Peripheral Dose Measurement for 6 MV Photon Beam
The objective of this study is to measure the peripheral dose (PD) at different depths and field sizes using film dosimetry. PD of 6 MV Siemens Primus linear accelerator photon beam for 10 cm square field and 2.5 cm diameter cone were measured at 1.5 cm and 10 cm depth, 100 cm source surface distance (SSD) with Kodak EDR2 film. PD for 10 cm square field and 2.5 cm cone were measured for the distance 1 cm to 5 cm from the geometric field edge. PD was calculated as a percentage of the central axis dose. The PD for both field sizes decreased with increasing distance from the beam edge. PD was also larger for 10 cm square field compared to 2.5 cm circular field for both depths. At 10 cm depth, the measured PD was 20% and 10% higher compared to that of 1.5 cm depth for 10 cm and 2.5 cm field size respectively. The PD for a given beam energy is a function of distance from the beam edge, field size and depth. At any depth measured, PD increases as the field size increases due to radiation scattered from the beam and scatter arising from within the medium. At deeper depth, more Compton electrons are produced and scattered to the peripheral region hence causes the PD to increase with depth. At any field size measured, peripheral dose increases as the depth increases. PD also increases as the field size increases.
McParland B. J., Fair H. I. (1990) A method of calculating peripheral dose distributions of photon beams below 10 MV. Med. Phys. 19:283-293
Stovall M., Blackwell C. R., Novack D. H. et al. (1995) Fetal dose from radiotherapy with photon beams: Report of AAPM Radiation Therapy Committee Task Group No. 36. Med. Phys. 22:63-82
Joosten A., Matzinger O., Jeanneret-Sozzi W. et. al. (2013) Evaluation of organ-specific peripheral doses after 2-dimensional, 3-dimensional and hybrid intensity modulated radiation therapy for breast cancer based on Monte Carlo and convolution/superposition algorithms: Implications for secondary cancer risk assessment. Radiother. Oncol. 106:33-41
Howell R. M., Scarboro S. B., Kry S. F. et. al. (2010) Accuracy of out-of-field dose calculations by a commercial treatment planning system. Phys Med Biol. 55:6999-9008.
Mazonakis M., Zacharopoulou F., Varveris H. et al. (2008) Peripheral dose measurements for 6 and 18 MV photon beams on a linear accelerator with multileaf collimator. Med. Phys. 35: 4396-4402
Tubiana M. (2009) Can we reduce the incidence of second primary malignancies occurring after radiotherapy? A critical review. Radiother. Oncol. 90:4-15
Shi C., Papanikolaou N., Yan Y. et. al.(2006) Analysis of the sources of uncertainty for EDR2 film-based IMRT quality assurance. J. Appl. Clin. Med. Phys. 7:2
Technical Report Series No. 398 (2000) Absorbed dose determination in external beam radiotherapy – An international code of practice for dosimetry based on standards of absorbed dose to water.
Kase K. R., Svensson G. K., Wolbarst A. B. et. al. (1983) Measurements of dose from secondary radiation outside a treatment field. Int. J. Radiat. Oncol. Biol. Phys. 9:1177-83.
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