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Planning Target Volumes for Cervix Cancer Radiotherapy using a Modified Convex Hull Technique
I. J. Radiation Oncology d Biology d Physics
S380
Volume 75, Number 3, Supplement, 2009
has been limited by toxicity to intraperitoneal organs, preventing delivery of sufficient dose to micro metastases. Newer intensity modulated radiation techniques such as Tomotherapy (Tomo) can often deliver a greater dose to target structures while better avoiding normal tissues. This study is a dosimetric comparison of the Tomo and two-field techniques for WART with the hypothesis that Tomo can deliver more homogeneous dose coverage of the peritoneum while minimizing irradiation of normal tissues. Materials/Methods: The CT scans (abdomen and pelvis) of five female patients’ status post hysterectomy were obtained between April 2008 and January 2009. Planning target volume (PTV) and organs at risk (OAR) were contoured using Pinnacle software. For each patient a Tomo plan for WART was generated using the Helical IMRT technique on Hi-Art software and a traditional two-field AP/PA plan was generated using the Parallel Opposed Pair technique on the Pinnacle software. Plans were optimized to deliver 30 Gy to the PTV (peritoneal cavity) while minimizing the dose delivered to the liver, kidneys, and spinal cord. The plans were compared using data from the dose-volume histograms, including the median dose (Dmedian), along with doses to 10% and 90% (D10 and D90) of the PTV and OAR volumes. Additionally, the percent PTV receiving 90%, 95%, 100%, 105%, and 110% of the prescribed dose was calculated (V90, V95, V100, V105, and V110). Significant differences were verified using the two-tailed t test. Results: The results suggest that coverage of the PTV was superior using Tomo versus the two-field approach (V90 of 99.5% vs. 78%, V95 of 99% vs. 73%, and V100 of 93% vs. 67%). Tomo resulted in fewer high-dose regions than the two-field technique (V105 of 5% vs. 30% and V110 of 0.05% vs. 3%). The OARs within the PTV were spared by delivering a lower median dose than conventional WART (For liver, Dmedian of 22.5 Gy vs. 30.1 Gy and for kidneys, Dmedian of 12.3 Gy vs. 18.5 Gy). The Tomo plan prevented high-dose regions in the kidneys (D90 of 9.6 Gy vs. 17 Gy), but the opposite effect was seen in the liver (D90 of 17.5 Gy vs. 9 Gy). Conclusions: Tomo delivers a more homogeneous dose coverage to the PTV with better OAR sparing as compared with the previously studied two-field method, making it a potential safe and effective therapy for peritoneal cancers. Author Disclosure: R.E. Vatner, None; K. Stook, None; M. Willard, None; R. Dowsett, None.
2443
Planning Target Volumes for Cervix Cancer Radiotherapy using a Modified Convex Hull Technique
V. Kelly1, J. Xie1, K. Lim1, K. Brock1, A. Lundin2, H. Rehbinder2, A. Fyles1, D. Jaffray1, M. Milosevic1, Y. Cho1, et al. 1
Princess Margaret Hospital, Toronto, ON, Canada, 2RaySearch Laboratories AB, Stockholm, Sweden
Purpose/Objective(s): Inter-fractional organ motion adversely affects the coverage of the clinical target volume (CTV) for cervix cancer patients. Planning target volumes (PTV) using a convex hull (CH) around combined CTV volumes have shown excellent target coverage for patients whose bladder filling is variable over the course of radiation treatment, at the expense of high dose to the rectum. A modified CH (mCH) technique is proposed in this study to reduce rectal dose without compromising target coverage. Materials/Methods: Nine cervix cancer patients with large changes in bladder filling during treatment were selected from a larger planning study. MRI scans were acquired for planning and weekly during treatment. Images were fused to a planning CT scan using bony alignment and CTV and organs at risk (OAR) contoured. The two image-sets with largest and smallest bladder were identified. The union of the CTVs from these image sets was constructed and a CH applied to the resulting volume. The CH was then modified by subtracting the rectal volume and adding a 3mm margin posteriorly (mCH PTV). IMRT plans were generated to cover 98% mCH PTV with 49 Gy. Contours were converted to 3D surface meshes for deformation analysis. Accumulated dose on the deformed organs were simulated using dose accumulation software (ORBIT Workstation, RaySearch Laboratories). Results: The average volume of mCH PTV was only 14% larger than a conventional 5mm PTV margin. The delivered dose using mCH showed excellent CTV coverage (D98% of 49.3 Gy on average) except for one patient (D98% of 47.3 Gy) whose rectum was full at the time of planning. Dose reduction to the rectum (average dose and V45 Gy) was statistically significant (t\0.1) when compared to the unmodified CH PTV plans. Conclusions: A non-uniform margin around combined CTV volumes using the mCH PTV technique was shown to successfully characterize patient-specific CTV motion and deformation for most patients. IMRT plans using mCH PTV demonstrate good target coverage and rectal saving for cervix cancer patients with variable bladder filling. Author Disclosure: V. Kelly, None; J. Xie, None; K. Lim, None; K. Brock, None; A. Lundin, RaySearch Laboratories AB, A. Employment; H. Rehbinder, RaySearch Laboratories AB, A. Employment; RaySearch Laboratories AB, E. Ownership Interest; A. Fyles, None; D. Jaffray, None; M. Milosevic, None; Y. Cho, None.
2444
Intensity-Modulated Radiation Therapy for Whole Pelvic Irradiation in Cervical Carcinoma Patients after Hysterectomy-Phase I–II Study of FUCH
Y. Lin1, L. Zhou1, S. Cai2, Z. Xu1, X. Guo1, Z. Zhang1, X. Fu1, G. Jiang1 Dept.Radiation oncology, Cancer Hospital, Fudan University, Shanghai, China, 2Dept.Genecology oncology, Cancer Hospital, Fudan University, Shanghai, China 1
Purpose/Objective(s): To establish the technique of intensity-modulated radiation therapy (IMRT) for whole pelvic irradiation in cervical carcinoma patients after hysterectomy in Fudan University Cancer Hospital (FUCH). In addition, to observe the treatment results and side effects of the treatment. Materials/Methods: All patients enrolled in this study should be cervical carcinoma after hysterectomy with high-risk of pelvic recurrence. The prior-clinical study was done in 10 patients to establish the technique of IMRT. (1) Patients were immobilized by vacuum-lock or belly-board with prone positions and set-up errors were measured three times a week at irradiation positions by comparison of DRR and EPID. Doses to bladder, intestine and colon were evaluated when bladder was full or empty. The setup errors were also measured at prone position with full and empty bladder. (2) CTV was defined as regional pelvis lymph nodes
S380
Volume 75, Number 3, Supplement, 2009
has been limited by toxicity to intraperitoneal organs, preventing delivery of sufficient dose to micro metastases. Newer intensity modulated radiation techniques such as Tomotherapy (Tomo) can often deliver a greater dose to target structures while better avoiding normal tissues. This study is a dosimetric comparison of the Tomo and two-field techniques for WART with the hypothesis that Tomo can deliver more homogeneous dose coverage of the peritoneum while minimizing irradiation of normal tissues. Materials/Methods: The CT scans (abdomen and pelvis) of five female patients’ status post hysterectomy were obtained between April 2008 and January 2009. Planning target volume (PTV) and organs at risk (OAR) were contoured using Pinnacle software. For each patient a Tomo plan for WART was generated using the Helical IMRT technique on Hi-Art software and a traditional two-field AP/PA plan was generated using the Parallel Opposed Pair technique on the Pinnacle software. Plans were optimized to deliver 30 Gy to the PTV (peritoneal cavity) while minimizing the dose delivered to the liver, kidneys, and spinal cord. The plans were compared using data from the dose-volume histograms, including the median dose (Dmedian), along with doses to 10% and 90% (D10 and D90) of the PTV and OAR volumes. Additionally, the percent PTV receiving 90%, 95%, 100%, 105%, and 110% of the prescribed dose was calculated (V90, V95, V100, V105, and V110). Significant differences were verified using the two-tailed t test. Results: The results suggest that coverage of the PTV was superior using Tomo versus the two-field approach (V90 of 99.5% vs. 78%, V95 of 99% vs. 73%, and V100 of 93% vs. 67%). Tomo resulted in fewer high-dose regions than the two-field technique (V105 of 5% vs. 30% and V110 of 0.05% vs. 3%). The OARs within the PTV were spared by delivering a lower median dose than conventional WART (For liver, Dmedian of 22.5 Gy vs. 30.1 Gy and for kidneys, Dmedian of 12.3 Gy vs. 18.5 Gy). The Tomo plan prevented high-dose regions in the kidneys (D90 of 9.6 Gy vs. 17 Gy), but the opposite effect was seen in the liver (D90 of 17.5 Gy vs. 9 Gy). Conclusions: Tomo delivers a more homogeneous dose coverage to the PTV with better OAR sparing as compared with the previously studied two-field method, making it a potential safe and effective therapy for peritoneal cancers. Author Disclosure: R.E. Vatner, None; K. Stook, None; M. Willard, None; R. Dowsett, None.
2443
Planning Target Volumes for Cervix Cancer Radiotherapy using a Modified Convex Hull Technique
V. Kelly1, J. Xie1, K. Lim1, K. Brock1, A. Lundin2, H. Rehbinder2, A. Fyles1, D. Jaffray1, M. Milosevic1, Y. Cho1, et al. 1
Princess Margaret Hospital, Toronto, ON, Canada, 2RaySearch Laboratories AB, Stockholm, Sweden
Purpose/Objective(s): Inter-fractional organ motion adversely affects the coverage of the clinical target volume (CTV) for cervix cancer patients. Planning target volumes (PTV) using a convex hull (CH) around combined CTV volumes have shown excellent target coverage for patients whose bladder filling is variable over the course of radiation treatment, at the expense of high dose to the rectum. A modified CH (mCH) technique is proposed in this study to reduce rectal dose without compromising target coverage. Materials/Methods: Nine cervix cancer patients with large changes in bladder filling during treatment were selected from a larger planning study. MRI scans were acquired for planning and weekly during treatment. Images were fused to a planning CT scan using bony alignment and CTV and organs at risk (OAR) contoured. The two image-sets with largest and smallest bladder were identified. The union of the CTVs from these image sets was constructed and a CH applied to the resulting volume. The CH was then modified by subtracting the rectal volume and adding a 3mm margin posteriorly (mCH PTV). IMRT plans were generated to cover 98% mCH PTV with 49 Gy. Contours were converted to 3D surface meshes for deformation analysis. Accumulated dose on the deformed organs were simulated using dose accumulation software (ORBIT Workstation, RaySearch Laboratories). Results: The average volume of mCH PTV was only 14% larger than a conventional 5mm PTV margin. The delivered dose using mCH showed excellent CTV coverage (D98% of 49.3 Gy on average) except for one patient (D98% of 47.3 Gy) whose rectum was full at the time of planning. Dose reduction to the rectum (average dose and V45 Gy) was statistically significant (t\0.1) when compared to the unmodified CH PTV plans. Conclusions: A non-uniform margin around combined CTV volumes using the mCH PTV technique was shown to successfully characterize patient-specific CTV motion and deformation for most patients. IMRT plans using mCH PTV demonstrate good target coverage and rectal saving for cervix cancer patients with variable bladder filling. Author Disclosure: V. Kelly, None; J. Xie, None; K. Lim, None; K. Brock, None; A. Lundin, RaySearch Laboratories AB, A. Employment; H. Rehbinder, RaySearch Laboratories AB, A. Employment; RaySearch Laboratories AB, E. Ownership Interest; A. Fyles, None; D. Jaffray, None; M. Milosevic, None; Y. Cho, None.
2444
Intensity-Modulated Radiation Therapy for Whole Pelvic Irradiation in Cervical Carcinoma Patients after Hysterectomy-Phase I–II Study of FUCH
Y. Lin1, L. Zhou1, S. Cai2, Z. Xu1, X. Guo1, Z. Zhang1, X. Fu1, G. Jiang1 Dept.Radiation oncology, Cancer Hospital, Fudan University, Shanghai, China, 2Dept.Genecology oncology, Cancer Hospital, Fudan University, Shanghai, China 1
Purpose/Objective(s): To establish the technique of intensity-modulated radiation therapy (IMRT) for whole pelvic irradiation in cervical carcinoma patients after hysterectomy in Fudan University Cancer Hospital (FUCH). In addition, to observe the treatment results and side effects of the treatment. Materials/Methods: All patients enrolled in this study should be cervical carcinoma after hysterectomy with high-risk of pelvic recurrence. The prior-clinical study was done in 10 patients to establish the technique of IMRT. (1) Patients were immobilized by vacuum-lock or belly-board with prone positions and set-up errors were measured three times a week at irradiation positions by comparison of DRR and EPID. Doses to bladder, intestine and colon were evaluated when bladder was full or empty. The setup errors were also measured at prone position with full and empty bladder. (2) CTV was defined as regional pelvis lymph nodes