International Journal of Particle Therapy最新文献

Sexual dysfunction is a common toxicity and detrimental for the quality of life of women treated with chemoradiotherapy for anal cancer. Sexual dysfunction occurs because the vagina is closely approximated to the anal canal and typically receives substantial doses of radiation. Strategies for mitigation have largely been focused on posttreatment therapy and symptom management. The use of daily vaginal dilator placement during radiotherapy to mitigate dose to the vagina has been previously explored with modest gains, while proton therapy is under active investigation for the treatment of anal cancer. Use of proton therapy for anal cancer reduces dose to some organs at risk but may inadvertently increase vaginal toxicity if the proton beam terminates in the vaginal tissue. Herein, we present the case histories of 2 women treated for squamous cell carcinoma of the anal canal with the novel combination of intensity-modulated proton therapy and daily vaginal dilator placement to maximally reduce dose to the vagina and protect it from areas of increased energy deposition at the end of the proton range.

Purpose: The purpose of this work is to study the feasibility of using an XRV-124 scintillation detector in measuring the collinearity of the x-ray system and uniform scanning proton beam.

Methods: A brass aperture for Snout 10 was manufactured. The center of the aperture had an opening of 1 cm in diameter (4 cm for the film measurements). The 2D kV x-ray images of the XRV-124 were acquired such that the marker inside the detector is aligned to the imaging isocenter. After obtaining the optimal camera settings, a uniform scanning proton beam was delivered for various ranges (12 g/cm² to 28 g/cm² in step size of 2 g/cm²). For each range, 10 monitor units (MU) of the first layer were delivered to the XRV-124 detector. Collinearity tests were repeated by using EDR2 and EBT3 films following our current quality assurance protocol in practice. The results from the XRV-124 measurements were compared against the collinearity results from EDR2 and EBT3 films.

Results and discussion: The collinearity results were evaluated in the horizontal (x) and vertical (y) directions. The average deviation in collinearity in the x-direction was -0.24 ± 0.30 mm, 0.57 ± 0.39 mm, and -0.27 ± 0.14 mm for EDR2, EBT3, and XRV-124, respectively. In the y-direction, the average deviation was 0.39 ± 0.07 mm, 0.29 ± 0.14 mm, and 0.39 ± 0.03 mm for EDR2, EBT3, and XRV-124, respectively.

Conclusion: The measurement results from the XRV-124 and films are in good agreement. Compared to film, the use of the XRV-124 detector for collinearity measurements in uniform scanning protons is more efficient and provides results in real time.

Purpose: Proton beam radiotherapy (PBT) has been used for the definitive treatment of localized prostate cancer with low rates of high-grade toxicity and excellent patient-reported quality-of-life metrics. Technological advances such as pencil beam scanning (PBS), Monte Carlo dose calculations, and polyethylene glycol gel rectal spacers have optimized prostate proton therapy. Here, we report the early clinical outcomes of patients treated for localized prostate cancer using modern PBS-PBT with hydrogel rectal spacing and fiducial tracking without the use of endorectal balloons.

Materials and methods: This is a single institutional review of consecutive patients treated with histologically confirmed localized prostate cancer. Prior to treatment, all patients underwent placement of fiducials into the prostate and insertion of a hydrogel rectal spacer. Patients were typically given a prescription dose of 7920 cGy at 180 cGy per fraction using a Monte Carlo dose calculation algorithm. Acute and late toxicity were evaluated using the Common Terminology Criteria for Adverse Events (CTCAE), version 5. Biochemical failure was defined using the Phoenix definition.

Results: From July 2018 to April 2020, 33 patients were treated (median age, 75 years). No severe acute toxicities were observed. The most common acute toxicity was urinary frequency. With a median follow-up of 18 months, there were no high-grade genitourinary late toxicities; however, one grade 3 gastrointestinal toxicity was observed. Late erectile dysfunction was common. One treatment failure was observed at 21 months in a patient treated for high-risk prostate cancer.

Conclusion: Early clinical outcomes of patients treated with PBS-PBT using Monte Carlo-based planning, fiducial placement, and rectal spacers sans endorectal balloons demonstrate minimal treatment-related toxicity with good oncologic outcomes. Rectal spacer stabilization without the use of endorectal balloons is feasible for the use of PBS-PBT.

Purpose: To present quantitative dosimetric evaluations of five proton pencil beam spot placement techniques.

Materials and methods: The spot placement techniques that were investigated include two grid-based (rectilinear grid and hexagonal grid, both commonly available in commercial planning systems) and three boundary-contoured (concentric contours, hybrid, and optimized) techniques. Treatment plans were created for two different target volumes, one spherical and one conical. An optimal set of planning parameters was defined for all treatment plans and the impact of spot placement techniques on the plan quality was evaluated in terms of lateral/distal dose falloff, normal tissue sparing, conformity and homogeneity of dose distributions, as well as total number of spots used.

Results: The results of this work highlight that for grid-based spot placement techniques, the dose conformity is dependent on target cross-sectional shape perpendicular to beam direction, which changes for each energy layer. This variable conformity problem is mitigated by using boundary contoured spot placement techniques. However, in the case of concentric contours, the conformity is improved but at the cost of decreased homogeneity inside the target. Hybrid and optimized spot placement techniques, which use contoured spots at the boundary and gridlike interior spot patterns, provide more uniform dose distributions inside the target volume while maintaining the improved dose conformity. The optimized spot placement technique improved target coverage, homogeneity of dose, and minimal number of spots. The dependence of these results on spot size is also presented for both target shapes.

Conclusion: This work illustrates that boundary-contoured spot placement techniques offer marked improvement in dosimetry metrics when compared to commercially available grid-based techniques for a range of proton scanned beam spot sizes.

Introduction: A subset of metastatic breast cancer patients present with oligometastatic disease involving the sternum. Given the proximity to traditional target structures, a proton radiation field can be expanded to include this region, providing definitive therapy for patients who are otherwise metastatic. We evaluated the feasibility and outcomes of a small series of patients who received comprehensive nodal irradiation inclusive of an isolated sternal metastasis using proton pencil beam scanning.

Materials and methods: Four patients with a diagnosis of metastatic breast cancer with an isolated metastasis to the sternum received multimodality therapy with curative intent and then underwent adjuvant pencil beam scanning with definitive treatment to the sternum. Dosimetric parameters and treatment outcomes were evaluated.

Results: With respect to treatment coverage, proton therapy was able to deliver comprehensive target structure coverage while maintaining modest doses to the organs at risk compared with photon techniques. At a median follow-up of 28 months from diagnosis, none of the patients have experienced relapse within the radiation portal or developed additional sites of metastatic disease.

Conclusion: Pencil beam scanning for oligometastatic breast cancer with isolated sternal lesions appears feasible without undue normal tissue exposure. Current treatment outcomes appear promising.