Patient-Specific Heart Constraint: A Tool for Optimization and Evaluation of Mean Heart Dose in Breast Cancer Patients

PurposeOur institution introduced a patient-specific heart constraint (PSHC) and a mean heart dose (MHD) constraint of 4 Gy for all patients receiving breast radiation therapy (RT) with a simultaneous boost (SIB). This was introduced as a method to calculate the predicted MHD before optimizing IMRT fields. We sought to determine whether the introduction of a PSHC reduced MHD, while maintaining optimally dosed treatment plans.Material/MethodsPatients were retrospectively divided into 2 groups, pre- and postintroduction of the PSHC. The breast and SIB Planning Target Volumes (PTVs) were prescribed to 50 Gy and 57 Gy, respectively, in 25 fractions. Plans were generated using a hybrid IMRT technique, 30 Gy using an open tangential field arrangement, and 27 Gy using IMRT fields. The PSHC was calculated using MHD of open tangential field × 2. A paired t test compared PTV coverage and heart doses between cohorts (P < .05 significant).ResultsA total of 264 patients were included (138 pre-PSHC and 126 post-PSHC) with 137 right-sided and 127 left-sided treatments. MHD was significantly reduced across both right-sided (–0.4 Gy, P < .0001) and left-sided (–1.2 Gy, P < .0001) treatments overall. Left-sided treatments were further examined between free breathing and deep inspiration breath-hold (DIBH). DIBH showed reduction in MHD, although it was not significant (–0.46 Gy, P = .34). Heart V5 Gy showed reduction in right-sided (–1%, P = .002) and left-sided (–9.2%, P < .0001) treatments overall. Left-sided free breathing showed significant reduction (–8.8%, P < .0001), and DIBH also showed significant reduction (–5.1%, P = .0034). Tumor bed doses remained above the 54.15 Gy (95% of 57 Gy) threshold for all plans.ConclusionIntroduction of a PSHC can reduce MHD and V5 Gy for patients receiving whole breast RT with SIB while maintaining optimally dosed plans, with the greatest benefit shown for left-sided, free-breathing treatments.     

Comparison of Techniques for Involved-Site Radiation Therapy in Patients With Lower Mediastinal Lymphoma

PurposePatients with lower mediastinal lymphoma (LML) benefit dosimetrically from proton therapy (PT) compared with intensity modulated radiation therapy (IMRT). The added dosimetric benefit of deep-inspiration breath-hold (DIBH) is unknown; therefore, we evaluated IMRT versus PT and free-breathing (FB) versus DIBH among patients with LML.Methods and MaterialsTwenty-one patients with LML underwent 4-dimensional computed tomography and 3 sequential DIBH scans at simulation. Involved-site radiation therapy target volumes and organ-at-risk contours were developed for both DIBH and FB scans. FB-IMRT, DIBH-IMRT, FB-PT, and DIBH-PT plans were generated for each patient for comparison.ResultsThe median difference in lung volume between the DIBH and FB scans was 1275 mL; the average difference in clinical target volume was 5.7 mL. DIBH-IMRT produced a lower mean lung dose (10.8 vs 11.9 Gy; P < .001) than FB-IMRT, with no difference in mean heart dose (MHD; 16.1 vs 15.0 Gy; P = .992). Both PT plans produced a significantly lower mean dose to the lung, heart, left ventricle, esophagus, and nontarget body than DIBH-IMRT. DIBH-PT reduced the median MHD by 4.2 Gy (P < .0001); left ventricle dose by 5.1 Gy (P < .0001); and lung V5 by 26% (P < .0001) versus DIBH-IMRT. The 2 PT plans were comparable, with DIBH-PT reducing mean lung dose (7.0 vs 7.7 Gy; P = .063) and with no difference in MHD (10.3 vs 9.5 Gy; P = .992).ConclusionsAmong patients with LML, DIBH (IMRT or PT) improved lung dosimetry over FB but had little influence on MHD. PT (DIBH and FB) significantly reduced lung, heart, esophagus, and nontarget body dose compared with DIBH IMRT, potentially reducing the risk of late complications.     

乳腺癌改良根治术后内乳淋巴结放疗患者VMAT与IMRT计划剂量学比较

目的 探讨容积调强弧形治疗(VMAT)和固定野动态调强放疗(IMRT)在左侧乳腺癌改良根治术后需辅助放疗并内乳淋巴结照射患者的剂量学差异。方法 对20例左侧乳腺癌患者制定VMAT和IMRT两种放疗计划。通过剂量体积直方图计算靶区和危及器官剂量学参数。对分类变量行χ²或Fisher′s精确概率法检验,连续变量根据正态性采用配对t检验或秩和检验。结果 IMRT靶区均匀性指数比VMAT高(P<0.05)。VMAT治疗时间较IMRT更短(P<0.01)。VMAT患侧肺V20Gy、V30Gy优于IMRT (P<0.05)。VMAT在冠脉左前降支Dmean、Dmax和心脏V30Gy、V40Gy、Dmean、Dmax优于IMRT (P<0.01)。食管DmeanVMAT优于IMRT (P<0.05),但健侧肺V5Gy、V10Gy和食管DmaxIMRT优于VMAT (P<0.05)。结论 VMAT可以显著减少心脏、健侧肺、脊髓、食管照射剂量,缩短治疗时间。对于左侧乳腺癌根治术后需辅助放疗并照射内乳淋巴结的患者,VMAT技术比IMRT技术可以更好保护正常组织。     

Dosimetric comparison between IMRT and VMAT in patients undergoing internal mammary lymph node radiotherapy after modified radical mastectomy

Objective To investigate the dosimetric differences in volumetric-modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) in patients receiving adjuvant radiotherapy and internal lymph node irradiation after left-sided modified radical mastectomy. Methods VMAT and IMRT radiotherapy plans were established for 20 patients undergoing left-sided modified radical mastectomy. The dosimetric parameters of the target area and organs at risk were calculated by the dose volume histogram. The categorical variables were tested by χ² or Fisher′s exact probability test. The continuous variables with normal distribution were analyzed by paired-t test or rank-sum test. Results Among the two radiotherapy techniques, the homogeneity index of IMRT was significantly higher than that of VMAT (P<0.05). The time of VMAT treatment was significantly shorter than that of IMRT (P<0.01). VMAT was superior to IMRT in V20Gy and V30Gy of the affected lung (both P<0.05). VMAT was superior to IMRT in the left anterior descending coronary artery Dmean, Dmax, and heart V30Gy, V40Gy, Dmean and Dmax(all P<0.01). The esophageal Dmean in the VMAT group was superior to that in the IMRT group (P<0.05). The V5Gy and V10Gy of the contralateral lung and the Dmax of the esophagus in the IMRT group were significantly better compared with those in the VMAT group (all P<0.05). Conclusions VMAT can significantly reduce the dose of the heart, contralateral lung, spinal cord, esophagus and other vital organs, and shorten the treatment time. For patients who need adjuvant radiotherapy and internal mammary lymph node irradiation after left-sided modified radical mastectomy, VMAT technology can better protect normal tissues than IMRT.     

Dosimetric Comparison of Volumetric Modulated Arc Therapy and Intensity Modulated Radiation Therapy for Soft Tissue Sarcoma of the Extremities

PurposeRadiation therapy is a standard part of limb conserving therapy for extremity soft tissue sarcoma (STS) at high risk of recurrence. Toxic effects increase with radiation dose and volume of normal tissue irradiated. This study sought to compare dosimetry of volumetric modulated arc therapy (VMAT) with intensity modulated radiation therapy (IMRT) and to investigate the optimal planning technique.Methods and MaterialsTwenty patients with extremity STS who underwent preoperative radiation therapy (50 Gy in 25 fractions) between 2016 and 2020 at a specialised sarcoma center were included. The original treatment techniques were sliding window IMRT or 3-dimensional conformal. VMAT plans were retrospectively generated according to the original tumor and organ-at-risk constraints. Quality assurance was performed as per departmental protocol. Wilcoxon signed-rank test was used to compare dosimetric parameters (for planning target volume [PTV], in-field bone, and soft tissue structures), monitor units (MUs), and treatment time.ResultsMedian patient age was 65 years and the majority were male (n = 14, 70%). The most common subtype was undifferentiated pleomorphic sarcoma (n = 14, 70%), and most tumors were located on the thigh (n = 12, 60%). Median PTV was 1110 cm³ and median volume of in-field bone 236 cm³. VMAT plans had significantly lower average MU (480 vs 862 MU, P < .001) and overall treatment time (300 vs 153 seconds, P < .001). PTV coverage favored VMAT, with marginally higher mean, minimum, and maximum doses and higher conformity index. However, differences were not statistically significant. Dose to infield bone and soft tissue structures were similar or slightly lower with VMAT.ConclusionsIn extremity STS, VMAT plans demonstrated a favorable trend toward tumor coverage and dose conformity compared with IMRT along with significantly lower MUs and half the overall treatment time.     

Dosimetric Comparison Between Helical Tomotherapy and Volumetric Modulated Arc Therapy in Patients With Malignant Pleural Mesothelioma

AimsTo carry out a dosimetric comparison and constraints feasibility proof of adjuvant radiotherapy through helical tomotherapy or volumetric modulated arc therapy (VMAT) for malignant pleural mesothelioma patients after pleurectomy/decortication.Materials and methodsRetrospective calculations were carried out on previously acquired simulations. A whole-pleura volume with 50.4 Gy in 28 fractions was prescribed, simulating a no residual tumour situation. Calculations were carried out using an anisotropic analytical algorithm with a 2.0 mm grid. Beam-on time, planning target volume (PTV) coverage, homogeneity index and organ at risk exposure were compared.ResultsSixteen patient plans were calculated per device. Constraints were met overall by both modalities. For helical tomotherapy and VMAT plans, median beam-on times were 13.8 (11.6–16.1) min and 6.4 (6.1–7.0) min; P = 0.006. The median left-sided radiotherapy PTV D₉₈ were 48.1 (48.0–48.8) Gy and 47.6 (46.5–48.3) Gy; P = 0.023. No significant difference for right-sided radiotherapy was found. PTV D₂ for left-sided radiotherapy was higher with VMAT (P = 0.014). For right-sided radiotherapy, helical tomotherapy showed higher doses (P = 0.039). No homogeneity index differences for left-sided radiotherapy (P = 1.00) and right-sided radiotherapy (P = 0.598) were seen. Significant organ at risk exposure differences were found on left-sided radiotherapy whole-lung V_20, as well as D₅₀ (both P = 0.008). Higher contralateral lung and ipsilateral kidney exposures were found with VMAT plans for both treatment sides.ConclusionAdjuvant radiotherapy after pleurectomy/decortication in malignant pleural mesothelioma patients, with a VMAT- or helical tomotherapy-based platform, is dosimetrically feasible. Lung sparing was mostly improved with helical tomotherapy. Technique selection must be carried out according to availability and clinical criteria.     

Radiation dose and cardiac risk in breast cancer treatment: An analysis of modern radiation therapy including community settings

Purpose

Adjuvant radiation therapy (RT) for breast cancer improves outcomes, but prior studies have documented substantive cardiac dose and cardiac risk. We assessed the mean heart dose (MHD) of RT and estimated the risk of RT-associated cardiac toxicity in women undergoing adjuvant RT for breast cancer in contemporary (predominantly) community practice.

Comparison of Three Dimensional Conformal Radiation Therapy,Intensity Modulated Radiation Therapy and Volumetric Modulated Arc Therapy for Low Radiation Exposure of Normal Tissue in Patients with Prostate Cancer

Radiotherapy has an important role in the treatment of prostate cancer. Three-dimensional conformalradiation therapy (3D-CRT), intensity modulated radiation therapy (IMRT) and volumetric modulated arctherapy (VMAT) techniques are all applied for this purpose. However, the risk of secondary radiation-inducedbladder cancer is significantly elevated in irradiated patients compared surgery-only or watchful waiting groups.There are also reports of risk of secondary cancer with low doses to normal tissues. This study was designed tocompare received volumes of low doses among 3D-CRT, IMRT and VMAT techniques for prostate patients. Tenprostate cancer patients were selected retrospectively for this planning study. Treatment plans were generatedusing 3D-CRT, IMRT and VMAT techniques. Conformity index (CI), homogenity index (HI), receiving 5 Gy ofthe volume (V5%), receiving 2 Gy of the volume (V2%), receiving 1 Gy of the volume (V1%) and monitor units(MUs) were compared. This study confirms that VMAT has slightly better CI while thev olume of low doseswas higher. VMAT had lower MUs than IMRT. 3D-CRT had the lowest MU, CI and HI. If target coverage andnormal tissue sparing are comparable between different treatment techniques, the risk of second malignancyshould be a important factor in the selection of treatment.     

Dose comparisons for conformal, IMRT and VMAT prostate plans

Purpose: Volumetric‐modulated arc therapy (VMAT) is a relatively new treatment technique in radiation therapy. A comparison study of conformal, intensity‐modulated radiation therapy (IMRT) and single‐ and double‐arc VMAT plans was undertaken to evaluate the dosimetric impact of this new technology in prostate cases. The research questions were as follows: how does VMAT dosimetry compare with IMRT and conformal plans?; does VMAT increase the volume of bowel receiving lower doses?; are one or two VMAT arcs required for standard prostate cases? Methods: Eight prostate cancer and post‐prostatectomy patients were randomly selected for this study. Conformal, IMRT and single and double Arc VMAT plans were generated and dosimetric evaluations were performed. Each plan was prescribed a total of 75.6 Gy over a course of 42 fractions to the planning target volume (PTV). Results: The Healthy Tissue Conformity Index and the conformation number results revealed the IMRT and two VMAT techniques to have superior dosimetry to the PTV compared with the conformal plans. The maximum dose delivered to the PTV was significantly higher with the single‐arc VMAT technique compared with the conformal or double‐arc VMAT plans. There were no significant differences between the planning techniques for the bladder and small bowel dosimetry. However, IMRT and VMAT plans delivered less radiation to the rectum and femoral heads, and a single‐arc VMAT plan was optimal for the right femoral head and the two VMAT techniques were optimal to the IMRT plans for the left femoral head. Conclusions: Single‐ and double‐arc VMAT consistently resulted in favourable or slightly superior dosimetry when compared with static gantry IMRT for prostate cases. Both the VMAT techniques and static gantry IMRT resulted in superior critical tissue sparing when compared with conformal plans.     

患者因素对乳腺癌保乳术后IMRT计划设计影响分析

目的 探讨患者VPTV、MHD、CLD、CTR对乳腺癌保乳术后IMRT计划设计的影响。方法 2016—2017年在我院接受全乳IMRT的48例女性乳腺癌保乳术后患者(左侧31例、右侧17例),放疗处方剂量为PTV 50 Gy,2 Gy/次。每个患者的调强计划同时使用物理参数和EUD对目标函数进行优化。采用一元和多元线性回归分析预测影响因子与OAR百分剂量体积、CI和HI间关系。结果 CTR和VPTV是左侧乳腺癌CI独立影响因素(R²值分别为0.56、0.56,P值分别为0.04、0)。CLD是左侧乳腺癌HI独立影响因素(R²=0.17,P=0.023),VPTV是右侧CI的独立影响因素(R²=0.48,P=0)。MHD和CTR是心脏VHeart30的预测因子。MHD和CLD是心脏DmaxHeart的预测因子。左侧乳腺癌预测公式为CI=0.38+0.32CTR,HI=1.06+0.02CLD。右侧CI=0.48。左侧Vlung20=12.68+3.18CLD,Vlung10=18.78+4.3CLD,Vlung5=26.2+5.2CLD,Dmeanlung=686.7+210.1CLD。心脏VHeart30=(-13.65)+30.5CTR+1.9MHD,DmaxHeart=5140.1+248.9MHD-195.6CLD。患者的心脏体积与MHD、VHeart10 、VHeart5、DmeanHeart和DmaxHeart无相关性。患者的全肺体积与CLD、Vlung20、Vlung10、Vlung5、Dmeanlung无相关性。左侧乳腺癌计划CI和HI的平均值分别为0.63±0.06(0.46~0.72)和1.09±0.02(1.074~1.14),右侧乳腺癌计划CI和HI的均值分别为0.65±0.08(0.48~0.76)和1.09±0.04(1.03~1.18)。结论 CTR、CLD和MHD可以预测左侧乳腺癌调强计划各个参数的合理性,右侧乳腺癌则不适用。据此生成的计算公式可以帮助物理师选择优选的射野设置方式,提高治疗计划的质量。     

Heart-Sparing Capability and Positional Reproducibility of Continuous Positive Airway Pressure in Left-Sided Breast Radiation Therapy

PurposeOur purpose was to investigate the interfraction and intrafraction reproducibility and practical applicability of continuous positive airway pressure (CPAP) for left breast volumetric modulated arc therapy (VMAT).Methods and MaterialsInterfraction reproducibility of the position of the heart was evaluated by measuring the heart-to-target distance on 20 planning computed tomography (CT) and 300 daily cone beam CT of 20 patients with left breast cancer treated with a 15-fraction VMAT. The dosimetric metrics of the whole heart and its substructures were compared between CPAP and free-breathing based VMAT plans. Intrafraction reproducibility was evaluated by measuring the motions of the breast target and diaphragm in 4-dimensional CT of 20 female patients with nonbreast cancer. Lastly, we analyzed the CPAP compliance data of 237 consecutive patients with left-sided breast cancer with and without internal mammary node irradiation (IMNI).ResultsThe heart position was reproducible as evidenced by an absolute average heart-to-target distance error of 2.0 ± 2.0 mm. Compared with free-breathing, CPAP significantly reduced the mean heart dose and the dose to the left ventricle and left anterior descending artery. The average intrafraction position variation of the breast target was 0.5 ± 0.5, 2.5 ± 2.0, and 1.8 ± 1.4 mm in the mediolateral, craniocaudal, and anteroposterior directions, respectively. CPAP was successfully applied in 221 patients (93%), with a mean heart dose of 1.6 ± 0.7 Gy (IMNI: 2.0 Gy and no IMNI: 1.1 Gy).ConclusionsCPAP has adequate heart-sparing capability and sufficient reproducibility in VMAT for left-sided breast cancer treatment, with a high compliance rate. Thus, CPAP is applicable in routine practice for left-sided breast cancer radiation therapy.     

A prospective trial of volumetric intensity-modulated arc therapy vs conventional intensity modulated radiation therapy in advanced head and neck cancer

AIM: To prospectively compare volumetric intensity-modulated arc therapy (VMAT) and conventional intensity-modulated radiation therapy (IMRT) in coverage of planning target volumes and avoidance of multiple organs at risk (OARs) in patients undergoing definitive chemoradiotherapy for advanced (stage III or IV) squamous cell cancer of the head and neck.METHODS: Computed tomography scans of 20 patients with advanced tumors of the larynx, naso-, oro- and hypopharynx were prospectively planned using IMRT (7 field) and VMAT using two arcs. Calculated doses to planning target volume (PTV) and OAR were compared between IMRT and VMAT plans. Dose-volume histograms (DVH) were utilized to obtain calculated doses to PTV and OAR, including parotids, cochlea, spinal cord, brainstem, anterior tongue, pituitary and brachial plexus. DVH’s for all structures were compared between IMRT and VMAT plans. In addition the plans were compared for dose conformity and homogeneity. The final treatment plan was chosen by the treating radiation oncologist.RESULTS: VMAT was chosen as the ultimate plan in 18 of 20 patients (90%) because the plans were thought to be otherwise clinically equivalent. The IMRT plan was chosen in 2 of 20 patients because the VMAT plan produced concentric irradiation of the cord which was not overcome even with an avoidance structure. For all patients, VMAT plans had a lower number of average monitor units on average (MU = 542.85) than IMRT plans (MU = 1612.58) (P < 0.001). Using the conformity index (CI), defined as the 95% isodose volume divided by the PTV, the IMRT plan was more conformal with a lower conformity index (CI = 1.61) than the VMAT plan (CI = 2.00) (P = 0.003). Dose homogeneity, as measured by average standard deviation of dose distribution over the PTV, was not different with VMAT (1.45 Gy) or IMRT (1.73 Gy) (P = 0.069). There were no differences in sparing organs at risk.CONCLUSION: In this prospective study, VMAT plans were chosen over IMRT 90% of the time. Compared to IMRT, VMAT plans used only one third of the MUs, had shorter treatment times, and similar sparing of OAR. Overall, VMAT provided similar dose homogeneity but less conformity in PTV irradiation compared to IMRT. This difference in conformity was not clinically significant.     

Radiotherapy for unresectable sinonasal cancers: Dosimetric comparison of intensity modulated radiation therapy with coplanar and non-coplanar volumetric modulated arc therapy

Background and purposeTo compare volumetric modulated arc therapy (VMAT) and intensity modulated radiation therapy (IMRT) plans for treatment of unresectable paranasal sinuses cancers (PNSCs) with different clinical presentations.Material and methodsFour patients treated for primary target volume only (group 1), four requiring elective nodal irradiation (group 2) and four with positive nodes in macroscopic disease (group 3) were selected. For each patient were generated 7 fields IMRT, coplanar VMAT (c-VMAT) and non-coplanar VMAT (nc-VMAT) treatment plans. Total doses were 70 Gy and 54 Gy to high dose planning target volume (HD-PTV) and low-dose-PTV, respectively. Dose–volume histogram, conformity and homogeneity index (CI and HI), and monitor units (MUs) per Gy were evaluated.ResultsVMAT provided significantly better target coverage, in terms of V_100% (Volume encompassed by the isodose 100%), than IMRT, in particular when nc-VMAT was used. In general, organ at risk sparing is similar with the three approaches, although nc-VMAT can allow a statistically significant reduction of dose to contralateral parotid gland and cochlea for all three groups.ConclusionsVMAT can offer significant improvement of treatment for all unresectable PNSCs over existing IMRT techniques. In particular, nc-VMAT may be a further advantage for those patients with sinonasal cancers and involvement of the nodes in whom large volumes and complex/irregular shape have to be irradiated, even if clinical benefits should be established in the future.     

Does inverse‐planned intensity‐modulated radiation therapy have a role in the treatment of patients with left‐sided breast cancer?

Introduction: The purpose of the study was to determine if multi‐field inverse‐planned intensity‐modulated radiation therapy (IMRT) improves on the sparing of organs at risk (heart, lungs and contralateral breast) when compared with field‐in‐field forward‐planned RT (FiF). Methods: The planning CT scans of 10 women with left‐sided breast cancer previously treated with whole‐breast RT on an inclined breast board with both arms supported above the head were retrieved. The whole breast planning target volume (PTV) was defined by clinical mark‐up and contoured on all relevant CT slices as were the organs at risk. For each patient, three plans were generated using FiF, five‐ and nine‐field inverse‐planned IMRT, all to a total dose of 50 Gy to the whole breast. Mean and maximum doses to the organs at risk and the homogeneity index (HI) of the whole‐breast PTV were compared. Results: The mean heart dose for the FiF plans was 2.63 Gy compared with 4.04 Gy for the five‐field and 4.30 Gy for the nine‐field IMRT plans, with no significant differences in the HI of the whole‐breast PTV in all plans. The FiF plans resulted in a mean contralateral breast dose of 0.58 Gy compared with 0.70 and 2.08 Gy for the five‐ and nine‐field IMRT plans, respectively. Conclusions: FiF resulted in a lower mean heart and contralateral breast dose with comparable HI of the whole‐breast PTV in comparison with inverse‐planned IMRT using five or nine fields.     

Dosimetric Comparison and Feasibility of Simultaneous Integrated Boost (SIB) in Treatment of Malignant Gliomas Using Intensity Modulated Radiotherapy (IMRT) or Volumetric Modulated Arc Therapy (VMAT)

Objective: To evaluate the dosimetric parameters of Simultaneous Integrated Boost in the treatment of malignantgliomas and compare the SIB plans of VMAT and IMRT. Methodology: CT and MRI of 28 patients were used forgenerating SIB plans with VMAT and IMRT. A dose of 2Gy per fraction was prescribed to the CPTV and 2.4Gy tothe GPTV for a total of 25 fractions. The plans were accepted only if they met the set of planning objectives definedin the protocol. Results: We could achieve the planning objectives in all the SIB plans. Although GPTV coverage wasstatistically better in VMAT (98.67% vs 98.19% ;p=0.024) the difference is not clinically meaningful. The conformityindex for GPTV was higher in IMRT (0.83 vs 0.76; p=0.001). The coverage of CPTV was better in IMRT(97.88% vs 96.87%; p=0.021). But the conformity index of CPTVannulus was higher in VMAT (0.72 vs 0.67; p=0.01).There was no difference in homogeneity index of GPTV and CPTV annulus between the plans. The mean dose receivedby normal brain was higher in IMRT (28Gy vs 24.2Gy; p<0.001). Ipsilateral optic nerve has received lesser Dmax inIMRT (44.2Gy vs 46.95Gy; p=0.02). No difference was seen in Dmax of brainstem, optic chiasm, contralateral opticnerve. The treatment times and monitor units were significantly less in VMAT. Conclusion: SIB is dosimetricallyfeasible for hypofractionation in malignant gliomas using IMRT and VMAT. IMRT plans had better boost conformity,lower ipsilateral optic nerve and brainstem maximum doses compared to VMAT. Whereas, VMAT had better coverage,better overall PTV conformity, lower normal brain mean dose, lower monitor units and lesser treatment times. Althoughplanning of VMAT is cumbersome and time consuming, the advantage of reducing treatment time is beneficial tothe patients’ comfort and better managing of patient load in high volume centres.     

Adjuvant Radiotherapy after Breast Conserving Treatment for Breast Cancer:A Dosimetric Comparison between Volumetric Modulated Arc Therapy and Intensity Modulated Radiotherapy

Background: Radiotherapy is an important treatment of choice for breast cancer patients after breastconservingsurgery, and we compare the feasibility of using dual arc volumetric modulated arc therapy (VMAT2),single arc volumetric modulated arc therapy (VMAT1) and Multi-beam Intensity Modulated Radiotherapy(M-IMRT) on patients after breast-conserving surgery. Materials and Methods: Thirty patients with breastcancer (half right-sided and half left-sided) treated by conservative lumpectomy and requiring whole breastradiotherapy with tumor bed boost were planned with three different radiotherapy techniques: 1) VMAT1; 2)VMAT2; 3) M-IMRT. The distributions for the planning target volume (PTV) and organs at risk (OARs) werecompared. Dosimetries for all the techniques were compared. Results: All three techniques satisfied the doseconstraint well. VMAT2 showed no obvious difference in the homogeneity index (HI) and conformity index(CI) of the PTV with respect to M-IMRT and VMAT1. VMAT2 clearly improved the treatment efficiency andcan also decrease the mean dose and V5Gy of the contralateral lung. The mean dose and maximum dose of thespinal cord and contralateral breast were lower for VMAT2 than the other two techniques. The very low dosedistribution (V1Gy) of the contralateral breast also showed great reduction in VMAT2 compared with the othertwo techniques. For the ipsilateral lung of right-sided breast cancer, the mean dose was decreased significantlyin VMAT2 compared with VMAT1 and M-IMRT. The V20Gy and V30Gy of the ipsilateral lung of the leftsidedbreast cancer for VMAT2 showed obvious reduction compared with the other two techniques. The heartstatistics of VMAT2 also decreased considerably compared to VMAT1 and M-IMRT. Conclusions: Comparedto the other two techniques, the dual arc volumetric modulated arc therapy technique reduced radiation doseexposure to the organs at risk and maintained a reasonable target dose distribution.