Dosimetry modeling for focal low-dose-rate prostate brachytherapy
Menée sur 9 patients atteints d'un cancer de la prostate, cette étude évalue la faisabilité de trois schémas d'irradiation (irradiation de l'ensemble ou de la moitié de la glande, irradiation ciblant les lésions uniquement) dans le cadre d'une curiethérapie à faible débit de dose
Purpose/Objectives(s) : Focal brachytherapy targeted to individual lesion(s) within the prostate may reduce side-effects experienced with whole-gland brachytherapy. The outcomes of a consensus meeting on focal prostate brachytherapy were used to investigate optimal dosimetry of focal low-dose-rate (LDR) prostate brachytherapy targeted using multi-parametric magnetic resonance imaging (mp-MRI) and transperineal template prostate mapping biopsy (TPM), including the effects of random and systematic seed displacements and inter seed attenuation (ISA). Methods and Materials : Nine patients were selected according to clinical characteristics and concordance of TPM and mp-MRI. Retrospectively, three treatment plans were analyzed for each case: whole-gland (WG), hemi-gland (HEMI) and ultra-focal (UF), with 145 Gy prescription dose and identical dose constraints for each plan. Plan robustness to seed displacement and ISA were assessed using Monte Carlo simulations. Results : WG, HEMI and UF plans used mean 28 needles and 81 seeds, 17 needles and 56 seeds and 12 needles and 25 seeds, respectively. Mean D90 and V100 were 181.3 Gy and 99.8% for the prostate in WG plans, 195.7 Gy and 97.8% for the hemi-prostate in HEMI plans and 218.3 Gy and 99.8% for the focal target in UF plans. Mean Urethra D10 was 205.9 Gy, 191.4 Gy and 92.4 Gy in WG, HEMI and UF plans, respectively. Mean Rectum D2cm3 was 107.5 Gy, 77.0 Gy and 42.7 Gy in WG, HEMI and UF plans, respectively. Focal plans were more sensitive to seed displacement errors: random shifts with standard deviation 4 mm reduced mean target D90 by 14.0%, 20.5% and 32.0% for WG, HEMI and UF plans, respectively. ISA has similar impact on DVH parameters for all plan types. Conclusions : Treatment planning for focal LDR brachytherapy is feasible. Dose constraints are easily met with a notable reduction to organs at risk. Treating smaller targets makes seed positioning more critical.
http://www.redjournal.org/article/S0360-3016(15)00249-7/abstract