Radiotherapy dose compensation for lung patients

The purpose of the present paper is to provide a more homogeneous dose distribution in the target volume from compensated anterior and posterior fields while the healthy lung is spared by de-weighting the lateral fields. A compensation computation which used linear iterations to compute the most homogeneous dose distribution across the target volume was applied to produce optimum compensator designs. The equivalent tissue-air ratio (E-TAR) inhomogeneity correction was applied for the computations using a GE target series II planning computer. The compensators designed were tested for accuracy in a modified water/lung phantom using a scanning diode and an anthropomorphic phantom using thermoluminescent dosimeters. A comparison has been made between the compensated and uncompensated plans for the first nine patients who we have treated with this technique. The dose profiles produced by the computation agreed with the prediction of the computed isodose plans to within +/- 2% at the target depth. The thermoluminescent dosimeter (TLD)-measured results in the anthropomorphic phantom agreed with the planning computer within +/- 3%. A comparison of nine compensated plans of radiotherapy patients for large-volume targets in the lung region showed a maximum variation in the target to be 19% uncompensated versus 10% compensated. By providing compensated treatment fields from anterior and posterior treatment portals, a homogeneous dose that conforms well to the target volume is provided. As an added bonus, this enables the lateral lung fields to be significantly de-weighted and the healthy lung is spared considerable dose.     

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.     

Correlating the depth of compensation to the 3-D shape of the breast to achieve homogeneous dose distribution using the electronic tissue compensation treatment technique

Our study aimed to correlate the overall 3-dimensional (3-D) shape of the breast to the compensation depth to produce a homogeneous dose distribution using the electronic tissue compensation (ECOMP) treatment technique. The study involved creating a number of semioval water phantoms with the diameter of the larger axis representing the breast separation and the shorter axis representing the distance from the chest wall to the apex of the breast. Multiple plans with 2 tangential fields were created for each phantom using different transmission penetration depths (TPDs) to determine the optimum TPD value based on the evaluation of dose uniformity and maximum hot spot. Optimum TPD values from the semioval water phantom plans were plotted on a graph as a function of separation and radius and were used as guidelines to choose the optimum TPD for the breast patient's cases. A total of 10 patients who had been treated with radiation therapy using ECOMP tangential fields were randomly selected. The separation and the radius of the breast were measured for 3 regions (superior, middle, and inferior) to retrospectively determine the optimum TPD from the graph for each region. These TPD values were then used to plan the breast cases. For all the patients studied, the optimized TPD technique produced a lower average homogeneity index (HI) value of 0.658 than the standard ECOMP technique of 0.856. These results showed that optimized TPD technique produced a more homogeneous dose distribution than the standard ECOMP technique. By measuring the breast size based on breast separation and the chest wall-to-apex distance at different locations along the superior-inferior axis of the breast, the optimum TPD can be determined at each location to provide a homogeneous dose distribution. A module can be created within the planning system to automatically assign the optimum TPD for both tangential fields so uniform fluence maps can be achieved throughout the whole breast volume. This method can serve as a guideline in ECOMP during the treatment planning to obtain a homogeneous dose distribution.     

A computerized three-dimensional treatment planning system utilizing interactive colour graphics.

A new computerized radiation treatment planning system has been developed to aid in three-dimensional treatment planning. Using interactive colour graphics in conjunction with a DPD 11/45 computer, the system can take multiple transverse contours and construct a perspective display of the treatment region showing organ surfaces as well as cross-sectional contours. With interactively selected orientations, the display allows easy perception of the relative positioning of the treatment volume and neighbouring anatomy. For external beam treatment planning, interactive computer simulation is used to select diaphragm sizes which best conform to the target area while avoiding sensitive structures. Dose calculations for the selected beams are carried out on multiple transverse planes. The calculational planes and surfaces are displayed in perspective with radiation dosage displayed in an interactively manipulated colour display. Altogether the system provides an easy assessment of the volume to be irradiated, interactive selection of optimal arrangements of treatment fields and a means for visualizing and evaluating the resulting dose distributions.     

Comparison of intracavitary brachytherapy and stereotactic body radiotherapy dose distribution for cervical cancer

PurposeTo compare the dose distribution characteristics of stereotactic body radiotherapy (SBRT) with intracavitary high-dose-rate (HDR) brachytherapy in patients with cervical carcinoma.Methods and MaterialsHDR intracavitary brachytherapy treatment plans for 11 women with cervical carcinoma were evaluated in this analysis. The total HDR brachytherapy dose was 28 Gy given in four fractions. HDR brachytherapy was delivered with the microSelectron HDR therapy unit (Nucletron B. V., Veenendaal, The Netherlands). SBRT plans for each patient were generated with MultiPlan for CyberKnife Robotic Radiosurgery System (Accuray Inc., Sunnyvale, CA). The dose distributions, dose–volume histograms, and maximum dose points of the target and critical organs were recorded for both plans.ResultsSBRT yielded significantly better target coverage; the median target coverage for the 100% isodose line was 50.7% for HDR brachytherapy plans, whereas it was 99.1% for SBRT plans. The dose distributions for critical organs were similar in both types of plans. The exceptions were the 25% isodose being significantly better in brachytherapy plans for rectum, and the 100% isodose exposure being higher in brachytherapy plans for rectum, bladder, and sigmoid colon. Some significant differences were also found in maximum doses received by a 2-cc volume of bladder in favor of SBRT plans. In addition, maximum bone marrow doses were significantly higher in SBRT plans.ConclusionSBRT plans achieved better target coverage and better dose distributions to critical organs except bone marrow compared with HDR brachytherapy plans in patients with locally advanced cervical cancer.     

Dosimetric Comparison of RapidArc with Fixed Gantry Intensity-Modulated Radiotherapy Treatment for Multiple Liver Metastases Radiotherapy

We wanted to compare the dosimetric difference and treatment efficiency of RapidArc and fixed gantry intensity-modulated radiotherapy treatment (IMRT) for multiple liver metastases. Computed tomography datasets of 10 patients were studied retrospectively. IMRT plans were generated using 5 fields and RapidArc using either 1 or 2 arcs. The dose distribution of planning target volume (PTV), organs at risk (OARs), and the normal tissue were compared. Monitor units and treatment time were scored to measure expected treatment efficiency. Both RapidArc and IMRT plans resulted in equivalent target coverage. There was no statistically significant difference for the maximum and the minimum dose of PTV. RapidArc plans achieved an improved conformity index compared with IMRT (RA1 = 1.68 ± 0.27, RA2 = 1.61 ± 0.25, IMRT = 1.80 ± 0.37). For OARs, all techniques respected planning objectives. RapidArc plans had a lower dose in V₄₀ of small bowel than IMRT, but were higher in mean dose of kidneys. Concerning the V₅, V₁₀, and V₁₅ of healthy tissue, RapidArc plans were higher than IMRT. However, the V₂₀, V₂₅, and V₃₀ of healthy tissue in RapidArc plans were lower than IMRT. Monitor units per fraction of RapidArc plans were about 40% or 46% of IMRT. Compared with IMRT plans, treatment time of RapidArc plans were reduced by 60% or 70%. All techniques respected planning objectives. RapidArc showed statistical improvements in conformity index and healthy tissue sparing with uncompromised target coverage. This, in combination with fewer monitor units and short delivery time, can lead to clinically significant advances for the treatment of multiple liver metastases.     

The feasibility and efficacy of new SBRT technique HyperArc for recurrent nasopharyngeal carcinoma: noncoplanar cone-based robotic system vs. noncoplanar high-definition MLC based Linac system

The purpose of this study was to evaluate the feasibility and efficacy of HyperArc (HA) for recurrent nasopharyngeal cancer (NPC) by comparing it with the CyberKnife system (CK). Fifteen patients with recurrent nasopharyngeal cancer who were treated using the noncoplanar cone-based robotic CK system were enrolled. CK was delivered with a median dose of 37.5 Gy in 5 fractions. The delivered CK treatment plans were the sources for the corresponding homogeneous HA (HA-H) and inhomogeneous HA (HA-IH) plans. The HA-H plans were generated to meet the corresponding treatment plan criteria for the CK plans. The HA-IH plans were designed to emulate the corresponding inhomogeneous CK isodose distributions. These three SBRT treatment plans were compared with target coverage, sparing of organs at risk (OARs), and dose distribution metrics. The HA-H and HA-IH plans consistently exhibited CTV and PTV coverage levels similar or better to those of the CK plans but significantly reduced the dose to OARs. Using the HA techniques (both HA-H and HA-IH plans), the mean maximal doses to the spinal cord, brainstem, optic nerves, and optic chiasm were reduced by approximately 60%, compared to the CK plans. The high dose spillage, conformity, and homogeneity indices of the HA-H plans were significantly better than those of the CK plans. The HA-IH plans showed faster dose falloff and similar conformity of the HA-H plans and dose heterogeneity of the CK plans. Here we demonstrated the HA treatment plan system for recurrent NPC is feasible, either homogeneous or inhomogeneous delivery. Excellent sparing of OARs and dosimetric distribution and very efficient delivery make HA an attractive SBRT technique for recurrent NPC treatment.     

乳腺癌保乳术后两野与多野动态调强的剂量学研究

目的 比较早期乳腺癌保乳术后切线2野动态调强与非共面多野调强放疗治疗靶区和危及器官的剂量学差异。方法 选取40例接受保乳术后放疗的左侧乳腺癌患者,在同一患者CT影像上,利用相同优化条件分别进行切线2野和非共面3、4、5野4种调强治疗计划设计。比较4种计划的靶区剂量分布、心脏、左肺及右侧乳腺受照剂量和体积,以及机器跳数的差异。结果 非共面4、5野调强计划适形度指数（CI）和均匀性指数（HI）均优于切线2野调强计划（P<0.05）,临床靶区（PTV）最大剂量（D_max）小于2野调强计划（P<0.05）,PTV最小剂量（D_min）大于2野调强计划（P<0.05）。3野与2野计划间无明显差异。4种计划的右乳接受5 Gy照射的百分体积（V₅）、心脏接受30 Gy照射的百分体积（V₃₀）及平均剂量（D_mean）、左肺接受20和5 Gy照射的百分体积（V₂₀、V₅）、平均剂量（D_mean）无明显差异,而机器跳数间差异有统计学意义（F=25.63,P<0.05）,2野调强跳数最少,5野最多。结论 保乳术后非共面4、5野调强计划与切线2野调强计划相比,靶区剂量分布更好,不明显增加正常组织、器官的受照射剂量,但机器跳数明显增加。     

Estimation of the mean effective organ doses for total body irradiation from Rando phantom measurements.

For the total body irradiation (TBI) procedure, it is necessary to compare the mean dose obtained from the tissue or organs and the estimated dose equivalent value from the computer program. Due to the easy-access of the Rando phantom and repeatability of TLDs and its output, the results from the experiment are quite encouraging for the verification of the dose distributions from total body irradiation at the given prescribed monitor units. The estimation of effective dose equivalent particularly across the lung sections was studied by combinations of using arms as the scatter volume to compensate for the inhomogeneity across the breast portion, as well as using the spoiler for skin-sparing purposes. The results were based upon various beam quality such as 4 MV, 6 MV, and 10 MV X rays. One series of experiments performed for this survey to ascertain the dose equivalent of the tissues was conducted. This paper describes the method and procedure for comparison between the measured data and computed data as a reference in the dosimetry of total body irradiation. Comparison of the measured and computed data for the largest collimated field shows that the calculated dose rates do not differ by more than 2% from the measured data. Because uncertainty is inherent in non-patient-like phantoms, the calculated data may be served as a reference for the dosimetry. For the total body irradiation setup, considering the radiation field size and treatment distances commonly employed, we conclude that the best combination of the patient setup will be (1) laying both arms down as compensation for lung inhomogeneity, and (2) the spoiler, which is made of acrylic about 8 mm thick and functions like a bolus, is needed to reduce the skin sparing effects and contribute the uniform dose distribution. The beam spoiler with the frame stands near the patient during the treatment.     

螺旋断层固定野和旋转调强放疗技术在全身照射中的应用对比研究

目的 探究使用螺旋断层固定野调强（TD）和螺旋断层旋转调强（HT）放射治疗技术在全身照射（TBI）中的应用对比,并评估TD治疗技术下计划的质量和执行效率,指导临床选择最佳的计划设计方案。方法 对郑州大学第一附属医院收治的8例身高在120 cm左右的已行TBI的急性白血病患者进行回顾性研究,分别选择TD和HT治疗技术进行计划设计,其中TD分别设计2~12内奇数个均分射野的计划,且起始角度分别从180°和0°开始,其余计划参数都保持一致。最后对设计好的计划剂量分布进行统计,比较TD与HT治疗技术下的计划在靶区的平均剂量（PTV_Dmean）、均匀性指数（HI）和危及器官（OARs）受量,以评估计划质量,并比较治疗出束时间以评估治疗效率。结果 9野的TD计划相对于HT计划在PTV_Dmean和靶区HI能达到一致效果,差异无统计学意义。但TD<9野的计划相对于HT计划在PTV_Dmean（t=-3.12、-5.41、-20.33、-4.56、-7.22、-11.27,P<0.05）和靶区HI（t=-2.94、-5.18、-15.66、-4.31、-5.51、-9.13,P<0.05）无剂量学优势,差异有统计学意义。同时TD计划中起始角度对PTV_Dmean和靶区HI没有影响。在危及器官方面,≥ 7野TD计划与HT计划在左肺平均剂量与右肺平均剂量差异无统计学意义;左眼晶状体计划危及体积（PRV）的最大剂量（2.14±0.60）Gy与右眼晶状体PRV最大剂量（3.05±0.10）Gy在3野TD计划与HT计划差异有统计学意义（t=0.77、0.63,P<0.05）,眼晶状体PRV在最大剂量方面具有一定优势。治疗出束时间差异无统计学意义。TD计划中起始角度对左右眼晶状体PRV最大剂量、左肺平均剂量及治疗出束时间没有影响。结论 对于≥ 9野的TD调强计划相对于HT计划在靶区、危及器官及治疗出束时间方面能达到一致的结果,但在眼晶状体PRV最大剂量方面具有一定优势。     

Dosimetric advantage and clinical implication of a micro-multileaf collimator in the treatment of prostate with intensity-modulated radiotherapy.

This paper investigates the dosimetric benefits of a micro-multileaf (4-mm leaf width) collimator (mMLC) for intensity-modulated radiation therapy (IMRT) treatment planning of the prostate cancer and its potential application for dose escalation and hypofractionation. We compared treatment plans for IMRT delivery using 2 different multileaf collimator (MLC) leaf widths (4 vs. 10 mm) for 10 patients with prostate cancer. Treatment planning was performed on the XknifeRT2 treatment planning system. All beams and optimization parameters were identical for the mMLC and MLC plans. All of the plans were normalized to ensure that 95% of the planning target volume (PTV) received 100% of the prescribed dose (74 Gy). The differences in dose distribution between the 2 groups of plans using the mMLC and the MLC were assessed by dose-volume histogram (DVH) analysis of the target and critical organs. Significant reductions in the volume of rectum receiving medium to higher doses were achieved using the mMLC. The average decrease in the volume of the rectum receiving 40, 50, and 60 Gy using the mMLC plans was 40.2%, 33.4%, and 17.7%, respectively, with p-values less than 0.0001 for V40 and V50 and 0.012 for V60. The mean dose reductions for D17 and D35 for the rectum were 20.0% (p < 0.0001) and 18.3% (p < 0.0002), respectively, when compared to those with the MLC plans. There were consistent reductions in all dose indices studied for the bladder. The target dose inhomogeneity was improved in the mMLC plans by an average of 32%. In the high-dose range, there was no significant difference in the dose deposited in the "hottest" 1 cc of the rectum between the 2 MLC plans for all cases (p > 0.78). Because of the reduction of rectal volume receiving medium to higher doses, dose to the prostate target can be escalated by about 20 Gy to over 74 Gy, while keeping the rectal dose (either denoted by D17 or D35) the same as those with the use of the MLC. The maximum achievable dose, derived when the rectum is allowed to reach the tolerance level, was found to be in the range of 113-172 Gy (using the tolerance value of D17). We conclude that the use of the mMLC for IMRT of the prostate may facilitate dose hypofractionation due to its dosimetric advantage in significantly improving the DVH parameters of the prostate and critical organs. When used for conventional fractionation scheme, mMLC for IMRT of the prostate may reduce the toxicity to the critical organs.     

Bestimmung von Organdosen und effektiven Dosen in der Radioonkologie

BACKGROUND AND PURPOSE: With an increasing chance of success in radiooncology, it is necessary to estimate the risk from radiation scatter to areas outside the target volume. The cancer risk from a radiation treatment can be estimated from the organ doses, allowing a somewhat limited effective dose to be estimated and compared. MATERIAL AND METHODS: The doses of the radiation-sensitive organs outside the target volume can be estimated with the aid of the PC program PERIDOSE developed by van der Giessen. The effective doses are determined according to the concept of ICRP, whereby the target volume and the associated organs related to it are not taken into consideration. RESULTS: Organ doses outside the target volume are generally < 1% of the dose in the target volume. In some cases, however, they can be as high as 3%. The effective doses during radiotherapy are between 60 and 900 mSv, depending upon the specific target volume, the applied treatment technique, and the given dose in the ICRU point. CONCLUSION: For the estimation of the radiation risk, organ doses in radiooncology can be calculated with the aid of the PC program PERIDOSE. While evaluating the radiation risk after ICRP, for the calculation of the effective dose, the advanced age of many patients has to be considered to prevent that, e.g., the high gonad doses do not overestimate the effective dose.     

Clinical application of digital tomosynthesis: a preliminary report

Digital tomosynthesis represents a new technique for digital manipulation of data acquired during a single tomographic sweep. With the aid of a computer, data can be processed to yield images in any parallel plane of the body. This technique allows rapid tomographic studies requiring a much lower radiation dose to the patient. Dynamic studies such as angiotomography are feasible, and application to digital subtraction intravenous angiography is also possible with this technique. Early experience with clinical application in patient studies is presented.     

Total scalp irradiation using helical tomotherapy.

Homogeneous irradiation of the scalp poses technical and dosimetric challenges due to the extensive, superficial, curved treatment volume. Conventional treatments on a linear accelerator use multiple matched electron fields or a combination of electron and photon fields. Problems with these techniques include dose heterogeneity in the target due to varying source-to-skin distance (SSD) and angle of beam incidence, significant dose to the brain, and the potential for overdose or underdose at match lines between the fields. Linac-based intensity-modulated radiation therapy (IMRT) plans have similar problems. This work presents treatment plans for total scalp irradiation on a helical tomotherapy machine. Helical tomotherapy is well-suited for scalp irradiation because it has the ability to deliver beamlets that are tangential to the scalp at all points. Helical tomotherapy also avoids problems associated with field matching and use of more than one modality. Tomotherapy treatment plans were generated and are compared to plans for treatment of the same patient on a linac. The resulting tomotherapy plans show more homogeneous target dose and improved critical structure dose when compared to state-of-the-art linac techniques. Target equivalent uniform dose (EUD) for the best tomotherapy plan was slightly higher than for the linac plan, while the volume of brain tissue receiving over 30 Gy was reduced by two thirds. Furthermore, the tomotherapy plan can be more reliably delivered than linac treatments, because the patient is aligned prior to each treatment based on megavoltage computed tomography (MVCT).     

The use of a semi-customized phantom for verification of conformal plans.

We have developed a technique for inverse treatment planning of prostate therapy designed to improve the degree of conformation between the dose distribution and the target volume. We compared the inverse plan with a "standard" four-field box technique as well as a four-field technique using oblique fields ("cross technique"). We validated the dosimetry of the inverse plan using Fricke gel solution in phantom specifically designed for this purpose. The phantom is a Plexiglas tank with a cross section, which approximates the dimensions of the pelvis. Anatomical data from computed tomography (CT) images of a patient were used to simulate organs in our phantom. This allows us to calculate dose distributions with the external geometry of the phantom and internal anatomy of the patient. Dose-volume histograms (DVHs) for the three different plans were calculated. The phantom containing the Fricke gel was irradiated according to the inverse plan. Magnetic resonance (MR) images was used to determine the dose distribution delivered to the phantom. We observe, on DVHs, that the inverse plan significantly reduces the dose to the rectum and the bladder but slightly increases the inhomogeneity inside the target volume. Correlation is good between isodoses on MR images and calculated isodoses. We conclude that inverse planning software can greatly improve the conformal degree of treatment to the prostate. This technique could be applied to other complex anatomic sites at which dose to organs at risk is a limiting factor and increased dose to the target volume is indicated. Our phantom and the Fricke gel solution are convenient to carry out validation of conformal treatments.     

Comparative evaluation of treatment plan quality for a prototype biology-guided radiotherapy system in the treatment of nasopharyngeal carcinoma

We aimed to compare prototype treatment plans for a new biology-guided radiotherapy (BgRT) machine in its intensity-modulated radiation therapy (IMRT) mode with those using existing IMRT delivery techniques in treatment of nasopharyngeal carcinoma (NPC). We retrospectively selected ten previous NPC patients treated in 33 fractions according to the NRG-HN001 treatment protocol. Three treatment plans were generated for each patient: a helical tomotherapy (HT) plan with a 2.5-cm jaw, a volumetric modulated arc therapy (VMAT) plan using 2 to 4 6-MV arc fields, and a prototype IMRT plan for a new BgRT system which uses a 6-MV photon beam on a ring gantry that rotates at 60 rotations per minute with a couch that moves in small incremental steps. Treatment plans were compared using dosimetric parameters to planning target volumes (PTVs) and organs at risk (OARs) as specified by the NRG-HN001 protocol. Plans for the three modalities had comparable dose coverage, mean dose, and dose heterogeneity to the primary PTV, while the prototype IMRT plans had greater dose heterogeneity to the non-primary PTVs, with the average homogeneity index ranging from 1.28 to 1.50 in the prototype plans. Six of all the 7 OAR mean dose parameters were lower with statistical significance in the prototype plans compared to the HT and VMAT plans with the other mean dose parameter being comparable, and all the 18 OAR maximum dose parameters were comparable or lower with statistical significance in the prototype plans. The average left and right parotid mean doses in the prototype plans were 10.5 Gy and 10.4 Gy lower than those in the HT plans, respectively, and were 5.1 Gy and 5.2 Gy lower than those in the VMAT plans, respectively. Compared to that with the HT and VMAT plans, the treatment time was longer with statistical significance with the prototype IMRT plans. Based on dosimetric comparison of ten NPC cases, the prototype IMRT plans achieved comparable or better critical organ sparing compared to the HT and VMAT plans for definitive NPC radiotherapy. However, there was higher dose heterogeneity to non-primary targets and longer estimated treatment time with the prototype plans.