Early Experience of Tomotherapy-based Intensity Article Early Experience of Tomotherapy-based Intensity-modulated Radiotherapy for Breast Cancer Treatment H. O’Donnell*, K

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  • Clinical Oncology (2009) 21: 294e301doi:10.1016/j.clon.2009.01.010

    Original Article

    Early Experience of Tomotherapy-based Intensity-modulatedRadiotherapy for Breast Cancer Treatment

    H. ODonnell*, K. Cookey, N. Walshy, P. N. Plowman*y*Department of Radiotherapy, St Bartholomews Hospital, London, UK; yDepartment of Radiotherapy,

    The Cromwell Hospital, London, UK

    ABSTRACT:Aims: New technology - specifically intensity-modulated radiotherapy (IMRT) - is now being applied to breastradiotherapy and a recent dosimetric analysis confirmed the advantages of IMRT over wedge-only plans. Suchapplication to everyday practice raises new issues and here we present the early experience of IMRT-based breastirradiation in a single centre.Materials and Methods: We present cases of breast cancer treated by Tomotherapy-based IMRT, where the perceivedadvantages of IMRT are considerable. Cases presented are bilateral disease, left breast irradiation, pectus excavatum,prominent contralateral prosthesis and internal mammary chain disease. We discuss the practicalities of such treatmentand the advantages over standard breast irradiation techniques.Results: Advantages include better conformity of treatment with lowering of dosages to underlying organs at risk, forexample ipsilateral lung and heart. There is improved coverage of the planning target volume, including regional nodes,without field junction problems. Planning, quality assurance and treatment delivery are more time consuming than forstandard breast irradiation and the low dose bath is increased.Conclusions: The standard radiotherapy tangential technique for breast/chest wall treatments has not significantlychanged over many decades, whereas across many other tumour sites there have been great advances in radiotherapytechnology. The dosimetric advantages of IMRT are readily apparent from our early experience. The wider spread of thelower dose zone (the low dose bath of radiation) is a potential concern regarding late oncogenesis and methods tominimise such risks should be considered. ODonnell, H. et al. (2009). Clinical Oncology 21, 294301

    2009 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.

    Key words: Breast radiotherapy, IMRT, tomotherapy

    Introduction

    Radiotherapy is an important part of treatment for manybreast cancer patients and it accounts for a substantialproportion of a radiotherapy departments workload d es-timated at 30e40% of most UK radiotherapy departmentsworkload by fractionation. Adjuvant breast radiotherapyleads to improved local control rates over breast-conserv-ing surgery alone [1]. Postoperative radiotherapy has alsobeen shown to be associated with increased survival d therecent appreciation of this 4e5% survival gain being animpetus to optimise locoregional control in this disease;this survival advantage also extends to node-positivepatients after total mastectomy [1]. The survival benefitis independent of systemic therapy and meta-analyses showthat an overall survival benefit is maintained even afterother deaths, unrelated to breast cancer, are taken intoaccount [1]. Studies within the last 10 years have showna survival advantage to node-positive patients receivingregional node radiotherapy in addition to adjuvant chemo-therapy; this has fuelled renewed interest in safe regional

    0936-6555/09/21029408 $36.00/0 2009 The Royal Col

    node radiotherapy, including the internal mammary nodechain [2].

    Radiotherapy planning and delivery continue to evolveacross most tumour sites. Standard tangential fieldsencompass the breast/chest wall with or without regionalnodes, whereas three-dimensional conformal radiotherapyenables one to encompass the target volume using fixed,shaped radiation beams of uniform intensity across the fieldor with modification by devices, such as wedges. Whetherassessed clinically or by computed tomography, the extentof glandular breast tissue can be difficult to localise andthere is documented interobserver variability in delinea-tion, most significantly for tumour bed boost radiotherapy[3]. The definition of the target becomes an ever moreimportant issue as the sophistication of conformationaltechnology increases and margins are reduced.

    Intensity-modulated radiotherapy (IMRT) uses inverseplanning and optimised non-uniform beam intensities withtreatment plans generated using computer algorithms. Assuch, IMRT techniques are significantly more complex thanthree-dimensional conformal radiotherapy and have the

    lege of Radiologists. Published by Elsevier Ltd. All rights reserved.

  • 295TOMOTHERAPY-BASED IMRT FOR BREAST CANCER

    potential to achieve superior dose homogeneity and normaltissue sparing, especially for targets and organs at risk (OAR)with complex shapes, such as the breast/chest wall [4].Tomotherapy is computed tomography-guided IMRT thatdelivers radiation helically, allowing precise delivery ofradiation while sparing the surrounding normal tissues. Theradiation source rotates around the patient and is modulatedby rapidly moving micro multileaf collimators, such that theradiation is delivered using multiple tiny beamlets, therebyoffering better conformity than standard LINAC-based IMRT,as illustrated by the cases described here.

    The use of helical tomotherapy, with the gantry rotatingaround the patient delivering radiation from any gantryangle, is not optimal for breast irradiation because whencompared with standard tangents, use of all gantry anglesresults in the delivery of low doses to areas in the body thatwould only receive a scatter dose during conventionalradiotherapy. The organs of particular concern being thecontralateral breast and lung. Topotherapy, which is notyet in clinical practice, uses the tomotherapy unit in fixedgantry positions with the beam intensity modulated by themicro collimators as the patient is moved through a station-ary gantry. The breast irradiation technique in use at theCromwell Hospital is a tomotherapy-based IMRT techniquedesigned to limit the low dose bath effect. The OAR areblocked so that beams do not enter through them in orderto irradiate the target, effectively creating a tangentialapproach. This technique uses a more limited number andangle of beams than standard helical tomotherapy.

    The introduction of such new techniques for breastradiotherapy raises new issues and here we illustrateexamples from our experience to date with tomotherapy-based IMRT. The cases presented demonstrate clinicalsituations that pose challenges to the clinician, dosimetristand physicist alike. They represent typical problems arisingin the context of breast irradiation and we discuss some ofthe practicalities, advantages and the potential pitfalls ofIMRT-based radiotherapy with reference to these cases. Weinclude examples of bilateral breast radiotherapy, regional

    Fig. 1 e Standard tangential radiotherapy treating different chest wall shaconventional tangents (shown in yellow).

    node irradiation (supraclavicular fossa and internal mam-mary node chain), radiotherapy after breast implantationand dose volume histogram (DVH) analyses for the OAR.

    Patients and Methods

    IMRT breast irradiation was carried out on a Hi-ArtTomotherapy (Wisconsin, USA) apparatus at The CromwellHospital, London. Patients presented here were selected asthey exemplified common difficulties experienced in breastirradiation and show the advantages of IMRT-based irradi-ation. All patients were positioned with both arms up ona MEDTEC wingboard with vacfix to immobilise the elbows.Patients were instructed on gentle breathing during (axial)scanning as per department protocol after performing anin-house study into variation with inhale/exhale techniqueson computed tomography. Each computed tomography dataset took about 1 min to acquire.

    Target Definition

    The aim of most radiotherapy treatments is to delivera homogenous dose. Most centres have or are moving towardsfull three-dimensional planning for breast irradiation.Patient factors such as breast size, chest wall shape andincline are considered when planning the gantry angles andcollimator rotations. Limiting factors are lung and cardiactissue, as measured at the time of the simulator image, andmedial and lateral borders are often compromised to reducethe extent of normal tissue irradiation. Nevertheless,tangential fields often encompass significant volumes oflung, cardiac and normal soft tissues and the amount ofvariation between patients can be large, as seen in Fig. 1.

    With adjuvant breast treatment, the breast tissue plus orminus locoregional lymph nodes is considered the clinicaltarget volume (CTV). This is a biological entity taking intoaccount risk of microscopic disease in the remaining breasttissue and in the draining lymph nodes and will vary

    pes showing the variation in the extent of normal tissue included by

  • 296 CLINICAL ONCOLOGY

    between patients. The planning target volume (PTV) isa geometric entity, and includes margins added to allow fororgan movement (inter-fraction and intra-fraction) and set-up error. Any potential advantages of three-dimensionalconformal radiotherapy or IMRT will diminish if the targetvolumes are not correctly identified and the precisedelineation of a target volume is critical whether for wholebreast, partial breast or concomitant boost radiotherapy.

    We carried out mapping of breast glandular tissue (CTV)as seen on the planning computed tomography scan. Toavoid interobserver variability in contouring, the sameclinician outlined all cases. Glandular tissue was visualisedon computed tomography with the following boundaries:anteriorly, 0.5 cm inside skin, posteriorly, to the chest wallto include clips or deep margins if appropriate, medially,0.5e1 cm to the ipsilateral midline to assist with contra-lateral breast sparing (not possible if medial