Implications of tissue heterogeneity for radiosurgery in head and neck tumors

Timothy D. Solberg, F. Eugene Holly, Antonio A F De Salles, Robert E. Wallace, James B. Smathers

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

Purpose: This study was undertaken to investigate the perturbation of small radiation beams by low density heterogeneities and to evaluate the ability of a Monte Carlo code to accout for such perturbation. Performance of an inexpensive film scanning system was also evaluated. Methods and Materials: Film and diode measurements were made in an acrylic phantom in which the size and position of an air gap were varied. Monte Carlo analysis was used to obtain additional verification of the measurements, to provide insight into photon and electron transport phenomena not directly measurable, and as a benchmark for the code. Results: With 10 MV photons and a 1 cm circular field, a small 3-mm air cavity placed 2.6 cm deep in acrylic (full buildup) results in a reduction in central axis dose of 21% immediately following the cavity. Equilibrium is then reestablished over the next centimeter, after which the dose exceeds that of the homogeneous case by 3-4%. The loss in central axis equilibrium is highly field-size dependent, with some loss occurring even for the largest (32 mm) collimator. In addition, the presence of the air cavity produces a significant increase in dose up to 2 cm lateral and outside the primary field. Conclusions: Tissue heterogeneities are not presently accounted for in radiosurgery calculations, yet have the ability to perturb dose significantly. Targets may potentially be underdosed, and adjacent critical structures overdosed. Inability to account for tissue heterogeneities may limit the use of the radiosurgery approach in some areas. A Monte Carlo approach may be the method of choice for small field dose calculation when tissue heterogeneities are encountered.

Original languageEnglish (US)
Pages (from-to)235-239
Number of pages5
JournalInternational Journal of Radiation Oncology, Biology, Physics
Volume32
Issue number1
DOIs
StatePublished - Apr 30 1995

Fingerprint

Radiosurgery
Neck
tumors
Air
Head
Photons
dosage
Benchmarking
Neoplasms
cavities
Electron Transport
air
perturbation
Radiation
photons
collimators
diodes
scanning
electrons

Keywords

  • Dosimetry
  • Stereotactic radiosurgery
  • Tissue heterogeneity

ASJC Scopus subject areas

  • Cancer Research
  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation

Cite this

Implications of tissue heterogeneity for radiosurgery in head and neck tumors. / Solberg, Timothy D.; Holly, F. Eugene; De Salles, Antonio A F; Wallace, Robert E.; Smathers, James B.

In: International Journal of Radiation Oncology, Biology, Physics, Vol. 32, No. 1, 30.04.1995, p. 235-239.

Research output: Contribution to journalArticle

Solberg, Timothy D. ; Holly, F. Eugene ; De Salles, Antonio A F ; Wallace, Robert E. ; Smathers, James B. / Implications of tissue heterogeneity for radiosurgery in head and neck tumors. In: International Journal of Radiation Oncology, Biology, Physics. 1995 ; Vol. 32, No. 1. pp. 235-239.
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abstract = "Purpose: This study was undertaken to investigate the perturbation of small radiation beams by low density heterogeneities and to evaluate the ability of a Monte Carlo code to accout for such perturbation. Performance of an inexpensive film scanning system was also evaluated. Methods and Materials: Film and diode measurements were made in an acrylic phantom in which the size and position of an air gap were varied. Monte Carlo analysis was used to obtain additional verification of the measurements, to provide insight into photon and electron transport phenomena not directly measurable, and as a benchmark for the code. Results: With 10 MV photons and a 1 cm circular field, a small 3-mm air cavity placed 2.6 cm deep in acrylic (full buildup) results in a reduction in central axis dose of 21{\%} immediately following the cavity. Equilibrium is then reestablished over the next centimeter, after which the dose exceeds that of the homogeneous case by 3-4{\%}. The loss in central axis equilibrium is highly field-size dependent, with some loss occurring even for the largest (32 mm) collimator. In addition, the presence of the air cavity produces a significant increase in dose up to 2 cm lateral and outside the primary field. Conclusions: Tissue heterogeneities are not presently accounted for in radiosurgery calculations, yet have the ability to perturb dose significantly. Targets may potentially be underdosed, and adjacent critical structures overdosed. Inability to account for tissue heterogeneities may limit the use of the radiosurgery approach in some areas. A Monte Carlo approach may be the method of choice for small field dose calculation when tissue heterogeneities are encountered.",
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