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[Air bubble effect during alloy cooling in shielding blocks radiotherapy]
A Ostinelli1, S Gelosa, M Frigerio
1Servizio di Fisica Sanitaria, Azienda Ospedaliera S. Anna, Como. fisrad@pn.itnet.it
La Radiologia Medica
|February 11, 1999
Summary
Air bubbles in radiotherapy alloy shielding are common regardless of alloy type or cooling method. While generally not significant, they may cause dose variations in critical small organ sparing treatments.
Area of Science:
- Medical Physics
- Radiotherapy Technology
- Materials Science
Context:
- Photon beam shaping in radiotherapy utilizes low melting point alloys.
- Air bubbles can form during alloy cooling, potentially affecting dose distribution.
- Understanding bubble formation is crucial for optimizing radiotherapy shielding.
Purpose:
- To investigate the occurrence and impact of air bubbles in alloy used for radiotherapy beam shaping.
- To evaluate bubble recurrence with new and remelted alloys and different cooling techniques.
- To assess the effect of air bubbles on dose inhomogeneity in shielded areas.
Summary:
- Air bubbles (up to 300 mm2) are consistently present in all alloy castings, irrespective of alloy type or cooling method (-20°C to 25°C).
- Casting inhomogeneities lead to film-density variations from 9% to 40%, with random bubble distribution.
- Bubble recurrence is independent of alloy reuse or cooling modalities.
Impact:
- Air bubbles generally have minimal impact on dose inhomogeneity in radiotherapy.
- Potential hot spots from bubbles require consideration for treatments demanding precise sparing of small critical organs, such as eye lens shielding.
- This research informs the design and quality control of alloy shielding in radiation oncology.