Presented at #ASMMIRT2016

1. Optimising breast dosimetry:
Improving homogeneity through the
application of angled IMRT fields
M. Squires (BMRS (RT) MA MIR JP MBA(cand.))
S. Cheers (BAppSc (MRS))

2. • Significant side effects associated with dose inhomogeneity
• Risk associated with low dose integral splay
• Options exist that maximise dose uniformity and minimise low dose
Background

3. • The angled segment technique offers two additional clinically feasible
protocols
• To give the planner control over homogeneity (HI) and low dose
conformity (CI)
Aim

4. • Twenty previously optimised tangent plans copied
• Single medially angled off IMRT beam appended to the existing
beamset
• Plans (n=20) optimised and normalised (PTV V47.5 = 99.00%)
Method 1: Single medial segment

5. • Additional (laterally) angled off IMRT beam appended
• Plans (n=20) optimised and normalised (PTV V47.5 = 99.00%)
Method 2: Dual segments

6. • Statistically similar average absolute maximum dose
(Dmax 54.55Gy vs. 54.71Gy, p=0.33)
• Reduced V107%
(14.71cc vs. 23.17cc, p<0.01)
• Low dose (V1) integral splay volume was maintained
(6410.04cc vs. 6402.45cc, p=0.44)
• But, reduced contralaterally
(V1 splay over midline 6.60cm vs. 6.80cm, p=0.04)
• Ipsilateral mean lung dose slightly reduced
(5.23Gy vs. 5.33Gy, p=0.04)
Results 1: Single medial segment

7. • Reduced average maximum dose
(Dmax 53.79Gy vs. 54.71Gy, p=0.03)
• Reduced V107%
(1.90cc vs. 23.17cc, p<0.01)
• Homogeneity improved
(HI= 0.11 vs. 0.13, p=0.03)
• Ipsilateral mean lung dose unaffected
(5.33Gy vs. 5.33Gy, p=0.48)
• Low dose (V1) integral splay increased by 1.5%
(6501.14cc vs. 6402.45cc, p=0.04)
• Low dose (V1) appeared further contralaterally
(8.40cm vs. 6.80cm over midline, p=0.02)
Results 2: Dual segments

8. Comparative results

9. • The addition of a medial segment serves to partially reduce high dose
volumes whilst limiting the increase in low dose (win-win)
• Dual segments serve to fully reduce hotspot size at the expense of
increased low dose contralateral splay
• Each technique provides greater scope to customise dosimetry to
meet specific patient needs
Conclusions

10. References & Acknowledgements
ROC Gosford
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