(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: CDC data shows obesity is on the rise and 40% of American adults are now considered obese. Obese patients present unique challenges with target coverage and normal tissue sparing. Here we investigated an obese breast cancer patient with large tissue separation and compared dose statistics from 3 different planning techniques: traditional 3D, Volumetric Modulated Arc Therapy (VMAT) and Intensity Modulated Radiotherapy (IMRT).
Methods: Patient X was a 54 year old woman with T2N2 cancer of the right breast. Largest tissue separation along treatment area was 45 cm. Physician prescribed 50.4 Gy to 95% of breast contour and 45 Gy to 95% of supraclavicular and axillary node contours. Normal tissue constraints: total lung V20 < 20%, ipsilateral lung V20 < 30%, heart mean dose < 3 Gy, contralateral lung V5 < 10%, contralateral breast mean dose < 4 Gy and breast max dose < 115%. Three Planning techniques were investigated: 3D supraclavicular field + tangents using 16X field in field, VMAT with six 6X arcs and IMRT with seventeen 6X non-coplanar beams. Plans were evaluated according to number of coverage and sparing constraints achieved.
Results: Conventional 3D: 95% breast PTV covered at 78.5% of prescription, max dose 120%. All normal tissue constraints were met. VMAT: 95% breast PTV covered at 93.1% of prescription, max dose 118.7%. Heart mean dose was 4.6 Gy and contralateral lung V5 was 34.1%. Non-coplanar IMRT: 95% breast PTV covered at 97%, max dose 117.3%. All normal tissue constraints were achieved.
Conclusion: Conventional plan designs can be inadequate for obese breast patients. 3D supraclavicular field with tangents resulted in least breast coverage and hottest plan. VMAT significantly improved coverage but spilled excessive dose into surrounding tissue. Non-coplanar IMRT yielded best plan where all constraints and coverage were met.
Keywords
Treatment Planning, Breast, Intensity Modulation
Taxonomy
TH- External beam- photons: treatment planning/virtual clinical studies
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