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Background and purpose We hypothesized that a plan’s robustness to anatomical changes can be improved by optimizing with multiple CT scans of a patient. The purpose of this study was to determine whether an intensity modulated proton therapy (IMPT) plan could be developed to meet dose criteria on both planning and adaptive CT plans. Material and methods Eight lung cancer patients who underwent adaptive IMPT were retrospectively selected. Each patient had two CTs: a primary planning CT (PCT) and an adaptive planning CT (ACT), and IMPT plans associated with the scans. PCT and ACT were then used in combination to optimize one plan (MCT plan). The doses to the target and organs at risk from the PCT plan, ACT plan, P-ACT plan (PCT plan calculated on ACT data), and MCT plans calculated on both CTs were compared. Results The MCT plan maintained the D 95% on both CTs (mean, 65.99 Gy on PCT and 66.02 Gy on ACT). Target dose coverage on ACT was significantly better with the MCT plan than with the P-ACT plan ( p = 0.01). MCT plans had slightly higher lung V 20 (0.6%, p = 0.02) than did PCT plans. The various plans showed no statistically significant difference in heart and spinal cord dose. Conclusions The results of this study indicate that an IMPT plan can meet the dose criteria on both PCT and ACT, and that MCT optimization can improve the plan’s robustness to anatomical change.

The capabilities of the Eclipse treatment planning system (TPS) (Varian Medical Systems, Palo Alto, CA) for proton therapy treatment planning are described. Various steps involved in the planning process to produce a 3-dimensional (3D) dose distribution both for the passive scattering and pencil beam scanning proton beam therapy are outlined. Mitigation of range and setup uncertainties through robust optimization is discussed. Use of verification plans for patient treatment field dosimetry quality assurance (QA) is presented. Limitations of the Eclipse TPS and future developments are discussed.

Purpose: To provide a series of suggestions for other Medical Physics practices to follow in order to provide effective radiation therapy treatments during the COVID-19 pandemic. Methods and Materials: We reviewed our entire Radiation Oncology infrastructure to identify a series of workflows and policy changes that we implemented during the pandemic that yielded more effective practices during this time. Results: We identified a structured list of several suggestions that can help other Medical Physics practices overcome the challenges involved in delivering high quality radiotherapy services during this pandemic. Conclusions: Our facility encompasses 4 smaller Houston Area Locations (HALs), a main campus with 8 distinct services based on treatment site (ie. Thoracic, Head and Neck, Breast, Gastrointestinal, Gynecology, Genitourinary, Hematologic Malignancies, Melanoma and Sarcoma and Central Nervous System/Pediatrics), a Proton Center facility, an MR-Linac, a Gamma Knife clinic and an array of brachytherapy services. Due to the scope of our services, we have gained experience in dealing with the rapidly changing pandemic effects on our clinical practice. Our paper provides a resource to other Medical Physics practices in search of workflows that have been resilient during these challenging times.

In proton therapy, passive scattered proton plans use compensators to conform the dose to the distal surface of the planning volume. These devices are custom made from acrylic or wax for each treatment field using either a plunge-drilled or smooth-milled compensator design. The purpose of this study was to investigate if there is a clinical benefit of generating passive scattered proton radiation treatment plans with the smooth compensator design. We generated 4 plans with different techniques using the smooth compensators. We chose 5 sites and 5 patients for each site for the range of dosimetric effects to show adequate sample. The plans were compared and evaluated using multicriteria (MCA) plan quality metrics for plan assessment and comparison using the Quality Reports [EMR] technology by Canis Lupus LLC. The average absolute difference for dosimetric metrics from the plunged-depth plan ranged from -4.7 to +3.0 and the average absolute performance results ranged from -6.6% to +3%. The manually edited smooth compensator plan yielded the best dosimetric metric, +3.0, and performance, + 3.0% compared to the plunged-depth plan. It was also superior to the other smooth compensator plans. Our results indicate that there are multiple approaches to achieve plans with smooth compensators similar to the plunged-depth plans. The smooth compensators with manual compensator edits yielded equal or better target coverage and normal tissue (NT) doses compared with the other smooth compensator techniques. Further studies are under investigation to evaluate the robustness of the smooth compensator design.

Background and purpose: There is concern over the stepped edges of multileaf collimator (MLC) fields for target coverage compared with those of cerrobend. Despite recent reports dispelling this concern, users are still cautious when using MLCs for small fields. Leaf orientation can be a problem if one is required to orient the leaves along an axis not ideal for conformity (such as dynamic or universal wedge cases). In this study we examined the dependence of MLC field conformity on field size and elongation. Materials and methods: We examined circles of varying diameter and ellipses of varying eccentricity with leaves oriented along the major and minor axes of ellipses. The tests were both geometric, comparing areas of overblocking or underblocking (leaves inside and outside the field), and dosimetric, using radiographic films at depth in the beam's eye view plane. Results: For the geometric comparison there is a rapid increase in non-conformity, defined as the percentage of overblocking or underblocking area, as the circle diameter decreases. For ellipses, when the leaves move along one axis direction, the conformity does not depend on the diameter of the same axis, but instead improves as the dimension of the axis in the non-leaf motion direction increases. The best conformity is achieved when the maximum number of leaves is used to shape the field. When the dosimetry is analyzed, the predictability of these trends decreases due to the impact of undulations (scatter), leaf inaccuracies and dosimetric uncertainties. Conclusions: We recommend that for small round fields MLC should be used with caution and that for ellipses the direction of leaf movement should be aligned with the minor axis whenever possible. Though these experiments are for idealized geometries, the observations can be applied to clinical fields. An MLC with a thinner leaf width could be beneficial for small round fields.

Photothermal grating spectroscopy is applied to study the nongeminate atom recombination of photodissociated iodine in liquids. A theoretical model is developed to describe the time dependence of diffraction signals. The excitation intensity dependence of diffraction from the anharmonic thermal grating, created by saturated optical absorption, is used to estimate the quantum yield ofthephotodissociation, which is critical to determine the number of iodine atoms produced and hence to the recombination rate. The rateconstant of nongeminate atom recombination is extracted from the dependence of the time-resolved photothermal diffraction signals on the atom concentration. From the relative amplitudes of the diffraction transients, we can also derive the enthalpy of the recombination reaction.

The laser-induced anharmonic thermal grating technique has been used to study the excited-state absorption and photoisomerization of two cyanine dyes, 3,3′-diethyloxatricarbocyanine iodide (DOTCI) and 1,3,3,1′,3′,3′-hexamethylindotricarbocyanine iodide (HITCI). An anomalous excitation intensity dependence of the diffraction efficiency is observed for both dye molecules; the anomaly is caused by diffraction from multiple thermal gratings which are 180° out of phase. The previously developed theory for anharmonic thermal gratings based on a quasi-plane-wave approximation (QPWA) cannot quantitatively fit the measured results. A more recently developed, general numerical method for calculating diffraction from anharmonic thermal gratings accounts for the observed anomalous behavior in terms of an excited-state and trap-state formation model. For DOTCI, the nonlinear absorption in ethanol is caused by the saturation of the ground-state absorption and strong excited-state absorption, while for HITCI, in addition to these two absorption processes, photoisomer absorption may also be an important process contributing to the nonlinear absorption at the excitation wavelength (532 nm).