External beam accelerated partial breast irradiation: dosimetric assessment of conformal and three different intensity modulated techniques

Updates on the APBI-IMRT-Florence Trial (NCT02104895) Technique: From the Intensity Modulated Radiation Therapy Trial to the Volumetric Modulated Arc Therapy Clinical Practice

Several phase 3 trials have demonstrated partial breast irradiation noninferiority compared with whole breast irradiation in terms of local control and similar or reduced toxicity. During recent years, especially owing to the COVID-19 pandemic, a growing interest in 5-fraction regimens emerged. The APBI-IMRT-Florence trial (NCT02104895) schedule (30 Gy in 5 fractions) might represent an appealing treatment option, being both a safe and effective partial breast irradiation schedule, with long-term reported results. The aim of this report is to support planners interested in implementing this technique and to warrant equal access to postoperative radiation treatment for most early breast cancer patient candidates. We report the current delivery technique optimized from the original protocol and the updated dose constraints for plan optimization. We also report a statistical analysis of dosimetric parameters on 50 patients treated in consecutive fractions. Treatment-related toxic effects were assessed using the acute radiation morbidity scoring criteria and late radiation morbidity scoring scheme from the Radiation Therapy Oncology Group and the European Organisation for Research and Treatment of Cancer. The mean volume of ipsilateral breast was 731 cm³ (standard deviation ± 450; range, 151-2205) and the mean planning target volume (PTV) was 139 cm³ (standard deviation ± 48; range, 55-259). There was good correlation between ipsilateral breast V_15Gy and the ratio between the PTV and ipsilateral breast volume (R² = .911). At a median follow-up of 4.5 years, 32% of patients (n = 16) developed any grade 1 acute toxic effect. No grade >1 toxic effect was observed. Sixteen percent of patients (n = 8) developed any grade 1 late toxic effect. No grade >1 toxic effect was observed. Physician-assessed cosmesis was reported as excellent (84%), good (14%), and fair (2%). The schedule of 30 Gy in 5 consecutive fractions might represent a safe, easy-to-deliver, and cost-effective option for appropriately selected patients affected by early breast cancer.

External Beam Accelerated Partial Breast Irradiation in Early Breast Cancer and the Risk for Radiogenic Pneumonitis

In order to evaluate the risk for radiation-associated symptomatic pneumonitis in a prospective external beam accelerated partial breast irradiation (APBI) trial, between 2011 and 2021, 170 patients with early stage breast cancer were enclosed in the trial. Patients were eligible for study participation if they had a histologically confirmed breast cancer or an exclusive ductal carcinoma in situ (DCIS), a tumor size ≤3 cm, free safety margins ≥2 mm, no involved axillary lymph nodes, tumor bed clips, and were ≥50 years old. Patients received APBI with 38 Gy with 10 fractions in 10 consecutive working days. The trial was registered at the German Clinical Trials Registry, DRKS-ID: DRKS00004417. Median follow-up was 56 (1−129) months. Ipsilateral lung MLD, V20, and V30 were 4.3 ± 1.4 Gy, 3.0 ± 2.0%, and 1.0 ± 1.0%, respectively. Radiogenic pneumonitis grade 2 appeared in 1/170 (0.6%) patients two months after radiotherapy. Ipsilateral MLD, V20, and V30 were 6.1 Gy, 7, and 3% in this patient. Additionally, individual radiosensitivity was increased in this specific patient. Compared to WBI, APBI leads to lower lung doses. Using APBI, the risk of symptomatic radiogenic pneumonitis is very low and may be limited, with an ipsilateral V20 < 3% to very exceptional cases associated with innate risk factors with an increased radiation susceptibility.

CyberKnife versus multicatheter interstitial brachytherapy for accelerated partial breast irradiation: a dosimetrical assessment with focus on organs at risk

Background

The purpose of the study was to dosimetrically compare multicatheter interstitial brachytherapy (MIBT) and stereotactic radiotherapy with CyberKnife (CK) for accelerated partial breast irradiation with special focus on dose to organs at risk (OARs).

Materials and methods

Treatment plans of thirty-one patients treated with MIBT were selected and additional CK plans were created on the same CT images. The OARs included ipsilateral non-target and contralateral breast, ipsilateral and contralateral lung, skin, ribs, and heart for left sided cases. The fractionation was identical (4 × 6.25 Gy). Dose-volume parameters were calculated for both techniques and compared.

Results

The D90 of the PTV for MIBT and CK were similar (102.4% vs. 103.6%, p = 0.0654), but in COIN the MIBT achieved lower value (0.75 vs. 0.91, p < 0.001). Regarding the V100 parameter of non-target breast CK performed slightly better than MIBT (V100: 1.1% vs. 1.6%), but for V90, V50 and V25 MIBT resulted in less dose. Every examined parameter of ipsilateral lung, skin, ribs and contralateral lung was significantly smaller for MIBT than for CK. Protection of the heart was slightly better with MIBT, but only the difference of D2cm³ was statistically significant (17.3% vs. 20.4%, p = 0.0311). There were no significant differences among the dose-volume parameters of the contralateral breast.

Conclusion

The target volume can be properly irradiated by both techniques with high conformity and similar dose to the OARs. MIBT provides more advantageous plans than CK, except for dose conformity and the dosimetry of the heart and contralateral breast. More studies are needed to analyze whether these dosimetrical findings have clinical significance.

Implementation of accelerated partial breast irradiation at the Oncology Institute of Vojvodina

Introduction. Early breast cancer is usually treated with breast conserving surgery followed by radiation treatment. Whole breast irradiation is standard of care so far, but currently there is an increasement in accelerated partial breast irradiation for selected patients which showed many advantages. The aim of this paper is to present the implementation of the accelerated partial breast irradiation in Oncology Institute of Vojvodina. Case outline. A 54-year-old woman was referred to radiotherapy after breast conserving surgery. After she met all of the inclusion criteria, she underwent accelerated partial breast irradiation with 38.5 Gy in 10 fractions. Active breathing control device was used during the treatment and cone beam computed tomography was performed before each fraction for purpose of target position control. She terminated therapy in good health condition with only adverse effect of mild radiation dermatitis of irradiated area. On the first follow up, she was without any symptom or sign of disease or complication. Conclusion. Accelerated partial breast irradiation is safe and effective. Radiation oncologist should be encouraged to implement this technique.

Multicatheter interstitial brachytherapy versus stereotactic radiotherapy with CyberKnife for accelerated partial breast irradiation: a comparative treatment planning study with respect to dosimetry of organs at risk

Background

The aim of the study was to dosimetrically compare multicatheter interstitial brachytherapy (MIBT) and stereotactic radiotherapy with CyberKnife (CK) for accelerated partial breast irradiation (APBI) especially concerning the dose of organs at risk (OAR-s).

Patients and methods

Treatment plans of thirty-two MIBT and CK patients were compared. The OAR-s included ipsilateral non-target and contralateral breast, ipsilateral and contralateral lung, skin, ribs, and heart for left-sided cases. The fractionation was identical (4 x 6.25 Gy) in both treatment groups. The relative volumes (e.g. V100, V90) receiving a given relative dose (100%, 90%), and the relative doses (e.g. D0.1cm³, D1cm³) delivered to the most exposed small volumes (0.1 cm³, 1 cm³) were calculated from dose-volume histograms. All dose values were related to the prescribed dose (25 Gy).

Results

Regarding non-target breast CK performed slightly better than MIBT (V100: 0.7% vs. 1.6%, V50: 10.5% vs. 12.9%). The mean dose of the ipsilateral lung was the same for both techniques (4.9%), but doses irradiated to volume of 1 cm³ were lower with MIBT (36.1% vs. 45.4%). Protection of skin and rib was better with MIBT. There were no significant differences between the dose-volume parameters of the heart, but with MIBT, slightly larger volumes were irradiated by 5% dose (V5: 29.9% vs. 21.2%). Contralateral breast and lung received a somewhat higher dose with MIBT (D1cm³: 2.6% vs. 1.8% and 3.6% vs. 2.5%).

Conclusions

The target volume can be properly irradiated by both techniques with similar dose distributions and high dose conformity. Regarding the dose to the non-target breast, heart, and contralateral organs the CK was superior, but the nearby organs (skin, ribs, ipsilateral lung) received less dose with MIBT. The observed dosimetric differences were small but significant in a few parameters at the examined patient number. More studies are needed to explore whether these dosimetric findings have clinical significance.

Is stereotactic CyberKnife radiotherapy or multicatheter HDR brachytherapy the better option dosimetrically for accelerated partial breast irradiation?

OBJECTIVE

To compare dosimetrically the stereotactic CyberKnife (CK) therapy and multicatheter high-dose-rate (HDR) brachytherapy (BT) for accelerated partial breast irradiation (APBI).

METHODS

Treatment plans of 25 patients treated with CK were selected, and additional plans using multicatheter HDR BT were created on the same CT images. The prescribed dose was 6.25/25 Gy in both plans to the target volume (PTV). The dose-volume parameters were calculated for both techniques and compared.

RESULTS

The D90 total dose of the PTV was significantly lower with CK than with HDR BT, D90 was 25.7 Gy, and 27.0 Gy (p < 0.001). However, CK plans were more conformal than BT, COIN was 0.87, and 0.81 (p = 0.0030). The V50 of the non-target breast was higher with CK than with BT: 10.5% and 3.3% (p = 0.0010), while there was no difference in the dose of the contralateral breast and contralateral lung. Dose to skin, ipsilateral lung, and ribs were higher with CK than with BT: D₁ was 20.6 Gy vs. 11.5 Gy (p = 0.0018) to skin, 11.4 Gy vs. 9.6 Gy (p = 0.0272) to ipsilateral lung and 18.5 Gy vs. 12.3 Gy (p = 0.0013) to ribs, while D_0.1 to heart was lower, 3.0 Gy vs. 3.2 Gy (p = 0.0476), respectively.

CONCLUSIONS

Multicatheter HDR BT yields more advantageous plans than stereotactic CyberKnife treatment in accelerated partial breast irradiation, except in terms of dose conformality and the dose to the heart. There was no difference in the dose of the contralateral breast and lung.

Cardiac doses of accelerated partial breast irradiation with perioperative multicatheter interstitial brachytherapy

PURPOSE

To quantify mean heart dose (MHD) and doses to the left anterior descending artery (LAD) and left ventricle (LV) in a retrospective series of patients who underwent perioperative accelerated partial breast irradiation with multicatheter interstitial brachytherapy (MIB-APBI).

METHODS

Sixty-eight patients with low-risk left breast cancer were treated with MIB-APBI at our institution between 2012 and 2017. Interstitial tubes were inserted during the tumorectomy and sentinel node biopsy and APBI was started 6 days later. The prescribed dose was 34 Gy in 10 fractions (twice a day) to the clinical target volume (CTV). The heart, LAD, and LV were contoured and the distance between each structure and the CTV was measured. The MHD, mean and maximum LAD doses (LAD mean/max), and mean LV doses (LV mean) were calculated and corrected to biologically equivalent doses in 2‑Gy fractionation (EQD2). We also evaluated the impact of the distance between the cardiac structures and the CTV and of the volume receiving the prescribed dose (V100) and high-dose volume (V150) on heart dosimetry.

RESULTS

Mean EQD2 for MHD, LAD mean/max, and mean LV were 0.9 ± 0.4 Gy (range 0.3-2.2), 1.6 ± 1.1 Gy (range, 0.4-5.6), 2.6 ± 1.9 Gy (range, 0.7-9.2), and 1.3 ± 0.6 Gy (range, 0.5-3.4), respectively. MHD, LAD mean/max, and LV mean significantly correlated with the distance between the CTV and these structures, but all doses were below the recommended limits (German Society of Radiation Oncology; DEGRO). The MHD and LV mean were significantly dependent on V100.

CONCLUSION

Perioperative MIB-APBI resulted in low cardiac doses in our study. This finding provides further support for the value of this technique in well-selected patients with early-stage left breast cancer.

DEGRO practical guideline for partial-breast irradiation

PURPOSE

This consensus statement from the Breast Cancer Working Group of the German Society for Radiation Oncology (DEGRO) aims to define practical guidelines for accelerated partial-breast irradiation (APBI).

METHODS

Recent recommendations for relevant aspects of APBI were summarized and a panel of experts reviewed all the relevant literature. Panel members of the DEGRO experts participated in a series of conferences, supplemented their clinical experience, performed a literature review, and formulated recommendations for implementing APBI in clinical routine, focusing on patient selection, target definition, and treatment technique.

RESULTS

Appropriate patient selection, target definition for different APBI techniques, and basic rules for appropriate APBI techniques for clinical routine outside of clinical trials are described. Detailed recommendations for APBI in daily practice, including dose constraints, are given.

CONCLUSION

Guidelines are mandatory to assure optimal results of APBI using different techniques.

Reducing the Risk of Secondary Lung Cancer in Treatment Planning of Accelerated Partial Breast Irradiation

Purpose: Adjuvant accelerated partial breast irradiation (APBI) results in low local recurrence risks. However, the survival benefit of adjuvant radiotherapy APBI for low-risk breast cancer might partially be offset by the risk of radiation-induced lung cancer. Reducing the lung dose mitigates this risk, but this could result in higher doses to the ipsilateral breast. Different external beam APBI techniques are equally conformal and homogenous, but the intermediate to low dose distribution differs. Thus, the risk of toxicity is different. The purpose of this study is to quantify the trade-off between secondary lung cancer risk and breast dose in treatment planning and to compare an optimal coplanar and non-coplanar technique. Methods: A total of 440 APBI treatment plans were generated using automated treatment planning for a coplanar VMAT beam-setup and a non-coplanar robotic stereotactic radiotherapy beam-setup. This enabled an unbiased comparison of two times 11 Pareto-optimal plans for 20 patients, gradually shifting priority from maximum lung sparing to maximum ipsilateral breast sparing. The excess absolute risks of developing lung cancer and breast fibrosis were calculated using the Schneider model for lung cancer and the Avanzo model for breast fibrosis. Results: Prioritizing lung sparing reduced the mean lung dose from 2.2 Gy to as low as 0.3 Gy for the non-coplanar technique and from 1.9 Gy to 0.4 Gy for the coplanar technique, corresponding to a 7- and 4-fold median reduction of secondary lung cancer risk, respectively, compared to prioritizing breast sparing. The increase in breast dose resulted in a negligible 0.4% increase in fibrosis risk. The use of non-coplanar beams resulted in lower secondary cancer and fibrosis risks (p < 0.001). Lung sparing also reduced the mean heart dose for both techniques. Conclusions: The risk of secondary lung cancer of external beam APBI can be dramatically reduced by prioritizing lung sparing during treatment planning. The associated increase in breast dose did not lead to a relevant increase in fibrosis risk. The use of non-coplanar beams systematically resulted in the lowest risks of secondary lung cancer and fibrosis. Prioritizing lung sparing during treatment planning could increase the overall survival of early-stage breast cancer patients by reducing mortality due to secondary lung cancer and cardiovascular toxicity.

Methodological Errors in Clinical Studies Published by Medical Journals of Ex-Yugoslav Countries

INTRODUCTION

Certain methodological principles should be inexcusably followed when designing clinical or observational research to avoid bias and presentation of results that do not reflect the truth about the phenomenon that is the object of the study.

AIM

The aim of this study was to compare the methodological quality of clinical trials and observational studies published in medical journals from ex-Yugoslav countries indexed in Pubmed/MEDLINE.

METHODS

Clinical studies published in medical journals of ex-Yugoslav countries were retrieved from the Pubmed/MEDLINE database, and the sample for analysis was randomly chosen from the retrieved publications. The rate of the most common errors in the design of clinical/observational studies was established by a careful reading of the sampled publications and their checking against predefined criteria.

RESULTS

The studies published in two countries that are now member states of the European Union (Slovenia and Croatia) have significantly higher citation rates, impact factor, and methodological quality scores than studies from other ex-Yugoslav countries. While publications from Croatia show clear improvement trend throughout the last two decades, which is visible also in the last 10 years in Slovenia and Bosnia and Herzegovina, quality of clinical research published in journals from Serbia was stagnating in the same period.

CONCLUSIONS

There are significant differences in methodological quality and scientometric characteristics of clinical research published in medical journals of ex-Yugoslav countries that could be mitigated by more intensive training of clinical researchers in statistics and research design, as well as by more rigorous editorial practices.

Measurement of dose exposure of image guidance in external beam accelerated partial breast irradiation: Evaluation of different techniques and linear accelerators

INTRODUCTION

Verifying the patient position is always an essential part of the treatment process, especially in hypofractionated treatments such as accelerated partial breast irradiation (APBI). The purpose of the study was to compare five image guidance techniques with respect to imaging dose and image quality.

METHODS AND MATERIALS

We chose five types of imaging methods applicable for APBI and measured their dose exposure on four different accelerators (Synergy, TrueBeam, Artiste and CyberKnife). Absorbed dose was measured with ionization chamber in thorax phantom. Besides dose exposure image quality was also compared.

RESULTS

The lowest dose exposure was measured with kV-kV planar imaging followed by kV-CBCT, MV-MV pair and MV-CBCT in ascending order. Average phantom dose with kV-kV image pair on CyberKnife was 0.01 cGy as the lowest and with MV-CBCT on Artiste was 7.11 cGy as the highest. Average dose exposures of MV-MV images with TrueBeam, Synergy and Artiste were 1.18 cGy, 2.13 cGy and 1.61 cGy, respectively, with similar image quality. For the same machines the doses of kV-CT imaging were comparable: 0.65 cGy, 0.65 cGy and 0.52 cGy, with some differences in image quality. MV-CBCT technique resulted in the highest dose and poorest image quality.

CONCLUSIONS

In APBI the position of the patient and tumour bed can be verified with many tools. When fiducials are available, often 2D imaging is enough to achieve appropriate positioning and the kV-kV method is recommended. Imaging with 2.5MV can also be a good solution instead of 6MV. Without fiducials 3D images should be acquired and the recommended method is the kV-CBCT.