PO54

Purpose Low dose rate (LDR) brachytherapy has been proven to be an effective modality for monotherapy treatment of low-intermediate risk prostate cancer. The most commonly used treatment workflow follows a pre-planning approach utilising trans-rectal ultrasound (TRUS) images acquired under sedation, or nomogram planning based on manual measurements of prostate volume and dimensions. This study presents an alternative approach in which diagnostic magnetic resonance images (MRI) are used for the purpose of treatment planning, eliminating the necessity of an additional operating theatre procedure for the purposes of treatment planning, whilst tailoring the plan specifically to the patient's anatomy. Materials and Methods A retrospective study (n=10) was performed comparing the MRI and TRUS pre-planned approaches. The MRI pre-planned approach was retrospectively simulated by creating an LDR brachytherapy plan on diagnostic MR images using the Varian Variseed (v9.0.03) brachytherapy treatment planning system according to local protocols. This plan was then copied onto previously obtained TRUS planning images for the same patient. TRUS and MRI pre-plans were compared by evaluating plan quality metrics such as: the volume of the prostate receiving 100% (V100%), 150% (V150%), and 200% (V200%), dose to 90% of the prostate volume (D90%), as well as the rectum V100%, and urethra V125%. The prescription dose used in each plan was 145 Gy. The number of needles and number of seeds used in each approach was also compared. Statistical significance was tested for via the paired two sides t-test (p < 0.05). A prospective comparison study of operating theatre time usage is ongoing. Results Retrospective comparison of the planning approaches showed no statistically significant differences in plan quality metrics, apart from for the rectum V100%. The TRUS and MRI pre-planned approaches achieved an average rectum V100% of 0.14 cc and 0.33 cc (p = 0.008), respectively. Both approaches easily met the clinical constraint of rectum V100% < 1 cc, and thus the difference between the techniques was not clinically significant. All other plan quality metrics met departmentally defined clinical planning constraints for both the TRUS and MRI planned technique. Preliminary results comparing operating theatre time usage has shown significant time savings using the MRI-pre planning technique. Conclusions The MRI pre-planned approach for LDR prostate brachytherapy has been shown to achieve dosimetrically equivalent plans to TRUS based pre-plans, using less operating theatre resources. This technique is a safe and effective form of LDR prostate brachytherapy treatment planning for eligible patients. Low dose rate (LDR) brachytherapy has been proven to be an effective modality for monotherapy treatment of low-intermediate risk prostate cancer. The most commonly used treatment workflow follows a pre-planning approach utilising trans-rectal ultrasound (TRUS) images acquired under sedation, or nomogram planning based on manual measurements of prostate volume and dimensions. This study presents an alternative approach in which diagnostic magnetic resonance images (MRI) are used for the purpose of treatment planning, eliminating the necessity of an additional operating theatre procedure for the purposes of treatment planning, whilst tailoring the plan specifically to the patient's anatomy. A retrospective study (n=10) was performed comparing the MRI and TRUS pre-planned approaches. The MRI pre-planned approach was retrospectively simulated by creating an LDR brachytherapy plan on diagnostic MR images using the Varian Variseed (v9.0.03) brachytherapy treatment planning system according to local protocols. This plan was then copied onto previously obtained TRUS planning images for the same patient. TRUS and MRI pre-plans were compared by evaluating plan quality metrics such as: the volume of the prostate receiving 100% (V100%), 150% (V150%), and 200% (V200%), dose to 90% of the prostate volume (D90%), as well as the rectum V100%, and urethra V125%. The prescription dose used in each plan was 145 Gy. The number of needles and number of seeds used in each approach was also compared. Statistical significance was tested for via the paired two sides t-test (p < 0.05). A prospective comparison study of operating theatre time usage is ongoing. Retrospective comparison of the planning approaches showed no statistically significant differences in plan quality metrics, apart from for the rectum V100%. The TRUS and MRI pre-planned approaches achieved an average rectum V100% of 0.14 cc and 0.33 cc (p = 0.008), respectively. Both approaches easily met the clinical constraint of rectum V100% < 1 cc, and thus the difference between the techniques was not clinically significant. All other plan quality metrics met departmentally defined clinical planning constraints for both the TRUS and MRI planned technique. Preliminary results comparing operating theatre time usage has shown significant time savings using the MRI-pre planning technique. The MRI pre-planned approach for LDR prostate brachytherapy has been shown to achieve dosimetrically equivalent plans to TRUS based pre-plans, using less operating theatre resources. This technique is a safe and effective form of LDR prostate brachytherapy treatment planning for eligible patients.