Search

Purpose: Pencil-beam scanning proton therapy has been considered a potential modality for the 3D form of spatially fractionated radiation therapy called lattice therapy. However, few practical solutions have been introduced in the clinic. Existing limitations include degradation in plan quality and robustness when using single-field versus multifield lattice plans, respectively. We propose a practical and robust proton lattice (RPL) planning method using multifield and evaluate its dosimetric characteristics compared to clinically acceptable photon lattice plans., Methods and Materials: Seven cases previously treated with photon lattice therapy were used to evaluate a novel RPL planning technique using 2-orthogonal beams: a primary beam (PB) and a robust complementary beam (RCB) that deliver 67% and 33%, respectively, of the prescribed dose to vertices inside the gross target volume (GTV). Only RCB is robustly optimized for setup and range uncertainties. The number and volume of vertices, peak-to-valley dose ratios (PVDRs), and volume of low dose to GTV of proton and photon plans were compared. The RPL technique was then used in the treatment of 2 patients and their dosimetric parameters were reported., Results: The RPL strategy was able to achieve the clinical planning goals. Compared to previously treated photon plans, the average number of vertices increased by 30%, the average vertex volume by 49% (18.2 ± 25.9 cc vs 12.2 ± 14.5 cc, P = .21), and higher PVDR (10.5 ± 4.8 vs 2.5 ± 0.9, P < .005) was achieved. In addition, RPL plans show more conformal dose with less low dose to GTV (V30%, 60.9% ± 7.2% vs 81.6% ± 13.9% and V10%, 88.3% ± 4.5% vs 98.6% ± 3.6% [P < .01]). The RPL plan for 2 treated patients showed PVDRs of 4.61 and 14.85 with vertices-to-GTV ratios of 1.52% and 1.30%, respectively., Conclusions: A novel RPL planning strategy using a pair of orthogonal beams was developed and successfully translated to the clinic. The proposed method can generate better quality plans, a higher number of vertices, and higher PVDRs than currently used photon lattice plans., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Purpose: A higher minimum monitor unit (minMU) for pencil-beam scanning proton beams in intensity-modulated proton therapy is preferred for more efficient delivery. However, plan quality may be compromised when the minMU is too large. This study aimed to identify the optimal minMU (OminMU) to improve plan delivery efficiency while maintaining high plan quality., Methods: We utilized clinical plans including six anatomic sites (brain, head and neck, breast, lung, abdomen, and prostate) from 23 patients previously treated with the Varian ProBeam system. The minMU of each plan was increased from the current clinical minMU of 1.1 to 3-24 MU depending on the daily prescribed dose (DPD). The dosimetric parameters of the plans were evaluated for consistency against a 1.1-minMU plan for target coverage as well as organs-at-risk dose sparing. DPD/minMU was defined as the ratio of DPD to minMU (cGy/MU) to find the OminMU by ensuring that dosimetric parameters did not differ by >1% compared to those of the 1.1-minMU plan., Results: All plans up to 5 minMU showed no significant dose differences compared to the 1.1-minMU plan. Plan qualities remained acceptable when DPD/minMU ≥35 cGy/MU. This suggests that the 35 cGy/MU criterion can be used as the OminMU, which implies that 5 MU is the OminMU for a conventional fraction dose of 180 cGy. Treatment times were decreased by an average of 32% (max 56%, min 7%) and by an average of 1.6 min when the minMU was increased from 1.1 to OminMU., Conclusion: A clinical guideline for OminMU has been established. The minMU can be increased by 1 MU for every 35 cGy of DPD without compromising plan quality for most cases analyzed in this study. Significant treatment time reduction of up to 56% was observed when the suggested OminMU is used., (© 2024 The Author(s). Journal of Applied Clinical Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.)

Purpose: Single vocal cord irradiation (SVCI) is a promising technique to maintain excellent oncologic control and potentially improve upon toxicities for treatment of early-stage glottic squamous cell carcinomas. We sought to investigate whether pencil beam scanning (PBS) proton therapy could improve upon the already favorable dose gradients demonstrated with volumetric modulated arc therapy (VMAT) SVCI., Patients and Methods: A 64-year-old gentleman was treated in our department with 6X-flattening filter-free VMAT SVCI to 58.08 Gy in 16 fractions for a T1a well-differentiated squamous cell carcinoma of the left true vocal cord and tolerated it well with good local control. Comparative PBS plans were created in Raystation for the Varian ProBeam with clinical target volume (CTVs) generated to mimic the prescription target volume extent of the VMAT planning target volumes when accounting for PBS plan robustness (±3 mm translational shifts, 3.5% density perturbation). A 3-field single-field optimization plan was selected as dosimetrically preferable. Dosimetric variables were compared., Results: Several organs at risk doses improved with PBS, including the maximum and mean dose to ipsilateral carotids, maximum and mean dose to contralateral carotid, maximum dose to the spinal cord, maximum and mean dose to inferior constrictor/cricopharyngeus, maximum and mean dose to the uninvolved vocal cord, and mean dose to the thyroid gland. There are tradeoffs in skin dose depending on location relative to the target-with the highest and lowest isodoses extending more into the skin with the VMAT plan but with the moderate isodose lines covering a wider area with the PBS plan, but we deemed it tolerable regardless., Conclusion: SVCI is a promising strategy for maintaining the oncologic effectiveness of whole-larynx photon radiation while potentially improving upon the historic toxicity profile. The favorable dose distribution with PBS with respect to organs at risk dosimetry for PBS may allow for further improvements upon VMAT SVCI strategies. Clinical implementation of PBS SVCI may be considered., Competing Interests: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Matthew J. Ferris, MD, reports a relationship with Maryland Proton Treatment Center that includes employment. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Purpose: Noncoplanar plans (NCPs) are commonly used for proton treatment of bilateral head and neck (HN) malignancies. NCP requires additional verification setup imaging between beams to correct residual errors of robotic couch motion, which increases imaging dose and total treatment time. This study compared the quality and robustness of NCPs with those of coplanar plans (CPs)., Methods and Materials: Under an IRB-approved study, CPs were created retrospectively for 10 bilateral HN patients previously treated with NCPs maintaining identical beam geometry of the original plan but excluding couch rotations. Plan robustness to the inter-fractional variation (IV) of both plans was evaluated through the Dose Volume Histograms (DVH) of weekly quality assurance CT (QACT) sets (39 total). In addition, delivery efficiency for both plans was compared using total treatment time (TTT) and beam-on time (BOT)., Results: No significant differences in plan quality were observed in terms of clinical target volume (CTV) coverage (D95) or organ-at-risk (OAR) doses (p > 0.4 for all CTVs and OARs). No significant advantage of NCPs in the robustness to IV was found over CP, either. Changes in D95 of QA plans showed a linear correlation (slope = 1.006, R 2  > 0.99) between NCP and CP for three CTV data points (CTV1, CTV2, and CTV3) in each QA plan (117 data points for 39 QA plans). NCPs showed significantly higher beam delivery time than CPs for TTT (539 ± 50 vs. 897 ± 142 s; p < 0.001); however, no significant differences were observed for BOT., Conclusion: NCPs are not more robust to IV than CPs when treating bilateral HN tumors with pencil-beam scanning proton beams. CPs showed plan quality and robustness similar to NCPs while reduced treatment time (∼6 min). This suggests that CPs may be a more efficient planning technique for bilateral HN cancer proton therapy., (© 2023 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.)

Background: Following mastectomy, immediate breast reconstruction often involves the use of temporary tissue expanders (TEs). TEs contain metallic ports (MPs), which complicate proton pencil-beam scanning (PBS) planning. A technique was implemented for delivering PBS post-mastectomy radiation (PMRT) to patients with TEs and MPs., Methods: A protocol utilizing a hybrid single- and multi-field optimization (SFO, MFO) technique was developed. Plans were robustly optimized using a Monte Carlo algorithm. A CTV&#95;eval structure including chest wall (CW) and regional nodal (RNI) targets and excluding the TE was evaluated. Organ at risk (OAR) dosimetry and acute toxicities were analyzed., Results: Twenty-nine women were treated with this technique. A 2-field SFO technique was used superior and inferior to the MP, with a 3 or 4-field MFO technique used at the level of the MP. Virtual blocks were utilized so that beams did not travel through the MP. A port-to-CW distance of 1 cm was required. Patients underwent daily image-guidance to ensure the port remained within a 0.5 cm internal planning volume (ITV). Median RT dose to CTV&#95;eval was 50.4 Gy (45.0-50.4). Median 95% CTV&#95;eval coverage was 99.5% (95-100). Optically stimulated luminescent dosimeter (OSLD) readings were available for 8 patients and correlated to the dose measurements in the treatment planning system (TPS); median OSLD ratio was 0.99 (range, 0.93-1.02)., Conclusions: Delivering PMRT with PBS for women with metal-containing TEs using a hybrid SFO/MFO technique is feasible, reproducible, and achieves excellent dose distributions. Specialized planning and image-guidance techniques are required to safely utilize this treatment in the clinic., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Purpose/objective(s): With reports of CNS toxicity in patients treated with proton therapy at doses lower than would be expected based on photon data, it has been proposed that heavy monitor unit (MU) weighting of pencil beam scanning (PBS) proton therapy spots may potentially increase the risk of toxicity. We evaluated the impact of maximum MU weighting per spot (maxMU/spot) restrictions on PBS plan quality, prior to implementing clinic-wide maxMU/spot restrictions., Materials/methods: PBS plans of 11 patients, of which 3 plans included boosts, for a total of 14 PBS sample cases were included. Per sample case, a single dosimetrist created 4 test plans, gradually reducing the maxMU/spot in the plan. Test Plan 1, unrestricted in maxMU/spot, was the reference for all restricted plan comparisons (comparison sets 2 vs. 1; 3 vs. 1; and 4 vs. 1). The impact of MU/spot restrictions on plan quality metrics were analyzed with Wilcoxon signed rank test analyses. Treatment delivery time was modeled for a representative case., Results: A total of 14 PBS sample cases, 7 (50%) single-field optimized, 7 (50%) multi-field optimized, 9 (64%) delivering > 3500 cGy, 9 (64%) with 3 beams, and 7 (50%) without a range shifter were included. There were no differences in plan quality metrics of target coverage (V95% and V100% prescription), conformality and gradient indices, hot spot volume (V105% prescription), and dose to normal brain (V10%/30%/50%/70%/90%/100% prescription) with reductions of allowable maxMU/spot across all comparison sets (p > 0.05). Max MU/spot restrictions did not increase treatment delivery time when analyzed for a representative case., Conclusion: MaxMU/spot restrictions within the thresholds evaluated in this study did not degrade overall plan quality metrics. Future studies should evaluate spot weighting with linear energy transfer/relative biologic effectiveness-informed planning to determine if spot weighting manipulation impacts clinical outcomes and mitigates toxicity., (Copyright © 2021. Published by Elsevier B.V.)

Purpose: Acute skin toxicity in the form of radiation dermatitis (RD) or skin hyperpigmentation (SH) is a common problem experienced by patients undergoing breast irradiation. Proton radiation has been thought to deliver higher doses to skin compared with photon radiation because of differences in the physical properties between photons and protons; however, limited literature exists directly comparing toxicity outcomes., Methods and Materials: The highest recorded grades of acute RD and SH were analyzed in 86 patients undergoing adjuvant radiation therapy to the breast with or without regional lymph nodes after lumpectomy (breast-conserving surgery) or mastectomy with either proton pencil-beam scanning (n = 39) or photon (n = 47) radiation therapy within a single institution to analyze differences in severity of acute skin reactions. For 34 of 47 photon and 33 of 39 proton patients, a "skin" contour was retroactively created in our treatment planning systems, and multiple dosimetric parameters were calculated to quantify objective radiation doses received by skin., Results: On χ 2 analysis, the highest reported grade of RD was significantly higher in women undergoing proton radiation compared with photon radiation; grade ≥2 RD was present in 69.2% versus 29.8% of patients receiving proton and photon therapy, respectively (P = .002). Rates of grade 3 RD were 5.1% versus 4.3% for proton versus photon radiation, respectively (P = .848). Overall, there were no significant differences in rates of SH between modalities. There were no grade 4 to 5 toxicities in either cohort., Conclusions: In a comparison with patients receiving photon radiation, a significantly higher rate of grade ≥2 RD was observed in patients undergoing proton radiation, with very low rates of grade 3 toxicity in both groups. Rates of SH did not differ significantly between modalities. Women should be counseled regarding the possibility of increased grade 2 toxicities, although this might present a dosimetric advantage for physicians when treating patients in the postmastectomy setting or when skin was involved on presentation., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The regeneration of the electromotor force E of the electric piles formed by two amalgam fillings was measured as a function of time t after the moment of interruption of the short contact of their poles. The measurements were carried out in 30 patients at a mean age of 27.0 +/- 08 years. Automatic recording of the equation E = f (t) demonstrated that in the first phase of from several to about a score of seconds the E value rose rapidly, while in the second phase lasting from several scores to over a thousand seconds the E value approached asymptotically its initial value Eo.

Using an electrogustometric method studies of the taste sensitivity in 112 smokers and 160 non-smokers were carried out. In order to eliminate the effects of age, standardized electrogustometric thresholds of taste perception for 272 subjects were calculated. Then the mean values of those thresholds for smokers and non-smokers and mean square errors of mean values were computed. With Student's difference test is was indicated that the difference between the mean value of standard electrogustometric threshold of taste perception for the non-smoking groups is statistically significant. That means that smoking results in a decreased taste sensitivity, irrespective of the subjects' age.

A study was carried out on the effect of the shape of impulses used in electroanalgesia on the reduction of tothache sensation. The measurements were done in 46 subjects and it was observed that the relative increment of ocurrent voltage producing pain of tooth 13 was after 10 minutes of electroanalgesia with rectangular impulses: P1 = (142.2 +/- 6.8)%, sinusoidal impulses: P2 = (80.6 +/- 6.3)%, and serrate impulses: P3 = (51.0 +/- 4.6)% in relation to the voltage causing pain of the same tooth before electroanalgesia. The mean age of the studied patients: 23.8 +/- 0.3 years. The greatest effect was obtained using rectangular impulses.