The effect of the number of computed tomographic slices on dose distributions and evaluation of treatment planning systems for radiation therapy of intact breast

Chee Wai Cheng, Indra J. Das, Baldassarre Stea

Research output: Contribution to journalArticle

38 Scopus citations


Purpose: This study was undertaken to answer the following questions in breast irradiation: (a) How many calculation planes are sufficient for three-dimensional (3-D) treatment planning? (b) Is pseudo-3-D planning system sufficiently accurate for 3-D treatment planning of a breast? Methods and Materials: We carried out dose calculations and differential dose-volume analysis on three representative patients covering the range of breast size encountered in a clinic. The breast volumes were reconstructed from computed tomography (CT) scans using three slices, five slices and the full CT scan respectively. An established 3-D dose algorithm and two pseudo-3-D commercial systems were used in the calculations. Comparison of isodose distributions were made between the central axis plane, a cephalic and a caudal plane 6 cm above or below the central axis respectively. Results: When comparing isodose distributions generated with conventional two-dimensional treatment planning with 3-D dose calculations, the former underestimated the size and magnitude of the hot spots in the medial and the lateral subcutaneous (SC) regions. When comparing the three-slice with the full CT model, while the three-slice model was found to be adequate for the "small" and the "medium" size patients, the full CT model provided a more accurate representation of dose distributions for the "large" patient. Comparison of a true 3-D algorithm with pseudo-3-D algorithms showed that while the latter systems were adequate for the "small" and the "medium" patients, significant differences were noted between the true 3-D and the pseudo-3-D algorithms for the "large" patient. Conclusion: For patients whose breast contours vary slowly within the tangential fields, a three-slice CT scan as well as a pseudo-3-1) approach appears to be adequate for clinical decision. However, for patients with large variation of contours within the tangential fields, a full scale CT scan with a true 3-D dose algorithm is more accurate than either the three-slice or the five-slice model.

Original languageEnglish (US)
Pages (from-to)183-195
Number of pages13
JournalInternational Journal of Radiation Oncology Biology Physics
Issue number1
Publication statusPublished - Aug 30 1994



  • Breast
  • Computed tomography
  • Dose volume histogram
  • Three-dimensional
  • Treatment planning

ASJC Scopus subject areas

  • Oncology
  • Radiology Nuclear Medicine and imaging
  • Radiation

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