Robustness of three external beam treatment techniques against inter-fractional positional variations of the metal port in breast tissue expanders

INTRODUCTION

Temporary breast tissue expanders contain a metal port that varies in position throughout the course of radiation treatments. The purpose of this study was to quantify the robustness of the three most common external beam treatment techniques (tangential three-dimensional conformal radiation therapy [3DCRT], volumetric modulated arc therapy [VMAT], and helical tomotherapy) against our measured inter-fractional positional variations of the port.

METHODS

For eight breast cases, a clinical plan was created for each of the three techniques. The dosimetric effect of our previously measured inter-fractional port errors was evaluated for two classes of error: internal port errors (IPEs) and patient registration errors (PREs). For both classes of error, daily variable and systematic errors were modeled, and their cumulative effects were compared against the originally planned doses.

RESULTS

For systematic IPE, the 1%-99% range in point dose differences inside a 5-mm target abutting the implant was the highest for tangential 3DCRT, and it was within 6% and 9% when calculated with Monte Carlo and collapsed cone calculation engines, respectively. Daily variable PRE resulted in mean changes of -3.0% and -3.5% to V_100%Rx of the target for VMAT and tomotherapy, respectively. For nearby organs, daily variable PRE resulted in changes to V_20Gy of the ipsilateral lung of less than 2% in all three techniques, while V_5Gy of the heart increased by as much as 6% in VMAT and 10% in tomotherapy.

CONCLUSIONS

When IPEs were modeled, dose variability was the largest in tangential 3DCRT, leading to areas of underdosage in the shadow of the port. When PREs were modeled, the target coverage and nearby organs were affected the most in VMAT and helical tomotherapy. In reality, port positional errors result from a combination of IPE and PRE, suggesting that VMAT and tomotherapy are more robust when patient registration errors are minimized, despite the presence of IPE.

Unplanned implant removal in locally advanced breast cancer

Study conducted to determine frequency and timing of unplanned breast implant removal after mastectomy, reconstruction, and postmastectomy radiation (PMRT). From 2010-2017, 52 patients underwent mastectomy, reconstruction, and PMRT. With median follow-up of 3.1 years, 23 patients (44%) experienced implant removal. Implant removal occurred in 9 (17%) patients before starting PMRT and 14 (27%) patients after starting PMRT. Implant removal rates were similar for hypofractionated PMRT compared with standard fractionation and for proton compared with photon PMRT. Implant removal is common for women undergoing mastectomy and reconstruction followed by PMRT. The risk is clinically significant even before starting radiation.

Identifying factors impacting the efficacy of postmastectomy radiotherapy in patients with early-stage breast cancer and one to two positive lymph nodes

INTRODUCTION

In women with T1-2 breast cancer and one to two positive axillary lymph nodes (LN) at low risk for recurrence, postmastectomy radiation therapy (PMRT) may provide insufficient benefit to justify its toxicity. This study evaluated the interaction of factors associated with overall survival (OS) after PMRT in these patients.

METHODS

The National Cancer Database was queried for women with T1-2 breast cancer undergoing mastectomy with one to two positive LN identified on lymphadenectomy. Patients were grouped according to number of positive LN and then stratified by PMRT use. Differences in OS were evaluated.

RESULTS

Multivariable modeling demonstrated an interaction effect of age on the efficacy of PMRT. In patients more than or equal to 60 years old, PMRT was associated with improved survival when adjusting for age and tumor grade in patients with 1 to 2 positive LN (risk ratio = 0.62, 95% confidence interval = 0.40-0.93, P = .018). In patients less than 60 years old, tumor size and grade, but not PMRT, were associated with improved OS.

CONCLUSION

For women with T1-2 breast cancer and one to two positive LN, PMRT's association with OS is influenced by age, tumor grade, and number of positive LN. PMRT appears to be associated with improvements in OS in older patients, but not younger patients, regardless of tumor size or nodal status.

Conformal electron beam radiotherapy using custom-made step bolus for postmastectomy chest wall irradiation: An institutional experience

Background

Postmastectomy radiation (PMRT) to the chest wall using electron beam treatment with uniform bolus was practiced at our institution. The planning target volume (PTV) included the chest wall and the internal mammary nodes (IMN) along with supraclavicular nodal regions. The varying thickness of the postmastectomy chest wall and the varying position of the IMN resulted in dose inhomogeneity in the PTV. In addition, there was the risk of increased lung and cardiac doses. In this prospective study, we report the making of a custom-made bolus using dental wax called "step bolus."

Materials and Methods

From March 2010 to January 2011, 167 patients received PMRT. As conformal photon plans were not acceptable in 48 patients, they were treated with single energy electrons and custom-made bolus.

Results

Addition of the step bolus improved dose distribution to the PTV reduced the mean lung dose %, the mean heart dose % and lung dose (D10, D20, D30, D50, and D70). Forty-seven patients had Grade 2, and one patient had Grade 3 skin toxicity. Acute symptomatic radiation pneumonitis was observed in one patient. At 5 years, 29 patients were alive with a median follow-up of 32 months and no local recurrences were observed. One patient died of myocardial infarction unrelated to treatment, one patient did not come for follow-up, 22 patients had systemic metastases, and 24 patients were disease free.

Conclusion

A custom-made step bolus using dental wax can be used for tissue compensation in electron beam therapy with resulting good local disease control and acceptable toxicity.

Progress and controversies: radiation therapy for invasive breast cancer

Radiation therapy is a critical component of the multidisciplinary management of invasive breast cancer. In appropriately selected patients, radiation not only improves local control, sparing patients the morbidity and distress of local recurrence, but it also improves survival by preventing seeding and reseeding of distant metastases from persistent reservoirs of locoregional disease. In recent years, considerable progress has been made toward improving our ability to select patients most likely to benefit from radiotherapy and to administer treatment in ways that maximize clinical benefit while minimizing toxicity and burden. This article reviews the role of radiation therapy in invasive breast cancer management, both after breast-conserving surgery and after mastectomy. It focuses particularly on emerging evidence that helps to define the clinical situations in which radiotherapy is indicated, the appropriate targets of treatment, and optimal approaches for minimizing both the toxicity and the burden of treatment, all in the context of the evolving surgical and systemic management of this common disease. It includes a discussion of new approaches in breast cancer radiotherapy, including hypofractionation and intensity modulation, as well as a discussion of promising avenues for future research.