[en] Highlights: • Of 180 patients who received 19 Gy high-dose-rate brachytherapy (HDR-BT) for localised prostate cancer, with a median follow up of 36 months, 19 (10.6%) patients developed biochemical recurrence of which 13 had a local relapse, including 7 at the site of dominant intraprostatic nodule (DIL). • The 19 biochemical recurrences (failures) were matched to 19 control patients, who were matched to pre-treatment CTV size, Gleason score, T stage, risk category and presence of a DIL. For these patients, clinical and dosimetric parameters were analysed to see if there were any predictors for biochemical recurrence, local recurrence or recurrence within the DIL. • There were no statistically significant differences in all OARs, CTV, PTV and DIL dosimetric parameters between the failures and controls. • In univariate analysis, there were no statistically significant clinical or dosimetric parameters that predicted for biochemical progression free survival, local recurrence free survival or DIL recurrence free survival. • Whilst a large proportion of patients recur at the site of original disease, and these results may support rationale for further dose escalation, in our cohort actual dose delivered to DIL was around 26 Gy. Other studies employing dose escalation to whole gland or focal boost have failed to show improved clinical outcomes to justify this approach, hence HDR-BT should be undertaken using a minimum of two fractions. Long-term follow up of single dose high-dose rate brachytherapy (HDR BT) for localised prostate cancer has revealed higher than expected rates of biochemical and local failure. This study aimed (i) to investigate the pattern of relapse within the prostate with reference to the initial site of disease in those patients; and (ii) to examine if there were any relationships between the HDR BT dosimetric parameters to these areas of recurrence.

[en] Purpose: To develop a methodology for the use of a commercial detector array in dosimetry audits of rotational radiotherapy. Materials and methods: The methodology was developed as part of the development of a national audit of rotational radiotherapy. Ten cancer centres were asked to create a rotational radiotherapy treatment plan for a three-dimensional treatment-planning-system (3DTPS) test and audited. Phantom measurements using a commercial 2D ionisation chamber (IC) array were compared with measurements using 0.125 cm³ IC, Gafchromic film and alanine pellets in the same plane. Relative and absolute gamma index (γ) comparisons were made for Gafchromic film and 2D-Array planes, respectively. Results: Comparisons between individual detectors within the 2D-Array against the corresponding IC and alanine measurement showed a statistically significant concordance correlation coefficient (both ρ_c > 0.998, p < 0.001) with mean difference of −1.1 ± 1.1% and −0.8 ± 1.1%, respectively, in a high dose PTV. In the γ comparison between the 2D-Array and film it was that the 2D-Array was more likely to fail planes where there was a dose discrepancy due to the absolute analysis performed. Conclusions: It has been found that using a commercial detector array for a dosimetry audit of rotational radiotherapy is suitable in place of standard systems of dosimetry

[en] Background: Rotational IMRT (VMAT and Tomotherapy) has now been implemented in many radiotherapy centres. An audit to verify treatment planning system modelling and treatment delivery has been undertaken to ensure accurate clinical implementation. Material and methods: 34 institutions with 43 treatment delivery systems took part in the audit. A virtual phantom planning exercise (3DTPS test) and a clinical trial planning exercise were planned and independently measured in each institution using a phantom and array combination. Point dose differences and global gamma index (γ) were calculated in regions corresponding to PTVs and OARs. Results: Point dose differences gave a mean (±sd) of 0.1 ± 2.6% and 0.2 ± 2.0% for the 3DTPS test and clinical trial plans, respectively. 34/43 planning and delivery combinations achieved all measured planes with >95% pixels passing γ < 1 at 3%/3 mm and rose to 42/43 for clinical trial plans. A statistically significant difference in γ pass rates (p < 0.01) was seen between planning systems where rotational IMRT modelling had been designed for the manufacturer’s own treatment delivery system and those designed independently of rotational IMRT delivery. Conclusions: A dosimetry audit of rotational radiotherapy has shown that TPS modelling and delivery for rotational IMRT can achieve high accuracy of plan delivery