The HeartSpare Plus 1A Trial: A dosimetric comparison of breast radiotherapy techniques to treat locoregional lymph nodes including the internal mammary chain (IMC)


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Alison Ranger1,Alex Dunlop2,Katie Hutchinson3,Marjory Mclennan3,Hannah Chantler3,Nikki Twyman3,Christopher Rose4,Helen Convery1,Ellen Donovan1,Emma Harris5,Charlotte Coles3,Anna Kirby1
1The Royal Marsden NHS Foundation Trust,2The Royal Marsden NHS Trust,3Cambridge University Hospitals Trust,4Cambridge Hospitals University Trust,5The Institute of Cancer Research

Abstract

Background

Published data reports a 3-5% disease-free survival benefit for women undergoing radiotherapy to locoregional lymph nodes including the IMC.  However, only 20% of UK radiotherapy departments currently offer adjuvant IMC radiotherapy.  This study explores planning solutions capable of delivering locoregional lymph node radiotherapy whilst minimising heart and lung doses.

Method

The breast and nodes of 14 existing patients scanned both in free breathing (FB) and breath hold (BH) were outlined following ESTRO consensus guidelines.  Comparative plans, prescribed to 40Gy/15 fractions, with objectives and contraints shown in table 1, were produced using 3 different techniques:  3D Conformal RT (wide-tangent), VMAT (‘bow-tie’ technique) and Tomotherapy (FB only).  The Wilcoxon-ranked sum test compared BH and FB for each modality (2.5% significance level).

Results

Planning ConstraintWT_BH WT_FBVMAT_BHVMAT_FBTomotherapyPTV_Beast V38 (%)>90%

95.2

(93-97.5)

95.2

(90.1-97.3)

97.2

(94.3-98.7)

95.4

(92-97.2)

91.4

(90-93.1)

PTV_nodes V32 (%)>90%

94.9

(89.9-97)

96.1

(96-99)

99.6

(99.6-100)

99.0

(98.1-99.8)

98.6

(97.7-100)

Heart V17Gy (%)<10%

2.2

(0-9.6)

10.2

(2.9-21)

1.6

(0-4.5)

6.4

(2.1-14)

3.4

(0-7.5)

Ipsilateral Lung V17Gy (%)<35%

27.7

(18.2-34.4)

34.1

(23.7-41.6)

28.7

(17.7-34.5)

32.2

(25.9-34.5)

33.9

(32.8-34.5)

Mean Contralateral Lung Dose (Gy)<4Gy

0.8

(0.4-3.2)

0.7

(0.5-1.0)

0.7

(0.5-0.9)

0.8

(0.7-1)

3.7

(3.3-4.0)

Mean Contralateral Breast Dose (Gy)<3.5Gy

1.6

(0.3-3.2)

1.3

(0.3-2.7)

1.1

(0.3-2.7)

1.5

(0.3-3.5)

2.3

(1.6-3.5)

Pass rate 13/146/1411/1110/108/8Mean Heart Dose (Gy)

Objective

<4Gy

2.6

(1.3-5.5)

5.5

(2.7-9.1)

2.3

(1.2-3.8)

4.1

(2.5-7)

6.3

(4.0-7.9)

Table 1.  Mean values (Range) for target volumes/organs at risk (OAR)

Conclusion

Acceptable plans were acheived using all techniques.  Breath hold reduces doses to the heart and ipsilateral lung (MHD: WT p=0.001, VMAT p=0.008).  Arc therapies increase coverage of the nodal volumes.  VMAT in BH offers superior coverage with minimum dose to the OARs.