Background. Due to improved visibility on MRI, contouring of the prostate is improved compared to CT. The aim of this study was to quantify the benefits of using MRI for treatment planning as... Show moreBackground. Due to improved visibility on MRI, contouring of the prostate is improved compared to CT. The aim of this study was to quantify the benefits of using MRI for treatment planning as compared to CT-based planning for temporary implant prostate brachytherapy. Material and methods. CT and MRI image data of 13 patients were used to delineate the prostate and organs at risk (OARs) and to reconstruct the implanted catheters (typically 12). An experienced treatment planner created plans on the CT-based structure sets (CT-plan) and on the MRI-based structure sets (MRI-plan). Then, active dwell-positions and weights of the CT-plans were transferred to the MRI-based structure sets (CT-plan(MRI-contours)) and resulting dosimetric parameters and tumour control probabilities (TCPs) were studied. Results. For the CT-plan(MRI-contours) a statistically significant lower target coverage was detected: mean V-100 was 95.1% as opposed to 98.3% for the original plans (p < 0.01). Planning on CT caused cold-spots that influence the TCP. MRI-based planning improved the TCPs by 6-10%, depending on the parameters of the radiobiological model used for TCP calculation. Basing the treatment plan on either CT- or MRI-delineations does not influence plan quality. Conclusion. Evaluation of CT-based treatment planning by transferring the plan to MRI reveals underdosage of the prostate, especially at the base side. Planning on MRI can prevent cold-spots in the tumour and improves the TCP. Show less
Dinkla, A.M.; Pieters, B.R.; Koedooder, K.; Meijnen, P.; Wieringen, N. van; Laarse, R. van der; ... ; Bel, A. 2013
Background and purpose: To determine the uncertainties in planned dose associated with catheter and organ movement during 48 hours of stepping source prostate brachytherapy.Material and methods:... Show moreBackground and purpose: To determine the uncertainties in planned dose associated with catheter and organ movement during 48 hours of stepping source prostate brachytherapy.Material and methods: Pulsed-dose. rate (PDR) prostate brachytherapy as a boost is given in 24 pulses every 2 hours, making the total treatment last 48 hours. The entire treatment is based on one plan, created on the planning CT (CT1). Two follow-up CTs (CT2 and CT3) were acquired; halfway through the treatment and at the end of treatment. On these repeat scans the catheters were reconstructed and PTV and OARs were delineated. The original treatment plan was calculated on the repeat CTs. Target coverage V-100%. D-90, dose to 2 cm(3) (D2cm(3)) of the rectum and bladder and dose to 0.1 cm(3) of the urethra were recorded from the recalculated DVHs.Results: On the two repeat CTs the V-100% decreased -1.5% and -2.3% as compared to the planning CT. For the rectum D2cm(3), the average increase was 14.8% (CT1-CT2) and 173% (CT1-CT3.). Increase in bladder D2cm(3) was on average 23.1% (CT1-CT2) and 24.8% (CT1-CT3). For the urethra D0.1cm(3) an average decrease of -2% (CT1-CT2) and -3.2% (CT2-CT3) was observed.Conclusions: Changes in target coverage during treatment were small and considered clinically irrelevant. However, an overall increase in dose to the OARs was found as compared to the planned dose, which should be taken into account during treatment planning. (C) 2012 Elsevier Ireland Ltd. All rights reserved. Show less
