Adaptive radiotherapy for soft tissue changes during helical tomotherapy for head and neck cancer

Purpose

The goal of the present study was to assess the frequency and impact of replanning triggered solely by soft tissue changes observed on the daily setup mega-voltage CT (MVCT) in head and neck cancer (H&;N) helical tomotherapy (HT).

Material and methods

A total of 11 patients underwent adaptive radiotherapy (ART) using MVCT. Preconditions were a soft tissue change >?0.5?cm and a tight mask. The dose–volume histograms (DVHs) derived from the initial planning kVCT (inPlan), the recalculated DVHs of the fraction (fx) when replanning was decided (actSit) and the DVHs of the new plan (adaptPlan) were compared. Assessed were the following: maximum dose (D_max), minimum dose (D_min), and mean dose (D_mean) to the planning target volume (PTV) normalized to the prescribed dose; the D_mean/fx to the parotid glands (PG), oral cavity (OC), and larynx (Lx); and the D_max/fx to the spinal cord (SC) in Gy/fx.

Results

No patient had palpable soft tissue changes. The median weight loss at the moment of replanning was 2.3?kg. The median PTV D_mean was 100% for inPlan, 103% for actSit, and 100% for adaptPlan. The PTV was always covered by the prescribed dose. A statistically significant increase was noted for all organs at risk (OAR) in the actSit. The D_mean to the Lx, the D_mean to the OC and the D_max to the SC were statistically better in the adaptPlan. No statistically significant improvement was achieved by ART for the PGs. No significant correlations between weight and volume loss or between the volume changes of the organs to each other were observed, except a strong positive correlation of the shrinkage of the PGs (ρ?=?+?0.77, p?=?0.005).

Conclusion

Soft tissue shrinkage without clinical palpable changes will not affect the coverage of the PTV, but translates into a higher delivered dose to the PTV itself and the normal tissue outside the PTV. The gain by ART in individual patients—especially in patients who receive doses close to the tolerance doses of the OAR—could be substantial.     

胰腺癌立体定向体部放疗摆位误差对靶区乏氧区的同步推量研究

目的 分析胰腺癌立体定向体部放射治疗（SBRT）乏氧区的同步推量（SIB）对靶区和危及器官的影响,预测肿瘤内部乏氧区的最佳推量。方法 回顾性分析10例胰腺癌SBRT患者治疗前后分别获取的共100组锥形束CT（CBCT）校正数据,导入计划系统重新计算靶区和危及器官剂量。引入两种肿瘤控制率（TCP）模型计算不同乏氧状态下的肿瘤控制率,找出肿瘤控制率与靶区剂量的关系。结果 治疗前摆位误差引起的计划靶区（PTV）和内靶区（ITV）的靶区覆盖率平均值分别下降8.9%和9.2%,治疗过程中摆位误差引起的PTV和ITV靶区覆盖率的平均值分别下降1.6%和1.3%。所有计划中危及器官剂量偏差的平均值在-0.11~0.26 Gy之间。氧增强比（OER）为1、1.5和3时,乏氧区同步推量的平均剂量（D_mean）预测值分别为31.4、34.0和37.2 Gy（Niemierko模型）或31.6、33.9和37.2 Gy（Poisson模型）。结论 经过CBCT校正以后,治疗过程中的误差对靶区覆盖率和危及器官的影响可忽略。不考虑肿瘤乏氧问题会极大影响肿瘤控制率的计算。为消除乏氧对肿瘤控制的影响,胰腺癌乏氧区（OER=3）的D_mean应至少为处方剂量的1.24倍。     

Adaptive Radiation Therapy for Localized Mesothelioma with Mediastinal Metastasis Using Helical Tomotherapy

The purpose of this study was to compare 2 adaptive radiotherapy strategies with helical tomotherapy. A patient having mesothelioma with mediastinal nodes was treated using helical tomotherapy with pretreatment megavoltage CT (MVCT) imaging. Gross tumor volumes (GTVs) were outlined on every MVCT study. Two alternatives for adapting the treatment were investigated: (1) keeping the prescribed dose to the targets while reducing the dose to the OARs and (2) escalating the target dose while maintaining the original level of healthy tissue sparing. Intensity modulated radiotherapy (step-and-shoot IMRT) and 3D conformal radiotherapy (3DCRT) plans for the patient were generated and compared. The primary lesion and nodal mass regressed by 16.2% and 32.5%, respectively. Adapted GTVs and reduced planning target volume (PTV) margins of 4 mm after 22 fractions decrease the planned mean lung dose by 19.4%. For dose escalation, the planned prescribed doses may be increased from 50.0 to 58.7 Gy in PTV₁ and from 60.0 to 70.5 Gy in PTV₂. The step-and-shoot IMRT plan was better in sparing healthy tissue but did not provide target coverage as well as the helical tomotherapy plan. The 3DCRT plan resulted in a prohibitively high planned dose to the spinal cord. MVCT studies provide information both for setup correction and plan adaptation. Improved healthy tissue sparing and/or dose escalation can be achieved by adaptive planning.     

基于深度学习的乳腺癌保乳术后调强放疗剂量分布预测

目的研究基于深度学习的方法预测乳腺癌保乳术后调强放疗(IMRT)剂量分布, 并评估其预测精度。方法回顾性分析2018年1月至2023年3月在上海国际医学中心接受IMRT的110例左侧乳腺癌保乳术后患者的调强放疗数据, 随机固定选择80例作为训练集, 随机固定10例作为验证集, 剩余20例作为测试集。首先将患者的计算机体层成像(CT)图像、感兴趣区、体素与靶区距离和对应的剂量分布四通道特征作为输入数据, 然后使用U-net网络进行训练得到预测模型, 利用该模型对测试集进行剂量预测, 验证体素与靶区距离特征在剂量预测中的影响, 并将剂量预测结果与实际手动计划剂量进行比较。结果加入体素与靶区距离特征的模型使预测精度更高, 测试集中20例患者的剂量评分和剂量体积直方图(DVH)评分分别为2.10±0.18和2.28±0.08, 与手动计划剂量分布更加接近(t=2.52、2.40, P<0.05)。靶区和危及器官(OAR)的剂量预测结果与手动计划剂量的偏差在4%以内, 健侧乳腺平均剂量增加了13 cGy, 均在临床可接受范围内。除PTV60的D2、D98(Di为i%的PTV体积接受的剂量)...     

An in silico comparative dosimetric study of postmastectomy locoregional irradiation using intensity-modulated vs 3-dimensional conventional radiotherapy

An in silico dosimetric evaluation of intensity-modulated radiation therapy (IMRT) vs 3-dimensional conventional radiation therapy (3D-CRT) treatment plans in postmastectomy radiation therapy (PMRT) to the chest wall and regional lymphatics was conducted. Twenty-five consecutive patients with breast cancer referred for locoregional PMRT, stages T_2-4 with N_1-3, were planned to receive 50?Gy in 25 fractions with IMRT. Additionally, a 3D-CRT plan was generated using identical contours for the clinical target volumes (CTV), planning target volumes (PTV), and organs at risk (OAR). Treatment plans were assessed using dose-volume histogram (DVH) parameters of D₉₈, D₉₅, D₅₀, D₂, and homogeneity index for individual CTVs and PTVs. OARs evaluated were ipsilateral and contralateral lungs, heart, spinal cord, and opposite breast. Most DVH parameters pertaining to CTVs and PTVs significantly favored IMRT. V₂₀ for ipsilateral and contralateral lungs, D₃₃ of heart and maximum dose to spinal cord favored IMRT (all p?<?0.001). The mean dose to the opposite breast was significantly lesser with 3D-CRT (5.8?±?1.8?Gy vs 2.0?±?1.0?Gy, p?<?0.001). Thus, except for the mean dose to the opposite breast, the compliance to DVH constraints applied to PTV and OARs were significantly better with IMRT. At a median follow-up of 76 months (7-91), none had locoregional failure or pulmonary or cardiac morbidity. For PMRT, requiring comprehensive irradiation to both chest wall and regional lymphatics, IMRT offers superior dosimetric advantages over 3D-CRT. This was also corroborated by long-term outcomes in these patients treated with IMRT.     

Three-dimensional treatment planning for vaginal cuff brachytherapy: Dosimetric effects on organs at risk according to patients position

PurposeAim of this study was to evaluate dose distribution within organs at risk (OARs) and planning target volume (PTV) based on three-dimensional treatment planning according to two different setup positions in endometrial carcinoma patients submitted to postoperative brachy-radiotherapy on vaginal vault.Methods and MaterialsPatients with endometrial cancer necessitating of adjuvant brachytherapy on vaginal vault were enrolled. Pelvic computed tomography studies were prospectively obtained in two different setup positions: extend legs (A position) and gynecological (B position). Contoured OARs were bladder, rectum, and small bowel. The PTV was identified as applicator's surface with an isotropic 5-mm margin expansion. Radiation dose delivered in 1 cc (D_1cc) and 2 cc (D_2cc) of OAR were calculated.ResultsCoverage of PTV and values of D_1cc and D_2cc obtained for bladder and small bowel were similar in the two positions. For rectum, both D_1cc and D_2cc had statistically significant lower values in A with respect to B position.ConclusionsBoth in A and B positions, radiation doses delivered do not exceed the dose constraints. However, A setup seems to significantly reduce doses to rectum while obtaining the same PTV coverage. The findings from our study provide evidence supporting the use of A position setup for delivering vaginal vault brachytherapy.     

Dosimetric impact of interfractional organs at risk variation during high-dose rate interstitial brachytherapy for gynecologic malignancies

We sought to develop a framework for the identification and management of patients at risk for organs at risk (OARs) overdosing due to interfractional anatomic variation during high-dose rate interstitial brachytherapy for gynecologic malignancies. We analyzed 40 high-dose rate interstitial brachytherapy fractions from 10 patients. Planned OAR doses were compared to delivered doses, which were calculated from computed tomography scans obtained prior to each treatment fraction. Doses were converted to equivalent doses in 2 Gy fractions (EQD2) and doses to the most exposed 2 cm³ (D_2cc) were reviewed. Patients were risk-stratified by identifying dose thresholds corresponding to a 10% or lower risk of receiving an OAR dose exceeding the corresponding planning constraint. For each OAR, 30% to 62.5% of patients received total doses greater than planned, although the magnitude of these differences was <4 Gy in over 75% of cases. Using EMBRACE II guidelines, one patient who had met the planning constraint for bladder and one for small bowel were found to have received doses exceeding the recommended limits. We next calculated thresholds for estimating the risk of OAR overdosing in individual patients and developed a framework based on these thresholds to direct time- and resource-intensive imaging and replanning efforts toward patients who are most likely to derive benefit. In summary, differential OAR dosing due to interfractional anatomic variation is common but likely rarely clinically meaningful. The proposed framework could decrease toxicity and maximize clinical efficiency.     

基于MHA-resunet神经网络的非小细胞肺癌VMAT放疗剂量分布预测研究

目的 应用深度学习神经网络高精度预测非小细胞肺癌(NSCLC)患者容积旋转调强放疗(VMAT)计划的剂量分布。方法 基于Res-Unet基础网络引入大核空洞卷积模块和多头注意力(MHA)机制构建了MHA-resunet网络。在此基础上,以随机数表法从上千例接受VMAT放疗NSCLC患者中选取151例患者,以CT图像、计划靶区(PTV)与危及器官(OARs)轮廓作为输入,以剂量分布图作为输出训练神经网络。然后将该网络的性能与常用的几种网络的性能进行比较,通过PTV与OARs内的体素级平均绝对误差(MAE)和临床剂量体积指标误差对网络性能进行评估。结果 基于MHA-resunet网络的预测剂量与真实计划剂量的平均绝对误差在靶区内为1.51 Gy,靶区的D₉₈、D₉₅误差均<1 Gy。与Res-Unet、Atten-Unet、DCNN 3种常用网络比较,MHA-resunet在靶区与除心脏外的OARs内的剂量误差均为最小。结论 MHA-resunet网络通过提高感受野来学习靶区与危及器官的相对位置关系,能够准确地预测接受VMAT放疗的NSCLC患者的剂量分布。     

Targeting the GTV in medically inoperable endometrial cancer using brachytherapy

PURPOSEWe aimed to determine the relationship between gross tumor volume (GTV) dose and tumor control in women with medically inoperable endometrial cancer, and to demonstrate the feasibility of targeting a GTV-focused volume using imaged-guided brachytherapy.METHODS AND MATERIALSAn endometrial cancer database was used to identify patients. Treatment plans were reviewed to determine doses to GTV, clinical target volume (CTV), and OARs. Uterine recurrence-free survival was evaluated as a function of CTV and GTV doses. Brachytherapy was replanned with a goal of GTV D98 EQD₂ ≥ 80 Gy, without regard for coverage of the uninvolved uterus and while respecting OAR dose constraints.RESULTSFifty-four patients were identified. In the delivered plans, GTV D90 EQD₂ ≥ 80 Gy was achieved in 36 (81.8%) patients. Uterine recurrence-free survival was 100% in patients with GTV D90 EQD₂ ≥ 80 Gy and 66.7% in patients with EQD₂ < 80 Gy (p = 0.001). On GTV-only replans, GTV D98 EQD₂ ≥ 80 Gy was achieved in 39 (88.6%) patients. Mean D_2cc was lower for bladder (47.1 Gy vs. 73.0 Gy, p < 0.001), and sigmoid (47.0 Gy vs. 58.0 Gy, p = 0.007) on GTV-only replans compared to delivered plans. Bladder D_2cc was ≥ 80 Gy in 11 (25.0%) delivered plans and four (9.1%) GTV-only replans (p = 0.043). Sigmoid D_2cc was ≥ 65 Gy in 20 (45.4%) delivered plans and 10 (22.7%) GTV-only replans (p = 0.021).CONCLUSIONSOAR dose constraints should be prioritized over CTV coverage if GTV coverage is sufficient. Prospective evaluation of image-guided brachytherapy to a reduced, GTV-focused volume is warranted.     

Comparing the robustness of different skin flash approaches using wide tangents,manual flash VMAT,and simulated organ motion robust optimization VMAT in breast and nodal radiotherapy

Compare the robustness of wide tangents (WT) and volumetric modulated arc therapy (VMAT) using different skin flash approaches in breast and nodal radiotherapy. Ten patients treated with WT using 2-cm flash were replanned with VMAT using no flash (NF), manual 2-cm flash (MF), and robust optimization (RO). Plan robustness was assessed for target coverage and organs at risk (OAR) by recalculating on 5 deformed CT scans (SOM1-5), daily cone beam (CBCT), and by shifting the isocenter 5 mm. VMAT NF gave poor coverage of CTVp with its smallest change of ?3.2% for V_38Gy on CBCT. VMAT RO plans showed the least variations in target coverage loss compared to WT and VMAT MF which dropped as anatomical swelling increased. CTVp D_0.5cc decreased on CBCT and increased most for VMAT MF plans (case max increase +3.3 Gy), whereas VMAT RO plans were relatively stable (case max increase +1.2 Gy). OAR dose changed little with anatomical changes (isocenter shifts more important with medial, posterior, and inferior increasing dose). Nodal coverage was superior for VMAT which led to the WT being less robust for coverage toward both geometric and anatomical uncertainties. All techniques except NF plans gave high levels of coverage under minor uncertainties. VMAT RO was highly robust for target coverage for anatomical changes. Manually editing control points on VMAT plans was time-consuming and less predictable. CBCT anatomical changes were modest resulting in small delivered dose changes. OAR dose changes were small with no significant differences between techniques.     

Automatic segmentation for adaptive planning in nasopharyngeal carcinoma IMRT: Time,geometrical, and dosimetric analysis

The aim of this study was to quantify the geometrical differences between manual contours and autocontours, the dosimetric impacts, and the time gain of using autosegmentation in adaptive nasopharyngeal carcinoma (NPC) intensity-modulated radiotherapy (IMRT) for a commercial system. A total of 20 consecutive Stages I to III NPC patients who had undergone adaptive radiation therapy (ART) re planning for IMRT treatment were retrospectively studied. Manually delineated organs at risks (OARs) on the replanning computed tomography (CT) were compared with the autocontours generated by VelocityAI using deformable registration from the original planning CT. Dice similarity coefficients and distance-to-agreements (DTAs) were used to quantify their geometric differences. IMRT test plans were generated with the assistance of RapidPlan based on the autocontours of OARs and manually segmented target volumes. The dose distributions were applied on the manually delineated OARs, their dose volume histograms and dose constraints compliances were analyzed. Times spent on target, OAR contouring, and IMRT replanning were recorded, and the total time of replanning using manual contouring and autocontouring were compared. The averaged mean DTA of all structures included in the study were less than 2 mm, and 90% of the patients fulfilled the mean distance agreement tolerance recommended by AAPM 132.¹ The averaged maximum DTA for brainstem, cord, optic chiasm, and optic nerves were all less than 4 mm, whereas temporal lobes and parotids have larger average maximum DTA of 4.7 mm and 6.8 mm, respectively. It was found that large contour discrepancies in temporal lobes and parotids were often associated with large magnitude of deformation (warp distance) in image registrations. The resultant maximum dose of manually segmented brainstem, cord, and temporal lobe and the median dose of manually segmented parotids were found to be statistically higher than those to their autocontoured counter parts in test plans. Dose constraints of the manually segmented OARs in test plans were only met in 15% of the cases. The average time of manual contouring and autocontouring were 108 and 10 minutes, respectively (p < 0.001). More than 30% of the total replanning time would be spent in manual OAR contouring. Manual OAR delineation takes up a significant portion of time spent in ART replanning and OAR autocontouring could considerably enhance ART workflow efficiency. Geometrical discrepancies between auto- and manual contours in head and neck OARs were comparable to typical interobserver variation suggested in various literatures; however, some of the corresponding dosimetric differences were substantial, making it essential to carefully review the autocontours.     

Dosimetric evaluation of a three-phase adaptive radiotherapy for nasopharyngeal carcinoma using helical tomotherapy

Adaptive radiotherapy (ART) has been introduced to correct the radiation-induced anatomic changes in head and neck cases during a treatment course. This study evaluated the potential dosimetric benefits of applying a 3-phase adaptive radiotherapy protocol in nasopharyngeal carcinoma (NPC) patients compared with the nonadaptive single-phase treatment protocol. Ten NPC patients previously treated with this 3-phase radiation protocol using Hi-Art Tomotherapy were recruited. Two new plans, PII-ART and PIII-ART, were generated based on the up-to-date computed tomography (CT) images and contours and were used for treatment in phase two (PII; after 25th fraction) and phase three (PIII; after 35th fraction), respectively. To simulate the situation of no replanning, 2 hybrid plans denoted as PII-NART and PIII-NART were generated using the original contours pasted on the PII- and PIII-CT sets by CT-CT fusion. Dosimetric comparisons were made between the NART plans and the corresponding ART plans. In both PII- and PIII-NART plans, the doses to 95% of all the target volumes (D₉₅) were increased with better dose uniformity, whereas the organs at risk (OARs) received higher doses compared with the corresponding ART plans. Without replanning, the total dose to 1% of brainstem and spinal cord (D₁) significantly increased 7.87 ± 7.26% and 10.69 ± 6.72%, respectively (P = 0.011 and 0.001, respectively), in which 3 patients would have these structures overdosed when compared with those with two replannings. The total maximum doses to the optic chiasm and pituitary gland and the mean doses to the left and right parotid glands were increased by 10.50 ± 10.51%, 8.59 ± 6.10%, 3.03 ± 4.48%, and 2.24 ± 3.11%, respectively (P = 0.014, 0.003, 0.053, and 0.046, respectively). The 3-phase radiotherapy protocol showed improved dosimetric results to the critical structures while keeping satisfactory target dose coverage, which demonstrated the advantages of ART in helical tomotherapy of NPC.     

Postmastectomy radiotherapy for left-sided breast cancer patients: Comparison of advanced techniques

Postmastectomy radiotherapy (PMRT) has been shown to improve the overall survival for invasive breast cancer patients, and many advanced radiotherapy technologies were adopted for PMRT. The purpose of our study is to compare various advanced PMRT techniques including fixed-beam intensity-modulated radiotherapy (IMRT), non-coplanar volumetric modulated arc therapy (NC-VMAT), multiple arc VMAT (MA-VMAT), and tomotherapy (TOMO). Results of standard VMAT and mixed beam therapy that were published by our group previously were also included in the plan comparisons. Treatment plans were produced for nine PMRT patients previously treated in our clinic. The plans were evaluated based on planning target volume (PTV) coverage, dose homogeneity index (DHI), conformity index (CI), dose to organs at risk (OARs), normal tissue complication probability (NTCP) of pneumonitis, lifetime attributable risk (LAR) of second cancers, and risk of coronary events (RCE). All techniques produced clinically acceptable PMRT plans. Overall, fixed-beam IMRT delivered the lowest mean dose to contralateral breast (1.56 ± 0.4 Gy) and exhibited lowest LAR (0.6 ± 0.2%) of secondary contralateral breast cancer; NC-VMAT delivered the lowest mean dose to lungs (7.5 ± 0.8 Gy), exhibited lowest LAR (5.4 ± 2.8%) of secondary lung cancer and lowest NTCP (2.1 ± 0.4%) of pneumonitis; mixed beam therapy delivered the lowest mean dose to heart (7.1 ± 1.3 Gy) and exhibited lowest RCE (8.6 ± 7.1%); TOMO plans provided the most optimal target coverage while delivering higher dose to OARs than other techniques. Both NC-VMAT and MA-VMAT exhibited lower values of all OARs evaluation metrics compare to standard VMAT. Fixed-beam IMRT, NC-VMAT, and mixed beam therapy could be the optimal radiation technique for certain breast cancer patients after mastectomy.     

Simple template-based optimization for pediatric total lymphoid irradiation (TLI) radiotherapy treatments

Total lymphoid irradiation (TLI) is used in the management of pediatric allogeneic hematopoietic stem cell transplantation (HSCT. This work aims to simplify the treatment planning process for TLI via a proposed template using the volumetric modulated arc therapy (VMAT) technique. Fifteen pediatric patients were planned, prescribed to 8 Gy in 4 fractions. Cost functions included in the template were the ones for the planning target volume (PTV), and conformality cost function (CCF) for the rest of the patient's volume. Conformity index (CI), homogeneity index (HI), conformation number (CN), gradient index (GI), integral dose, and doses to the organs at risk achieved with the template were reported. Cost function influence over various indexes was studied by Wilcoxon signed ranks test. Same 15 patients were planned with 3-dimensional conventional radiotherapy (3D-CRT) technique for comparison. Mean CI and HI were 1.33 and 0.13, respectively, which indicates good dose conformation and homogeneity. Mean CN and GI values were 0.69 and 4.51, respectively. Mean PTV coverage was reached (V_100% > 95%). No correlation between the CCF and indexes values was found (p > 0.05). Doses to organs at risk (OARs) were as low as possible without losing PTV coverage. VMAT plan showed higher levels of conformation and similar homogeneity as 3D-CRT plans. Doses to OARs were inferior with VMAT except for the right kidney. The proposed template simplifies the planning of TLI treatments, and it is able to create acceptable plans with little modification in order to reduce doses to certain organs like the kidneys or the heart. VMAT technique showed higher conformation and lower doses to OAR compared to 3D-CRT.     

Superiority of Equivalent Uniform Dose (EUD)-Based Optimization for Breast and Chest Wall*

We investigate whether IMRT optimization based on generalized equivalent uniform dose (gEUD) objectives for organs at risk (OAR) results in superior dosimetric outcomes when compared with multiple dose-volume (DV)–based objectives plans for patients with intact breast and postmastectomy chest wall (CW) cancer. Four separate IMRT plans were prepared for each of the breast and CW cases (10 patients). The first three plans used our standard in-house, physician-selected, DV objectives (phys-plan); gEUD-based objectives for the OARs (gEUD-plan); and multiple, “very stringent,” DV objectives for each OAR and PTV (DV-plan), respectively. The fourth plan was only beam-fluence optimized (FO-plan), without segmentation, which used the same objectives as in the DV-plan. The latter plan was to be used as an “optimum” benchmark without the effects of the segmentation for deliverability. Dosimetric quantities, such as V_20Gy for the ipsilateral lung and mean dose (D_mean) for heart, contralateral breast, and contralateral lung were used to evaluate the results. For all patients in this study, we have seen that the gEUD-based plans allow greater sparing of the OARs while maintaining equivalent target coverage. The average ipsilateral lung V_20Gy reduced from 22 ± 4.4% for the FO-plan to 18 ± 3% for the gEUD-plan. All other dosimetric quantities shifted towards lower doses for the gEUD-plan. gEUD-based optimization can be used to search for plans of different DVHs with the same gEUDs. The use of gEUD allows selective optimization and reduction of the dose for each OAR and results in a truly individualized treatment plan.     

An evaluation of adaptive planning by assessing the dosimetric impact of weight loss throughout the course of radiotherapy in bilateral treatment of head and neck cancer patients

The purpose of this study was to investigate the dosimetric impact of weight loss in head and neck (H&N) patients and examine the effectiveness of adaptive planning. Data was collected from 22 H&N cancer patients who experienced weight loss during their course of radiotherapy. The robustness of Intensity Modulated Radiation Therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) treatment plans were compared including the potential need for replanning. The dosimetric impact of weight loss was evaluated by calculating a verification plan for each patient on an assessment CT scan taken during the course of treatment. Using a regression analysis, significance was tested for the dosimetric change in target volumes and 10 specific organs at risk (OAR) using an anatomical separation difference in the H&N at corresponding levels. For both the IMRT and VMAT plans, a significant correlation was found for the dose to 5% of the high risk Planning Target Volume (PTV) (D₅), dose to 95% of the intermediate risk PTV and Clinical Target Volume (CTV) (D₉₅), and the percentage of the pharynx receiving 65 Gy. An independent t-test was also performed for each metric in the VMAT and IMRT plans showing the dose to 95% of the intermediate risk PTV as significant. No quantitative method for finding the threshold of anatomical separation difference requiring a replan was established. Based on the increase in dose to organs at risk and increased target coverage due to separation loss, it was concluded that adaptive radiotherapy may not always be necessary when alignment of bony anatomy and remaining soft tissue is within tolerance. Physician judgment and preference is needed in such situations.     

Dosimetric comparison of intensity-modulated radiation therapy for early-stage glottic cancers with and without the air cavity in the planning target volume

For early-stage glottic cancers, intensity-modulated radiation therapy (IMRT) has been shown to have comparable local control to 3D-conformal radiotherapy with the advantage of decreased dose to the carotid arteries. The planning target volume (PTV) for early glottic cancers typically includes the entire larynx, plus a 3 to 5 mm uniform margin. The air cavity within the larynx creates a challenge for the inverse optimization process as the software attempts to “build up” dose within the air. This unnecessary attempt at dose build-up in air can lead to hot spots within the rest of the PTV and surrounding soft tissue. We hypothesized that removal of the air from the PTV would decrease hot spots and allow for a more homogeneous plan while still maintaining adequate coverage of the PTV.We analyzed 20 consecutive patients with early-stage glottic cancer, T1-2N0, who received IMRT at our institution from April 2015 to December 2016. Each patient received 63 to 65.25 Gy in 2.25 Gy per fraction. Two plans were created for each case: one in which the PTV included the laryngeal air cavity and one in which the air cavity was subtracted from the PTV to create a new PTV-air structure. Dosimetric variables were collected for PTV-air structure from both IMRT plans, including V100%, D98% D2%, and D0.2%. Dosimetric variables for spinal cord and the carotid arteries were also recorded. Homogeneity index (HI) defined as D98/D2 was calculated. Two-sided t-tests were used to compare dosimetric variables.The median PTV volume was 69.9 cc (standard deviation [SD] ± 28.7 cc) and the median air cavity volume removed was 11.0 cc (SD ± 3.4 cc). A 2-sided t-test revealed a statistically significant decrease in max dose (112.7% vs 108.8%, p value = 0.0002) and improvement of HI (0.93 vs 0.91, p value = 0.0023) for the PTV air in the IMRT plan optimized for PTV air, which had air excluded, compared to the IMRT plan optimized for PTV with air included. There was no significant worsening of PTV-air coverage or significant increase in doses to the organs at risk (OARs).The removal of the air cavity from the PTV for early-stage glottic cancers does not compromise PTV coverage or sparing of OARs and can result in a more homogeneous IMRT plan. A more homogeneous plan has the potential to reduce treatment morbidity, although further study is warranted to investigate the clinical impact of air cavity removal from the PTV.     

A study of the dosimetric characteristics between different fixed-field IMRT and VMAT in early-stage primary mediastinal B-cell lymphoma

This analysis was designed to compare dosimetric parameters among different fixed-field intensity-modulated radiation therapy (IMRT) solutions and volumetric-modulated arc therapy (VMAT) to identify which can achieve the lowest risk of organs at risk (OARs) and treatment delivery efficiently. A total of 16 patients (8 male and 8 female) with early-stage primary mediastinal large B-cell lymphoma (PMBCL) were enrolled with planned gross tumor volume (PGTV) 45?Gy and planning target volume (PTV) 40?Gy. Four different plans were generated: 5-, 7, 9-field IMRT, and VMAT. The dose distributions for PGTV and PTV OARs (lungs, left ventricle, heart, thyroid gland, and breasts) were compared. The monitor units (MUs) and treatment delivery time were also evaluated. Mean conformity index (CI) and homogeneity index (HI) for PGTV in 5F-, 7F-, 9F-IMRT, and VMAT were 1.01 and 1.10, 1.01 and 1.10, 1.01 and 1.10, and 1.01 and 1.11 (p?=?0.963 and 0.843), whereas these 2 indices for PTV were 1.04 and 1.22, 1.03 and 1.19, 1.03 and 1.17, and 1.08 and 1.14 (p?=?0.964 and 0.969), respectively. D_mean (Gy), V4 (%), D50 (Gy), and D80 (Gy) to the left and right breasts increased by 0.7?Gy and 0.1?Gy, 6.8% and 7.7%, 0.9?Gy and 1.7?Gy, and 1.0?Gy and 1.5?Gy in VMAT, respectively. The 9-beam IMRT plan had the highest MUs (25,762.4 MUs) and the longest treatment delivery time (10.7 minutes); whereas, the VMAT had the lowest MUs (13,345.0) and the shortest treatment delivery time (5.9 minutes). Seven- and 9-field IMRT and VMAT provide improved tumor coverage compared with 5F-IMRT, whereas VMAT shows higher treatment delivery efficiency than IMRT technique. Seven- and 9-field IMRT slightly reduce the low dose radiation exposure of breasts compared with VMAT technique. The 7- and 9-field IMRT and VMAT techniques both can be safely and efficiently delivered to patients with PMBCL.