Volumetric modulated arc radiotherapy for esophageal cancer

A treatment planning study was performed to evaluate the performance of volumetric arc modulation with RapidArc (RA) against 3D conformal radiation therapy (3D-CRT) and conventional intensity-modulated radiation therapy (IMRT) techniques for esophageal cancer. Computed tomgraphy scans of 10 patients were included in the study. 3D-CRT, 4-field IMRT, and single-arc and double-arc RA plans were generated with the aim to spare organs at risk (OAR) and healthy tissue while enforcing highly conformal target coverage. The planning objective was to deliver 54 Gy to the planning target volume (PTV) in 30 fractions. Plans were evaluated based on target conformity and dose-volume histograms of organs at risk (lung, spinal cord, and heart). The monitor unit (MU) and treatment delivery time were also evaluated to measure the treatment efficiency. The IMRT plan improves target conformity and spares OAR when compared with 3D-CRT. Target conformity improved with RA plans compared with IMRT. The mean lung dose was similar in all techniques. However, RA plans showed a reduction in the volume of the lung irradiated at V_20Gy and V_30Gy dose levels (range, 4.62–17.98%) compared with IMRT plans. The mean dose and D_35% of heart for the RA plans were better than the IMRT by 0.5–5.8%. Mean V_10Gy and integral dose to healthy tissue were almost similar in all techniques. But RA plans resulted in a reduced low-level dose bath (15–20 Gy) in the range of 14–16% compared with IMRT plans. The average MU needed to deliver the prescribed dose by RA technique was reduced by 20–25% compared with IMRT technique. The preliminary study on RA for esophageal cancers showed improvements in sparing OAR and healthy tissue with reduced beam-on time, whereas only double-arc RA offered improved target coverage compared with IMRT and 3D-CRT plans.     

乳腺癌根治术后放疗中不同补偿物使用策略对剂量分布的影响

目的比较和评估不同的补偿物的使用策略在乳腺癌根治术后常规调强放射治疗中对剂量分布的影响。方法选择2021年4月至10月于复旦大学附属肿瘤医院收治50例乳腺癌根治术后患者,计划靶区包括胸壁、内乳淋巴结、腋窝淋巴结和锁骨上淋巴结4个部分,处方剂量为50 Gy/25次。每位患者分别制作使用3种不同厚度补偿物(3、5、10 mm)的调强放疗计划,统计和评估不同补偿物厚度和使用次数对靶区覆盖率、胸壁皮肤高剂量体积和周围正常组织的剂量影响。结果补偿物全程使用时,使用10 mm补偿物的靶区V95%较使用3、5 mm的低(F=3.40,P<0.05),使用3 mm补偿物的适形指数(CI)最高(F=50.05,P<0.05),3种计划皮肤V105%和V110%对比差异无统计学意义(P>0.05)。随着使用次数的减少,靶区V95%和皮肤V105%均降低,补偿物使用20次时,靶区V95%的值变化很小(<1%),而皮肤V105%急剧降低为初始值的一半左右。补偿物使用15次时,3种计划的靶区V95%,CI和均匀性指数(HI)对比差异无统计学意义(P>0.05),使用3 mm补偿物的Dmax值较使用5、10 mm低(F=9.21,P<0.05)。正常组织方面,补偿物厚度和使用次数对心脏和患侧肺的剂量分布影响很小,差异不致引起生物学效应的不同。结论对于乳腺癌根治术后调强放疗技术,不同补偿物厚度对靶区、皮肤、心脏和肺的剂量影响很小。补偿物的使用次数是决定靶区覆盖和皮肤剂量的重要决定因素。     

Dosimetric comparison of pencil beam scanning proton therapy with or without multi-leaf collimator versus volumetric-modulated arc therapy for treatment of malignant glioma

This study aimed to examine the dosimetric effect of intensity-modulated proton therapy (IMPT) with a multi-leaf collimator (MLC) in treating malignant glioma. We compared the dose distribution of IMPT with or without MLC (IMPT_MLC+ or IMPT_MLC-, respectively) using pencil beam scanning and volumetric-modulated arc therapy (VMAT) in simultaneous integrated boost (SIB) plans for 16 patients with malignant gliomas. High- and low-risk target volumes were assessed using D_2%, V_90%, V_95%, homogeneity index (HI), and conformity index (CI). Organs at risk (OARs) were evaluated using the average dose (D_mean) and D_2%. Furthermore, the dose to the normal brain was evaluated using from V_5Gy to V_40Gy at 5 Gy intervals. There were no significant differences among all techniques regarding V_90%, V_95%, and CI for the targets. HI and D_2% for IMPT_MLC+ and IMPT_MLC- were significantly superior to those for VMAT (p < 0.01). The D_mean and D_2% of all OARs for IMPT_MLC+ were equivalent or superior to those of other techniques. Regarding the normal brain, there was no significant difference in V_40Gy among all techniques whereas V_5Gy to V_35Gy in IMPT_MLC+ were significantly smaller than those in IMPT_MLC- (with differences ranging from 0.45% to 4.80%, p < 0.05) and VMAT (with differences ranging from 6.85% to 57.94%, p < 0.01). IMPT_MLC+ could reduce the dose to OARs, while maintaining target coverage compared to IMPT_MLC- and VMAT in treating malignant glioma.     

Radiation therapy of synchronous bilateral breast carcinoma (SBBC) using multiple techniques

The purpose of this study was to establish intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy (VMAT) treatment plans for synchronous bilateral breast cancer (SBBC) and to compare those plans with the previous treatment plans using 3D conformal radiation therapy (3DCRT). The differences among the treatments were also statistically compared regarding dosimetry distribution and treatment efficiency. The research was conducted with 10 SBBC patients. The study established IMRT (12 fields with a single isocenter) and VMAT (2 partial arcs with a single isocenter) treatment plans for SBBC patients and then compared those plans with 3DCRT (8 fields with multiple isocenters). The plans were evaluated based on a dose-volume histogram analysis. For planning target volumes (PTVs), the mean doses and the values of V_95%, V_105%, conformity index, and homogeneity index were reported. For the organs at risk, the analysis included the mean dose, maximum dose, and V_XGy, depending on the organs (lungs, heart, and liver). To objectively evaluate the efficiency of the treatment plans, each plan's beam times, treatment times (including set-up time), and monitor units were compared. Tukey test and one-way analysis of variance were used to compare the PTV and organs at risk values of the 3 techniques. Additionally, the independent-samples t-test was used to compare the 2 techniques (IMRT and VMAT) based on the values of Rt. PTV and Lt. PTV (p?<?0.05). For PTV dose distribution, IMRT showed increases of approximately 1.2% in D_mean and of approximately 5.7% in V_95% dose distribution compared with 3DCRT. In comparison to VMAT, 3DCRT showed about 3.0% higher dose distribution in D_mean and V_95%. IMRT was the best in terms of conformity index and homogeneity index (p?<?0.05), whereas 3DCRT and VMAT did not significantly differ from each other. In terms of dose distribution on lungs, heart, and liver, the percentage of volume at high doses such as V_30Gy and V_40Gy was approximately 70% lower for IMRT and approximately 40% lower for VMAT than for 3DCRT. For distribution volumes of low doses such as V_5% and V_10%, that for 3DCRT was approximately 60% smaller than for IMRT and approximately 70% smaller than for VMAT. Comparison between IMRT and VMAT showed that the IMRT was superior in all distribution factors. VMAT showed better treatment efficiency than 3DCRT or IMRT. Among the SBBC radiotherapy treatment plans, IMRT was superior to 3DCRT and VMAT in terms of PTV dose distribution, whereas VMAT showed the most outstanding treatment efficiency.     

胸上段食管癌螺旋断层放疗和容积旋转调强放疗的剂量学比较

目的 比较胸上段食管癌螺旋断层(HT)与容积旋转调强放疗(VMAT)计划的剂量学差异。方法 随机抽样法选取10例胸上段食管癌患者,分别设计HT和VMAT双弧照射调强放疗计划,肿瘤靶区体积(GTV)给予66 Gy/30次,计划靶区体积(PTV)给予50 Gy/30次。根据剂量体积直方图(DVH)评价靶区的D_1%、D_5%、D_95%、D_99%、适形指数(CI)、均匀性指数(HI)和危及器官(OAR)受量,比较治疗时间和机器跳数(MU)的差异。结果 HT组GTV和PTV的D_99%高于VMAT组(t=4.476、3.756,P<0.05);GTV与PTV的D_1%、D_5%、D_95%、HI和CI差异均无统计学意义(P>0.05)。HT组全肺V₁₀、V₁₅、V₂₀和全肺平均剂量(MLD)均显著低于VMAT组(t=-3.369、-4.824、-4.869、-3.657,P<0.05);全肺V₅、V₃₀和脊髓D_max差异均无统计学意义(P >0.05)。HT组治疗时间和MU数均远大于VMAT组(t=13.970、7.982,P<0.05)。结论 HT与VMAT技术均能满足胸上段食管癌放疗剂量要求。HT技术能显著减小双肺受量,而VMAT技术具备明显的效率优势。     

Chest wall radiotherapy with volumetric modulated arcs and the potential role of flattening filter free photon beams

Purpose

The goal of the work was to assess the role of RapidArc treatments in chest wall irradiation after mastectomy and determine the potential benefit of flattening filter free beams.

Methods and material

Planning CT scans of 10?women requiring post-mastectomy chest wall radiotherapy were included in the study. A dose of 50?Gy in 2?Gy fractions was prescribed. Organs at risk (OARs) delineated were heart, lungs, contralateral breast, and spinal cord. Dose–volume metrics were defined to quantify the quality of concurrent treatment plans assessing target coverage and sparing of OARs. Plans were designed for conformal 3D therapy (3DCRT) or for RapidArc with double partial arcs (RA). RapidArc plans were optimized for both conventional beams as well as for unflattened beams (RAF). The goal for this planning effort was to cover 100% of the planning target volume (PTV) with ≥?90% of the prescribed dose and to minimize the volume inside the PTV receiving >?105% of the dose. The mean ipsilateral lung dose was required to be lower than 15?Gy and V_20?Gy?Results All techniques met planning objectives for PTV and for lung (3DCRT marginally failed for V_20?Gy). RA plans showed superiority compared to 3DCRT in the medium to high dose region for the ipsilateral lung. Heart irradiation was minimized by RAF plans with ~4.5?Gy and ~15?Gy reduction in maximum dose compared to RA and 3DCRT, respectively. RAF resulted in superior plans compared to RA with respect to contralateral breast and lung with a reduction of ~1.7?Gy and 1.0?Gy in the respective mean doses.

Conclusion

RapidArc treatment resulted in acceptable plan quality with superior ipsilateral tissue sparing compared to traditional techniques. Flattening filter free beams, recently made available for clinical use, might provide further healthy tissue sparing, particularly in contralateral organs, suggesting their applicability for large and complex targets.     

Bilateral implant reconstruction does not affect the quality of postmastectomy radiation therapy

To determine if the presence of bilateral implants, in addition to other anatomic and treatment-related variables, affects coverage of the target volume and dose to the heart and lung in patients receiving postmastectomy radiation therapy (PMRT). A total of 197 consecutive women with breast cancer underwent mastectomy and immediate tissue expander (TE) placement, with or without exchange for a permanent implant (PI) before radiation therapy at our center. PMRT was delivered with 2 tangential beams + supraclavicular lymph node field (50 Gy). Patients were grouped by implant number: 51% unilateral (100) and 49% bilateral (97). The planning target volume (PTV) (defined as implant + chest wall + nodes), heart, and ipsilateral lung were contoured and the following parameters were abstracted from dose-volume histogram (DVH) data: PTV D_95% > 98%, Lung V₂₀Gy > 30%, and Heart V₂₅Gy > 5%. Univariate (UVA) and multivariate analyses (MVA) were performed to determine the association of variables with these parameters. The 2 groups were well balanced for implant type and volume, internal mammary node (IMN) treatment, and laterality. In the entire cohort, 90% had PTV D_95% > 98%, indicating excellent coverage of the chest wall. Of the patients, 27% had high lung doses (V₂₀Gy > 30%) and 16% had high heart doses (V₂₅Gy > 5%). No significant factors were associated with suboptimal PTV coverage. On MVA, IMN treatment was found to be highly associated with high lung and heart doses (both p < 0.0001), but implant number was not (p = 0.54). In patients with bilateral implants, IMN treatment was the only predictor of dose to the contralateral implant (p = 0.001). In conclusion, bilateral implants do not compromise coverage of the target volume or increase lung and heart dose in patients receiving PMRT. The most important predictor of high lung and heart doses in patients with implant-based reconstruction, whether unilateral or bilateral, is treatment of the IMNs. Refinement of radiation techniques in reconstructed patients who require comprehensive nodal irradiation is warranted.     

A predictive model for determining rectum and bladder dose constraints in prostate volumetric modulated arc therapy

Generic dose-volume constraints of the rectum/bladder (R/B) are used in inverse planning to reduce doses to these organs for patients undergoing prostate radiotherapy. A retrospective study was undertaken to assess correlations between the overlap of the R/B with the planning target volume (PTV) and the dose received during planning to organs at risk (OARs). Data for 105 prostate cancer patients who had volumetric modulated arc therapy (VMAT) to the intact prostate and proximal seminal vesicles at Nepean Cancer Care Centre from 2011 to 2015 were analyzed. R/B volume, R/B-PTV overlap volume, and R/B-PTV overlap percent metrics were collected with VMAT planning objectives. Characteristics were evaluated for correlation with different planning outcomes. The percentage overlap between the R/B and PTV were highly correlated to the doses to the relevant OAR, with a coefficient of determination (R²) of 0.63 for the rectum volume percentage receiving more than 75 Gy (RV_75Gy) and R² of 0.91 for the bladder volume percentage receiving more than 70 Gy (BV_70Gy). We identified a cut-off value of 10.14% (sensitivity 84.62%, specificity 80.43%) as predictive of RV_75Gy < 10% and a cut-off of 7.95% (sensitivity 97.62%, specificity 92.06%) as predictive of BV_70Gy < 15%. A 95% prediction interval assisted in identifying individualized R/B planning goals. The R/B-PTV percentage overlap has a high reliability in estimating sparing of the R/B. This prediction model can be used to improve planning efficiency and create customised automated OAR planning goals in prostate VMAT plans. By doing this, the radiation doses received by these OARs can be minimized.     

浸润型胸腺瘤术后单能与混合能量光子束调强放疗计划剂量学分析

目的 比较浸润型胸腺瘤术后患者单能与混合能量光子束调强放射治疗(IMRT)计划之间剂量学差异,探讨混合能量光子束计划在临床的应用价值。方法 随机抽取12例胸腺瘤术后病例的CT定位图像,在治疗计划系统上勾画临床靶体积(CTV)并外扩为计划靶体积(PTV)、危及器官(OAR)及其他正常组织。每个病例分别制定6和10 MV与混合能量光子束的3种固定野调强放疗(FF-IMRT)计划,优化与计算剂量后统计各种计划的机器跳数(MU),并使用剂量体积直方图(DVH)工具比较PTV的体积剂量、适形指数(CI)、均匀指数(HI)和OAR剂量。结果 PTV近似最大剂量D_2%混合能量光子束计划优于6 MV光子束(t=3.107,P <0.05);6 MV光子束HI与混合能量光子束计划比较,差异有统计学意义(t=2.924,P<0.05);CI三者之间差异均有统计学意义。6 MV计划的MU大于10 MV及混合光子束计划。双侧肺V₅、V₁₀、V₂₀、V₃₀和平均剂量(D_mean)指标各个类型计划之间大部分差异有统计学意义,且混合能量光子束计划优于其他两种计划。心脏V₃₀、V₄₀指标6 MV与混合光子计划的结果接近,但均优于10 MV光子束的计划。结论 混合能量光子束IMRT计划如果合理选择射野角度和射野数量,依据入射角度选择光子束的能量,可充分利用低能及高能光子束的不同特点,总体上可以改善IMRT计划的质量,对于浸润型胸腺瘤术后病例具有一定的临床参考价值。     

RapidPlan development of VMAT plans for cervical cancer patients in low- and middle-income countries

Cervical cancer has a high incidence and mortality rate in low- and middle-income countries (LMICs) largely due to limited resources and insufficient staffing. Knowledge-based planning (KBP) could alleviate understaffing issues by streamlining the radiotherapy treatment planning process. Varian's KBP system (RapidPlan) was used to develop a model capable of producing volumetric modulated arc therapy (VMAT) plans for cervical cancer patients. Plan data from 46 patients previously treated at MD Anderson Cancer Center (MDACC) were used to create and train the model which was then applied to 32 patients excluded from the training process. Dose volume histogram (DVH) values for the planning target volume (PTV_High), bladder, rectum, and bowel were evaluated for the validation plans and found to have satisfied the required PTV coverage and organ-at-risk (OAR) dose constraints. The average value for PTV_High D_95.0% was 48.0 Gy (sd = 3.0 Gy) for existing clinical plans and 48.4 Gy (sd = 2.6 Gy) for the validation plans. The mean dose for the bladder, rectum, and bowel was 39.8 Gy (sd = 3.9 Gy), 41.6 Gy (sd = 5.2 Gy), and 21.6 Gy (sd = 5.0 Gy) for existing clinical plans and 38.9 Gy (sd = 4.0 Gy), 40.3 Gy (sd = 4.8 Gy), and 21.5 Gy (sd = 4.6 Gy) for validation plans, respectively. A TOST test showed that the p values for the PTV_High D_95.0% (p < 0.001), rectum V_30Gy (p = 0.039), and mean dose to the bladder (p = 0.0014), rectum (p = 0.025), and bowel (p = 0.006) were statistically significant within a 5% equivalence margin of the clinical value thereby providing strong evidence of equivalence. Based on this statistical analysis, it was determined that the model was capable of generating treatable VMAT plans for cervical cancer patients.     

The dosimetric advantages of perirectal hydrogel spacer in men with localized prostate cancer undergoing stereotactic ablative radiotherapy (SABR)

To evaluate the dosimetric differences for patients receiving a perirectal hydrogel spacer (PR-HS) using SpaceOAR undergoing stereotactic ablative radiotherapy (SABR) for localized prostate cancer with the CyberKnife VSI system. Gold fiducial markers and a PR-HS was inserted in 22 consecutive patients with histologically confirmed localized prostate cancer. For planning comparison, dosimetry from the clinical plans was compared against replans based on a simulated rectum volume designed to recreate a clinically appropriate spacer-less anatomy for each patient. Both sets were planned to 36.25 Gy in 5 fractions using the treatment planning system associated with the CyberKnife VSI system. The aim was to ensure equivalent target coverage for both plans and to evaluate doses to the organs-at-risk (OARs): rectum, bladder and penile bulb. The median PR-HS implant volume was 11.2 cc (range 8.8 to 14.9 cc). The maximal median perirectal separation was 15.5 mm (10.5 to 20.7 mm). Statistically significant reductions were noted for the 3 OARs, with no statistically significant difference in planning target volumes or clinical target volume coverage. All rectal dose constraints were significantly improved in the PR-HS plans with a percentage dose difference of at least 24% (rectum V_18.1Gy (%)) to 60.5% (rectum V_36Gy (cc)). The bladder and penile bulb dose constraints parameters were also significantly improved: the bladder V_37Gy was reduced by 17.1%, V_18.1Gy was reduced by 4.2%; the penile bulb D_50% was reduced by 7.7%. The use of PR-HS was able to significantly reduce planned dose to the rectum, bladder and penile bulb with SABR techniques associated with the CyberKnife VSI system.