Is there a preferred IMRT technique for left-breast irradiation?

Marloes Jeulink,Philip Meijnen,Wilko F.A.R. Verbakel,Max Dahele,Ben J. Slotman

doi:10.1120/jacmp.v16i3.5266

Marloes Jeulink, Philip Meijnen + Show 3 more

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https://doi.org/10.1120/jacmp.v16i3.5266

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Abstract

Not all clinics have breath‐hold radiotherapy available for left‐breast irradiation. However intensity‐modulated radiotherapy (IMRT) has also been advocated as a means of lowering heart doses. There is currently no large‐scale, long‐term follow‐up data after breast IMRT and, since dose distributions may differ from classic tangent‐based radiotherapy, caution is needed to avoid unexpected worsening of the late toxicity profile. We compared four IMRT techniques for free‐breathing left‐breast irradiation. Consistent with the aforementioned concerns, our goal in planning was to prioritize organ at risk (OAR) sparing in a way that mimicked tangent‐based radiotherapy. Ten simultaneous integrated boost treatment plans (PTVelective=15×2.67 Gy;PTVboost=15×3.35 Gy) were created using 1) hybrid‐IMRT (H‐IMRT), 2) full IMRT (F‐IMRT), and 3) volumetric‐modulated arc therapy with two partial arcs (2ARC) and 4) six partial arcs (6ARC). Reduction in OAR mean and low dose was prioritized. End‐points included OAR sparing (e.g., heart, left anterior descending artery [LAD+3 mm], lungs, and contralateral breast) and PTV coverage/dose homogeneity. Under these conditions we found the following: 1) H‐IMRT provided the best mean and low dose OAR sparing, PTVelective coverage (mean V95%=98%),PTVboost coverage (V95%=98%), and PTV homogeneity. However, it delivered most intermediate–high dose to the heart, LAD+3 mm and ipsilateral lung; 2) 6ARC had the best intermediate–high dose sparing, followed by F‐IMRT, but this was at the expense of more dose in the contralateral lung and breast and worse PTV coverage (PTVelective mean V95%=96%/97% and PTVboost mean V95%=91%/96% for 6ARC/F‐IMRT). When trying to spare mean and low dose to OARs, the preferred IMRT technique for left‐breast irradiation without breath‐hold was H‐IMRT. This is currently the standard solution in our institution for left‐breast radiotherapy under free‐breathing and breath‐hold conditions.PACS numbers: 87.53kn, 87.53Jw, 87.55.D‐, 87.55.de, 87.55.dk

Highlights

Cardiac toxicity has been a major concern in left-breast irradiation.[1,2] The use of physical techniques such as voluntary deep inspiration breath-hold (DIBH) to displace the target volume away from the heart have found favor as a means of protecting the heart.[3]. It is clear, that for various reasons such techniques are not universally available.[4,5] In this context, a number of authors have shown that using intensity-modulated radiotherapy (IMRT) can reduce heart doses.[6,7] there are some uncertainties around the use of full IMRT
For example: 1) it is generally associated with a larger volume of low dose spread to healthy tissue which has led to concerns about increased risk of second cancers;(8) 2) a linear correlation between heart toxicity and estimated mean dose has been reported,(2) but this does not answer the question of whether a little high dose to the heart is better or not than more low dose; and 3) classic tangential breast radiotherapy techniques are characterized by sparing of the nontreated breast and contralateral lung and deliver a variable volume of high-dose radiation to the heart and ipsilateral lung
H-IMRT and Full IMRT (F-IMRT) achieved PTVelective and PTVboost coverage of V95% > 95%. 2ARC was associated with considerably lower PTVelective coverage than other techniques, its PTVboost coverage was comparable to 6ARC

Summary

Introduction

Cardiac toxicity has been a major concern in left-breast irradiation.[1,2] The use of physical techniques such as voluntary deep inspiration breath-hold (DIBH) to displace the target volume (breast) away from the heart have found favor as a means of protecting the heart.[3]. For example: 1) it is generally associated with a larger volume of low dose spread to healthy tissue which has led to concerns about increased risk of second cancers;(8) 2) a linear correlation between heart toxicity and estimated mean dose has been reported,(2) but this does not answer the question of whether a little high dose to the heart (e.g., with tangential radiotherapy) is better or not than more low dose (e.g., with IMRT); and 3) classic tangential breast radiotherapy techniques are characterized by sparing of the nontreated breast and contralateral lung and deliver a variable volume of high-dose radiation to the heart and ipsilateral lung. Our aim was to take the typical dose distribution of the classic tangent-based field arrangement as a benchmark and to compare dosimetric characteristics of four previously described IMRT techniques under conditions of free-breathing, left-breast irradiation using a simultaneous integrated boost technique (SIB).(6,7,11-15) Our primary goal was to investigate their suitability for treatments that stress a reduction in mean and low doses to the heart, lungs, and contralateral breast. Of note is that this general strategy is in line with the recent RTOG 1005 protocol for whole-breast and SIB irradiation.[16]

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