Customized Computed Tomography-Based Boost Volumes in Breast-Conserving Therapy: Use of Three-Dimensional Histologic Information for Clinical Target Volume Margins

Oncoplastic breast surgery - a pictorial classification system for surgeons and radiation oncologists (OPSURGE)

INTRODUCTION

Changes to the tumour bed following oncoplastic breast surgery complicate the administration of adjuvant radiotherapy. Consensus guidelines have called for improved interdisciplinary communication to aid adjuvant boost radiotherapy. We propose a framework of tumour bed classification following oncoplastic surgery to enhance understanding and communication between the multidisciplinary breast cancer team and facilitate effective and more precise delivery of adjuvant boost radiotherapy.

METHODS

A classification system was devised by grouping oncoplastic procedures based on skin incision, tissue mobilization, tumour bed distortion, seroma formation and flap reconstruction. The system is supplemented by a colour-coded pictorial guide to tumour bed rearrangement with common oncoplastic procedures.

RESULTS

A 5-tier framework was developed. Representative images were produced to describe tumour bed alterations.

CONCLUSION

The proposed framework (OPSURGE) improves the identification of the primary tumour bed after initial breast-conserving surgery, which is imperative to both the surgeon in planning re-excision and the radiation oncologist in planning boost radiotherapy.

A New Method for Partial Breast Reconstruction: 3-Year New Zealand Experience

In New Zealand, oncoplastic surgery is common, but partial breast reconstruction presents challenges for radiation therapy targeting. Tissue rearrangement creates ambiguity when targeting the tumor bed, with resultant overestimation of treatment volumes. Thus, adoption of advanced methods of radiation therapy have been hindered. This pilot study describes use of a novel three-dimensional implant that provides a scaffolding for tissue ingrowth during partial breast reconstruction and delineates the tumor bed more precisely to assist radiation planning and mammographic surveillance. After informed consent, 15 women were implanted with the three-dimensional bioabsorbable implant. The device was sutured to the tumor bed during lumpectomy, and tissue flaps were mobilized and attached to the implant. Visualization of the marker and radiation treatment volumes were recorded and compared. The implant provided volume replacement and helped to maintain breast contour. Cosmetic outcomes were excellent; no device- or radiation-related complications occurred. One patient had a postoperative hematoma that resolved after percutaneous drainage; there were no postoperative infections. Three-year follow-up shows no tumor recurrences and no untoward effects. When compared to conventional radiation targeting, use of the implant showed that a greater than 50 percent reduction in treatment volume was possible in some cases. Three-year mammograms show no significant artifact, normal tissue ingrowth, and minimal fibrosis. This study describes a method of oncoplastic breast reconstruction using an implantable device that marks the site of tumor excision and provides for volume replacement with tissue ingrowth. Patients tolerated it well, and radiation therapy planning, positioning, and treatment were facilitated.

Interobserver variability (between radiation oncologist and radiation therapist) in tumor bed contouring after breast-conserving surgery

PURPOSE

To examine interobserver variability between the radiation oncologist (RTO) and the radiation therapist (RTT) in delineating the tumor bed (TB) in early breast cancer (BC).

METHODS

We retrospectively analyzed patients who received a radiotherapy boost to the TB. In a first group, the clinical target volume (CTV) for the boost was the surgical bed, defined by using surgical clips. In a second group, the CTV was defined by identifying a seroma cavity or a metallic find on the scar. These contours were compared in terms of volume, number of slices, and Dice similarity coefficient (DSC).

RESULTS

Forty patients were assessed: 20 had surgical clips (group 1) while the other 20 had none (group 2). There was no difference in the number of slices contoured by the 2 operators for group 1, but a statistically significant difference emerged in the volumes: the RTT identified a TB that was a mean 45% smaller than the one identified by the RTO. Random differences were found between the 2 operators for group 2. The TBs delineated for this group were significantly larger (P<0.05) than those identified by the RTT for group 1. The mean Dice value between the RTO's and the RTT's TBs was 0.69±0.07 (range 0.53-0.81) for group 1 and 0.37±0.18 (range 0-0.58) for group 2 (P<0.05).

CONCLUSIONS

This study showed that the use of clips coincided with less interoperator variability. With appropriate training, the RTT may play an important part in the multidisciplinary radiotherapy team.

Impact of a Novel Bioabsorbable Implant on Radiation Treatment Planning for Breast Cancer

BACKGROUND

Techniques for accurately delineating the tumor bed after breast-conserving surgery (BCS) can be challenging. As a result, the accuracy, and efficiency of radiation treatment (RT) planning can be negatively impacted. Surgically placed clips or the post-surgical seroma are commonly used to determine target volume; however, these methods can lead to a high degree of uncertainty and variability. A novel 3-dimensional bioabsorbable marker was used during BCS and assessed for its impact on RT planning.

METHODS

One hundred and ten implants were sutured to the margins of the tumor bed excision site in 108 patients undergoing BCS. Routine CT imaging of the breast tissue was performed for RT planning, and the marker was assessed for visibility and utility in target delineation. RT regimens, target volumes and associated treatment costs were analyzed.

RESULTS

In all patients, the marker was easily visible and in 95.7 % of cases, it proved useful for RT planning. 36.8 % of patients received conventional whole breast irradiation plus boost, 56.6 % received hypo-fractionation plus boost, and 6.6 % received accelerated partial breast irradiation. A shift toward increased use of hypo-fractionated regimens was noted over the three year period of this study. There were no device-related complications or cancer recurrences in this group of patients.

CONCLUSIONS

This study demonstrated the use of a novel 3-dimensional marker as a safe and effective method for delineating the tumor bed with a significant utility for RT planning. With routine use of the device, an increased use of hypofractionation with a resultant 25 % cost savings was noted.

Boost delineation in breast radiation therapy: Isotropic versus anisotropic margin expansion

PURPOSE

The purpose of this article is to compare isotropic and anisotropic margin expansion with regard to the size of the clinical target volume boost (CTV_boost) and the interobserver variability (IOV).

METHODS AND MATERIALS

Lumpectomy cavities marked with 3 or more surgical clips were delineated by 6 radiation oncologists who specialized in breast radiation therapy. CTV_{boost anisotropic} was created by manually expanding the tumor bed with an anisotropic margin of 15 mm (20 mm in case of extensive intraductal component) minus the surgical free margins in 6 directions (anteroposterior, craniocaudal, and superoinferior). For the CTV_{boost isotropic}, the tumor bed was enlarged with an isotropic margin of 15 mm (20 mm in case of extensive intraductal component) minus the minimal surgical free margin. The volumes of the delineated CTV_boost (cm³) were measured. To assess the IOV, the Jaccard index (JI), defined as the intersection divided by the size of the union of the sample sets, was used (ideal value = 1). The JI was calculated for each case and each observer pair. Linear mixed models were used for all analyses.

RESULTS

A total of 444 delineated tumor beds were evaluated. The mean volume of the CTV_boost almost doubled by expanding the tumor bed with an isotropic margin compared with anisotropic margins (CTV_{boost isotropic} 94 mL [12.5-331.0] vs CTV_{boost anisotropic} 50 mL [3.2-332.7]; P = .0006). The IOV, assessed by the JI, significantly decreased by using isotropic versus anisotropic margin expansion (JI_{CTV boost isotropic} 0.73 [0.02-0.92] vs JI_{CTV boost anisotropic} 0.51 [0.0-0.8]; P< .0001). Because of the known positive correlation of the IOV and larger volumes, we corrected for CTV_boost volumes. With this correction, the difference in IOV remains highly significant (P < .0001) in favor of isotropic margin expansion.

CONCLUSIONS

The use of anisotropic margin expansion from tumorbed to CTV_{boost isotropic} significantly reduced the volume of the delineated CTV_boost with a factor of 1.9 compared with isotropic margin expansion, but it substantially increased the interobserver variability.

Comparison of two radiation techniques for the breast boost in patients undergoing neoadjuvant treatment for breast cancer

OBJECTIVE

After breast conservative surgery (BCS) and whole-breast radiotherapy (WBRT), the use of boost irradiation is recommended especially in patients at high risk. However, the standard technique and the definition of the boost volume have not been well defined.

METHODS

We retrospectively compared an anticipated pre-operative photon boost on the tumour, administered with low-dose fractionated radiotherapy, and neoadjuvant chemotherapy with two different sequential boost techniques, administered after BCS and standard adjuvant WBRT: (1) a standard photon beam (2) and an electron beam technique on the tumour bed of the same patients. The plans were analyzed for the dosimetric coverage of the CT-delineated irradiated volume. The minimal dose received by 95% of the target volume (D95), the minimal dose received by 90% of the target volume (D90) and geographic misses were evaluated.

RESULTS

15 patients were evaluated. The sequential photon and electron boost techniques resulted in inferior target volume coverage compared with the anticipated boost technique, with a median D95 of 96.3% (range 94.7-99.6%) and 0.8% (range 0-30%) and a median D90 of 99.1% (range 90.2-100%) and 54.7% (range 0-84.8%), respectively. We observed a geographic miss in 26.6% of sequential electron plans. The results of the anticipated boost technique were better: 99.4% (range 96.5-100%) and 97.1% (range 86.2-99%) for median D90 and median D95, respectively, and no geographic miss was observed. We observed a dose reduction to the heart, with left-sided breast irradiation, using the anticipated pre-operative boost technique, when analyzed for all dose-volume parameters. When compared with the sequential electron plans, the pre-operative photon technique showed a higher median ipsilateral lung Dmax.

CONCLUSION

Our data show that an anticipated pre-operative photon boost results in a better coverage with respect to the standard sequential boost while also saving the organs at risk and consequently fewer side effects.

ADVANCES IN KNOWLEDGE

This is the first dosimetric study that evaluated the association between an anticipated boost and neoadjuvant chemotherapy treatment.

Preoperative radiation therapy significantly increases patient eligibility for accelerated partial breast irradiation using 3D-conformal radiotherapy

INTRODUCTION

Three-dimensional-conformal radiation (3D-CRT) is the most common approach used in National Surgical Adjuvant Breast and Bowel Project (NSABP) B-39 for accelerated partial breast irradiation (APBI). Administration of APBI-3D-CRT in the preoperative (preop) setting has been shown to decrease the planning target volume. The impact of this decrease on patient eligibility for APBI has not been evaluated in a comparative manner.

MATERIALS AND METHODS

Forty patients with 41 previously treated breast cancers (≤4 cm) were analyzed. A spherical preop tumor volume was created using the largest reported radiographic dimension and centered within the contoured lumpectomy cavity. Plans were created and optimized using the preop tumor volume and postoperative lumpectomy cavity using NSABP B-39 guidelines. The primary end point was to evaluate for differences in patient eligibility and normal tissue exposure.

RESULTS

Thirty-five tumors (85%) in the preop versus 19 tumors (46%) in the postoperative setting were eligible for 3D-CRT-APBI using NSABP B-39 criteria (P=0.0002). The most common reason for ineligibility was due to >60% of the ipsilateral breast volume receiving 50% of the dose. Other reasons included dose to the contralateral breast, heart, and ipsilateral lung. Preop 3D-CRT-APBI was associated with statistically significant improvements in dose sparing to the heart, ipsilateral normal breast tissue, contralateral breast, chest wall, ipsilateral lung, and skin.

CONCLUSIONS

Dosimetrically, the use of preop radiation would increase patient eligibility for 3D-CRT-APBI and decrease dose to normal tissues, which will potentially decrease toxicity and improve cosmesis. These results provide the basis for a recently activated prospective study of preop 3D-CRT-APBI.

Target localisation for tumour bed radiotherapy in early breast cancer

INTRODUCTION

To compare clinical and CT techniques in localisation of the tumour bed in patients undergoing adjuvant breast radiotherapy for breast cancer.

METHODS

Patients were CT scanned in the treatment position following clinical delineation of the whole breast, surgical scar and boost volume. Computed tomography boost volumes were contoured in three dimensions. A definitive treatment plan was generated to encompass the CT-localised planning target volume (PTV) with ≥90% isodose using electrons. A hypothetical plan was also generated to cover the clinically determined boost field for comparison. The primary end point was the difference in PTV coverage by the 90% isodose between the plans based on clinically and CT localised boost volumes.

RESULTS

The plans for 50 patients were evaluated. The median percentage of PTV encompassed by the 90% isodose using the clinical and CT techniques was 29% (range 5-90%) and 83% (range 25-100%), respectively. PTV coverage by the 90% isodose using the clinical technique was at least 10% less than that using CT technique in 88% of patients (95% confidence interval 77-95%; P < 0.0001).

CONCLUSION

Tumour bed boost PTV coverage was insufficient using clinical determination as compared with CT localisation. This study supports CT planning for target volume localisation of the tumour bed boost in patients treated with breast-conserving therapy for breast cancer.

Current challenges in clinical target volume definition: tumour margins and microscopic extensions

Determination of optimal clinical target volume (CTV) margins around gross tumour volume (GTV) for modern radiotherapy techniques, requiring more precise target definitions, is controversial and complex. Tumour localisation has been greatly improved using molecular imaging integrated with conventional imaging techniques. However, the exact incidence and extent of microscopic disease, to be encompassed by CTV, cannot be visualised by any techniques developed to date and remain uncertain. As a result, the CTV is generally determined by clinicians based on their experience and patients' histopathological data. In this article we review histopathological studies addressing the extent of subclinical disease and its possible correlation with tumour characteristics in various tumour sites. The data have been tabulated to facilitate a comparison between proposed margins by different investigations and with current margins generally accepted for each tumour site. It is concluded that there is a need for further studies to reach a consensus on the optimal CTV pertaining to each tumour site.

Quality indicators for breast cancer: revisiting historical evidence in the context of technology changes

Radiation therapy for breast cancer has considerably changed over the years, from simple simulator-based 2-dimensional techniques to sophisticated image-guided individualized treatments, with maximally protected normal structures. This has led to a substantial improvement in the outcome of breast cancer patients in terms of disease control, survival, and quality of life. This progress is based on clinical research and paralleled by progress in delivering sophisticated radiation treatment. Clinical trials resulted in identifying patients groups who will benefit from radiation treatment. They also stimulated the development of quality assurance tools and guidelines, which are now applied in daily clinical practice. The new technical opportunities to optimize dose distributions in patients require dedicated quality assurance measures because they may be more sensitive to variations throughout the treatment. Still, a large source of variation and uncertainty in radiation therapy remains in the definition of target volumes, which is clinically significant in terms of dosimetric target coverage as well as exposure of healthy tissues. This striving for continuous improvement of patient selection and treatment will lead to further improvement of local control while at the same time improving functional and cosmetic outcome and avoiding severe late complications, including cardiac toxicity.

Reducing interobserver variation of boost-CTV delineation in breast conserving radiation therapy using a pre-operative CT and delineation guidelines

AIMS

To investigate whether using a pre-operative CT scan (Preop-CT) (1) decreases interobserver variation of boost-CTV delineation in breast conserving therapy (BCT), and (2) influences the size of the delineated volumes.

PATIENTS AND METHODS

Thirty cT1-2N0-1 breast cancer patients underwent a CT-scan in radiation treatment position, prior to and after lumpectomy. Five observers delineated a boost-CTV, both with and without access to the Preop-CT. For each patient and for each observer pair, the conformity index (CI) and the distance between the centres of mass (COMd) for both boost volumes were calculated. In addition, all delineated volumes including the standard deviation (SD) with respect to the median delineation were calculated.

RESULTS

Using a Preop-CT reduced the mean COMd of the boost-CTV from 1.1cm to 1.0 cm (p<0.001). No effect was seen on the CI, but the boost-CTV volume reduced from 42 cc to 36 cc (p=0.005), implying a reduction of interobserver variation. We saw no significant change in the SD.

CONCLUSION

Use of a Preop-CT in BCT results in a modest but statistically significant reduction in interobserver variation of the boost-CTV delineations and in a significant reduction in the boost-CTV volume.

Excised and irradiated volumes in relation to the tumor size in breast-conserving therapy

In early-stage breast cancer and DCIS patients, breast-conserving therapy is today's standard of care. The purpose of this study was to evaluate the relation between the microscopic tumor diameter (mTD), the excised specimen (ES) volume, and the irradiated postoperative complex (POC) volume, in patients treated with breast-conserving therapy. In 186 patients with pTis-2N0 breast cancer, the mTDs, ES, and POC volumes (as delineated on the radiotherapy-planning CT scan), were retrospectively determined. Linear regression analysis was performed to study the association between the mTD, and the ES and POC volumes. The explained variance (r (2)) was calculated to establish the proportion of variation in the outcome variable that could be explained by the determinant (P ≤ 0.05). Moreover, the influence of tumor characteristics, age, surgical procedures, and breast size was studied. Median mTD was 1.2 cm (range 0.1-3.6 cm), median ES volume was 60 cm(3) (range 6-230 cm(3)) and median POC volume was 15 cm(3) (range 0.5-374 cm(3)). The POC was not clearly visible on the majority of the CT scans, based on a median assigned cavity visualization score of 3 (range 1-5). The explained variance for the mTD on the ES volume was low (r(2) = 0.08, P < 0.001). A slightly stronger association was observed in palpable tumors (r(2) = 0.23, P < 0.001) and invasive lobular carcinomas (r(2) = 0.39, P = 0.01). Furthermore, weak associations were observed between POC volume and mTD (r(2) = 0.04, P = 0.01), and POC and ES volume (r(2) = 0.23, P < 0.001). A weak association was observed between breast volume and ES volume (r(2) = 0.27, P < 0.001). In conclusion, both the excised and the irradiated POC volumes did not show a clinically relevant association with the mTD in women with early-stage breast cancer treated with breast-conserving therapy. Future studies should focus on improvement of surgical localization, development of image-guided, minimally invasive operation techniques, and more accurate image-guided target volume delineation in radiotherapy.

How does knowledge of three-dimensional excision margins following breast conservation surgery impact upon clinical target volume definition for partial-breast radiotherapy?

BACKGROUND AND PURPOSE

To compare partial-breast clinical target volumes generated using a standard 15 mm margin (CTV(standard)) with those generated using three-dimensional surgical excision margins (CTV(tailored 30)) in women who have undergone wide local excision (WLE) for breast cancer.

MATERIAL AND METHODS

Thirty-five women underwent WLE with placement of clips in the anterior, deep and coronal excision cavity walls. Distances from tumour to each of six margins were measured microscopically. Tumour bed was defined on kV-CT images using clips. CTV(standard) was generated by adding a uniform three-dimensional 15 mm margin, and CTV(tailored 30) was generated by adding 30 mm minus the excision margin in three-dimensions. Concordance between CTV(standard) and CTV(tailored 30) was quantified using conformity (CoI), geographical-miss (GMI) and normal-tissue (NTI) indices. An external-beam partial-breast irradiation (PBI) plan was generated to cover 95% of CTV(standard) with the 95% isodose. Percentage-volume coverage of CTV(tailored 30) by the 95% isodose was measured.

RESULTS

Median (range) coronal, superficial and deep excision margins were 15.0 (0.5-76.0)mm, 4.0 (0.0-60.0)mm and 4.0 (0.5-35.0)mm, respectively. Median CoI, GMI and NTI were 0.62, 0.16 and 0.20, respectively. Median coverage of CTV(tailored 30) by the PBI-plan was 97.7% (range 84.9-100.0%). CTV(tailored 30) was inadequately covered by the 95% isodose in 4/29 cases. In three cases, the excision margin in the direction of inadequate coverage was <or=2mm.

CONCLUSIONS

CTVs based on 3D excision margin data are discordant with those defined using a standard uniform 15 mm TB-CTV margin. In women with narrow excision margins, the standard TB-CTV margin could result in a geographical miss. Therefore, wider TB-CTV margins should be considered where re-excision does not occur.