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703 poster COMBINED RADIOTHERAPY OF PROSTATE CANCER: HDR BOOST VS LDR BOOST.
B RACHYTHERAPY: P ROSTATE C ANCER
703 poster COMBINED RADIOTHERAPY OF PROSTATE CANCER: HDR BOOST VS LDR BOOST. I. Albitskiy1 , A. Vinikovetskaya2 1 RUSSIAN S CIENTIFIC C ENTRE FOR R OENTGEN -R ADIOLOGY, Department of Radiation Oncology Radiological Sciences/Radiology, Moscow, Russian Federation 2 RUSSIAN S CIENTIFIC C ENTRE FOR R OENTGEN -R ADIOLOGY, department of CT, Moscow, Russian Federation
Purpose: To compare different combined irradiation techniques of prostate cancer treatment on effectiveness, frequency and expressiveness of irradiation damages. Materials: We studied the results of treatment in two groups of patients. Group 1 - 56 patients after combined irradiation with LDR boost, group 2 45 patients after combined irradiation with HDR boost. Brachytherapy was the first part of treatment with additional EBRT in both groups. All patients are standard by age, stage (T2-3N0M0) of disease and prognostic (intermediate and poor) factors. The median follow-up is 29 months. The median age of patients is 64 years. Results: The 3-years BFFS is no significantly higher in the HDR group 86,6±5,0% vs. 91,1±4,7%, and there were no loco-regional relapse in the group 2, versus 4 2 local, 2 pelvic lymph node metastasis in LDR group. Late irradiation damages in groups 1 and 2: rectitis 48,9±4,3% vs. 37,7±4,1%, grade 2 - 28,6±3,7% vs. 13,33±3,9%, cystitis 46,2±2,6% vs. 44,4±2,9%, grade 3 - 8,9±3,2% vs. 4,4±2,8%. The differences in irradiation damage expressiveness are significant in two groups. Conclusions: So, we consider combined irradiation technique with HDR boost more preferable in prostate cancer patients because of better results and lower complication level. 704 poster CT-BASED PROSTATE BRACHYTHERAPY TREATMENT PLANS SHOW LOWER TARGET COVERAGE WHEN EVALUATED ON MRI ANATOMY A. Dinkla1 , B. Pieters1 , H. van der Grient1 , N. van Wieringen1 , K. Koedooder1 , R. van der Laarse2 , A. Bel1 1 AMC, Radiotherapy, Amsterdam, Netherlands 2 Q UALITY R ADIATION T HERAPY, Zeist, Netherlands Purpose: For brachytherapy treatment planning in prostate cancer, accurate definition of prostate and organs at risk (OARs) is required. Delineation of the prostate is more accurate on MRI than on CT images. Despite the lower visibility of the prostate boundaries, CT is mainly used for treatment planning of PDR/HDR prostate brachytherapy. This is because it is widely available and known to visualize the location of implanted catheters accurately. By also defining the contours on MRI, the effect of using CT-based contours on the actual treatment can be investigated. The aim of this study is to assess the impact of using CT on relevant DVH parameters by calculating DVHs from CT and MRI anatomy. Materials: In this retrospective study, post-implant CT and MRI image data of 13 patients were used to delineate the prostate and OARs. The implanted catheters (typically 12) were reconstructed on CT. An experienced planner created treatment plans based on the CT structure set. DVHs of all organs (CT and MRI) were calculated to study the relevant parameters (V100, D90, rectum V80, urethra V140) that define the quality of the treatment plan. Results: We detected a statistically significant lower target coverage (defined as V100%) when the CT-based treatment plans were evaluated on the actual target (i.e. MRI contours). Also, D90 on MRI appeared to be lower than the D90 on CT. Finally, doses to OARs delineated on MRI were on average higher than doses to OARs delineated on CT (Table I).
Conclusions: Evaluation of CT-based treatment plans on the MRI anatomy showed decreased V100 and D90, and increased rectum V80 and urethra V140. We found that the values of DVH parameters are worse than expected
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from CT-based planning. We conclude that using CT for planning increases the risk of treatment errors. Therefore, we recommend using MRI for prostate brachytherapy treatment planning.
703 poster COMBINED RADIOTHERAPY OF PROSTATE CANCER: HDR BOOST VS LDR BOOST. I. Albitskiy1 , A. Vinikovetskaya2 1 RUSSIAN S CIENTIFIC C ENTRE FOR R OENTGEN -R ADIOLOGY, Department of Radiation Oncology Radiological Sciences/Radiology, Moscow, Russian Federation 2 RUSSIAN S CIENTIFIC C ENTRE FOR R OENTGEN -R ADIOLOGY, department of CT, Moscow, Russian Federation
Purpose: To compare different combined irradiation techniques of prostate cancer treatment on effectiveness, frequency and expressiveness of irradiation damages. Materials: We studied the results of treatment in two groups of patients. Group 1 - 56 patients after combined irradiation with LDR boost, group 2 45 patients after combined irradiation with HDR boost. Brachytherapy was the first part of treatment with additional EBRT in both groups. All patients are standard by age, stage (T2-3N0M0) of disease and prognostic (intermediate and poor) factors. The median follow-up is 29 months. The median age of patients is 64 years. Results: The 3-years BFFS is no significantly higher in the HDR group 86,6±5,0% vs. 91,1±4,7%, and there were no loco-regional relapse in the group 2, versus 4 2 local, 2 pelvic lymph node metastasis in LDR group. Late irradiation damages in groups 1 and 2: rectitis 48,9±4,3% vs. 37,7±4,1%, grade 2 - 28,6±3,7% vs. 13,33±3,9%, cystitis 46,2±2,6% vs. 44,4±2,9%, grade 3 - 8,9±3,2% vs. 4,4±2,8%. The differences in irradiation damage expressiveness are significant in two groups. Conclusions: So, we consider combined irradiation technique with HDR boost more preferable in prostate cancer patients because of better results and lower complication level. 704 poster CT-BASED PROSTATE BRACHYTHERAPY TREATMENT PLANS SHOW LOWER TARGET COVERAGE WHEN EVALUATED ON MRI ANATOMY A. Dinkla1 , B. Pieters1 , H. van der Grient1 , N. van Wieringen1 , K. Koedooder1 , R. van der Laarse2 , A. Bel1 1 AMC, Radiotherapy, Amsterdam, Netherlands 2 Q UALITY R ADIATION T HERAPY, Zeist, Netherlands Purpose: For brachytherapy treatment planning in prostate cancer, accurate definition of prostate and organs at risk (OARs) is required. Delineation of the prostate is more accurate on MRI than on CT images. Despite the lower visibility of the prostate boundaries, CT is mainly used for treatment planning of PDR/HDR prostate brachytherapy. This is because it is widely available and known to visualize the location of implanted catheters accurately. By also defining the contours on MRI, the effect of using CT-based contours on the actual treatment can be investigated. The aim of this study is to assess the impact of using CT on relevant DVH parameters by calculating DVHs from CT and MRI anatomy. Materials: In this retrospective study, post-implant CT and MRI image data of 13 patients were used to delineate the prostate and OARs. The implanted catheters (typically 12) were reconstructed on CT. An experienced planner created treatment plans based on the CT structure set. DVHs of all organs (CT and MRI) were calculated to study the relevant parameters (V100, D90, rectum V80, urethra V140) that define the quality of the treatment plan. Results: We detected a statistically significant lower target coverage (defined as V100%) when the CT-based treatment plans were evaluated on the actual target (i.e. MRI contours). Also, D90 on MRI appeared to be lower than the D90 on CT. Finally, doses to OARs delineated on MRI were on average higher than doses to OARs delineated on CT (Table I).
Conclusions: Evaluation of CT-based treatment plans on the MRI anatomy showed decreased V100 and D90, and increased rectum V80 and urethra V140. We found that the values of DVH parameters are worse than expected
S 281
from CT-based planning. We conclude that using CT for planning increases the risk of treatment errors. Therefore, we recommend using MRI for prostate brachytherapy treatment planning.