Assessment of radionuclide impurities in [18F]fluoromethylcholine ([18F]FMCH)

PURPOSE

[¹⁸F]Fluoromethylcholine ([¹⁸F]FMCH) is a radiopharmaceutical used in positron emission tomography (PET) imaging for the study of prostate, breast, and brain tumors. It is usually synthesized in cyclotron facilities where ¹⁸F is produced by proton irradiation of [¹⁸O]H₂O through ¹⁸O(p,n)¹⁸F reaction. Due to the activation of target materials, the bombardment causes unwanted radionuclidic impurities in [¹⁸O]H₂O, that need to be removed during the radiopharmaceutical synthesis. Thus, the aim of this study is to quantify the radionuclide impurities in the ¹⁸F production process and in the synthesized [¹⁸F]FMCH, demonstrating the radionuclidic purity of this radiopharmaceutical.

METHODS

Long-lived radionuclide impurities were experimentally assessed using high-resolution gamma and liquid scintillation spectrometries, while short-lived impurities were monitored analyzing the decay curve of the irradiated [¹⁸O]H₂O with an activity calibrator. As spectrometric radionuclide library, a Geant4 Monte Carlo simulation of the ¹⁸F-target assembly was previously performed.

RESULTS

³H, ^52,54Mn, ^56,57,58Co, ^95m,96Tc, ¹⁰⁹Cd, and ¹⁸⁴Re were found in the irradiated [¹⁸O]H₂O, but no radionuclide was found in the non-irradiated [¹⁸O]H₂O neither in the final [¹⁸F]FMCH solution with an activity concentration greater than the minimum detectable activity concentration. A total impurity activity <6.2 kBq was measured in the irradiated [¹⁸O]H₂O, whereas a [¹⁸F]FMCH radionuclide purity >99.9999998% was estimated. Finally, the decay curve of the irradiated [¹⁸O]H₂O revealed a very low maximum of ¹³N activity (<0.03% of ¹⁸F) even immediately after the end of bombardment.

CONCLUSIONS

This study demonstrated the radionuclidic purity of [¹⁸F]FMCH according to the EU Pharmacopeia.

Evaluation of equivalent dose to eye lens through dose equivalent Hp(3)

PURPOSE

Individual dosimetry allows to quantify doses from ionizing radiation of exposed workers. Scientific and epidemiological evidences highlight the need for adequate measures for a greater protection of the eye and a reduction in annual doses. ICRP Publication 103, illustrating the operational dose quantity Hp(d) for the individual monitoring, proposes a depth d = 3 mm for eye lens monitoring, indicating that even the Hp(0.07) can be used. In this study, it was investigated if there are differences in the evaluation of the equivalent dose to eye lens (H_lens) using Hp(3) or Hp(0.07).

MATERIALS AND METHODS

A slab phantom calibration was performed by an Accredited Calibration Laboratory in terms of Hp(3) and Hp(0.07) using ext-rad TLD-100 (LiF:Mg,Ti) dosimeters. Hp(0.07) and Hp(3) were measured for 26 exposed workers to assess H_lens. The measuring took place monthly in 2017 to obtain both semestral and annual doses.

RESULTS

H_lens(0.07) was always smaller than H_lens(3). However, the differences were not statistically significant (Mann-Whitney test, p > 0.05) for both semestral and annual doses. The percentage differences were 7 ± 3%, 6 ± 3% and 7 ± 2% for I semester, II semester and whole year, respectively. The mean underestimation index <10%, intra-class correlation coefficient >0.99, coefficient of variation <3% and the excellent correlation (R² ≈ 0.999) for both semestral and annual doses highlighted that Hp(0.07) can be used to evaluate H_lens instead of Hp(3).

CONCLUSIONS

No statistical evidence was found that the use of Hp(0.07) underestimates the equivalent dose to eye lens obtained through Hp(3).

Potential skin morbidity reduction with intensity-modulated proton therapy for breast cancer with nodal involvement

Background: Different modern radiation therapy treatment solutions for breast cancer (BC) and regional nodal irradiation (RNI) have been proposed. In this study, we evaluate the potential reduction in radiation-induced skin morbidity obtained by intensity modulated proton therapy (IMPT) compared with intensity modulated photon therapy (IMXT) for left-side BC and RNI. Material and Methods: Using CT scans from 10 left-side BC patients, treatment plans were generated using IMXT and IMPT techniques. A dose of 50 Gy (or Gy [RBE] for IMPT) was prescribed to the target volume (involved breast, the internal mammary, supraclavicular, and infraclavicular nodes). Two single filed optimization IMPT (IMPT₁ and IMPT₂) plans were calculated without and with skin optimization. For each technique, skin dose-metrics were extracted and normal tissue complication probability (NTCP) models from the literature were employed to estimate the risk of radiation-induced skin morbidity. NTCPs for relevant organs-at-risk (OARs) were also considered for reference. The non-parametric Anova (Friedman matched-pairs signed-rank test) was used for comparative analyses. Results: IMPT improved target coverage and dose homogeneity even if the skin was included into optimization strategy (HI_IMPT2 = 0.11 vs. HI_IMXT = 0.22 and CI_IMPT2 = 0.96 vs. CI_IMXT = 0.82, p < .05). A significant relative skin risk reduction (RR = NTCP_IMPT/NTCP_IMXT) was obtained with IMPT₂ including the skin in the optimization with a RR reduction ranging from 0.3 to 0.9 depending on the analyzed skin toxicity endpoint/model. Both IMPT plans attained significant OARs dose sparing compared with IMXT. As expected, the heart and lung doses were significantly reduced using IMPT. Accordingly, IMPT always provided lower NTCP values. Conclusions: IMPT guarantees optimal target coverage, OARs sparing, and simultaneously minimizes the risk of skin morbidity. The applied model-based approach supports the potential clinical relevance of IMPT for left-side BC and RNI and might be relevant for the setup of cost-effectiveness evaluation strategies based on NTCP predictions, as well as for establishing patient selection criteria.

Skin toxicity after chest wall/breast plus level III-IV lymph nodes treatment with helical tomotherapy

INTRODUCTION

To evaluate the incidence of toxicity in breast cancer with helical tomotherapy (HT).

MATERIALS AND METHODS

51 patients with breast cancer were assigned to postoperative radiotherapy by means of HT to the chest wall/breast plus draining nodes. During HT treatment, toxicity was monitored and were assessed using the Common Terminology Criteria for Adverse Events 4.0 scale.

RESULTS

Acute skin G3 toxicity observed in 1.9% cases. No acute or late G4 toxicity was observed. At a median follow-up of 21 months 2 patients have late G1 toxicity.

CONCLUSIONS

HT was associated with a low incidence of low-grade skin toxicity.

Is volumetric modulated arc therapy with constant dose rate a valid option in radiation therapy for head and neck cancer patients?

Background

Intensity-modulated radiotherapy (IMRT) improves dose distribution in head and neck (HN) radiation therapy. Volumetric-modulated arc therapy (VMAT), a new form of IMRT, delivers radiation in single or multiple arcs, varying dose rates (VDR-VMAT) and gantry speeds, has gained considerable attention. Constant dose rate VMAT (CDR-VMAT) associated with a fixed gantry speed does not require a dedicated linear accelerator like VDR-VMAT. The present study explored the feasibility, efficiency and delivery accuracy of CDR-VMAT, by comparing it with IMRT and VDR-VMAT in treatment planning for HN cancer.

Methods and materials

Step and shoot IMRT (SS-IMRT), CDR-VMAT and VDR-VMAT plans were created for 15 HN cancer patients and were generated by Pinnacle³ TPS (v 9.8) using 6 MV photon energy. Three PTVs were defined to receive respectively prescribed doses of 66 Gy, 60 Gy and 54 Gy, in 30 fractions. Organs at risk (OARs) included the mandible, spinal cord, brain stem, parotids, salivary glands, esophagus, larynx and thyroid. SS-IMRT plans were based on 7 co-planar beams at fixed gantry angles. CDR-VMAT and VDR-VMAT plans, generated by the SmartArc module, used a 2-arc technique: one clockwise from 182° to 178° and the other one anti-clockwise from 178° to 182°. Comparison parameters included dose distribution to PTVs (D_mean, D_2%, D_50%, D_95%, D_98% and Homogeneity Index), maximum or mean doses to OARs, specific dose-volume data, the monitor units and treatment delivery times.

Results

Compared with SS-IMRT, CDR-VMAT significantly reduced the maximum doses to PTV1 and PTV2 and significantly improved all PTV3 parameters, except D_98% and D_95%. It significantly spared parotid and submandibular glands and was associated with a lower D_mean to the larynx. Compared with VDR-VMAT, CDR-VMAT was linked to a significantly better D_mean, to the PTV3 but results were worse for the parotids, left submandibular gland, esophagus and mandible. Furthermore, the D_mean to the larynx was also worse. Compared with SS-IMRT and VDR-VMAT, CDR-VMAT was associated with higher average monitor unit values and significantly shorter average delivery times.

Conclusions

CDR-VMAT appeared to be a valid option in Radiation Therapy Centers that lack a dedicated linear accelerator for volumetric arc therapy with variable dose-rates and gantry velocities, and are unwilling or unable to sanction major expenditure at present but want to adopt volumetric techniques.

Comparing four radiotherapy techniques for treating the chest wall plus levels III-IV draining nodes after breast reconstruction

OBJECTIVE

To compare the dosimetric outcomes of four radiotherapy (RT) techniques for treating the chest wall plus draining nodes after mastectomy and breast reconstruction.

METHODS

Three-dimensional conformal radiotherapy, linac-based intensity modulated RT, helical tomotherapy (HT) and direct tomotherapy treatments were planned for 40 breast cancer patients. Dose prescription was 50 Gy. Plans were compared in terms of doses to the planning target volume, organs at risk and the homogeneity index. The non-parametric Friedman test for paired data and the Conover post hoc analysis were used for data analysis.

RESULTS

HT provided the highest D90 and D98% and the lowest HI, V107% and D2%. HT was associated with the lowest D2% and V25 Gy to the heart in left-sided treatments but the mean cardiac dose was highest. HT provided the highest V5 Gy and V20 Gy to the ipsilateral lung, but the V30 Gy was lower. The contralateral breast and lung were more exposed with HT.

CONCLUSION

The present dosimetric study together with daily use of CT-MV image guided RT have led us to opt for HT after mastectomy and breast reconstruction and to draw up a suitable protocol for treating the chest wall and levels III and IV draining nodes. Advances in knowledge: HT is a suitable for treating the chest wall and levels III and IV draining nodes.

Comparison of Helical Tomotherapy and Direct Tomotherapy in Bilateral Whole Breast Irradiation in a Case of Bilateral Synchronous Grade 1 and Stage 1 Breast Cancer

Patient: Female, 60

Final Diagnosis: Complete remission

Symptoms: None

Medication: —

Clinical Procedure: Radiotherapy

Specialty: Oncology

Helical tomotherapy for duodenal adenocarcinoma in an elderly patient: A case report

To evaluate the efficacy and feasibility of external beam radiotherapy (EBRT) for duodenal adenocarcinoma in an 84-year-old female who underwent EBRT (2.2 Gy/d for a total dose of 46.2 Gy) using helical tomotherapy (HT). Toxicity was evaluated on the National Cancer Institute’s common toxicity criteria (CTCAE 3.0). The patient completed the treatment without G3-G4 toxicity. After 22-mo follow-up, she is alive and well, in complete remission with no late side effects. HT seems to be feasible and effective for duodenal adenocarcinoma in old to very old patients.