Volume 2, Issue 1

Original research papers

Medical Physics


Firas Ghareeb, Sofia Silva, Joana Lencart, Fatima Borges, Joao A.M. Santos

Pages: 20-25

DOI: 10.21175/RadJ.2017.01.005

Received: 1 MAR 2016, Received revised: 30 APR 2016, Accepted: 8 MAY 2016, Published online: 20 APR 2017

A pediatric anthropomorphic phantom was irradiated using a standard 3DCRT treatment plan with and without including the couch in the Treatment Planning System (TPS; Varian Eclipse 13.5, AAA algorithm) calculations. The 2D scatter dose distributions at several planes away from the isocenter were measured using a Gafchromic EBT3 radiochromic film, and compared with the calculated ones at several distances from the isocenter. The out-of-field dose distributions (from TPS and EBT3) differ considerably, particularly where the cranio-caudal beam has left the body but is still near the surface of the phantom and near the couch interception. Further investigation was conducted to estimate the impact of the beam angle on the dose distribution. A 5x5 cm 6MV photon beam was used to irradiate a fiber carbon slab (couch top material) at different angles of incidence and the scattered radiation was measured with an ionization chamber placed 20 cm away from the isocenter. The results showed a 5% increase in scattered radiation between the angles of 00 and 850. This is an indication that scatter from the couch must be taken into account when estimating out-of-field dose distributions and that the TPS, even when the couch is included in the calculation, is not sufficiently accurate to predict these doses.
  1. H. Suit et al., "Secondary carcinogenesis in patients treated with radiation: a review of data on radiation-induced cancers in human, non-human primate, canine and rodent subjects," Radiation research, vol. 167, no. 1, pp. 12-42, 2007.
    DOI: 10.1667/RR0527.1
    PMid: 17214511
  2. X. G. Xu, B. Bednarz, and H. Paganetti, "A review of dosimetry studies on external-beam radiation treatment with respect to second cancer induction,", Physics in medicine and biology, vol. 53, no. 13, pp. R193-241, 2008.
    DOI: 10.1088/0031-9155/53/13/R01
    PMid: 18540047
    PMCid: PMC4009374
  3. W. D. Newhauser, and M. Durante, "Assessing the risk of second malignancies after modern radiotherapy," Nature Reviews Cancer, vol. 11, no. 6, pp. 438-448, 2011.
    DOI: 10.1038/nrc3069
    PMid: 21593785
    PMCid: PMC4101897
  4. M. Tubiana, "Can we reduce the incidence of second primary malignancies occurring after radiotherapy? A critical review," Radiotherapy and Oncology, vol. 91, no. 1, pp. 4-15, 2009
    DOI: 10.1016/j.radonc.2008.12.016
    PMid: 19201045
  5. M. L. Taylor, T. Kron, and R. D. Franich, "Assessment of out-of-field doses in radiotherapy of brain lesions in children," International Journal of Radiation Oncology Biology Physics, vol. 79, no. 3, pp. 927-933, 2011.
    DOI: 10.1016/j.ijrobp.2010.04.064
    PMid: 20732763
  6. C. La Tessa et al., "Out-of-field dose studies with an anthropomorphic phantom: Comparison of X-rays and particle therapy treatments," Radiotherapy and Oncology, vol. 105, no. 1, pp. 133-138, 2012.
    DOI: 10.1016/j.radonc.2012.04.004
    PMid: 22575675
  7. M. L. Taylor and T. Kron, "Consideration of the radiation dose delivered away from the treatment field to patients in radiotherapy," Journal of Medical Physics, vol. 36, no. 2, pp. 59-71, 2011.
    DOI: 10.4103/0971-6203.79686
    PMid: 21731221
    PMCid: PMC3119954
  8. J. Valentin, "Low-dose extrapolation of radiation-related cancer risk," Annals of the ICRP, vol. 35, no. 4, pp. 1-140, 2004.
    DOI: 10.1016/j.icrp.2004.12.002
    DOI: 10.1016/j.icrp.2005.11.002
    PMid: 16782497
  9. Health risks from exposure to low levels of ionizing radiation, BEIR VII phase 2, 2006.
    Retrieved from: https://www.nap.edu/catalog/11340/health-risks-from-exposure-to-low-levels-of-ionizing-radiation
    Retrieved on: Dec. 12, 2015.
  10. R. M. Howell et al., "Accuracy of out-of-field dose calculations by a commercial treatment planning system," Physics in medicine and biology, vol. 55 no. 23, p. 6999, 2010.
    DOI: 10.1088/0031-9155/55/23/S03
    PMid: 21076191
    PMCid: PMC3152254
  11. J. Sorriaux et al., "Evaluation of Gafchromic® EBT3 films characteristics in therapy photon, electron and proton beams," Physica Medica, vol. 29, no. 6, pp. 599-606, 2013.
    DOI: 10.1016/j.ejmp.2012.10.001
    PMid: 23107430
  12. V. C. Borca et al., "Dosimetric characterization and use of GAFCHROMIC EBT3 film for IMRT dose verification," Journal of Applied Clinical Medical Physics, vol. 14, no. 2, 2013.
  13. R. Harrison, "Introduction to dosimetry and risk estimation of second cancer induction following radiotherapy," Radiation Measurements, vol. 57, pp. 1-8, 2013.
    DOI: 10.1016/j.radmeas.2013.01.018
  14. D. Higgins, P. Whitehurst, and A. Morgan, "The effect of carbon fiber couch inserts on surface dose with beam size variation," Medical Dosimetry, vol. 26, no. 3, pp. 251-254, 2001.
    DOI: 10.1016/S0958-3947(01)00071-1
  15. S. McCormack, J. Diffey, and A. Morgan, "The effect of gantry angle on megavoltage photon beam attenuation by a carbon fiber couch insert," Medical Physics, vol. 32, no. 2, pp. 483-487, 2005.
    DOI: 10.1118/1.1852792
    PMid: 15789595
  16. Absorbed dose determination in external beam radiotherapy: An international code of practice for dosimetry based on standards of absorbed dose to water, Technical Report Series, no. 398, International Atomic Energy Agency, Vienna, 2000.
    Retrieved from: http://www-pub.iaea.org/MTCD/publications/PDF/TRS398_scr.pdf
    Retrieved on: Jan. 15, 2016.
  17. L. Menegotti, A. Delana, and A. Martignano, "Radiochromic film dosimetry with flatbed scanners: a fast and accurate method for dose calibration and uniformity correction with single film exposure," Medical Physics, vol. 35, no. 7, pp. 3078-3085, 2008.
    DOI: 10.1118/1.2936334
    PMid: 18697531
  18. D. Lewis et al., "An efficient protocol for radiochromic film dosimetry combining calibration and measurement in a single scan," Medical Physics, vol. 39, no. 10, pp. 6339-6350, 2012.
    DOI: 10.1118/1.4754797
    PMid: 23039670