(Monday, 7/15/2019) 1:15 PM - 1:45 PM
Room: Exhibit Hall | Forum 3
Purpose: Post-mastectomy radiotherapy patients are often treated with bolus materials to increase skin dose hence reduce the risk of chest wall recurrence. This investigation quantifies variations of bolus materials in preparation to give recommendations for consistency in their clinical applications.
Methods: This study utilized Superflab, SuperStuff, Adapt-itTM thermoplastic sheets, brass mesh, and towels cut in squares soaked in water. Bolus materials were 20 and 30cm2 in size and 5mm and 10mm thickness, the brass mesh was 45cm2 in size and 1.5mm thick (2mm tissue-equivalent). For all measurements, ionization charges with same monitor units each were collected using a PPC05 plane-parallel chamber, at central axis of 5x5cm2, 10x10cm2, 15x15cm2 and 25x25cm2 field sizes of 6 and 18MV photon energies at the surface, 5, 10 and 20mm depths for no bolus and with all bolus materials. Because the current practice uses wet towels, three therapists created 5 and 10mm equivalent-thicknesses boluses to measure subject variability; and quality assurance boluses were created by measuring amounts of towels and water to formulate tissue-equivalent recipe. Dry towels of 20cm2 and 30cm2 weighed 19-21g and 40g, respectively.
Results: Readings without bolus at the surface for 6MV differed by -44.4, -40.9, and -37.2% using 5mm Superflab as baselines for 5x5cm2, 10x10cm2, 15x15cm2 field sizes, respectively. These values were 49.7,-45.8, and -41.6% when 10mm Superflab was used as baseline. For 18MV, the values were -58.1, -50.8, and -44.4%; and -67.9, -60.8, and -53.8% for 5 and 10mm Superflab, respectively as baselines. Subject variability percent differences ranged from 3-7% for 6MV and 7-11% for 18MV. All bolus materials exhibited similar properties to Superflab for 5 and 10mm thickness and for both energies. The mesh brass bolus was activated with 18MV (14.6mR/hr at surface).
Conclusion: To increase skin dose throughout treatments, consistent preparation of towels is recommended.
Keywords
Dosimetry, Breast, Quality Assurance
Taxonomy
Not Applicable / None Entered.
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