modifier. To obtain a polymer gel dosimeter calibration curve, 8 test vials containing the gel were irradiated at dose levels of 1, 2, 3, 5, 7, 10, 15, and 20 Gy. We performed radiosurgery treatment on the gel and film by delivering the radiation to the target as a marginal dose and saving the spinal cord as an OAR. Results: We measured both the gel and the film dosimeter in the axial plane. Quantitative evaluation of these results is expressed as DTA. The results show good agreement between the 2 methods at the selected plane. The DTA values of the 80% and 50% isodose lines were within 1.0 mm and 3.0 mm, respectively. The DTA value of the OAR profile was within 1.0 mm in both gel and film dosimetry. In the coronal direction between the gel and the treatment planning calculations with 1 plane passing through the isocenter. The DTA values of the 80% and 50% isodose lines were within 1.0 mm and 3.0 mm, respectively. In the sagittal direction from the gel and the treatment planning calculations with 1 plane passing through the isocenter plane. The DTA values of the 80% and 50% isodose lines were within 1.1 mm and 2.0 mm, respectively. Conclusions: The data shown in this study support the conclusion that gel dosimetry can produce 3D dose mapping of sufficient quality for dosimetry verification. We observed good agreement between the measured and the calculated dose distribution, within 1 mm in the high-dose gradient region. In addition to sufficiently verifying the 3D dose distributions, we found that the gel dosimeter was a useful tool for preclinical dosimetry before performing radiosurgery treatment. Therefore, use of gel dosimetry is sufficient for verifying complex dose distributions in the field of radiosurgery. EP-1366 TO EVALUATE THE DELIVERY EFFICIENCY OF SLIDING-WINDOW VERSUS STEP AND SHOOT TECHNIQUES USING PORTAL DOSIMETRY V. Fusco1, R. Caivano2, M. Cozzolino2, G. Califano2, A. Fiorentino1, C. Chiumento1, S. Clemente2 1 IRCCS CROB, Radiotherapy, Rionero in Vulture, Italy 2 IRCCS CROB, Medical Physics, Rionero in Vulture, Italy Purpose/Objective: To evaluate the delivery efficiency of dynamic (DMLC) and segmental (SMLC, also known as ''step-and-shoot'') Intensity Modulated Radiation Therapy (IMRT) techniques, using Portal Dosimetry (PD) in Treatment Planning System Eclipse (8.6 version). Materials and Methods: 7 Head and Neck (HN) patients treated in our Institute with IMRT DMLC technique were retrospectively selected for the study. Plans were also re-calculated with SMLC at 5, 10 and 20 levels of intensity. A total of 107 fields/sub fields were analyzed. The dosimetric verification was performed with Portal Dosimetry system into Eclipse, the agreement between calculated and measured fluence was evaluated using the gamma index (maximum γmax, average γavg, percentage of points with γ%≤1). The images were acquired at a source-detector distance (SDD) of 100 cm, in integrated mode with 30 frames per second (fps), projecting each field on the EPID at gantry 0°. Measures, keeping the real clinical gantry angles, were also carried out to assess the effect of gantry rotation on the dosimetric results. Results: For all techniques measurements are well within the acceptable criteria γavg< 0.5, γ% ≤ 1 greater than 95% (99.8%, 99.7%, 99.4%, 99.0% for DMLC and SMLC 20,10,5 respectively). γmax improves (+19.5%) increasing the numbers of intensity levels from 5 to 20 and using DMLC (+34%). Delivery efficiency for all tecniques was affected by gantry angles and leaves traveling direction, improvements for SMLC compared to DMLC were observed increasing the number of intensity levels. Conclusions: A good agreement between calculated and measured fluence was obtained for both DMLC and SMLC techniques and levels. The effect of gantry rotation as well as leaves traveling direction opposite to the gravitational force influence results for all techniques in particular for SMLC at low intensity levels.