Best of the Best Oral Presentation Clinical Oncology Society of Australia Annual Scientific Meeting 2020

A dosimetric study evaluating five different treatment techniques for whole breast radiotherapy (#74)

Amanda J Harding 1 , Brock Lamprecht 1 , Jennifer Harvey 1 , Erika Muscat 1 , Kate Howe 1 , G Tao Mai 1 , Tamara Barry 1 , Elizabeth Brown 1 2 , Margot Lehman 1 , Cathy Hargrave 1 2 , Anne Bernard 3
  1. Princess Alexandra Hospital Radiation Oncology, Woolloongabba, QLD, Australia
  2. School of Clinical Sciences, Queensland University of Technology, Brisbane, QLD, Australia
  3. QCIF Facility for Advanced Bioinformatics, Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia

Aims: Breast cancer patients present for radiation therapy (RT) with a large variation in body habitus, organ at risk (OAR) location and planning tumour volumes (PTV).¹,² Consequently, RT plan quality can vary.  The purpose of this study was to compare the dose to OARs and PTVs between three‐dimensional conformal radiation therapy (3DCRT), hybrid intensity modulated radiation therapy (IMRT), hybrid volumetric modulated arc therapy (VMAT), VMAT reduced arcs (bowtie) and VMAT bowtie (BT) flattening filter free (FFF) plans.

Methods: Thirty early stage whole breast patient computerised tomography (CT) datasets were divided into left and right sided cases across size categories: small, medium and large. PTV and OAR volumes were created on each dataset and planned using: 3DCRT, hybrid IMRT (HYI), hybrid VMAT (HYV), BT and BTFFF techniques.  Plan dosimetry was assessed using conformity (CI) and homogeneity (HI) indices, OAR dose and PTV coverage. The difference in continuous outcomes between techniques was assessed using linear mixed model analysis. Ethics approval was granted.

Results: BT techniques showed equivalent PTV coverage and significantly improved CI (p<0.001) over all other techniques.  Heart doses on left sided cases were lower across all measures for BT techniques.  Heart maximum, non-target tissue (NTT), and ipsilateral lung doses were significantly lower (p<0.001) in the BT plans compared with 3DCRT techniques across left and right sided plans.  Right sided cases had the highest mean doses to the heart 0.76Gy, contralateral lung 0.39Gy and contralateral breast structure 0.47Gy for BTFFF compared with the lowest doses of 0.61Gy, 0.2Gy and 0.37Gy respectively using 3DCRT.

Conclusion: BT techniques provided superior CI, HI, NTT and ipsilateral OAR doses compared with 3DCRT and hybrid plans.  Increased dose to the contralateral lungs and breast in BT techniques compared with 3DCRT, HYI and HYV techniques was deemed clinically acceptable as these are within primary departmental goal tolerances.

  1. 1. De Langhe S, Mulliez T, Veldeman L, et al. Factors modifying the risk for developing acute skin toxicity after whole‐breast intensity modulated radiotherapy. BMC Cancer 2014;14:711–720.
  2. 2. Morganti A, Cilla S, de Gaetano A, et al. Forward planned intensity modulated radiotherapy (IMRT) for whole breast postoperative radiotherapy. Is it useful? When? J Appl Clin Med Phys 2011;2:34–51.