The impact of a high‐definition multileaf collimator for spine SBRT

Abstract

PurposeAdvanced radiotherapy delivery systems designed for high‐dose, high‐precision treatments often come equipped with high‐definition multi‐leaf collimators (HD‐MLC) aimed at more finely shaping radiation dose to the target. In this work, we study the effect of a high definition MLC on spine stereotactic body radiation therapy (SBRT) treatment plan quality and plan deliverability.Methods and MaterialsSeventeen spine SBRT cases were planned with VMAT using a standard definition MLC (M120), HD‐MLC, and HD‐MLC with an added objective to reduce monitor units (MU). M120 plans were converted into plans deliverable on an HD‐MLC using in‐house software. Plan quality and plan deliverability as measured by portal dosimetry were compared among the three types of plans.ResultsOnly minor differences were noted in plan quality between the M120 and HD‐MLC plans. Plans generated with the HD‐MLC tended to have better spinal cord sparing (3% reduction in maximum cord dose). HD‐MLC plans on average had 12% more MU and 55% greater modulation complexity as defined by an in‐house metric. HD‐MLC plans also had significantly degraded deliverability. Of the VMAT arcs measured, 94% had lower gamma passing metrics when using the HD‐MLC.ConclusionModest improvements in plan quality were noted when switching from M120 to HD‐MLC at the expense of significantly less accurate deliverability in some cases.

Multi‐institution validation of a new high spatial resolution diode array for SRS and SBRT plan pretreatment quality assurance

“…It is also critical to capture accurate beam edge shape using detectors that do not broaden the penumbra during water tank data scanning for TPS commissioning. These challenges make it more difficult to deliver plans with high modulation 90–96,101 …”

“…Though highly modulated plans have been shown to generate sharper dose gradients than possible with standard circular cones, 89 others have reported concern with complex treatment deliveries. Specifically, high modulation is associated with lower passing rates 90–96 …”

“…Specifically, high modulation is associated with lower passing rates. [90][91][92][93][94][95][96] High-modulation results in deliveries where the planning target volume contains a larger proportion of radiation from OOF and penumbra locations as compared to in-field deliveries. There are two aspects to this issuemodeling and measurement.…”

“…These challenges make it more difficult to deliver plans with high modulation. [90][91][92][93][94][95][96]101 In measuring highly modulated plans, size and energy response of detectors must be considered. Ion chambers are much larger than diodes, resulting in volume averaging of dose in high-gradient regions.…”

Comparison between radiochromic film and Sun nuclear edge diode detector during the commissioning of small field size radiosurgery cones

“…Usually, for these treatments small photon fields, formed by circular collimators or multileaf collimators, are used [1]. Micro Multi-leaf collimators have thicknesses less than 3 mm and have the advantage over the stereotactic cone of shaping the tumor more precisely [2]. On the other hand, the stereotactic cone allows a greater dose reduction (falloff) at the edges of the radiation field compared to the MLC, in addition to a smaller penumbra, which makes them advantageous in some circumstances [3].…”