Patient positioning variations to reduce dose to normal tissues during 3D conformal radiotherapy for high-risk prostate cancer

BACKGROUND AND PURPOSE: The goal of this work was to assess optimal treatment positioning of 3D conformal radiotherapy (3DCRT) for high-risk prostate cancer patients. PATIENTS AND METHODS: Treatment plans of 25 patients in different patient positions were evaluated: with knee and ankle support (KAS) in the supine position and with a belly board (BB) in the prone position both with full (FB) and empty bladder (EB). Planning target volumes (PTVs) for pelvis, prostate and vesicles, prostate, and organs at risk (OARs) were delineated. Dose and overlapping volumes were evaluated. RESULTS: Overlapping volumes were significantly smaller with a FB than with an EB. No significant differences were found in overlapping volumes with respect to patient fixation systems, but the percentage values of dose to the OARs showed significantly better results employing KAS than a BB. A FB reduced the dose volumes to the OARs. Comparison with respect to circumference of abdomen (CA) showed significantly smaller overlapping at large CA in most of the cases. CONCLUSION: Supine position is suggested with KAS combined with a FB (especially in cases of larger CA) when using 3DCRT with planning technique modification for high-risk prostate cancer patients to reduce the dose of OARs, based on our results.     

Estimation of exposure dose on MDCT examination--the measurement of organ dose and effective dose by anthropomorphic phantom

In order to evaluate the exposure dose in CT examinations, we measured the tissue and organ doses by test site in 4-row, 16-row, and 64-row multi detector CT by using an anthropomorphic phantom and fluorescent glass dosimeters. Furthermore, we calculated the effective dose by using the tissue weighting factor recommended by the ICRP in 2007. The effective dose in the head and neck examinations was 1.4-3.1 mSv, whereas the maximum skin dose was 278.9 mGy in head perfusion CT. The effective dose in examinations of the body trunk was 10.1-35.2 mSv. In addition, the organ dose and skin dose in the scanning range was similar to the CTDI(vol) in head and neck examinations, while it was higher than the CTDI(vol) in examinations of the body trunk. The exposure dose of patients undergoing CT is high in comparison to other radiological examinations. As a result, due to consecutive examinations, an absorbed dose of more than 100 mGy is possible. A future problem therefore remains how to lower the overall exposure dose with the introduction of new radiographic diagnostic modalities, such as phase scan or coronary CT angiography.     

Toxicity and outcome of pelvic IMRT for node-positive prostate cancer

Background and purpose

This study reports on the treatment techniques, toxicity, and outcome of pelvic intensity-modulated radiotherapy (IMRT) for lymph node-positive prostate cancer (LNPPC, T1-4, c/pN1 cM0).

Patients and methods

Pelvic IMRT to 45–50.4?Gy was applied in 39?cases either after previous surgery of involved lymph nodes (n?=?18) or with a radiation boost to suspicious nodes (n?=?21) with doses of 60–70?Gy, usually combined with androgen deprivation (n?=?37). The prostate and seminal vesicles received 70–74?Gy. In cases of previous prostatectomy, prostatic fossa and remnants of seminal vesicles were given 66–70?Gy. Treatment-related acute and late toxicity was graded according to the RTOG criteria.

Results

Acute radiation-related toxicity higher than ?grade?2 occurred in 2?patients (with the need for urinary catheter/subileus related to adhesions after surgery). Late toxicity was mild (grade 1–2) after a median follow-up of 70?months. Over 50% of the patients reported no late morbidity (grade 0). PSA control and cancer-specific survival reached 67% and 97% at over ?5?years.

Conclusion

Pelvic IMRT after the removal of affected nodes or with a radiation boost to clinically positive nodes led to an acceptable late toxicity (no grade 3/4 events), thus justifying further evaluation of this approach in a larger cohort.     

Three-dimensional gamma analysis of dose distributions in individual structures for IMRT dose verification

Our purpose in this study was to implement three-dimensional (3D) gamma analysis for structures of interest such as the planning target volume (PTV) or clinical target volume (CTV), and organs at risk (OARs) for intensity-modulated radiation therapy (IMRT) dose verification. IMRT dose distributions for prostate and head and neck (HN) cancer patients were calculated with an analytical anisotropic algorithm in an Eclipse (Varian Medical Systems) treatment planning system (TPS) and by Monte Carlo (MC) simulation. The MC dose distributions were calculated with EGSnrc/BEAMnrc and DOSXYZnrc user codes under conditions identical to those for the TPS. The prescribed doses were 76 Gy/38 fractions with five-field IMRT for the prostate and 33 Gy/17 fractions with seven-field IMRT for the HN. TPS dose distributions were verified by the gamma passing rates for the whole calculated volume, PTV or CTV, and OARs by use of 3D gamma analysis with reference to MC dose distributions. The acceptance criteria for the 3D gamma analysis were 3/3 and 2 %/2 mm for a dose difference and a distance to agreement. The gamma passing rates in PTV and OARs for the prostate IMRT plan were close to 100 %. For the HN IMRT plan, the passing rates of 2 %/2 mm in CTV and OARs were substantially lower because inhomogeneous tissues such as bone and air in the HN are included in the calculation area. 3D gamma analysis for individual structures is useful for IMRT dose verification.     

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.     

Comparison between effective radiation dose of CBCT and MSCT scanners for dentomaxillofacial applications

Objectives

To compare the effective dose levels of cone beam computed tomography (CBCT) for maxillofacial applications with those of multi-slice computed tomography (MSCT).

Study design

The effective doses of 3 CBCT scanners were estimated (Accuitomo 3D^®, i-CAT^®, and NewTom 3G^®) and compared to the dose levels for corresponding image acquisition protocols for 3 MSCT scanners (Somatom VolumeZoom 4^®, Somatom Sensation 16^® and M×8000 IDT^®). The effective dose was calculated using thermoluminescent dosimeters (TLDs), placed in a Rando^® Alderson phantom, and expressed according to the ICRP 103 (2007) guidelines (including a separate tissue weighting factor for the salivary glands, as opposed to former ICRP guidelines).

Results

Effective dose values ranged from 13 to 82 μSv for CBCT and from 474 to 1160 μSv for MSCT. CBCT dose levels were the lowest for the Accuitomo 3D^®, and highest for the i-CAT^®.

Conclusions

Dose levels for CBCT imaging remained far below those of clinical MSCT protocols, even when a mandibular protocol was applied for the latter, resulting in a smaller field of view compared to various CBCT protocols. Considering this wide dose span, it is of outmost importance to justify the selection of each of the aforementioned techniques, and to optimise the radiation dose while achieving a sufficient image quality. When comparing these results to previous dosimetric studies, a conversion needs to be made using the latest ICRP recommendations.     

A dosimetric comparison of RapidArc and IMRT with hypofractionated simultaneous integrated boost to the prostate for treatment of prostate cancer

Objective:

To compare the dosimetric results and treatment delivery efficiency among RapidArc® (Varian Medical Systems, Palo Alto, CA), 7-field intensity-modulated radiotherapy (7-f IMRT) and 9-field IMRT (9-f IMRT) with hypofractionated simultaneous integrated boost to the prostate.

Methods:

RapidArc, 7-f IMRT and 9-f IMRT plans were created for 21 consecutive patients treated for high-risk prostate cancer using the Eclipse™ treatment planning system (Varian Medical Systems). All plans were designed to deliver 70.0 Gy in 28 fractions to the prostate planning target volume (PTV) while simultaneously delivering 50.4 Gy in 28 fractions to the pelvic nodal PTV. Target coverage and sparing of organs at risk (OARs) were compared across techniques. The total number of monitor units (MUs) and the treatment time were used to assess treatment delivery efficiency.

Results:

RapidArc resulted in slightly superior conformity and homogeneity of prostate PTV, whereas all plans were comparable with respect to dose to the nodal PTV. Although OARs sparing for RapidArc and 7-f IMRT plans were almost equivalent, 9-f IMRT achieved better sparing of the rectum and bladder than RapidArc and 7-f IMRT. RapidArc provided the highest treatment delivery efficiency with the lowest MUs and shortest treatment time.

Conclusion:

RapidArc resulted in similar OAR sparing to 7-f IMRT, whereas 9-f IMRT provided the best OAR sparing. Treatment delivery efficiency is significantly higher for RapidArc.

Advances in knowledge:

This study validated the feasibility and limitations of RapidArc in the treatment of high-risk prostate cancer with complex pelvic target volumes.Radiotherapy has played an important role in the treatment of locally advanced prostate cancer. Several randomised controlled trials have demonstrated that high-dose radiotherapy improves prostate-specific antigen control, and a recently published meta-analysis [1] showed that high-dose radiotherapy is superior to conventional-dose radiotherapy in preventing biochemical or clinical failure and prostate cancer-specific death. However, dose escalation has been limited by toxicity in conventional techniques. Therefore, prostate cancer is one of the most common tumour sites treated with intensity-modulated radiation therapy (IMRT), which enables the delivery of highly conformal dose distribution to the target while reducing the dose to critical organs. IMRT also has the ability to produce inhomogeneous dose distribution, which allows for simultaneous differential dose delivery to multiple tumour targets (simultaneous integrated boost). Despite the obvious benefits of IMRT, there are some disadvantages. The potential downsides of IMRT include the increased time required for radiotherapy delivery and increased monitor units (MUs) needed compared with conventional three-dimensional conformal radiation therapy.Volumetric-modulated arc therapy (VMAT) is a relatively new rotational radiation therapy technique based on the idea of delivering IMRT with continuous dynamic modulation of the dose rate, field aperture and gantry speed. Compared with IMRT, the potential benefit of VMAT is the increase in delivery efficiency, including a shorter treatment time and a lower number of MUs.Several recent studies have compared VMAT with IMRT for prostate radiotherapy [2–13]. Although shortened treatment time is a common finding, there are inconsistencies in the dosimetric outcome. Many studies considering relatively simple target volumes that included prostate only or prostate with seminal vesicles found that VMAT achieved equal or better normal tissue sparing over IMRT [2,3,5,6,8–10,12]. However, very few studies have focused on more complex pelvic target volumes, including the prostate, seminal vesicles and pelvic lymph nodes [4,7,11,13]. Some of these studies found largely equivalent sparing of organs at risk (OARs) between VMAT and IMRT [7,13]. However, other planning studies have reported contradictory results. Yoo et al [4] noted superior OARs sparing with IMRT to VMAT. Myrehaug et al [11] found VMAT to have no consistent dosimetric advantage over IMRT. Thus, those studies have yielded mixed results. Our study aims to expand such studies to quantitatively evaluate VMAT for prostate cancer cases with complex pelvic target volumes and simultaneous integrated boost techniques.RapidArc® is one of the VMAT techniques implementing the progressive resolution optimisation algorithm in the Eclipse™ planning system by Varian Medical Systems (Palo Alto, CA). In the present study, we compare the performance of RapidArc, 7-field IMRT (7-f IMRT) and 9-field IMRT (9-f IMRT) with hypofractionated simultaneous integrated boost to the prostate for patients with high-risk prostate cancer. This study focused on the evaluation of the dosimetric results and treatment delivery efficiency.     

基于DPM的调强放疗计划剂量验证工具的实现

目的 基于简单快速蒙特卡罗程序DPM（dose planning method）,通过植入照射源模型并改进程序,解决DPM中无法实现任意角度入射和非规则非均匀野模拟的问题,使其成为调强放疗计划系统的实用蒙特卡罗剂量验证工具。方法 通过加速器反演出的能谱结合优化给出的强度图模拟加速器的粒子输运过程。使用虚拟点源结合反演出加速器能谱模拟了加速器的照射源部分,基于DPM的粒子输运物理模型,结合调强放疗计划中的照射野强度分布,以及出射粒子的权重与强度图中的强度相结合,实现了算法。结果 通过将DPM模拟计算的规则野结果与三维水箱测量数据对比了百分深度剂量（PDD）和百分离轴剂量（OAR）,误差在野内<2%,半影2~3mm。以及DPM模拟计算非规则野的结果与有限笔形束剂量计算方法FSPB计算结果的对比,趋势符合,γ分析通过率为95.1%,误差都在允许范围内。校验了改进的DPM的功能和计算精度。结论 植入简便照射源模型的DPM程序相较于经典蒙特卡罗程序,速度较快,计算精度和时间可以满足临床需求,可以作为调强放疗计划系统中剂量验证工具。     

PET-CT检查致前列腺癌患者辐射剂量研究

目的 评估¹⁸F-Choline、¹¹C-Choline和⁶⁸Ga-PSMA PET-CT检查致前列腺癌患者的有效剂量和器官剂量。方法 回顾性研究2017年5月至2018年6月广西医科大学附属肿瘤医院接受PET-CT检查的150例前列腺癌患者,按照注射正电子放射性药物类型分为3组,每组50例。CT定位扫描电压和电流分别为120 kV和35 mA,全身CT扫描电和电流分别为120 kV和（135.6±9.4） mA。PET部分的剂量利用基于医学内照射剂量（MIRD）计算方法的OLINDA/EXM （version 1.1）软件行计算。利用有效剂量转换因子和ImPACT （version 1.0.4） CT剂量计算器计算CT部分剂量,CT剂量指数（CTDI）利用标准体模测量和ImPACT CT计算,组织权重因子取自国际放射防护委员会（ICRP）103号报告,PET和CT剂量之和为患者总有效剂量。结果 注射¹⁸F-Choline、¹¹C-Choline和⁶⁸Ga-PSMA的活度分别为（279.2±13.2）、（350.2±39.9）和（186.8±19.4） MBq,有效剂量分别为（5.0±0.2）、（1.6±0.2）和（3.0±0.3） mSv,差异有统计学意义（F=837.0,P<0.001）。CT有效剂量为（11.4±0.2） mSv。3组总有效剂量分别为（16.4±0.3）、（13.0±0.3）和（14.4±0.4） mSv。PET检查3组器官当量剂量平均值比较,差异有统计学意义（F=381.2~1 637.7,P<0.001）。¹⁸F-Choline和⁶⁸Ga-PSMA PET-CT检查器官当量剂量最高为肾脏,而¹¹C-Choline PET-CT检查最高为甲状腺。结论 PET-CT检查致前列腺癌患者的有效剂量为13.0~16.4 mSv,其中绝大部分的剂量来自CT扫描。¹¹C-Choline PET-CT检查致患者的辐射剂量最低,有望成为潜在的前列腺癌PET显像药物。     

基于危及器官预测剂量分布与gEUD混合目标的调强放疗计划优化

目的 提出一种可充分利用危及器官预测剂量分布信息,同时最大限度地改善输出计划质量的调强放疗计划优化方法。方法 构建以危及器官预测剂量分布作为优化引导的新型通量分布优化模型,考虑到预测的不确定性,模型中同时耦合了危及器官的等效均匀剂量目标（gEUD）以在预测引导的基础上进一步改善最优化求解空间。为验证优化方法的有效性,实验选取8例宫颈癌调强放射治疗（IMRT）计划,利用该方法对其重新优化后比较所得计划与原始计划间在剂量分布和特定剂量学指征项上的质量差异。结果 该优化方法具有可行解且收敛快速,所得优化计划与原始计划相比,靶区内热点减少,其剂量均匀性提高;危及器官受量也均有改善,直肠V₃₀和V₄₅分别减小了（6.60±3.53）%和（17.03±7.44）%,差异有统计学意义（t=-4.954、-6.055,P<0.05）,膀胱V₃₀和V₄₅分别减小（14.74±5.61）%和（14.99±4.53）%,差异有统计学意义（t=-6.945、-8.759,P<0.05）。结论 所提出的基于预测剂量分布和gEUD混合目标的调强放疗计划优化方法可有效地利用预测剂量分布,并保障输出计划的优质性。     

Measuring absorbed dose for i-CAT CBCT examinations in child,adolescent and adult phantoms

Objectives:

Design and construct child and adolescent head phantoms to measure the absorbed doses imparted during dental CBCT and compare with the absorbed dose measured in an adult phantom.

Methods:

A child phantom was developed to represent the smallest patients receiving CBCT, usually for craniofacial developmental concerns, and an adolescent phantom was developed to represent healthy orthodontic patients. Absorbed doses were measured using a thimble ionization chamber for the custom-built child and adolescent phantoms and compared with measurements using a commercially available adult phantom. Imaging was performed with an i-CAT Next Generation (Imaging Sciences International, Hatfield, PA) CBCT using two different fields of view covering the craniofacial complex (130 mm high) or maxilla/mandible (60 mm high).

Results:

Measured absorbed doses varied depending on the location of the ionization chamber within the phantoms. For CBCT images obtained using the same protocol for all phantoms, the highest absorbed dose was measured in all locations of the small child phantom. The lowest absorbed dose was measured in the adult phantom.

Conclusions:

Images were obtained with the same protocol for the adult, adolescent and child phantoms. A consistent trend was observed with the highest absorbed dose being measured in the smallest phantom (child), while the lowest absorbed dose was measured in the largest phantom (adult). This study demonstrates the importance of child-sizing the dose by using dedicated paediatric protocols optimized for the imaging task, which is critical as children are more sensitive to harmful effects of radiation and have a longer life-span post-irradiation for radiation-induced symptoms to develop than do adults.     

IMRT for the treatment of prostate cancer: a comparison of a forward-planned technique and an inverse-planned technique utilizing a dose gradient method.

Radiation therapy has been a major treatment option for patients with prostate cancer with documented efficacy over the last 30 years. Recent research has shown a correlation between improved local control, disease-free survival, and overall survival and dose delivered. Excessive dose to the rectum is one of the leading causes of morbidity in the treatment of prostate cancer. The RTOG and others have suggested dose limitations based on various treatment parameters. Intensity-modulated radiation therapy (IMRT) is becoming more widely used, with the goal of improving dose coverage while limiting morbidity. In an effort to evaluate our inverse-planning technique relative to our forward-planned technique based on rectal dose, 2 plans were generated on 10 patients. One plan was generated with 9-field forward planning, using 2 posterior obliques to decrease dose to the rectum. The other plan utilized inverse IMRTplanning. To evaluate dose to the rectum, we compared the dose gradient from the posterior edge of the prostate across the anterior third of the rectal wall. This gradient, which is not part of the IMRT planning objectives, proved useful in assessing plan differences, and led to new dose objectives for certain IMRT plans.     

Female breast radiation exposure during thorax multidetector computed tomography and the effectiveness of bismuth breast shield to reduce breast radiation dose

OBJECTIVE: The purpose of our study was to determine the breast radiation dose when performing routine thoracic multidetector computed tomography (MDCT). We also evaluated dose reduction and the effect on image quality of using a bismuth breast shield when performing thoracic MDCT. MATERIAL AND METHODS: The dose reduction achievable by shielding the adult (18 years or older) female breasts was studied in 50 women who underwent routine thoracic MDCT. All examinations were performed with a 16-MDCT scanner (Sensation Cardiac 16; Siemens Medical Solutions). To compare the shielded/unshielded breast dose, the examination was performed with (right breast) and without (left breast) breast shielding in all patients. With this technique, the superficial breast doses were calculated. To determine the average glandular breast radiation dose, we imaged an anthropomorphic dosimetric phantom into which calibrated dosimeters were placed to measure the dose to breast. The phantom was imaged using the same protocol. Radiation doses to the breasts with and without the breast shielding were measured and compared using the Student t test. RESULTS: In the qualitative evaluation of the MDCT scans, all were considered to be of diagnostic quality. We did not see any differences in quality between the shielded and unshielded lung. The mean radiation doses to the breasts with the shield and to those without the shield were 8.6 +/- 2.33 versus 14.46 +/- 3.94 mGy, respectively. The breast shield enabled a 40.53% decrease in radiation dose to the breast. The difference between the dose received by the breasts with and that received by the breasts without bismuth shielding was significant, with a P value of less than 0.001. CONCLUSIONS: Bismuth in-plane shielding for routine thoracic MDCT decreased radiation dose to the breast without qualitative changes in image quality. The other radiosensitive superficial organs (eg, testes and thyroid gland) specifically must be protected with shielding.