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  4. Comparison of Proton Therapy with Pencil Scanning Beams, Rapid-Arc Technique, and High Energy Electron Beams for Boosting Tumor Bed of Hypofractionated Radiation Therapy for Patients with Early-Stage Breast Cancer

Comparison of Proton Therapy with Pencil Scanning Beams, Rapid-Arc Technique, and High Energy Electron Beams for Boosting Tumor Bed of Hypofractionated Radiation Therapy for Patients with Early-Stage Breast Cancer

M Tsai*1, H Lin1 , C Chong2 , S Lu1 , C Wang1 , S Kuo1 1 National Taiwan University Hospital, Taipei, Taiwan 2 Yonglin Healthcare Foundation, Taipei, Taiwan

Presentations

(Wednesday, 7/17/2019) 10:00 AM - 10:30 AM

Room: Exhibit Hall | Forum 1

Purpose: To assess the impact of HypoRT-boost of various radiations (protons, x-rays, electrons) to patients

Methods: All plans of this study were generated by Eclipse(Varian Medical System, Palo Alto, CA, USA). Three patients with left breast cancer were selected. A total dose of 40-Gy(RBE) in 15 daily-fraction and 10-Gy(RBE) in 4 daily-sequential-boost was prescribed. The initial plans were generated using 6-MV-photons(AAA-algorithm,V15.5). Three boost plans, including proton(PCS-algorithm,V13.7), electron(EMC-algorithm,V15.5), and photon (PO-algorithm,V15.5) were created for each patient. Two proton beams (IMPT), en-face and anterior-oblique beams, were used to create the proton plans. A 12-MeV-en-face electron-beam(EB) was used to create the electron plans. Single partial-arc(6MV) with RapidArc tech. was applied to create the photon plans. The goal of the planning was to cover 99%CTV with 95%prescribed dose and minimize the volume of 107%dose. Homogeneity and conformal indices were calculated. Dosimetric statistics of OARs(heart, skin, contra- and ipsi-lateral breast and lung) were assessed. Range uncertainty(3.5%) and setup-error(3mm) were considered.

Results: All techniques achieved the goal of CTV-coverage except EB of case#2. IMPT provided the best inhomogeneity. RA-p showed the best conformity and EB was the worst. Contra-lateral lung and breast were spared by all techniques(mean˂ 0.31-Gy). The ispi-lateral lung received ˂ 13.0, 0.8%, and 0.3% of prescribed dose for photons, electrons, and protons, respectively. The IMPT generated the lowest dose to heart; Skin was best spared by RA-p and followed by IMPT and EB. The uncertainties resulted in 0.52% and 1.02% deterioration of CTV-coverage for RA-p and IMPT. The V3Gy of left lung and heart increased to 1.96% and 2.90% for RA-p and 4.00% and 3.07% for IMPT, respectively.

Conclusion: The RA-p and IMPT are preferred for boosting tumor bed. They provide outstand dose conformity, homogeneity and OAR sparing. Preliminarily, IMPT tends to outperform RA-p for boosting tumor beds, even under the 3.5%/3mm scenarios.

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