Dosimetric comparison of helical tomotherapy,volumetric-modulated arc therapy,intensity-modulated radiotherapy,and field-in-field technique for synchronous bilateral breast cancer

Purpose: To compare the dosimetric characteristics of helical tomotherapy (HT), volumetric-modulated arc therapy (VMAT), intensity-modulated radiotherapy (IMRT), and tangential field-in-field technique (FIF) for the treatment of synchronous bilateral breast cancer (SBBC). Methods and Materials: Ten patients with early-stage unilateral breast cancer were selected for simulating the patients with SBBC in this retrospective analysis. Treatment plans with HT, VMAT, IMRT, and FIF were generated for each patient with a total dose of 50.4 Gy in 28 fractions to the target. Plan quality, namely conformity index (CI), homogeneity index (HI), dose-volume statistics of organs at risk (OARs), and beam-on time (BOT), were evaluated. Results: HT plans showed a lower mean heart dose (3.53 ± 0.31Gy) compared with the other plans (VMAT = 5.6 ± 1.36 Gy, IMRT = 3.80 ± 0.76 Gy, and FIF = 4.84 ± 2.13 Gy). Moreover, HT plans showed a significantly lower mean lung dose (p < 0.01) compared with the other plans: mean right lung doses were 6.81 ± 0.67, 10.32 ± 1.04, 9.07 ± 1.21, and 10.03 ± 1.22 Gy and mean left lung doses were 6.33 ± 0.87, 8.82 ± 0.91, 7.84 ± 1.07, and 8.64 ± 0.99 Gy for HT, VMAT, IMRT, and FIF plans, respectively. The mean dose to the left anterior descending artery was significantly lower in HT plans (p < 0.01) than in the other plans: HT = 19.41 ± 0.51 Gy, VMAT = 25.77 ± 7.23 Gy, IMRT = 27.87 ± 6.48 Gy, and FIF = 30.95 ± 10.17 Gy. FIF plans showed a worse CI and HI compared with the other plans. VMAT plans showed shorter BOT (average, 3.9 ± 0.2 minutes) than did HT (average, 11.0 ± 3.0 minutes), IMRT (average, 6.1 ± 0.5 minutes), and FIF (average, 4.6 ± 0.7 minutes) plans. Conclusions: In a dosimetric comparison for SBBC, HT provided the most favorable dose sparing of OARs. However, HT with longer BOT may increase patient discomfort and treatment uncertainty. VMAT enabled shorter BOT with acceptable doses to OARs and had a better CI than did FIF and IMRT.     

Cardiac dose-sparing effects of deep-inspiration breath-hold in left breast irradiation

Background

Given the reduction in death from breast cancer, as well as improvements in overall survival, adjuvant radiotherapy is considered the standard treatment for breast cancer. However, left-sided breast irradiation was associated with an increased rate of fatal cardiovascular events due to incidental irradiation of the heart. Recently, considerable efforts have been made to minimize cardiac toxicity of left-sided breast irradiation by new treatment methods such as deep-inspiration breath-hold (DIBH) and new radiation techniques, particularly intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). The primary aim of this study was to evaluate the effect of DIBH irradiation on cardiac dose compared with free-breathing (FB) irradiation, while the secondary objective was to compare the advantages of IMRT versus VMAT plans in both the FB and the DIBH position for left-sided breast cancer.

Methods

In all, 25 consecutive left-sided breast cancer patients underwent CT simulation in the FB and DIBH position. Five patients were excluded with no cardiac displacement following DIBH-CT simulation. The other 20 patients were irradiated in the DIBH position using respiratory gating. Four different treatment plans were generated for each patient, an IMRT and a VMAT plan in the DIBH and in the FB position, respectively. The following parameters were used for plan comparison: dose to the heart, left anterior descending coronary artery (mean dose, maximum dose, D25% and D45%), ipsilateral, contralateral lung (mean dose, D20%, D30%) and contralateral breast (mean dose). The percentage in dose reduction for organs at risk achieved by DIBH for both IMRT and VMAT plans was calculated and compared for each patient by each treatment plan.

Results

DIBH irradiation significantly reduced mean dose to the heart and left anterior descending coronary artery (LADCA) using both IMRT (heart –20%; p = 0.0002, LADCA –9%; p = 0.001) and VMAT (heart –23%; p = 0.00003, LADCA –16%; p = 0.01) techniques as compared with FB radiation. There were no significant changes in left lung dose by IMRT; however, with VMAT planning, mean dose to the left lung was reduced by –4% (p = 0.0004). In addition, DIBH significantly increased the mean dose to the contralateral breast with IMRT (+14%, p = 0.002) and significantly reduced the dose to the contralateral breast with VMAT planning (–9%, p = 0.003) compared with the FB position. Additionally, in comparison with VMAT, the IMRT technique reduced mean heart dose both in the FB and the DIBH-position by –30% (p = 0.0004) and –26% (p = 0.002), respectively. Furthermore, IMRT increased the mean dose to the left lung in both the FB and the DIBH position (+5%, p = 0.003, p = 0.006), respectively. There were no significant changes in dose to the right lung and contralateral breast either in the FB or DIBH position between IMRT and VMAT techniques.

Conclusion

Left-sided breast irradiation is best performed in the DIBH position, since a considerable dose sparing to the heart and LADCA can be achieved by using either IMRT or VMAT techniques. A significant additional decrease in heart and LADCA dose by IMRT in both FB and DIBH irradiation was seen compared with VMAT.

     

乳腺癌根治术后双弧VMAT与IMRT计划的剂量学比较

目的 比较乳腺癌根治术后双弧的容积旋转调强放射治疗(VMAT)与5野的静态调强放射治疗(IMRT)2种计划之间的剂量学差异,评估VMAT技术在乳腺癌根治术后的剂量学特点与应用能力.方法 选取28例乳腺癌根治术后患者(左侧10例,右侧18例),分别制定双90度弧段的VMAT与5野的IMRT 2种计划,主要的计划评估参数为靶区的肿瘤控制概率(TCP)、适形指数(CI)、均匀指数(HI)以及接受相应处方剂量水平照射体积百分比V₉₅、V₁₁₀,危及器官(OAR)评估包括患侧肺的正常组织并发症概率(NTCP)、D_mean、V₅、V₂₀、V₃₀,心脏的NTCP值、D_mean、V₂₅,健侧乳腺的D_mean、机器跳数(MU)以及治疗时间.结果 VMAT计划与IMRT计划的TCP值分别为(96±2)%、(90±2)%(t=-6.28,P<0.01);HI值分别为0.15±0.04,0.22±0.02(t=13.29,P<0.05);肿瘤位于左侧时,心脏NTCP值在VMAT计划与IMRT计划中分别为(1.0±0.12)%,(1.7±0.13)%(t=2.14,P<0.05);肿瘤位于右侧时,2种计划心脏的NTCP差异无统计学意义,平均剂量分别为(3.27±0.26)、(6.0±0.47)Gy(t=9.21, P<0.01);VMAT计划在MU少于IMRT计划(t=9.58,P<0.01),治疗时间短于IMRT计划(t=8.40,P<0.05).结论 乳腺癌根治术后,VMAT计划具有更强的临床应用能力,且表现出更优的剂量学特点.     

Improvement in plan quality after Implementation of clinical goals in a large network of cancer centers

Clinical Goals (CG) is a tool available in the Varian Eclipse planning system to objectively and visually evaluate the quality of treatment plans based upon user-defined dose-volume parameters. We defined a set of CG for Stereotactic Radiosurgery (SRS) and Intensity-Modulated Radiotherapy (IMRT) based on published data and guidelines and implemented this in a network of cancer centers in India (American Institute of Oncology). A dosimetric study was performed to compare brain SRS and breast IMRT plan quality before and after CG implementation.The CG defined for SRS plans were target V_100% ≥ 98%, dose gradient measure (GM) ≤ 0.5 cm, conformity index (CI) 1.0 to 1.2. For breast IMRT plans, CG defined target V_100% ≥ 97%, V_95% ≥ 95%, V_107% ≤ 2%, V_105% ≤ 10%, and D_max ≤ 2.4 Gy. Dose limits to organs-at-risk (OAR) were summarize in supplemental materials. Twenty brain SRS and 10 breast IMRT treatment plans that were previously delivered on patients were selected and re-planned using CG. The pre and postoptimized plan parameters were compared using student t-tests.For brain SRS plans, the V₁₀₀, GM, and CI for the pre- and post-Clinical-Goals plans were 93.22% ± 7.2% vs 97.96% ± 0.29% (p = 0.009), 0.63 ± 0.16 vs 0.42 ± 0.05 (p < 0.001) and 1.07 ± 0.18 vs 1.06 ± 0.06 (p = 0.79), respectively. There were no differences in max dose to OARs. In breast IMRT plans, the target V_107% for pre and postimplemented plans were 16.50% ± 10.98% vs 0.32% ± 0.32%, respectively (p = 0.001). The average target V_105% were 44.00% ± 15.72% and 8.69% ± 4.53%, respectively (p < 0.001). No differences were found in the average target V_100% (p = 0.128) and V_95% (p = 0.205). The average target D_max were 112.28% ± 1.59% and 109.14% ± 0.73%, respectively (p < 0.001). There were only minor differences in doses to OARs.The implementation of CG in Varian Eclipse significantly improved SRS and IMRT plan quality with enhanced coverage, dose GM, and CI without increased dose to OARs.     

Dosimetric comparison of TomoDirect,helical tomotherapy,VMAT, and ff-IMRT for upper thoracic esophageal carcinoma

BackgroundThe new TomoDirect (TD) modality offers a nonrotational option with discrete beam angles. We aim to compare dosimetric parameters of TD, helical tomotherapy (HT), volumetric-modulated arc therapy (VMAT), and fixed-field intensity-modulated radiotherapy (ff-IMRT) for upper thoracic esophageal carcinoma (EC).MethodsTwenty patients with cT2-4N0-1M0 upper thoracic esophageal squamous cell carcinoma (ESCC) were enrolled. Four plans were generated using the same dose objectives for each patient: TD, HT, VMAT with a single arc, and ff-IMRT with 5 fields (5F). The prescribed doses were used to deliver 50.4 Gy/28F to the planning target volume (PTV50.4) and then provided a 9 Gy/5F boost to PTV59.4. Dose-volume histogram (DVH) statistics, dose uniformity, and dose homogeneity were analyzed to compare treatment plans.ResultsFor PTV59.4, the D₂, D₉₈, D_mean, and V_100% values in HT were significantly lower than other plans (all p < 0.05), and those in TD were significantly lower than VMAT and ff-IMRT (all p < 0.05). However, there was no significant difference in the D₂ and D_mean values between VMAT and ff-IMRT techniques (p > 0.05). The homogeneity index (HI) differed significantly for the 4 techniques of TD, HT, VMAT, and ff-IMRT (0.03 ± 0.01, 0.02 ± 0.01, 0.06 ± 0.02, and 0.05 ± 0.01, respectively; p < 0.001). The HI for TD was similar to HT (p = 0.166), and had statistically significant improvement compared to VMAT (p < 0.001) and ff-IMRT (p = 0.003). In comparison with the 4 conformity indices (CIs), there was no significant difference (p > 0.05). For PTV50.4, the D₂ and D_mean values in HT were significantly lower than other plans (all p < 0.05), and those in TD were significantly lower than VMAT and ff-IMRT (all p < 0.05). However, there was no significant difference in the D₂ and D_mean values between VMAT and ff-IMRT techniques (p > 0.05). No D₉₈ and V_100% parameters differed significantly among the 4 treatment types (p > 0.05). HT plans were provided for statistically significant improvement in HI (0.03 ± 0.01) compared to TD plans (0.05 ± 0.01, p = 0.003), VMAT (0.08 ± 0.03, p < 0.001), ff-IMRT (0.08 ± 0.01, p < 0.001). The HI revealed that TD was superior to VMAT and ff-IMRT (p < 0.05). The CI differed significantly for the 4 techniques of TD, HT, VMAT, and ff-IMRT (0.59 ± 0.10, 0.69 ± 0.11, 0.64 ± 0.09, and 0.64 ± 0.11, respectively; p = 0.035). The best CI was yielded by HT. We found no significant difference for the V₅, V₁₀, V₁₅, V₃₀, and the mean lung dose (MLD) among the 4 techniques (all p > 0.05). However, the V₂₀ differed significantly among TD, HT, VMAT, and ff-IMRT (21.50 ± 7.20%, 19.50 ± 5.55%, 17.65 ± 5.45%, and 16.35 ± 5.70%, respectively; p = 0.047). Average V₂₀ for the lungs was significantly improved by the TD plans compared to VMAT (p = 0.047), and ff-IMRT (p = 0.008). The V₅ value of the lung in TD was 49.30 ± 13.01%, lower than other plans, but there was no significant difference (p > 0.05). The D₁ of the spinal cord showed no significant difference among the 4 techniques (p = 0.056).ConclusionsAll techniques are able to provide a homogeneous and highly conformal dose distribution. The TD technique is a good option for treating upper thoracic EC involvement. It could achieve optimal low dose to the lungs and spinal cord with acceptable PTV coverage. HT is a good option as it could achieve quality dose conformality and uniformity, while TD generated superior conformality.     

乳腺癌保乳术后部分乳腺三种放疗计划的剂量学比较

目的 比较容积弧形调强（VMAT）、固定野动态调强（IMRT）及三维适形放疗（3D-CRT）技术对乳腺癌保乳术后采用部分乳腺放疗的剂量学差异。方法 选取20例临床分期为T_1-2N₀M₀的早期乳腺癌保乳术后患者进行VMAT,并同时设计IMRT及3D-CRT,比较3种计划的剂量学参数,包括剂量-体积直方图（DVH）、靶区剂量适形度、靶区及危及器官的剂量、机器跳数及治疗时间。结果 IMRT及VMAT计划靶区剂量分布优于3D-CRT计划,其中最大剂量,平均剂量及适形指数（CI）组间比较差异具有统计学意义（F=14.86、8.57、18.23,P<0.05）。正常组织受量：VMAT计划在患侧乳腺V₅上优于IMRT及3D-CRT计划（F=5.83,P<0.05）;IMRT在患侧肺V₂₀、V₅及D₅上有优势（F=16.39、3.62、4.81,P<0.05）;在对侧肺的统计中,IMRT计划在最大剂量及D₅上可以得到比VMAT和3D-CRT更低的剂量（F=3.99、3.43,P<0.05）;VMAT、3D-CRT和IMRT计划所需机器跳数值分别为621.0±111.9、707.3±130.9、1161.4±315.6,计划间的差异有统计学意义（F=31.30,P<0.05）。VMAT、3D-CRT和IMRT计划所需治疗时间分别为（1.5±0.2）、（7.0±1.6）、（11.5±1.9）min。结论 IMRT和VMAT计划靶区剂量分布优于3D-CRT计划,而不提高患侧肺剂量。对于部分乳腺癌的放疗,容积弧形调强放疗在降低机器跳数和减少治疗时间方面具有明显优势。     

Stereotactic body radiation therapy planning with duodenal sparing using volumetric-modulated arc therapy vs intensity-modulated radiation therapy in locally advanced pancreatic cancer: A dosimetric analysis

Stereotactic body radiation therapy (SBRT) achieves excellent local control for locally advanced pancreatic cancer (LAPC), but may increase late duodenal toxicity. Volumetric-modulated arc therapy (VMAT) delivers intensity-modulated radiation therapy (IMRT) with a rotating gantry rather than multiple fixed beams. This study dosimetrically evaluates the feasibility of implementing duodenal constraints for SBRT using VMAT vs IMRT. Non–duodenal sparing (NS) and duodenal-sparing (DS) VMAT and IMRT plans delivering 25 Gy in 1 fraction were generated for 15 patients with LAPC. DS plans were constrained to duodenal D_max of<30 Gy at any point. VMAT used 1 360° coplanar arc with 4° spacing between control points, whereas IMRT used 9 coplanar beams with fixed gantry positions at 40° angles. Dosimetric parameters for target volumes and organs at risk were compared for DS planning vs NS planning and VMAT vs IMRT using paired-sample Wilcoxon signed rank tests. Both DS VMAT and DS IMRT achieved significantly reduced duodenal D_mean, D_max, D_1cc, D_4%, and V_20 Gy compared with NS plans (all p≤0.002). DS constraints compromised target coverage for IMRT as demonstrated by reduced V_95% (p = 0.01) and D_mean (p = 0.02), but not for VMAT. DS constraints resulted in increased dose to right kidney, spinal cord, stomach, and liver for VMAT. Direct comparison of DS VMAT and DS IMRT revealed that VMAT was superior in sparing the left kidney (p<0.001) and the spinal cord (p<0.001), whereas IMRT was superior in sparing the stomach (p = 0.05) and the liver (p = 0.003). DS VMAT required 21% fewer monitor units (p<0.001) and delivered treatment 2.4 minutes faster (p<0.001) than DS IMRT. Implementing DS constraints during SBRT planning for LAPC can significantly reduce duodenal point or volumetric dose parameters for both VMAT and IMRT. The primary consequence of implementing DS constraints for VMAT is increased dose to other organs at risk, whereas for IMRT it is compromised target coverage. These findings suggest clinical situations where each technique may be most useful if DS constraints are to be employed.     

Node-positive left-sided breast cancer: does VMAT improve treatment plan quality with respect to IMRT?

Purpose

The aim of the present work was to explore plan quality and dosimetric accuracy of intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) for lymph node-positive left-sided breast cancer.

Methods

VMAT and IMRT plans were generated with the Pinnacle³ V9.0 treatment planning system for 10 lymph node-positive left-sided breast cancer patients. VMAT plans were created using a single arc and IMRT was performed with 4 beams using 6, 10, and 15 MV photon energy, respectively. Plans were evaluated both manually and automatically using ArtiView?. Dosimetric plan verification was performed with a 2D ionization chamber array placed in a full scatter phantom.

Results

Photon energy had no significant influence on plan quality for both VMAT and IMRT. Large variability in low doses to the heart was found due to patient anatomy (range V_5 Gy 26.5–95?%). Slightly more normal tissue dose was found for VMAT (e.g., V_Tissue30%?=?22?%) than in IMRT (V_Tissue30%?=?18?%). The manual and ArtiView? plan evaluation coincided very accurately for most dose metrics (difference <?1?%). In VMAT, 96.7?% of detector points passed the 3?%/3 mm gamma criterion; marginally better accuracy was found in IMRT (98.3?%).

Conclusion

VMAT for node-positive left-sided breast cancer retains target homogeneity and coverage when compared to IMRT and allows maximum doses to organs at risk to be reduced. ArtiView? enables fast and accurate plan evaluation.     

Dosimetric comparison of volumetric modulated arc therapy and intensity-modulated radiation therapy for pancreatic malignancies

Volumetric-modulated arc therapy (VMAT) has been previously evaluated for several tumor sites and has been shown to provide significant dosimetric and delivery benefits when compared with intensity-modulated radiation therapy (IMRT). To date, there have been no published full reports on the benefits of VMAT use in pancreatic patients compared with IMRT. Ten patients with pancreatic malignancies treated with either IMRT or VMAT were retrospectively identified. Both a double-arc VMAT and a 7-field IMRT plan were generated for each of the 10 patients using the same defined tumor volumes, organs at risk (OAR) volumes, dose, fractionation, and optimization constraints. The planning tumor volume (PTV) maximum dose (55.8 Gy vs. 54.4 Gy), PTV mean dose (53.9 Gy vs. 52.1 Gy), and conformality index (1.11 vs. 0.99) were statistically similar between the IMRT and VMAT plans, respectively. The VMAT plans had a statistically significant reduction in monitor units compared with the IMRT plans (1109 vs. 498, p < 0.001). In addition, the doses to the liver, small bowel, and spinal cord were comparable between the IMRT and VMAT plans. However, the VMAT plans demonstrated a statistically significant reduction in the mean left kidney V₂₅ (9.4 Gy vs. 2.3 Gy, p = 0.018), mean right kidney V₁₅ (53.4 Gy vs. 45.9 Gy, p = 0.035), V₂₀ (32.2 Gy vs. 25.5 Gy, p = 0.016), and V₂₅ (21.7 Gy vs. 14.9 Gy, p = 0.001). VMAT was investigated in patients with pancreatic malignancies and compared with the current standard of IMRT. VMAT was found to have similar or improved dosimetric parameters for all endpoints considered. Specifically, VMAT provided reduced monitor units and improved bilateral kidney normal tissue dose. The clinical relevance of these benefits in the context of pancreatic cancer patients, however, is currently unclear and requires further investigation.     

Dosimetric comparison of helical tomotherapy and VMAT for anal cancer: A single institutional experience

To compare the dosimetric results of helical tomotherapy (HT) and volumetric arc therapy (VMAT) in the treatment of anal cancer. Plans were created for 20 (n = 20) patients treated for anal cancer using HT and 2 arc VMAT. Dosimetric comparison was assessed for doses to targets and organs at risk (small bowel, bladder, external genitalia, and femoral heads). Delivery time and dosimetric verification results were also compared. HT showed a higher V95% for both primary and nodal targets (V95% increase by 0.5% to 1.3%; p = ≤0.05). No differences were seen in V105%, V107%, or V110 % between techniques. HT provided better sparing of the small bowel for dose levels V30, V35, and V40 (p = 0.005, 0.001, and 0.030), but was similar at higher doses. Similarly HT provided better bladder dose at V35 only (p = 0.020). Doses to femoral heads and genitalia were similar. Delivery time was higher for the HT plans (4.58 ± 1.1 min) than VMAT (3.13 ± 0.2 minutes) (p = 0.011). Dose verification results were 99.5 ± 0.9% and 100 ± 0% (HT, n = 6) vs 95.0 ± 3.1% and 99.2 ± 0.8% (VMAT, n = 20) for global gamma criteria 3%/3 mm and 4%/4 mm, respectively. Both HT and VMAT produced high quality plans that frequently met most of the dose objectives apart from genitalia V20, V40, bladder V35, and V50. Although absolute dose differences were small, the PTV V95%, small bowel V30, V35, and V40 and bladder V35 were statistically better in the HT plans. VMAT provided a shorter delivery time by 1.45 minutes; however, our HT plans were more likely to pass tighter plan dose verification criteria than VMAT.     

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.     

VMAT partial arc technique decreases dose to organs at risk in whole pelvic radiotherapy for prostate cancer when compared to full arc VMAT and IMRT

Whole pelvic radiotherapy (WPRT) can sterilize microscopic lymph node metastases in treatment of prostate cancer. WPRT, compared to prostate only radiotherapy (PORT), is associated with increased acute gastrointestinal, and hematological toxicities. To further explore minimizing normal tissue toxicities associated with WPRT in definitive IMRT for prostate cancer, this planning study compared dosimetric differences between static 9-field-IMRT, full arc VMAT, and mixed partial-full arc VMAT techniques. In this retrospective study, 12 prostate cancer patients who met the criteria for WPRT were randomly selected for this study. The initial volume, PTV46, included the prostate, seminal vesicles, and pelvic nodes with margin and was prescribed to 4600 cGy. The cone-down volume, PTV78, included the prostate and proximal seminal vesicles with margin to a total dose of 7800 cGy. For each CT image set, 3 plans were generated for each of the PTVs: an IMRT plan, a full arc (FA) VMAT plan, and a mixed partial-full arc (PFA) VMAT plan, using 6MV photons energy. According to RTOG protocols none of the plans had a major Conformity Index (CI) violation by any of the 3 planning techniques. PFA plan had the best mean CI index of 1.00 and significantly better than IMRT (p = 0.03) and FA (p = 0.007). For equivalent PTV coverage, the average composite gradient index of the PFA plans was better than the IMRT and the FA plans with values 1.92, 2.03, and 2.01 respectively. The defference was statistically significant between PFA/IMRT and PFA/FA, with p- values of < 0.001. The IMRT plans and the PFA plans provided very similar doses to the rectum, bladder, sigmoid colon, and femoral heads, which were lower than the dose in the FA plans. There was a significant decrease in the mean dose to the rectum from 4524 cGy with the FA to 4182 cGy with the PFA and 4091 cGy with IMRT (p < 0.001). The percent of rectum receiving 4000 cGy was also the highest with FA at 66.1% compared to 49.9% (PFA) and 47.5% (IMRT). There was a significant decrease in the mean dose to the bladder from 3922 cGy (FA) to 3551 cGy (PFA) and 3612 cGy (IMRT) (p < 0.001). The percent of bladder receiving 4000 cGy was also the highest with FA at 45.4% compared to 36.6% (PFA) and 37.4% (IMRT). The average mean dose to the sigmoid colon decreased from 4177 cGy (FA) to 3893 cGy (PFA) and 3819 cGy (IMRT). The average mean dose to the femoral heads decreased from 2091 cGy (FA) to 2026 cGy (PFA) and 1987 cGy (IMRT). Considering the improvement in plan quality indices recorded in this study including the dose gradient and the dose to organs at risk, mixed partial-full arc plans may be the preferred VMAT treatment technique over full arc plans for prostate cancer treatments that include nodal volumes.     

鼻咽癌三种调强放疗计划剂量学对比研究

目的 对比鼻咽癌常规固定野调强（IMRT）、容积旋转调强（VMAT）以及断层调强（HT）3种不同调强放疗计划的剂量学差异。方法 选择18例接受VMAT治疗的鼻咽癌患者,以相同处方剂量和目标条件分别重新进行IMRT和HT计划设计。比较3种计划靶区的均匀度（HI）、适形度（CI）、最大剂量以及平均剂量。危及器官的最大量和平均量以及感兴趣区的剂量体积、计划执行时间和机器跳数（MU）。结果 3种计划在靶区的覆盖率满足临床要求。IMRT计划在靶区的HI和CI方面结果最差,HT计划结果最优。危及器官方面,IMRT计划受量最高,HT计划的脊髓、脑干和腮腺受量最低;但对于视神经、晶状体以及视交叉HT计划的受量最高而VMAT计划的受量最低。IMRT的治疗时间（8.0±0.5） min高于VMAT（3.9±0.1）min和HT（7.4±0.9）min。与VMAT相比,IMRT每次治疗为（711.4±78.7）MU,高于VMAT的（596.4±33.7）MU。结论 鼻咽癌IMRT、VMAT以及HT计划在靶区覆盖和危及器官保护上都可以达到临床要求,在靶区的适形度和均匀性上HT计划优于VMAT和IMRT,但在治疗时间和加速器的机器跳数上VMAT较有优势。     

Dosimetric comparison of vaginal vault brachytherapy vs applicator-guided stereotactic body radiotherapy with volumetric modulated arc therapy and helical tomotherapy for endometrium cancer patients

We performed this dosimetric study to compare a nonstandard volumetric modulated arc therapy (VMAT) and helical tomotherapy (HT) techniques with high-dose rate (HDR) brachytherapy (BRT) plan of vaginal vault in patients with postoperative endometrial cancer (EC). Twelve postoperative patients with early stage EC were included in this study. Three plans were performed for each patient; dosimetric and radiobiological comparisons were made using dose-volume histograms and equivalent dose for determining the planning target volume (PTV) coverages in brachytherapy and external beam radiotherapy, and organs-at-risk (OARs) doses between three different delivery techniques. All the plans achieved adequate dose coverage for PTV; however, the VMAT plan yielded better dose conformity, and the HT plan showed better homogeneity for target volume. With respect to the OARs, the bladder D_2cc was significantly lower in the BRT plan than in the VMAT and HT plans, with the highest bladder D_2cc value being observed in the HT plan. However, no difference was observed in the rectum D_2cc of the three plans. Other major advantages of the BRT plan over the VMAT and HT plans were the relatively lower body integral doses and femoral head doses as well as the fact that the integral doses were significantly lower in the BRT plan than in the VMAT and HT plans. This is the first dosimetric comparison of vaginal vault treatment for EC with BRT, VMAT, and HT plans. Our analyses showed the feasibility of stereotactic body radiotherapy technique as an alternative to HDR-BRT for postoperative management of EC patients.     

Treatment and Dosimetric Advantages Between VMAT, IMRT, and Helical TomoTherapy in Prostate Cancer

We investigated the possible treatment and dosimetric advantage of volumetric modulated arc therapy (VMAT) over step-and-shoot intensity-modulated radiation therapy (step-and-hhoot IMRT) and helical tomotherapy (HT). Twelve prostate cancer patients undergoing VMAT to the prostate were included. Three treatment plans (VMAT, step-and-shoot IMRT, HT) were generated for each patient. The doses to clinical target volume and 95% of planning target volume were both ≥78 Gy. Target coverage, conformity index, dose to rectum/bladder, monitor units (MU), treatment time, equivalent uniform dose (EUD), normal tissue complication probability (NTCP) of targets, and rectum/bladder were compared between techniques. HT provided superior conformity and significantly less rectal volume exposed to 65 Gy and 40 Gy, as well as EUD/NTCP of rectum than step-and-shoot IMRT, whereas VMAT had a slight dosimetric advantage over step-and-shoot IMRT. Notably, significantly lower MUs were needed for VMAT (309.7 ± 35.4) and step-and-shoot IMRT (336.1 ± 16.8) than for HT (3368 ± 638.7) (p < 0.001). The treatment time (minutes) was significantly shorter for VMAT (2.6 ± 0.5) than step-and-shoot IMRT (3.8 ± 0.3) and HT (3.8 ± 0.6) (p < 0.001). Dose verification of VMAT using point dose and film dosimetry met the accepted criteria. VMAT and step-and-shoot IMRT have comparable dosimetry, but treatment efficiency is significantly higher for VMAT than for step-and-shoot IMRT and HT.     

Heart-sparing effect of postmastectomy radiotherapy for breast cancer patients: A dosimetric study of cardiac substructures

We investigated to what extent can the dose-volumes of the coronary artery and the cardiac substructures be reduced by using IMRT technique in left-sided breast cancer patients. We chose 40 pN2M0 patients treated with postmastectomy IMRT. The original treatment plans were retrieved and the (internal mammary nodes) IMNs and cardiac substructure delineations were added. Three sets of dose-volume parameters including the original plans without internal mammary irradiation (IMNI), the plans with IMNI, and the plans with dose constraints to the heart, were derived. In left-sided patients, when IMNI was included, the V30 for right ventricle (RV), left ventricle (LV), pulmonic valve (PV), and left anterior descending artery (LADA) were 56.37% ± 7.9%, 25.3% ± 7.3%, 48.3% ± 6.3%, and 69.7% ± 6.4%, respectively. Of the 4 main coronary arteries, LADA had the highest dose followed by the left main coronary artery (LMCA). LADA had a V40 of 62% ± 9.7% vs 13.5% ± 3.5%, and a V50 of 27.5% ± 4.7% vs 0, with and without IMNI. For the right-sided patients, the V30s for all the heart substructures were 0 with or without IMNI. When we set a dose constraint of V40 < 10% for the LADA in the left-sided patients, the PTV volumes covered by 50 Gy decreased by only 1%. IMNI increased the V30 of the right and left ventricle and significantly increased the V40 and V50 to the LADA of left-sided breast cancer patients. IMRT markedly reduces the dose to the main coronary arteries and the right and left ventricle.