X Lin

SU-F-T-349: Dosimetric Comparison of Three Different Simultaneous Integrated Boost Irradiation Techniques for Multiple Brain Metastases: Intensity-Modulatedradiotherapy, Hybrid Intensity-Modulated Radiotherapy and Volumetric Modulated Arc Therapy

PURPOSE To study the dosimetric impact of intensity-modulated radiotherapy (IMRT), hybrid intensity-modulated radiotherapy (h-IMRT) and volumetric modulated arc therapy(VMAT) for whole-brain radiotherapy (WBRT) with simultaneous integrated boost in patients with multiple brain metastases. METHODS Ten patients with multiple brain metastases were included in this analysis. The prescribed dose was 45 Gy to the whole brain (PTVWBRT) and 55 Gy to individual brain metastases (PTVboost) delivered simultaneously in 25 fractions. Three treatment techniques were designed: the 7 equal spaced fields IMRT plan, hybrid IMRT plan and VMAT with two 358°arcs. In hybrid IMRT plan, two fields(90°and 270°) were planned to the whole brain. This was used as a base dose plan. Then 5 fields IMRT plan was optimized based on the two fields plan. The dose distribution in the target, the dose to the organs at risk and total MU in three techniques were compared. RESULTS For the target dose, conformity and homogeneity in PTV, no statistically differences were observed in the three techniques. For the maximum dose in bilateral lens and the mean dose in bilateral eyes, IMRT and h-IMRT plans showed the highest and lowest value respectively. No statistically significant differences were observed in the dose of optic nerve and brainstem. For the monitor units, IMRT and VMAT plans showed the highest and lowest value respectively. CONCLUSION For WBRT with simultaneous integrated boost in patients with multiple brain metastases, hybrid IMRT could reduce the doses to lens and eyes. It is feasible for patients with brain metastases.

SU‐E‐T‐713: Study On Application of Beam Angle Optimization for Multiple Intracranial Metastases

Purpose: To study the dosimetric impact of different angle fields IMRT and the feasibility of beam angle optimization (BAO) for multiple intracranial metastases. Methods: 11 patients with multiple intracranial metastases were included in this analysis. In Varian Eclipse TPS two treatment techniques were designed for each patient: the 7 equal spaced fields and 7 fields by beam angle optimization IMRT. Two plans were designed for each patient with the same dose-volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and normal brain tissues and total MU in two techniques were compared to explore the dosimetric differences. Results: For the target dose, conformity and homogeneity in PTV, no statistically differences were observed in the two plans. Compared to 7 equal spaced fields IMRT plans, IMRT plans with BAO reduced the maximum dose to left and right lens by an average of 45%, 37%, the mean dose to left and right eyes were reduced by an average of 42.6%,44.5% .The maximum dose of the right optic nerve and the mean dose of normal brain tissue were reduced by an average of 23%,3% respectively. The above data were statistically significant. IMRT plans with BAO reduced the maximum dose of the brainstem and the optic chiasm, the number of MU, but the Result were not statistically significant (p> 0.05). Conclusion: Compared to 7 equal spaced fields IMRT plans, IMRT plans with BAO showed the similar target dose and reduced the dose of the organs at risk. For multiple intracranial metastases, IMRT plans with BAO were feasible and beneficial.

SU-E-T-736: The Impact of Beam Angle Optimization of Intensity-Modulated Radiotherapy for Postoperative Radiotherapy of Cervical Cancer

Purpose: To evaluate the dosimetric characteristics of intensity-modulated radiotherapy (IMRT) treatment plan with beam angle optimization. Methods: Ten post-operation patients with cervical cancer were included in this analysis. Two IMRT plans using seven beams were designed in each patient. A standard coplanar equi-space beam angles were used in the first plan (plan 1), whereas the selection of beam angle was optimized by beam angle optimization algorithm in Varian Eclipse treatment planning system for the same number of beams in the second plan (plan 2). Two plans were designed for each patient with the same dose-volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and total MU were compared. Results: For conformity and homogeneity in PTV, no statistically differences were observed in the two plans. For the mean dose in bladder, plan 2 were significantly lower than plan 1(p<0.05). No statistically significant differences were observed between two plans for the mean doses in rectum, left and right femur heads. Compared with plan1, the average monitor units reduced 16% in plan 2. Conclusion: The IMRT plan based on beam angle optimization for cervical cancer could reduce the dose delivered to bladder and also reduce MU. Therefore there were some dosimetric advantages in the IMRT plan with beam angle optimization for cervical cancer.

SU‐E‐T‐29: A Dosimetric Study of Volumetric Modulated Arc Therapy with Simultaneous Integrated Boost for Rectal Cancer

Purpose: To compare the dosimetric differences among fixed field intensity-modulated radiotherapy (IMRT) and double-arc volumetricmodulated arc therapy (VMAT) plans with simultaneous integrated boost in rectal cancer. Methods: Ten patients with rectal cancer previously treated with IMRT were included in this analysis. For each patient, two treatment techniques were designed for each patient: the fixed 7 fields IMRT and double-arc VMAT with RapidArc technique. The treatment plan was designed to deliver in one process with simultaneous integrated boost (SIB). The prescribed doses to the planning target volume of the subclinical disease (PTV1) and the gross disease (PTV2) were 45 Gy and 55 Gy in 25 fractions, respectively. The dose distribution in the target, the dose to the organs at risk, total MU and the delivery time in two techniques were compared to explore the dosimetric differences. Results: For the target dose and homogeneity in PTV1 and PTV2, no statistically differences were observed in the two plans. VMAT plans showed a better conformity in PTV1. VMAT plans reduced the mean dose to bladder, small bowel, femur heads and iliac wings. For iliac wings, VMAT plans resulted in a statistically significant reduction in irradiated volume of 15 Gy, 20 Gy, 30 Gy but increased the 10 Gy irradiated volume. VMAT plans reduced the small bowel irradiated volume of 20 Gy and 30 Gy. Compared with IMRT plans, VMAT plans showed a significant reduction of monitor units by nearly 30% and reduced treatment time by an average of 70% Conclusion: Compared to IMRT plans, VMAT plans showed the similar target dose and reduced the dose of the organs at risk, especially for small bowel and iliac wings. For rectal cancer, VMAT with simultaneous integrated boost can be carried out with high quality and efficiency.

SU-E-T-814: Whole Breast Irradiation with Two Different Intensity Modulation Radiotherapy Techniques

Purpose: Breast cancer now mainly received forward intensity modulation radiotherapy (f-IMRT) and inverse IMRT (i-IMRT). The purpose of this study was to observe the differences of two treatment methods. Methods: 10 patients after left breast-conserving surgery were selected to receive radiotherapy. For each patient, two treatment plans (f-IMRT and i-IMRT) were designed. For f-IMRT plans, two tangent beams were designed to the target, and in each tangent orientation two or three segment beams were designed to reduced high dose region in the target and the dose of lung received. For i-IMRT plans, two tangent beams were designed to the target and the treatment planning system optimize the dose according to the optimization parameters. For each plan 50Gy was prescribed. Results: In f-IMRT and i-IMRT plans, the average target conformal index (CI) were (0.67±0.06) and (0.66±0.06), (P>0.05); average homogeneity index (HI) were (28.2±6.0)% and (26.1±6.8)%, (P>0.05); volume of left lung received 20Gy (V20) were (18.7±3.3)% and (17.0±2.8)%, (P 0.05); Monitor Unit (MU) were (262±5)MU and (308±14)MU. Conclusion: Compared with i-IMRT plan, for breast cancer, the differences of CI and HI were not significant. Because of fewer MU, f-IMRT plan could reduce the machine abrasion and treatment time, but dose of normal tissue received were higher significantly than i-IMRT plan.

SU‐E‐T‐618: Dosimetric Comparison of Manual and Beam Angle Optimization of Gantry Angles in IMRT for Cervical Cancer

PURPOSE To evaluate the dosimetric characteristics of intensity-modulated radiotherapy (IMRT) treatment plan with beam angle optimization. METHODS Ten post-operation patients with cervical cancer were included in this analysis. Two IMRT plans using seven beams were designed in each patient. A standard coplanar equi-space beam angles were used in the first plan (plan 1), whereas the selection of beam angle was optimized by beam angle optimization algorithm in Varian Eclipse treatment planning system for the same number of beams in the second plan (plan 2). Two plans were designed for each patient with the same dose-volume constraints and prescription dose. All plans were normalized to the mean dose to PTV. The dose distribution in the target, the dose to the organs at risk and total MU were compared. RESULTS For conformity and homogeneity in PTV, no statistically differences were observed in the two plans. For the mean dose in bladder, plan 2 were significantly lower than plan 1(p<0.05). No statistically significant differences were observed between two plans for the mean doses in rectum, left and right femur heads. Compared with plan1, the average monitor units reduced 16% in plan 2. CONCLUSION The IMRT plan based on beam angle optimization for cervical cancer could reduce the dose delivered to bladder and also reduce MU. Therefore there were some dosimetric advantages in the IMRT plan with beam angle optimization for cervical cancer.

SU-E-T-640: Dosimetric Comparison of Intensity-Modulated Arc Therapy and Intensity-Modulated Tadiotherapy of Cervical Carcinoma

PURPOSE To compare the dosimetric differences between intensity-modulated arc therapy (ARC) and intensity-modulated tadiotherapy (IMRT) plans for cervical carcinoma. METHODS 15 cervical carcinoma cases were sdudied. All plans were prescribed 50 Gy in 25 fractions. Two treatment plans (ARC and IMRT) were generated using Varian Eclipse treatment planning system. Evaluate the dose parameters of targets, organs at risk (OAR), monitor units and treatment time, using dose-volume histogram (DVH). RESULTS The CI and HI of PTV was better in ARC plan than IMRT plan,but there were no statistical differences (P>0.05). There were statistical differences between V20,V25,V30,V35of health tissues. There were statistical differences between V15,V20,V25of femurs. There were statistical differences between V20,V25,V30of small bowel. The V35,V40,V45 of bladder and rectum increased in ARC plan but there were statistical differences. The number of MU resulted to be MUIMRT=1677±212, MUARC=894±213. The MU of ARC plan were 47% less on average than IMRT plan. The mean treatment time for ARC was decreased 40% compared with IMRT. CONCLUSION The ARC was equal to IMRT on the target coverage and the dose of OAR. The ARC plan has fewer machine monitor units and lesss treatment time and significantly improves the treatment efficiency.

SU‐E‐T‐626: A Dosimetric Study of Different MLC Expansion Aperture for the Radiotherapy of Lung Cancer

Purpose: To find a appropriate MLC expansion aperture for the radiotherapy of lungcancer. Methods: Ten patients with central lungcancer treated with radiotherapy were enrolled in this study. Ten plans were designed for each patient using varian Eclipse treatment planning system. The gantry directions and weights of fields,position of ISO, dose normalization point and the prescription dose were same in the ten plans. The only difference was the MLC aperture margin(the distance between MLC and PTV edge in BEV) .The MLC margin were 3 millimeters to 12 millimeters in the ten plans. The dose distribution in the target and the dose to the organs at risk were compared. Results: With the MLC aperture margin increased, the target volume receiving prescription dose and the dose to the organs at risk also increased together, the homogeneity in target became better and better and the conformity in target became worse and worse.When the MLC aperture margins were 3mm,4mm and 5mm,the target volume receiving prescription dose were less than 90% and have not meet the clinical requirement. When the MLC aperture margins were 10mm, 11mm and 12mm,the target volume receiving prescription dose were more than 98%, the homogeneity in target showed best,but the conformity in target were worse and the dose to the organs at risk were significantly higher. When the MLC aperture margins were 6mm,7mm, 8mm and 9mm, the target volume receiving prescription dose could meet the clinical requirement, the homogeneity and the conformity in target were moderate,Doses to organs at risk were acceptable. In the four plans,no statistically significant differences were observed in the maximum dose to spinalcord. Conclusions: For the treatment plan of lungcancer radiotherapy,the study recommended the ideal MLC aperture margin were 6mm~9mm.In practical treatment plans,we could choose the most appropriate aperture margin value according to the specific tumor size, shape and position.

SU‐E‐T‐836: Dosimetric Comparison of Intensity‐Modulated Radiotherapy and Volumetric Modulated Arc Radiotherapy for the Treatment of Multiple Intracranial Metastases

Purpose: To evaluate the dosimetric differences of intensity‐modulated radiotherapy(IMRT) and volumetric modulated arc radiotherapy (V‐MAT)for multiple intracranial metastases. Methods: Ten patients with multiple intracranial metastases were included in this analysis. Three treatment techniques were designed for each patient: intensity‐modulated radiotherapy with seven fixed field(IMRT), volumetric modulated arc radiotherapy with single 358° coplanar arc(V‐MAT1) and volumetric modulated arc radiotherapy with double 358° coplanar arcs(V‐MAT2) . Dose prescription was 60Gy to PTV in 30 fractions. All plans were normalized to the mean dose to PTV.The dose distribution in the target,the dose to the organs at risk,total MU and delivery time in three techniques were compared. Results: The best conformity and homogeneity in PTV were observed in V‐MAT2 plans,no statistically significant differences were observed between IMRT and V‐MAT1.For the maximum dose in lens,eyes and brainstem,the two V‐MAT plans were significantly lower than IMRT plan(p<0.05). For the maximum dose in optic nerves,the V‐MAT2 plans were statistically lower than IMRT plan(p<0.05).For the mean dose to normal braintissue, no statistically differences were observed in the three techniques. V‐MAT2 plans showed the highest values in the normal braintissue volume receiving 5Gy and 10 Gy doses.In the normal braintissue volume receiving 20Gy,30Gy and 40 Gy doses,IMRT and V‐MAT2 plans showed the highest and lowest values respectively. Compared with IMRT plans,the average monitor units reduced 29% and 24% in V‐MAT 1 and V‐MAT2 plans and the delivery time was significantly shorter in V‐MAT plans. Conclusions: Comparing to IMRT plans, V‐MAT plans showed similar or better in the target dose distribution,reduced irradiation doses on organs in risk and moreover significantly decreased the monitor units and delivery time.

SU‐FF‐T‐525: The Study On the Effects of MLC Leakage‐Ray and Scattered‐Ray to Eyes and Lens in Whole Brain Radiotherapy

Purpose: to study the effects of multi‐leaf collimator(MLC) leakage‐ray and scattered‐ray to eyes and lens in radiotherapy of patients with brainmetastasistumor.Methods and Materials: 10 patients treated by whole brainradiotherapy were selected, for each of which two model treatment plans were designed. Plan_1: Two fields in 90° (field_1) and 270° (field_2) were arranged to the brain, while the angle of collimators were fixed in 0°. Plan_2: The same angle of fields were arranged, but the angle of collimators were modified with rotation of 45° in field_1 and −45° in field_2, respectively. In this case, the lens and most of eyes were out of irradiated volume, so that most of leakage‐ray and scattered‐ray effecting to them were reduced. The whole brain was irradiated to the prescription dose. The dose of lens and eyes received were evaluated by dose‐volume histogram (DVH). Results: two plans both met the clinical demands with almost same dose distribution to whole brain. Compared to Plan_1, the maximum dose on left lens decreased on average 100.5cGy (t = 8.299, P<0.01), and the maximum dose on right lens decreased on average 109.5cGy (t = 7.567, P<0.01); the mean dose on left eyes decreased on average 151.6cGy (t = 3.252, P<0.01), and the mean dose of right eyes decreased on average 124.2cGy (t = 3.256, P<0.01). Conclusions: in the whole brainradiotherapy, the effects of leakage‐ray and scattered‐ray to lens and eyes were significant. Therefor, it is necessary and salutary to modify the angle of collimators in order to reduce the dose on lens and eyes remarkably.