Mixed modality treatment planning of accelerated partial breast irradiation: to improve complex dosimetry cases

Abstract

BackgroundAlthough 3D-conformal accelerated partial breast irradiation (APBI) is widely used, several questions still remain such as what are the optimal treatment planning modalities. Indeed, some patients may have an unfavorable anatomy and/or inadequate dosimetric constraints could be fulfilled ("complex cases"). In such cases, we wondered which treatment planning modality could be applied to achieve 3D-conformal APBI (2 mini-tangents and an "en face" electron field or non-coplanar photon multiple fields; or a mixed technique combining non-coplanar photon multiple fields with an "en face" electron beam).MethodsFrom October 2007 to March 2010, 55 patients with pT1N0 breast cancer were enrolled in a phase II APBI trial. Among them, 7 patients were excluded as they were considered as "complex cases". A dosimetric comparison was performed according to the 3 APBI modalities mentioned above and assessed: planning treatment volume (PTV) coverage, PTV/whole breast ratio, lung and heart distance within irradiated field and exposure of organs at risk (OAR).ResultsAdequate PTV coverage was obtained with the 3 different treatment planning. Regarding OAR exposure, the "mixed technique" seemed to reduce the volume of non-target breast tissue in 4 cases compared to the other techniques (in only 1 case), with the mean V50% at 44.9% (range, 13.4 - 56.9%) for the mixed modality compared to 51.1% (range, 22.4 - 63.4%) and 51.8% (range, 23.1 - 59.5%) for the reference and non-coplanar techniques, respectively. The same trend was observed for heart exposure.ConclusionsThe mixed technique showed a promising trend of reducing the volume of non-target breast tissue and heart exposure doses in APBI "complex cases".

Individually selected teletherapy technique for accelerated partial breast irradiation

“…The dosimetry of IMRT and VMAT over the standard conformal technique has been analysed in several studies [12,[26][27][28][29][30][31]. The use of inverse treatment planning improved conformity and, in most cases, also the exposure of selected risk organs decreased.…”

“…Due to the rising number of patients needing APBI, and to eliminate the special infrastructural and expertise needs of brachytherapy, the implementation of conformal teletherapy methods, such as 3D-conformal radiation therapy (3D-CRT) with multiple static photon and/or electron fields, intensity-modulated RT (IMRT), volumetric-modulated arc therapy (VMAT), tomotherapy, robotic radiosurgery systems and proton beam therapy has begun emerging [8][9][10][11]. The utilization of a mixed technique combining photon with an 'en face' electron field may result in improved planning target volume (PTV) coverage and organ at risk (OAR) exposure [10][11][12][13][14]. IMRT optimizes dose distribution using structure-based planning and alterable intensity beam fluencies, providing improved dose homogeneity within the PTV, and reduced high dose exposure of normal tissues.…”

Partial breast radiotherapy with simple teletherapy techniques

“…In certain PBI cases, the dose distribution and OAR exposure may be optimized by the combination of photon and electron fields. [23][24][25] Only 1 contemporary study has reported the use of sole electron fields for PBI. 26,27 Altogether 40 patients with relatively small breasts received electron irradiation of a dose of 25 Â 2 Gy; this technique resulted in the lowest rate (17.5%) of fat necrosis of grade I to III, as compared with that in the brachytherapy and WBI arms.…”

Individualised radiotherapy serving reduced toxicity in breast and prostate cancer

“…The addition of electrons to photon beams provides more conformal but less homogenous dose distribution as compared to the photon only technique. We have found five studies dealing with the mixed beam technique in APBI [83,[90][91][92][93]. All agreed that this approach may lower the ipsilateral breast dose; lung and heart doses varied according to study, and obviously the situation of the tumour bed [92].…”

“…Many studies analysed the dosimetry of inverse-planning techniques over standard 3D-CRT [83][84][85][86][87][88]. The use of IMRT or VMAT improved conformity in all studies, and in most of them selected OARs' exposure as well.…”