Field‐in‐field breast planning for a jawless, double‐stack MLC LINAC using flattening‐filter‐free beams

Abstract

BackgroundThis study intends to develop an efficient field‐in‐field (FiF) planning technique with the Eclipse treatment planning system (TPS) to determine the feasibility of using the Halcyon treatment delivery system for 3D treatment of breast cancer.MethodsTen treatment plans were prepared on the Halcyon treatment planning system and compared to the same patients’ clinically delivered TrueBeam plans which used flattened 6 MV and 10 MV beams. Patients selected for this study were treated via simple, tangential breast irradiation and did not receive radiotherapy of the supraclavicular or internal mammary lymph nodes. Planning target volumes (PTV) volumes ranged from 519 cc to 1211 cc with a mean target volume of 877 cc. Several planning techniques involving collimator, gantry rotation, and number of FiF segments were investigated as well as the use of the dynamically flattened beam (DFB) — a predefined MLC pattern that is designed to provide a flattened beam profile at 10 cm depth on a standard water phantom. For comparison, the clinically delivered TrueBeam plans remained unaltered except for normalization of the target coverage to more readily compare the two treatment delivery techniques.ResultsUsing the physician defined PTV, normalized such that 98% of the volume was covered by 95% of the prescribed dose, the Halcyon plans were deemed clinically acceptable and comparable to the TrueBeam plans by the radiation oncologist. Resulting average global maximum doses in the test patients were identical between the TrueBeam and Halcyon plans (108% of Rx) and a mean PTV dose of 102.5% vs 101.6%, respectively.ConclusionsFrom this study a practical and efficient planning method for delivering 3D conformal breast radiotherapy using the Halcyon linear accelerator has been developed. When normalized to the clinically desired coverage, hot spots were maintained to acceptable levels and overall plan quality was comparable to plans delivered on conventional C‐arm LINACs.

Technical Note: Dosimetric characterization of the dynamic beam flattening MLC sequence on a ring shaped, Jawless Linear Accelerator with double stacked MLC

“…With that stated, the DBF sequence can be used in conjunction with more advanced planning technique such as field-in-field if desired. 5 Prior to considering the potential applications of this novel technique, a comprehensive evaluation and characterization of the dosimetric features and the machine performance are necessary. The goal of this work was to acquire the data necessary to adequately characterize these dynamically flattened beams and compare the measured dosimetric parameters with those predicted by the treatment planning system (TPS).…”

“…This is particularly applicable for busy radiotherapy centers with large patient loads. With that stated, the DBF sequence can be used in conjunction with more advanced planning technique such as field‐in‐field if desired . Prior to considering the potential applications of this novel technique, a comprehensive evaluation and characterization of the dosimetric features and the machine performance are necessary.…”

Using flattening filter free beams in electronic tissue compensation whole breast irradiation with deep inspiration breath hold

“…Traditionally, whole breast or chest wall irradiation has been treated with two tangential fields, which has superior delivery robustness compared with IMRT plans with alternative beam arrangements yet often shows an equivalent dosimetry. With the tangential beam 18% and 39%, 10,12,14,15,18 in our study the delivery time was significantly reduced for 6X-FFF plans with a 32% average decrease. This difference could substantially reduce the strain of the DIBH on patients and make this heart-sparing treatment technique more com- were kept constant, the 6X-FFF QA plans were considered to be a much closer analogue to the 6X plan than the 6X-FFF plan for the delivery accuracy comparison.…”

“…IMRT plans using the helical TomoTherapy system (Accuray Incorporated, Sunnyvale, CA, USA) have been shown to provide superior dose conformity and homogeneity which mostly comes from the inverse planning 11 . On the more recently available Halcyon system (Varian Medical Systems, Palo Alto, CA, USA), the FFF plans were also shown to be comparable to the flattened plans on conventional LINACs 12–14 . but showed an increase in superficial dose of 10% 15 .…”

“…are gaining popularity in the clinic, there have been some similar studies to ours that compared FFF and flattened beams for breast planning. 10,14 However, despite the findings from these publications that FFF had comparable plan quality and a reduced delivery time than their flattened counterparts, FFF plans are very rarely used in the current clinical practice of whole breast irradiation. Likely contributing to this lack of clinical application may be the lack of a necessity for shortened delivery time in the general breast RT setting and the concerns against IMRT which has often been the focus of these earlier FFF breast investigations.…”