Room: Room 209
Purpose: To apply the gantry-static couch-motion optimization (GsCMO) technique to photon breast boost treatment planning improving the plan quality and lowering the dose to organs- at-risk.
Methods: The GsCMO technique is an arc-type treatment delivery where gantry is kept static while couch moves with an increment of two degrees (both arcs look like butterfly wings). We used two tangential arcs (lateral and medial) which were simulated at two static gantry angles and couch moved in an increment of two degrees. This study compared the GsCMO technique with standard wedge pair technique in supine position and in decubitus position. Comparison with electron treatment plan was not performed because the electron beams could not reach under breast fold and deep-seated cavities, resulting in undercoverage of the PTV distally. A retrospective study was done on breast patients (n=10, right breast) who received 10Gy boost after 50Gy to whole breast. Each case was re-planned using all three techniques. Dose volume histogram (DVH) comparison was conducted for organs-at-risk between GsCMOT (supine), wedge pair (supine) and wedge pair (decubitus) techniques.
Results: Percentage decrease of dose to right lung (-25%Â±9%), heart (-18%Â±7%) and left lung (-12%Â±3%) was noticed for the GsCMO technique as compared to wedge pair techniques. There is no exit dose to ipsilateral lung and heart for GsCMOT because the fields are tangential.
Conclusion: With GsCMOT, we have seen an improvement in dose reduction to ipsilateral lung, heart and contralateral lung. This isocentric based non-coplaner technique is suitable for deep seated breast boost cavities and avoid uncomfortable decubitus position.