仰卧位计划设计与俯卧位计划设计中肺体积受量的比较

目的比较胸椎棘突部转移肿瘤予仰卧位与俯卧位射波刀计划设计的肺体积受量，为降低正常肺组织的损伤提供参考依据。方法选取胸椎棘突部转移肿瘤9例，分别采用仰卧位计划设计与俯卧位计划设计，比较两种计划设计中肺体积受量的变化。结果仰卧位计划设计与俯卧位计划设计比较，机器跳数多14862～36337MU，肺V5高5．20～7．90Gy，肺V20高2．61～5．73Cy。脊髓体积剂量相差-2．21-2．67Gy，皮肤体积受量相差-3．93～7．85Gy，食管体积剂量相差0．28～6．39Gy。结论俯卧位计划设计比仰卧位计划设计能更好地保护肺组织，提高射线的利用率。     

Significance of prone positioning in planning treatment for esophageal cancer

The treatment of esophageal cancer is made difficult by the close proximity of the esophagus to the spinal cord and the requirement to treat the esophageal target volume to doses greater than or equal to 60 Gy while limiting the spinal cord dose to less than or equal to 46 Gy. By placing the patient in the prone position, the esophagus can be displaced away from the spinal cord. We explored the results of this commonly used technique on 16 patients who have undergone simulation in both supine and prone positions. Both AP and lateral orthogonal radiographs were obtained in both positions. The distance between contrast material in the esophagus and spinal cord was noted in at least four transverse planes through the thoracic esophagus on each of the 16 patients. These four transverse planes were located at 3 cm above the carina, at the carina, 3 cm below the carina and 6 cm below the carina. The mean displacement (+/- 1 SD) of the esophagus away from the spinal cord when the patient was in the prone position compared to supine at each of these levels was 1.3 (+/- 0.8) cm, 1.8 (+/- 0.9) cm, 1.8 (+/- 1.0) cm, and 1.9 (+/- 1.1) cm. The range of displacement for all 64 displacement determinations was 0 to 4.2 cm with a mean of 1.7 cm. To evaluate further the consequences of prone positioning on treatment planning and doses received to target volumes and critical structures, we performed 3-dimensional treatment planning with a patient in both prone and supine positions. The requirements were to achieve a tumor volume dose of 60 Gy while keeping the spinal cord dose below 46 Gy. Two types of conventional treatment plans were examined in prone and supine positions. A 6-field plan consisted of delivery of 40 Gy through a large 3-field beam arrangement followed by delivery of 20 Gy through a similar 3-field cone down. An 8-field plan involved the delivery of 30 Gy through AP/PA beams followed by a 3-field beam arrangement to 40 Gy and a subsequent 3-field cone-down for the final 20 Gy. Comparison of dose volume histograms revealed that the 6-field plan spared relatively more heart whereas the 8-field plan spared relatively more lung. Regarding the primary consideration of coverage of target volume with avoidance of spinal cord, prone positioning was superior to supine positioning whether 6- or 8-field arrangements were used.     

子宫颈癌调强放射治疗中不同体位的剂量学研究

 目的　比较分析子宫颈癌调强放射治疗（IMRT）中不同治疗体位对相邻正常器官受照剂量分布和受照体积的影响。方法　11例子宫颈鳞癌ⅡB～ⅢB患者在CT模拟定位机下分别行俯卧位和仰卧位定位扫描,将定位资料传输至治疗计划系统（TPS）,勾画两种不同体位下的临床靶区（CTV）和计划靶区（PTV）,并分别设计两种不同体位IMRT计划。处方剂量：95 %的PTV接受46 Gy（2 Gy／次,23次）,通过剂量体积直方图（DVH）分析比较两种治疗体位下,小肠等器官的不同受照剂量和体积的差别。结果　在符合PTV剂量要求的前提下,采用俯卧位体位小肠的受照体积在46～30 Gy剂量范围内比仰卧位体位时的受照体积明显减小（P＜0.05）,在低剂量范围内（＜20 Gy）,小肠的受照体积减小不明显（P＞0.05）。对膀胱、直肠、股骨头、脊髓两种体位的剂量体积差异无统计学意义（P＞0.05）。结论　子宫颈癌行IMRT时采用俯卧位能更好地保护小肠,建议对子宫颈癌行IMRT时采用俯卧位。     

Patient positioning in prostate radiotherapy: is prone better than supine?

PURPOSE: To assess potential dose reductions to the rectum and to the bladder with three-dimensional conformal radiotherapy (3D-CRT) to the prostate in the prone as compared with the supine position; and to retrospectively evaluate treatment position reproducibility without immobilization devices. METHODS AND MATERIALS: Eighteen patients with localized prostate cancer underwent pelvic CT scans and 3D treatment planning in prone and supine positions. Dose-volume histograms (DVHs) were constructed for the clinical target volume, the rectum and the bladder for every patient in both treatment positions. "Comparative DVHs" (cDVHs) were defined for the rectum and for the bladder: cDVH was obtained by subtracting the organ volume receiving a given dose increment in the prone position from the corresponding value in the supine position. These values were then integrated over the entire dose range. The prescribed dose to the planning target volume (PTV) was 74 Gy using a 6-field technique. To evaluate reproducibility, portal films were subsequently reviewed in 12 patients treated prone and 10 contemporary patients treated supine (controls). No immobilization devices were used. Deviations in the anterio-posterior (X) and cranio-caudal (Y) axes were measured. Mean treatment position variation, total setup variation, systematic setup variation, and random setup variation were obtained. RESULTS: Prone position was associated with a higher dose to the rectum or to the bladder in 6 (33%) and 7 (39%) patients, respectively. A simultaneously higher dose to rectum and bladder was noted in 2 (11%) patients in prone and in 7 (39%) patients in supine. Rectal and bladder volumes were frequently larger in prone than in supine: mean prone/supine volume ratios were 1.21 (SD, 0.68) and 1.03 (SD, 1.32), respectively. In these cases cDVH analysis more often favored the prone position. Mean treatment position variation and total setup variation were similar for both prone and supine plans. A higher systematic setup variation was observed in prone positioning: 2.7 mm vs. 1.9 mm (X axis) and 4.1 mm vs. 2.2 mm (Y axis). The random variation was similar for both prone and supine: 4. 0 mm vs. 3.6 mm (X axis) and 3.7 mm vs. 3.6 mm (Y axis). CONCLUSIONS: Prone position 3D-CRT is frequently, but not always, associated with an apparent dose reduction to the rectum and/or to the bladder for prostate cancer patients. As suggested by the increased mean prone/supine rectal volume ratio, the advantage of prone positioning for the rectum may be artifactual, at least partly reflecting a position-dependent rectal air volume, which may significantly vary from treatment to treatment. In the absence of immobilization devices, daily setup reproducibility appears less accurate for the prone position, primarily due to systematic setup variations.     

A Volumetric Dosimetry Analysis of Vertebral Body Fracture Risk After Single Fraction Spine Stereotactic Body Radiation Therapy

PurposeVertebral compression fractures (VCF) are a common and severe complication of spine stereotactic body radiation therapy (SBRT). We sought to analyze how volumetric dosimetry and clinical factors were associated with the risk of VCF.Methods and MaterialsWe evaluated 173 spinal segments that underwent single fraction SBRT in 85 patients from a retrospective database. Vertebral bodies were contoured and dosimetric values were calculated. Competing risk models were used to evaluate the effect of clinical and dosimetry variables on the risk of VCF.ResultsOur primary endpoint was development of a post-SBRT VCF. New or progressive fractures were noted in 21/173 vertebrae (12.1%); the median time to fracture was 322 days. Median follow-up time was 426 days. Upon multivariable analysis, the percentages of vertebral body volume receiving >20 Gy and >24 Gy were significantly associated with increased risk of VCF (hazard ratio, 1.036, 1.104; P = .029, .044, respectively). No other patient or treatment factors were found to be significant on multivariable analysis. Sensitivity analysis revealed that the percentages of vertebral body volume receiving >20 Gy and >24 Gy required to obtain 90% sensitivity for predicting vertebral body fracture were 24% and 0%, respectively.ConclusionsVCF is a common complication after SBRT, with a crude incidence of 12.1%. Treatment plans that permit higher volumes receiving doses >20 Gy and >24 Gy to the vertebral body are associated with increased risk of VCF. To achieve 90% sensitivity for predicting VCF post-SBRT, the percentage of vertebral volume receiving >20 Gy should be <24% and maximum point dose should be <24 Gy. These results may help guide clinicians when evaluating spine SBRT treatment plans to minimize the risk of developing posttreatment VCF.     

Three-dimensional photon dosimetry: a comparison of treatment of the intact breast in the supine and prone position

PURPOSE: To compare the adequacy of target coverage, dose homogeneity, and volume of normal tissue irradiated in treatment of the intact breast in the supine and prone position. METHODS AND MATERIALS: Fifteen patients with early breast cancer who presented for treatment to the intact breast after excisional biopsy were studied. A specially designed device was used for the prone setup to displace the contralateral breast away from the tangential field borders. Treatment planning computed tomography was performed for each patient in both the supine and prone positions. Dosimetric data were obtained in both positions and isodose distributions were calculated for each patient in both positions. RESULTS: The volume of breast receiving greater than 5% of the prescribed dose was significantly less in the prone position. Medial wedges were either not used or their angles were reduced for all patients in the prone position compared with the supine position. The average volume of lung receiving >10 Gy and >20 Gy was significantly less in the prone positions. The volume of heart irradiated at critical dose levels did not vary consistently in the prone and supine positions. The integral dose delivered to the contralateral breast was not significantly different. CONCLUSION: Treatment of the intact breast in the prone position may result in improved dose homogeneity within the target volume as well as sparing of normal lung compared with treatment in the conventional supine position.     

A randomized trial of supine vs. prone positioning in patients undergoing escalated dose conformal radiotherapy for prostate cancer.

BACKGROUND AND PURPOSE: The optimal treatment position for patients receiving radical radiation therapy for prostate cancer has been a source of controversy. To resolve this issue, we conducted a randomized trial to evaluate the effects of supine and prone positioning on organ motion, positioning errors, and dose to critical organs during escalated dose conformal irradiation for localized prostate cancer and patient and therapist satisfaction with setup technique. PATIENTS AND METHODS: Twenty eight patients were randomized to commence treatment immobilized in the supine or prone position and were subsequently changed to the alternate positioning for the latter half of their treatment. Patients underwent CT simulation and conformal radiotherapy planning and treatment in both positions. The clinical target volume encompassed the prostate gland. Alternate day lateral port films were compared to corresponding simulator radiographs to measure the isocentre positioning errors (IPE). Prostate motion (PM) and total positioning error (TPE) were measured from the same films by the displacements of three implanted fiducial markers. Dose volume histograms (DVHs) for the two treatment positions were compared at the 95, 80 and 50% dose (D%) levels. The patients and radiation therapists completed weekly questionnaires regarding patient comfort and ease of setup. RESULTS: Seven patients, who started in the supine position, subsequently refused prone position and received their whole treatment supine. Small bowel in the treatment volume, not present in the supine position, prevented one patient from being treated prone. PM in anterior posterior direction was statistically significantly less in the supine position (P<0.05). There was no significant difference in superior inferior PM for the two treatment positions. No statistically significant difference between supine and prone positioning was observed in isocentre positioning error (IPE) or total positioning error (TPE) due to a policy of daily pre-treatment correction. However, more pre-treatment corrections were required for patients in the prone position. The DVH analysis demonstrated larger volumes of the bladder wall, rectal wall and small bowel within the D95, D80 and D50% when comparing the planning target volumes (PTVs) actually treated for prone positioning. When the prone PTV was expanded to account for the greater PM encountered in that position, a statistically significant difference (P<0.007) was observed in favour of the supine position at all dose levels. In the prone position, four patients had small bowel within the 60 Gray (Gy) isodose and in the supine position, no patients had small bowel in the 60 or 38Gy volumes. Supine position was significantly more comfortable for the patients and setup was significantly easier for the radiation therapists. The median patient comfort score was 0.79 (Standard deviation (SD) 0.03) supine and 0.45 (SD 0.05) prone (P<0.001) The therapist convenience of setup was 0.80 (SD 0.016) supine and 0.54 (SD 0.025) prone (P<0.005). No statistically significant difference was seen for the other parameters studied. CONCLUSIONS: We demonstrated significantly less PM in the supine treatment position. There was no difference for either treatment position in IPE or TPE, however, more pre-treatment corrections were required in the prone position. Prone position required a larger PTV with resulting increased dose to critical organs. There were statistically significant improvements at all dose levels for small bowel, rectal wall and bladder wall doses in the supine position once corrections were made for differences in organ motion. Linear analogue scores of patient comfort and radiation therapist convenience demonstrated statistically significant improvement in favour of the supine position. Supine positioning has been adopted as the standard for conformal prostatic irradiation at our centre.     

A prone technique for treatment of the breast, supraclavicular and axillary nodes

Radiation therapy to women with large pendulous breasts presents dosimetric challenges when the whole breast (WB) and supraclavicular and axillary (SCF + AX) nodes need to be encompassed. The aim of this case study was to demonstrate the feasibility of planning and treating a pendulous breasted patient in the prone position. Computerised tomography (CT) images were acquired of the patient in both the prone and supine positions. A Perspex plate was added to the CDR Systems Inc. (Calgary, Canada) prone breastboard to minimize SCF + AX contour variations. Dosimetry was performed on both CT scans and the resultant treatment plans were evaluated for conformity, homogeneity, dose to the lung and maximum doses to the spinal cord (SC) and irradiated volume. The daily set-up in the prone position was monitored for stability and reproducibility. The patient completed her treatment course in the prone position. Minimal daily interventions were required to ensure the position was reproduced. Grade 3 skin toxicity was recorded in the SCF + AX region where the Perspex plate was added to the prone positioning device. There was minimal difference in dosimetry between prone and supine plans in the SCF + AX region. The prone WB plan showed improved homogeneity (prone 0.15; supine 0.22) and conformity (prone 0.90; supine 0.77). A simple addition to the breastboard has enabled a pendulous breasted woman with SC + AX involvement to be treated in the prone position. Set-up of this technique is achievable on a daily basis with minimal impact on workflow. It is a feasible alternative to supine treatment for this patient group.     

Dose discrepancy between planning system estimation and measurement in spine stereotactic body radiation therapy: A case report

Stereotactic body radiation therapy (SBRT) to treat spinal metastases has shown excellent clinical outcomes for local control. High dose gradients wrapping around spinal cord make this treatment technically challenging. In this work, we present a spine SBRT case where a dosimetric error was identified during pre‐treatment dosimetric quality assurance (QA). A patient with metastasis in T7 vertebral body consented to undergo SBRT. A dual arc volumetric modulated arc therapy plan was generated on the Pinnacle treatment planning system (TPS) with a 6 MV Elekta machine using gantry control point spacing of 4°. Standard pre‐treatment QA measurements were performed, including ArcCHECK, ion chamber in CTV and spinal cord (SC) region and film measurements in multiple planes. While the dose measured at CTV region showed good agreement with TPS, the dose measured to the SC was significantly higher than reported by TPS in the original and repeat plans. Acceptable agreement was only achieved when the gantry control point spacing was reduced to 3°. A potentially harmful dose error was identified by pre‐treatment QA. TPS parameter settings used safely in conventional treatments should be re‐assessed for complex treatments.     

直肠癌放疗不同技术和体位对小肠受照剂量的比较

目的:分析直肠癌放射治疗过程中,不同放疗技术和不同治疗体位对小肠受照射体积的影响。方法:选取18例直肠癌患者,膀胱充盈的状态下,治疗体位为仰卧位和俯卧位下分别扫描两组定位CT图像,分别传输至计划系统。在两组CT图像上分别制作三维适形（3D-CRT）和调强放射治疗（IMRT）计划,比较小肠在接受不同剂量的受照绝对体积差异（V5~45）。结果:相同体位,IMRT相比3D-CRT,小肠V45明显降低,V15两者基本接近。采用相同放疗技术,俯卧位相比仰卧位小肠V45和V15均明显降低。结论:直肠癌放射治疗,相比放疗技术,治疗体位对小肠受照体积的影响更大。     

A phase II trial for the optimisation of treatment position in the radiation therapy of prostate cancer

BACKGROUND: Patient immobilisation and position are important contributors to the reproducibility and accuracy of radiation therapy. In addition the choice of position can alter the external contour of the treated area and has the potential to alter the spatial relationship between internal organs. The published literature demonstrates variation in the use of the prone and supine position for prostate cancer radiation therapy. Previous investigators using different protocols for patient preparation, imaging and target volume definition have demonstrated changes in the calculated therapeutic ratio comparing the two positions. We did not use rigid immobilisation, laxatives, rectal catheters or bladder voiding and assessed if in the prone position would cause a reduction of the dose to the rectum. We performed a prospective comparison of the two positions in 26 patients to determine if the differences in the spatial relation between the rectum and the planning target volume (PTV) would impact on dose-volume histograms to organs at risk (OAR). We also determined if any such improvement might permit dose escalation. MATERIALS AND METHODS: Twenty-six patients with clinically localized prostate cancer consented to participate in this study. All patients underwent a planning CT scan in both the prone and supine treatment positions. The PTV and OAR were drawn on each set of scans by one of the investigators. The PTV included the prostate and seminal vesicles with a 1cm margin except posteriorly where this margin was reduced to 5mm. The outer circumference of the bladder, rectal wall, small bowel (when present) was drawn along with femoral heads. 3D conformal treatment plans were computed using Helax TMS version 6.1B. A 3-field treatment technique was employed with energy of 10/15 MV. The prescribed dose was 70 Gy and the PTV was encompassed by the 95% isodose and the maximum dose was always less than 107%. Cumulative dose-volume histograms were calculated for the PTV, rectum, bladder, femoral heads and small bowel (when present). These non-uniform histograms for both the prone and supine treatment positions were transformed into uniform ones using the effective volume method [Kutcher J, Burman C. Calculation of probability factors for non-uniform normal tissue irradiation: the effective volume method. Med Phys 1987;14:487]. RESULTS: Twenty-one of the 26 (80%) patients had a lower effective volume of rectum irradiated if the prone instead of the supine treatment position was used. The median value of the effective volume in the supine treatment position was 31.74 Gy while the median value in the prone position was 22.48 Gy. The dose escalation was applied to the patients in the prone treatment position until the effective volume for the rectum was the same as that in the supine position. The range of dose escalation possible for these patients was 0.1-7.9 Gy. These patients could potentially have the dose escalated from the prescribed dose of 70 Gy for the supine position without any increase in side effects. For the five patients where no potential benefit was found when changing treatment position, only two patients displayed a significant (>1 Gy) advantage for the supine treatment position. Twenty-one of the 26 patients also showed an advantage for the prone treatment position in relation to bladder dose. CONCLUSION: The use of the prone position reduced the dose to the unprepared rectum and unvoided bladder in the majority of cases. It should be considered particularly in cases where large posterior seminal vesicles cause significant overlap between the planning target volume and the rectum.     

基于射波刀Xsight spine prone tracking模式治疗脊柱肿瘤患者的摆位准确性分析

  目的  射波刀脊柱肿瘤治疗提供了两种追踪模式,即脊柱追踪系统（Xsight spine tracking,XST）和俯卧位脊柱追踪系统（Xsight spine prone tracking,XSPT）。本研究通过比较两种脊柱追踪模式的摆位误差,评估射波刀采用XSPT模式治疗脊柱肿瘤患者的摆位准确性。  方法  回顾性分析2020年7月至2021年6月在北京大学第三医院行射波刀治疗的腰骶脊柱肿瘤患者18例,分别采用仰卧位（真空垫固定）和俯卧位（热塑体网与俯卧板固定）进行CT模拟定位。按照XST与XSPT两种追踪方式设计治疗计划,治疗中分别记录两种体位脊柱追踪的摆位修正误差,平移修正为进出、左右、升降方向,角度修正为顺时针-逆时针旋转、仰俯、倾斜。同时采集俯卧位治疗模式下同步呼吸追踪的相关误差。两种追踪模式的摆位修正误差参数通过配对t检验方法进行分析,比较两组修正误差的差异。同时分析俯卧位同步呼吸相关误差,评估呼吸模型的预测准确性。  结果  升降方向仰卧位修正误差为（0.18±0.16）mm,俯卧位为（0.31±0.26）mm,差异具有统计学意义（P<0.05）;进出方向仰卧位修正误差为（0.27±0.24）mm,俯卧位为（0.50±0.40）mm,差异具有统计学意义（P<0.05）。俯卧位呼吸模型相关误差左右、进出和升降的平均值分别为（0.21±0.11）mm、（0.41±0.38）mm和（0.68±0.42）mm。  结论  治疗中受呼吸运动的影响,相比于仰卧位定位方式,俯卧位在升降与进出方向摆位误差相对较大,但俯卧位治疗方式具有同步呼吸追踪系统,且该系统可以实现治疗过程中呼吸动度的实时修正。俯卧位脊柱追踪模式的一致性与准确性同样能够满足临床治疗需求。      

The impact of imaging modality (CT vs MRI) and patient position (supine vs prone) on tangential whole breast radiation therapy planning

Purpose

The purpose of this study was to evaluate the impact of magnetic resonance imaging (MRI) versus computed tomography (CT)-derived planning target volumes (PTVs), in both supine and prone positions, for whole breast (WB) radiation therapy.

Phase I clinical evaluation of near-simultaneous computed tomographic image-guided stereotactic body radiotherapy for spinal metastases

PURPOSE: To evaluate in a Phase I study the safety, feasibility, and patient-positioning accuracy of treating patients with intensity-modulated, near-simultaneous, computed tomographic (CT) image-guided stereotactic body radiotherapy (SBRT). PATIENTS AND METHODS: Fifteen consecutive patients with metastatic spinal disease who met protocol eligibility criteria were entered into a Phase I clinical trial. Each patient received five treatments of intensity-modulated, near-simultaneous CT image-guided SBRT, for a total of 75 treatments with 90 isocenter setups during the course of the study. Patients uniformly received 30 Gy (if possible) of radiotherapy in 5 fractions to the clinical target volume. The total dose was constrained by limiting the spinal cord to a maximum dose of 10 Gy. To verify correct daily patient positioning before each treatment and to determine the daily treatment setup error after radiation delivery, axial CT scans were taken before and immediately after each treatment without moving the patient from the treatment position, for comparison with the planning CT scan. Toxicity was measured using the Common Toxicity Criteria, the Late Effects of Normal Tissue scoring system and a neurologic function scale. Follow-up was conducted 4 weeks after completion of SBRT, and then 2, 3, 6, 9, 12, and every 6 months thereafter. RESULTS: The procedure was technically feasible to perform in all patients. No neurologic toxicity was observed in any patient. The median follow-up time was 9 months (range 6-16). The Clopper-Pearson upper bound on the probability of paralysis with 95% confidence is no greater than 0.181. The positional setup error was determined to be within 1 mm of planning isocenter. CONCLUSIONS: This Phase I study shows that intensity-modulated, near simultaneous, CT image-guided SBRT is a feasible, and highly precise technique for the noninvasive treatment of spinal metastases. Although no paralysis has developed in the 15 patients treated, continued monitoring for spinal cord toxicity is warranted, as larger numbers of patients will be needed to more precisely define the upper bound on the probability of spinal cord myelopathy.     

Influence of patient positioning on dose-volume histogram and normal tissue complication probability for small bowel and bladder in patients receiving pelvic irradiation: a prospective study using a 3D planning system and a radiobiological model

Purpose: A prospective study was undertaken to evaluate the influence of patient positioning (prone position using a belly board vs. supine position) on the dose-volume histograms (DVHs) of organs of risk, and to analyze its possible clinical relevance using radiobiological models.

Methods and Materials: From November 1996 to August 1997 a computed tomography (CT) scan was done in the prone position using a belly board and in supine position in 20 consecutive patients receiving postoperative pelvic irradiation because of rectal cancer. Using a three-dimensional (3D) planning system (Helax, TMS®) the DVH for small bowel, bladder, a standard planning target volume (PTV) of postoperative irradiation of rectal cancer, the intersection of volume of PTV and small bowel (PTV ∩ V_SB), respectively, of PTV and bladder (PTV ∩ V_B) were defined in each axial CT slice. The normal tissue complication probability (NTCP) was determined by the radiobiological model of Lyman and Kutcher using the tolerance data of Emami. For evaluation of late toxicity /β ratio was 2.5; for evaluation of acute toxicity, it was 10. Total dose was 50.4 Gy (1.8 Gy/fraction) (ICRU 50).

Results: Using the prone position compared to the supine position, the median volume of PTV ∩ V_B was reduced by 18.5 cm³ (62%). Median dose (related to the reference dose) to the bladder was 44.5% (22.4 Gy) in prone and 66.05% (33.3 Gy) in supine position (p < 0.001). Median V_B within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose was significantly lower in the prone position when compared to the supine position. Using the radiobiological models, however, there was no difference of NTCP between prone position or supine position. In the prone position, median volume of PTV ∩ V_SB was reduced by 32.5 cm³ (54%). The median dose to small bowel was 30.85% (15.4 Gy) in the prone position and 47.35% (23.9Gy) in the supine position (p < 0.001). Significant differences between prone and supine position were found for median V_SB within the 90% (45.4 Gy), 80% (40.3 Gy), 60% (30.2 Gy), and 40% (20.2 Gy) isodose. According to the method of Lyman, median NTCP of small bowel was significant lower in prone than in supine position.

Conclusion: The prone position with a standard belly board should be the standard positioning technique for patients receiving adjuvant postoperative radiation therapy following surgery of rectal cancer. Both irradiated volume and total dose to the organs of risk can be reduced significantly. As a consequence of this, radiation induced toxicity will be minimized.     

COMBINATION OF PRONE POSITION AND INTENSITY-MODULATED RADIATION THERAPY （IMRT） REDUCES SMALL BOWEL DOSES IN RADIATION THERAPY FOR GYNECOLOGIC MALIGNANCIES

Small bowel sequelae including obstruction, enteritis, and diarrhea, are among the most important acute and chronic toxicities in gynecologic carcinoma patients treated with pelvic radiotherapy[1, 2]. The total dose of radiation delivered to the pelvic organs by the whole pelvic external irradiation and intracavitary insertions is the most significant factor affecting the probability of these complications. The incidence of late bowel complications after pelvic irradiation isreported to be rel…     

Technique to match mantle and para-aortic fields

A technique is described to match the mantle and para-aortic fields used in treatment of Hodgkin's disease, when the patient is treated alternately in supine and prone position. The approach is based on referencing the field edges to a point close to the vertebral column, where uncontrolled motion is minimal and where accurate matching is particularly important. Fiducial surface points are established in the simulation process to accomplish this objective. Dose distributions have been measured to study the combined effect of divergence differences, changes in body angulation and setup errors. Even with the most careful technique, the use of small cord blocks of 50% transmission is an advisable precaution for the posterior fields.     

Impact of IMRT and leaf width on stereotactic body radiotherapy of liver and lung lesions

PURPOSE: The present study explored the impact of intensity-modulated radiotherapy (IMRT) on stereotactic body RT (SBRT) of liver and lung lesions. Additionally, because target dose conformity can be affected by the leaf width of a multileaf collimator (MLC), especially for small targets and stereotactic applications, the use of a micro-MLC on "uniform intensity" conformal and intensity-modulated SBRT was evaluated. METHODS AND MATERIALS: The present study included 10 patients treated previously with SBRT in our institution (seven lung and three liver lesions). All patients were treated with 3 x 12 Gy prescribed to the 65% isodose level. The actual MLC-based conformal treatment plan served as the standard for additional comparison. In total, seven alternative treatment plans were made for each patient: a standard (actual) plan and an IMRT plan, both calculated with Helax TMS (Nucletron) using a pencil beam model; and a recalculated standard and a recalculated IMRT plan on Helax TMS using a point dose kernel approach. These four treatment plans were based on a standard MLC with 1-cm leaf width. Additionally, the following micro-MLC (central leaf width 3 mm)-based treatment plans were calculated with the BrainSCAN (BrainLAB) system: standard, IMRT, and dynamic arc treatments. For each treatment plan, various target parameters (conformity, coverage, mean, maximal, and minimal target dose, equivalent uniform doses, and dose-volume histogram), as well as organs at risk parameters (3 Gy and 6 Gy volume, mean dose, dose-volume histogram) were evaluated. Finally, treatment efficiency was estimated from monitor units and the number of segments for IMRT solutions. RESULTS: For both treatment planning systems, no significant difference could be observed in terms of target conformity between the standard and IMRT dose distributions. All dose distributions obtained with the micro-MLC showed significantly better conformity values compared with the standard and IMRT plans using a regular MLC. Dynamic arc plans were characterized by the steepest dose gradient and thus the smallest V(6 Gy) values, which were on average 7% smaller than the standard plans and 20% lower than the IMRT plans. Although the Helax TMS IMRT plans show about 18% more monitor units than the standard plan, BrainSCAN IMRT plans require approximately twice the number of monitor units relative to the standard plan. All treatment plans optimized with a pencil beam model but recalculated with a superposition method showed significant qualitative, as well as quantitative, differences, especially with respect to conformity and the dose to organs at risk. CONCLUSION: Standard conformal treatment techniques for SBRT could not be improved with inversely planned IMRT approaches. Dose calculation algorithms applied in optimization modules for IMRT applications in the thoracic region need to be based on the most accurate dose calculation algorithms, especially when using higher energy photon beams.     

Feasibility of intensity-modulated radiation therapy in the treatment of advanced cervical chordoma

AIMS AND BACKGROUND: Postoperative radiation is often given in cases of cervical chordoma because of the high incidence of local recurrence. The tumor mass usually surrounds the spinal cord and infiltrates vertebral bone. A combined technique using protons or electrons to boost the initial photon fields is generally applied. We evaluated the use of dynamic intensity-modulated radiation therapy as an alternative technique for treating advanced cervical chordoma. METHODS AND STUDY DESIGN: A female patient with incomplete resection of a vertebral chordoma surrounding C2-C3 was irradiated with a total dose of 58 Gy (ICRU point) in 2 Gy daily fractions for 29 days between December 2001 and January 2002. Beam arrangement consisted of seven 6 MV non-opposed coplanar fields. Pretreatment quality assurance included checking of the absolute dose at reference points and 2D dose map analysis. Treatment was delivered with a 120-leaf collimator in sliding window mode. To verify the daily setup, portal images at 0 degrees and 90 degrees were compared with the simulation images before treatment delivery (manual matching) and after treatment delivery (automatic anatomy matching). RESULTS AND CONCLUSIONS: The mean dose to the planning target volume (PTV) was 57.6 +/- 2.1 Gy covering 95% of the PTV per 95% isodose. The minimum dose to the PTV (D99) was 53.6 Gy in the overlapping area between the PTV and the spinal cord planning organ at risk volume (PRV). The maximum dose to the spinal cord was 42.2 Gy and to the spinal cord PRV (8 mm margin) 53.7 Gy. The mean dose to the parotid glands was 37.4 Gy (homolateral gland) and 19.5 Gy (contralateral gland). Average deviation in setup was -1.1 +/- 2.5 mm (anterior-posterior), 2.4 +/- 1.3 mm (latero-lateral), 0.7 +/- 0.9 mm (craniocaudal) and -0.43 +/- 1 degree (rotation). CONCLUSIONS: In the treatment of chordomas surrounding the spinal cord, intensity-modulated radiotherapy can provide high dose homogeneity and PTV coverage. Frequent digital portal image-based setup control is able to reduce random positioning errors for head and neck cancer patients immobilized with conventional thermoplastic masks.