Medical physics practice guideline 4.b: Development, implementation, use and maintenance of safety checklists.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the US. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the US. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: Must and must not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. While must is the term to be used in the guidelines, if an entity that adopts the guideline has shall as the preferred term, the AAPM considers that must and shall have the same meaning. Should and should not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Deep inspiration breath hold level variability and deformation in locoregional breast irradiation.

PURPOSE: The purpose of this study was to evaluate the dosimetric effect of breath hold level variability and deformation on breast, chest wall, internal mammary chain (IMC) nodes, and heart. METHODS AND MATERIALS: Left-sided post-lumpectomy (n = 12) and postmastectomy (n = 3) patients underwent deep inspiration breath hold (DIBH) and exhale breath hold (EBH) computed tomography (CT) scans. Forward-planned locoregional breast plans were created on the DIBH scan. Two effects were modeled assuming no setup uncertainties: residual motion within the gating window and systematically shallow breath hold levels (BHLs). Real-time position management (RPM) was used to monitor BHL at simulation and during treatment. The RPM data were scaled to simulate BHL variation within symmetric gating window widths of ±1, 3, 5, and 7 mm; the dosimetric impact of this motion was simulated in the treatment planning system. Systematically "shallow" BHL errors were modeled using deformable image registration to map the patient trajectory from DIBH to EBH (n = 12). The deformable vector fields were scaled to produce synthetic CT scans modeling patient position during breath holds 1, 3, 5, and 7 mm shallower than simulator BHL. The original treatment plans were applied to the synthetic CTs and dose was recalculated. RESULTS: Acceptable plan quality was maintained for most patients with motion within gating windows up to ±7 mm. Patients with shallow median BHLs experienced loss of coverage at simulated gating windows ±5 mm or larger. At systematic 3 mm shallow BHL error, 4/12 patients had clinical target volume IMC V80% < 99%; this increased to 11/12 patients at 5 mm. Change in heart dose from systematic BHL errors was negligible. CONCLUSIONS: Motion within gating windows has minimal dosimetric impact for most BHL variability; however, loss of IMC coverage can occur even for small gating windows when BHLs are systematically shallow. This can be mitigated by restricting lower BHL tolerances or accounting for known uncertainties in planning.

Experimental validation of the van Herk margin formula for lung radiation therapy.

PURPOSE: To validate the van Herk margin formula for lung radiation therapy using realistic dose calculation algorithms and respiratory motion modeling. The robustness of the margin formula against variations in lesion size, peak-to-peak motion amplitude, tissue density, treatment technique, and plan conformity was assessed, along with the margin formula assumption of a homogeneous dose distribution with perfect plan conformity. METHODS: 3DCRT and IMRT lung treatment plans were generated within the ORBIT treatment planning platform (RaySearch Laboratories, Sweden) on 4DCT datasets of virtual phantoms. Random and systematic respiratory motion induced errors were simulated using deformable registration and dose accumulation tools available within ORBIT for simulated cases of varying lesion sizes, peak-to-peak motion amplitudes, tissue densities, and plan conformities. A detailed comparison between the margin formula dose profile model, the planned dose profiles, and penumbra widths was also conducted to test the assumptions of the margin formula. Finally, a correction to account for imperfect plan conformity was tested as well as a novel application of the margin formula that accounts for the patient-specific motion trajectory. RESULTS: The van Herk margin formula ensured full clinical target volume coverage for all 3DCRT and IMRT plans of all conformities with the exception of small lesions in soft tissue. No dosimetric trends with respect to plan technique or lesion size were observed for the systematic and random error simulations. However, accumulated plans showed that plan conformity decreased with increasing tumor motion amplitude. When comparing dose profiles assumed in the margin formula model to the treatment plans, discrepancies in the low dose regions were observed for the random and systematic error simulations. However, the margin formula respected, in all experiments, the 95% dose coverage required for planning target volume (PTV) margin derivation, as defined by the ICRU; thus, suitable PTV margins were estimated. The penumbra widths calculated in lung tissue for each plan were found to be very similar to the 6.4 mm value assumed by the margin formula model. The plan conformity correction yielded inconsistent results which were largely affected by image and dose grid resolution while the trajectory modified PTV plans yielded a dosimetric benefit over the standard internal target volumes approach with up to a 5% decrease in the V20 value. CONCLUSIONS: The margin formula showed to be robust against variations in tumor size and motion, treatment technique, plan conformity, as well as low tissue density. This was validated by maintaining coverage of all of the derived PTVs by 95% dose level, as required by the formal definition of the PTV. However, the assumption of perfect plan conformity in the margin formula derivation yields conservative margin estimation. Future modifications to the margin formula will require a correction for plan conformity. Plan conformity can also be improved by using the proposed trajectory modified PTV planning approach. This proves especially beneficial for tumors with a large anterior-posterior component of respiratory motion.