jsmc-10156
PENUMBRA AND OUTPUT FACTORS MEASUREMENTS FOR SMALL AND NON-SMALL FIELDS IN RADIOTHERAPY
Zarean Y. Saeed a, Kharman A. Faraj b, Hunar A. Hassan a, Araz M. Wahbi a and Akhtar Shamsaldin a
a Zhianawa Cancer Center, Sulaimani City, Kurdistan Region, Iraq.
b Department of Physics, College of Science, University of Sulaimani, Sulaimani City, Kurdistan Region, Iraq.
Submitted: 19/2/2018; Accepted: 15/5/2018; Published 1/8/2018
DOI Link: https://doi.org/10.17656/jsmc.10156
ABSTRACT
Background
The use of radiotherapy linear accelerators in special procedures require strict quality assurance procedures to ensure the level of confidence in the accuracy of dose delivered. The radiation beam needs to be precisely targeted to maximize the dose to the target volume cancer, and minimize the dose to the surrounding healthy tissue.
Objectives
The aim of this study was to measure the penumbra and output factors of different ionization chambers for small and non-small fields using two photon energies.
Methods
The penumbra and output factors were measured using PinPoint, Roos, Farmer and Semiflex chambers at a depth of 10 cm and photon beam energies of 6 MV and 10 MV for both small (1×1, 2×2, 3×3) cm2 and non-small fields (4×4, 5×5, 10×10) cm2 defined by conventional multi-leaf collimators. As the same detectors, field sizes, photon energies were used to measure the output factors. The Percentage dose depth of the beam measured for all field sizes and beam energies.
Results
Our results showed that the extension of the Roos chamber was less than the other chambers and the output factors corresponding to non-small field 5×5 cm2 and above had identical values and exhibited similar Percentage dose depth (PDD) curves, while in those corresponding to small field 3×3 cm2 and below exhibited different output factors and PDD curves.
Conclusion
We conclude that the size of the chamber has a significant effect on the output factor and penumbra and the PinPoint chamber is the most suitable choice of chambers for use as an output detector from those available in Zhianawa cancer center.
KEYWORDS
Small field, penumbra, Output factor, Ionizing chambers, Intensity modulated radiation therapy.
References
1. Khan, Faiz M., and John P. Gibbons. Khan's the physics of radiation therapy. Lippincott Williams & Wilkins, 2014. P.184.
2. Williams, Jerry R., and David I. Thwaites. Radiotherapy physics in practice. USA:Oxford University Press, 1993.
3. Boyer, Arthur L., and Timothy Schultheiss. Effects of dosimetric and clinical uncertainty on complication-free local tumor control. Radiotherapy and Oncology,1998, 11,1, 65-71.
4. Murray, L. J., and M. H. Robinson. Radiotherapy: technical aspects. Medicine, 2011,39.12, 698-704.
5. Zhu, Timothy C., Bengt E. Bjärngard, and Hobart Shackford. "X-ray source and the output factor." Medical physics,1995, 22,6, 793-798.
6. Zhu, Timothy C., and Bengt E. Bjärngard. The head-scatter factor for small field sizes. Medical physics,1994, 21,1, 65-68.
7. Ding, George X., Dennis M. Duggan, and Charles W. Coffey. Commissioning stereotactic radiosurgery beams using both experimental and theoretical methods. Physics in medicine and biology, 2006, 51,10, 2549.
8. Boyer Arthur L., Ochran T.G., Nyerick C.E., Waldron T.J., CJ Huntzinger. Clinical dosimetry for implementation of a multileaf collimator. Medical physics,1992, 19,5, 1255–1261.
9. Li, Shidong, Rashid A, He S, Djajaputra D.A new approach in dose measurement and error analysis for narrow photon beams (beamlets) shaped by different multileaf collimators using a small detector. Medical physics, 2004, 31,7, 2020–2032.
10. Jones, Andrew O., Indra J. Das, and Frederick L. Jones. A Monte Carlo study of IMRT beamlets in inhomogeneous media. Medical physics, 2003, 30,3, 296-300.
11. Hossein Hassani, Hassan Ali Nedaie, Mohammad Hassan Zahmatkesh and KavehShirani. A dosimetric study of small photon fields using polymer gel and Gafchromic EBT films. Medical dosimetry,2014, 39, 102–107.
12. Timothy C. Zhu Small Field: dosimetry in electron disequilibrium region. Journal of Physics: Conference Series 250 (2010).
13. Yarahmadi M., Nedaie H.A., Allahverdi M., Asnaashari Kh., . Sauer O.A. Small photon field dosimetry using EBT2 Gafchromic film and Monte Carlo simulation. International Journal of Radiation Research,2013, 11,4,215–224.
14. Wuerfel J.U. Dose measurements in small fields. Medical Physics international journal,2013, 1, 1,81–90.
15. Wolfram U. Lauba. The volume effect of detectors in the dosimetry of small fields used in IMRT. Med. Phys.2003, 30,3,341–347.
16. Jamil Lambert, Yongbai Yin, David R McKenzie, Susan H. Law, Anna Ralston and Natalka Suchowerska. A prototype scintillation dosimeter customized for small and dynamic megavoltage radiation fields. Phys. Med. Biol. 2010, 55, 1115–1126.
17. Martens C., De Wagter C. and De Neve.W.,The value of the PinPoint ion chamber for characterization of small field segments used in intensity-modulated radiotherapy. Phys. Med. Biol.2000, 45, 2519–2530.
18. Marsolat,F., Tromson D., Tranchant N., Pomorski M., Lazaro-Ponthus D., Bassinet C., Huet C., Derreumaux S., Chea M., Boisserie G., Alvarez J., Bergonzo P., Diamond dosimeter for small beam stereotactic radiotherapy. Diamond & Related Materials,2013, 33, 63–70.
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