Accelerated Partial Breast Irradiation: Caution and Concern From an ASTRO Task Force

Alternatives to Standard Fractionation Radiation Therapy After Lumpectomy: Hypofractionated Whole-Breast Irradiation and Accelerated Partial-Breast Irradiation

Adjuvant whole-breast irradiation (WBI) after lumpectomy has been an established standard of care for decades. Standard-fractionation WBI delivered over 5 to 7 weeks can achieve durable tumor control with low toxicity but can be inconvenient for patients and cost ineffective. Hypofractionated WBI can be completed in 3 to 4 weeks and, based on long-term randomized data, is the preferred standard of care in select patients. Accelerated partial-breast irradiation can be delivered using even shorter treatment regimens. Although the available data on accelerated partial-breast irradiation is more limited, early results suggest it is an effective alternative to WBI in select patients.

Stromal-epithelial responses to fractionated radiotherapy in a breast cancer microenvironment

Background

The stromal-epithelial-cell interactions that are responsible for directing normal breast-tissue development and maintenance play a central role in the progression of breast cancer. In the present study, we continued our development of three-dimensional (3-D) cell co-cultures used to study cancerous mammary cell responses to fractionated radiotherapy. In particular, we focused on the role of the reactive stroma in determining the therapeutic ratio for post-surgical treatment.

Methods

Cancerous human mammary epithelial cells (MRC-7) were cultured in a 3-D collagen matrix with human fibroblasts (MRC-5) stimulated by various concentrations of transforming growth factor beta 1 (TGF-β1). These culture samples were designed to model the post-lumpectomy mammary stroma in the presence of residual cancer cells. We tracked over time the changes in medium stiffness, fibroblast-cell activation (MRC-5 converted to cancer activated fibroblasts (CAFs)), and proliferation of both cell types under a variety of fractionated radiotherapy protocols. Samples were exposed to 6 MV X-rays from a linear accelerator in daily fraction sizes of 90, 180 and 360 cGy over five days in a manner consistent with irradiation exposure during radiotherapy.

Results

We found in fractionation studies with MRC-5 fibroblasts and CAFs that higher doses per fraction may be more effective early on in deactivating cancer-harboring cellular environments. Higher-dose fraction schemes inhibit contractility in CAFs and prevent differentiation of fibroblasts, thereby metabolically uncoupling tumor cells from their surrounding stroma. However, higher dose fraction appears to increase ECM stiffening.

Conclusions

The findings suggest that dose escalation to the region with residual disease can deactivate the reactive stroma, thus minimizing the cancer promoting features of the cellular environment. Large-fraction irradiation may be used to sterilize residual tumor cells and inhibit activation of intracellular transduction pathways that are promoted during the post-surgical wound-healing period. The higher dose fractions may slow wound healing and increase ECM stiffening that could stimulate proliferation of surviving cancer cells.

Intraoperative radiotherapy as a protocol for the treatment of initial breast cancer

OBJECTIVE

To report on preliminary outcomes of single-dose intraoperative radiotherapy for early-stage breast cancer based on local recurrence rates and complications.

METHODS

Fifty postmenopausal women with <2.5cm breast tumors and clinically normal axillary lymph nodes were submitted to quadrantectomy, sentinel lymph node biopsy and intraoperative radiotherapy and studied. Mean follow-up time was 52.1 months.

RESULTS

Mean patient age was 65.5 years; mean tumor diameter was 1.41cm 82% of nodules were hormonal receptor positive and HER-2 negative. All patients received a 21 Gy radiation dose for a mean time of 8.97 minutes. Distant metastases were not observed. Local recurrence was documented in three cases, with identical histological diagnosis as the primary tumors. Thirty-five (70%) patients had local fibrosis, with gradual improvement and complete resolution over 18 months. Postoperative infection and seroma formation were not observed.

CONCLUSION

Partial radiotherapy is a potentially feasible and promising technique. Careful patient selection is recommended before a longer follow-up period has elapsed to confirm intraoperative radiotherapy safety and efficacy.

Investigation of variability in image acquisition and contouring during 3D ultrasound guidance for partial breast irradiation

Background

Three-dimensional ultrasound (3DUS) at simulation compared to 3DUS at treatment is an image guidance option for partial breast irradiation (PBI). This study assessed if user dependence in acquiring and contouring 3DUS (operator variability) contributed to variation in seroma shifts calculated for breast IGRT.

Methods

Eligible patients met breast criteria for current randomized PBI studies. 5 Operators participated in this study. For each patient, 3 operators were involved in scan acquisitions and 5 were involved in contouring. At CT simulation (CT1), a 3DUS (US1) was performed by a single radiation therapist (RT). 7 to 14 days after CT1 a second CT (CT2) and 3 sequential 3DUS scans (US2a,b,c) were acquired by each of 3 RTs. Seroma shifts, between US1 and US2 scans were calculated by comparing geometric centers of the seromas (centroids). Operator contouring variability was determined by comparing 5 RT’s contours for a single image set. Scanning variability was assessed by comparing shifts between multiple scans acquired at the same time point (US1-US2a,b,c). Shifts in seromas contoured on CT (CT1-CT2) were compared to US data.

Results

From an initial 28 patients, 15 had CT visible seromas, met PBI dosimetric constraints, had complete US data, and were analyzed. Operator variability contributed more to the overall variability in seroma localization than the variability associated with multiple scan acquisitions (95% confidence mean uncertainty of 6.2 mm vs. 1.1 mm). The mean standard deviation in seroma shift was user dependent and ranged from 1.7 to 2.9 mm. Mean seroma shifts from simulation to treatment were comparable to CT.

Conclusions

Variability in shifts due to different users acquiring and contouring 3DUS for PBI guidance were comparable to CT shifts. Substantial inter-observer effect needs to be considered during clinical implementation of 3DUS IGRT.

Stromal responses to fractionated radiotherapy

PURPOSE

Recently, several landmark randomized trials were published that justify the use of alternative fractionation schemes, e.g., hypofractionation, in adjuvant applications of whole-breast radiotherapy following breast-conserving surgery. We are studying effects of fractionated photon radiotherapy on stromal cell biology to understand how fractionation parameters influence the cellular microenvironment.

METHODS AND MATERIALS

Three-dimensional (3-D) collagen matrices, fibroblasts, and transforming growth factor beta 1 (TGF-β1) were combined to model microenvironmental components of mammary stroma. We explored the effects of fractionation schemes on collagen matrix stiffness and fibroblast activation using this culture model. Samples were exposed to 6 MV X-rays from a linear accelerator in daily fraction sizes of 90, 180 and 360 cGy over three days in a manner consistent with irradiation exposure during radiotherapy.

RESULTS

Fibroblast-cell activation and collagen sample stiffness both increased over time for all samples, but marked changes were noted when samples were irradiated and/or stimulated with growth factors in relation to the magnitude of the stimulus. We found a significant reduction in fibroblast proliferation and activation with fraction size but a modest and irreversible increase in matrix stiffness as the dose increased. Overall, larger fraction sizes reduced conditions leading to the formation of a reactive stroma.

CONCLUSION

There is a significant reduction in fibroblast activation and a modest increase in matrix stiffness with increasing fraction size over a 72-hour observation time in 3-D cultures modeling mammary stroma. However, expanded in vitro studies with more mammary components are needed to evaluate the net effects of stromal reactivity to radiotherapy. Our results suggest that the stromal cell microenvironment is an important consideration when optimizing fractionation schedules.

Partial breast irradiation techniques in early breast cancer

Whole breast irradiation represents an integral part of combined breast-conserving treatment of early breast cancer. A new concept includes replacing traditionally fractionated whole breast postoperative radiotherapy by accelerated partial breast irradiation. The latter involves a variety of techniques and may be applied intraoperatively or shortly after the surgery. The intraoperative techniques include photon or electron external beam irradiation and interstitial high dose rate (HDR) brachytherapy, whereas the postoperative techniques comprise interstitial brachytherapy, be it HDR, pulse dose rate (PDR) or low dose rate (LDR), intracavitary brachytherapy and external beam radiotherapy using electrons, photons or protons. This article presents accelerated partial breast irradiation techniques, ongoing phase III trials evaluating their value and recommendations for clinical practice.

Intraoperative radiotherapy as accelerated partial breast irradiation for early breast cancer : beware of one-stop shops?

Intraoperative radiotherapy (IORT) was originally introduced in breast cancer treatment as an "anticipated boost" during the procedure of breast conserving surgery (BCS). In addition to whole breast irradiation (WBI), it has yielded excellent long-term results [31, 38]. Under the assumption that the majority of in-breast tumor recurrences (IBTR) occur in the originally affected site, accelerated partial breast irradiation (APBI) as the sole treatment modality was initiated in several studies and with different techniques, one of which was IORT first with electrons, later also with conventional x-rays [29]. The question whether and for whom the gold standard of WBI may be replaced by APBI - especially IORT - alone has recently been one of the most controversial issues of adjuvant therapy for breast cancer. Two recently published studies by Veronesi et al. [36] and Vaidya et al. [35] presenting shortterm results of single shot IORT with electrons (ELIOT) and with an orthovoltage system (TARGIT), respectively, have further invigorated this discussion as illustrated by several letters to the editor commenting on the TARGIT study. While Vaidya et al. [35] indicate their results of IORT alone as "an alternative to WBI for selected patients" and one editorial even proclaims it as standard [6], all the authors of the respective letters [10, 16, 27, 33] strongly disagree with this conclusion. The present editorial comments on the two publications and, furthermore, provides respective statements of the breast cancer expert panel of the German Society of Radiation Oncology (DEGRO).

The influence of different IMRT techniques on the peripheral dose: a comparison between sMLM-IMRT and helical tomotherapy

PURPOSE

To investigate how segmented multileaf modulation-(sMLM-)based intensity-modulated radiotherapy (IMRT) and dynamic helical tomotherapy (ToTh) affect the peripheral dose (PD) outside the treated region.

MATERIAL AND METHODS

A cuboid Perspex phantom was scanned in a computed tomograph. Different artificial cases were contoured consisting of OARs surrounded by cylindrically shaped planning target volumes (PTVs) with different dimensions. Radiotherapy plans were generated with the sMLM system Konrad (Siemens) and with the ToTh planning system. The plans were optimized in such a way that the dose-volume histograms showed comparable results. The sMLM plans were applied with a linac Primus (Siemens OCS), the ToTh plans with the HiArt system (TomoTherapy); both with 6 MV. Measurements of PDs were performed along the longitudinal axis of the phantom outside the primary beam at different distances from the edge of the PTV (horizontal PD) and also at different depths at a fixed distance from the isocenter (vertical PD). Additional experiments to separate the scatter dose caused by the phantom were performed. This was realized by removing the part of the phantom lying in the primary beam, then applying the same plans like before.

RESULTS

All PD values were normalized to the median dose of the PTV. The PD values for the different PTVs decrease with decreasing PTV size. They also decrease with increasing distance from the isocenter. The horizontal values are in a range of 7% for the largest PTV (diameter = 15 cm) near the primary dose region to 0.2% for the smallest PTV (diameter = 5 cm) far from the primary dose region. The ToTh values are higher than the sMLM values by a maximal factor of 2 near the primary dose region. They become more similar with increasing distance from the edge of the PTV in longitudinal direction. The PD values are nearly equal at a distance of 25 cm from the edge of the PTV. The vertical PDs are higher for the ToTh at depths of > 1 cm but higher for sMLM close to the surface. By removing the scatter cube, the horizontal PD values at middle distances are reduced to one third of the PD values with scatter cube for ToTh (0.5%) and to one half for sMLM (0.8%). This means that without scatter cube the PD for ToTh is lower than that for sMLM. The measured PD values without scatter cube are in the same dimension as published data.

CONCLUSION

The increasing PDs and their trend with increasing PTV size can be explained by Compton scattering of photons from the irradiated volume toward the off-axis measuring points. The further increase of the PD in case of ToTh relative to sMLM is not easy to explain. Different presumptions are possible. The larger field length (in longitudinal direction) of the ToTh plans (consisting of the "real" field length and the overlap) relative to the sMLM plans could be one reason for the higher PD values. The softer energy spectrum of the HiArt machine with more sideward Compton scattering contributions could be another reason.

Adenocarcinoma of a neovagina constructed according to the Baldwin-Mori technique

The Authors describe a case of cancerization of a neovagina constructed according to the Baldwin-Mori technique, occurring 39 years after the initial operation. Description of the clinical case is followed by a number of anatomo-pathological considerations. The risk of cancerization and the adverse events associated with this type of neovagina militate against the use of autologous transplant operations in neovagina construction.