Related Experiment Videos
Optimization of a cord shielding technique for electrons.
J A Antolak1, J W Scrimger, E Mah
1Department of Medical Physics, Cross Cancer Institute, Edmonton, Alberta, Canada.
Summary
A common technique for shielding the spinal cord during head and neck cancer treatment with electron beams is inadequate. This method fails to ensure the target tumor volume receives the prescribed radiation dose.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy
Background:
- Large anterior electron fields are used for head and neck tumor irradiation.
- A wax bolus is typically employed for spinal cord shielding, with thickness determined by the R80 depth.
Purpose of the Study:
- To evaluate the accuracy of a standard wax bolus technique for spinal cord shielding and target volume coverage in electron beam therapy for head and neck tumors.
- To investigate the impact of electron scatter on dose distribution.
Main Methods:
- Utilized CT data from a thyroid cancer patient to create 3D neck contours.
- Employed the Alberta Treatment Planning system and a 3D implementation of the M.D. Anderson (Hogstrom) algorithm for dose calculations.
- Iteratively adjusted bolus shape and thickness to optimize dose distribution.
Main Results:
- The standard bolus technique inadequately covers the target volume with the 80% isodose line, despite adequate spinal cord shielding.
- Lateral scatter non-equilibrium introduced by the bolus explains the observed dose discrepancies.
- Optimized bolus design improved dose coverage, showing reasonable agreement with measured data.
Conclusions:
- The conventional wax bolus technique for electron beam therapy in head and neck cancers is inappropriate due to inaccurate dose distribution.
- Treatment planning must account for electron transport and scatter phenomena to ensure treatment integrity.
- Further investigation and optimization of electron beam techniques are necessary to meet therapeutic goals.