In vivo thermoluminescence dosimetry dose verification of transperineal 192Ir high-dose-rate brachytherapy using CT-based planning for the treatment of prostate cancer

PURPOSE: To evaluate the potential of in vivo thermoluminescence dosimetry to estimate the accuracy of dose delivery in conformal high-dose-rate brachytherapy of prostate cancer. METHODS AND MATERIALS: A total of 50 LiF, TLD-100 cylindrical rods were calibrated in the dose range of interest and used as a batch for all fractions. Fourteen dosimeters for every treatment fraction were loaded in a plastic 4F catheter that was fixed in either one of the 6F needles implanted for treatment purposes or in an extra needle implanted after consulting with the patient. The 6F needles were placed either close to the urethra or in the vicinity of the median posterior wall of the prostate. Initial results are presented for 18 treatment fractions in 5 patients and compared to corresponding data calculated using the commercial treatment planning system used for the planning of the treatments based on CT images acquired postimplantation. RESULTS: The maximum observed mean difference between planned and delivered dose within a single treatment fraction was 8.57% +/- 2.61% (root mean square [RMS] errors from 4.03% to 9.73%). Corresponding values obtained after averaging results over all fractions of a patient were 6.88% +/- 4.93% (RMS errors from 4.82% to 7.32%). Experimental results of each fraction corresponding to the same patient point were found to agree within experimental uncertainties. CONCLUSIONS: Experimental results indicate that the proposed method is feasible for dose verification purposes and suggest that dose delivery in transperineal high-dose-rate brachytherapy after CT-based planning can be of acceptable accuracy.     

Diffusion-weighted MR imaging including bi-exponential fitting for the detection of recurrent or residual tumour after (chemo)radiotherapy for laryngeal and hypopharyngeal cancers

Objectives

To assess whether diffusion-weighted magnetic resonance imaging (DW-MRI) including bi-exponential fitting helps to detect residual/recurrent tumours after (chemo)radiotherapy of laryngeal and hypopharyngeal carcinoma.

Methods

Forty-six patients with newly-developed/worsening symptoms after (chemo)radiotherapy for laryngeal/hypopharyngeal cancers were prospectively imaged using conventional MRI and axial DW-MRI. Qualitative (visual assessment) and quantitative analysis (mono-exponentially: total apparent diffusion coefficient [ADC_T], and bi-exponentially: perfusion fraction [F_P] and true diffusion coefficient [ADC_D]) were performed. Diffusion parameters of tumour versus post-therapeutic changes were compared, with final diagnosis based on histopathology and follow-up. Mann-Whitney U test was used for statistical analysis.

Results

Qualitative DW-MRI combined with morphological images allowed the detection of tumour with a sensitivity of 94% and specificity 100%. ADC_T and ADC_D values were lower in tumour with values 120 ± 49 × 10⁻⁵ mm²/s and 113 ± 50 × 10⁻⁵ mm²/s, respectively, compared with post-therapeutic changes with values 182 ± 41 × 10⁻⁵ mm²/s (P < 0.0002) and 160 ± 47 × 10⁻⁵ mm²/s (P < 0.003), respectively. F_P values were significantly lower in tumours than in non-tumours (13 ± 9% versus 31 ± 16%, P < 0.0002), with F_P being the best quantitative parameter for differentiation between post-therapeutic changes and recurrence.

Conclusions

DW-MRI in combination with conventional MRI substantially improves detection and exclusion of tumour in patients with laryngeal and hypopharyngeal cancers after treatment with (chemo)radiotherapy on both qualitative and quantitative analysis, with F_P being the best quantitative parameter in this context.

Key Points

• DW-MRI is increasingly used to detect tumour recurrence.

• DW-MRI allows accurate post-treatment recurrence detection in laryngeal or hypopharyngeal cancer

• ADC values in recurrent tumour are lower than in benign tissue alterations

• Both qualitative and quantitative DW-MRI approaches allow detection of recurrence

• DW-MRI can easily be added to daily clinical routine imaging