June 28, 2021
Frontiers in Breast Treatment Planning
When it comes to treating breast plans, it’s likely the vast majority of dosimetrists and physicists feel pretty confident in their approach. Breast cancer is among the most prevalent clinical indications, so whatever the technique used to treat it—from tangent fields to breath-holds—our departments get plenty of practice. We have developed our routines. And there may be nothing wrong with that; modern planning for breast cancer has evolved over several decades, with good clinical evidence to support currently available treatment planning practices.

But when new methods emerge, it’s worth considering whether these methods could improve (or replace) the status quo efforts. Below, we’ll introduce you to a novel technique for challenging boosts, discuss the merits of a method that has yet to reach its prime, and reveal which breast planning method wins the trophy for overall planning efficiency and effectiveness.

When In Doubt, Add An Arc

When treating the breast with a boost to the lumpectomy cavity, many departments opt for electrons for conformal coverage of the PTV. But in some cases, the PTV may lie at a depth that is out of the practical reach of electrons. In this case, boost fields can be designed as mini-tangents in an attempt to cover the target. But this comes with the compromise of non-conformal coverage and irradiation of a much larger volume than necessary.

There’s a solution for that. A technique developed by Pearson, Wan, and Bogue at the University of Toledo makes one straightforward addition to their mini-tangents that dramatically improves conformality: a single arc.

The simple addition of a conformal arc ranging from 50° to 180° to complement the tangent fields results in surprising PTV conformality and reduces dose accumulation outside of the target. According to their study, adding an arc to mini-tangents dropped V105% from an average of 85.8cc to just 6.4cc. With that comes an overall decrease in the amount of breast receiving the prescription dose and more homogeneous target coverage.

Of course, the sheer nature of the arc implies the delivery of a small amount of exit dose to surrounding structures. The ipsilateral lung sees slightly higher doses from this technique, as does the heart (more exaggerated for left breast cases). This tradeoff must be considered on a case-by-case basis, but ultimately, this new method for deep-seated seromas has potential.

Interested in planning with arcs using EZFluence? We’re here to help. Email info@radformation.com and our support team will walk you through how to plan this technique using EZFluence.

The Best Of Both Worlds

For the treatment of intact breasts, electronic compensation (EComp) is a popular method of creating a uniform dose distribution using a sliding window delivery. For many, this technique replaced cumbersome physical wedges and is faster to treat while providing excellent coverage. However, because of the method of delivery, some are reluctant to use high energies due to potential neutron production.

Hybrid IMRT solves the large separation issue by pairing open fields and modulated fields to accommodate variation in body habitus. In this technique, high energies are typically used on the open field, allowing skin-sparing, depth penetration, and a reduction of hot spots, while the lower-energy modulated field creates homogeneous coverage of the target volume. While not a new concept (hybrid IMRT was described in a 2005 paper by Charles Mayo, et al.), implementation of the technique has lagged. But for those who are already using electronic compensation for breast planning, adding the open field component has its benefits.

Learn how BC Cancer-Victoria experiences dramatic time savings using EZFluence for Hybrid IMRT.

And the Winner Is…

With so many different approaches to breast treatment planning, how do they compare? That was the question posed in a recent paper, Dosimetric comparative study of 3DCRT, IMRT, VMAT, Ecomp, and Hybrid techniques for breast radiation therapy by Chen, et al. The team went about their investigation using 30 breast patient data sets, creating retrospective treatment plans for each using seven different techniques. They then evaluated each plan objectively using a number of different plan quality metrics, including PTV coverage, dose delivered to critical OARs, total MUs, and planning time.

The results showed marginal (but significant!) deviations for parameters such as conformity index and homogeneity index, while other metrics varied widely. The average time required for 3DCRT and EComp (14 and 15 minutes, respectively) was dramatically lower than that required for IMRT (36 min for tangents, 80 min for multi-field IMRT).

In the end, after weighing substantial data, electronic compensation was found to be the favorite among the seven techniques because of its “effectiveness and efficiency.” Among the fastest to time, EComp also provides excellent prescription coverage, conformality, and OAR sparing.

Some physicists reading this might take issue with this conclusion since this analysis only takes into account the time involved for these techniques in the planning phase. Many sites require patient-specific QA for EComp delivery, which may ratchet the sum total time investment required.

We all approach breast planning from different angles, but if you find yourself looking for alternative solutions for boosts or patients with large separation, the above are solid additions to your dosimetry toolbox. What’s your go-to method for breast planning?

written by Tyler Blackwell

Tyler Blackwell is a board-certified medical physicist with extensive clinical experience in radiation therapy. He is active in several AAPM committees, has served as secretary-treasurer for the Northwest Chapter of AAPM, and is an ABR orals examiner. Tyler dabbles in real estate investing and loves preparing breakfast for his two kiddos.

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