Improving treatment efficiency via photon optimizer (PO) MLC algorithm for synchronous single‐isocenter/multiple‐lesions VMAT lung SBRT

Abstract

PurposeElderly patients with multiple primary or oligometastases (<5 lesions) lesions with associated co‐morbidities may not retain their treatment position for the traditional long SBRT treatment time with individual isocenters for each lesion. Treating multiple lesions synchronously using a single‐isocenter volumetric arc therapy (VMAT) plan would be more efficient with the use of the most recently adopted photon optimizer (PO) MLC algorithm and improve the patient comfort. Herein, we quantified the clinical performance of PO versus its predecessor progressive resolution optimizer (PRO) algorithm for single‐isocenter/multiple‐lesions VMAT lung SBRT.Materials and methodsFourteen patients with metastatic non‐small‐cell lung cancer lesions (two to five, both uni‐ and bilateral lungs) received a highly conformal single‐isocenter co/non‐coplanar VMAT (2–6 arcs) SBRT treatment plan. Patients were treated with a 6X‐FFF beam and Acuros algorithm with a single‐isocenter placed between/among the lesions, using PO for MLC optimization. Average isocenter to tumor distance was 5.5 ± 1.9 cm. Mean combined PTV derived from 4D‐CT scans was 38.7 ± 22.7 cc. Doses were 54 Gy/50 Gy in 3/5 fractions prescribed to 70%–80% isodose line so that at least 95% of the PTV receives 100% of prescribed dose. Plans were re‐optimized using PRO algorithm. Plans were compared via ROTG‐0915 protocol criteria for target conformity, heterogeneity and gradient indices, and dose to organs‐at‐risk (OAR). Additionally, total number of monitor units (MU), modulation factor (MF) and beam‐on time were compared.ResultsAll plans met SBRT protocol requirements for target coverage and OAR doses. Comparison of target coverage and dose to the OAR showed no statistical significance between the two plans. PO had 1042 ± 753 (P < 0.001) less MU than PRO resulting in a beam‐on time of about 0.75 ± 0.5 min (P < 0.001) less, on average. For similar dose distribution, a significant reduction of beam delivery complexity was observed with PO (average MF = 3.7 ± 0.7) vs PRO MLC algorithm (average MF = 4.4 ± 1.3) (P < 0.001).ConclusionsPO MLC algorithm improved treatment efficiency without compromising plan quality when compared to PRO algorithm for single‐isocenter/multi‐lesions VMAT lung SBRT. Shorter beam‐on time can potentially reduce intrafraction motion errors and improve patient compliance. PO MLC algorithm is recommended for future clinical lung SBRT plan optimization.

Progressive resolution optimizer (PRO) predominates over photon optimizer (PO) in sparing of spinal cord for spine SABR VMAT plans

“…However, for VMAT PRO , improvements in plan dosimetric quality can lead to increases in overall plan complexity and total MUs, which can compromise treatment deliverability and e ciency, respectively. Similar studies have investigated the optimization algorithms in terms of dosimetric quality for various SABR treatment sites, such as the lungs and brain [13][14][15]. Visak et al investigated the dosimetric quality of VMAT PRO and VMAT PO in 12 lung SABR patients with a single dose of 30 Gy [14].…”

Margin calculation for multiple lung metastases treated with single-isocenter SBRT

“…Single-isocenter lung SBRT is an emerging technique for oligometastatic disease [5][6][7][8][9]. Nevertheless, there are little data about treatment margins for this technique taking into account relative inter-lesion position variation.…”

“…Using a single isocenter for multiple targets in combination with intensity-modulated radiotherapy (IMRT), or volumetric modulated arc therapy (VMAT), recently gained interest. It may result in a more efficient workflow, reduce the number of monitor units (MU) and thereby reduce the cumulative patient dose, overall planning/treatment time, and improve cost-effectiveness [5][6][7][8][9][10]. However, a major challenge in lung SBRT as opposed to intracranial single-isocenter treatments, is that different parts of the lung are known to move independently, and the inter-target distance may vary on a day-to-day basis [11].…”

Knowledge-based planning for multi-isocenter VMAT total marrow irradiation

“…Target and critical structures were contoured and planned using the Eclipse treatment planning system and RapidPlan version 15.6 (Varian Medical Systems, Palo Alto, CA). Although the patients had been contoured in the consistent way, we observed a gradual improvement in plan quality -as defined in the Evaluation section -with the upgrade of Varian optimization software over the past decade to exploit advanced techniques and user interface such as Photon Optimizer algorithm (26,27) and Arc Geometry tool (28). To minimize the dosimetric performance variation in the reference set for the evaluation of our KBP, we identified a benchmark cohort of recent 11 clinically approved plans optimized by a single planner at UIC with similar target volumes.…”