Practice Patterns in the Delivery of Radiation Therapy After Mastectomy Among the University of California Athena Breast Health Network

Robustness of VMAT to setup errors in postmastectomy radiotherapy of left-sided breast cancer: Impact of bolus thickness

BACKGROUND

Volumetric modulated arc therapy (VMAT) with varied bolus thicknesses has been employed in postmastectomy radiotherapy (PMRT) of breast cancer to improve superficial target coverage. However, impact of bolus thickness on plan robustness remains unclear.

METHODS

The study enrolled ten patients with left-sided breast cancer who received radiotherapy using VMAT with 5 mm and 10 mm bolus (VMAT-5B and VMAT-10B). Inter-fractional setup errors were simulated by introducing a 3 mm shift to isocenter of the original plans in the anterior-posterior, left-right, and inferior-superior directions. The plans (perturbed plans) were recalculated without changing other parameters. Dose volume histograms (DVH) were collected for plan evaluation. Absolute dose differences in DVH endpoints for the clinical target volume (CTV), heart, and left lung between the perturbed plans and the original ones were used for robustness analysis.

RESULTS

VMAT-10B showed better target coverage, while VMAT-5B was superior in organs-at-risk (OARs) sparing. As expected, small setup errors of 3 mm could induce dose fluctuations in CTV and OARs. The differences in CTV were small in VMAT-5B, with a maximum difference of -1.05 Gy for the posterior shifts. For VMAT-10B, isocenter shifts in the posterior and right directions significantly decreased CTV coverage. The differences were -1.69 Gy, -1.48 Gy and -1.99 Gy, -1.69 Gy for ΔD95% and ΔD98%, respectively. Regarding the OARs, only isocenter shifts in the posterior, right, and inferior directions increased dose to the left lung and the heart. Differences in VMAT-10B were milder than those in VMAT-5B. Specifically, mean heart dose were increased by 0.42 Gy (range 0.10 ~ 0.95 Gy) and 0.20 Gy (range -0.11 ~ 0.72 Gy), and mean dose for the left lung were increased by 1.02 Gy (range 0.79 ~ 1.18 Gy) and 0.68 Gy (range 0.47 ~ 0.84 Gy) in VMAT-5B and VMAT-10B, respectively. High-dose volumes in the organs were increased by approximate 0 ~ 2 and 1 ~ 3 percentage points, respectively. Nevertheless, most of the dosimetric parameters in the perturbed plans were still clinically acceptable.

CONCLUSIONS

VMAT-5B appears to be more robust to 3 mm setup errors than VMAT-10B. VMAT-5B also resulted in better OARs sparing with acceptable target coverage and dose homogeneity. Therefore 5 mm bolus is recommended for PMRT of left-sided breast cancer using VMAT.

A prospective feasibility study of a 1-mm bolus for postmastectomy radiotherapy

BACKGROUND

The optimal chest wall bolus regimen for postmastectomy radiotherapy (PMRT) remains unknown. We aimed to prospectively evaluate the use of a 1-mm-thick daily tissue-equivalent bolus in patients who received PMRT using thermoluminescent dosimeters (TLDs) and skin toxicity assessment.

METHODS

Patients with a 1-mm-thick daily bolus during PMRT were prospectively enrolled at The Juntendo University Hospital. The surface dose was measured in vivo under the 1-mm-thick bolus on the chest wall. We assessed the acute skin toxicity weekly during PMRT, and 1, 2, 4, and 12 weeks after the completion of PMRT.

RESULTS

A total of 19 patients aged 32-79 years old received PMRT from July 2019 to January 2020. All patients completed the protocol treatment without interruptions, and the median follow-up was 32 weeks. In vivo dosimetry analysis revealed surface doses between 77 and 113% of the prescribed dose, with a mean of 92% of the prescribed radiation dose, and a standard deviation of 7% being delivered. Grade 2 dermatitis was found in 10 patients (53%), and Grade 3 dermatitis was found in one patient (5%). All cases of Grade 2 and 3 dermatitis were improved 4 weeks after PMRT. There were no cases of Grade 4 dermatitis and no chest wall recurrences during the treatment or follow-up period.

CONCLUSIONS

Results confirmed the feasibility of using a 1-mm-thick daily bolus for PMRT, exhibiting an appropriate dose buildup and acceptable skin toxicity without treatment interruptions.

TRIAL REGISTRATION

The University Hospital Medical Information Network Clinical Trials Registry, UMIN000035773 . Registered 1 July 2019.

Impact of radiation dose on complications among women with breast cancer who underwent breast reconstruction and post-mastectomy radiotherapy: A multi-institutional validation study

Purpose

Emerging data suggest that higher radiation doses in post-mastectomy radiotherapy may be associated with an increased risk of reconstruction complications. This study aimed to validate previous findings regarding the impact of radiation dose on complications among women with breast cancer using a multi-center dataset.

Methods

Fifteen institutions participated, and women with breast cancer who received radiotherapy after either autologous or prosthetic breast reconstruction were included. The primary endpoint was major post-radiation therapy complications requiring re-operation for explantation, flap failure, or bleeding control.

Results

In total, 314 patients were included. Radiotherapy was performed using both conventional fractionation and hypofractionation in various schedules. The range of the radiation therapy dose in Equivalent Dose in 2 Gy fractions (EQD2; α/β = 3.5) varied from 43.4 to 71.0 Gy (median dose: 48.6 Gy). Boost radiation therapy was administered to 49 patients. Major post-radiation therapy complications were observed in 24 (7.6%) patients. In multivariate analysis, an increasing EQD2 per Gy (odds ratio [OR]: 1.58, 95% confidence interval [CI]: 1.26–1.98; p < 0.001), current smoking status (OR: 25.48, 95% CI: 1.56–415.65; p = 0.023), and prosthetic breast reconstruction (OR: 9.28, 95% CI: 1.84–46.70; p = 0.007) were independently associated with an increased risk of major complications.

Conclusion

A dose-response relationship between radiation dose and the risk of complications was validated in this multi-center dataset. In this context, we hypothesize that the use of hypofractionated radiotherapy (40 Gy in 15 fractions) may improve breast reconstruction outcomes. Our multi-center prospective observational study (NCT03523078) is underway to further validate this hypothesis.

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Radiation dose is associated with the risk of breast reconstruction complications.

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We conducted a retrospective multi-center observational study of 314 women in Korea.

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Complication-related risk factors were identified using multivariate analysis.

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Use of hypofractionated radiation therapy may improve breast reconstruction outcomes.

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A prospective multi-center study is under way to further validate our findings.

Dosimetric assessment of bolus for postmastectomy radiotherapy

There remains wide variation in the use of chest wall boluses for postmastectomy radiotherapy, which may result from the need for 2 treatment plans with the commonly used half-time tissue-equivalent 5-mm-thick bolus to achieve a full surface dose. To establish a bolus method requiring one treatment plan, we assessed the surface dose of a thinner daily bolus for all treatment fractions and compared it against the half-time 5-mm-thick bolus. In this basic study, we specifically investigated dosage achieved when using the following: (1) the existing bolus protocol, a half-time 5-mm-thick tissue-equivalent Clearfit bolus (Fujidenolo Inc., Aichi, JP); (2) no bolus; and (3) daily 1-, 2-, and 3-mm-thick Clearfit boluses at 4 and 6 MV photons. Dosimetric measurements were then taken in an anthropomorphic phantom to study the effect of each regimen on the surface doses, and the mean surface doses of the daily thinner boluses were compared with the existing bolus protocol by the Welch 2-sample t test. The mean surface doses for the existing bolus protocol, no bolus, and daily 1-, 2-, and 3-mm-thick boluses were 68% (range, 59% to 77%), 53% (41% to 66%), 73% (60% to 83%), 77% (66% to 87%), and 82% (75% to 91%) of the prescription dose at 4 MV, respectively; the corresponding values at 6 MV were 71% (63% to 79%), 50% (39% to 60%), 72% (56% to 83%), 81% (68% to 90%), and 89% (80 to 97%) of the prescription dose. The mean surface doses were comparable between the existing bolus protocol and the 1-mm-thick daily bolus at 4 and 6 MV. In conclusion, the mean surface dose of a 1-mm-thick bolus approximate that of a half-time 5-mm-thick bolus at 4 and 6 MV. As such, we have started a prospective clinical study on the safety and efficacy of a 1-mm-thick bolus for postmastectomy radiotherapy.

The Impact of a Postmastectomy Chest Wall Scar Boost on Local Recurrence-free Survival in High-risk Patients

INTRODUCTION

A scar boost following postmastectomy radiation to a total dose of > 50 Gy can be considered in cases of invasive breast cancer with high-risk features including advanced tumor stage, lymphovascular space invasion (LVSI), and positive margins. The purpose of this study was to determine the impact of a scar boost on 5-year local recurrence-free survival (LRFS).

MATERIALS AND METHODS

We retrospectively analyzed 140 patients with invasive breast cancer treated with mastectomy and postmastectomy radiation at a single institution between 2007 and 2016. Patients received 50 to 50.4 Gy to the chest wall and the majority of scar boosts were 9 to 10 Gy. LRFS was examined using the Kaplan-Meier method and univariable Cox regression.

RESULTS

A total of 140 patients met inclusion criteria with a median follow-up time of 48 months. Ninety-four (67.1%) patients did receive a scar boost and 46 (32.9%) patients did not. On subset analysis of patients with LVSI or positive margins, 5-year LRFS was 79.3% in patients treated with scar boost compared with 71.1% in patients without a scar boost (P = .537). In patients with T3 or T4 disease, 5-year LRFS was 80.9% in those who received scar boost and 71.6% in patients who did not (P = .967). The use of a scar boost was not associated with a significant improvement in LRFS on Cox regression (hazard ratio, 0.83; 95% confidence interval, 0.37-1.84; P = .654).

CONCLUSION

Use of a scar boost following postmastectomy radiation decreased the absolute percentages of local recurrences in patients with high-risk features; however, this did not translate into a statistically significant benefit.

CancerLinQ: Origins, Implementation, and Future Directions

Rapid-learning health systems have been proposed as a potential solution to the problem of quality in medicine, by leveraging data generated from electronic health systems in near-real time to improve quality and reduce cost. Given the complex, dynamic nature of cancer care, a rapid-learning health system offers large potential benefits to oncology practice. In this article, we review the rationale for developing a rapid-learning health system for oncology and describe the sequence of events that led to the development of ASCO’s CancerLinQ (Cancer Learning Intelligence Network for Quality) initiative, as well as the current state of CancerLinQ, including its importance to efforts such as the Beau Biden Cancer Moonshot. We then review the considerable challenges facing optimal implementation of a rapid-learning health system such as CancerLinQ, including integration of rapidly expanding multiomic data, capturing big data from a variety of sources, an evolving competitive landscape, and implementing a rapid-learning health system in a way that satisfies many stakeholders, including patients, providers, researchers, and administrators.

An Innovative Risk-Reducing Approach to Postmastectomy Radiation Delivery after Autologous Breast Reconstruction

INTRODUCTION

Postmastectomy radiation therapy (PMRT) has known deleterious side effects in immediate autologous breast reconstruction. However, plastic surgeons are rarely involved in PMRT planning. Our institution has adopted a custom bolus approach for all patients receiving PMRT. This offers uniform distribution of standard radiation doses, thereby minimizing radiation-induced changes while maintaining oncologic safety. We present our 8-year experience with the custom bolus approach for PMRT delivery in immediate autologous breast reconstruction.

METHODS

All immediate autologous breast reconstruction patients requiring PMRT after 2006 were treated with the custom bolus approach. Retrospective chart review was performed to compare the postirradiation complications, reconstruction outcomes, and oncologic outcomes of these patients with those of previous patients at our institution who underwent standard bolus, and to historical controls from peer-reviewed literature.

RESULTS

Over the past 10 years, of the 29 patients who received PMRT, 10 were treated with custom bolus. Custom bolus resulted in fewer radiation-induced skin changes and less skin tethering/fibrosis than standard bolus (0% vs 10% and 20% vs 35%, respectively), and less volume loss and contour deformities compared with historical controls (10% vs 22.8% and 10% vs 30.7%, respectively).

CONCLUSIONS

Custom bolus PMRT minimizes radiation delivery to the internal mammary vessels, anastomoses, and skin; uniformly doses the surgical incision; and provides the necessary radiation dose to prevent recurrence. Because custom bolus PMRT may reduce the deleterious effects of radiation on reconstructive outcomes while maintaining safe oncologic results, we encourage all plastic surgeons to collaborate with radiation oncologists to consider this technique.

Post-mastectomy radiation therapy without usage of a bolus may be a reasonable option

To clarify the efficacy and toxicity of post-mastectomy radiation therapy (PMRT) without usage of a bolus, we identified 129 consecutive patients who received PMRT at the National Cancer Center Hospital East between 2003 and 2012. Seven of the 129 patients who received breast reconstruction before PMRT were excluded. All patients received PMRT of 6 MV photons, without usage of a bolus. The median follow-up duration for all eligible patients was 47.7 months (range: 4.0-123.2). Local, locoregional and isolated locoregional recurrence was found in 12 (9.8%), 14 (11%) and 5 patients (4.1%), respectively. The 3- and 5-year cumulative incidence of local recurrence, locoregional recurrence and isolated locoregional recurrence was 9.2 and 10.7%, 10.8 and 12.4%, and 4.3 and 4.3%, respectively. Although Grade 2 dermatitis was found in 11 patients (9.0%), no Grade 3-4 dermatitis was found. On univariate analysis, only a non-luminal subtype was a significant predictor for local recurrence (P < 0.001). On multivariate analysis, a non-luminal subtype remained as an independent predictor for local recurrence (P = 0.003, odds ratio: 10.9, 95% confidence interval: 2.23-53.1). In conclusion, PMRT without usage of a bolus resulted in a low rate of severe acute dermatitis without an apparent increase in local recurrence. PMRT without usage of a bolus may be reasonable, especially for patients with a luminal subtype.