Analysis and Study of the Impact of Upgrading the Treatment Head of Elekta Precise Linear Accelerator on the Beam Profile Parameters of 6 MV and 15 MV Photon Beams

210 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli Analysis and Study of the Impact of Upgrading the Treatment Head of Elekta Precise Linear Accelerator on the Beam Profile Parameters of 6 MV and 15 MV Photon Beams. 1*Abdurraouf M. Aghila, 1Ali R. Khalf, 2Faraj A. Elmasrub 1Physics Department, Faculty of Education-Tripoli, University of Tripoli, Tripoli, Libya. 2National Cancer Institute of Sabratha, Sabratha, Libya. *Corresponding: ab.agh[email protected] ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ ــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ ـــــــــــــــــــــــــــــــــــــــــــــــــــــــــــ يطخلا لجعملا زاهج سأر ريوطت ريثأت ليلحتو ةسارد Elekta Precise ىلع عطقملا تلاماعم ا تاذ تانوتوفلا مزحل يبناجلا ةقاطل6 MV و15 MV. Article history Received: Nov 5, 2024 Accepted: Nov 27, 2024 :صخلملا يلاوحل ةدعاسم وأ ةيساسأ جلاع ةقيرطك لمعي ثيح ،ةثيبخلا مارولأا جلاع يف اًمساح اًرود يعاعشلإا جلاعلا بعلي50 ىضرم نم % ةيناطرسلا مارولأا نأ بجي ،ةيلاثم جئاتن ىلع لوصحلل . زواجتت لا ةفوصوملا عاعشلإا تاعرجةلصاولاو ± هل ططخملا فدهلا مجحل5 .٪ ريثأت يف ةساردلا هذه ثحبتريوطت ( يطخلا لجعملاElekta Preciseب ) ىفشتسمب يعاعشلإا جلاعلا مسق يعماجلا سلبارط ،سلبارط يف ( يسايق عاعشإ سأر نم ،ايبيلSH ددعتم سأر ىلإ )حئارشلا (MLC صئاصخ ىلع ) مزحنوتوفلاتا اًديدحتو ،تارتيمراب ةيبناجلا عطاقملا عاعشلإل تاقاطل6 MV و15 MV ماظن مادختساب .لا حسملا داعبلأا يثلاثPTW MP3-M ،لا لمشت تاسايق ةيعاعشلإا حطست ةمزح عاعشلإا دعبو لبق لظلا هبشو رظانتلاوزاهجلا ريوطت ةيجلاع لوقحل .ةفلتخم قامعأو تفشك يف ريبك فلاتخا نع ةساردلا هذه جئاتن تارتيمراب ثيح لجعملا زاهج ريوطت دعب عاعشلإل ةيبناجلا عطاقملا حطست يف ةيبسنلا تافلاتخلاا تناك ةمزحلإا عاعش66.30 % ةمزحل تانوتوفلا6 MV و24.64 % تانوتوفلا ةمزحل15 MV . ةفاضإ يف لجسم يبسن فلاتخا ىلعأ ناك ،كلذ ىلإلوط ةقطنم هبش لا لظ 31.76 ةقاطل % تانوتوفلا6 MV و17.65 ةقاطل % تانوتوفلا15 MV ةداعإ ةدشب هب ىصوملاو يرورضلا نمف ،يلاتلابو . تاسايق ءارجإ تانايب ةمطنأ يف اهمادختسا متي يتلاو عاعشلإل ةبناجلا عطاقملل ليغشتلا ةيادب ىدل ةعرجلا عيزوتب ؤبنتلل جلاعلا طيطخت.ىضرملا :ةيحاتفملا تاملكلا ملاق حئارشلا ددعتم ددحم ،عاعشلإل ةيبناجلا عطا ،يسايق ددحم ،حطستلا ،لثامتلا ، ،لظلا هبشElekta Preces Linac. A B S T R A C T: Radiotherapy plays a crucial role in the management of malignant tumors, serving as an essential or adjunct treatment modality for approximately 50% of cancer patients. For optimal outcomes, the prescribed and delivered radiation doses to the planning target volume must align within ± 5%. This study investigates the impact of upgrading the Elekta Precise Linear Accelerator (LINAC) at the Radiotherapy Department of Tripoli University Hospital in Tripoli, Libya, from a standard radiation head (SH) to a multileaf collimator (MLC) head on photon beam characteristics, specifically the beam profile parameters for energies of 6 MV and 15 MV. Utilizing a PTW MP3-M 3D water scanning system, detailed dosimetric measurements— including beam flatness, symmetry, and penumbra—were conducted before and after the upgrade across various field sizes and depths. The results of this study reveal a significant difference in beam profile parameters post-upgrade. The relative differences in beam flatness were 66.30% for the 6 MV beam and 24.64% for the 15 MV beam. Additionally, the highest recorded relative difference in beam penumbra was 31.76% for the 6 MV beam energy and 17.65% for the 15 MV beam energy. Consequently, it is essential and strongly recommended that the collected beam profile data be recommissioned since it is provided to the treatment planning system used to predict dose distribution in cancer patients. Keywords: Beam Profile, MLC, SH Collimator, Flatness, Symmetry, Penumbra, Elekta Preces Linac. Introduction: Currently, radiotherapy is one of the most commonly used oncological therapies in the treatment of malignant tumors. Furthermore, it is considered an essential or complementary part of treatment in approximately 50% of cancer patients [1,2,3]. For 211 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli radiotherapy to be effective and achieve a controlled cure rate without excessive healthy tissue complications, the prescribed and delivered dose to a planning target volume (PTV) must agree within ± 5% [4, 5, 6]. The delivered radiation dose is influenced by several factors, some are related to tumor specifications, while others are associated with the radiation machine used. The Linear accelerator has been a vital tool in contemporary external beam radiation therapy since 1953 [7]. The design of Linear accelerators can vary between manufacturers in terms of the specific components used, the overall layout of the machine, and the control systems employed. Different manufacturers may prioritize different features or technologies in their designs, leading to variations in performance and capabilities [8, 9, 10]. The year 2013 witnessed an upgrade of the first linear accelerator (LINAC) machine installed in the Radiotherapy Department at Tripoli University Hospital (TUH) in Libya during the year 2004. The machine was an Elekta Precise LINAC with multiple photon and electron beam energies and a standard radiation head (SH) with asymmetric jaws. The upgrade involves replacing the SH with a multileaf collimator head (MLC) to define the radiation field geometry. The new head has two banks, each containing 40 leaves with a nominal width projection of 10 mm at the isocenter [11]. The design of the treatment head of a LINAC has a significant influence on the dose distribution. Since the radiation dose distribution is influenced by the characteristics of the radiation beam, such as the percentage depth dose and beam profile, variations in this quantity are expected due to the upgrade that the LINAC has undergone. According to Task Group 53 [12] of the American Association of Physicists in Medicine, the machine should be recommissioned after significant maintenance, adjustments, or other alterations to the beam modifications. Additionally, the results of Aghila et al [13]. in their study of the impact of upgrading the LINAC showed significant differences in percentage depth dose parameters. Therefore, this study aimed to examine and assess the impacts of upgrading the Elekta Precise LINAC on the beam profile parameters for photon beams of energies 6 MV and 15 MV. The investigation involved detailed measurements and analyses of the beam profiles before and after the upgrade. Various dosimetric parameters of the beam profile, such as beam flatness, symmetry, and penumbra, were evaluated to quantify the changes resulting from the enhancements. Materials and Methods: 212 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli An Elekta Precise linear accelerator (Elekta Ltd., Crawley, UK) with two treatment modes, photon and electron beams, was employed for the measurements in this study. The photon mode energies were 4 MV, 6 MV, and 15 MV before the upgrade, and they were 6 MV, 10 MV, and 15 MV beam energies following the upgrade. However, the electron mode energies were 4 MeV, 6 MeV, 8 MeV, 10 MeV, 15 MeV, and 18 MeV before the upgrade, while after the upgrade, the energy of 12 MeV was added to the previous energies. The beam profile measurements were obtained using a motorized PTW MP3-M 3D water scanning system (PTW, Freiburg, Germany), a water tank of inner size 59.6 cm × 59.4 cm × 50.25 cm, a TANDEM electrometer, a TBA control unit, and two 0.125 cm3 Semiflex ionization chambers for in-field and reference. MEPHISTO mc2 navigation software (PTW, Freiburg) version 1.6 was used for data processing and analysis. The measurements of beam profile preand post-upgrade were conducted at a constant source-to-surface distance of 100 cm for various field sizes ranging from 3 × 3 𝑐𝑚2 to 35 ×35 𝑐𝑚2 at specific depths (depth of maximum dose cm (dmax), 5 cm, 10 cm, 20 cm, and 30 cm). The angles of the gantry and the collimator were at 0o during the measurements. The International Atomic Energy Agency (IAEA) Technical Report Series 277 and 398 dosimetry protocols [14, 15] were followed for the beam profile measurements. Results and Discussion: The beam profile, which is the absorbed dose distribution at a given depth in water phantom parallel to the water surface and perpendicular to the beam central axis [16, 17], is influenced by the primary of accelerated electron, thickness, and atomic number of target that the accelerated electrons collide with, and the flattening filter [18]. It should be noted that the data on radiation dose distribution along the central and off-axis, together with other parameter measurements, are essential for predicting the radiation dose within patients via the treatment planning systems [19]. For calculations of beam flatness, beam symmetry, and beam penumbra, the beam profiles were normalized to 100% at the central axis to their corresponding field sizes. The relative difference (RD) between the parameter values preand post-upgrade was calculated using the following formula: 𝑅𝐷 =|𝑉1−𝑉2| (𝑉1+𝑉2)2 ⁄×100 Where: 𝑉1 the value pre-upgrade, 𝑉2 the value post-upgrade. 213 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli Beam profile: Beam profile measurements for selected field sizes (5×5 cm2, 10×10 cm2, 20×20 cm2, and 30×30 cm2) of energies 6 MV and 15 MV are presented in Figures 1 and 2, respectively. The profiles were measured at depths of depth of dose maximum dmax cm, 5 cm, 10 cm, 20 cm, and 30 cm. -100 -50 0 50 100 0 20 40 60 80 100 120 -150 -100 -50 0 50 100 150 0 20 40 60 80 100 120 -200 -100 0 100 200 0 20 40 60 80 100 120 -300 -200 -100 0 100 200 300 0 20 40 60 80 100 120 Relative dose % Off axis distance ( mm ) dmax (5x5) cm MLC ; dmax (5x5) cm SH 5 (5x5) cm MLC ; 5 (5x5) cm SH 10 (5x5) cm MLC ; 10 (5x5) cm SH 20 (5x5) cm MLC ; 20 (5x5) cm SH 30 (5x5) cm MLC ; 30 (5x5) cm SH Photon Energy : 6 MV Field size : 5x5 cm2Photon Energy : 6 MV Field size : 10x10 cm2 Off axis distance ( mm ) Relative dose % dmax (10x10) cm MLC ; dmax (10x10) cm SH 5 (10x10) cm MLC ; 5 (10x10) cm SH 10 (10x10) cm MLC ; 10 (10x10) cm SH 20 (10x10) cm MLC ; 20 (10x10) cm SH 30 (10x10) cm MLC ; 30 (10x10) cm SH Off axis distance ( mm ) Relative dose % Photon Energy : 6 MV Field size : 20x20 cm2 dmax (20x20) cm MLC ; dmax (20x20) cm SH 5 (20x20) cm MLC ; 5 (20x20) cm SH 10 (20x20) cm MLC ; 10 (20x20) cm SH 20 (20x20) cm MLC ; 20 (20x20) cm SH 30 (20x20) cm MLC ; 30 (20x20) cm SH Off axis distance ( mm ) Relative dose % Photon Energy : 6 MV Field size : 30x30 cm2 dmax (30x30) cm MLC ; dmax (30x30) cm SH 5 (30x30) cm MLC ; 5 (30x30) cm SH 10 (30x30) cm MLC ; 10 (30x30) cm SH 20 (30x30) cm MLC ; 20 (30x30) cm SH 30 (30x30) cm MLC ; 30 (30x30) cm SH Figure 1: Beam profiles of size 5x5 cm2, 10x10 cm2, 20x20 cm2 and 30x30 cm2 for photon energy of 6 MV. 214 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli -100 -50 0 50 100 0 20 40 60 80 100 120 -100 -50 0 50 100 0 20 40 60 80 100 120 -200 -150 -100 -50 0 50 100 150 200 0 20 40 60 80 100 120 -300 -200 -100 0 100 200 300 0 20 40 60 80 100 120 Off axis distance ( mm ) Relative dose % Photon Energy : 15 MV Field size : 5x5 cm2 dmax (5x5) cm MLC ; dmax (5x5) cm SH 5 (5x5) cm MLC ; 5 (5x5) cm SH 10 (5x5) cm MLC ; 10 (5x5) cm SH 20 (5x5) cm MLC ; 20 (5x5) cm SH 30 (5x5) cm MLC ; 30 (5x5) cm SH Photon Energy : 15 MV Field size : 10x10 cm2 Off axis distance ( mm ) Relative dose % dmax (10x10) MLC ; dmax (10x10) SH 5 (10x10) cm MLC ; 5 (10x10) cm SH 10 (10x10) cm MLC ; 10 (10x10) cm SH 20 (10x10) cm MLC ; 20 (10x10) cm SH 30 (10x10) cm MLC ; 30 (10x10) cm SH Photon Energy : 15 MV Field size : 20x20 cm2 Off axis distance ( mm ) Relative dose % dmax (20x20) cm MLC ; dmax (20x20) cm SH 5 (20x20) cm MLC ; 5 (20x20) cm SH 10 (20x20) cm MLC ; 10 (20x20) cm SH 20 (20x20) cm MLC ; 20 (20x20) cm SH 30 (20x20) cm MLC ; 30 (20x20) cm SH Off axis distance ( mm ) Relative dose % Photon Energy : 15 MV Field size : 30x30 cm2 dmax (30x30) cm MLC ; dmax (30x30) cm SH 5 (30x30) cm MLC ; 5 (30x30) cm SH 10 (30x30) cm MLC ; 10 (30x30) cm SH 20 (30x30) cm MLC ; 20 (30x30) cm SH 30 (30x30) cm MLC ; 30 (30x30) cm SH Figure 2: Beam profiles of size 5x5 cm2, 10x10 cm2, 20x20 cm2 and 30x30 cm2 for photon energy of 15 MV. Figures 1 ظ and 2 illustrate a well-distribution of radiation dose on both sides of the central axis. The radiation dose is uniformly distributed and then decreases towards the edges to form a penumbra region. Measured field size: Figures 3 and 4 illustrate a detailed analysis of the percentage difference in field sizes for 6 MV and 15 MV photon beams, respectively, following an upgrade in collimation technology. Figure 3 shows that the 6 MV photon beam has minimal variations, with differences ranging from 0.1% to 1.77% across different field sizes. On the other hand, Figure 4 indicates larger differences for the 15 MV beam, ranging from 2.1% to 3.3%, highlighting that collimation system effects are more significant at higher energy levels. 215 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli 5x5 10x10 20x20 30x30 0 5 10 15 20 25 30 35 Full width at half maximum Field size For 6 MV (cm2) Photon beam of energy 6 MV MLC Collimator field Actual field size SH Collimator field 0.1% 1.8% 0.1% 1.4% 0.2% 2.0% 0.4% 1.0% Figure 3: Nominal field size vs measured FWHM for photon energy of 6 MV. 5x5 10x10 20x20 30x30 0 5 10 15 20 25 30 35 3.3% Full width at half maximum Field size For 15 MV (cm2) Photon beam of energy 15 MV MLC Collimator field Actual field size SH Collimator field 2.6% 2.2% 2.9% 3.2% 2.1% 2.2% 2.0% Figure 4: Nominal field size vs measured FWHM for photon energy of 15 MV. Beam flatness: The results of beam flatness values of 6 MV and 15 MV photon beam energies measured at various depths (dmax cm, 5 cm, 10 cm, 20 cm, and 30 cm) and field sizes (5×5 216 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli cm2, 10×10 cm2, 20×20 cm2, and 30×30 cm2), for both the SH and the ML Collimators, are presented in Tables 1 and 2, respectively. Table 3 shows the Relative difference (RD) in beam flatness values between the SH and ML collimators across two distinct photon beam energies: 6 MV and 15 MV. Table 1: represent the beam flatness values of 6 MV beam energy at various depths and field sizes for both the SH and ML collimator. Field size Collimator type Depth (cm) dmax 5 10 20 30 5x5 cm2 ML Collimator 2.42 3.2 3.56 3.68 3.83 SH Collimator 4.82 5.31 5.73 5.92 6.16 10x10 cm2 ML Collimator 0.77 1.39 1.97 2.87 3.5 SH Collimator 1.11 1.81 2.52 3.63 4.12 20x20 cm2 ML Collimator 1.56 1.83 1.93 3.89 5.28 SH Collimator 1.07 1.28 2.23 4.36 5.82 30x30 cm2 ML Collimator 1.31 1.57 1.95 4.31 6.45 SH Collimator 1.00 1.23 1.82 4.51 6.73 Table 2: represent the beam flatness values of 15 MV beam energy at various depths and field sizes for both the SH and ML collimator. Field size Collimator type Depth (cm) dmax 5 10 20 30 5x5 cm2 ML Collimator 4.84 5.44 5.58 5.02 5.29 SH Collimator 6.20 6.25 6.43 6.52 6.61 10x10 cm2 ML Collimator 1.04 1.59 2.28 2.98 3.41 SH Collimator 1.30 1.7 2.3 3 3.4 20x20 cm2 ML Collimator 1.24 1.57 1.72 2.39 3.15 SH Collimator 2.14 2.41 2.38 2.73 3.72 30x30 cm2 ML Collimator 1.49 1.89 2.26 3.27 5.13 SH Collimator 3.85 3.95 4.41 4.49 5.47 Table 3: represent the relative difference in beam flatness values between the Jaw collimator and Multileaf collimators for 6 MV and 15 MV photon beam energies. Beam energy Field size (cm2) Depth (cm) dmax 5 10 20 30 6 MV 5x5 66.3% 49.59% 46.72% 46.67% 46.65% 10x10 36.17% 26.25% 24.5% 23.38% 16.27% 20x20 37.26% 35.37% 14.42% 11.39% 9.73% 30x30 26.84% 24.29% 6.9% 4.54% 4.25% 217 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli 15 MV 5x5 24.64% 13.86% 14.15% 26% 22.18% 10x10 22.22% 6.69% 0.87% 0.67% 0.29% 20x20 53.25% 42.21% 32.2% 13.28% 16.59% 30x30 88.39% 70.55% 64.47% 31.44% 6.42% For 6 MV photon beam energy, the results presented in Table 1 show that the range of beam flatness values for the SH collimator is 0.77% to 6.45%, while for the ML collimator, it is 1.00% to 6.73%. For 15 MV photon beam energy, as shown in Table 2, the range of beam flatness values for the SH collimator is 1.30% to 6.61%, and for the ML collimator, it is 1.04% to 5.29%. Moreover, as shown in Tables 1 and 2, the values of beam flatness increase with increasing depth of measurements. The results are in agreement with those of R. I. Chowdhury et al [20]. The RD in beam flatness values between the SH and ML collimators, as shown in Table 3, are significant, and the highest RD values occur at a depth of maximum dose for both photon beam energies. For the 6 MV photon beam energy, the results indicate a substantial RD in beam flatness associated with various field sizes at dmax, where the 5x5 cm² field size shows the highest difference of 66.30%. As the measurement depth increases, these differences generally diminish across all field sizes, with the 30x30 cm² field size demonstrating a significantly lower relative difference of only 4.25%. The 15 MV photon beam energy reveals variable RDs in beam flatness across different field sizes and depths. A significant RD of 24.64% is observed at dmax for the 5x5 cm² field, with marked fluctuations noted at deeper levels. The maximum discrepancy recorded for the 15 MV photon beam energy was 88.39% at a 30x30 cm² field size and a depth of 5 cm. Beam symmetry: The beam symmetry values for 6 MV and 15 MV photon beam energies were measured at various depths (dmax cm, 5 cm, 10 cm, 20 cm, and 30 cm) and field sizes (5×5 cm², 10×10 cm², 20×20 cm², and 30×30 cm²) for both the SH and ML collimators, with the results detailed in Tables 4 and 5, respectively. Additionally, Table 6 presents the RD in beam symmetry values between the SH and ML collimators for the two-photon beam energies of 6 MV and 15 MV. 218 ددعلا20 دلجملا ،1 (ربمسيد 2024 ) لجمـــــيلك ةـــــيبرتلا ةـــــلبارط ةــــــس Journal of the Faculty of Education Tripoli Table 4: represent the beam symmetry values of 6 MV beam energy at various depths and field sizes for both the SH and ML collimator. Field size Collimator type Depth (cm) dmax 5 10 20 30 5x5 cm2 ML Collimator 1.11 1.25 0.71 0.26 1.08 Jaw Collimator 0.92 1.02 0.59 0.21 0.91 10x10 cm2 ML Collimator 0.08 1.08 0.91 0.67 0.24 Jaw Collimator 0.1 0.9 1.07 0.53 0.19 20x20 cm2 ML Collimator 0.86 0.73 0.95 0.48 0.71 Jaw Collimator 1.1 0.92 0.79 0.61 0.59 30x30 cm2 ML Collimator 0.1 0.24 0.38 0.49 0.7 Jaw Collimator 0.08 0.19 0.31 0.38 0.52 Table 5: represent the beam symmetry values of 15 MV beam energy at various depths and field sizes for both the SH and ML collimator. Field size Collimator type Depth (cm) dmax 5 10 20 30 5x5 cm2 ML Collimator 0.53 1.1 0.92 1.15 1.85 SH Collimator 0.38 0.77 0.75 0.84 1.31 10x10 cm2 ML Collimator 0.78 1.79 1.92 1.19 1.66 SH Collimator 0.6 1.43 1.45 0.93 1.24 20x20 cm2 ML Collimator 1.32 1.72 1.13 1.31 1.53 SH Collimator 1.13 1.45 1.41 1.07 1.24 30x30 cm2 ML Collimator 1.02 1.04 0.51 1.43 1.11 SH Collimator 0.78 0.82 0.58 1.2 0.91 Table 6: represent the relative difference in beam symmetry values between the SH and ML collimators for 6 MV and 15 MV photon beam energies. Beam energy Field size (cm2) Depth (cm) dmax 5 10 20 30 6 MV 5x5 32.97 35.29 20.36 31.16 34.18 10x10 26.09 22.36 27.89 24.53 28.97 20x20 15.51 17.03 22.05 20.17 20.94 30x30 26.67 23.66 12.84 17.49 19.8 15 MV 5x5 18.72 20.26 18.46 21.28 17.09 10x10 22.22 18.18 16.16 23.33 23.26 20x20 24.49 23.03 18.39 23.85 18.46 30x30 22.22 23.26 20.29 25.29 29.51