A comparison of brachytherapy techniques for partial breast irradiation

Interstitial multi-catheter breast brachytherapy: Technical aspects and experience feedback in a comprehensive cancer center

PURPOSE

To focus on technical aspects of the implementation of interstitial high dose rate brachytherapy, with a step-by-step approach.

MATERIALS AND METHODS

Patients were selected during multidisciplinary tumor boards, according to inclusion criteria adapted from GEC-ESTRO guidelines. A CT scan was performed a few days before implantation. On pre-implant CT, using surgical scar and clips, surgical and pathological reports, and preoperative images, we delineated the tumor bed to be included in the Clinical Target Volume (CTV), according to GEC ESTRO Recommendations. A 3D virtual implant simulation of the best catheter positions was performed in order to cover the target volume. Implantation was then carried out under local anaesthetic using 3D projections of the catheter inlets and outlets. Dosimetry was performed on post-implantation CT scan. A dose of 34Gy was delivered in 10 fractions. Acute and late side effects, and local control were evaluated 2 and 8 months after treatment.

RESULTS

Between July 2017 and January 2020, 20 patients were treated with accelerated partial breast irradiation. Dose constraints regarding target volume coverage, overdose, dose homogeneity, conformation index and organs at risk were met in 94.7%, 100%, 63.2%, 0% and 89.5% of the treatment plans, respectively. Grade 1-2 acute adverse events were observed in 21% of patients, with no grade 3-4 events.

CONCLUSION

The first dosimetric results and early clinical tolerance and efficacy achieved by the implementation of breast interstitial multicatheter brachytherapy in routine clinical practice are very encouraging, and confirm the interest of extending this practice.

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.

A reliable skin toxicity predictor in permanent breast seed implant brachytherapy

PURPOSE

To establish skin dose-outcome relationships using a reliable metric in permanent breast seed implant (PBSI).

METHODS

Sixty-seven consecutive patients who underwent PBSI at our institution were included. Skin doses were calculated using two skin dose indices: maximum point dose to the skin surface, D_max, and D_0.2cc for a 2-mm internal skin rind (a surrogate to the dose to 1 cm² area of skin) from CT-based postoperative treatment plans. Toxicity data were extracted from patients' charts and photographs. The associations between skin dose and skin toxicity were investigated using the analysis of variance, and the predictive performance of skin dose measures was evaluated using receiver operating characteristic curves.

RESULTS

For acute reactions, 49.3% of patients had Grade 1, 4.5% Grade 2, and 1.5% Grade 3 toxicity. For telangiectasia at 3 years, very minor and minimally apparent telangiectasia was observed in 25% of patients. Moderate but asymptomatic telangiectasia was observed in 9.1% of cases. Both metrics were significantly associated with the occurrence of acute toxicity and telangiectasia at 3 years (p < 0.01). The predictive values for D_max and D_0.2cc were 0.779 and 0.763, respectively, (p < 0.0001) for acute skin toxicity and 0.786 and 0.810 for telangiectasia (p < 0.0002). Extreme dose outliers (up to 878 Gy) and a high variability were observed for D_max but not for D_0.2cc, illustrating the superior reliability of D_0.2cc.

CONCLUSION

D_0.2cc, as an alternate skin dose measure to D_max, is a robust metric for measuring skin dose that is simple to calculate, yet is clinically relevant and not prone to inaccuracies inherent to point dose measurement.

Defining dose constraints for catheter insertion sites to minimize toxicity after interstitial breast brachytherapy

PURPOSE

The purpose of this study was to define dose constraints for catheter insertion sites to minimize probability of prominent post-therapy skin marks after interstitial breast brachytherapy.

METHODS AND MATERIALS

Forty patients who had undergone interstitial breast brachytherapy were studied at followup at least 2 years after the procedure. Their implant marks were compared with background skin and areola and scored as Gr0 = invisible (same color as surrounding skin), Gr1 = darker than surrounding skin but lighter than areola or hypopigmentation, and Gr2 = same color as areola or darker. Highest point doses received in each plane of implant and their corresponding closest distances from clinical target volume, 85% isodose, and closest catheter dwell point were used for analysis. A logistic regression was performed to ascertain effects of various dosimetric parameters on the probability of Gr2 marks. Receiver operating characteristic curve was generated to derive cutoffs.

RESULTS

A total of 280 dose points were studied. Median values for various parameters were 1.4 Gy (0.24-3.74) for Dose max and 1.6 cm, 1.5 cm, and 1.0 cm for Dist CTV min, Dist Iso min, and Dist Dwell min, respectively. On logistic regression, increasing Dose max alone was associated with an increased likelihood of developing Gr2 marks. Each unit increase of Dose max increased probability of development of Gr2 skin marks by 5.0% (2.391-10.328). Receiver operating characteristic analysis also showed greatest odd ratio (8.0), sensitivity (74.8%), and specificity (73%) for Dose max.

CONCLUSIONS

It seems prudent to restrict dose to catheter insertion sites for better cosmesis.

High-dose-rate Brachytherapy as Adjuvant Local rEirradiation for Salvage Treatment of Recurrent breAst cancer (BALESTRA): a retrospective mono-institutional study

PURPOSE

To evaluate clinical results of catheter-based interstitial high-dose-rate (HDR) brachytherapy (BT) as adjuvant treatment in previously irradiated recurrent breast cancer.

MATERIAL AND METHODS

Between January 2011 and September 2015, 31 consecutive patients with histologically confirmed recurrent breast cancer after conservative surgery and conventional whole breast radiotherapy, were retreated with a second conservative surgical resection and reirradiated with adjuvant interstitial HDR-BT. None of the brachytherapy implant was performed during the quadrantectomy procedure. A dose of 34 Gy in 10 fractions, 2 fractions per day, with a minimal interval of 6 hours was delivered.

RESULTS

At the time of the implant, the median age of patients was 59.7 years (range, 39.3-74.9 years). The median time from first treatment until BT for local recurrence was 11.9 years (range, 2.5-27.8 years). The median interval between salvage surgery and BT was 3.6 months (range, 1-8.2 months). No acute epidermitis or soft tissue side effects higher than grade 2 were recorded, with good cosmetic results in all patients. Most of the patients presented grade 1-2 late side effects. Only one patient developed grade 3 liponecrosis. After a median follow-up of 73.7 months (range, 28.8-102.4 months), the overall survival and cancer specific survival were 87.1% and 90.3%, respectively; 5-year local control and 5-year progression-free survival rate were 90.3% and 83.9%, respectively.

CONCLUSIONS

Our preliminary analysis showed that HDR-BT is a feasible treatment for partial breast reirradiation offering very low complications rate and fast procedure. Higher patients' cohort is warranted in order to define the role of this treatment modality in the breast conservative management of local recurrence.

Dual-Receptor-Targeted (DRT) Radiation Nanomedicine Labeled with 177Lu Is More Potent for Killing Human Breast Cancer Cells That Coexpress HER2 and EGFR Than Single-Receptor-Targeted (SRT) Radiation Nanomedicines

Resistance to HER2-targeted therapies in breast cancer (BC) is associated in some cases with an increased expression of epidermal growth factor receptors (EGFR). We describe a dual-receptor-targeted (DRT) radiation nanomedicine for local intratumoral (i.t.) treatment of BC composed of 15 nm sized gold nanoparticles (AuNPs) modified with trastuzumab (TmAb) to target HER2 and panitumumab (PmAb) to target EGFR. The AuNPs were modified with poly(ethylene glycol) (PEG_3k) linked to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelators to complex the β-particle emitter, ¹⁷⁷Lu. Our aim was to compare the properties of these DRT-AuNP-¹⁷⁷Lu with single-receptor-targeted (SRT)-TmAb-AuNP-¹⁷⁷Lu or PmAb-AuNP-¹⁷⁷Lu or nontargeted (NT)-AuNP-¹⁷⁷Lu using human BC cells that expressed HER2, EGFR, or both receptors. To construct these radiation nanomedicines, PEG_5K was linked to TmAb or PmAb, while PEG_3k was linked to DOTA. These polymers were conjugated to AuNP via two Au-thiol bonds using a terminal lipoic acid (LA) group on the polymers. NT-AuNP-¹⁷⁷Lu were constructed without modification with TmAb or PmAb. MDA-MB-231-H2N, MDA-MB-468, and BT-474 human BC cells were designated as HER2^mod/EGFR^mod, EGFR^high/HER2^neg, and HER2^high/EGFR^low, respectively, based on the expression of these receptors. Specific binding to HER2 and/or EGFR was assessed by incubating BC cells with DRT-AuNP-¹⁷⁷Lu or TmAb-AuNP-¹⁷⁷Lu or PmAb-AuNP-¹⁷⁷Lu, or NT-AuNP-¹⁷⁷Lu in the absence or presence of an excess of TmAb or PmAb or both competitors. Binding and internalization of AuNP by BC cells were assessed by dark-field microscopy. Cell fractionation studies were conducted to quantify AuNP-¹⁷⁷Lu bound and internalized. The cytotoxicity of DRT-AuNP-¹⁷⁷Lu was determined in clonogenic survival (CS) assays after an exposure of 5 × 10⁵ BC cells to 3 MBq (1.4 × 10¹² AuNP) for 16 h and then seeding and culturing the cells for 7-15 days. CS was compared to exposure to TmAb-AuNP-¹⁷⁷Lu and PmAb-AuNP-¹⁷⁷Lu or NT-AuNP-¹⁷⁷Lu. The absorbed doses to the nucleus in these CS assays were estimated. DRT-AuNP-¹⁷⁷Lu were specifically bound by BC cells that expressed HER2 or EGFR or both receptors. In contrast, SRT-TmAb-AuNP-¹⁷⁷Lu and PmAb-AuNP-¹⁷⁷Lu were bound and internalized only by BC cells that expressed HER2 or EGFR, respectively. NT-AuNP-¹⁷⁷Lu exhibited very low binding to BC cells. DRT-AuNP-¹⁷⁷Lu and SRT-TmAb-AuNP-¹⁷⁷Lu or PmAb-AuNP-¹⁷⁷Lu were internalized by BC cells in accordance with the receptor expression. Importantly, DRT-AuNP-¹⁷⁷Lu were more potent in vitro than PmAb-AuNP-¹⁷⁷Lu for killing MDA-MB-231-H2N cells that coexpress HER2 and EGFR (CS = 18.8 ± 1.0 vs 51.5 ± 10.4%; P = 0.006). Furthermore, DRT-AuNP-¹⁷⁷Lu were more potent for killing BT-474 cells with high HER2 but low EGFR expression than TmAb-AuNP-¹⁷⁷Lu (CS = 8.9 ± 3.3 vs 20.7 ± 2.4%; P = 0.007) or PmAb-AuNP-¹⁷⁷Lu (CS = 63.9 ± 1.7%; P < 0.0001). Even for MDA-MB-468 cells that overexpress EGFR but have negligible HER2, DRT-AuNP-¹⁷⁷Lu were more potent for cell killing than PmAb-AuNP-¹⁷⁷Lu (CS = 3.2 ± 3.0 vs 7.5 ± 1.8%; P = 0.001) or TmAb-AuNP-¹⁷⁷Lu (63.2 ± 3.2%; P = 0.0002). All targeted forms of AuNP-¹⁷⁷Lu were more cytotoxic to BC cells than those of NT-AuNP-¹⁷⁷Lu. High absorbed doses (36-119 Gy) were deposited in the nucleus of BC cells by DRT-AuNP-¹⁷⁷Lu. We conclude that a DRT radiation nanomedicine is more potent for killing BC cells that coexpress HER2 and EGFR than SRT radiation nanomedicines. These results are promising for further evaluation of these DRT-AuNP-¹⁷⁷Lu in vivo for the local radiation treatment of human BC tumors that coexpress HER2 and EGFR in mice following i.t. injection, especially tumors that are resistant to HER2-targeted therapies.

A systematic review of clinical outcomes and radiotherapy-associated toxicity in multicatheter accelerated partial breast irradiation

BACKGROUND

To integrate relevant clinical data of multicatheter accelerated partial breast irradiation (mAPBI) for reaching a comprehensive conclusion.

METHODS

We did 3 meta-analyses for clinical outcomes including 1740 women from 4 articles, for acute radiotherapy (RT)-associated toxicity including 1255 patients from 5 articles, and for late RT-related toxicity involving 1565 patients from 9 papers. Clinical outcomes analyses were stratified by molecular subtypes, lymph nodes status, receptor status, and human epidermal growth factor receptor 2 (HER2) status.

RESULTS

For the Luminal A/B phenotypes, the disease relapse and failure in survival significantly decreased when compared with triple negative (TN)/HER2-amplified subtypes (P < .00001). The 5-year regional nodal recurrence (RNR), 5-year distant metastasis-free survival (DMFS) and 5-year disease free-survival (DFS) of TN patients were significantly superior to HER2-overexpression patients (P < .00001). The 5-year cause-specific survival (CSS), 5-year DMFS and 5-year overall survival (OS) in women with lymph nodes-negative were significantly improved versus patients with lymph nodes-positive (P = .0001). Conversely, the positive status of HER2 compared with negative one significantly increased the rate of local recurrence (LR) (P = .02). For acute toxicity, the morbidity of dermatitis was significantly higher than hematoma and implant infection (P = .01, P < .0001, respectively). For late toxicity, the occurrences of fibrosis (32%) and telangiectasia (14%) were significantly higher than other complications (P < .0001).

CONCLUSION

HER2-enriched subtype compared with other subtypes has significantly increased disease relapse and failure in survival. HER2-positive status is positively associated with an increased incidence of LR. Dermatitis is the most common acute RT-related toxicity and fibrosis is the first rife late RT-related toxicity.

Intratumoral Injection of Low-Energy Photon-Emitting Gold Nanoparticles: A Microdosimetric Monte Carlo-Based Model

Gold nanoparticles (Au NPs) distributed in the vicinity of low-dose rate (LDR) brachytherapy seeds could multiply their efficacy thanks to the secondary emissions induced by the photoelectric effect. Injections of radioactive LDR gold nanoparticles (LDR Au NPs), instead of conventional millimeter-size radioactive seeds surrounded by Au NPs, could further enhance the dose by distributing the radioactivity more precisely and homogeneously in tumors. However, the potential of LDR Au NPs as an emerging strategy to treat cancer is strongly dependent on the macroscopic diffusion of the NPs in tumors, as well as on their microscopic internalization within the cells. Understanding the relationship between interstitial and intracellular distribution of NPs, and the outcomes of dose deposition in the cancer tissue is essential for considering future applications of radioactive Au NPs in oncology. Here, LDR Au NPs (¹⁰³Pd:Pd@Au-PEG NPs) were injected in prostate cancer tumors. The particles were visualized at time-points by computed tomography imaging ( in vivo), transmission electron microscopy ( ex vivo), and optical microscopy ( ex vivo). These data were used in a Monte Carlo-based dosimetric model to reveal the dose deposition produced by LDR Au NPs both at tumoral and cellular scales. ¹⁰³Pd:Pd@Au-PEG NPs injected in tumors produce a strong dose enhancement at the intracellular level. However, energy deposition is mainly confined around vesicles filled with NPs, and not necessarily close to the nuclei. This suggests that indirect damage caused by the production of reactive oxygen species might be the leading therapeutic mechanism of tumor growth control, over direct damage to the DNA.

Clinical implementation of a novel Double-Balloon single-entry breast brachytherapy applicator

PURPOSE

The purpose of the study was to describe the clinical utilization of a novel Double-Balloon applicator for accelerated partial breast irradiation (APBI).

METHODS AND MATERIALS

The Double-Balloon single-entry breast applicator contains a single central treatment catheter, as well as four peripheral catheters that can be differentially loaded to customize radiation dose coverage. An inner balloon is filled with up to 7-30 cm³ of saline to increase separation between the peripheral catheters, and an outer balloon is filled with up to 37-115 cm³ of saline to displace breast tissue from the peripheral catheters. Treatment planning objectives include coverage of the breast planning target volume to a minimum of V₉₀ > 90%, limiting dose heterogeneity such that V₂₀₀ < 10 cm³ and V₁₅₀ < 50 cm³, and limiting maximum dose to skin (<100% of prescription dose) and ribs (<145% of prescription dose).

RESULTS

High-dose-rate APBI was delivered to 11 women using this device (34 Gy in 10 twice daily fractions). The mean V₉₀ was 98.2% (range 94.2-99.4%). The mean skin D_max with the Double-Balloon applicator was 83.3% (range 75.6-99.5%). The mean breast V₂₀₀ was 5.8 cm³ (range 2.3-10.2 cm³), and the mean breast V₁₅₀ was 32.9 cm³ (range 25.0-41.7 cm³). Pretreatment quality assurance was performed using CT prior to each morning fraction and ultrasound prior to each afternoon fraction.

CONCLUSIONS

The Double-Balloon applicator can be easily introduced into a previously existing brachytherapy program. APBI plans created with this applicator achieve excellent planning target volume coverage, while limiting skin dose and maintaining breast V₂₀₀ < 10 cm³.

American Brachytherapy Society consensus report for accelerated partial breast irradiation using interstitial multicatheter brachytherapy

PURPOSE

To develop a consensus report for the quality practice of accelerated partial breast irradiation (APBI) using interstitial multicatheter brachytherapy (IMB).

METHODS AND MATERIALS

The American Brachytherapy Society Board appointed an expert panel with clinical and research experience with breast brachytherapy to provide guidance for the current practice of IMB. This report is based on a comprehensive literature review with emphasis on randomized data and expertise of the panel.

RESULTS

Randomized trials have demonstrated equivalent efficacy of APBI using IMB compared with whole breast irradiation for select patients with early-stage breast cancer. Several techniques for placement of interstitial catheters are described, and importance of three-dimensional planning with appropriate optimization is reviewed. Optimal target definition is outlined. Commonly used dosing schemas include 50 Gy delivered in pulses of 0.6-0.8 Gy/h using pulsed-dose-rate technique and 34 Gy in 10 fractions, 32 Gy in eight fractions, or 30 Gy in seven fractions using high-dose-rate technique. Potential toxicities and strategies for toxicity avoidance are described in detail. Dosimetric constraints include limiting whole breast volume that receives ≥50% of prescription dose to <60%, skin dose to ≤100% of prescription dose (≤60-70% preferred), chest wall dose to ≤125% of prescription dose, Dose Homogeneity Index to >0.75 (>0.85 preferred), V₁₅₀ < 45 cc, and V₂₀₀ < 14 cc. Using an optimal implant technique coupled with optimal planning and appropriate dose constraints, a low rate of toxicity and a good-to-excellent cosmetic outcome of ≥90% is expected.

CONCLUSIONS

IMB is an effective technique to deliver APBI for appropriately selected women with early-stage breast cancer. This consensus report has been created to assist clinicians in the appropriate practice of APBI using IMB.

Intratumorally Injected 177Lu-Labeled Gold Nanoparticles: Gold Nanoseed Brachytherapy with Application for Neoadjuvant Treatment of Locally Advanced Breast Cancer

Improvements in the treatment of locally advanced breast cancer (LABC) are needed. Our objective was to study a radiation nanomedicine (gold nanoseeds) composed of 30-nm gold nanoparticles (AuNP) modified with polyethyleneglycol (PEG) chains linked to DOTA for complexing the β-particle emitter (177)Lu and to panitumumab for targeting epidermal growth factor receptors (EGFR) ((177)Lu-T-AuNP) as a novel neoadjuvant brachytherapy for LABC. Nontargeted gold nanoseeds ((177)Lu-NT-AuNP) were constructed without panitumumab for comparison.

METHODS

(177)Lu-T-AuNP or (177)Lu-NT-AuNP was injected intratumorally in CD-1 athymic mice bearing subcutaneous EGFR-positive MDA-MB-468 human breast cancer tumors. Biodistribution and small-animal SPECT/CT imaging studies were performed to evaluate tumor and normal organ localization. A short-term (15 d) study was conducted to select the most effective amount of (177)Lu-T-AuNP or (177)Lu-NT-AuNP for treatment with long-term observation (90-120 d). Normal organ toxicities were assessed by monitoring body weight, blood cell counts, and serum alanine aminotransferase and creatinine. Radiation-absorbed doses in the tumor and normal organs were estimated by Monte Carlo N-Particle version 5.0 modeling.

RESULTS

Tumor radioactivity concentrations were high at 1 h after injection (>300-400 percentage injected dose per gram [%ID/g]) but decreased by 2-3-fold at 48 h after injection. Normal organ uptake was low (<0.5 %ID/g) except for the liver and spleen (<3 %ID/g), increasing by 2-5-fold at 48 h after injection. Treatment with 4.5 MBq (6 × 10(11) AuNP) of (177)Lu-T-AuNP or (177)Lu-NT-AuNP arrested tumor growth over 90 d without normal organ toxicity, whereas tumors continued to grow in mice treated with unlabeled T-AuNP or (177)Lu-labeled PEG polymer not linked to AuNP. Survival was prolonged up to 120 d in mice treated with (177)Lu-T-AuNP or (177)Lu-NT-AuNP. Radiation-absorbed doses to the tumor were 30 and 22 Gy for (177)Lu-T-AuNP and (177)Lu-NT-AuNP, respectively. Some tumor regions received high radiation doses (250-1,300 Gy). Normal organ doses were low (0.04-0.6 Gy).

CONCLUSION

Gold nanoseeds injected intratumorally were highly effective for inhibiting the growth of breast cancer tumors in CD-1 athymic mice and caused no normal organ toxicity. These results are promising for their application for neoadjuvant brachytherapy of LABC. Because EGFR targeting was not required, the approach is broadly applicable to LABC with different phenotypes.

Transition from Paris dosimetry system to 3D image-guided planning in interstitial breast brachytherapy

PURPOSE

The purpose of this study is to evaluate our first experience with 3D image-guided breast brachytherapy and to compare dose distribution parameters between Paris dosimetry system (PDS) and image-based plans.

MATERIAL AND METHODS

First 49 breast cancer patients treated with 3D high-dose-rate interstitial brachytherapy as a boost were selected for the study. Every patient underwent computed tomography, and the planning target volume (PTV) and organs at risk (OAR) were outlined. Two treatment plans were created for every patient. First, based on a Paris dosimetry system (PDS), and the second one, imaged-based plan with graphical optimization (OPT). The reference isodose in PDS implants was 85%, whereas in OPT plans the isodose was chosen to obtain proper target coverage. Dose and volume parameters (D90, D100, V90, V100), doses at OARs, total reference air kerma (TRAK), and quality assurance parameters: dose nonuniformity ratio (DNR), dose homogeneity index (DHI), and conformity index (COIN) were used for a comparison of both plans.

RESULTS

The mean number of catheters was 7 but the mean for 20 first patients was 5 and almost 9 for the next 29 patients. The mean value of prescribed isodose for OPT plans was 73%. The mean D90 was 88.2% and 105.8%, the D100 was 59.8% and 75.7%, the VPTV90 was 88.6% and 98.1%, the VPTV100 was 79.9% and 98.9%, and the TRAK was 0.00375 Gym(-1) and 0.00439 Gym(-1) for the PDS and OPT plans, respectively. The mean DNR was 0.29 and 0.42, the DHI was 0.71 and 0.58, and the COIN was 0.68 and 0.76, respectively.

CONCLUSIONS

The target coverage in image-guided plans (OPT) was significantly higher than in PDS plans but the dose homogeneity was worse. Also, the value of TRAK increased because of change of prescribing isodose. The learning curve slightly affected our results.

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.

Validation of a novel robot-assisted 3DUS system for real-time planning and guidance of breast interstitial HDR brachytherapy

PURPOSE

In current clinical practice, there is no integrated 3D ultrasound (3DUS) guidance system clinically available for breast brachytherapy. In this study, the authors present a novel robot-assisted 3DUS system for real-time planning and guidance of breast interstitial high dose rate (HDR) brachytherapy treatment.

METHODS

For this work, a new computer controlled robotic 3DUS system was built to perform a hybrid motion scan, which is a combination of a 6 cm linear translation with a 30° rotation at both ends. The new 3DUS scanner was designed to fit on a modified Kuske assembly, keeping the current template grid configuration but modifying the frame to allow the mounting of the 3DUS system at several positions. A finer grid was also tested. A user interface was developed to perform image reconstruction, semiautomatic segmentation of the surgical bed as well as catheter reconstruction and tracking. A 3D string phantom was used to validate the geometric accuracy of the reconstruction. The volumetric accuracy of the system was validated with phantoms using magnetic resonance imaging (MRI) and computed tomography (CT) images. In order to accurately determine whether 3DUS can effectively replace CT for treatment planning, the authors have compared the 3DUS catheter reconstruction to the one obtained from CT images. In addition, in agarose-based phantoms, an end-to-end procedure was performed by executing six independent complete procedures with both 14 and 16 catheters, and for both standard and finer Kuske grids. Finally, in phantoms, five end-to-end procedures were performed with the final CT planning for the validation of 3DUS preplanning.

RESULTS

The 3DUS acquisition time is approximately 10 s. A paired Student t-test showed that there was no statistical significant difference between known and measured values of string separations in each direction. Both MRI and CT volume measurements were not statistically different from 3DUS volume (Student t-test: p > 0.05) and they were significantly correlated to 3DUS measurement (Pearson test: MRI p < 0.05 and CT p < 0.001). The mean angular separation distance between catheter trajectories segmented from 3DUS and CT images was 0.42° ± 0.24°, while the maximum and mean trajectory separations were 0.51 ± 0.19 and 0.37 ± 0.17 mm, respectively. Overall, the new finer grid has performed significantly better in terms of dosimetric indices. The planning target volume dosimetric indices were not found statistically different between 3DUS and CT planning (Student t-test, p > 0.05). Both the skin and the pectoral muscle dosimetric indices were within ABS guidelines.

CONCLUSIONS

A novel robot-assisted 3DUS system was designed and validated. To their knowledge, this is the first system capable of performing real-time guidance and planning of breast multicatheter HDR brachytherapy treatments. Future investigation will test the feasibility of using the system in the clinic and for permanent breast brachytherapy.

Radiotherapy planning using MRI

The use of magnetic resonance imaging (MRI) in radiotherapy (RT) planning is rapidly expanding. We review the wide range of image contrast mechanisms available to MRI and the way they are exploited for RT planning. However a number of challenges are also considered: the requirements that MR images are acquired in the RT treatment position, that they are geometrically accurate, that effects of patient motion during the scan are minimized, that tissue markers are clearly demonstrated, that an estimate of electron density can be obtained. These issues are discussed in detail, prior to the consideration of a number of specific clinical applications. This is followed by a brief discussion on the development of real-time MRI-guided RT.

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

PURPOSE

Noninvasive image-guided breast brachytherapy delivers conformal HDR (192)Ir brachytherapy treatments with the breast compressed, and treated in the cranial-caudal and medial-lateral directions. This technique subjects breast tissue to extreme deformations not observed for other disease sites. Given that, commercially-available software for deformable image registration cannot accurately co-register image sets obtained in these two states, a finite element analysis based on a biomechanical model was developed to deform dose distributions for each compression circumstance for dose summation.

MATERIAL AND METHODS

The model assumed the breast was under planar stress with values of 30 kPa for Young's modulus and 0.3 for Poisson's ratio. Dose distributions from round and skin-dose optimized applicators in cranial-caudal and medial-lateral compressions were deformed using 0.1 cm planar resolution. Dose distributions, skin doses, and dose-volume histograms were generated. Results were examined as a function of breast thickness, applicator size, target size, and offset distance from the center.

RESULTS

Over the range of examined thicknesses, target size increased several millimeters as compression thickness decreased. This trend increased with increasing offset distances. Applicator size minimally affected target coverage, until applicator size was less than the compressed target size. In all cases, with an applicator larger or equal to the compressed target size, > 90% of the target covered by > 90% of the prescription dose. In all cases, dose coverage became less uniform as offset distance increased and average dose increased. This effect was more pronounced for smaller target-applicator combinations.

CONCLUSIONS

The model exhibited skin dose trends that matched MC-generated benchmarking results within 2% and clinical observations over a similar range of breast thicknesses and target sizes. The model provided quantitative insight on dosimetric treatment variables over a range of clinical circumstances. These findings highlight the need for careful target localization and accurate identification of compression thickness and target offset.

Partial breast irradiation: targeting volume or breast molecular subtypes?

The eligibility criteria for partial breast irradiation (APBI) are mainly based on histopathological factors, which not always explain the clinical behaviour of breast cancers. International guidelines represent useful platform to collect data for continued refinement of patient selection, but the clinical applicability to APBI series showed some limitations, particularly among the intermediate and high-risk groups. The heterogeneity of APBI techniques, along with the heterogeneity of breast cancer, generates clinical results, where the predictive value of the histopathological factors can assume different weight. There is a need of further refinement and implementation of risk factors. Currently, the impact of breast cancer subtype on local control is matter of investigation, and treatment decision about radiotherapy is generally made without regard to the breast cancer subtype. However, receptor status information is easily available and some histopathological factors have not a definite role, there is no uniform interpretation. As molecular classification becomes more feasible in the clinical practice, it will provide added value to conventional clinical tumour characteristics in predicting local recurrence in breast cancer and may play an important role as predictor of eventual patient outcomes.

Decline of cosmetic outcomes following accelerated partial breast irradiation using intensity modulated radiation therapy: results of a single-institution prospective clinical trial

PURPOSE

To report the final cosmetic results from a single-arm prospective clinical trial evaluating accelerated partial breast irradiation (APBI) using intensity modulated radiation therapy (IMRT) with active-breathing control (ABC).

METHODS AND MATERIALS

Women older than 40 with breast cancer stages 0-I who received breast-conserving surgery were enrolled in an institutional review board-approved prospective study evaluating APBI using IMRT administered with deep inspiration breath-hold. Patients received 38.5 Gy in 3.85-Gy fractions given twice daily over 5 consecutive days. The planning target volume was defined as the lumpectomy cavity with a 1.5-cm margin. Cosmesis was scored on a 4-category scale by the treating physician. Toxicity was scored according to National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE version 3.0). We report the cosmetic and toxicity results at a median follow-up of 5 years.

RESULTS

A total of 34 patients were enrolled. Two patients were excluded because of fair baseline cosmesis. The trial was terminated early because fair/poor cosmesis developed in 7 of 32 women at a median follow-up of 2.5 years. At a median follow-up of 5 years, further decline in the cosmetic outcome was observed in 5 women. Cosmesis at the time of last assessment was 43.3% excellent, 30% good, 20% fair, and 6.7% poor. Fibrosis according to CTCAE at last assessment was 3.3% grade 2 toxicity and 0% grade 3 toxicity. There was no correlation of CTCAE grade 2 or greater fibrosis with cosmesis. The 5-year rate of local control was 97% for all 34 patients initially enrolled.

CONCLUSIONS

In this prospective trial with 5-year median follow-up, we observed an excellent rate of tumor control using IMRT-planned APBI. Cosmetic outcomes, however, continued to decline, with 26.7% of women having a fair to poor cosmetic result. These results underscore the need for continued cosmetic assessment for patients treated with APBI by technique.

Shortened radiation therapy schedules for early-stage breast cancer: a review of hypofractionated whole-breast irradiation and accelerated partial breast irradiation

Breast-conserving therapy consisting of segmental mastectomy followed by whole-breast irradiation (WBI) has become widely accepted as an alternative to mastectomy as a treatment for women with early-stage breast cancer. WBI is typically delivered over the course of 5-6 weeks to the whole breast. Hypofractionated whole-breast irradiation and accelerated partial breast irradiation have developed as alternative radiation techniques for select patients with favorable early-stage breast cancer. These radiation regimens allow for greater patient convenience and the potential for decreased health care costs. We review here the scientific rationale behind delivering a shorter course of radiation therapy using these distinct treatment regimens in this setting as well as an overview of the published data and pending trials comparing these alternative treatment regimens to WBI.

Comparison of planning techniques when air/fluid is present using the strut-adjusted volume implant (SAVI) for HDR-based accelerated partial breast irradiation

The presence of air/fluid surrounding implantable devices used for partial breast irradiation may significantly impact dose coverage to at-risk tissue. Of the 67 total patients retrospectively evaluated for this study, 32 (48%) had greater than 1 cc volume of air/fluid extending outside of the strut-adjusted volume implant (SAVI) device surface and were selected for comparison of planning approaches. The planning approaches utilized two different definitions of PTV_EVAL. One definition of a PTV_EVAL (PTV_EVALSAVI) was based on expanding 1 cm beyond the SAVI device only while accounting for the air/fluid using the NSABP Protocol B-39/RTOG Protocol 0413. The second PTV_EVAL definition (PTV_EVALCAV) was based on expanding 1 cm beyond the cavity (SAVI device plus air/fluid volume). The results indicate use of the B-39 formalism to account for air/fluid displacing the PTV_EVAL may overestimate the dose coverage to the at-risk tissue, especially for large contiguous volumes of air/fluid. Using the SAVI device to optimize dose covering the PTV_EVALCAV volume surrounding the cavity improves dosimetric coverage to at-risk tissue by 11.3% and 8.7% for V100 and V90, respectively, while the average V150 and V200 indices for PTV_EVALCAV increased by 9.1 cc and 5.0cc, respectively, and the average maximum rib and skin doses increased by 11.1% and 6.1%, respectively. The maximum skin dose, rib dose, V150, and V200 all met the planning objectives despite any increase in these parameters.

The American Brachytherapy Society consensus statement for accelerated partial breast irradiation

PURPOSE

To develop clinical guidelines for the quality practice of accelerated partial breast irradiation (APBI) as part of breast-conserving therapy for women with early-stage breast cancer.

METHODS AND MATERIALS

Members of the American Brachytherapy Society with expertise in breast cancer and breast brachytherapy in particular devised updated guidelines for appropriate patient evaluation and selection based on an extensive literature search and clinical experience.

RESULTS

Increasing numbers of randomized and single and multi-institution series have been published documenting the efficacy of various APBI modalities. With more than 10-year followup, multiple series have documented excellent clinical outcomes with interstitial APBI. Patient selection for APBI should be based on a review of clinical and pathologic factors by the clinician with particular attention paid to age (≥50 years old), tumor size (≤3cm), histology (all invasive subtypes and ductal carcinoma in situ), surgical margins (negative), lymphovascular space invasion (not present), and nodal status (negative). Consistent dosimetric guidelines should be used to improve target coverage and limit potential for toxicity following treatment.

CONCLUSIONS

These guidelines have been created to provide clinicians with appropriate patient selection criteria to allow clinicians to use APBI in a manner that will optimize clinical outcomes and patient satisfaction. These guidelines will continue to be evaluated and revised as future publications further stratify optimal patient selection.

A survey of quality control practices for high dose rate (HDR) and pulsed dose rate (PDR) brachytherapy in the United Kingdom

PURPOSE

A survey of quality control (QC) currently undertaken in UK radiotherapy centres for high dose rate (HDR) and pulsed dose rate (PDR) brachytherapy has been conducted. The purpose was to benchmark current accepted practice of tests, frequencies and tolerances to assure acceptable HDR/PDR equipment performance. It is 20 years since a similar survey was conducted in the UK and the current review is timed to coincide with a revision of the IPEM Report 81 guidelines for quality control in radiotherapy.

MATERIAL AND METHODS

ALL RADIOTHERAPY CENTRES IN THE UK WERE INVITED BY EMAIL TO COMPLETE A COMPREHENSIVE QUESTIONNAIRE ON THEIR CURRENT BRACHYTHERAPY QC PRACTICE, INCLUDING: equipment type, patient workload, source calibration method, level of image guidance for planning, prescribing practices, QC tests, method used, staff involved, test frequencies, and acceptable tolerance limits.

RESULTS

Survey data was acquired between June and August 2012. Of the 64 centres invited, 47 (73%) responded, with 31 centres having brachytherapy equipment (3 PDR) and fully completing the survey, 13 reporting no HDR/PDR brachytherapy, and 3 intending to commence HDR brachytherapy in the near future. All centres had comprehensive QC schedules in place and there was general agreement on key test frequencies and tolerances. Greatest discord was whether source strength for treatment planning should be derived from measurement, as at 58% of centres, or from the certified value, at 42%. IPEM Report 81 continues to be the most frequently cited source of QC guidance, followed by ESTRO Booklet No. 8.

CONCLUSIONS

A comprehensive survey of QC practices for HDR/PDR brachytherapy in UK has been conducted. This is a useful reference to which centres may benchmark their own practice. However, individuals should take a risk-assessment based approach, employing full knowledge of local equipment, clinical procedures and available test equipment in order to determine individual QC needs.