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Axillary Nodes Radiotherapy Boost Field Dosimetric Impact Study: Oblique Field and Field Optimization in 3D Conventional Breast Cancer Radiation Treatment

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M Su

M Su1*, S Sura2 , (1) Mount Sinai School of Medicine, Elmhurst, NY


SU-E-T-596 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To evaluate dosimetric impact of two axillary nodes (AX) boost techniques: (1) posterior-oblique optimized field boost (POB), (2) traditional posterior-anterior boost (PAB) with field optimization (O-PAB), for a post-mastectomy breast patient with positive axillary lymph nodes.

Methods: Five patients, 3 left and 2 right chest walls, were included in this study. All patients were simulated in 5mm CT slice thickness. Supraclavicular (SC) and level I/II/III AX were contoured based on the RTOG atlas guideline. Five treatment plans, (1) tangential chest wall, (2) oblique SC including AX, (3) PAB, O-PAB and POB, were created for each patient. Three plan sums (PS) were generated by sum one of (3) plan with plan (1) and (2). The field optimization was done through PS dose distribution, which included a field adjustment, a fractional dose, a calculation location and a gantry angle selection for POB. A dosimetric impact was evaluated by comparing a SC and AX coverage, a PS maximum dose, an irradiated area percentage volume received dose over 105% prescription dose (V105), an ipsi-laterial mean lung dose (MLD), an ipsi-laterial mean humeral head dose (MHHD), a mean heart dose (MHD) (for left case only) and their DVH amount these three technique.

Results: O_PAB, POB and PAB dosimetric results showed that there was no significant different on SC and AX coverage (p>0.43) and MHD (p>0.16). The benefit of sparing lung irradiation from PAB to O-PAB to POB was significant (p<0.004). PAB showed a highest PS maximum dose (p<0.005), V105 (p<0.023) and MLD (compared with O-PAB, p=0.055). MHHD showed very sensitive to the patient arm positioning and anatomy. O-PAB convinced a lower MHHD than PAB (p=0.03).

Conclusion: 3D CT contouring plays main role in accuracy radiotherapy. Dosimetric advantage of POB and O-PAB was observed for a better normal tissue irradiation sparing.

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