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Skin Dose in Radiation Treatment of Left Breast: Analysis in the Context of Prone Versus Supine Technique

A Saini1*, W Lee2 , C Hwang3 , M Biagioli4 , I Das5 , (1) Florida Hospital, Orlando, FL,(2) Florida Hospital, Orlando, FL, ,(3) Florida Hospital, Orlando, FL, (4) Florida Hospital, Orlando, FL, (5) NYU, Ambler, PA


(Sunday, 7/14/2019)  

Room: ePoster Forums

Purpose: Various technique such as deep inspiration breath hold, and prone breast have been attempted successfully to reduce dose to cardiac components including LAD and LV. However inadequate skin dose can lead to skin recurrence. This study was undertaken to analyze skin dose in prone and supine treatment of same patients with variable grid size dose calculation.

Methods: Fifty patients scanned in both prone and supine position and radiation treatment was planned for the left breast cancer with 6 MV beam for prescribed dose of 42.66 Gy in 16 fractions. Calculation was performed using advance dose engine AAA from Eclipse 13.7 using 2.5 mm and 1 mm grid size. Gantry angles of treatment beams were recorded in each technique to see the frequency distribution of the beam angle. Dose from surface up to 5 mm depth which was optimized for breast eval (PTV) were tabulated.

Results: Mean dose for prone vs supine for 1 mm grid size at surface is (32.25% vs 32.95%; P<0.62), 1mm (66.87% vs65.05%; P<0.86), 2mm (81.86% vs 81.27%; P<0.26), 3mm (87.8% vs & 89.1%; P<0.003),4mm(91.92% vs 94.5%; P<0.00)& 5mm (95.3% vs 98.2%; P,0.00). Mean dose for prone vs supine for 2.5 mm grid size at surface (36.75% vs 38.16%; P<0.34), 1mm (60.38% vs 62.15%; P<0.14), 2mm (77.35% vs 79.65%; P<0.02), 3mm (87.1% vs & 88.59%; P<0.00),4mm (91.60% vs 94.63%; P<0.00)& 5mm (95.10% vs 97.8%; P<0.00) its shown in Figure 1 & 2. Average median angle for prone relative to skin surface is 4.3 degree as compared to 52.7 degree for supine treatment.

Conclusion: Based on identical patient population It proves that prone technique provides inferior dose compared to supine. Its because in prone technique beam is almost perpendicular to the surface. Care should be taken to augment skin dose if desired by bolus or beam spoiler.


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