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To systematically investigate the performance of the analytical anisotropic algorithm (AAA) within the extremes of small tumor volumes and near-minimum lung and tumor tissue densities in order to identify combinations of these parameters where the use of AAA could result in a therapeutically unacceptable loss of tumor coverage on an energy and fractionation-specific basis.Clinically appropriate volumetric modulated arc therapy (VMAT) treatment plans were generated with AAA for 180 unique combinations of lung density (0.05-0.30 g/cmThe strongest predictors of a statistically significant reduction in tumor coverage were lung density ≤0.15 g/cmThe accuracy of AAA rapidly diminishes near the minima of clinical lung density, particularly in combination with small tumors and when using a photon energy of 10 MV. The magnitude of the effect can be more dramatic than previously reported data suggests and could potentially compromise the ablative qualities of treatments performed within these environments, particularly with less aggressive fractionation approaches.

Purpose We transitioned from a low-dose-rate (LDR) to a high-dose-rate (HDR) prostate brachytherapy program. The objective of this study was to describe our experience developing a prostate HDR program, compare the LDR and HDR dosimetry, and identify the impact of several targeted interventions in the HDR workflow to improve efficiency. Methods and Materials We performed a retrospective cohort study of patients treated with LDR or HDR prostate brachytherapy. We used iodine-125 seeds (145 Gy as monotherapy, and 110 Gy as a boost) and preoperative planning for LDR. For HDR, we used iridium-192 (13.5 Gy × 2 as monotherapy and 15 Gy × 1 as a boost) and computed tomography–based planning. Over the first 18 months, we implemented several targeted interventions into our HDR workflow to improve efficiency. To evaluate the progress of the HDR program, we used linear mixed-effects models to compare LDR and HDR dosimetry and identify changes in the implant procedure and treatment planning durations over time. Results The study cohort consisted of 122 patients (51 who received LDR and 71 HDR). The mean D90 was similar between patients who received LDR and HDR (P = .28). HDR mean V100 and V95 were higher (P < .0001), but mean V200 and V150 were lower (P < .0001). HDR rectum V100 and D1cc were lower (P < .0001). The HDR mean for the implant procedure duration was shorter (54 vs 60 minutes; P = .02). The HDR mean for the treatment planning duration dramatically improved with the implementation of targeted workflow interventions (3.7 hours for the first quartile to 2.0 hours for the final quartile; P < .0001). Conclusions We successfully developed a prostate HDR brachytherapy program at our institution with comparable dosimetry to our historic LDR patients. We identified several targeted interventions that improved the efficiency of treatment planning. Our experience and workflow interventions may help other institutions develop similar HDR programs.

Purpose: To evaluate the dosimetric characteristics of two commercially available detector arrays, the MapCHECK2 diode array and the PTW Octavius® II ionchamber array, and to assess their use with patient‐specific step‐and‐shoot IMRT QA delivered from treatment specific gantry angles. Methods: Detector properties were compared in their response to varying dose rates, field sizes, and gantry angles. Ten patient‐specific IMRTQuality Assurance (QA) plans were analyzed. The selected patient files were separated into high and low degrees of modulation, e.g. Head and Neck vs. Prostate. Delivered doses to PTW and MapCHECK2 were evaluated with 5% 3mm and Van Dyk Gamma analysis criteria. Results: For both arrays, our findings showed a 1% difference in the measurement for the 100MU/min to 600 MU/min dose rate change for the 10 × 10 cm2field size. A pearson product‐moment correlation test calculated to evaluate eachdetector's deviation from TPS for increasing field size resulted correlation coefficients of −0.8 and 0.01 for PTW and MapCHECK2 respectively, exhibiting PTW's field size dependence which increases by 5% for a 10×10 o 1×1 field. The average 5 × 5 cm2 measurement deviation from the TPS over all angles resulted in 2% and 4% absolute error for PTW and MapCHECK2 respectively, with MapCHECK2 erring up to 36% only at the lateral beams angles 90° and 270° (±10°). For the other angles the absolute error decreased to 1% for MapCHECK2. All 10 patient‐specific IMRT QAs passed the gamma criteria on both detector arrays.Conclusions: BothMapCHECK2 and PTW detector arrays can be used for treatment angle specific IMRT QA. Care must be taken for gantry angles within 10° of the detector plane of MapCHECK2. This is less pronounced for rotational delivery where a smaller portion of the beams will contribute to the total dose from these directions.