IMRT to Escalate the Dose to the Prostate while Treating the Pelvic Nodes

Background and Purpose: To assess and quantify the benefit of introducing intensity–modulated radiotherapy (IMRT) over conventional approaches to cover the pelvic nodes while escalating the dose to the prostate gland.Material and Methods: The pelvic lymphatics were planned to receive 50 Gy at 2 Gy per fraction by four–field box (4FB) technique and standard field blocks drawn on digitally reconstructed radiographs (DRR), 4FB with field blocks according to the position of pelvic nodes as contoured on serial planning CT slices, or IMRT. The lateral fields included three different variations of field blocks to assess the role of various degrees of rectal shielding. The boost consisted in 26 Gy in 13 fractions delivered via six–field three–dimensional conformal radiotherapy (3DCRT) or IMRT. By the combination of a pelvic treatment and boost, several plans were obtained for each patient, all normalized to be isoeffective with regard to prostate–planning target volume (PTV–P) coverage. Plans were compared with respect to dose–volume histogram (DVH) of pelvic nodes/seminal vesicles–PTV (PTV–PN/SV), rectum, bladder and intestinal cavity. Reported are the results obtained in eight patients.Results: Pelvic IMRT with a conformal boost provided superior sparing of both bladder and rectum over any of the 4FB plans with the same boost. For the rectum the advantage was around 10% at V70 and even larger for lower doses. Coverage of the pelvic nodes was adequate with initial IMRT with about 98% of the volume receiving 100% of the prescribed dose. An IMRT boost provided a gain in rectal sparing as compared to a conformal boost. However, the benefit was always greater with pelvic IMRT followed by a conformal boost as compared to 4FB with IMRT boost. Finally, the effect of utilizing an IMRT boost with initial pelvic IMRT was greater for the bladder than for the rectum (at V70, about 9% and 3% for the bladder and rectum, respectively).Conclusion: IMRT to pelvic nodes with a conformal boost allows dose escalation to the prostate while respecting current dose objectives in the majority of patients and it is dosimetrically superior to 4FB. An IMRT boost should be considered for patients who fail to meet bladder dose objectives.     

脑胶质瘤三维适形放射治疗与调强放射治疗的剂量学比较

目的 评价脑胶质瘤调强放射治疗较三维适形放射治疗的剂量学优势。方法 本研究采用10例脑胶质瘤患者,针对所有患者分别进行3D CRT和IMRT的计划设计,利用剂量体积直方图评价不同照射技术中靶区和正常组织照射剂量、适形度指数和不均匀性指数。处方剂量为60 Gy。结果 IMRT计划脑干最大剂量和受照体积、患侧腮腺平均剂量和脊髓最大剂量均低于3D CRT计划。对于靶区适形度指数,IMRT计划优于3D CRT计划;对于不均匀性指数,两种计划模式的差异没有统计学意义。结论 在脑胶质瘤放疗中应用 IMRT可以明显降低脑干的剂量和受照体积,为靶区剂量的提高提供了可能性。     

Sparing of the penile bulb and proximal penile structures with intensity-modulated radiation therapy for prostate cancer

Quality of life is an important consideration in the treatment of early prostate cancer. Laboratory and clinical data suggest that higher radiation doses delivered to the bulb of penis and proximal penile structures correlates with higher rates of post-radiation impotence. The goal of this investigation was to determine if intensity-modulated radiation therapy (IMRT) spares dose to the penile bulb while maintaining coverage of the prostate. 10 consecutive patients with clinically organ confined prostate cancer were planned with 3D conformal radiation therapy (3D-CRT) or IMRT to give a dose of 74 Gy without specifically constraining the plans to spare the penile bulb. All 10 patients were ultimately treated with IMRT. Dose-volume histograms were evaluated and the doses to prostate, rectum, bladder and penile bulb were compared. IMRT reduced the mean penile bulb doses compared with 3D-CRT (33.2 Gy vs 48.9 Gy, p<0.001), the percentage of penile bulb receiving over 40 Gy (37.7% vs 67.2%, p<0.001) and the dose received by >95% of penile bulb (5.3 Gy vs 11.7 Gy, p=0.003). Maximum penile bulb doses were higher with IMRT (81.2 Gy vs 73.1 Gy, p<0.001) although the volume of this high dose region was small. Both methods resulted in similar coverage of the prostate. The volume of rectum receiving 70 Gy was significantly reduced with IMRT (18.4% vs 21.9%, p=0.003) but the volumes of bladder receiving 70 Gy were similar (p=0.3). IMRT may potentially reduce long term sexual morbidity by reducing the dose to the majority of the penile bulb.     

Development of a simultaneous boost IMRT class solution for a hypofractionated prostate cancer protocol

The purpose of this work was to develop a robust technique for planning intensity-modulated radiation therapy (IMRT) for prostate cancer patients who are to be entered into a proposed hypofractionated dose escalation study. In this study the dose escalation will be restricted to the prostate alone, which may be regarded as a concurrent boost volume within the overall planning target volume (PTV). The dose to the prostate itself is to be delivered in 3 Gy fractions, and for this phase of the study the total prostate dose will be 57 Gy in 19 fractions, with 50 Gy prescribed to the rest of the PTV. If acute toxicity results are acceptable, the next phase will escalate doses to 60 Gy in 20 x 3 Gy fractions. There will be 30 patients in each arm. This work describes the class solution which was developed to create IMRT plans for this study, and which enabled the same set of inverse planning parameters to be used during optimization for every patient with minimal planner intervention. The resulting dose distributions were compared with those that would be achieved from a 3D conformal radiotherapy (3DCRT) technique that used a multileaf collimator (MLC) but no intensity modulation to treat the PTV, followed by a sequential boost to raise the prostate to 57 Gy. The two methods were tested on anatomical data sets for a series of 10 patients who would have been eligible for this study, and the techniques were compared in terms of doses to the target volumes and the organs at risk. The IMRT method resulted in much greater sparing of the rectum and bladder than the 3DCRT technique, whilst still delivering acceptable doses to the target volumes. In particular, the volume of rectum receiving the minimum PTV dose of 47.5 Gy was reduced from a mean value of 36.9% (range 23.4% to 61.0%) to 18.6% (10.3% to 29.0%). In conclusion, it was found possible to use a class solution approach to produce IMRT dose escalated plans. This IMRT technique has since been implemented clinically for patients enrolled in the hypofractionated dose escalation study.     

脑胶质瘤三维适形放射治疗与调强放射治疗的剂量学比较

目的 评价脑胶质瘤调强放射治疗较三维适形放射治疗的剂量学优势.方法 本研究采用10例脑胶质瘤患者,针对所有患者分别进行3D CRT和IMRT的计划设计,利用剂量体积直方图评价不同照射技术中靶区和正常组织照射剂量、适形度指数和不均匀性指数.处方剂量为60 Gy.结果 IMRT计划脑干最大剂量和受照体积、患侧腮腺平均剂量和脊髓最大剂量均低于3D CRT计划.对于靶区适形度指数,IMRT计划优于3D CRT计划;对于不均匀性指数,两种计划模式的差异没有统计学意义.结论 在脑胶质瘤放疗中应用IMRT可以明显降低脑干的剂量和受照体积,为靶区剂量的提高提供了可能性.     

Escalated median dose for pituitary macroadenomas using intensity-modulated radiation therapy.

Three-dimensional conformal radiotherapy (3D CRT) has become an established treatment for pituitary macroadenomas. This study is an investigation into the possible dosimetric advantages of intensity-modulated radiotherapy for such critically located tumors. Three consecutive patients with pituitary macroadenoma previously treated with 3D CRT were replanned with inverse-planned IMRT using Helax-TMS (V.6.0, Helax AB, Uppsala, Sweden. Fusion of computed tomography (CT) with postoperative magnetic resonance imaging (MRI) was performed within the planning system to define the gross tumor volume (GTV), planning target volume (PTV), and normal structures including the optic chiasm. Dose-volume histograms (DVHs) for the 3D CRT plans were then compared with those of the corresponding prospective IMRT plans. Both techniques maintained critical structure doses below tolerance levels while maintaining a minimum dose of 45 Gy to 100% of the PTV. While IMRT plans deliver consistently more heterogeneous dose distributions to the PTV, the median PTV dose is elevated in the IMRT plans compared with the 3D CRT plans. For critically located tumors like these pituitary macroadenomas, IMRT allows escalation of the median dose to the tumor without an accompanying loss in critical structure sparing or creating unacceptable cold spots within the PTV.     

直肠癌术前放疗中三维适形放疗与调强适形放疗的剂量学比较分析

目的 比较三维适形放疗(3D-CRT)与5野、7野调强适形放疗(IMRT)的剂量分布,以探讨IMRT对直肠癌术前放疗的价值。方法 对10例术前新辅助放化疗直肠癌患者,分别设计3D- CRT、5野IMRT、7野IMRT计划,应用剂量体积直方图(DVH),比较3种治疗计划的靶区适形度指数(CI)、不均匀性指数(HI)和正常器官受量。结果 适形度指数(CI)7野IMRT计划＞5野IMRT＞3D- CRT,不均匀性指数(HI)5野IMRT计划＞7野IMRT＞3D- CRT。5野、7野IMRT计划比3D- CRT均可以减少高剂量照射小肠、膀胱、股骨头体积,7野IMRT计划比5野可以减少高剂量照射的骨髓和膀胱的体积。结论 直肠癌术前放疗中IMRT计划在靶区剂量适形度方面均优于3D- CRT计划,对正常组织的保护也存在明显的优势。7野IMRT计划较5野IMRT计划技术有更好的剂量适形度与剂量均匀性。     

Comparative Treatment Planning on Localized Prostate Carcinoma

Purpose: To assess the potential benefit of proton–beam therapy in comparison to 3–D conformal photon therapy and photon– based intensity–modulated radiotherapy (IMRT) in prostate carcinoma for various stages of disease.Material and Methods: In five patients a 3–D conformal proton–based (two lateral beams) irradiation technique was compared with 3–D conformal photon–beam radiotherapy (four–field box) and IMRT (seven beams). For each patient different target volumes (CTVs) were defined according to early, intermediate and advanced stages of disease: CTV I consisted of the prostate gland, CTV II encompassed prostate and basis of seminal vesicles, and CTV III the prostate and seminal vesicles. Corresponding planning target volumes PTV I–III were defined by uniformly adding a margin of 5 mm to CTV I–III. Dose–volume histograms (DVHs) were analyzed for the different PTVs and various organs at risk (OARs), i.e., rectal wall, bladder, both femoral heads. In addition, maximum and mean doses were derived for the various structures and irradiated non–target tissue volumes were compared for PTV I–III and the different irradiation techniques. Finally, dose conformity and target dose homogeneity were assessed.Results: With photon– and proton–based radiotherapy techniques similar dose distributions were determined for PTV I–III: mean and maximum PTV dose values were between 99–104% and 102–107% of the normalized total doses (70 Gy), respectively. Conformity indices varied from 1.4 to 1.5 for the photon techniques, whereas for proton–beam radiotherapy values ranged from 1.1 to 1.4. Both the 3–D conformal and the IMRT photon treatment technique resulted in increased mean doses (~ 40–80%) for OARs when compared to protons. With both photon techniques non–target tissue volumes were irradiated to higher doses (mean dose difference ≥ 70%) compared to proton–beam radiotherapy. Differences occurred mainly at the low and medium dose levels, whereas in high dose levels similar values were obtained. In comparison to conformal 3–D treatments IMRT reduced doses to OARs in the medium dose range, especially for the rectal wall.Conclusion: IMRT enabled dose reductions to OARs in the medium dose range compared to 3–D conformal radiotherapy. A rather simple two–field proton–based treatment technique further reduced doses to OARs compared to photon–beam radiotherapy. The advantageous dose distribution of proton–beam therapy for prostate cancer may result in reduced side effects, which needs to be confirmed in clinical studies.     

乳腺癌术后放疗3种治疗计划的剂量学研究

目的 评估螺旋断层调强放疗(helical tomotherapy,HT)、常规直线加速器逆向调强放疗(IMRT)和三维适形放疗(3D- CRT)3种治疗计划对乳腺癌术后胸壁照射的剂量影响和正常组织受照剂量体积对比。方法 选择10例早期乳腺癌改良根治术后患者CT定位图像,由同一医生勾画PTV,统一处方剂量50 Gy/ 25次。每例图像分别做HT、IMRT和3D- CRT 3种治疗计划,并对心脏、健侧肺和患侧肺受照射剂量体积、靶区适形度指数、剂量均匀指数和处方剂量所覆盖的靶体积等物理参数进行比较。结果 95%和100%的处方剂量覆盖的PTV体积在HT、IMRT和3D- CRT组分别为99.13%和95.87%、97.80%和94.05%、96.37%和87.29%。HT、IMRT 和3D-CRT组的适形指数和靶区均匀指数分别为0.80±0.10和1.09±0.03、0.65±0.07和1.14±0.02、0.40±0.08和1.17±0.04。心脏V₅~V₂₀以3D- CRT组最少,其次是HT组。患侧肺V₅接受的照射剂量体积以3D- CRT组最小,与HT和IMRT两组相比差异均有统计学意义。健侧肺V₅和V₁₀以3D- CRT组最少。结论 乳腺癌术后胸壁照射的靶区适形度和剂量均匀指数HT组最好;心脏、健侧肺和患侧肺低剂量区最小的依次是3D-CRT、HT和IMRT组。     

Intensity-modulated radiotherapy for a prostate patient with a metal prosthesis

When treating prostate patients having a metallic prosthesis with radiation, a 3D conformal radiotherapy (3DCRT) treatment plan is commonly created using only those fields that avoid the prosthesis in the beam’s-eye view (BEV). With a limited number of portals, the resulting plan may compromise the dose sparing of the rectum and bladder. In this work, we investigate the feasibility of using intensity-modulated radiotherapy (IMRT) to treat prostate patients having a metallic prosthesis. Three patients, each with a single metallic prosthesis, who were previously treated at the University of Chicago Medical Center for prostate cancer, were selected for this study. Clinical target volumes (CTV = prostate + seminal vesicles), bladder, and rectum volumes were identified on CT slices. Planning target volumes (PTV) were generated in 3D by a 1-cm expansion of the CTVs. For these comparative studies, treatment plans were generated from CT data using 3DCRT and IMRT treatment planning systems. The IMRT plans used 9 equally-spaced 6-MV coplanar fields, with each field avoiding the prosthesis. The 3DCRT plans used 5 coplanar 18-MV fields, with each field avoiding the prosthesis. A 1-cm margin around the PTV was used for the blocks. Each of the 9-field IMRT plans spared the bladder and rectum better than the corresponding 3DCRT plan. In the IMRT, plans, a bladder volume receiving 80% or greater dose decreased by 20–77 cc, and a volume rectal volume receiving 80% or greater dose decreased by 24–40 cc. One negative feature of the IMRT plans was the homogeneity across the target, which ranged from 95% to 115%.     

Exploring the Feasibility of Dose Escalation Positron Emission Tomography–Positive Disease with Intensity-Modulated Radiation Therapy and the Effects on Normal Tissue Structures for Thoracic Malignancies

The pattern of failure is one of the major causes of mortality among thoracic patients. Studies have shown a correlation between local control and dose. Intensity-modulated radiation therapy (IMRT) has resulted in conformal dose distributions while limiting dose to normal tissue. However, thoracic malignancies treated with IMRT to highly conformal doses up to 70 Gy still have been found to fail. Thus, the need for dose escalation through simultaneous integrated boost (SIB) may prove effective in minimizing reoccurrences. For our study, 28 thoracic IMRT plans were reoptimized via dose escalation to the gross tumor volume (GTV) and planning target volume (PTV) of 79.2 Gy and 68.4 Gy, respectively. Reoccurrences in surrounding regions of microscopic disease are rare therefore, dose-escalating regional nodes (outside GTV) were not included. Hence, the need to edit GTV margins was acceptable for our retrospective study. A median dose escalation of approximately 15 Gy (64.8–79.2 Gy) via IMRT using SIB was deemed achievable with minimal percent differences received by critical structures compared with the original treatment plan. The target's mean doses were significantly increased based on p-value analysis, while the normal tissue structures were not significantly changed.     

碳离子放射治疗泪囊泪腺肿瘤的剂量学研究

目的 比较碳离子治疗泪囊泪腺肿瘤相对于光子放疗的剂量学差异。方法 利用上海市质子重粒子医院治疗的10例术后残留的泪囊腺肿瘤患者CT图像,重新制定碳离子计划,光子容积调强计划（VMAT）与固定野光子调强计划（IMRT）,所有患者处方均为给予临床靶区54 Gy相对生物学效能（RBE）/18次,并给予临床加量靶区同步加量至63 Gy（RBE）/18次。在计划靶区覆盖相似情况下,比较正常组织受量。结果 在计划靶区覆盖差异无统计学意义的情况下,与光子VMAT和与IMRT相比,碳离子计划患侧与健侧的眼球平均剂量、视神经近似最大剂量（D_2%）与平均剂量均降低（患侧：t=7.35、3.79、4.66、8.48、2.52、2.76,P<0.05;健侧：t=3.87、10.49、9.16、4.43、6.53、5.12,P<0.05）;脑组织平均剂量由（5.65±3.58）和（5.76±2.09）Gy（RBE）降至（0.81±0.90）Gy（RBE）,差异具有统计学意义（t=6.76、17.33,P<0.05）。结论 与光子VMAT与IMRT相比,碳离子计划能有效降低泪囊泪腺肿瘤周围视觉器官受照体积与剂量,具有降低放疗不良反应的潜在优势。     

Improvement of treatment plans developed with intensity-modulated radiation therapy for concave-shaped head and neck tumors

PURPOSE: To improve dose conformity and normal tissue sparing in patients with concave-shaped head and neck cancers by using tomotherapy and static step-and-shoot intensity-modulated radiation therapy (IMRT) and by comparing results with those of three-dimensional (3D) conformal radiation therapy (CRT) and two-dimensional (2D) radiation therapy. MATERIALS AND METHODS: Treatment planning in 10 patients with concave-shaped head and neck tumors was performed by using tomotherapy and step-and-shoot IMRT, 3D CRT, and 2D techniques. IMRT plans were modified by placing "virtual critical structures" in regions outside the target where hot spots occurred. These modified plans were used for comparison because they provided better dose conformity. Critical structures were the spinal cord, the parotid glands, and the mandible. Comparisons were performed by means of dose-volume histograms, clinical target volume (CTV), target covered by 95% isodose (D(95%)), dose received by 5% of the critical structure volume (D(5%)), maximum dose, mean dose, and normal tissue complication probability for critical structures. RESULTS: Original IMRT plans showed more conformal dose distributions than those in 3D CRT and 2D plans. However, hot spots developed in the posterior and anterior neck. Introduction of virtual critical structures in IMRT plans resulted in removal of these hot spots without affecting target coverage. Modified IMRT plans also demonstrated better CTV coverage than that in 3D CRT and 2D plans. The average D(95%) was 97.3% with tomotherapy, 97.1% with step-and-shoot IMRT, 84.7% with 3D CRT, and 69.4% with 2D techniques. D(5%) for the spinal cord changed from approximately 45 Gy with 3D plans and 46 Gy with 2D plans to approximately 28 Gy with IMRT. CONCLUSION: IMRT demonstrated better target coverage and sparing of critical structures than that of 3D CRT and 2D techniques. Use of virtual critical structures resulted in removal of hot spots around the spinal cord.     

Adjuvant Radiotherapy for Gastric Cancer: A Dosimetric Comparison of 3-Dimensional Conformal Radiotherapy,Tomotherapy® and Conventional Intensity Modulated Radiotherapy Treatment Plans

Some patients with gastric cancer benefit from post-operative chemo-radiotherapy, but adequately irradiating the planning target volume (PTV) whilst avoiding organs at risk (OAR) can be difficult. We evaluate 3-dimensional conformal radiotherapy (CRT), conventional intensity-modulated radiotherapy (IMRT) and helical tomotherapy (TT). TT, 2 and 5-field (F) CRT and IMRT treatment plans with the same PTV coverage were generated for 5 patients and compared. Median values are reported. The volume of left/right kidney receiving at least 20Gy (V20) was 57/51% and 51/60% for 2 and 5F-CRT, and 28/14% for TT and 27/19% for IMRT. The volume of liver receiving at least 30Gy (V30) was 45% and 62% for 2 and 5F-CRT, and 37% for TT and 35% for IMRT. With TT, 98% of the PTV received 95-105% of the prescribed dose, compared with 45%, 34% and 28% for 2F-CRT, 5F-CRT and IMRT respectively. Using conventional metrics, conventional IMRT can achieve comparable PTV coverage and OAR sparing to TT, but at the expense of PTV dose heterogeneity. Both irradiate large volumes of normal tissue to low doses. Additional studies are needed to demonstrate the clinical impact of these technologies.     

Intensity-modulated radiotherapy increases dose to the brachial plexus compared with conventional radiotherapy for head and neck cancer

Objective

The preferential use of intensity-modulated radiotherapy (IMRT) over conventional radiotherapy (CRT) in the treatment of head and neck cancer has raised concerns regarding dose to non-target tissue. The purpose of this study was to compare dose-volume characteristics with the brachial plexus between treatment plans generated by IMRT and CRT using several common treatment scenarios.

Method

The brachial plexus was delineated on radiation treatment planning CT scans from 10 patients undergoing IMRT for locally advanced head and neck cancer using a Radiation Therapy Oncology Group-endorsed atlas. No brachial plexus constraint was used. For each patient, a conventional three-g0ield shrinking-g0ield plan was generated and the dose-volume histogram (DVH) for the brachial plexus was compared with that of the IMRT plan.

Results

The mean irradiated volumes of the brachial plexus using the IMRT vs the CRT plan, respectively, were as follows: V50 (18±5 ml) vs (11±6 ml), p = 0.01; V60 (6±4 ml) vs (3±3 ml), p = 0.02; V66 (3±1 ml) vs (1±1 ml), p = 0.04, V70 (0±1 ml) vs (0±1 ml), p = 0.68. The maximum point dose to the brachial plexus was 68.9 Gy (range 62.3–78.7 Gy) and 66.1 Gy (range 60.2–75.6 Gy) for the IMRT and CRT plans, respectively (p = 0.01).

Conclusion

Dose to the brachial plexus is significantly increased among patients undergoing IMRT compared with CRT for head and neck cancer. Preliminary studies on brachial plexus-sparing IMRT are in progress.Although intensity-modulated radiotherapy (IMRT) is widely considered the current standard in the radiotherapeutic management of head and neck cancer, investigators are increasingly recognising that this technology is associated with significant beam path doses to non-target structures that previously received little dose using previous, less conformal techniques [1]. Indeed, since the clinical implementation of IMRT at our institution, we have observed a striking number of patients returning for follow-up with symptoms thought to be related to radiation-induced brachial plexopathy. The purpose of this study was to compare dose-volume characteristics to the brachial plexus between treatment plans generated by IMRT and conventional radiotherapy (CRT) using several common head and neck cancer treatment scenarios.     

Chromosomal Aberration in Peripheral Lymphocytes and Doses to the Active Bone Marrow in Radiotherapy of Prostate Cancer

BACKGROUND AND PURPOSE: Radiotherapy plays an important role in the management of prostate cancer. Epidemiological data indicate a small but significant risk of radiation-induced leukemia after radiotherapy which might be related to the high mean bone marrow dose associated with radiotherapy of prostate cancer. The purpose of the study was to investigate the relation between the mean bone marrow dose and unstable chromosome aberrations in peripheral blood lymphocytes in patients undergoing conformal radiotherapy for prostate cancer as a possible indicator of risk. Endometrial cancer patients were also included for comparison. PATIENTS AND METHODS: Nine patients, six with prostate cancer (60-73 years old) and three with endometrial cancer (61-81 years old) treated with radiotherapy were included in the study. The non-bony spaces inside the pelvic bones were outlined on every CT slice using the treatment planning system and mean doses to the bone marrow calculated. Blood samples of the patients were obtained at different times before, during and at the end of treatment. Lymphocytes were cultured in the usual way and metaphases scored for dicentric aberrations. RESULTS: 46 samples from nine patients were obtained. The mean number of metaphases analyzed per sample was 180 with a range from 52 to 435. The mean bone marrow doses for prostate cancer patients ranged from 2.8 to 4.2 Gy and for endometrial cancer patients from 12.8 to 14.8 Gy. The aberration yield increased with the planning target volume and the mean bone marrow dose. CONCLUSION: The yield of dicentric aberrations for prostate cancer patients correlated closely with the mean bone marrow dose albeit the induction of dicentrics occurred in mature T lymphocytes most of which were probably in transit through the irradiated volumes. Therefore, the observed relationship between dicentrics and mean bone marrow doses are indirect.