Purpose:To demonstrate a new quality assurance (QA) technique for single isocenter volumetric modulated arc therapy (VMAT) plans for stereotactic radiosurgery of multiple brain metastases and to compare quantitative QA results using this method with results using a cylindrical diode array and full field coronal films.Methods:This study employs a phantom built of 28 thin slabs to accommodate radiochromic film insertions near all planning target volume (PTV) locations, providing target specific data for individual PTVs. Single isocenter VMAT plans were designed for two patients with 5 and 11 intra‐cranial metastases. Both plans were modified three times to create plans that overdosed a target by 10%, and underdosed a target by 10 % and 20%. Gamma analyses were performed for full field coronal films, the diode array measurements and for individual PTVs with the proposed film stack method using square ROIs centered on the PTVs, measuring twice the length of the PTV's equivalent sphere diameter. Passing gamma criteria was 95% of points passing at 5%/1mm and a threshold of 10% of the prescription dose.Results:Of the 6 introduced errors, 1 was detected by the diode array gamma test (93.1% pass rate). Pass rates for the other 5 ranged from 95.4–98.8%. None of the errors were detected using the full field film gamma test (pass rates: 98.7–99.9%). Using the proposed film stack method, 5 of 6 errors were detected by failed gamma tests (pass rates: 51, 53, 71, 87.3, 93.9 and 97.8%). The two high pass rates were due to attempts to underdose a PTV that measured too high in the original plan.Conclusion:The results suggest that current methods may be lacking quantitative value and rely heavily on challenging qualitative evaluation, while the proposed method offers a much needed practical method for meaningful quantitative results.

Purpose: Modern radiotherapy increasingly employs large immobilization devices, gantry attachments, and couch rotations for treatments. All of which raise the risk of collisions between the patient and the gantry / couch. Collision detection is often achieved by manually checking each couch position in the treatment room and sometimes results in extraneous imaging if collisions are detected after image based setup has begun. In the interest of improving efficiency and avoiding extra imaging, we explore the use of a surface imaging based collision detection model. Methods: Surfaces acquired from AlignRT (VisionRT, London, UK) were transferred in wavefront format to a custom Matlab (Mathworks, Natick, MA) software package (CCHECK). Computed tomography (CT) scans acquired at the same time were sent to CCHECK in DICOM format. In CCHECK, binary maps of the surfaces were created and overlaid on the CT images based on the fixed relationship of the AlignRT and CT coordinate systems. Isocenters were added through a graphical user interface (GUI). CCHECK then compares the inputted surfaces to a model of the linear accelerator (linac) to check for collisions at defined gantry and couch positions. Note, CCHECK may be used with or without a CT. Results: The nominal surface image field of view is 650 mm × 900 mm, with variance based on patient position and size. The accuracy of collision detections is primarily based on the linac model and the surface mapping process. The current linac model and mapping process yield detection accuracies on the order of 5 mm, assuming no change in patient posture between surface acquisition and treatment. Conclusions: CCHECK provides a non‐ionizing method to check for collisions without the patient in the treatment room. Collision detection accuracy may be improved with more robust linac modeling. Additional gantry attachments (e.g. conical collimators) can be easily added to the model.

Purpose:Hybrid density override schemes have been shown to yield more accurate dose modeling for lung SBRT than plans calculated on free breathing (FB) or time average (AVG) CT scans. Before hybrid schemes are clinically implemented, comparisons are needed between dose delivered to a moving gross tumor volume (GTV) by plans calculated on hybrid scans (HP) and plans calculated on FB and AVG scans.Methods:Volumetric arc therapy plans were created on HP, FB, and AVG scans for 10 patients with FB and 4D‐CT scans. Five of the cases had target volumes contained entirely in lung, 5 had target volumes that included chestwall. The HP were created by overriding the internal target volume (ITV) to GTV density, and the planning target volume minus ITV shell to a density between GTV and lung. If chestwall was in the target its density was not changed. Plans were copied to the 10 4D‐CT phases and recalculated to evaluate the impact of tumor motion on each technique. The GTV doses from the initial plans were compared to mean doses over the 4D‐CT phases. Doses were calculated with the anisotropic analytical algorithm.Results:The minimum GTV dose ratios from the 4D to initial plans were 0.95 +/−0.11, 0.97 +/−0.11, 0.94 +/−0.13 (2 SD), for the FB, AVG, and HP plans, respectively. The mean GTV dose ratios were 1.00 +/−0.07, 1.01 +/−0.03, 0.97 +/−0.09, for the FB, AVG, and HP plans, respectively. The individual minimum dose ratios for HP to FB or AVG were all < 10%, the mean ratios agreed < 10% for 90% of the comparisons.Conclusion:The FB, AVG, and HP plans showed consistent results when considering motion. The interpretation of the planning system dose and prescription definition with HP techniques should be similar to current practices.

Purpose:Deep inspiration breath hold (DIBH) for left‐sided breast cancer has been shown to reduce heart dose. Surface imaging helps to ensure accurate breast positioning, but does not guarantee a reproducible breath hold (BH) at DIBH treatments. We examine the effects of variable BH positions for DIBH treatments.Methods:Twenty‐Five patients with free breathing (FB) and DIBH scans were reviewed. Four plans were created for each patient: 1) FB, 2) DIBH, 3) FB_DIBH – the DIBH plans were copied to the FB images and recalculated (image registration was based on breast tissue), and 4) P_DIBH – a partial BH with the heart shifted midway between the FB and DIBH positions. The FB_DIBH plans give “worst case” scenarios for surface imaging DIBH, where the breast is aligned by surface imaging but the patient is not holding their breath. Students t‐tests were used to compare dose metrics.Results:The DIBH plans gave lower heart dose and comparable breast coverage versus FB in all cases. The FB_DIBH plans showed no significant difference versus FB plans for breast coverage, mean heart dose, or maximum heart dose (p >= 0.10). The mean heart dose differed between FB_DIBH and FB by < 2 Gy for all cases, the maximum heart dose differed by < 2 Gy for 21 cases. The P_DIBH plans showed significantly lower mean heart dose than FB (p = 0.01). The mean heart doses for the P_DIBH plans were < FB for 22 cases, the maximum dose < FB for 18 cases.Conclusions:A DIBH plan delivered to a FB patient set‐up with surface imaging will yield similar dosimetry to a plan created and delivered FB. A DIBH plan delivered with even a partial BH can give reduced heart dose compared to FB techniques when the breast tissue is well aligned.