非小细胞肺癌放射治疗不同模式的剂量学分析

目的分析常规放射治疗计划、三维适形放射治疗(3DCRT)计划和调强适形放射治疗(IMRT)计划治疗非小细胞肺癌(NSCLC)的疗效,评估3DCRT和IMRT与常规治疗的优越性。方法对经病理证实的50例中晚期NSCLC(Ⅲ～Ⅳ期)患者进行回顾性分析,计划靶区处方剂量66Gy,利用治疗计划系统(TPS)对每例患者分别设计常规、3DCRT和IMRT三种放疗计划,通过剂量体积直方图,比较三种计划对肿瘤靶区和正常组织器官的剂量分布。结果 (1)靶区适行度:处方剂量为66Gy时,三维适形放射治疗和调强适形放射治疗达此剂量的计划靶区(PTV)体积和95%PTV体积下的照射剂量均高于常规治疗,同时,调强适形放射治疗均高于三维适形放射治疗。(2)除全肺V20的IMRT检测外,3DCRT和IMRT治疗的肺受剂量均比常规治疗高。在全肺V5和全肺V10检测中,3DCRT比IMRT剂量低,其余检测中3DCRT比IMRT剂量高。(3)三种计划脊髓最大受照剂量均<45Gy。脊髓,食管及心脏受照剂量3DCRT均较常规放疗低,并且差异均有统计学意义(P<0.05)。结论 (1)3DCRT和IMRT较常规放射治疗明显提高了靶区的照射剂量和靶区的准确性,从而在相同处方剂量情况下提高了治疗肿瘤的控制率。(2)3DCRT和IMRT与常规放疗比较,对肺的保护性存在一定的局限性。(3)3DCRT和IMRT在一定程度上可降低正常组织受照剂量和并发症的发生概率,减少正常组织的放射损伤。(4)IMRT在靶区剂量分布上明显优于常规放射治疗和3DCRT,同时能在一定程度上更好的保护正常组织。     

肝癌三维适形放疗设野方法的研究

目的：探讨肝癌三维适形放射治疗照射野的设计方法。方法：利用上海拓能（Topslane）公司的三维治疗计划系统对112例肝癌患者，根据医生要求的CTV和周围的敏感器官限制受量，进行三维适形放射治疗计划设计，结合剂量曲线分布情况和剂量体积直方图（DVH）选择最佳治疗方案。结果：以肿瘤中心点为剂量归一点，80％～90％的剂量线均能包绕靶区体积，而周围正常组织受量都在理想的范围内。结论：对肝癌的三维治疗计划设计时，要根据病人不同的病变部位采取不同的设野方法，这样能使靶区剂量分布均匀，适形度好，同时也有效地保护了敏感器官，从而提高肿瘤剂量及肿瘤局部控制率。     

调强放射治疗在子宫颈癌治疗中的剂量学分析

 目的　比较调强放疗（IMRT）、三维适形放疗（3D-CRT）在子宫颈癌放疗中危及器官（OAR）的剂量学差异。方法　对36例子宫颈癌患者均同时制定IMRT放疗计划和3D-CRT放疗计划,临床靶区（CTV）包括子宫、子宫颈、阴道等原发肿瘤区域及其以下的淋巴结引流区域。淋巴结引流区的勾画主要以盆腔伴行血管外放1.0 cm 得到,闭孔淋巴结从骨盆内缘内外扩1.8 cm,CTV不包括骨盆组织。比较计划靶区（PTV）在45 Gy和50 Gy情况下各敏感组织的受照剂量-体积情况。PTV由CTV 边界在三维头脚方向外放1.0 cm,其他方向外放0.7 cm得到。结果　通过剂量体积直方图比较两组计划敏感组织的受照体积变化,在处方剂量45 Gy剂量时,30、40、45 Gy的敏感组织剂量体积IMRT计划均优于3D-CRT计划。在盆壁淋巴结引流区剂量达到50 Gy时,IMRT计划敏感组织受量亦优于45 Gy时3D-CRT计划。结论　子宫颈癌IMRT可以使周围OAR得到较好的保护,具备临床应用的剂量学优势。     

肝癌三维适形放疗设野方法的研究

目的:探讨肝癌三维适形放射治疗照射野的设计方法.方法: 利用上海拓能(Topslane)公司的三维治疗计划系统对112例肝癌患者,根据医生要求的CTV和周围的敏感器官限制受量,进行三维适形放射治疗计划设计,结合剂量曲线分布情况和剂量体积直方图(DVH)选择最佳治疗方案.结果: 以肿瘤中心点为剂量归一点,80%～90%的剂量线均能包绕靶区体积,而周围正常组织受量都在理想的范围内.结论: 对肝癌的三维治疗计划设计时,要根据病人不同的病变部位采取不同的设野方法,这样能使靶区剂量分布均匀,适形度好,同时也有效地保护了敏感器官,从而提高肿瘤剂量及肿瘤局部控制率.     

恶性脑胶质瘤三维适形放疗与调强适形放疗剂量学对比研究

背景与目的：恶性胶质瘤细胞对射线敏感性低，增加肿瘤区的放射剂量可能进一步延长局控和生存期。然而由于正常组织耐受量限制，普通三维适形技术（3 dimensional convention radiation therapy，3D—CRT）难以进一步提高剂量，本研究旨在利用三维治疗计划系统（3 dimensional treatment planning system，3DTPS）对恶性脑胶质瘤3D—CRT和逆向调强适形放疗（intensity modulated radiation therapy，IMRT）计划作剂量学比较，探讨IMRT在恶性脑胶质瘤放疗中应用的可行性，为临床应用IMRT技术提高恶性脑胶质瘤靶区剂量提供理论基础。方法：选择2006年7月-2007年10月本科收治的11例经病理证实的恶性胶质瘤术后患者，分别用3D—TPS对每例患者做出3D—CRT和IMRT计划。比较两种方法中靶区覆盖情况、适形指数、危及器官所受照射剂量、照射范围以外正常组织的剂量差别。结果：IMRT计划中PGTV的Dmean、PTV1和PTV2的Dmax和Dmin均高于3D—CRT（P〈0．05）、靶区适形度更好（CI95％1．39vs2．74，P〈0．001），脑干、垂体、晶体、双眼、视交叉、右侧视神经的照射剂量、照射靶区以外正常组织总体及25～30Gy受照积分剂量低于3D—CRT（P〈0．05）；两种计划对肿瘤靶区范围的覆盖（P=0．70）及靶区剂量均匀性（P=0．41）、左侧视神经受量（P=0．08）、小于25Gy的靶区外正常组织积分剂量IMRT略高于3D—CRT，差异无显著性（P〉0．05）。结论：与3D—CRT比较IMRT能够提高靶区适形度及肿瘤放疗剂量、更好的保护危及器官、有效提高治疗增益比、且没有提高暴露在低剂量照射范围内的正常组织的体积和总体剂量，缩短了治疗时间。     

宫颈癌术后盆腔调强放疗计划方法的剂量学比较研究

目的 比较两种调强放疗(IMRT)方法 (对骨髓进行单独限最的BMS-IMRT,未对骨髓进行单独限量的IMRT)在宫颁癌靶体积剂量覆盖及危及器官保护方面的差异,探讨宫颈癌患者术后盆腔外照射骨髓保护的合理方法 .方法 对10例宫颈癌术后患者进行模拟CT增强扫描,在计划系统内勾画临床靶体积(CTV),CTV均匀外扩1.0 cm生成计划靶体积(PTV),同时勾画小肠、直肠、膀胱、骨髓.进而设计出BMS-IMRT和IMRT的2种治疗计划,处方剂量为45 Gy分25次,1.8 Gy/次.所有计划都使95%靶区体积达到处方剂量要求.并用ADAC Pinnacle~3计划系统提供的卷积或迭加算法对两种放疗技术的治疗计划进行剂量计算,比较靶区及危及器官剂量分布、剂量体积直方图参数.结果 BMS-IMRT计划的靶区剂量均匀性不如IMRT,但其适形度优于IMRT计划,BMS-IMRT放疗计划中骨髓的V_5、V_(10)、V_(20)、V_(30)、V_(40)分别比IMRT降低1.81%、8.61%、31.81%、29.50%、28.29%,而小肠、膀胱、直肠等危及器官的受量差别不大.结论 对于宫颈癌术后患者BMS-IMRT降低了骨髓低剂量受照体积,从而有助于降低急性骨髓抑制发生概率、提高患者生活质量,值得在临床工作中推广应用.     

鼻咽癌挡铅野中野适形权重优化计划初探

目的：利用挡铅野中野技术与射野权重优化，调节各方向剂量强度，探讨野中野适形与IMRT的相似性。方法：以1例鼻咽癌为研究对象，对该病例做适形计划和常规二维计划，并与IMRT相比较，评价计划靶区及危及器官的受照剂量、DVH及各特征指标值。结果：野中野与常规二维计划靶区平均剂量分别为75．9Gy、73．0Gy；腮腺受量V35分别为49％、88％，对比调强靶区平均剂量74Gy、腮腺V弘约为50％。结论：在没有多叶光栅MLC时，野中野适形计划及对危及器官的保护方面明显优于常规二维计划：在靶区均匀性与调强计划有较小差异。能实现近似IMRT的结果，解决常规二维难以胜任的凹形靶区和危及器官的高损伤情况，具有较好的临床价值。     

椎体转移瘤固定射束调强技术与容积旋转调强技术的比较

目的探讨椎体转移瘤固定射束调强技术(IMRT)与容积旋转调强技术(VMAT)的比较。方法随机选取8例胸部椎体转移瘤患者,重新制订IMRT和VMAT计划。计划质量根据靶区剂量学参数、危及器官受照剂量、等剂量曲线和剂量体积直方图(DVH)进行比较。计划实施效率用机器跳数(MUs)和治疗时间来衡量。结果 VMAT的靶区均匀性、适形度、最大受照剂量、平均剂量都明显优于IMRT(P<0.05),位于环形靶区中心位置的脊髓受量也低于IMRT(P<0.05),但两种技术的肺受照剂量差异无统计学意义(P>0.05)。结论对于椎体转移瘤环形靶区的照射,VMAT的适形度、均匀性及其对脊髓的保护均优于IMRT。     

直肠癌放射治疗方案剂量学比较

目的：研究直肠癌不同放射治疗计划的剂量学差异。方法：对18例直肠癌患者分别设计三维适形（3DCRT）和调强放射治疗计划（IMRT）,利用剂量体积直方图来比较2种计划中靶区、危机器官的剂量学差异。结果：IMRT与3DCRT相比,靶区适合度指数（CI）、靶区剂量不均匀性指数（HI）均更接近1,Dmean也更接近处方剂量,差异有统计学意义（P〈0.05）;与3 DCRT相比,IMRT中小肠的D30%、Dmean、Dmax,膀胱的D30%、D50%、Dmean更低;IMRT中小肠的D50%,股骨头的D5%、Dmean比3DCRT高,但仍远低于剂量限值。结论：IMRT技术对直肠癌进行治疗时,靶区适合度和靶区剂量均匀性更好,危及器官受量能够得到很好的控制。     

肺癌合并纵隔淋巴结转移的三维适形放疗和调强放疗的剂量学研究

目的比较肺癌合并纵隔淋巴结转移的三维适形放疗（3 DCRT）和调强放疗（IMRT）的剂量学差异,为临床应用提供参考。方法选择2007年8月至2008年2月行IMRT放射治疗的11例肺癌纵隔转移患者,利用其CT模拟定位图像分别设计IMRT计划和3DCRT计划,结合等剂量曲线以及剂量体积直方图（DVH）对IMRT计划和3 DCRT计划进行适形性、靶区均匀性和对各关键器官受量进行比较。处方剂量66Gy／33次,治疗时间6周;要求95％靶区体积达到95％以上的处方剂量。SPSS14．0统计软件进行t检验。结果IMRT靶区的适形度优于3DCRT（P〈0．05）,IMRT靶区内超过处方剂量110％体积相比3DCRT放疗靶区内超过处方剂量110％体积减小;在对肺组织的保护上,IMRT肺V20、V30、V40数值均明显小于3 DCRT（P〈0．05）。结论对临床靶区体积大、形状不规则的肺癌合并纵隔淋巴结转移患者,IMRT治疗是较好的选择。     

Comparison of treatment plans involving intensity-modulated radiotherapy for nasopharyngeal carcinoma

PURPOSE: To compare intensity-modulated radiotherapy (IMRT) treatment plans with conventional treatment plans for a case of locally advanced nasopharyngeal carcinoma. METHODS AND MATERIALS: The study case was planned using two types of IMRT techniques, as well as a three-dimensional conformal radiotherapy technique (3D-CRT), and a traditional treatment method using bilateral opposing fields. These four plans were compared with respect to dose conformality, dose-volume histogram (DVH), dose to the sensitive normal tissue structures, and ease of treatment delivery. RESULTS: The planned dose distributions were more conformal to the tumor target volume in the IMRT plans than those in the conventional plans. With similar dose coverage of the clinical target volume (CTV), defined as delivery of minimum of 60 Gy to >/= 95% of CTV, the IMRT plans achieved better sensitive normal tissue structure sparing, while concomitantly delivering a minimum dose of 68 Gy to >/= 95% of the gross tumor volume (GTV) at a higher dose per fraction. CONCLUSIONS: Compared to conventional techniques, IMRT techniques provide improved tumor target coverage with significantly better sparing of sensitive normal tissue structures in the treatment of locally advanced nasopharyngeal carcinoma. With improvement of the delivery efficiency, IMRT should provide the optimal treatment for all nasopharyngeal carcinoma. Further studies are needed to establish the true clinical advantage of this new modality.     

Systematic set-up errors for IMRT in the head and neck region: effect on dose distribution.

BACKGROUND AND PURPOSE: There is a general concern about intensity modulated radiation therapy (IMRT) treatments being more sensitive to patient positioning than conventional treatments. The aim of this study was to evaluate the International Commission on radiation units and measurements (ICRU) method for taking systematic set-up errors into account for IMRT treatments and to compare the effects on the dose distribution with the effects of conventional treatments. MATERIAL AND METHODS: A planning margin to account for set-up errors was added to the clinical target volumes and to the spinal cords, for three head and neck patients, according to the ICRU. No margin was added to organs at risk with mainly parallel structure if they were situated adjacent to the target volume, for example, the parotid glands. The effects of set-up errors in six IMRT plans and three conventional plans were simulated in the planning system and analysed with physical dose parameters. RESULTS AND CONCLUSIONS: In general, the ICRU method of taking set-up errors into account works satisfactorily for IMRT treatments as well as for conventional treatments with no difference between the treatment techniques. The sensitivity to set-up errors regarding the target volume is dependent on the quality of the treatment plan, i.e. the part of the target covered with a dose >95 and <105% and the effect in the critical organs is dependent on the sharpness of the dose gradients outside the critical organ. However, the method makes it difficult to include organs at risk with mainly parallel structure if they are situated adjacent to the target volume.     

Comparison of three-dimensional conformal radiation therapy and intensity-modulated radiation therapy systems

The use of three-dimensional conformal radiation therapy (3DCRT) has now become common practice in radiation oncology departments around the world. Using beam's eye viewing of volumes defined on a treatment planning computed tomography scan, beam directions and beam shapes can be selected to conform to the shape of the projected target and minimize dose to critical normal structures. Intensity-modulated radiation therapy (IMRT) can yield dose distributions that conform closely to the three-dimensional shape of the target volume while still minimizing dose to normal structures by allowing the beam intensity to vary across those shaped fields. Predicted dose distributions for patients with tumors of the prostate, nasopharynx, and paraspinal region are compared between plans made with 3DCRT programs and those with inverse-planned IMRT programs. The IMRT plans are calculated for either static or dynamic beam delivery methods using multileaf collimators. Results of these comparisons indicate that IMRT can yield significantly better dose distributions in some situations at the expense of additional time and resources. New technologies are being developed that should significantly reduce the time needed to plan, implement, and verify these treatments. Current research should help define the future role of IMRT in clinical practice.     

三维适形与调强放疗技术在胃癌术后放疗中的剂量学比较

目的比较胃癌放疗中三维适形放疗(3DCRT)和调强放疗(IMRT)技术的剂量学差异,为临床应用提供参考。方法采用3DCRT治疗的5例胃癌术后患者,放疗时使用了主动呼吸门控技术,以减少呼吸引起的器官运动。IMRT计划采用7个共面等间距野,仅用于剂量学比较。患者靶区设定的处方剂量为至少95%计划靶体积(PTV)接受45.00 Gy,至少99%PTV接受42.75 Gy。根据积分剂量体积直方图(DVH)比较PTV受量和相关正常器官的受量差异和剂量分布。结果与IMRT相比3DCRT的剂量均匀性和适形度略差,但两者在PTV受量上剂量相似。对左、右肾受15 Gy剂量的体积百分比(V_(15))而言,3DCRT好于IMRT;从正常肝的平均受量及V_(30)上看,IMRT稍优于优势;在脊髓的受量上两者相似。结论3DCRT技术在主动呼吸门控辅助下,PTV和部分正常器官的受量上可接近或者达到采用相等野数的IMRT的结果。     

Treatment planning and delivery of intensity-modulated radiation therapy for primary nasopharynx cancer

PURPOSE: To implement intensity-modulated radiation therapy (IMRT) for primary nasopharynx cancer and to compare this technique with conventional treatment methods. METHODS AND MATERIALS: Between May 1998 and June 2000, 23 patients with primary nasopharynx cancer were treated with IMRT delivered with dynamic multileaf collimation. Treatments were designed using an inverse planning algorithm, which accepts dose and dose-volume constraints for targets and normal structures. The IMRT plan was compared with a traditional plan consisting of phased lateral fields and a three-dimensional (3D) plan consisting of a combination of lateral fields and a 3D conformal plan. RESULTS: Mean planning target volume (PTV) dose increased from 67.9 Gy with the traditional plan, to 74.6 Gy and 77.3 Gy with the 3D and IMRT plans, respectively. PTV coverage improved in the parapharyngeal region, the skull base, and the medial aspects of the nodal volumes using IMRT and doses to all normal structures decreased compared to the other treatment approaches. Average maximum cord dose decreased from 49 Gy with the traditional plan, to 44 Gy with the 3D plan and 34.5 Gy with IMRT. With the IMRT plan, the volume of mandible and temporal lobes receiving more than 60 Gy decreased by 10-15% compared to the traditional and 3D plans. The mean parotid gland dose decreased with IMRT, although it was not low enough to preserve salivary function. CONCLUSION: Lower normal tissue doses and improved target coverage, primarily in the retropharynx, skull base, and nodal regions, were achieved using IMRT. IMRT could potentially improve locoregional control and toxicity at current dose levels or facilitate dose escalation to further enhance locoregional control.     

Optimization of conformal thoracic radiotherapy using cone-beam CT imaging for treatment verification

PURPOSE: Megavoltage cone-beam computed tomography (MVCBCT) has been proposed for treatment verification in conformal radiotherapy. However, the doses required for such imaging may compromise the quality of the delivered dose distribution. The present paper explores the effect of cone-beam imaging on dose homogeneity and critical organ dose and the use of our new tool, adapted intensity-modulated radiation therapy (AIMRT). METHODS AND MATERIALS: Three types of treatment plans were devised (3D-CRT [three-dimensional conformal radiotherapy], IMRT [intensity-modulated radiotherapy], and AIMRT) based on 4 patients with thoracic malignancies. MVCBCT fields were then integrated into the plans. The MVCBCT technique used 21 imaging portals at 10 degrees intervals. The MVCBCT apertures were shaped to conform to the planning target volume with a 6-mm margin. In a second set of plans, the field size was expanded by a further 2 cm. The unoptimized MVCBCT dose distribution was incorporated into the IMRT plan using AIMRT. RESULTS: Normal-tissue complication probability with MVCBCT is acceptable for all plans at the 66.6 Gy level, but exceeds tolerance for both 3D-CRT alone and 3D-CRT with MVCBCT at higher doses. In contrast, the use of AIMRT planning with MVCBCT allowed safe dose escalation to 85 Gy. Expanding the MVCBCT aperture provided better anatomic visibility with an acceptable lung dose. The results using IMRT with MVCBCT fell between the values measured for 3D-CRT and AIMRT with MVCBCT. CONCLUSION: The present study is the first to demonstrate that MVCBCT can be incorporated into 3D-CRT and IMRT planning with minimal effect on planning target volume homogeneity and dose to critical structures. This paves the way for highly conformal radiotherapy at greater doses delivered with increased confidence and safety.     

Feasibility of sparing lung and other thoracic structures with intensity-modulated radiotherapy for non-small-cell lung cancer

PURPOSE: To investigate the possibility of using intensity-modulated radiotherapy (IMRT) to reduce the irradiated volumes of the normal lung and other critical structures in the treatment of non-small-cell lung cancer (NSCLC) and to investigate the effect of IMRT on the potential of spreading low doses to large volumes of normal tissues in such treatment. METHODS AND MATERIALS: A retrospective treatment planning study was performed to compare IMRT and conventional three-dimensional conformal radiation therapy (3D-CRT) for 10 NSCLC patients (Stage I-IIIB). In the IMRT plans, three to nine coplanar beams were designed to treat 95% of the planning target volume with 63 Gy and to minimize the volumes of the normal lung, esophagus, heart, and spinal cord irradiated above their tolerance doses. The two types of plans were compared with respect to the planning target volume coverage, dose-volume histograms, and other dosimetric indexes of the normal structures. RESULTS: Comparing the nine-beam IMRT plan with the 3D-CRT plan, the percentage of lung volume that received >20 Gy and the mean lung dose were reduced for all cases, with a median reduction of 8% and 2 Gy, respectively. An additional reduction of the >5-Gy volume and >10-Gy volume for the lung and thoracic tissue was more difficult with IMRT, although still possible using fewer beams in IMRT. The integral dose to the entire thorax was equivalent and even reduced for 8 of 10 cases using IMRT. CONCLUSION: It is possible to reduce the volumes of low doses (such as the >10-Gy volume and >20-Gy volume) for thoracic normal tissues using IMRT. The increased integral dose and low-dose volumes can be avoided for IMRT if such concerns are addressed carefully in the inverse planning process and with optimization of the IMRT beam configuration.     

简化调强技术在鼻咽癌外照射中应用的剂量学研究

背景与目的：放射治疗是治疗鼻咽癌的首选方法。该文旨在研究简化调强放射治疗(simplified intensity-modulated radiation therapy,sIMRT )与调强放疗(intensity-modulated radiation therapy,IMRT)技术在鼻咽癌(nasopharyngeal carcinoma,NPC)放射治疗中的剂量学差异。方法：对10例NPC患者以相同处方剂量和目标条件分别设计9野IMRT和sIMRT计划,比较两种计划靶区剂量分布和剂量适形指数(conformity index,CI)与均匀性指数(homogeneity index,HI),不同危及器官(organ at risk,OAR)剂量参数、机器总跳数(MU)和总子野数。结果：IMRT和sIMRT的CI、HI分别为0.647、0.057和0.633、0.071(t=2.14,P=0.062;t=-6.21,P=0.000),sIMRT计划的靶区均匀性略差于IMRT,但两种治疗计划均能满足临床剂量学的要求。两种计划中各OAR剂量参数差异无统计学意义(t=-0.51~2.22,P=0.053~0.621) 。sIMRT计划的机器总跳数和总子野数均少于IMRT计划。结论：鼻咽癌sIMRT计划的靶区剂量覆盖与IMRT计划相当,均匀性略差于IMRT;危及器官受照剂量相当,但sIMRT技术可显著减少机器总跳数和总子野数,对患者数量大的治疗中心提高治疗效率具有较高的优势。     

A prospective trial of volumetric intensity-modulated arc therapy vs conventional intensity modulated radiation therapy in advanced head and neck cancer

AIM: To prospectively compare volumetric intensity-modulated arc therapy (VMAT) and conventional intensity-modulated radiation therapy (IMRT) in coverage of planning target volumes and avoidance of multiple organs at risk (OARs) in patients undergoing definitive chemoradiotherapy for advanced (stage III or IV) squamous cell cancer of the head and neck.METHODS: Computed tomography scans of 20 patients with advanced tumors of the larynx, naso-, oro- and hypopharynx were prospectively planned using IMRT (7 field) and VMAT using two arcs. Calculated doses to planning target volume (PTV) and OAR were compared between IMRT and VMAT plans. Dose-volume histograms (DVH) were utilized to obtain calculated doses to PTV and OAR, including parotids, cochlea, spinal cord, brainstem, anterior tongue, pituitary and brachial plexus. DVH’s for all structures were compared between IMRT and VMAT plans. In addition the plans were compared for dose conformity and homogeneity. The final treatment plan was chosen by the treating radiation oncologist.RESULTS: VMAT was chosen as the ultimate plan in 18 of 20 patients (90%) because the plans were thought to be otherwise clinically equivalent. The IMRT plan was chosen in 2 of 20 patients because the VMAT plan produced concentric irradiation of the cord which was not overcome even with an avoidance structure. For all patients, VMAT plans had a lower number of average monitor units on average (MU = 542.85) than IMRT plans (MU = 1612.58) (P < 0.001). Using the conformity index (CI), defined as the 95% isodose volume divided by the PTV, the IMRT plan was more conformal with a lower conformity index (CI = 1.61) than the VMAT plan (CI = 2.00) (P = 0.003). Dose homogeneity, as measured by average standard deviation of dose distribution over the PTV, was not different with VMAT (1.45 Gy) or IMRT (1.73 Gy) (P = 0.069). There were no differences in sparing organs at risk.CONCLUSION: In this prospective study, VMAT plans were chosen over IMRT 90% of the time. Compared to IMRT, VMAT plans used only one third of the MUs, had shorter treatment times, and similar sparing of OAR. Overall, VMAT provided similar dose homogeneity but less conformity in PTV irradiation compared to IMRT. This difference in conformity was not clinically significant.     

Dose-volume comparison of proton therapy and intensity-modulated radiotherapy for prostate cancer

PURPOSE: The contrast in dose distribution between proton radiotherapy (RT) and intensity-modulated RT (IMRT) is unclear, particularly in regard to critical structures such as the rectum and bladder. METHODS AND MATERIALS: Between August and November 2006, the first 10 consecutive patients treated in our Phase II low-risk prostate proton protocol (University of Florida Proton Therapy Institute protocol 0001) were reviewed. The double-scatter proton beam plans used in treatment were analyzed for various dosimetric endpoints. For all plans, each beam dose distribution, angle, smearing, and aperture margin were optimized. IMRT plans were created for all patients and simultaneously analyzed. The IMRT plans were optimized through multiple volume objectives, beam weighting, and individual leaf movement. The patients were treated to 78 Gray-equivalents (GE) in 2-GE fractions with a biologically equivalent dose of 1.1. RESULTS: All rectal and rectal wall volumes treated to 10-80 GE (percentage of volume receiving 10-80 GE [V(10)-V(80)]) were significantly lower with proton therapy (p < 0.05). The rectal V(50) was reduced from 31.3% +/- 4.1% with IMRT to 14.6% +/- 3.0% with proton therapy for a relative improvement of 53.4% and an absolute benefit of 16.7% (p < 0.001). The mean rectal dose decreased 59% with proton therapy (p < 0.001). For the bladder and bladder wall, proton therapy produced significantly smaller volumes treated to doses of 10-35 GE (p < 0.05) with a nonsignificant advantage demonstrated for the volume receiving < or =60 GE. The bladder V(30) was reduced with proton therapy for a relative improvement of 35.3% and an absolute benefit of 15.1% (p = 0.02). The mean bladder dose decreased 35% with proton therapy (p = 0.002). CONCLUSION: Compared with IMRT, proton therapy reduced the dose to the dose-limiting normal structures while maintaining excellent planning target volume coverage.