A prone technique for treatment of the breast, supraclavicular and axillary nodes

RADIATION ONCOLOGY—TECHNICAL ARTICLE jmiro_2389 362..367

A prone technique for treatment of the breast, supraclavicularand axillary nodesNicole Mason,1 Deborah Macfarlane,1 Robyn Guidi,1 Rebecca Owen1 and Michael Poulsen2

1Radiation Therapy Services and 2Division Radiation Oncology, Princess Alexandra Hospital, Radiation Oncology Mater Centre, Brisbane, Queensland,

Australia

N Mason DipSc (Ther Rad); D MacfarlaneBAppSc (MRT); R Guidi MHS (MRS); R OwenPhD; M Poulsen MBBS, FRANZCR, MD.

CorrespondenceMrs Nicole Mason, Radiation Oncology Mater

Centre, 31 Raymond Terrace, South Brisbane,

Qld 4101, Australia.

Email: [email protected]

Conflict of interest: None.

Submitted 9 August 2011; accepted 26 January

2012.

doi:10.1111/j.1754-9485.2012.02389.x

Summary

Radiation therapy to women with large pendulous breasts presents dosimetricchallenges when the whole breast (WB) and supraclavicular and axillary(SCF + AX) nodes need to be encompassed. The aim of this case study was todemonstrate the feasibility of planning and treating a pendulous breastedpatient in the prone position. Computerised tomography (CT) images wereacquired of the patient in both the prone and supine positions. A Perspex platewas added to the CDR Systems Inc. (Calgary, Canada) prone breastboard tominimize SCF + AX contour variations. Dosimetry was performed on both CTscans and the resultant treatment plans were evaluated for conformity,homogeneity, dose to the lung and maximum doses to the spinal cord (SC)and irradiated volume. The daily set-up in the prone position was monitoredfor stability and reproducibility. The patient completed her treatment coursein the prone position. Minimal daily interventions were required to ensure theposition was reproduced. Grade 3 skin toxicity was recorded in the SCF + AXregion where the Perspex plate was added to the prone positioning device.There was minimal difference in dosimetry between prone and supine plansin the SCF + AX region. The prone WB plan showed improved homogeneity(prone 0.15; supine 0.22) and conformity (prone 0.90; supine 0.77). A simpleaddition to the breastboard has enabled a pendulous breasted woman withSC + AX involvement to be treated in the prone position. Set-up of thistechnique is achievable on a daily basis with minimal impact on workflow. Itis a feasible alternative to supine treatment for this patient group.

Key words: axilla; breast; prone; radiation oncology; supraclavicular.

Introduction

Women requiring radiation therapy to the whole breast(WB), supraclavicular and axillary nodes (SCF + AX)are traditionally treated supine.1–4 This usually resultsin good dosimetry, except in women with large pen-dulous breasts where breast tissue falls superiorlyinto the supraclavicular area and creates tissuefolds laterally and inferiorly. Lung and heart dosesbecome unacceptably high and skin reactions are oftensevere.

Many investigations have demonstrated that treatingpatients with pendulous breasts in the prone positionlowers lung and heart toxicities5–10; however, most ofthese studies did not include patients requiringSCF + AX nodal treatment. The addition of a Perspexplate to the CDR Systems Inc. prone breastboard(Calgary, Canada) has resulted in a simplistic beamarrangement that includes the SCF + AX. In this casestudy, we demonstrate that the dosimetry in theSCF + AX region in prone patients is equivalent tothe dosimetry in supine patients and that treatment is

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Journal of Medical Imaging and Radiation Oncology 56 (2012) 362–367

© 2012 The AuthorsJournal of Medical Imaging and Radiation Oncology © 2012 The Royal Australian and New Zealand College of Radiologists362

feasible. We detail positioning and offer solutions to thedaily challenges of reproducibility.

Methods and materials

Clinical case study

A 44-year-old premenopausal woman presented with aT2N2aM0 (Stage IIIA) self-detected lesion in the upperouter quadrant of the right breast having undergone apartial mastectomy and axillary dissection. The histopa-thology revealed a Grade 3 invasive ductal carcinoma withlymphovascular invasion present in the primary tumour,and 6 out of 18 axillary nodes involved with malignancy.The tumour was positive for oestrogen receptor, proges-terone receptor and HER 2. She proceeded to adjuvantchemotherapy with Taxotere, Carboplatin and Herceptinand was then referred for radiotherapy after completionof six cycles of Taxotere and Carboplatin.

This patient had large pendulous breasts and wasobese. Good shoulder movement was present and shewas able to lie prone comfortably. The patient wasscanned both supine and prone in order to make dosi-metric comparisons. A dose of 47.5 Gy reference dose(RD) in 25 fractions was prescribed to SCF and axillaryapex and 50 Gy RD in 25 fractions to the WB, boostingthe primary site to 60 Gy using mini-tangential fields.For this case study, the dosimetric comparison does notinclude the primary boost.

Simulation

Prone

The patient was assessed in the supine position and notsurprisingly a large volume of breast tissue fell superi-

orly, laterally and inferiorly. This prompted a decision toinvestigate a prone option. The multidisciplinary teamconsidered how to best position the patient such thather breast and shoulder region were exposed but sup-ported, and away from the equipment that may limitbeam arrangement. By increasing the gap betweenthe breast blocks on the positioning device, the breastand SCF + AX region were made accessible. A CTscan, using a Siemens Sensation/Somatom wide boreCT (Siemens AG, Medical Solutions, Germany), wasacquired at 3 mm slice thickness from the tip of nose toinclude the entire breast and lung volume inferiorly.This showed breast tissue falling anterior to the SCFregion. (Fig. 1) In order to flatten the tissue in this areaa 3 mm Perspex plate was added to the superior blockof the prone breastboard extending partially into thegap. (Fig. 2)

The patient was positioned so the junction betweenbreast and SCF + AX was 10 mm superior to the loweredge of the Perspex plate. Our aim was to use this forreproducibility. The Perspex plate flattened the anteriorsurface of the SCF + AX. It allowed visualisation of thearea to ensure tissue folds were minimised and elimi-nated beams passing through the breastboard. Sagittaland coronal lasers were used to determine tattoo pointsfor shoulder, chin and head position reproducibility.(Fig. 3) A reference tattoo was placed laterally in themid-thoracic region to assist with set-up. A repeat CTscan confirmed that the Perspex plate placement hadaddressed our concerns. (Fig. 1)

Supine

The patient was positioned on a Civco Medical Solution(Kiowa, IA) breastboard. A CT scan was performed usingthe same scanning protocol as for the prone technique.

Fig. 1. Comparison of sagittal and trans-

verse CT data sets.

Radiotherapy for prone breast, SCF + AX nodes

© 2012 The AuthorsJournal of Medical Imaging and Radiation Oncology © 2012 The Royal Australian and New Zealand College of Radiologists 363

The supine scan would be used in the event that the newprone position was not deemed acceptable.

Planning

Treatment volumes

Both datasets were imported into the Pinnacle Treat-ment Planning System V 8.0 (Phillips Medical Systems,Seattle, WA). The SCF + AX PTV, including supraclavicu-lar nodes, axillary apex and the position of the junctionwere defined on both data sets by the Radiation Oncolo-gist (RO). WB PTV, prone and supine, were created usinga 5 mm contraction of the external breast skin surfaceand a 6 mm contraction from the superior, inferior andposterior field borders.

Dosimetric comparison

The five-field beam arrangement for both the prone andsupine positions consisted of two half-beam tangentialfields to the breast and three half-beam fields to theSCF + AX PTV matching at the junction. No couch anglerequired. The three-field SCF + AX prone technique con-sisted of an anterior (gantry 180°), left anterior oblique(gantry 220°) and a right posterior oblique (gantry 35°)beam arrangement. The supine field arrangement andresultant isodose distribution in the SCF + AX PTV isshown in Figure 4. The plans were compared using theConformation Number (CN) which simultaneously takes

into account the quality of coverage of the target volumeand the volume of healthy tissue receiving the prescribedreference dose and above;11 the Homogeneity Index (HI)that characterises the uniformity of the absorbed-dosedistribution within the target volume;12 the maximumdose; hotspot;12 V20 of the lung on the affected side;mean lung dose and maximum spinal cord (SC) dose.

Treatment

Prone

A practice set-up was scheduled one week prior to treat-ment to make sure the patient’s position could be repro-duced. It was an opportunity to familiarise the treatmentstaff with the new prone technique and test the physicalgantry angles and imaging arrangements. The initialset-up was time consuming but feasibility of the tech-nique was established.

Daily online image matching was performed with anaction level of 5 mm using a Varian Clinac iX LinearAccelerator (Varian Medical Systems Inc, Palo Alto, CA).For each treatment an online posterior kilovoltage (kV)image and a right lateral megavoltage (MV) image weretaken for isocentre verification. (Fig. 5) This configura-tion was used to avoid rotation of the gantry betweenexposures, thereby reducing the risk of collision. Fieldpositioning was assessed using the head of clavicle andvertebral bodies as matchpoints, as the spinal canal wasnot clearly visible due to the rotated patient position. Thematchpoints on the MV image were anterior chestwalland superior aspect of breast tissue. This image wasused to ensure that superior coverage of the breast wasnot compromised by a move from the posterior kV. Thepatient was repositioned if the overshoot of superiorbreast tissue was less than 10 mm.

Results

The patient completed her treatment course withoutinterruption. The prone position was shown to bestable and reproducible. An overview of online imagesdemonstrated a lateral couch shift was required in 9 of25 treatments. A mean superior move of 6 mm was

Fig. 2. Perspex plate positioning on breast-

board.

Fig. 3. Patient straightened using both longitudinal and coronal lasers and

positioning tattoo points.

N Mason et al.


required in 19 of 25 treatments. No anterior/posteriormove was required. On two occasions, the patient wascompletely repositioned. The dosimetric comparison ofsupine and prone treatment plans are summarised inTable 1. The dosimetry for supine and prone SCF + AXPTV fields was equivalent; CN (0.26 for both) and HIvalues (0.11 compared to. 0.10). The maximum dose tothe SC was reduced from 29.7 Gy to 20.0 Gy by usingthe prone technique. The prone position for the WB PTVproved dosimetrically superior to the supine position.This has been well documented in previous studies.5–10

The CN and HI values indicate homogeneity, with onlythe supine technique resulting in a hotspot.

Discussion

The prone WB technique is used for pendulous breastedpatients. In this case study, we have demonstrated afeasible alternate treatment for pendulous breastedpatients with breast cancer that involves the SCF + AXregion. The new prone technique achieves equivalentdosimetry in the SCF + AX PTV to the supine techniqueand the patient benefits from improved dosimetry inthe WB.

Gielda et al.’s compared the dosimetry between athree-field prone and a three-field supine breast tech-nique in pendulous breasted women. They concludedthat the prone technique achieved equivalent SCF + AXPTV coverage with improved lung sparing. They did notproceed to treat patients due to the complexity of junc-tion geometry, and machine capabilities.14 Our solutionof adding a Perspex plate to the prone breastboardaddresses contour variations within the SCF + AX region,allowing production of an equivalent plan that is able tobe delivered. Table 1 compares dosimetric benefits ofthe prone and supine techniques used in the presentstudy. The main benefit is the Perspex plate acted as atool for set-up reproducibility.

Practical considerations

The challenge we encountered in this novel prone set-upwas daily reproducibility and achieving it in a timelymanner. This was largely due to the size of the patientand the difficulties with lying prone for an extendedperiod of time. Patients need to be carefully selectedensuring they have full shoulder, arm and neck mobi-lity with no pain association. Difficulties also occur in

Fig. 4. Isodose distributions of prone and supine right SCF + AX region. PTV in yellow colourwash, 95% isodose line in magenta. Field arrangement prone: Anterior

180°, LAO 220°, RPO 35°. Field arrangement supine: Anterior 0°, LAO 20°, Posterior 180°.



stabilisation when the contra-lateral breast is very largeand mobile. We were able to stabilise this patient byrotating her torso towards the affected side, reducingweight from the unaffected breast. Minimising stomachfolds within the gap of the breastboard by pulling theabdomen inferiorly is advisable. Manipulating thepatient’s body was difficult on a daily basis because of

the close proximity of the patient and breastboard to thetreatment unit. This was compounded by manual han-dling concerns of making adjustments at the isocentreheight. We overcame these problems by using lowerbreastboard blocks and lower lasers. To improve shoul-der stabilisation the addition of a personalised vacuumbag was discussed; however, it was decided that the

Fig. 5. Online right lateral megavoltage (MV) and posterior kilovoltage (kV) isocentric images and corresponding Digitally Reconstructed Radiographs.

Table 1. Dosimetric comparison between prone and supine techniques

Formula WB PTV prone SC + AX PTV prone WB PTV supine SC + AX PTV supine

Volume (cm3) 1630.0 129.8 2196.0 77.3

Conformation number (CN) CNTV

TV

TV

VRI RI

RI

= × 0.90 0.26 0.77 0.26

Homogeneity index (HI) HID D

D=

−2 98

50

% %

%

0.15 0.11 0.22 0.10

Dmax (Gy) 54.9 51.2 55.2 51.2

Hotspot (Gy) – 51.5 54.3 52.7

V20 Rt lung (%) 1.3 26.0

Mean dose Rt lung (Gy) 1.9 12.8

Max spinal cord Dose (Gy) 20.0 29.7

Abbreviations: Dmax,13 TVRI, target volume covered by reference isodose; SC + AX PTV, supraclavicular and axillary nodes planning target volume; TV,

target volume; VRI, volume of the reference isodose.11; WB PTV, whole breast planning target volume.

N Mason et al.


patient’s SCF region would be elevated as a result andthe effect of contour flattening would be negated. It mayalso cause an increased bolus effect.

In the final weeks of treatment, this patient developeda Grade 3 skin reaction on the anterior upper chest dueto loss of skin sparing in the region of the Perspex plate.This caused pain during the set-up process and increasedthe time for positioning. Pain relief was prescribed andset-up integrity was maintained. Grade 2 dysphagiawas evident during the fifth week of treatment. All sideeffects resolved by 6 weeks post-treatment. A similarskin reaction in a subsequent prone patient wasobserved following treatment using the same fieldarrangement. To minimise this side effect, a third patientwas planned using an anterior oblique (gantry 210°) andposterior oblique (gantry 30°) field arrangement in theSCF + AX region. The RO accepted an increased dosecontribution posteriorly to reduce the anterior skin dose.No additional concerns have been identified.

Development of a fixable perforated carbon fibre insertwould provide tissue sparing, potentially reduce skinreaction seen in these patients and facilitate set-up index-ing. Visualisation would be compromised, however in theera of in-room imaging for patient positioning this is areasonable trade-off. Clinical investigation into the sever-ity of skin reactions, both acute and late, is warranted.

Conclusion

A simple addition of a Perspex plate to the prone posi-tioning device for breast cancer patients has enabledlarge pendulous breasted women with SCF + AX involve-ment to be treated prone. Equivalent dosimetric resultswere achieved in the SCF + AX PTV to the standardsupine technique. Our department continues to refinethis technique. It remains an option for large breastedwomen with SCF + AX node involvement as it offers thedosimetric benefits of WB radiation therapy that can onlybe achieved in the prone position.

Acknowledgements

The authors wish to acknowledge the support of thefollowing people in the undertaking of this case study:Lisa Roberts; Alison Jenkins and Jane Beukema.

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A prone technique for treatment of the breast, supraclavicular and axillary nodes

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