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Feasibility of Composing External Beam Radiotherapy and HDR Brachytherapy of Cervical Cancer Using Deformable Image Registration
I. J. Radiation Oncology d Biology d Physics
S464
Volume 81, Number 2, Supplement, 2011
after radiation therapy showed postmenopausal status (less than 40 pg/ml) in all measured patients. The values of NTx and TRACP-5b were not changed significantly in a year after treatment. Conclusions: The decrease of BMD in irradiated bone and estradiol after pelvic radiation therapy was found within a year. Though NTx and TRACP-5b were not changed significantly, decrease of estradiol is known to cause osteoporosis. Longer follow-up and optimal treatment is essential to patients care after pelvic radiation therapy. Author Disclosure: J. Saitoh: None. Y. Suzuki: None. T. Ohno: None. S. Noda: None. M. Wakatsuki: None. N. Okonogi: None. Y. Ohkubo: None. H. Ushijima: None. T. Oike: None. T. Nakano: None.
2530
Laparoscopic Para-aortic Lymphadenectomy (LPL) In Staging Of Locally Advanced Cervical Cancer
J. Luna, T. Iglesias, J. Olivera, J. Vara, I. Prieto, A. Chavez, A. Perez, J. Cristobal, H. Di Fiore, O. Martinez Fundaci on Jimenez Dıaz - Capio, Madrid, Spain Purpose/Objective(s): 15 - 30% of the patients with locally advanced cervical cancer present para-aortic lymph node metastases at diagnosis. A careful staging is essential to provide the best treatment. Although PET-CT represents a significant advance, its sensitivity to detect para-aortic metastases ranges from 73 - 92%. Therefore, surgical lymph node evaluation remains the gold standard in detecting para-aortic metastases. However, it is invasive and delays treatment of the primary lesion. We present our experience in performing laparoscopic para-aortic lymph node dissection (LPL). Materials/Methods: From November 2009 to February 2011, 17 patients with locally advanced cervical cancer (stages IB-IVB) were included. Mean age 48 years (range 30 - 73). Pathology: Squamous cell carcinoma 70%, Adenocarcinoma 30%. As radiographic evaluation, pelvic MRI and CT were performed. Afterwards, LPL was performed. Ovarian transposition in the same surgical procedure was offered to pre-menopausal patients. All patients received concurrent chemoradiotherapy and brachytherapy with radical intent after LPL. Results: MRI detected pathologic lymph nodes in 29.41% of the patients (5 patients). CT scan showed pathologic pelvic lymph nodes in 35.29% (6 patients) and para-aortic in 11.76% (2 patients). The mean number of retrieved nodes was 12 (2 - 35), increasing the number as increased the learning curve. 3 patients (17.64%) had metastatic para-aortic lymph nodes, while CT only had detected pathological lymph nodes in 1 patient. In another patient with abnormal CT lymph nodes were negative after surgery. With a median follow up of 10 months, only one patient (5.8%) presented side effects It was the first LPL performed (patient HIV(+) with an abdominal abscess and peritonitis), and the complications had been solved completely. Chemoradiation treatment was not delayed as a result of laparoscopy. General and intestinal tolerance did not deteriorate with respect to previously recorded in patients without surgery or with retroperitoneal lymphadenectomy. No Grade III-IV side effects were reported. Conclusions: The laparoscopic para-aortic lymphadenectomy is an effective technique for staging in locally advanced cervical cancer, provides essential information for the design of radiotherapy volumes, with a very low morbidity rate, a short postoperative recovery time, and without delaying treatment of the primary lesion. Author Disclosure: J. Luna: None. T. Iglesias: None. J. Olivera: None. J. Vara: None. I. Prieto: None. A. Chavez: None. A. Perez: None. J. Cristobal: None. H. Di Fiore: None. O. Martinez: None.
2531
Feasibility of Composing External Beam Radiotherapy and HDR Brachytherapy of Cervical Cancer Using Deformable Image Registration
S. Li, Z. Liu, P. Chan, B. Micaily, C. Miyamoto Temple University Hospital, Philadelphia, PA Purpose/Objective(s): Combination of external beam (EB) and intracavitary brachytherapy (IB) are the standard treatment of cervical and medically inoperable endometrioid carcinomas. Integrated dose distributions from EB and IB plans are currently unavailable due to large anatomic changes. This study combined EB and IB plans using deformable image registration. Materials/Methods: Plans from six patients with prescription dose (PD) of 45 Gy to PTV in 25 fractions and 5.4 Gy MLB to pelvis nodes in 3 fractions from EBRT plus 12 to 30 Gy to GTV in 2 to 5 fractions from IB were evaluated. The GTV, bladder, and rectum were defined in every CT-based IB plans (Oncentra, Nucletron) and CTV and PTV were added in composite EB plans (Pinnacle, Philips). DICOM image, dose, and structure data sets were transferred to a deformable image registration system (Velocity) and rigid matching was first performed followed by deformable registration with multiple passes. Each registration was verified by checking the tandem continuity and GTValignment. The anterior rectal wall and posterior bladder wall should also be matched in the deformable registration. The final deformation was applied for transformation of the dose matrix and associated structures. DVHs of the transformed structures are created from the summarized or composite plans. Results: GTV, rectum, and bladder in IB plans are significantly (40%) smaller than that in EB plans. The minimal GTV dose is in 60 - 80% of PD and the mean GTV dose is in 110 - 130% of PD. Rectums and bladders defined in IB received similar hotspot
Results From Composite Plans of 6 EB and IB Patient Type of Tumor/Applicator
Total PD (Gy)
Min. GTV Dose (Gy)
Mean GTV Dose (Gy)
Mean Bladder Dose (Gy)
Max Bladder Dose (Gy)
Mean Rectal Dose (Gy)
Max Rectal Dose (Gy)
Endorm. Ca. T1N1M0/FS Endorm.Ca. T2bNXM0/FS Cervical Ca. T2bN0M0 /FS Ext Cervix T2N0M0/Cylinder Cervical Ca. T3bNxM0/Ring Cervical Ca. T1b2N0M0
80 80 80 57 80 80
63 64 66 51 58 60
85 106 105 60 105 100
31 53 58 40 54 50
70 200 91 61 76 74
29 55 55 39 52 53
90 80 300 65 71 81
Proceedings of the 53rd Annual ASTRO Meeting dose in range of 90 - 120% of PD. But rectums and bladders in EB plans can have hotspot dose of .200%PD due to some registration errors particularly in the longitudinal displacements cause by applicator insertion. Conclusions: Deformable image registration allows us to track dose distribution along different treatment modalities. However, deformable registrations have notable errors in matching the rectum and bladder. Use of CT contrast agent in bladder and rectum as well as the CT-MRI compatible FS applicator increased the registration error. Author Disclosure: S. Li: None. Z. Liu: None. P. Chan: None. B. Micaily: None. C. Miyamoto: None.
2532
Dosimetric Evaluation of TomoTherapy based Whole Pelvic Intensity Modulated Radiation Therapy with and without Bone Marrow Sparing in Gynecologic Cancers
C. S. Platta, A. Bayliss, D. McHaffie, M. Straub, K. Bradley University of Wisconsin Hospitals & Clinics, Madison, WI Purpose/Objective(s): Pelvic radiation therapy with concurrent chemotherapy is the standard of care for locally advanced cervical carcinoma. While effective, this treatment approach is associated with acute hematologic toxicity. Published literature reports that pelvic bone marrow (BM) dosimetric parameters of V10.90%, V10.85%, and V20.80% are associated with higher rates of hematologic toxicity. In this study, we sought to investigate the ability of TomoTherapy based BM sparing intensity modulated radiation therapy (BMS-IMRT) in reducing dose to the pelvic BM while evaluating the dose distribution to nearby critical structures and effect on PTV coverage. Materials/Methods: Eight patients with cervical or endometrial carcinoma previously treated using TomoTherapy based IMRT were selected for the analysis. Contours were standardized for small bowel, rectum, bladder, femoral heads, and PTV volume. Pelvic BM volumes were contoured using the external contour of the bone, with contours extending from 1 cm above the most superior aspect of the PTV, inferiorly to the base of the iliac crest. IMRT objectives were assigned based on RTOG 0418 with the addition of a BM constraint (max dose\50.4, V10\85%) for the BMS-IMRT plans. All patients were planned using version 3.x TomoTherapy software. Importances and penalties were allowed to change to meet the specific objectives. Statistical analysis was performed using a paired t-test to detect significant differences in dose distribution. Results: The average V5, V10, V15 and V20 for BM with the IMRT plans were 99.2%, 95.3%, 91.1%, and 83.8%, respectively. When the BMS-IMRT technique was applied, these values decreased significantly to 98.1% (p = 0.030), 84.4% (p = 0.003), 79.9% (p = 0.003), and 76.8% (p = 0.007), respectively. There was no significant change in normal tissue doses or PTV coverage, with or without use of the BM sparing technique. For small bowel, V40 = 25.1% for IMRT and V40 = 26.4% for BMS-IMRT (p = 0.125). For bladder, V50 was 18.8% and 18.9% (p = 0.322) for IMRT and BMS-IMRT, respectively. For rectum, V30 = 53.6% for IMRT and V30 = 52.6% for BMS-IMRT (p = 0.215). For PTV V50.4 was 96.0% for both groups. Conclusions: BMS-IMRT significantly reduced radiation dose to the pelvic BM while maintaining the ability to limit dose to the small bowel, bladder and rectum. The constraints set forth by RTOG 0418 were easily met in the BMS-IMRT plans without sacrifice of PTV coverage or relaxation of other normal tissue constraints. Author Disclosure: C.S. Platta: None. A. Bayliss: None. D. McHaffie: None. M. Straub: None. K. Bradley: None.
2533
Clinical Acute Side Effects And Dosimetric Study Of Helical Tomotherapy And Conventional Intensity Modulated Radiation Therapy In 126 Postoperative Cervical Cancer Patients
G. Zhou, C. Xie, R. Ge, H. Zhang, S. Xu, X. Dai, W. Yang PLA 301 General Hospital, Beijing, China Purpose/Objective(s): To report the acute side effects of helical tomotherapy (HT) versus conventional Intensity Modulated radiotherapy (IMRT) for postoperative cervical carcinoma and their dosimetric comparison in organs at risk (OARs). Materials/Methods: Between September 2008 and October 2010, a total of 126 postoperative cervical carcinoma patients were treated, including 68 cases for HT and 58 cases for conventional step and shoot IMRT technique. The prescription doses were given as 46 - 50.4Gy/23 - 28Fx to the whole pelvis to cover the intended PTV volume and 60Gy/28Fx to lymph nodes at risk. A large volume of internal GI organs were in fields and IMRT implementation was critical in assessing the dose volume effects of toxicities. We adopted the RTOG/EORTC (Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer) criteria and calculated dose volume histograms (DVH) to evaluate the acute side effects of rectum and bladder, conformity index (CI) and homogeneity index (HI) of target volume as well as V30, V40, V50 of rectum and bladder were reported. Analytical Person chi square testing was utilized to report the statistical significance in our study. Results: During radiation therapy course, the reported grade I side effects of HT and IMRT groups were 27.94% and 46.55% (X2 = 4.68, p\0.05) in the rectum, 17.65% and 24.13% (chi-square = 1.93, p.0.05) in the bladder, respectively. The CI of HT and IMRT were 0.73 ± 0.082 and 1.047 ± 0.026 (p = 0.044). The HI of HT and IMRT were 1.047 ± 0.026 and 1.130 ± 0.017 (p = 0.000). The 100% dose coverage of the clinical target volume (V100) was 96.15 ± 1.83 in HT and 94.42 ± 1.45 in IMRT (p = 0.02). V30 for both HT and IMRT were 63.59 ± 17.70, and 69.39 ± 7.60 (p = 0.186) of rectum; 68.78 ± 14.66 and 78.23 ± 11.48 (p = 0.029) of bladder. V40 and V50 of HT with rectum and bladder were also with clinical dosimetric benefits compared to IMRT technique. Details were reported as the summary in a tabular format. With the same prescription dose and dose constraints, organ sparing can be better achieved with HT planning. In HT planning, pitch number is 2.5 and the total treatment is made comparatively similar to the conventional IMRT technique. Conclusions: Helical tomotherapy treatment plan normally would provide better CI and HI indexes, while generate better sparing dosimetry distribution for OARs such as rectum and bladder, even kidneys than conventional IMRT plans. Low dose sparing with OARs of HT improves the short term grade I toxicity and clinical observation has identified the benefits of sparing critical organs in large treatment fields by using HT treatments. Author Disclosure: G. Zhou: None. C. Xie: None. R. Ge: None. H. Zhang: None. S. Xu: None. X. Dai: None. W. Yang: None.
S465
S464
Volume 81, Number 2, Supplement, 2011
after radiation therapy showed postmenopausal status (less than 40 pg/ml) in all measured patients. The values of NTx and TRACP-5b were not changed significantly in a year after treatment. Conclusions: The decrease of BMD in irradiated bone and estradiol after pelvic radiation therapy was found within a year. Though NTx and TRACP-5b were not changed significantly, decrease of estradiol is known to cause osteoporosis. Longer follow-up and optimal treatment is essential to patients care after pelvic radiation therapy. Author Disclosure: J. Saitoh: None. Y. Suzuki: None. T. Ohno: None. S. Noda: None. M. Wakatsuki: None. N. Okonogi: None. Y. Ohkubo: None. H. Ushijima: None. T. Oike: None. T. Nakano: None.
2530
Laparoscopic Para-aortic Lymphadenectomy (LPL) In Staging Of Locally Advanced Cervical Cancer
J. Luna, T. Iglesias, J. Olivera, J. Vara, I. Prieto, A. Chavez, A. Perez, J. Cristobal, H. Di Fiore, O. Martinez Fundaci on Jimenez Dıaz - Capio, Madrid, Spain Purpose/Objective(s): 15 - 30% of the patients with locally advanced cervical cancer present para-aortic lymph node metastases at diagnosis. A careful staging is essential to provide the best treatment. Although PET-CT represents a significant advance, its sensitivity to detect para-aortic metastases ranges from 73 - 92%. Therefore, surgical lymph node evaluation remains the gold standard in detecting para-aortic metastases. However, it is invasive and delays treatment of the primary lesion. We present our experience in performing laparoscopic para-aortic lymph node dissection (LPL). Materials/Methods: From November 2009 to February 2011, 17 patients with locally advanced cervical cancer (stages IB-IVB) were included. Mean age 48 years (range 30 - 73). Pathology: Squamous cell carcinoma 70%, Adenocarcinoma 30%. As radiographic evaluation, pelvic MRI and CT were performed. Afterwards, LPL was performed. Ovarian transposition in the same surgical procedure was offered to pre-menopausal patients. All patients received concurrent chemoradiotherapy and brachytherapy with radical intent after LPL. Results: MRI detected pathologic lymph nodes in 29.41% of the patients (5 patients). CT scan showed pathologic pelvic lymph nodes in 35.29% (6 patients) and para-aortic in 11.76% (2 patients). The mean number of retrieved nodes was 12 (2 - 35), increasing the number as increased the learning curve. 3 patients (17.64%) had metastatic para-aortic lymph nodes, while CT only had detected pathological lymph nodes in 1 patient. In another patient with abnormal CT lymph nodes were negative after surgery. With a median follow up of 10 months, only one patient (5.8%) presented side effects It was the first LPL performed (patient HIV(+) with an abdominal abscess and peritonitis), and the complications had been solved completely. Chemoradiation treatment was not delayed as a result of laparoscopy. General and intestinal tolerance did not deteriorate with respect to previously recorded in patients without surgery or with retroperitoneal lymphadenectomy. No Grade III-IV side effects were reported. Conclusions: The laparoscopic para-aortic lymphadenectomy is an effective technique for staging in locally advanced cervical cancer, provides essential information for the design of radiotherapy volumes, with a very low morbidity rate, a short postoperative recovery time, and without delaying treatment of the primary lesion. Author Disclosure: J. Luna: None. T. Iglesias: None. J. Olivera: None. J. Vara: None. I. Prieto: None. A. Chavez: None. A. Perez: None. J. Cristobal: None. H. Di Fiore: None. O. Martinez: None.
2531
Feasibility of Composing External Beam Radiotherapy and HDR Brachytherapy of Cervical Cancer Using Deformable Image Registration
S. Li, Z. Liu, P. Chan, B. Micaily, C. Miyamoto Temple University Hospital, Philadelphia, PA Purpose/Objective(s): Combination of external beam (EB) and intracavitary brachytherapy (IB) are the standard treatment of cervical and medically inoperable endometrioid carcinomas. Integrated dose distributions from EB and IB plans are currently unavailable due to large anatomic changes. This study combined EB and IB plans using deformable image registration. Materials/Methods: Plans from six patients with prescription dose (PD) of 45 Gy to PTV in 25 fractions and 5.4 Gy MLB to pelvis nodes in 3 fractions from EBRT plus 12 to 30 Gy to GTV in 2 to 5 fractions from IB were evaluated. The GTV, bladder, and rectum were defined in every CT-based IB plans (Oncentra, Nucletron) and CTV and PTV were added in composite EB plans (Pinnacle, Philips). DICOM image, dose, and structure data sets were transferred to a deformable image registration system (Velocity) and rigid matching was first performed followed by deformable registration with multiple passes. Each registration was verified by checking the tandem continuity and GTValignment. The anterior rectal wall and posterior bladder wall should also be matched in the deformable registration. The final deformation was applied for transformation of the dose matrix and associated structures. DVHs of the transformed structures are created from the summarized or composite plans. Results: GTV, rectum, and bladder in IB plans are significantly (40%) smaller than that in EB plans. The minimal GTV dose is in 60 - 80% of PD and the mean GTV dose is in 110 - 130% of PD. Rectums and bladders defined in IB received similar hotspot
Results From Composite Plans of 6 EB and IB Patient Type of Tumor/Applicator
Total PD (Gy)
Min. GTV Dose (Gy)
Mean GTV Dose (Gy)
Mean Bladder Dose (Gy)
Max Bladder Dose (Gy)
Mean Rectal Dose (Gy)
Max Rectal Dose (Gy)
Endorm. Ca. T1N1M0/FS Endorm.Ca. T2bNXM0/FS Cervical Ca. T2bN0M0 /FS Ext Cervix T2N0M0/Cylinder Cervical Ca. T3bNxM0/Ring Cervical Ca. T1b2N0M0
80 80 80 57 80 80
63 64 66 51 58 60
85 106 105 60 105 100
31 53 58 40 54 50
70 200 91 61 76 74
29 55 55 39 52 53
90 80 300 65 71 81
Proceedings of the 53rd Annual ASTRO Meeting dose in range of 90 - 120% of PD. But rectums and bladders in EB plans can have hotspot dose of .200%PD due to some registration errors particularly in the longitudinal displacements cause by applicator insertion. Conclusions: Deformable image registration allows us to track dose distribution along different treatment modalities. However, deformable registrations have notable errors in matching the rectum and bladder. Use of CT contrast agent in bladder and rectum as well as the CT-MRI compatible FS applicator increased the registration error. Author Disclosure: S. Li: None. Z. Liu: None. P. Chan: None. B. Micaily: None. C. Miyamoto: None.
2532
Dosimetric Evaluation of TomoTherapy based Whole Pelvic Intensity Modulated Radiation Therapy with and without Bone Marrow Sparing in Gynecologic Cancers
C. S. Platta, A. Bayliss, D. McHaffie, M. Straub, K. Bradley University of Wisconsin Hospitals & Clinics, Madison, WI Purpose/Objective(s): Pelvic radiation therapy with concurrent chemotherapy is the standard of care for locally advanced cervical carcinoma. While effective, this treatment approach is associated with acute hematologic toxicity. Published literature reports that pelvic bone marrow (BM) dosimetric parameters of V10.90%, V10.85%, and V20.80% are associated with higher rates of hematologic toxicity. In this study, we sought to investigate the ability of TomoTherapy based BM sparing intensity modulated radiation therapy (BMS-IMRT) in reducing dose to the pelvic BM while evaluating the dose distribution to nearby critical structures and effect on PTV coverage. Materials/Methods: Eight patients with cervical or endometrial carcinoma previously treated using TomoTherapy based IMRT were selected for the analysis. Contours were standardized for small bowel, rectum, bladder, femoral heads, and PTV volume. Pelvic BM volumes were contoured using the external contour of the bone, with contours extending from 1 cm above the most superior aspect of the PTV, inferiorly to the base of the iliac crest. IMRT objectives were assigned based on RTOG 0418 with the addition of a BM constraint (max dose\50.4, V10\85%) for the BMS-IMRT plans. All patients were planned using version 3.x TomoTherapy software. Importances and penalties were allowed to change to meet the specific objectives. Statistical analysis was performed using a paired t-test to detect significant differences in dose distribution. Results: The average V5, V10, V15 and V20 for BM with the IMRT plans were 99.2%, 95.3%, 91.1%, and 83.8%, respectively. When the BMS-IMRT technique was applied, these values decreased significantly to 98.1% (p = 0.030), 84.4% (p = 0.003), 79.9% (p = 0.003), and 76.8% (p = 0.007), respectively. There was no significant change in normal tissue doses or PTV coverage, with or without use of the BM sparing technique. For small bowel, V40 = 25.1% for IMRT and V40 = 26.4% for BMS-IMRT (p = 0.125). For bladder, V50 was 18.8% and 18.9% (p = 0.322) for IMRT and BMS-IMRT, respectively. For rectum, V30 = 53.6% for IMRT and V30 = 52.6% for BMS-IMRT (p = 0.215). For PTV V50.4 was 96.0% for both groups. Conclusions: BMS-IMRT significantly reduced radiation dose to the pelvic BM while maintaining the ability to limit dose to the small bowel, bladder and rectum. The constraints set forth by RTOG 0418 were easily met in the BMS-IMRT plans without sacrifice of PTV coverage or relaxation of other normal tissue constraints. Author Disclosure: C.S. Platta: None. A. Bayliss: None. D. McHaffie: None. M. Straub: None. K. Bradley: None.
2533
Clinical Acute Side Effects And Dosimetric Study Of Helical Tomotherapy And Conventional Intensity Modulated Radiation Therapy In 126 Postoperative Cervical Cancer Patients
G. Zhou, C. Xie, R. Ge, H. Zhang, S. Xu, X. Dai, W. Yang PLA 301 General Hospital, Beijing, China Purpose/Objective(s): To report the acute side effects of helical tomotherapy (HT) versus conventional Intensity Modulated radiotherapy (IMRT) for postoperative cervical carcinoma and their dosimetric comparison in organs at risk (OARs). Materials/Methods: Between September 2008 and October 2010, a total of 126 postoperative cervical carcinoma patients were treated, including 68 cases for HT and 58 cases for conventional step and shoot IMRT technique. The prescription doses were given as 46 - 50.4Gy/23 - 28Fx to the whole pelvis to cover the intended PTV volume and 60Gy/28Fx to lymph nodes at risk. A large volume of internal GI organs were in fields and IMRT implementation was critical in assessing the dose volume effects of toxicities. We adopted the RTOG/EORTC (Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer) criteria and calculated dose volume histograms (DVH) to evaluate the acute side effects of rectum and bladder, conformity index (CI) and homogeneity index (HI) of target volume as well as V30, V40, V50 of rectum and bladder were reported. Analytical Person chi square testing was utilized to report the statistical significance in our study. Results: During radiation therapy course, the reported grade I side effects of HT and IMRT groups were 27.94% and 46.55% (X2 = 4.68, p\0.05) in the rectum, 17.65% and 24.13% (chi-square = 1.93, p.0.05) in the bladder, respectively. The CI of HT and IMRT were 0.73 ± 0.082 and 1.047 ± 0.026 (p = 0.044). The HI of HT and IMRT were 1.047 ± 0.026 and 1.130 ± 0.017 (p = 0.000). The 100% dose coverage of the clinical target volume (V100) was 96.15 ± 1.83 in HT and 94.42 ± 1.45 in IMRT (p = 0.02). V30 for both HT and IMRT were 63.59 ± 17.70, and 69.39 ± 7.60 (p = 0.186) of rectum; 68.78 ± 14.66 and 78.23 ± 11.48 (p = 0.029) of bladder. V40 and V50 of HT with rectum and bladder were also with clinical dosimetric benefits compared to IMRT technique. Details were reported as the summary in a tabular format. With the same prescription dose and dose constraints, organ sparing can be better achieved with HT planning. In HT planning, pitch number is 2.5 and the total treatment is made comparatively similar to the conventional IMRT technique. Conclusions: Helical tomotherapy treatment plan normally would provide better CI and HI indexes, while generate better sparing dosimetry distribution for OARs such as rectum and bladder, even kidneys than conventional IMRT plans. Low dose sparing with OARs of HT improves the short term grade I toxicity and clinical observation has identified the benefits of sparing critical organs in large treatment fields by using HT treatments. Author Disclosure: G. Zhou: None. C. Xie: None. R. Ge: None. H. Zhang: None. S. Xu: None. X. Dai: None. W. Yang: None.
S465