What Can Proton Beam Therapy Achieve for Patients with Pectus Excavatum Requiring Left Breast, Axilla and Internal Mammary Nodal Radiotherapy?

AIMS

Exposure of the heart to radiation increases the risk of ischaemic heart disease, proportionate to the mean heart dose (MHD). Radiotherapy techniques including proton beam therapy (PBT) can reduce MHD. The aims of this study were to quantify the MHD reduction achievable by PBT compared with volumetric modulated arc therapy in breath hold (VMAT-BH) in patients with pectus excavatum (PEx), to identify an anatomical metric from a computed tomography scan that might indicate which patients will achieve the greatest MHD reductions from PBT.

MATERIALS AND METHODS

Sixteen patients with PEx (Haller Index ≥2.7) were identified from radiotherapy planning computed tomography images. Left breast/chest wall, axilla (I-IV) and internal mammary node (IMN) volumes were delineated. VMAT and PBT plans were prepared, all satisfying target coverage constraints. Signed-rank comparisons of techniques were undertaken for the mean dose to the heart, ipsilateral lung and contralateral breast. Spearman's rho correlations were calculated for anatomical metrics against MHD reduction achieved by PBT.

RESULTS

The mean MHD for VMAT-BH plans was 4.1 Gy compared with 0.7 Gy for PBT plans. PBT reduced MHD by an average of 3.4 Gy (range 2.8-4.4 Gy) compared with VMAT-BH (P < 0.001). PBT significantly reduced the mean dose to the ipsilateral lung (4.7 Gy, P < 0.001) and contralateral breast (2.7 Gy, P < 0.001). The distance (mm) at the most inferomedial extent of IMN volume (IMN to heart distance) negatively correlated with MHD reduction achieved by PBT (Spearman's rho -0.88 (95% confidence interval -0.96 to -0.67, P < 0.001)).

CONCLUSION

For patients with PEx requiring left-sided breast and IMN radiotherapy, a clinically significant MHD reduction is achievable using PBT, compared with the optimal photon technique (VMAT-BH). This is a patient group in whom PBT could have the greatest benefit.

A first-in-man phase I study of R306465, a histone deacetylase (HDAC) inhibitor exploring pharmacokinetics (PK) and pharmacodynamics (PD) utilizing an electrochemiluminescent immunoassay in patients (p) with advanced tumours

3578

Background: R306565 is an aromatic hydroxamic acid with predominant inhibitory effects on Class 1 HDAC enzymes (with IC50 ∼10 nM). HDAC inhibitors (HDACi) affect gene expression at the transcriptional level, leading to cell cycle arrest and induction of apoptosis. Methods: P with solid tumours or lymphoma were given R306465 orally daily for 3 weeks (w) out of 4 in an escalating schedule. Objectives include safety, tolerability, PK (including food effect exploration), PD evaluation and circulating tumour cell (CTC) quantitation. Results: Four dose levels (100, 200, 300 and 400 mg) have been evaluated involving 15 p (7 male), age range 29–72 (median 59 y) and ECOG PS 0–2. A total of 37 cycles have been administered. Most common adverse events (AE) were Grade (G) 1–3 fatigue (87%), G1–2 nausea (66%), G1–2 vomiting (33%), G1–2 diarrhoea (40%), and G1–2 anorexia (40%). Dose limiting toxicity of G3 fatigue was seen in 1/6 p in the 400mg cohort. PK parameters were approximately dose proportional. Plasma concentrations increased in the fed state. PD effect of histone H3 acetylation (AcH3) in peripheral blood mononuclear cells (PBMC) was determined quantitatively with a novel validated electrochemiluminescent immunoassay developed in-house (applying Mesoscale Discovery technology). Although some interpatient variability exists, increased AcH3 was observed in 2/6 p in the 400 mg cohort, while the percentage rise in AcH3 was minimal for cohorts 1–3. Peak AcH3 achieved in 2 p dosed at 400 mg was approximately 5–10 fold increase over baseline. Using CellSearch technology for quantitation of CTCs, 8/14 p had detectable CTCs at baseline; the CTC trend will be presented. 4 p had stable disease (SD) for = 4 months. Conclusions: R306465 could be safely administered on a daily dosing schedule for 3 of 4 w up to 400 mg. Common toxicities seen were gastrointestinal and fatigue. Maximum tolerated dose has not been reached. PK suggests dose proportionality. Promising PD data showing increased acetylation in PBMC at 400 mg, further supports the utilization of the immunoassay platform in HDACi clinical trials.

No significant financial relationships to disclose.

An open, pharmacokinetic (PK) and mass balance study of 14C-AZD2171, incorporating DCE-CT evaluations

14140

Background: AZD2171 is an oral, highly potent and selective VEGF signaling inhibitor in clinical development. Methods: Patients with solid metastatic tumors received a single radiolabeled oral dose of 14C- AZD2171 45 mg; blood samples and all excretions were collected for evaluating the PK and metabolic profiles. After sufficient radioactivity recovery, patients started once-daily oral dosing with AZD2171 30 mg. The primary objective of the study was to determine the rates and routes of excretion of AZD2171 using 14C-AZD2171. Efficacy (RECIST), safety and tolerability were secondary objectives. The potential effects of AZD2171 on DCE-CT vascular parameters were also explored. Results: Six patients received treatment and remained on study for 64–171 days. In 5/6 patients, the amount of radioactivity recovered in the urine and feces samples within 168-hours post- dosing ranged from 84.8–93.0%; the analogous amount in the remaining patient was only 34.1%. In all patients, mean radioactivity recovered was 58.8% in feces and 20.8% in urine. Radioactivity appeared to be confined to plasma. Three patients (2 renal cell carcinoma; 1 mesothelioma) had a best RECIST response of stable disease (SD); 1 patient had a confirmed reduction in max tumor diameter of 10% to <30%. Two patients had progressive disease and 1 patient was non-evaluable. The most common adverse events (AEs) were diarrhea (n=5) and hypertension (n=3); no grade 3 or 4 AEs occurred more than once. There was evidence of reductions in DCE-CT parameters post treatment, particularly perfusion, permeability surface product (PSP) and positive enhancement integral. For each of these parameters, a decrease from baseline outside the baseline reference range was recorded for 3 patients (including 2 with SD) at 1 month after the start of daily dosing of AZD2171. Overall, within-patient variability (W-PV) was generally low for all DCE-CT parameters measured and was consistently lower than between-patient variability. The W-PV was largest for PSP (18%) and lowest for mean transit time (7%). Conclusions: The primary route of AZD2171 elimination appears to be hepatic. AZD2171 was well tolerated and clinically meaningful disease stabilization was seen. Changes in tumor vascular parameters were detected by DCE-CT.

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