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Volumetric Modulated Arc Therapy in a Large Body Habitus Patient with Left Breast Cancer: A Dosimetric Study

Waseem Sharieff and Heping Xu

Background: Women with large body habitus present unique challenges for breast cancer radiation planning. We describe volumetric modulated arc therapy (VMAT) planning and its associated challenges for loco-regional radiotherapy of left sided cancer; we also describe strategies to overcome these challenges.

Methods: We performed a dosimetric comparison of loco-regional radiotherapy using three dimensional conformal radiotherapy (3D CRT) with VMAT. Our patient was a 49 year old female patient who underwent left modified radical mastectomy for stage IIB (pT1 pN1) breast cancer. She had a chest wall separation of >40 cm. Dose prescription to planning target volumes were 50 Gy of chest wall (PTV50_ eval), 45 Gy to levels II-III axilla (PTV45) and 40 Gy to internal mammary nodes (PTV40) – all in 25 fractions. To assess chest wall motion, we used fluoroscopy and breath hold scan; we fused breath hold scan to the free breathing planning scan, and slice by slice examined the chest wall motion.

Results: In 3D CRT, 95% of PTV50_eval could be covered by 95% dose with hotspots of dose up to 115%. PTV40 could not be adequately covered because of excessive doses to the heart and lung. VMAT achieved planning objectives on target volumes and organs-at-risk. Breath hold scan revealed ≤ 5 mm chest wall motion.

Conclusion: Compared to 3D CRT in woman with large body habitus, VMAT can produce superior dosimetric plan. Chest wall motion must be carefully assessed. Breath hold scan is a useful tool in addition to fluoroscopy to assess chest wall motion, and could be incorporated in VMAT for treatment delivery.