Dosimetric comparison of two afterloaders and treatment planning systems in vaginal high-dose-rate brachytherapy.

Purpose: In treatment planning for high-dose-rate (HDR) single-channel vaginal cylinder brachytherapy, dose distribution along the cylinder is influenced by the anisotropy of the source. Differences in anisotropy are due to differences in source dimensions and characteristics. In this study, we compared HDR vaginal cylinder brachytherapy treatment plans from two afterloader/treatment planning systems. Material and methods: Seventy-five plans with prescription to the surface were generated for cylinders in Varian BrachyVision and Elekta Oncentra. To understand the impact of source anisotropy on dose distribution to the surface of the cylinder, potential effect caused by differences in cylinder geometry between systems was eliminated by re-planning Varian cylinder using Elekta source model. Mean relative dose was calculated for each point as well as the dome and length of the cylinder. Related-samples Wilcoxon signed-rank tests were performed to compare the mean relative dose between systems. Results: Treatment plans with VariSource iX source and cylinder demonstrated 16.2% lower (p < 0.001) dose at the tip compared to Elekta v.3. Average dose to the points along the dome of cylinder was 128.4% ±17.9% prescription dose with VariSource iX source and cylinder, and 99.9% ±4.3% with Elekta v.3 source and cylinder. For the same cylinder geometry, the effect of source characteristics produced up to 36.8% difference in dose homogeneity. When cylinder types were planned with the same source, there was no significant difference in dose distribution. Conclusions: This study demonstrates that the effect of source characteristics produced up to 37% difference in dose homogeneity when comparing two afterloader/treatment planning systems, independent of cylinder geometry. This insight on variation in dose surrounding source system is imperative for dosimetry considerations. Depending on the choice of afterloader, the extent of EQD2 for tumor control versus normal tissue toxicity can vary.

Radiation Effects on Methamphetamine Pharmacokinetics and Pharmacodynamics in Rats.

BACKGROUND AND OBJECTIVES: Whole-body radiation exposure has been shown to alter the pharmacokinetics of certain drugs in both animal models and humans, but little is known about the effect of radiation on psychoactive medications. These drugs may have altered pharmacokinetics when administered during or after space travel or therapeutic or accidental radiation exposure, resulting in reduced efficacy or increased toxicity. METHODS: Methamphetamine was used to determine the effects of acutely administered 1, 3, and 6 Gy radiation on drug pharmacokinetics and pharmacodynamics. Male Wistar rats were exposed to 0, 1, 3, or 6 Gy X-ray radiation on day 0. The serum pharmacokinetics of subcutaneously administered 1 mg/kg methamphetamine was determined on day 3. Methamphetamine-induced (1 mg/kg) locomotor activity was measured on day 5. Brain methamphetamine concentrations were determined 2 h after methamphetamine administration (1 mg/kg) on day 6. Renal and hepatic serum biomarkers were assessed on days 3 and 6, with liver histology performed on day 6. RESULTS: While serum half-life and unchanged methamphetamine urine clearance were unaffected by any radiation dose, maximum methamphetamine concentrations and methamphetamine and amphetamine metabolite area under the serum concentration-time curve values from 0 to 300 min were significantly reduced after 6 Gy radiation exposure. Additionally, methamphetamine-induced locomotor activity and the brain to serum methamphetamine concentration ratio were significantly elevated after 6 Gy radiation. CONCLUSIONS: While 1-6 Gy radiation exposure did not affect methamphetamine elimination, 6 Gy exposure had effects on both subcutaneous absorption and brain distribution. These effects should be considered when administering drugs during or after radiation exposure.

Phase 1 Combination Study of the CHK1 Inhibitor Prexasertib and the PARP Inhibitor Olaparib in High-grade Serous Ovarian Cancer and Other Solid Tumors.

PURPOSE: Checkpoint kinase 1 (CHK1) plays a central role in the response to replication stress through modulation of cell-cycle checkpoints and homologous recombination (HR) repair. In BRCA-deficient cancers with de novo or acquired PARP inhibitor resistance, the addition of the CHK1 inhibitor prexasertib to the PARP inhibitor olaparib compromises replication fork stability, as well as HR proficiency, allowing for sensitization to PARP inhibition. PATIENTS AND METHODS: This study followed a 3+3 design with a 7-day lead-in of olaparib alone, followed by 28-day cycles with prexasertib administered on days 1 and 15 in combination with an attenuated dose of olaparib on days 1-5 and 15-19. Pharmacokinetic blood samples were collected after olaparib alone and following combination therapy. Patients enrolled to the expansion phase of the study underwent paired tumor biopsies for pharmacodynamic (PD) assessments. RESULTS: Twenty-nine patients were treated. DLTs included grade 3 neutropenia and grade 3 febrile neutropenia. The MTD/recommended phase 2 dose (RP2D) was prexasertib at 70 mg/m2 i.v. with olaparib at 100 mg by mouth twice daily. Most common treatment-related adverse events included leukopenia (83%), neutropenia (86%), thrombocytopenia (66%), and anemia (72%). Four of 18 patients with BRCA1-mutant, PARP inhibitor-resistant, high-grade serous ovarian cancer (HGSOC) achieved partial responses. Paired tumor biopsies demonstrated reduction in RAD51 foci and increased expression of γ-H2AX, pKAP1, and pRPA after combination exposure. CONCLUSIONS: Prexasertib combined with olaparib has preliminary clinical activity in BRCA-mutant patients with HGSOC who have previously progressed on a PARP inhibitor. PD analyses show that prexasertib compromises HR with evidence of induction of DNA damage and replication stress.

A first radiotherapy application of functional bulboclitoris anatomy, a novel female sexual organ-at-risk, and organ-sparing feasibility study.

OBJECTIVE: The bulboclitoris (clitoris and vestibular bulbs) is the primary organ responsible for female sexual arousal and orgasm. Effects of radiotherapy on the bulboclitoris are unknown, as its structure/function has yet to be described in radiotherapy, and it overlaps only partially with the external genitalia structure. Our aim was to: describe bulboclitoris structure, function and delineation; compare volume of and dose delivered to the bulboclitoris vs external genitalia; and, compare bulboclitoris-sparing IMRT (BCS-IMRT) to standard IMRT (S-IMRT) to determine reoptimization feasibility. METHODS: Our expert team (anatomist, pelvic radiologist, radiation oncologist) reviewed bulboclitoris anatomy and developed contouring guidance for radiotherapy. 20 female patients with anal cancer treated with chemoradiation were analyzed. Sexual organs at risk (OARs) included the external genitalia and the bulboclitoris. Volumes, dice similarity coefficients (DSCs) and dose received using S-IMRT were compared. Plans were reoptimized using BCS-IMRT. Dose-volume histograms (DVHs) for PTVs and all OARs were compared for BCS-IMRT vs S-IMRT. RESULTS: Bulboclitoris structure, function and delineation are described herein. The bulboclitoris occupies 20cc (IQR:12-24), largely distinct from the external genitalia (DSC <0.05). BCS-IMRT was superior to S-IMRT in reducing the dose to the bulboclitoris, with the greatest reductions in V30 and V40, with no significant changes in dose to other OARs or PTV 1/V95. CONCLUSION: The bulboclitoris can be contoured on planning imaging, largely distinct from the external genitalia. Compared with S-IMRT, BCS-IMRT dramatically reduced dose to the bulboclitoris in anal cancer planning. BCS-IMRT might safely reduce sexual toxicity compared with standard approaches. ADVANCES IN KNOWLEDGE: The structure and function of the bulboclitoris, the critical primary organ responsible for female sexual arousal and orgasm, has yet to be described in the radiotherapy literature. Structure, function and delineation of the bulboclitoris are detailed, delineation and bulboclitoris-sparing IMRT were feasible, and sparing reduces the dose to the bulboclitoris nearly in half in female patients receiving IMRT for anal cancer, warranting further clinical study.

Immune modulating activity of the CHK1 inhibitor prexasertib and anti-PD-L1 antibody LY3300054 in patients with high-grade serous ovarian cancer and other solid tumors.

BACKGROUND: Checkpoint kinase 1 (CHK1) has dual roles in both the DNA damage response and in the innate immune response to genotoxic stress. The combination of CHK1 inhibition and immune checkpoint blockade has the potential to enhance anti-tumoral T-cell activation. METHODS: This was an open-label phase 1 study evaluating the CHK1 inhibitor prexasertib and the anti-PD-L1 antibody LY3300054. After a lead-in of LY3300054 (Arm A), prexasertib (Arm B) or the combination (Arm C), both agents were administered intravenously at their respective recommended phase 2 doses (RP2Ds) on days 1 and 15 of a 28-day cycle. Flow cytometry of peripheral blood was performed before and during treatment to analyze effects on immune cell populations, with a focus on T cell subsets and activation. Plasma cytokines and chemokines were analyzed using the Luminex platform. RESULTS: Among seventeen patients enrolled, the combination was tolerable at the monotherapy RP2Ds, 105 mg/m2 prexasertib and 700 mg LY3300054. Dose-limiting toxicities included one episode each of febrile neutropenia (Arm C) and grade 4 neutropenia lasting > 5 days (Arm B). One patient had immune-related AST/ALT elevation after 12 cycles. Three patients with CCNE1-amplified, high-grade serous ovarian cancer (HGSOC) achieved partial response (PR), 2 lasting > 12 months; a fourth such patient maintained stable disease > 12 months. Analysis of peripheral blood demonstrated evidence of CD8 + T-cell activation in response to treatment. CONCLUSIONS: Prexasertib in combination with PD-L1 blockade was tolerable and demonstrated preliminary activity in CCNE1-amplified HGSOC with evidence of cytotoxic T-cell activation in patient blood samples. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03495323. Registered April 12, 2018.

Lhermitte's Sign following VMAT-Based Head and Neck Radiation-Insights into Mechanism.

PURPOSE/OBJECTIVES: We observed a number of patients who developed Lhermitte's sign (LS) following radiation to the head and neck (H/N), since instituting volumetric modulated arc therapy (VMAT). We aimed to investigate the incidence of LS following VMAT-based RT without chemotherapy, and determine the dosimetric parameters that predict its development. We explored whether the role of inhomogeneous dose distribution across the spinal cord, causing a "bath-and-shower" effect, explains this finding. METHODS AND MATERIALS: From 1/20/2010-12/9/2013, we identified 33 consecutive patients receiving adjuvant RT using VMAT to the H/N without chemotherapy at our institution. Patients' treatment plans were analyzed for dosimetric parameters, including dose gradients along the anterior, posterior, right, and left quadrants at each cervical spine level. Institutional Review Board approval was obtained. RESULTS: 5 out of 33 (15.2%) patients developed LS in our patient group, all of whom had RT to the ipsilateral neck only. LS patients had a steeper dose gradient between left and right quadrants across all cervical spine levels (repeated-measures ANOVA, p = 0.030). Within the unilateral treatment group, LS patients received a higher mean dose across all seven cervical spinal levels (repeated-measures ANOVA, p = 0.046). Dose gradients in the anterior-posterior direction and mean doses to the cord were not significant between LS and non-LS patients. CONCLUSIONS: Dose gradients along the axial plane of the spinal cord may contribute to LS development; however, a threshold dose within the high dose region of the cord may still be required. This is the first clinical study to suggest that inhomogeneous dose distributions in the cord may be relevant in humans. Further investigation is warranted to determine treatment-planning parameters associated with development of LS.

Commissioning a 50-100 kV X-ray unit for skin cancer treatment.

This study provides the authors' experience along with dosimetric data from the commissioning of two Sensus SRT-100 50-100 kV X-ray units. Data collected during the commissioning process included: a) HVL, b) output (dose rate), c) applicator cone factors, and d) percentage depth dose. A Farmer-type chamber (PTW-N23333), and a thin-window parallel plate ion chamber (PTW-N23342) were used for dose rate measurements and dose profiles were measured with EBT3 GafChromic film. The average HVL values for 50, 70, and 100 kV of the two treatment units were found to be 0.52, 1.15, and 2.20 mm Al, respectively. The HVL's were 5%-9% lower when measured with the Farmer chamber, as compared to measurements with the parallel plate chamber, for energies of 70 and 100 kV. Dose rates were also measured to be 3%-4% lower with the Farmer chamber. The dose rate variation between the two units was found to be 2%-9% for 50, 70, and 100 kV. The dose uniformity over a circle of 2 cm diameter was within 4% in four cardinal directions; however, the dose profiles for the 5 cm applicator were nonuniform, especially in the cathode-anode direction. Measurements indicated as much as 15% lower dose for the 50 kV beam at field edge on the anode side, when normalized to the center. The crossline profile was relatively more symmetric, with a maximum deviation of 10% at the field edge. All ion chamber readings agreed with film measurements within 3%. The nonuniform profile produced by these units may introduce uncertainty in dose rate measurements, especially for larger applicators. Since there is no intrinsic tool (crosshair or field light) for alignment with the beam axis, the user should take care when positioning the chamber for output measurements. The data obtained with a Farmer-type chamber should be used cautiously and as a reference only for the SRT-100 X-ray treatment unit.