1
|
Quoc SD, Fujibuchi T, Arakawa H, Hamada K. Simulating the head of a TrueBeam linear particle accelerator and calculating the photoneutron spectrum on the central axis of a 10-MV photon using particle and heavy-ion transport system code. RADIATION PROTECTION DOSIMETRY 2024; 200:779-790. [PMID: 38767288 DOI: 10.1093/rpd/ncae124] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/14/2023] [Revised: 03/15/2024] [Accepted: 05/06/2024] [Indexed: 05/22/2024]
Abstract
Photon energy is higher than the (γ,n) threshold, allowing it to interact with the nuclei of materials with high z properties and liberate fast neutrons. This represents a potentially harmful source of radiation for humans and the environment. This study validated the Monte Carlo simulation, using the particle and heavy-ion transport code system (PHITS) on a TrueBeam 10-MV linear particle accelerator's head shielding model and then used this PHITS code to simulate a photo-neutron spectrum for the transport of the beam. The results showed that, when comparing the simulated to measured PDD and crosslines, 100% of the γ-indexes were <1 (γ3%/3mm) for both simulations, for both phase-space data source and a mono energy source. Neutron spectra were recorded in all parts of the TrueBeam's head, as well as photon neutron spectra at three points on the beamline.
Collapse
Affiliation(s)
- Soai Dang Quoc
- Division of Medical Quantum Science, Department of Health Sciences, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Toshioh Fujibuchi
- Division of Medical Quantum Science, Department of Health Sciences, Faculty of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan
| | - Hiroyuki Arakawa
- Division of Medical Quantum Science, Department of Health Sciences, Faculty of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka, Fukuoka 812-8582, Japan
| | - Keisuke Hamada
- Division of Medical Quantum Science, Department of Health Sciences, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
- Department of Radiological Technology, National Hospital Organization Kyushu Cancer Center, 3-1-1 Notame Minami-ku, Fukuoka, Fukuoka 811-1395, Japan
| |
Collapse
|
2
|
Masjedi H. In response to "Measurement of neutron yield for a medical linear accelerator below 10 MV". Med Phys 2024; 51:2350-2351. [PMID: 38573715 DOI: 10.1002/mp.16989] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Accepted: 02/01/2024] [Indexed: 04/05/2024] Open
Affiliation(s)
- Hamidreza Masjedi
- Researcher at Medical Imaging Research Centre, Shiraz University of Medical Sciences, Shiraz, Iran
| |
Collapse
|
3
|
Gauter-Fleckenstein B, Schönig S, Mertens L, Oppitz H, Siebenlist K, Ehmann M, Fleckenstein J. Effect of simultaneous integrated boost concepts on photoneutron and distant out-of-field doses in VMAT for prostate cancer. Strahlenther Onkol 2024; 200:219-229. [PMID: 37707518 PMCID: PMC10876496 DOI: 10.1007/s00066-023-02138-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2023] [Accepted: 08/08/2023] [Indexed: 09/15/2023]
Abstract
BACKGROUND A simultaneous integrated boost (SIB) may result in increased out-of-field (DOOF) and photoneutron (HPN) doses in volumetric modulated arc therapy (VMAT) for prostate cancer (PCA). This work therefore aimed to compare DOOF and HPN in flattened (FLAT) and flattening filter-free (FFF) 6‑MV and 10-MV VMAT treatment plans with and without SIB. METHODS Eight groups of 30 VMAT plans for PCA with 6 MV or 10 MV, with or without FF and with uniform (2 Gy) or SIB target dose (2.5/3.0 Gy) prescriptions (CONV, SIB), were generated. All 240 plans were delivered on a slab-phantom and compared with respect to measured DOOF and HPN in 61.8 cm distance from the isocenter. The 6‑ and 10-MV flattened VMAT plans with conventional fractionation (6- and 10-MV FLAT CONV) served as standard reference groups. Doses were analyzed as a function of delivered monitor units (MU) and weighted equivalent square field size Aeq. Pearson's correlation coefficients between the presented quantities were determined. RESULTS The SIB plans resulted in decreased HPN over an entire prostate RT treatment course (10-MV SIB vs. CONV -38.2%). Omission of the flattening filter yielded less HPN (10-MV CONV -17.2%; 10-MV SIB -22.5%). The SIB decreased DOOF likewise by 39% for all given scenarios, while the FFF mode reduced DOOF on average by 60%. A strong Pearson correlation was found between MU and HPN (r > 0.9) as well as DOOF (0.7 < r < 0.9). CONCLUSION For a complete treatment, SIB reduces both photoneutron and OOF doses to almost the same extent as FFF deliveries. It is recommended to apply moderately hypofractionated 6‑MV SIB FFF-VMAT when considering photoneutron or OOF doses.
Collapse
Affiliation(s)
- Benjamin Gauter-Fleckenstein
- Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, 68167, Mannheim, Germany.
| | - Sebastian Schönig
- Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, 68167, Mannheim, Germany
| | - Lena Mertens
- Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, 68167, Mannheim, Germany
| | - Hans Oppitz
- Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, 68167, Mannheim, Germany
| | - Kerstin Siebenlist
- Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, 68167, Mannheim, Germany
| | - Michael Ehmann
- Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, 68167, Mannheim, Germany
| | - Jens Fleckenstein
- Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Theodor-Kutzer Ufer 1-3, 68167, Mannheim, Germany
| |
Collapse
|
4
|
Prasada DNY, Ciamaudi N, Fadli M, Tursinah R, Pawiro SA. Evaluation of the linac neutron dose profile for various depths and field sizes: a Monte Carlo study. Biomed Phys Eng Express 2021; 7. [PMID: 34619664 DOI: 10.1088/2057-1976/ac2dd5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2021] [Accepted: 10/07/2021] [Indexed: 11/12/2022]
Abstract
High-energy medical linear accelerator (Linac) has been widely used for treating cancer patients. However, with its effectiveness, high-energy linac yields an undesirable amount of neutron contamination. An MCNPX code version 2.6.0 was used for calculating photoneutron contamination from Varian Clinac iX 15 MV linac heads in this study. The fast neutrons were dominantly produced inside the linac head. The neutron fluence, absorbed dose, and dose equivalent calculations occurred inside a linac head and a water phantom model. The fast neutrons begin to be moderated after 1 cm inside the water phantom by calculating the energy spectra. Variations in the field sizes from 2 × 2, 5 × 5, 10 × 10, and 15 × 15 cm2show that the neutron production yield would increase for larger field sizes. The maximum neutron dose equivalents are 3.745; 7.687; 11.794 and 14.197μSv/MU for 2 × 2, 5 × 5, 10 × 10 and 15 × 15 cm2field sizes, respectively. These calculations predict the photoneutron characteristics with more detail inside a treated patient during radiation therapy procedures.
Collapse
Affiliation(s)
- Dewa Ngurah Yudhi Prasada
- Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, Indonesia.,Department of Radiation Oncology, MRCCC Siloam Hospitals, Jakarta, Indonesia
| | - Nikita Ciamaudi
- Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, Indonesia
| | - Muhamad Fadli
- Department of Radiation Oncology, MRCCC Siloam Hospitals, Jakarta, Indonesia
| | - Rasito Tursinah
- Centre for Applied Nuclear Science and Technology, National Nuclear Energy Agency, Bandung, Indonesia
| | - Supriyanto Ardjo Pawiro
- Department of Physics, Faculty of Mathematics and Natural Sciences, Universitas Indonesia, Depok, Indonesia
| |
Collapse
|
5
|
Wang H, Chen K, Shi Y, Huang X, Sun W, Hou K, Jin Y, Jiang X, Yang D, Dong L. Technical Note: Induced radioactivity in stereotactic body radiation therapy with a flattening-filter-free 10 MV beam model. Med Phys 2021; 48:2010-2017. [PMID: 33524168 DOI: 10.1002/mp.14747] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Revised: 11/11/2020] [Accepted: 01/25/2021] [Indexed: 01/03/2023] Open
Abstract
PURPOSE The induced radioactivity in stereotactic body radiation therapy with a flattening-filter-free 10 MV beam model (10 FFF SBRT) was investigated for the risk to therapists. METHODS This study was performed on a Varian TrueBeam linac. The induced radioisotopes were identified by γ spectroscopy. The dose rate from the induced activity was measured for 12 treatment cycles in 4 h continuously. The impacts of the characteristic factors of 10 FFF SBRT on the dose rate were investigated, including monitor units (MU), beam rate, field size, and flattening filter. The dose rate was compared between the SBRT plans and conventional fractionation plans. A mathematical model was used to analyze the results and estimate the annual dose to therapists. RESULTS (a) The induced radioisotopes included 24 Na, 28 Al, 38 Cl, 56 Mn, 66 Cu, 187 W, and 196 Au. (b) In 4 h, the total dose contribution ratios were more than 70% for 28 Al, about 20% for 56 Mn, and 10% for all other long-lived radioisotopes, combining doses at the isocenter and end of the treatment couch. (c) The dose rate showed a nonlinear growth with increasing MU and beam rate. The variation of the dose rate was complicated with the jaw field and not sensitive to the MLC field. The removal of the flattening filter reduced the dose rate by about 40%. The dose level of SBRT was two to three times that of conventional fractionation. (d) The estimated annual dose to therapists was up to 0.20 mSv/y. CONCLUSIONS The induced radioactivity in 10 FFF SBRT was higher compared with that in 10 MV conventional fractionation. More MU and higher beam rate were the primary factors that caused the increase. The therapists should wait longer after beam-off to reduce the occupational dose. In addition, aluminum and manganese should be less used in the treatment room.
Collapse
Affiliation(s)
- Huidong Wang
- Department of Radiation Oncology & Therapy, The First Hospital of Jilin University, Changchun, China
| | - Kunzhi Chen
- Department of Radiation Oncology & Therapy, The First Hospital of Jilin University, Changchun, China
| | - Yinghua Shi
- Department of Radiation Oncology & Therapy, The First Hospital of Jilin University, Changchun, China
| | | | - Wuji Sun
- College of Physics, Jilin University, Changchun, China
| | - Kairan Hou
- College of Physics, Jilin University, Changchun, China
| | - Yongli Jin
- China Institute of Atomic Energy, Beijing, China
| | - Xin Jiang
- Department of Radiation Oncology & Therapy, The First Hospital of Jilin University, Changchun, China
| | - Dong Yang
- College of Physics, Jilin University, Changchun, China
| | - Lihua Dong
- Department of Radiation Oncology & Therapy, The First Hospital of Jilin University, Changchun, China.,Jilin Provincial Key Laboratory of Radiation Oncology & Therapy, The First Hospital of Jilin University, Changchun, China
| |
Collapse
|
6
|
Vysakh R, Musthafa MM, Midhun CV, Niyas P, Anjana PT, Krishnan MPA, Ranjith CP, Irfad MP, Ganapathi Raman R. Experimental determination of thermal neutron fluence around Elekta Versa HD linear accelerator for various photon energies. Biomed Phys Eng Express 2020; 6:055018. [PMID: 33444249 DOI: 10.1088/2057-1976/abac90] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A complex neutron spectrum generated along with a useful photon beam imposes an additional radiation protection risk around medical linear accelerators (linac). The thermal neutron component of this complex neutron spectrum formed during different photon modes of operation of Elekta Versa HD linac has been quantified using Indium foil activation technique. The thermal neutron fluence (Φ th ) at isocenter for 15 MV, 10 MV and 10 MV FFF beams was found to be 2.45 × 105, 4.35 × 104 and 3.2 × 104 neutrons cm-2 Gy-1, respectively. The analysis shows a reduction in the Φ th as the flattening filter is being taken out from the beam path. A negative correlation in Φ th with respect to field size has been observed with an average 18% reduction in Φ th per monitor units as field size changes from 10 cm × 10 cm to 40 cm × 40 cm. For particular field size and photon energy, Φ th was found to be uniform across the patient plane. From the measured gamma ray spectrum inside the treatment room six major isotopes have been identified which were 122Sb, 187W, 82Br, 56Mn, 24Na and 28Al.
Collapse
Affiliation(s)
- R Vysakh
- Department of Physics, Noorul Islam Centre for Higher Education, Kumaracoil- 629 180, Kanyakumari District, Tamil Nadu, India. Department of Medical Physics and Radiation Safety, MVR Cancer Centre & Research Institute, Calicut, India
| | | | | | | | | | | | | | | | | |
Collapse
|
7
|
Gauter-Fleckenstein B, Nguyen J, Jahnke L, Gaiser T, Rudic B, Büttner S, Wenz F, Borggrefe M, Tülümen E. Interaction between CIEDs and modern radiotherapy techniques: Flattening filter free-VMAT, dose-rate effects, scatter radiation, and neutron-generating energies. Radiother Oncol 2020; 152:196-202. [PMID: 31973882 DOI: 10.1016/j.radonc.2019.12.007] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2019] [Revised: 12/07/2019] [Accepted: 12/12/2019] [Indexed: 10/25/2022]
Abstract
BACKGROUND AND PURPOSE Providing evidence for radiotherapy (RT)-induced effects on cardiac implantable electric devices (CIEDs) with focus on flattening filter free-volumetric modulated arc therapy (FFF-VMAT) at 6 and 10 MV as well as 3D-conformal radiotherapy (3D-CRT) at 18 MV. MATERIALS AND METHODS 68 CIEDs (64 implantable cardioverter-defibrillators (ICDs) and 4 cardiac pacemakers (PMs)) were located on the left chest position on a slab phantom and irradiated under telemetrical surveillance either directly, or distant to 3D-CRT or FFF-VMAT, dose-rate 2500 cGy/min, and target dose of 150 Gy. Devices were placed within, close by (2.5 cm and 5 cm), and distant (35 cm) to the radiation field. Scatter radiation (SR) and photon neutrons (PN) were recorded. CIEDs were investigated in following groups: 1a) 18 MV 3D-CRT - 4 ICDs/4 PMs out of radiation field, 1b) 18 MV open field - 4 ICDs/4 PMs within radiation field, 2) 6 MV FFF-VMAT, 15 ICDs in 35 cm distance to VMAT, 3) 10 MV-FFF VMAT, 15 ICDs in 35 cm distance to VMAT, 4) 6 MV FFF-VMAT, 15 ICDs in 2.5 cm distance to VMAT, 5) 10 MV FFF-VMAT, 15 ICDs in 2.5 cm distance to VMAT. RESULTS No incidents occurred at 6 MV FFF. 10 MV FFF-VMAT and 18 MV 3D-CRT resulted in data loss, reset, and erroneous sensing with inhibition of pacing (leading to inadequate defibrillation) in 8/34 ICDs and 2/4 PMs which were not located within radiation. Direct radiation triggered instantaneous defibrillation in 3/4 ICDs. CONCLUSIONS 6 MV FFF-VMAT is safe even at high dose-rates of 2500 cGy/min, regardless whether CIEDs are located close (2.5 cm) or distant (35 cm) to the radiation beam. CIEDs should never be placed within radiation and energy should always be limited to 6 MV. At 6 MV, VMAT at high dose-rates can be used to treat tumors, which are located close to CIEDs.
Collapse
Affiliation(s)
- Benjamin Gauter-Fleckenstein
- Department of Radiation Oncology, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Germany.
| | - Julia Nguyen
- Medical Faculty Mannheim, Heidelberg University, Germany
| | - Lennart Jahnke
- Department of Radiation Oncology, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Germany
| | - Timo Gaiser
- Institute of Pathology, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Germany
| | - Boris Rudic
- First Department of Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Germany; DZHK (German Centre for Cardiovascular Research) partner site, Mannheim, Germany
| | - Sylvia Büttner
- Department of Biomathematics and Medical Statistics, University Medical Center Mannheim, University of Heidelberg, Germany
| | - Frederik Wenz
- Department of Radiation Oncology, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Germany
| | - Martin Borggrefe
- First Department of Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Germany; DZHK (German Centre for Cardiovascular Research) partner site, Mannheim, Germany
| | - Erol Tülümen
- First Department of Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Germany; DZHK (German Centre for Cardiovascular Research) partner site, Mannheim, Germany
| |
Collapse
|
8
|
Delany R, Tudor GSJ. A relative comparison of neutron production between conventional and energy-matched flattening-filter-free (FFF) 10MV modes for an elekta linear accelerator. Biomed Phys Eng Express 2019. [DOI: 10.1088/2057-1976/ab2c6f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
9
|
Dosimetric comparison of flattened and flattening filter-free beams for liver stereotactic body irradiation in deep inspiration breath hold, and free breathing conditions. JOURNAL OF RADIOTHERAPY IN PRACTICE 2019. [DOI: 10.1017/s146039691800064x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
AbstractAimThe aim of this study is to evaluate the influence of flattened and flattening filter-free (FFF) beam 6 MV photon beam for liver stereotactic body radiation therapy by using volumetric modulated arc therapy (VMAT) technique in deep inspiration breath hold (DIBH) and free breathing condition.Materials and methodsEight liver metastasis patients (one to three metastasis lesions) were simulated in breath hold and free breathing condition. VMAT-based treatment plans were created for a prescription dose of 50 Gy in 10 fractions, using a 230° coplaner arc and 60° non-coplanar arc for both DIBH and free breathing study set. Treatment plans were evaluated for planning target volume (PTV) dose coverage, conformity and hot spots. Parallel and serial organs at risk were compared for average and maximum dose, respectively. Dose spillages were evaluated for different isodose volumes from 5 to 80%.ResultMean D98% (dose received by 98% target volume) for FFF in DIBH, flattened beam in DIBH, FFF in free breathing and flatten beam in free breathing dataset were 48·9, 47·81, 48·5 and 48·3 Gy, respectively. D98% was not statistically different between FFF and flatten beam (p = 0·34 and 0·69 for DIBH and free breathing condition). PTV V105% (volume receiving 105% dose) for the same set were 3·76, 0·25, 1·2 and 0·4%, respectively. Mean heterogeneity index for all study sets and beam models varies between 1·05 and 1·07. Paddik conformity index using unflattened and flattened beam in DIBH at 98% prescription dose were 0·91 and 0·79, respectively. Maximum variation of isodose volume was observed for I-5%, which was ranging between 2288·8 and 2427·2 cm3. Increase in isodose value shows a diminishing difference in isodose volumes between different techniques. DIBH yields a significant reduction in the chest wall dose compared with free breathing condition. Average monitor units for FFF beam in DIBH, flattened beam in DIBH, FFF beam in free breathing CT dataset and flattened beam in free breathing CT dataset were 1318·6 ± 265·1, 1940·3 ± 287·6, 1343·3 ± 238·1 and 2192·5 ± 252·6 MU.ConclusionDIBH and FFF is a good combination to reduce the treatment time and to achieve better tumour conformity. No other dosimetric gain was observed for FFF in either DIBH or free breathing condition.
Collapse
|
10
|
Evaluation of in-field neutron production for medical LINACs with and without flattening filter for various beam parameters - Experiment and Monte Carlo simulation. RADIAT MEAS 2018. [DOI: 10.1016/j.radmeas.2018.04.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
11
|
Montgomery L, Evans M, Liang L, Maglieri R, Kildea J. The effect of the flattening filter on photoneutron production at 10 MV in the Varian TrueBeam linear accelerator. Med Phys 2018; 45:4711-4719. [PMID: 30141186 DOI: 10.1002/mp.13148] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2018] [Revised: 07/25/2018] [Accepted: 08/08/2018] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Neutrons are an unavoidable by-product of high-energy radiation therapy treatments that deliver unwanted nontarget dose to patients. Use of flattening-filter-free (FFF) photon beams has been shown to significantly reduce photoneutron production per monitor unit (MU) of dose delivered. The purpose of this investigation was to characterize the photoneutron production of the 10 MV and 10 MV FFF beams of the Varian TrueBeamTM linear accelerator. METHODS Neutron fluence spectra were measured using a Nested Neutron SpectrometerTM (NNS, Detec Inc., Gatineau, Canada). The ratios of neutron fluence and ambient dose equivalent for the 10 MV FFF beam relative to the 10 MV beam, dubbed FF-ratios (FFF/FF), were used to characterize the difference between the two beams. FF-ratios were compared under the following three conditions (a) per MU, at various locations in the treatment room, (b) per MU, with the linac jaws opened and closed, and (c) per electron striking the bremsstrahlung target, as opposed to per MU, at one location with the jaws closed. RESULTS On average, the neutron fluence for the 10 MV FFF beam was 37% lower per MU than the 10 MV beam (FF-ratio = 0.63). The FF-ratio in neutron fluence and ambient dose equivalent did not vary by much between different locations within the treatment room. However, the FF-ratio in neutron ambient dose equivalent was reduced significantly when the linac jaws were opened compared to closed, which implies that the jaws contribute more to the photoneutron spectrum of the 10 MV FFF beam than to the 10 MV beam. Finally, it was found that the 10 MV FFF beam produces more photoneutrons per electron striking the bremsstrahlung target than the 10 MV beam (FF-ratio = 2.56). CONCLUSIONS The photoneutron fluence per MU produced by the 10 MV FFF beam is 37% lower than the 10 MV beam of a Varian TrueBeam linac. Accordingly, a reduction in neutron dose received by patients is achieved through use of the unflattened beam, provided that treatment plans for each beam require approximately the same number of MU. It was found to be instructive to compare the photoneutron yield per source electron between the two beams as it helped provide an understanding of the physics underlying photoneutron production in both beams.
Collapse
Affiliation(s)
- Logan Montgomery
- Medical Physics Unit, McGill University, Montreal, QC, H4A3J1, Canada
| | - Michael Evans
- Medical Physics Unit, McGill University, Montreal, QC, H4A3J1, Canada
| | - Liheng Liang
- Medical Physics Unit, McGill University, Montreal, QC, H4A3J1, Canada.,Department of Radiation Oncology, Jewish General Hospital, Montreal, QC, H3T1E2, Canada
| | - Robert Maglieri
- Medical Physics Unit, McGill University, Montreal, QC, H4A3J1, Canada
| | - John Kildea
- Medical Physics Unit, McGill University, Montreal, QC, H4A3J1, Canada
| |
Collapse
|
12
|
Kry SF, Bednarz B, Howell RM, Dauer L, Followill D, Klein E, Paganetti H, Wang B, Wuu CS, George Xu X. AAPM TG 158: Measurement and calculation of doses outside the treated volume from external-beam radiation therapy. Med Phys 2017; 44:e391-e429. [DOI: 10.1002/mp.12462] [Citation(s) in RCA: 164] [Impact Index Per Article: 23.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2016] [Revised: 05/17/2017] [Accepted: 05/25/2017] [Indexed: 12/14/2022] Open
Affiliation(s)
- Stephen F. Kry
- Department of Radiation Physics; MD Anderson Cancer Center; Houston TX 77054 USA
| | - Bryan Bednarz
- Department of Medical Physics; University of Wisconsin; Madison WI 53705 USA
| | - Rebecca M. Howell
- Department of Radiation Physics; MD Anderson Cancer Center; Houston TX 77054 USA
| | - Larry Dauer
- Departments of Medical Physics/Radiology; Memorial Sloan-Kettering Cancer Center; New York NY 10065 USA
| | - David Followill
- Department of Radiation Physics; MD Anderson Cancer Center; Houston TX 77054 USA
| | - Eric Klein
- Department of Radiation Oncology; Washington University; Saint Louis MO 63110 USA
| | - Harald Paganetti
- Department of Radiation Oncology; Massachusetts General Hospital and Harvard Medical School; Boston MA 02114 USA
| | - Brian Wang
- Department of Radiation Oncology; University of Louisville; Louisville KY 40202 USA
| | - Cheng-Shie Wuu
- Department of Radiation Oncology; Columbia University; New York NY 10032 USA
| | - X. George Xu
- Department of Mechanical, Aerospace, and Nuclear Engineering; Rensselaer Polytechnic Institute; Troy NY 12180 USA
| |
Collapse
|
13
|
Li D, Deng X, Xue Y, Lou Z, Zhang Y, Guo W, Wang J. Neutron dose distribution in the treatment room for an accelerator in the flattening filter-free mode. PRECISION RADIATION ONCOLOGY 2017. [DOI: 10.1002/pro6.11] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Affiliation(s)
- Dingjie Li
- The Affiliated Cancer Hospital of Zhengzhou University; Zhengzhou China
| | - Xiaowu Deng
- The Affiliated Cancer Hospital of Zhongshan University; Guangzhou China
| | - Ying Xue
- The Affiliated Cancer Hospital of Zhengzhou University; Zhengzhou China
| | - Zhaoyang Lou
- The Affiliated Cancer Hospital of Zhengzhou University; Zhengzhou China
| | - Yougai Zhang
- The Affiliated Cancer Hospital of Zhengzhou University; Zhengzhou China
| | - Wei Guo
- The Affiliated Cancer Hospital of Zhengzhou University; Zhengzhou China
| | - Jianhua Wang
- The Affiliated Cancer Hospital of Zhengzhou University; Zhengzhou China
| |
Collapse
|
14
|
Budgell G, Brown K, Cashmore J, Duane S, Frame J, Hardy M, Paynter D, Thomas R. IPEM topical report 1: guidance on implementing flattening filter free (FFF) radiotherapy. Phys Med Biol 2016; 61:8360-8394. [DOI: 10.1088/0031-9155/61/23/8360] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
|
15
|
Measurement of Photo-Neutron Dose from an 18-MV Medical Linac Using a Foil Activation Method in View of Radiation Protection of Patients. NUCLEAR ENGINEERING AND TECHNOLOGY 2016. [DOI: 10.1016/j.net.2015.11.003] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
|
16
|
Konefał A, Orlef A, Bieniasiewicz M. Measurements of neutron radiation and induced radioactivity for the new medical linear accelerator, the Varian TrueBeam. RADIAT MEAS 2016. [DOI: 10.1016/j.radmeas.2015.12.039] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
|
17
|
Dobler B, Khemissi A, Obermeier T, Hautmann MG, Katsilieri Z, Kölbl O. Re-irradiating spinal column metastases using IMRT and VMAT with and without flattening filter - a treatment planning study. Radiat Oncol 2016; 11:33. [PMID: 26932561 PMCID: PMC4774147 DOI: 10.1186/s13014-016-0603-0] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2015] [Accepted: 02/18/2016] [Indexed: 01/16/2023] Open
Abstract
Background The aim of this study was to investigate the potential of the flattening filter free (FFF) mode of a linear accelerator for intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) for patients with in-field recurrence of vertebral metastases. Methods An Elekta Synergy Linac with Agility™ head is used to simulate the treatment of ten patients with locally recurrent spinal column metastases. Four plans were generated for each patient treating the vertebrae sparing the spinal cord: Dual arc VMAT and nine field step and shoot IMRT each with and without flattening filter. Plan quality was assessed considering target coverage and sparing of the spinal cord and normal tissue. All plans were verified by a 2D-ionisation-chamber-array, peripheral doses were measured and compared to calculations. Delivery times were measured and compared. The Wilcoxon test was used for statistical analysis with a significance level of 0.05. Results Target coverage, homogeneity index and conformity index were comparable for both flat and flattening filter free beams. The volume of the spinal cord receiving the allowed maximum dose to keep the risk of radiation myelopathy at 0 % was at the same time significantly reduced to below the clinically relevant 1 ccm using FFF mode. In addition the mean dose deposited in the surrounding healthy tissue was significantly reduced in the FFF mode. All four techniques showed equally good gamma scores for plan verification. FFF plans required considerably more MU per fraction dose. Regardless of the large number of MU, out-of-field point dose was significantly lower for FFF plans, with an average reduction of 33 % and mean delivery time was significantly reduced by 22 % using FFF beams. When compared to IMRT FF, VMAT FFF offered even a reduction of 71 % in delivery time and 45 % in peripheral dose. Conclusions FFF plans showed a significant improvement in sparing of normal tissue and the spinal cord, keeping target coverage and homogeneity comparable. In addition, delivery times were significantly reduced for FFF treatments, minimizing intrafractional motion as well as strain for the patient. Shortest delivery times were achieved using VMAT FFF. For radiotherapy of spinal column metastases VMAT FFF may therefore be considered the preferable treatment option for the combination of Elekta Synergy Linacs and Oncentra® External Beam v4.5 treatment planning system.
Collapse
Affiliation(s)
- Barbara Dobler
- Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany.
| | - Amine Khemissi
- Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany.
| | - Tina Obermeier
- Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany.
| | - Matthias G Hautmann
- Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany.
| | - Zaira Katsilieri
- Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany.
| | - Oliver Kölbl
- Department of Radiotherapy, Regensburg University Medical Center, Regensburg, Germany.
| |
Collapse
|
18
|
McGeachy P, Villarreal-Barajas JE, Zinchenko Y, Khan R. Modulated photon radiotherapy (XMRT): an algorithm for the simultaneous optimization of photon beamlet energy and intensity in external beam radiotherapy (EBRT) planning. Phys Med Biol 2016; 61:1476-98. [PMID: 26808280 DOI: 10.1088/0031-9155/61/4/1476] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
This is a proof of principle study on an algorithm for optimizing external beam radiotherapy in terms of both photon beamlet energy and fluence. This simultaneous beamlet energy and fluence optimization is denoted modulated photon radiotherapy (XMRT). XMRT is compared with single-energy intensity modulated radiotherapy (IMRT) for five clinically relevant test geometries to determine whether treating beamlet energy as a decision variable improves the dose distributions. All test geometries were modelled in a cylindrical water phantom. XMRT optimized the fluence for 6 and 18 MV beamlets while IMRT optimized with only 6 MV and only 18 MV. CERR (computational environment for radiotherapy research) was used to calculate the dose deposition matrices and the resulting dose for XMRT and IMRT solutions. Solutions were compared via their dose volume histograms and dose metrics, such as the mean, maximum, and minimum doses for each structure. The homogeneity index (HI) and conformity number (CN) were calculated to assess the quality of the target dose coverage. Complexity of the resulting fluence maps was minimized using the sum of positive gradients technique. The results showed XMRT's ability to improve healthy-organ dose reduction while yielding comparable coverage of the target relative to IMRT for all geometries. All three energy-optimization approaches yielded similar HI and CNs for all geometries, as well as a similar degree of fluence map complexity. The dose reduction provided by XMRT was demonstrated by the relative decrease in the dose metrics for the majority of the organs at risk (OARs) in all geometries. Largest reductions ranged between 5% to 10% in the mean dose to OARs for two of the geometries when compared with both single-energy IMRT schemes. XMRT has shown potential dosimetric benefits through improved OAR sparing by allowing beam energy to act as a degree of freedom in the EBRT optimization process.
Collapse
Affiliation(s)
- Philip McGeachy
- Department of Physics and Astronomy, University of Calgary, Calgary, AB T2N 1N4, Canada. Department of Medical Physics, Tom Baker Cancer Centre, Calgary, AB T2N 4N2, Canada
| | | | | | | |
Collapse
|
19
|
Newhauser WD, de Gonzalez AB, Schulte R, Lee C. A Review of Radiotherapy-Induced Late Effects Research after Advanced Technology Treatments. Front Oncol 2016; 6:13. [PMID: 26904500 PMCID: PMC4748041 DOI: 10.3389/fonc.2016.00013] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Accepted: 01/12/2016] [Indexed: 01/01/2023] Open
Abstract
The number of incident cancers and long-term cancer survivors is expected to increase substantially for at least a decade. Advanced technology radiotherapies, e.g., using beams of protons and photons, offer dosimetric advantages that theoretically yield better outcomes. In general, evidence from controlled clinical trials and epidemiology studies are lacking. To conduct these studies, new research methods and infrastructure will be needed. In the paper, we review several key research methods of relevance to late effects after advanced technology proton-beam and photon-beam radiotherapies. In particular, we focus on the determination of exposures to therapeutic and stray radiation and related uncertainties, with discussion of recent advances in exposure calculation methods, uncertainties, in silico studies, computing infrastructure, electronic medical records, and risk visualization. We identify six key areas of methodology and infrastructure that will be needed to conduct future outcome studies of radiation late effects.
Collapse
Affiliation(s)
- Wayne D. Newhauser
- Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA
- Department of Physics, Mary Bird Perkins Cancer Center, Baton Rouge, LA, USA
| | | | - Reinhard Schulte
- Department of Basic Sciences, Loma Linda University Medical Center, Loma Linda, CA, USA
| | - Choonsik Lee
- Radiation Epidemiology Branch, National Institutes of Health, Rockville, MD, USA
| |
Collapse
|
20
|
Najem M, Abolaban F, Podolyák Z, Spyrou N. Neutron production from flattening filter free high energy medical linac: A Monte Carlo study. Radiat Phys Chem Oxf Engl 1993 2015. [DOI: 10.1016/j.radphyschem.2015.01.040] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
|
21
|
Xiao Y, Kry SF, Popple R, Yorke E, Papanikolaou N, Stathakis S, Xia P, Huq S, Bayouth J, Galvin J, Yin FF. Flattening filter-free accelerators: a report from the AAPM Therapy Emerging Technology Assessment Work Group. J Appl Clin Med Phys 2015; 16:5219. [PMID: 26103482 PMCID: PMC5690108 DOI: 10.1120/jacmp.v16i3.5219] [Citation(s) in RCA: 108] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2014] [Revised: 02/06/2015] [Accepted: 01/23/2015] [Indexed: 11/23/2022] Open
Abstract
This report describes the current state of flattening filter‐free (FFF) radiotherapy beams implemented on conventional linear accelerators, and is aimed primarily at practicing medical physicists. The Therapy Emerging Technology Assessment Work Group of the American Association of Physicists in Medicine (AAPM) formed a writing group to assess FFF technology. The published literature on FFF technology was reviewed, along with technical specifications provided by vendors. Based on this information, supplemented by the clinical experience of the group members, consensus guidelines and recommendations for implementation of FFF technology were developed. Areas in need of further investigation were identified. Removing the flattening filter increases beam intensity, especially near the central axis. Increased intensity reduces treatment time, especially for high‐dose stereotactic radiotherapy/radiosurgery (SRT/SRS). Furthermore, removing the flattening filter reduces out‐of‐field dose and improves beam modeling accuracy. FFF beams are advantageous for small field (e.g., SRS) treatments and are appropriate for intensity‐modulated radiotherapy (IMRT). For conventional 3D radiotherapy of large targets, FFF beams may be disadvantageous compared to flattened beams because of the heterogeneity of FFF beam across the target (unless modulation is employed). For any application, the nonflat beam characteristics and substantially higher dose rates require consideration during the commissioning and quality assurance processes relative to flattened beams, and the appropriate clinical use of the technology needs to be identified. Consideration also needs to be given to these unique characteristics when undertaking facility planning. Several areas still warrant further research and development. Recommendations pertinent to FFF technology, including acceptance testing, commissioning, quality assurance, radiation safety, and facility planning, are presented. Examples of clinical applications are provided. Several of the areas in which future research and development are needed are also indicated. PACS number: 87.53.‐j, 87.53.Bn, 87.53.Ly, 87.55.‐x, 87.55.N‐, 87.56.bc
Collapse
Affiliation(s)
- Ying Xiao
- Thomas Jefferson University Hospital.
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
22
|
Králík M, Šolc J, Vondráček V, Šmoldasová J, Farkašová E, Tichá I. Spectral fluence of neutrons generated by radiotherapeutic linacs. RADIATION PROTECTION DOSIMETRY 2015; 163:373-380. [PMID: 24925899 DOI: 10.1093/rpd/ncu192] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Spectral fluences of neutrons generated in the heads of the radiotherapeutic linacs Varian Clinac 2100 C/D and Siemens ARTISTE were measured by means of the Bonner spheres spectrometer whose active detector of thermal neutrons was replaced by an activation detector, i.e. a tablet made of pure manganese. Measurements with different collimator settings reveal an interesting dependence of neutron fluence on the area defined by the collimator jaws. The determined neutron spectral fluences were used to derive ambient dose equivalent rate along the treatment coach. To clarify at which components of the linac neutrons are mainly created, the measurements were complemented with MCNPX calculations based on a realistic model of the Varian Clinac.
Collapse
Affiliation(s)
- Miloslav Králík
- Czech Metrology Institute, Prague 10 CZ-102 00, Czech Republic
| | - Jaroslav Šolc
- Czech Metrology Institute, Prague 10 CZ-102 00, Czech Republic
| | | | - Jana Šmoldasová
- Czech Metrology Institute, Prague 10 CZ-102 00, Czech Republic
| | - Estera Farkašová
- Thomayer's Hospital, Vídeňská 80, Prague 4 CZ-140 59, Czech Republic
| | - Ivana Tichá
- Thomayer's Hospital, Vídeňská 80, Prague 4 CZ-140 59, Czech Republic
| |
Collapse
|
23
|
Howell RM, Burgett EA. Secondary neutron spectrum from 250-MeV passively scattered proton therapy: measurement with an extended-range Bonner sphere system. Med Phys 2014; 41:092104. [PMID: 25186404 PMCID: PMC4149696 DOI: 10.1118/1.4892929] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2013] [Revised: 07/25/2014] [Accepted: 07/28/2014] [Indexed: 12/25/2022] Open
Abstract
PURPOSE Secondary neutrons are an unavoidable consequence of proton therapy. While the neutron dose is low compared to the primary proton dose, its presence and contribution to the patient dose is nonetheless important. The most detailed information on neutrons includes an evaluation of the neutron spectrum. However, the vast majority of the literature that has reported secondary neutron spectra in proton therapy is based on computational methods rather than measurements. This is largely due to the inherent limitations in the majority of neutron detectors, which are either not suitable for spectral measurements or have limited response at energies greater than 20 MeV. Therefore, the primary objective of the present study was to measure a secondary neutron spectrum from a proton therapy beam using a spectrometer that is sensitive to neutron energies over the entire neutron energy spectrum. METHODS The authors measured the secondary neutron spectrum from a 250-MeV passively scattered proton beam in air at a distance of 100 cm laterally from isocenter using an extended-range Bonner sphere (ERBS) measurement system. Ambient dose equivalent H*(10) was calculated using measured fluence and fluence-to-ambient dose equivalent conversion coefficients. RESULTS The neutron fluence spectrum had a high-energy direct neutron peak, an evaporation peak, a thermal peak, and an intermediate energy continuum between the thermal and evaporation peaks. The H*(10) was dominated by the neutrons in the evaporation peak because of both their high abundance and the large quality conversion coefficients in that energy interval. The H*(10) 100 cm laterally from isocenter was 1.6 mSv per proton Gy (to isocenter). Approximately 35% of the dose equivalent was from neutrons with energies ≥20 MeV. CONCLUSIONS The authors measured a neutron spectrum for external neutrons generated by a 250-MeV proton beam using an ERBS measurement system that was sensitive to neutrons over the entire energy range being measured, i.e., thermal to 250 MeV. The authors used the neutron fluence spectrum to demonstrate experimentally the contribution of neutrons with different energies to the total dose equivalent and in particular the contribution of high-energy neutrons (≥20 MeV). These are valuable reference data that can be directly compared with Monte Carlo and experimental data in the literature.
Collapse
Affiliation(s)
- Rebecca M Howell
- Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030
| | - E A Burgett
- Department of Nuclear Engineering, Idaho State University, Pocatello, Idaho 83201
| |
Collapse
|
24
|
Hälg RA, Besserer J, Boschung M, Mayer S, Lomax AJ, Schneider U. Measurements of the neutron dose equivalent for various radiation qualities, treatment machines and delivery techniques in radiation therapy. Phys Med Biol 2014; 59:2457-68. [PMID: 24778349 DOI: 10.1088/0031-9155/59/10/2457] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
In radiation therapy, high energy photon and proton beams cause the production of secondary neutrons. This leads to an unwanted dose contribution, which can be considerable for tissues outside of the target volume regarding the long term health of cancer patients. Due to the high biological effectiveness of neutrons in regards to cancer induction, small neutron doses can be important. This study quantified the neutron doses for different radiation therapy modalities. Most of the reports in the literature used neutron dose measurements free in air or on the surface of phantoms to estimate the amount of neutron dose to the patient. In this study, dose measurements were performed in terms of neutron dose equivalent inside an anthropomorphic phantom. The neutron dose equivalent was determined using track etch detectors as a function of the distance to the isocenter, as well as for radiation sensitive organs. The dose distributions were compared with respect to treatment techniques (3D-conformal, volumetric modulated arc therapy and intensity-modulated radiation therapy for photons; spot scanning and passive scattering for protons), therapy machines (Varian, Elekta and Siemens linear accelerators) and radiation quality (photons and protons). The neutron dose equivalent varied between 0.002 and 3 mSv per treatment gray over all measurements. Only small differences were found when comparing treatment techniques, but substantial differences were observed between the linear accelerator models. The neutron dose equivalent for proton therapy was higher than for photons in general and in particular for double-scattered protons. The overall neutron dose equivalent measured in this study was an order of magnitude lower than the stray dose of a treatment using 6 MV photons, suggesting that the contribution of the secondary neutron dose equivalent to the integral dose of a radiotherapy patient is small.
Collapse
Affiliation(s)
- R A Hälg
- Radiotherapy Hirslanden, Medical Physics, CH-8032 Zurich, Switzerland
| | | | | | | | | | | |
Collapse
|
25
|
Najem M, Spyrou N, Podolyák Z, Abolaban F. The physical characteristics of the 15MV Varian Clinac 2100C unflattened beam. Radiat Phys Chem Oxf Engl 1993 2014. [DOI: 10.1016/j.radphyschem.2013.04.035] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
|
26
|
Wang X, Charlton MA, Esquivel C, Eng TY, Li Y, Papanikolaou N. Measurement of neutron dose equivalent outside and inside of the treatment vault of GRID therapy. Med Phys 2013; 40:093901. [DOI: 10.1118/1.4816653] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
27
|
Christensen JD, Kirichenko A, Gayou O. Flattening filter removal for improved image quality of megavoltage fluoroscopy. Med Phys 2013; 40:081713. [DOI: 10.1118/1.4812678] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
|
28
|
Kalantzis G, Qian J, Han B, Luxton G. Fidelity of dose delivery at high dose rate of volumetric modulated arc therapy in a truebeam linac with flattening filter free beams. J Med Phys 2013; 37:193-9. [PMID: 23293450 PMCID: PMC3532747 DOI: 10.4103/0971-6203.103604] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Revised: 07/20/2012] [Accepted: 09/12/2012] [Indexed: 11/04/2022] Open
Abstract
The purpose of this study is to assess fidelity of radiation delivery between high and low dose rates of the flattening filter free (FFF) modes of a new all-digital design medical linear accelerator (Varian TrueBeam™), particularly for plans optimized for volumetric modulated arc therapy (VMAT). Measurements were made for the two energies of flattening filter free photon beams with a Varian TrueBeam™ linac: 6 MV (6 XFFF) at 400 and 1400 MU/min, and 10 MV (10 XFFF) at 400 and 2400 MU/min. Data acquisition and analysis was performed with both ionization chambers and diode detector system Delta(4), for square radiation fields and for 8 VMAT treatment plans optimized for SBRT treatment of lung tumors. For the square fields, a percent dose difference between high and low dose rate of the order of 0.3-0.4% for both photon energies was seen with the ionization chambers, while the contribution to the difference from ion recombination was found to be negligible. For both the VMAT and square-field deliveries, the Delta(4) showed the same average percent dose difference between the two dose rates of ~0.8% and ~0.6% for 10 MV and 6 MV, respectively, with the lower dose rate values giving the greater measured dose compared to the high dose rate. Thus, the VMAT deliveries introduced negligible dose differences between high and low dose rate. Finally, reproducibility of dose measurements was good for both energies.
Collapse
Affiliation(s)
- Georgios Kalantzis
- Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California, USA
| | | | | | | |
Collapse
|
29
|
Fogliata A, Garcia R, Knoos T, Nicolini G, Clivio A, Vanetti E, Khamphan C, Cozzi L. Definition of parameters for quality assurance of flattening filter free (FFF) photon beams in radiation therapy. Med Phys 2012; 39:6455-64. [PMID: 23039680 DOI: 10.1118/1.4754799] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Flattening filter free (FFF) beams generated by medical linear accelerators have recently started to be used in radiotherapy clinical practice. Such beams present fundamental differences with respect to the standard filter flattened (FF) beams, making the generally used dosimetric parameters and definitions not always viable. The present study will propose possible definitions and suggestions for some dosimetric parameters for use in quality assurance of FFF beams generated by medical linacs in radiotherapy. METHODS The main characteristics of the photon beams have been analyzed using specific data generated by a Varian TrueBeam linac having both FFF and FF beams of 6 and 10 MV energy, respectively. RESULTS Definitions for dose profile parameters are suggested starting from the renormalization of the FFF with respect to the corresponding FF beam. From this point the flatness concept has been translated into one of "unflatness" and other definitions have been proposed, maintaining a strict parallelism between FFF and FF parameter concepts. CONCLUSIONS Ideas for quality controls used in establishing a quality assurance program when introducing FFF beams into the clinical environment are given here, keeping them similar to those used for standard FF beams. By following the suggestions in this report, the authors foresee that the introduction of FFF beams into a clinical radiotherapy environment will be as safe and well controlled as standard beam modalities using the existing guidelines.
Collapse
Affiliation(s)
- A Fogliata
- Oncology Institute of Southern Switzerland, Medical Physics Unit, Bellinzona CH-6500, Switzerland.
| | | | | | | | | | | | | | | |
Collapse
|
30
|
Hälg RA, Besserer J, Boschung M, Mayer S, Schneider U. Monitor units are not predictive of neutron dose for high-energy IMRT. Radiat Oncol 2012; 7:138. [PMID: 22883384 PMCID: PMC3487990 DOI: 10.1186/1748-717x-7-138] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2012] [Accepted: 08/02/2012] [Indexed: 11/10/2022] Open
Abstract
Abstract
Background
Due to the substantial increase in beam-on time of high energy intensity-modulated radiotherapy (>10 MV) techniques to deliver the same target dose compared to conventional treatment techniques, an increased dose of scatter radiation, including neutrons, is delivered to the patient. As a consequence, an increase in second malignancies may be expected in the future with the application of intensity-modulated radiotherapy. It is commonly assumed that the neutron dose equivalent scales with the number of monitor units.
Methods
Measurements of neutron dose equivalent were performed for an open and an intensity-modulated field at four positions: inside and outside of the treatment field at 0.2 cm and 15 cm depth, respectively.
Results
It was shown that the neutron dose equivalent, which a patient receives during an intensity-modulated radiotherapy treatment, does not scale with the ratio of applied monitor units relative to an open field irradiation. Outside the treatment volume at larger depth 35% less neutron dose equivalent is delivered than expected.
Conclusions
The predicted increase of second cancer induction rates from intensity-modulated treatment techniques can be overestimated when the neutron dose is simply scaled with monitor units.
Collapse
|
31
|
Huang Y, Siochi RA, Bayouth JE. Dosimetric properties of a beam quality-matched 6 MV unflattened photon beam. J Appl Clin Med Phys 2012; 13:3701. [PMID: 22766941 PMCID: PMC5716519 DOI: 10.1120/jacmp.v13i4.3701] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2011] [Revised: 03/23/2012] [Accepted: 04/10/2012] [Indexed: 11/23/2022] Open
Abstract
The purpose of this study was to report the characteristics of an equivalent quality unflattened (eqUF) photon beam in clinical implementation and to provide a generalized method to describe unflattened (UF) photon beam profiles. An unflattened photon beam with a beam quality equivalent to the corresponding flat 6 MV photon beam (WF) was obtained by removing the flattening filter from a Siemens ONCOR Avant‐Garde linear accelerator and adjusting the photon energy. A method independent from the WF beam profile was presented to describe UF beam profiles and other selected beam characteristics were examined. The short‐term beam stability was examined by dynamic beam profiles, recorded every 0.072 s in static and gated delivery, and the long‐term stability was evidenced by the five‐year clinical quality assurance records. The dose rate was raised fivefold using the eqUF beam. The depth of maximum dose (dmax) shifted 3 mm deeper, but the percent depth dose beyond dmax was very similar to that of the WF beam. The surface dose and out‐of‐field dose were lower, but the penumbra was slightly wider. The variation in head scatter and phantom scatter with changes in field size was smaller; the variation in the profile shape with change in depth was also smaller. The eqUF beam is stable 0.072 s after the beam is turned on, and the five‐year beam stability was comparable to that of the WF beam. A fivefold dose rate increase was observed in the eqUF beam with similar beam characteristics to other reported UF beam data except for a deeper dmax and a slightly wider penumbra. The initial and long‐term stability of the eqUF beam profile is on parity with the WF beam. The UF beam profile can be described in the generalized method independently without relying on the WF beam profile. PACS number: 87.55.de
Collapse
Affiliation(s)
- Yunfei Huang
- Department of Radiation Oncology, Division of Medical Physics, University of Iowa Hospitals and Clinics, Iowa City, Iowa 52242
| | | | | |
Collapse
|
32
|
Martinez-Ovalle SA, Barquero R, Gomez-Ros JM, Lallena AM. Neutron dosimetry in organs of an adult human phantom using linacs with multileaf collimator in radiotherapy treatments. Med Phys 2012; 39:2854-66. [PMID: 22559658 DOI: 10.1118/1.4704527] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To calculate absorbed doses due to neutrons in 87 organs/tissues for anthropomorphic phantoms, irradiated in position supine (head first into the gantry) with orientations anteroposterior (AP) and right-left (RLAT) with a 18 MV accelerator. Conversion factors from monitor units to μGy per neutron in organs, equivalent doses in organs/tissues, and effective doses, which permit to quantify stochastic risks, are estimated. METHODS MAX06 and FAX06 phantoms were modeled with MCNPX and irradiated with a 18 MV Varian Clinac 2100C/D accelerator whose geometry included a multileaf collimator. Two actual fields of a pelvic treatment were simulated using electron-photon-neutron coupled transport. Absorbed doses due to neutrons were estimated from kerma. Equivalent doses were estimated using the radiation weighting factor corresponding to an average incident neutron energy 0.47 MeV. Statistical uncertainties associated to absorbed doses, as calculated by MCNPX, were also obtained. RESULTS Largest doses were absorbed in shallowest (with respect to the neutron pathway) organs. In μGyMU(-1), values of 2.66 (for penis) and 2.33 (for testes) were found in MAX06, and 1.68 (for breasts), 1.05 (for lenses of eyes), and 0.94 (for sublingual salivary glands) in FAX06, in AP orientation. In RLAT, the largest doses were found for bone tissues (leg) just at the entrance of the beam in the body (right side in our case). Values, in μGyMU(-1), of 1.09 in upper leg bone right spongiosa, for MAX06, and 0.63 in mandible spongiosa, for FAX06, were found. Except for gonads, liver, and stomach wall, equivalent doses found for FAX06 were, in both orientations, higher than for MAX06. Equivalent doses in AP are higher than in RLAT for all organs/tissues other than brain and liver. Effective doses of 12.6 and 4.1 μSvMU(-1) were found for AP and RLAT, respectively. The organs/tissues with larger relative contributions to the effective dose were testes and breasts, in AP, and breasts and red marrow, in RLAT. Equivalent and effective doses obtained for MAX06/FAX06 were smaller (between 2 and 20 times) than those quoted for the mathematical phantoms ADAM/EVA in ICRP-74. CONCLUSIONS The new calculations of conversion coefficients for neutron irradiation in AP and RLAT irradiation geometries show a reduction in the values of effective dose by factors 7 (AP) and 6 (RLAT) with respect to the old data obtained with mathematical phantoms. The existence of tissues or anatomical regions with maximum absorbed doses, such as penis, lens of eyes, fascia (part of connective tissue), etc., organs/tissues that classic mathematical phantoms did not include because they were not considered for the study of stochastic effects, has been revealed. Absorbed doses due to photons, obtained following the same simulation methodology, are larger than those due to neutrons, reaching values 100 times larger as the primary beam is approached. However, for organs far from the treated volume, absorbed photon doses can be up to three times smaller than neutron ones. Calculations using voxel phantoms permitted to know the organ dose conversion coefficients per MU due to secondary neutrons in the complete anatomy of a patient.
Collapse
Affiliation(s)
- S A Martinez-Ovalle
- Grupo de Física Nuclear Aplicada y Simulación, Universidad Pedagógica y Tecnológica de Colombia, Tunja, Colombia
| | | | | | | |
Collapse
|
33
|
Reggiori G, Mancosu P, Castiglioni S, Alongi F, Pellegrini C, Lobefalo F, Catalano M, Fogliata A, Arcangeli S, Navarria P, Cozzi L, Scorsetti M. Can volumetric modulated arc therapy with flattening filter free beams play a role in stereotactic body radiotherapy for liver lesions? A volume-based analysis. Med Phys 2012; 39:1112-8. [PMID: 22320821 DOI: 10.1118/1.3679858] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To compare volumetric modulated arc therapy with flattening filter free (FFF) and flattening filter (FF) beams in patients with hepatic metastases subject to hypofractionated radiotherapy (RT). METHODS A planning study on 13 virtual lesions of increasing volume was performed. Two single arc plans were optimized with the RapidArc technique using either FFF or FF beams. A second planning study was performed on ten patients treated for liver metastases to validate conclusions. In all cases, a dose of 75 Gy in 3 fractions was prescribed to the planning target volume (PTV) and plans were evaluated in terms of coverage, homogeneity, conformity, mean dose to healthy liver and to healthy tissue. For each parameter, results were expressed in relative terms as the percentage ratio between FFF and FF data. RESULTS In terms of PTV coverage, conformity index favored FFF for targets of intermediate size while FF resulted more suitable for small (<100 cm(3)) and large (>300 cm(3)) targets. Plans optimized with FFF beams resulted in increased sparing of healthy tissue in ≈85% of cases. Despite the qualitative results, no statistically significant differences were found between FFF and FF results. Plans optimized with un-flattened beams resulted in higher average MU∕Gy than plans with FF beams. A remarkable and significant difference was observed in the beam-on time (BOT) needed to deliver plans. The BOT for FF plans was 8.2 ± 1.0 min; for FFF plans BOT was 2.2 ± 0.2 min. CONCLUSIONS RapidArc plans optimized using FFF were dosimetrically equivalent to those optimized using FF beams, showing the feasibility of SBRT treatments with FFF beams. Some improvement in healthy tissue sparing was observed when using the FFF modality due to the different beam's profile. The main advantage was a considerable reduction of beam-on time, relevant for SBRT techniques.
Collapse
|
34
|
Krmar M, Baucal M, Bozic N, Jovancevic N, Ciraj-Bjelac O. Neutron dose equivalent measured at the maze door with various openings for the jaws and MLC. Med Phys 2012; 39:1278-81. [PMID: 22380359 DOI: 10.1118/1.3682313] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE This study was undertaken to explore the effects of the jaws and the MLC openings on the neutron dose equivalent (DE) at the maze door and neutron flux at the patient plane. METHODS The neutron dose equivalent was measured at the maze entrance door of a 15 MV therapy linear accelerator room. All measurements were performed using various field sizes up to 40 cm × 40 cm. Activation detectors constructed from natural Indium (In) were exposed at Cd envelope to neutrons in order to estimate relative changes of epithermal neutron fluences in the patient plane. RESULTS Our study showed that the dose equivalent at the maze door is at the highest when the jaw are closed and that maximal jaws opening reduces the DE by more than 20%. The neutron dose equivalent at the maze door measured for radiation fields defined by jaws do not differ significantly from the DE measured when MLC determines the same size radiation field. The epithermal capture reaction rate measured using different jaw openings differs by approximately 10%. When an MLC leaf is inserted into a fixed geometry for one opening of the jaws, an increase of the epithermal neutron capture reaction rate in Indium activation detectors was observed. CONCLUSIONS There is no significant difference in the neutron DE when MLC defines radiation field instead of jaws. This leads to the conclusion that the overall number of neutrons remains similar and it does not depend on how primary photon beam was stopped-by the jaws or the MLC. An increase of the fast neutron capture reaction rate when MLC leaves are inserted probably originates from the neutron scattering.
Collapse
Affiliation(s)
- M Krmar
- Physics Department, University of Novi Sad, Novi Sad, Serbia.
| | | | | | | | | |
Collapse
|
35
|
Mancosu P, Castiglioni S, Reggiori G, Catalano M, Alongi F, Pellegrini C, Arcangeli S, Tozzi A, Lobefalo F, Fogliata A, Navarria P, Cozzi L, Scorsetti M. Stereotactic body radiation therapy for liver tumours using flattening filter free beam: dosimetric and technical considerations. Radiat Oncol 2012; 7:16. [PMID: 22296849 PMCID: PMC3292972 DOI: 10.1186/1748-717x-7-16] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2011] [Accepted: 02/01/2012] [Indexed: 12/25/2022] Open
Abstract
Purpose To report the initial institute experience in terms of dosimetric and technical aspects in stereotactic body radiation therapy (SBRT) delivered using flattening filter free (FFF) beam in patients with liver lesions. Methods and Materials From October 2010 to September 2011, 55 consecutive patients with 73 primary or metastatic hepatic lesions were treated with SBRT on TrueBeam using FFF beam and RapidArc technique. Clinical target volume (CTV) was defined on multi-phase CT scans, PET/CT, MRI, and 4D-CT. Dose prescription was 75 Gy in 3 fractions to planning target volume (PTV). Constraints for organs at risk were: 700 cc of liver free from the 15 Gy isodose, Dmax < 21 Gy for stomach and duodenum, Dmax < 30 Gy for heart, D0.1 cc < 18 Gy for spinal cord, V15 Gy < 35% for kidneys. The dose was downscaled in cases of not full achievement of dose constraints. Daily cone beam CT (CBCT) was performed. Results Forty-three patients with a single lesion, nine with two lesions and three with three lesions were treated with this protocol. Target and organs at risk objectives were met for all patients. Mean delivery time was 2.8 ± 1.0 min. Pre-treatment plan verification resulted in a Gamma Agreement Index of 98.6 ± 0.8%. Mean on-line co-registration shift of the daily CBCT to the simulation CT were: -0.08, 0.05 and -0.02 cm with standard deviations of 0.33, 0.39 and 0.55 cm in, vertical, longitudinal and lateral directions respectively. Conclusions SBRT for liver targets delivered by means of FFF resulted to be feasible with short beam on time.
Collapse
Affiliation(s)
- Pietro Mancosu
- IRCCS Istituto Clinico Humanitas, Rozzano (Milano), Italy.
| | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
36
|
Sharma SD. Unflattened photon beams from the standard flattening filter free accelerators for radiotherapy: Advantages, limitations and challenges. J Med Phys 2011; 36:123-5. [PMID: 21897556 PMCID: PMC3159217 DOI: 10.4103/0971-6203.83464] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022] Open
Affiliation(s)
- Sunil Dutt Sharma
- Radiological Physics and Advisory Division, Bhabha Atomic Research Centre, CTCRS Building, Anushaktinagar, Mumbai - 400 094, India. E-mail:
| |
Collapse
|
37
|
Georg D, Knöös T, McClean B. Current status and future perspective of flattening filter free photon beams. Med Phys 2011; 38:1280-93. [PMID: 21520840 DOI: 10.1118/1.3554643] [Citation(s) in RCA: 218] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE Flattening filters (FFs) have been considered as an integral part of the treatment head of a medical accelerator for more than 50 years. The reasons for the longstanding use are, however, historical ones. Advanced treatment techniques, such as stereotactic radiotherapy or intensity modulated radiotherapy have stimulated the interest in operating linear accelerators in a flattening filter free (FFF) mode. The current manuscript reviews treatment head physics of FFF beams, describes their characteristics and the resulting potential advantages in their medical use, and closes with an outlook. METHODS A number of dosimetric benefits have been determined for FFF beams, which range from increased dose rate and dose per pulse to favorable output ratio in-air variation with field size, reduced energy variation across the beam, and reduced leakage and out-of-field dose, respectively. Finally, the softer photon spectrum of unflattened beams has implications on imaging strategies and radiation protection. RESULTS The dosimetric characteristics of FFF beams have an effect on treatment delivery, patient comfort, dose calculation accuracy, beam matching, absorbed dose determination, treatment planning, machine specific quality assurance, imaging, and radiation protection. When considering conventional C-arm linacs in a FFF mode, more studies are needed to specify and quantify the clinical advantages, especially with respect to treatment plan quality and quality assurance. CONCLUSIONS New treatment units are already on the market that operate without a FF or can be operated in a dedicated clinical FFF mode. Due to the convincing arguments of removing the FF, it is expected that more vendors will offer dedicated treatment units for advanced photon beam therapy in the near future. Several aspects related to standardization, dosimetry, treatment planning, and optimization need to be addressed in more detail in order to facilitate the clinical implementation of unflattened beams.
Collapse
Affiliation(s)
- Dietmar Georg
- Department of Radiotherapy, Division of Medical Radiation Physics, Medical University of Vienna/AKH Vienna, A-1090 Vienna, Austria.
| | | | | |
Collapse
|
38
|
Wang X, Esquivel C, Nes E, Shi C, Papanikolaou N, Charlton M. The neutron dose equivalent evaluation and shielding at the maze entrance of a Varian Clinac 23EX treatment room. Med Phys 2011; 38:1141-9. [PMID: 21520826 DOI: 10.1118/1.3533713] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To evaluate the neutron and photon dose equivalent rate (H(n,D) and H(G)) at the outer maze entrance and the adjacent treatment console area after the installation of a Varian Clinac 23EX accelerator with a higher beam energy than its predecessor. The evaluation was based on measurements and comparison with several empirical calculations. The effectiveness of borated polyethylene (BPE) boards, as a maze wall lining material, on neutron dose and photon dose reduction is also reported. METHODS A single energy Varian 6 MV photon linear accelerator (linac) was replaced with a Varian Clinac 23EX accelerator capable of producing 18 MV photons in a vault originally designed for the former accelerator. In order to evaluate and redesign the shielding of the vault, the neutron dose equivalent H(n,D) was measured using an Andersson-Braun neutron Rem meter and the photon dose equivalent HG was measured using a Geiger Müller and an ion chamber gamma-ray survey meter at the outer maze entrance. The measurement data were compared to semiempirical calculations such as the Kersey method, the modified Kersey method, and a newly proposed method by Falcão et al. Additional measurements were taken after BPE boards were installed on the maze walls as a neutron absorption lining material. RESULTS With the gantry head tilted close to the inner maze entrance and with the jaws closed, both neutron dose equivalent and photon dose equivalent reached their maximum. Compared to the measurement results, the Kersey method overestimates the neutron dose equivalent H(n,D) by about two to four times (calculation/measurement ratio approximately 2.4-3.8). Falcão's method largely overestimates the H(n,D) (calculation/measurement ratio approximately 3.9-5.5). The modified Kersey method has a calculation to measurement ratio about 0.6-0.9. The photon dose equivalent calculation including McGinley's capture gamma dose equivalent equation estimates about 77%-98% of the measurement. After applying BPE boards as a lining material on the inner corner of the maze wall, the H(n,D) and the H(G) at maze entrance were decreased by 41% and 59%, respectively. CONCLUSIONS This work indicates that the Kersey method overestimates the neutron dose equivalent H(n,D) for a Varian Clinac 23EX accelerator. The Falcão method overestimates the H(n,D) partially due to the discrepancy in the International Commission on Radiological Protection (ICRP) conversion factors caused by the uncertainties of the estimated average neutron energy. The modified Kersey method gives the closest estimation of a Varian Clinac 23EX accelerator operated at 18 MV photon mode in a maze with a similar design as in the authors' study. However, it should be used with caution because of its tendency to underestimate the H(n,D). A borated polyethylene lining can provide a cost effective method to reduce neutron and photon dose equivalent at the maze door for an existing linac vault, following the installation of a higher energy linac.
Collapse
Affiliation(s)
- Xudong Wang
- University of Texas Health Science Center, San Antonio, Texas 78229, USA.
| | | | | | | | | | | |
Collapse
|
39
|
Naseri A, Mesbahi A. A review on photoneutrons characteristics in radiation therapy with high-energy photon beams. Rep Pract Oncol Radiother 2010; 15:138-44. [PMID: 24376940 DOI: 10.1016/j.rpor.2010.08.003] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2010] [Revised: 08/09/2010] [Accepted: 08/19/2010] [Indexed: 11/26/2022] Open
Abstract
In radiation therapy with high-energy photon beams (E > 10 MeV) neutrons are generated mainly in linacs head thorough (γ,n) interactions of photons with nuclei of high atomic number materials that constitute the linac head and the beam collimation system. These neutrons affect the shielding requirements in radiation therapy rooms and also increase the out-of-field radiation dose of patients undergoing radiation therapy with high-energy photon beams. In the current review, the authors describe the factors influencing the neutron production for different medical linacs based on the performed measurements and Monte Carlo studies in the literature.
Collapse
Affiliation(s)
- Alireza Naseri
- Radiation Therapy Department, Imam Hospital, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Asghar Mesbahi
- Radiation Therapy Department, Imam Hospital, Tabriz University of Medical Sciences, Tabriz, Iran ; Medical Physics Department, Medical School, Tabriz University of Medical Sciences, Tabriz, Iran
| |
Collapse
|
40
|
Kry SF, Vassiliev ON, Mohan R. Out-of-field photon dose following removal of the flattening filter from a medical accelerator. Phys Med Biol 2010; 55:2155-66. [DOI: 10.1088/0031-9155/55/8/003] [Citation(s) in RCA: 89] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
41
|
Howell RM, Kry SF, Burgett E, Hertel NE, Followill DS. Secondary neutron spectra from modern Varian, Siemens, and Elekta linacs with multileaf collimators. Med Phys 2009; 36:4027-38. [PMID: 19810475 PMCID: PMC2738742 DOI: 10.1118/1.3159300] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2008] [Revised: 04/19/2009] [Accepted: 05/31/2009] [Indexed: 11/07/2022] Open
Abstract
Neutrons are a by-product of high-energy x-ray radiation therapy (threshold for [gamma,n] reactions in high-Z material -7 MeV). Neutron production varies depending on photon beam energy as well as on the manufacturer of the accelerator. Neutron production from modern linear accelerators (linacs) has not been extensively compared, particularly in terms of the differences in the strategies that various manufacturers have used to implement multileaf collimators (MLCs) into their linac designs. However, such information is necessary to determine neutron dose equivalents for different linacs and to calculate vault shielding requirements. The purpose of the current study, therefore, was to measure the neutron spectra from the most up-to-date linacs from three manufacturers: Varian 21EX operating at 15, 18, and 20 MV, Siemens ONCOR operating at 15 and 18 MV, and Elekta Precise operating at 15 and 18 MV. Neutron production was measured by means of gold foil activation in Bonner spheres. Based on the measurements, the authors determined neutron spectra and calculated the average energy, total neutron fluence, ambient dose equivalent, and neutron source strength. The shapes of the neutron spectra did not change significantly between accelerators or even as a function of treatment energy. However, the neutron fluence, and therefore the ambient dose equivalent, did vary, increasing with increasing treatment energy. For a given nominal treatment energy, these values were always highest for the Varian linac. The current study thus offers medical physicists extensive information about the neutron production of MLC-equipped linacs currently in operation and provides them information vital for accurate comparison and prediction of neutron dose equivalents and calculation of vault shielding requirements.
Collapse
Affiliation(s)
- Rebecca M Howell
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030, USA.
| | | | | | | | | |
Collapse
|
42
|
Diallo I, Haddy N, Adjadj E, Samand A, Quiniou E, Chavaudra J, Alziar I, Perret N, Guérin S, Lefkopoulos D, de Vathaire F. Frequency Distribution of Second Solid Cancer Locations in Relation to the Irradiated Volume Among 115 Patients Treated for Childhood Cancer. Int J Radiat Oncol Biol Phys 2009; 74:876-83. [DOI: 10.1016/j.ijrobp.2009.01.040] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2008] [Revised: 01/16/2009] [Accepted: 01/16/2009] [Indexed: 11/28/2022]
|
43
|
Kry SF, Howell RM, Salehpour M, Followill DS. Neutron spectra and dose equivalents calculated in tissue for high-energy radiation therapy. Med Phys 2009; 36:1244-50. [PMID: 19472632 PMCID: PMC2736753 DOI: 10.1118/1.3089810] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2008] [Revised: 02/06/2009] [Accepted: 02/06/2009] [Indexed: 12/14/2022] Open
Abstract
Neutrons are by-products of high-energy radiation therapy and a source of dose to normal tissues. Thus, the presence of neutrons increases a patient's risk of radiation-induced secondary cancer. Although neutrons have been thoroughly studied in air, little research has been focused on neutrons at depths in the patient where radiosensitive structures may exist, resulting in wide variations in neutron dose equivalents between studies. In this study, we characterized properties of neutrons produced during high-energy radiation therapy as a function of their depth in tissue and for different field sizes and different source-to-surface distances (SSD). We used a previously developed Monte Carlo model of an accelerator operated at 18 MV to calculate the neutron fluences, energy spectra, quality factors, and dose equivalents in air and in tissue at depths ranging from 0.1 to 25 cm. In conjunction with the sharply decreasing dose equivalent with increased depth in tissue, the authors found that the neutron energy spectrum changed drastically as a function of depth in tissue. The neutron fluence decreased gradually as the depth increased, while the average neutron energy decreased sharply with increasing depth until a depth of approximately 7.5 cm in tissue, after which it remained nearly constant. There was minimal variation in the quality factor as a function of depth. At a given depth in tissue, the neutron dose equivalent increased slightly with increasing field size and decreasing SSD; however, the percentage depth-dose equivalent curve remained constant outside the primary photon field. Because the neutron dose equivalent, fluence, and energy spectrum changed substantially with depth in tissue, we concluded that when the neutron dose equivalent is being determined at a depth within a patient, the spectrum and quality factor used should be appropriate for depth rather than for in-air conditions. Alternately, an appropriate percent depth-dose equivalent curve should be used to correct the dose equivalent at the patient surface.
Collapse
Affiliation(s)
- Stephen F Kry
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, Texas 77030, USA.
| | | | | | | |
Collapse
|
44
|
Kry SF, Howell RM, Polf J, Mohan R, Vassiliev ON. Treatment vault shielding for a flattening filter-free medical linear accelerator. Phys Med Biol 2009; 54:1265-73. [PMID: 19190359 DOI: 10.1088/0031-9155/54/5/011] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The requirements for shielding a treatment vault with a Varian Clinac 2100 medical linear accelerator operated both with and without the flattening filter were assessed. Basic shielding parameters, such as primary beam tenth-value layers (TVLs), patient scatter fractions, and wall scatter fractions, were calculated using Monte Carlo simulations of 6, 10 and 18 MV beams. Relative integral target current requirements were determined from treatment planning studies of several disease sites with, and without, the flattening filter. The flattened beam shielding data were compared to data published in NCRP Report No. 151, and the unflattened beam shielding data were presented relative to the NCRP data. Finally, the shielding requirements for a typical treatment vault were determined for a single-energy (6 MV) linac and a dual-energy (6 MV/18 MV) linac. With the exception of large-angle patient scatter fractions and wall scatter fractions, the vault shielding parameters were reduced when the flattening filter was removed. Much of this reduction was consistent with the reduced average energy of the FFF beams. Primary beam TVLs were reduced by 12%, on average, and small-angle scatter fractions were reduced by up to 30%. Head leakage was markedly reduced because less integral target current was required to deliver the target dose. For the treatment vault examined in the current study, removal of the flattening filter reduced the required thickness of the primary and secondary barriers by 10-20%, corresponding to 18 m(3) less concrete to shield the single-energy linac and 36 m(3) less concrete to shield the dual-energy linac. Thus, a shielding advantage was found when the linac was operated without the flattening filter. This translates into a reduction in occupational exposure and/or the cost and space of shielding.
Collapse
Affiliation(s)
- Stephen F Kry
- Department of Radiation Physics, The University of Texas M.D Anderson Cancer Center, Houston, TX, USA.
| | | | | | | | | |
Collapse
|
45
|
Vassiliev ON, Kry SF, Chang JY, Balter PA, Titt U, Mohan R. Stereotactic radiotherapy for lung cancer using a flattening filter free Clinac. J Appl Clin Med Phys 2009; 10:14-21. [PMID: 19223837 PMCID: PMC5720505 DOI: 10.1120/jacmp.v10i1.2880] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2008] [Revised: 08/10/2008] [Accepted: 09/25/2008] [Indexed: 12/25/2022] Open
Abstract
The objective of this study was to assess the feasibility of stereotactic radiotherapy for early stage lung cancer using photon beams from a Varian Clinac accelerator operated without a flattening filter. Treatment plans were generated for 10 lung cancer patients with isolated lesions less than 3 cm in diameter. For each patient, two plans were generated, one with and one without the flattening filter. Plans were generated with Eclipse 8.0 (Varian Medical Systems) commissioned with beam data measured on a Clinac 21EX (Varian Medical Systems) operated with and without the flattening filter. Removal of the flattening filter increased the dose rate. The median beam‐on time per field was reduced from 25 sec (with the filter) to 11 sec (without the filter), increasing the feasibility of breath‐hold treatments and the efficiency of gated treatments. Differences in a dose heterogeneity index for the planning target volume between plans with flattened and unflattened beams were statistically insignificant. Differences in mean doses to organs at risk were small, typically about 10 cGy over the entire treatment. The study concludes that radiotherapy with unflattened beams is feasible and requires substantially less beam‐on time, facilitating breath‐hold and gating techniques. PACS numbers: 87.56.bd, 87.53.Ly
Collapse
Affiliation(s)
- Oleg N Vassiliev
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, U.S.A
| | - Stephen F Kry
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, U.S.A
| | - Joe Y Chang
- Department Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, U.S.A
| | - Peter A Balter
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, U.S.A
| | - Uwe Titt
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, U.S.A
| | - Radhe Mohan
- Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, Texas, U.S.A
| |
Collapse
|