Multi-axis dose accumulation of noninvasive image-guided breast brachytherapy through biomechanical modeling of tissue deformation using the finite element method

Phase II Trial of Five-Fraction Accelerated Partial Breast Irradiation Using Noninvasive Image-Guided Breast Brachytherapy

PURPOSE/OBJECTIVE(S)

NIBB has potential advantages over other APBI techniques by delivering highly conformal radiation with minimal collateral dose to the heart and lung compared with external beam techniques, but unlike other brachytherapy techniques NIBB is non-invasive. Previous data has shown encouraging outcomes using a 10-fraction regimen. To improve efficiency, convenience, and cost, reduction in the fraction number is desirable. Final results of a prospective phase II trial are reported.

MATERIALS/METHODS

NIBB APBI was delivered using 28.5Gy in 5 fractions daily over 1 week. Patient eligibility criteria required: invasive carcinoma ≤2.0 cm or DCIS ≤3.0 cm, ER positive (if invasive), lymph node negative, LVI absent, and lumpectomy with margins negative by 2mm. The primary endpoint was grade ≥ 2 subcutaneous fibrosis/induration <30%. Secondary endpoints included any late toxicity, cosmetic outcome, and local control.

RESULTS

40 patients were treated with a median follow-up of 59.7 months. The mean age was 67 years (50-89 years) and tumor size was 1.0cm (0.3-2.0cm). 80% had invasive carcinoma. The mean breast separation with compression was 6.7cm (3.5-8.9cm). The 5-year actuarial local control was 96.6% and overall survival was 96.9%. Grade 2 and 3 late toxicities were 15% and 0%, respectively. The rate of grade 2 subcutaneous fibrosis/induration was 2.5% (+/-2.5%) meeting the study's primary endpoint. The most common late toxicity of any grade was skin telangiectasia; 22.5% grade 1 and 15% grade 2. Only breast separation was associated with telangiectasia risk, p=0.002. Overall cosmetic outcome was excellent, good, and fair/poor in 75%, 25%, and 0%, respectively.

CONCLUSIONS

NIBB APBI delivered in 5 fractions results in a low rate of late toxicity and a high rate of good/excellent cosmetic outcomes. Telangiectasia risk can be minimized by keeping breast separation ≤7.0cm. The local failure rate was appropriately low. Further investigation of this technique is warranted.

Multi-institutional registry study evaluating the feasibility and toxicity of accelerated partial breast irradiation using noninvasive image-guided breast brachytherapy

PURPOSE

The noninvasive image-guided breast brachytherapy (NIBB) technique is a novel noninvasive yet targeted method for accelerated partial breast irradiation. We established a multi-institutional registry to evaluate the toxicity and efficacy of this technique across various practice settings.

METHODS AND MATERIALS

Institutions using the NIBB technique were invited to participate. Data for acute/late toxicity, cosmetic outcome, and tumor recurrence were collected. Toxicity and cosmetic outcome were graded based on the Common Terminology Criteria for Adverse Events version 3.0 and NRG/Radiation Therapy Oncology Group scale, respectively. Treatment variables were analyzed for association with outcomes.

RESULTS

A total of 252 patients from eight institutions were analyzed. The median age was 69 years. The mean tumor size was 1.1 cm (0.1-4.0 cm). Treatment was delivered 10 fractions (34-36 Gy) in 75% and five fractions (28.5 Gy) in 22%. B.i.d. fractionation was used in 9%. Acute radiation dermatitis was Grade 0-1, 2, and 3 in 77%, 19%, and 4%, respectively. One hundred ninety-one patients with a median followup of 18 months (4-72 months) were evaluable for late outcomes. Late toxicity Grades 2 and 3 were observed in 8.8% and 1%, respectively. Cosmetic outcome was excellent, good, and fair/poor in 62%, 36%, and 2%, respectively. B.i.d. fractionation was associated with higher acute and late toxicity. Second-generation applicators were associated with lower late toxicity and better cosmetic outcome. Actuarial freedom from ipsilateral breast tumor recurrence and true recurrence were 98.3% and 98.3% at 2 years and 90.9% and 95.4% at 5 years, respectively.

CONCLUSIONS

Accelerated partial breast irradiation using NIBB was well tolerated with a low rate of acute and late toxicity across various practice settings. Ipsilateral breast tumor recurrence and cosmetic outcomes were favorable. b.i.d. fractionation was associated with higher toxicity. Longer followup is needed to confirm late endpoints.

Phase 2 Trial of Accelerated Partial Breast Irradiation (APBI) Using Noninvasive Image Guided Breast Brachytherapy (NIBB)

PURPOSE

Noninvasive image guided breast brachytherapy (NIBB) is a novel approach to delivery of accelerated partial breast irradiation (APBI) that may hold advantages over established techniques. NIBB is not invasive but maintains a high level of precision by using breast immobilization via breast compression and image guidance; it therefore does not require large planning tumor volume margins. We present the primary outcomes of this prospective phase 2 study (BrUOG Br-251).

METHODS AND MATERIALS

Eligible patients with early-stage breast cancer underwent NIBB APBI using a dose 34 Gy in 10 fractions delivered daily or twice a day. Treatment was delivered using an Ir-192 high-dose-rate source via specialized applicators. Two orthogonal treatment axes were used for each fraction. The primary endpoints were late toxicity and cosmesis assessed at 2 and 5 years. Toxicity was assessed using the National Cancer Institute Common Terminology Criteria for Adverse Events v3.0. Cosmesis was assessed using the NRG/Radiation Therapy Oncology Group scale. Ipsilateral breast tumor recurrence was defined as any recurrence or new primary in the treated breast.

RESULTS

Forty patients underwent protocol treatment. Median patient age was 68 years (50-92 years). Mean tumor size was 1.1 cm (0.3-3.0 cm). Among the cohort, 62.5% had invasive carcinoma and 37.5% had ductal carcinoma in situ. Thirty-nine percent elected to receive hormone therapy. No grade ≥3 late toxicities were observed at any time point. Grade 2 toxicity was 5% and 10% at 2 and 5 years, respectively. Telangiectasia grade 1 and 2 occurred in 27.5% and 5%, respectively. Breast separation of >7 cm was associated with telangiectasia (P < .01). The rate of good to excellent cosmetic outcome was 95% at 2 years and 100% at 5 years. With a median follow-up of 68 months, the actuarial 5-year freedom from ipsilateral breast tumor recurrence was 93.3% (±4.8%), and overall survival was 93.7% (±4.4%).

CONCLUSIONS

NIBB to deliver APBI is well tolerated with a low incidence of significant late toxicity and has favorable cosmetic outcomes. Continued evaluation of the NIBB APBI technique in a larger cohort is warranted.

Evaluation of impact of an external breast shield (FlexiShield) in electronic brachytherapy for breast IORT: A phantom study

PURPOSE

To investigate Axxent (iCAD, Inc., San Jose, CA) electronic brachytherapy balloon deformation and its dosimetric impact because of an external flexible shield (FlexiShield [FS]; iCAD, Inc.).

METHODS AND MATERIALS

Prostheses breast tissue phantom overlaid three spherical balloon applicators to simulate three clinical scenarios depending on minimum skin-to-balloon surface spacing (SS): balloon with SS of 2 cm, 1 cm, and balloon with 1 cm SS and touching the chest wall. Two sets of megavoltage CT (MVCT) scans were obtained with or without FS for 15 different sizes of balloons. For 45 pairs of MVCT scans, balloon deformation was measured in superior-inferior (d_SI) dimension on coronal and sagittal planes and anterior-posterior (d_AP) and lateral (d_LAT) dimensions on the equatorial plane of balloon. SS was also compared. A treatment plan was made on each MVCT scan. Doses at four balloon surface points and skin were compared. Conformity index value was also compared to evaluate three-dimensional dose distribution. Clinically, 20 Gy was prescribed to the surface of balloon.

RESULTS

Balloon deformation was observed with compression in SI and AP dimensions and expansion in lateral dimension. Average SI compression was 0.5 mm. Average d_Lat - d_AP was 2.4 mm, which resulted in elevated point doses at AP dimension by 10.8% of prescribed dose and reduced point doses at lateral dimension by 4.6%. FS decreased SS by 1.8 mm, increasing skin dose by 1.2 Gy, on average. Conformity index value was decreased from 0.922 to 0.908, on average.

CONCLUSIONS

This phantom study demonstrates that use of skin shielding during breast intraoperative radiation therapy can cause balloon deformation and SS reduction, resulting in dosimetric changes that are disregarded in current practice.

Evaluation of BEBIG HDR (60)Co system for non-invasive image-guided breast brachytherapy

Purpose

HDR ⁶⁰Co system has recently been developed and utilized for brachytherapy in many countries outside of the U.S. as an alternative to ¹⁹²Ir. In addition, the AccuBoost^® technique has been demonstrated to be a successful non-invasive image-guided breast brachytherapy treatment option. The goal of this project is to evaluate the possibility of utilizing the BEBIG HDR ⁶⁰Co system for AccuBoost treatment. These evaluations are performed with Monte Carlo (MC) simulation technique.

Material and methods

In this project, the MC calculated dose distributions from HDR ⁶⁰Co for various breast sizes have been compared with the simulated data using an HDR ¹⁹²Ir source. These calculations were performed using the MCNP5 code. The initial calculations were made with the same applicator dimensions as the ones used with the HDR ¹⁹²Ir system (referred here after as standard applicator). The activity of the ⁶⁰Co source was selected such that the dose at the center of the breast would be the same as the values from the ¹⁹²Ir source. Then, the applicator wall-thickness for the HDR ⁶⁰Co system was increased to diminish skin dose to levels received when using the HDR ¹⁹²Ir system. With this geometry, dose values to the chest wall and the skin were evaluated. Finally, the impact of a conical attenuator with the modified applicator for the HDR ⁶⁰Co system was analyzed.

Results

These investigations demonstrated that loading the ⁶⁰Co sources inside the thick-walled applicators created similar dose distributions to those of the ¹⁹²Ir source in the standard applicators. However, dose to the chest wall and breast skin with ⁶⁰Co source was reduced using the thick-walled applicators relative to the standard applicators. The applicators with conical attenuator reduced the skin dose for both source types.

Conclusions

The AccuBoost treatment can be performed with the ⁶⁰Co source and thick-wall applicators instead of ¹⁹²Ir with standard applicators.