A comparison of coplanar four-field techniques for conformal radiotherapy of the prostate.

BACKGROUND AND PURPOSE: Conformal radiotherapy of the prostate is an increasingly common technique, but the optimal choice of beam configuration remains unclear. This study systematically compares a number of coplanar treatment plans for four-field irradiation of two different clinical treatment volumes: prostate only (PO) and the prostate plus seminal vesicles (PSV). MATERIALS AND METHODS: A variety of four-field coplanar treatment plans were created for PO and PSV volumes in each of ten patients. Plans included a four-field 'box' plan, a symmetric plan having bilateral anterior and posterior oblique fields, a plan with anterior oblique and lateral fields, a series of asymmetric plans, and a three-field plan having anterior and bilateral fields for comparison. Doses of 64 and 74 Gy were prescribed to the isocentre. Plans were compared using the volume of rectum irradiated to greater than 50% (V50), 80% (V80) and 90% (V90) of the prescribed dose. Tumour control probabilities (TCP) and normal tissue complication probabilities (NTCP) for the rectum, bladder and femoral heads were also evaluated. Femoral head dose was limited such that less than 10% of each femoral head received 70% of the prescribed dose. RESULTS: For the PO group, the optimal plan consisted of anterior oblique and lateral fields (Rectal V80 = 23.8+/-5.0% (1 SD)), while the box technique (V80 = 26.0+/-5.8%) was less advantageous in terms of rectal sparing (P = 0.001). Similar results were obtained for the PSV group (Rectal V80 = 43.9+/-5.0% and 47.3+/-5.5% for the two plan types, respectively, P = 0.001). The three-field plan was comparable to the optimal four-field plan but gave higher superficial body dose. With dose escalation from 64 to 74 Gy, the mean TCP for the optimal plan rose from 52.0+/-2.8% to 74.1+/-2.0%. Meanwhile, rectal NTCP for the optimal plan rose by 3.5% (PO) or 8.4% (PSV), compared to 4.7% (PO) or 10.1% (PSV) for the box plan. CONCLUSIONS: For PO volumes, a plan with gantry angles of 35 degrees, 90 degrees, 270 degrees and 325 degrees offers a high level of rectal sparing and acceptable dose to the femoral heads for all patients, while for PSV volumes, the corresponding plan has gantry angles of 20 degrees, 90 degrees , 270 degrees and 340 degrees. Using these plans, the gain in TCP resulting from dose escalation can be achieved with a smaller increase in anticipated rectal NTCP.     

Optimization of coplanar six-field techniques for conformal radiotherapy of the prostate

PURPOSE: To determine the optimal coplanar treatment technique for six-field conformal radiotherapy of prostate only (PO) or prostate plus seminal vesicles (PSV). METHODS AND MATERIALS: A series of 6-MV six-field coplanar treatment plans were created for PO and PSV volumes in 10 patients prescribed to both 64 and 74 Gy. All plans consisted of laterally-symmetric anterior oblique, lateral, and posterior oblique fields. The posterior oblique fields were varied through 20-45 degrees relative to the lateral fields, and for each of these angles, the anterior oblique fields were varied through 25-65 degrees relative to lateral. The plans were compared by means of rectal volumes irradiated to 80% or more of the prescribed dose (V80); normal tissue complication probability (NTCP) for rectum, bladder, and femoral heads; and tumor control probability (TCP). Femoral head tolerance was designated as 52 Gy to no more than 10% volume. RESULTS: For the PO group, anterior oblique fields at 50 degrees from lateral and posterior oblique fields at 25 degrees from lateral produced the lowest V80, together with femoral head doses which were appropriate for most patients (V80 = 24.4+/-5.3% [1 SD]). Compared to a commonly-used six-field (reference) plan with both anterior and posterior oblique fields at 35 degrees from lateral (V80 = 26.3+/-5.9%), this represented an improvement (p = 0.001). For the PSV group, the optimal anterior and posterior oblique fields were at 65 degrees and 30 degrees from lateral, respectively (V80 = 47.5+/-6.3%). Relative to the reference plan (V80 = 49.4+/-5.6%), this was a marginal improvement (p = 0.07). CONCLUSION: The optimized six-field plans provide increased rectal sparing at both standard and escalated doses. Moreover, the gain in TCP resulting from dose escalation can be achieved with a smaller increase in rectal NTCP using the optimized six-field plans.     

Treatment planning evaluation of non-coplanar techniques for conformal radiotherapy of the prostate.

BACKGROUND AND PURPOSE: To evaluate the benefit of using non-coplanar treatment plans for irradiation of two different clinical treatment volumes: prostate only (PO) and the prostate plus seminal vesicles (PSV). MATERIAL AND METHODS: An inverse planning algorithm was used to produce three-field, four-field, five-field and six-field non-coplanar treatment plans without intensity-modulation in ten patients. These were compared against a three-field coplanar plan. A dose of 74 Gy was prescribed to the isocentre. Plans were compared using the minimum dose to the planning target volume (PTV), maximum dose to the small bowel, and irradiated volumes of rectum, bladder and femoral head. Biological indices were also evaluated. RESULTS: For the PO group, volume of rectum irradiated to 60 Gy (V(60)) was 22.5+/-3.7% for the coplanar plan, and 21.5+/-5.3% for the five-field non-coplanar plan, which was the most beneficial (p=0.3). For the PSV group, the five-field non-coplanar plan was again the most beneficial. Rectal V(60) was in this case reduced from 41.5+/-10.4% for the coplanar plan to 35.2+/-9.3% for the non-coplanar plan (p=0.02). CONCLUSIONS: The use of non-coplanar beams in conformal prostate radiotherapy provides a small increase in rectal sparing, more significantly with PSV volumes than for PO volumes.     

A comparison of multileaf collimator with conformal blocks for the boost phase of dose-escalated conformal prostate radiotherapy.

A multileaf collimator (MLC) is compared with conformal blocks for delivering the boost phase of dose-escalated conformal prostate radiotherapy. When using conformal blocks, the volume of rectum irradiated to 90% (V90) is lower (1.4+/-1.3%, 1 SD) for a three-field plan with gantry angles 0 degree, 90 degrees, 270 degrees than for a six-field plan with gantry angles 50 degrees, 90 degrees, 130 degrees, 230 degrees, 270 degrees, 310 degrees (2.1 +/- 1.3%, P = 0.002). However, when using an MLC in which the leaves and wedge are oriented at right angles, V90 is higher (4.7 +/- 3.0%) for a three-field plan than for a six-field plan (2.7 +/- 1.6%, P=0.05). The larger increase in V90 for the three-field plan when changing from conformal blocks to MLC is mainly due to the limitation imposed upon the MLC orientation by the use of wedges.     

Optimal starting gantry angles using equiangular-spaced beams with intensity modulated radiation therapy for prostate cancer on RTOG 0126: a clinical study of 5 and 7 fields.

BACKGROUND AND PURPOSE: To investigate the effects of starting gantry angle and number of equiangular-spaced beams for prostate cancer radiotherapy on the Radiation Therapy Oncology Group (RTOG) 0126 protocol using intensity-modulated radiation therapy (IMRT). MATERIALS AND METHODS: Ten localized prostate cancer patients were prescribed to 79.2Gy in 44 fractions. Static IMRT plans using five and seven equiangular-spaced beams were generated. The starting gantry angles were incremented by 5 degrees resulting in 15 (5 beams) and 11 (7 beams) plans per patient. Constant target coverage was ensured for all plans in order to isolate the variation in the rectal and bladder metrics as a function of starting gantry angle. RESULTS: The variation with starting gantry angle in rectal metrics using 5 beams was statistically significant (p<0.001) with dosimetric importance. The 5-beam rectal V 75Gy and V 70Gy demonstrated a class solution with a characteristic 'W' pattern and two optimal starting gantry angles near 20 degrees and 50 degrees . Statistically insignificant differences were observed for the bladder metrics using 5 beams. There was little dosimetric variation in the rectal and bladder metrics with 7 beams. Nearly equivalent rectal V 75Gy was achieved between 5 optimal equiangular-spaced beams starting at 20 degrees (class solution) and 7 equiangular-spaced beams starting at 0 degrees for most patients. CONCLUSIONS: The use of an optimal starting gantry angle for 5 equiangular-spaced beams, as indicated by a class solution in this study, will facilitate rectal sparing and can produce plans that are equivalent to those employing 7 equiangular-spaced beams.     

Do differences in target volume definition in prostate cancer lead to clinically relevant differences in normal tissue toxicity?

PURPOSE: Many studies have described the quantitated differences between clinicians in target volume definition in prostate cancer. However, few studies have looked at the clinical effects of this. We aimed to assess the relevance and sequelae of such differences. METHODS AND MATERIALS: Five experienced radiation oncologists were given the clinical details of 5 patients with early-stage prostate cancer and asked to define the clinical target volume, consisting of the prostate and seminal vesicles (CTV1) and the prostate alone (CTV2), on specified planning CT scans of the pelvis. Planning target volumes (PTV1) were generated by automatic expansion of the CTV1 by a 1-cm margin. The PTV2 was defined as the CTV2. The rectum and bladder were defined by a single experienced clinician for each plan without knowledge of the involved clinician marking the CTVs. The Pinnacle planning system was used to generate the plans, using four-field conformal radiotherapy, to deliver 64 Gy in 32 fractions to the PTV1 followed by a boost of 10 Gy to the PTV2 (Medical Research Council RT01 trial protocol). Dose-volume histograms were generated for the whole bladder and rectum for each plan and the volume receiving a specific percentage of the dose (e.g., V(90)) calculated for 74 Gy, followed by estimates of normal tissue complication probabilities (NTCPs) for the bladder and rectum. RESULTS: Statistically significant differences were found in the CTV1 and CTV2 and, consequently, the PTV1 among the 5 clinicians (p < 0.0005). Most of the discrepancies occurred at the delineation of the prostatic apex and seminal vesicles, with the smallest variance noted at the rectum-prostate and bladder-prostate interfaces. No statistically significant differences were found among clinicians for the rectal V(90), V(85), V(80), V(70), or V(50) or for the bladder V(85), V(80), V(70), or V(50). A difference was noted among consultants for the bladder V(90) (p = 0.015), although no correlation was found between the bladder V(90) and the size of the outlined volumes. No statistically significant differences were found between the estimates of bladder (p = 0.1) and rectal (p = 0.09) NTCPs. CONCLUSION: The statistically significant difference in outlined volumes of the CTV1, CTV2, and PTV1 among the 5 clinicians is in keeping with the findings of previous studies. However, the interclinician variability did not result in clinically relevant outcomes with respect to the irradiated volume of rectum and bladder or NTCP. This may have been because the outlined areas in which interclinician differences were smallest (the rectal-prostate and prostate-bladder interfaces) are the areas that have the greatest effect on normal tissue toxicity. For the areas in which the interclinician correlation was lowest (the prostatic apex and distal seminal vesicles), the effects on normal tissue toxicity are smallest. The results of this study suggest that interclinician outlining differences in prostate cancer may have less clinical relevance than was previously thought.     

Rectal dose reduction with IMRT for prostate radiotherapy

Dose escalation in radiation therapy has led to increased control rates with some clinical trial evidence that rectal toxicity may be reduced when using intensity-modulated radiotherapy (IMRT) over 3D conformal radiotherapy (3DCRT) for dose-escalated prostate radiotherapy. However, IMRT for prostate patients is not yet standard in many Australian radiation oncology centres. This study investigates dosimetric changes that can be observed between IMRT and 3DCRT in prostate radiotherapy. Fifteen patients were selected for analysis. Two target definitions were investigated – prostate-only and prostate plus seminal vesicles (p + SVs). A five-field 3DCRT and seven-field IMRT plan were created for each patient and target definition. The planning target volume coverage was matched for both plans. Doses to the rectum, bladder and femoral heads were compared using dose volume histograms. The rectal normal tissue complication probabilities (NTCPs) were calculated and compared for the 3DCRT and IMRT plans. The delivery efficiency was investigated. The IMRT plans resulted in reductions in the V25, V50, V60, V70 and V75 Gy values for both the prostate-only and p + SVs targets. Rectal NTCP was reduced with IMRT for three different sets of model parameters. The reductions in rectal dose and NTCP were much larger for the p + SVs target. Delivery of IMRT plans was less efficient than for 3DCRT plans. IMRT resulted in superior plans based on dosimetric and biological endpoints. The dosimetric gains with IMRT were greater for the more complex p + SVs target. The gains made came at the cost of decreased delivery efficiency.     

Adequate margins for random setup uncertainties in head-and-neck IMRT

PURPOSE: To investigate the effect of random setup uncertainties on the highly conformal dose distributions produced by intensity-modulated radiotherapy (IMRT) for clinical head-and-neck cancer patients and to determine adequate margins to account for those uncertainties. METHODS AND MATERIALS: We have implemented in our clinical treatment planning system the possibility of simulating normally distributed patient setup displacements, translations, and rotations. The planning CT data of 8 patients with Stage T1-T3N0M0 oropharyngeal cancer were used. The clinical target volumes of the primary tumor (CTV(primary)) and of the lymph nodes (CTV(elective)) were expanded by 0.0, 1.5, 3.0, and 5.0 mm in all directions, creating the planning target volumes (PTVs). We performed IMRT dose calculation using our class solution for each PTV margin, resulting in the conventional static plans. Then, the system recalculated the plan for each positioning displacement derived from a normal distribution with sigma = 2 mm and sigma = 4 mm (standard deviation) for translational deviations and sigma = 1 degrees for rotational deviations. The dose distributions of the 30 fractions were summed, resulting in the actual plan. The CTV dose coverage of the actual plans was compared with that of the static plans. RESULTS: Random translational deviations of sigma = 2 mm and rotational deviations of sigma = 1 degrees did not affect the CTV(primary) volume receiving 95% of the prescribed dose (V(95)) regardless of the PTV margin used. A V(95) reduction of 3% and 1% for a 0.0-mm and 1.5-mm PTV margin, respectively, was observed for sigma = 4 mm. The V(95) of the CTV(elective) contralateral was approximately 1% and 5% lower than that of the static plan for sigma = 2 mm and sigma = 4 mm, respectively, and for PTV margins <5.0 mm. An additional reduction of 1% was observed when rotational deviations were included. The same effect was observed for the CTV(elective) ipsilateral but with smaller dose differences than those for the contralateral side. The effect of the random uncertainties on the mean dose to the parotid glands was not significant. The maximal dose to the spinal cord increased by a maximum of 3 Gy. CONCLUSIONS: The margins to account for random setup uncertainties, in our clinical IMRT solution, should be 1.5 mm and 3.0 mm in the case of sigma = 2 mm and sigma = 4 mm, respectively, for the CTV(primary). Larger margins (5.0 mm), however, should be applied to the CTV(elective), if the goal of treatment is a V(95) value of at least 99%.     

胸上段食管癌三维适形和调强放疗剂量学对比研究

目的 筛选胸上段食管癌不同适形和调强放疗计划优选方案.方法 8例胸上段食管癌cT模拟后参考食管钡餐造影和食管镜结果勾画GTV,按统一标准外扩CTV和PTV,实施3、4、6个野适形治疗计划和3、4、5、7、9、11个野IMRT计划和s-IMRT计划,以95%PTV体积获得6000 cGy处方剂量进行归一,分析各治疗计划靶区剂量分布和危及器官受量,进行剂量学对比研究.结果 3套适形计划之间,PTV剂量参数和体积参数均相近(P＞0.05);6个野适形计划全肺V20高于4个野(P＜0.05),3、6个野适形计划MLD也高于4个野(P＜0.05).6套调强治疗计划中,3个野IMRT计划PTV D100低于9、11个野IMRT计划(P＜0.05);4个野IMRT计划IV高于9、11个野IMRT计划(P＜0.05);9、11个野IMRT计划PTV适形指数CI、剂量参数D95、体积参数V100和V95较57个野IMRT和s-IMRT计划无明显优势(P＞0.05);各IMRT计划之间危及器官受量相近(P＞0.05).胸上段食管癌4个野适形计划PTV CI、PTV剂量参数和体积参数均低于5、7个野IMRT计划和s-IMRT计划(P＜0.05);4个野适形计划全肺V20均高于5、7个野IMRT计划和s-IMRT计划(P＜0.05).结论 胸上段食管癌三维适形放疗中4个野适形计划可为优选方案,调强放疗中5、7个野IMRT计划和s-IMRT计划可为优选方案.胸上段食管癌5、7个野IMRT计划和s-IMRT计划优于4个野适形计划.     

Beam intensity modulation using tissue compensators or dynamic multileaf collimation in three-dimensional conformal radiotherapy of primary cancers of the oropharynx and larynx, including the elective neck

Introduction: The treatment of midline tumors in the head and neck by conventional radiotherapy almost invariably results in xerostomia. This study analyzes whether a simple three-dimensional conformal radiotherapy (3D-CRT) technique with beam intensity modulation (BIM) (using a 10-MV beam of the MM50 Racetrack Microtron) can spare parotid and submandibular glands without compromising the dose distribution in the planning target volume (PTV).

Methods: For 15 T2 tumors of the tonsillar fossa with extension into the soft palate (To) and 15 T3 tumors of the supraglottic larynx (SgL), conventional treatment plans, consisting of lateral parallel opposed beams, were used for irradiation of both the primary tumor (70 Gy) and the elective neck regions (46 Gy). Separately, for each tumor a 3-D conformal treatment plan was developed using the 3-D computer planning system, CadPlan, and Optimize, a noncommercial program to compute optimal beam profiles. Beam angles were selected with the intention of optimal sparing of the salivary glands. The intensity of the beams was then modulated to achieve a homogeneous dose distribution in the target for the given 3D-CRT techniques. The dose distributions, dose–volume histograms (DVHs) of target and salivary glands, tumor control probabilities (TCPs), salivary gland volumes absorbing a biologically equivalent dose of greater than 40 or 50 Gy, and normal tissue complication probabilities (NTCPs) of each treatment plan were computed. The parameters of the 3D-CRT plans were compared with those of the conventional plans.

Results: In comparison with the conventional technique, the dose homogeneity in the target volume was improved by the conformal technique for both tumor sites. In addition, for the SgL conformal technique, the average volumes of the parotid glands absorbing a BED of greater than 40 Gy (V40) decreased by 23%, and of the submandibular glands by 7% (V40) and 6% (V50). Consequently, the average NTCPs for the parotid and submandibular glands were reduced by 7% and 6%, respectively. For the To conformal techniques, the V40 of the parotid glands was decreased on average by 31%, resulting in an average reduction of the NTCP by 49%. Both the average V50 and the NTCP of the submandibular glands were decreased by 7%.

Conclusion: For primary tumors of the oropharynx, the parotid glands could be spared to a considerable degree with the 3D-CRT technique. However, particularly the ipsilateral submandibular gland could not be spared. For primary tumors of the larynx, the 3D-CRT technique allows sparing of all salivary glands to a considerable and probably clinically relevant degree. Moreover, the conformal techniques resulted in an increased dose homogeneity in the PTV of both tumor sites.     

Radiotherapy of prostate cancer with or without intensity modulated beams: a planning comparison

PURPOSE: To evaluate whether intensity modulated radiotherapy (IMRT) by static segmented beams allows the dose to the main portion of the prostate target to escalate while keeping the maximal dose at the anterior rectal wall at 72 Gy. The value of such IMRT plans was analyzed by comparison with non-IMRT plans using the same beam incidences. METHODS AND MATERIALS: We performed a planning study on the CT data of 32 consecutive patients with localized adenocarcinoma of the prostate. Three fields in the transverse plane with gantry angles of 0 degrees, 116 degrees, and 244 degrees were isocentered at the center of gravity of the target volume (prostate and seminal vesicles). The geometry of the beams was determined by beam's eye view autocontouring of the target volume with a margin of 1.5 cm.In study 1, the beam weights were determined by a human planner (3D-man) or by computer optimization using a biological objective function with (3D-optim-lim) or without (3D-optim-unlim) a physical term to limit target dose inhomogeneity.In study 2, the 3 beam incidences mentioned above were used and in-field uniform segments were added to allow IMRT. Plans with (IMRT-lim) or without (IMRT-unlim) constraints on target dose inhomogeneity were compared. In the IMRT-lim plan, target dose inhomogeneity was constrained between 15% and 20%.After optimization, plans in both studies were normalized to a maximal rectal dose of 72 Gy. Biological (tumor control probability [TCP], normal tissue complication probability [NTCP]) and physical indices for tumor control and normal tissue complication probabilities were computed, as well as the probability of the uncomplicated local control (P+).Results: The IMRT-lim plan was superior to all other plans concerning TCP (p < 0.0001). The IMRT-unlim plan had the worst TCP. Within the 3D plans, the 3D-optim-unlim had the best TCP, which was significantly different from the 3D-optim-lim plan (p = 0.0003).For rectal NTCP, both IMRT plans were superior to all other plans (p < 0.0001). The IMRT-unlim plan was significantly better than the IMRT-lim plan (p < 0.0001). Again, 3D-optim-unlim was superior to the other 3D plans (p < 0. 0007).Physical endpoints for target showed the mean minimal target dose to be the lowest in the IMRT-unlim plan, caused by a large target dose inhomogeneity (TDI). Medial target dose, 90th percentile, and maximal target dose were significantly higher in both IMRT plans.Physical endpoints for the rectum showed the IMRT-unlim plan to be superior compared to all other plans. There was a strong correlation between the 65th percentile (Rp65) and rectal NTCP (correlation coefficient > or =89%). For bladder, maximal bladder dose was significantly higher in the IMRT-unlim plan compared to all other plans (p < or = 0.0001).P+ was significantly higher in both IMRT-plans than in all other plans. The 3D-optim-unlim plan was significantly better than the two other 3D plans (p < 0.0001). CONCLUSION: IMRT significantly increases the ratio of TCP over NTCP of the rectum in the treatment of prostate cancer. However, constraints for TDI are needed, because a high degree of TDI reduced minimal target dose. IMRT improved uncomplicated local control probability. In our department, IMRT by static segmented beams is planned and delivered in a cost-effective way. IMRT-lim has replaced non-modulated conformal radiotherapy as the standard treatment for prostate cancer.     

Conformal radiotherapy of stage III non–small cell lung cancer: a class solution involving non–coplanar intensity-modulated beams

Purpose: We developed a semiautomatic class solution to irradiate centrally located Stage III non–small cell lung cancer (NSCLC), involving a beam intensity modulation technique and optimization using a biophysical cost function.Methods and Materials: Treatment for 10 patients with Stage III NSCLC was planned, using a conventional three- or four-beam three-dimensional (3D) technique and two techniques involving, respectively, seven (BIM1) and five (BIM2) noncoplanar beam incidences with intensity modulation. Two planning target volumes were defined: PTV1 included macroscopic tumor volume and PTV2 included macroscopic and microscopic disease. Beams were divided into beam parts (segments) and their outlines were defined during virtual simulation. Optimization using a biophysical cost function determined beam weights, segment weights, and wedge angles. Biological end points included tumor control probability of both target volumes (TCP1 and TCP2) and normal tissue complication probability (NTCP) of heart, lung, and spinal cord. The resulting uncomplicated local control probability (UCLP) was calculated. Physical end points included dose at PTV1 expressed as a dose minimum and dose maximum. Target-dose inhomogeneity was constrained in all plans.Results: Concerning tumor evaluation, TCP1 was 74% (range 54–89%) for the 3D plan, 78.0% (range 62–94%) for BIM1, and 86.0% (range 59–93%) for BIM2. TCP1 1 TCP2 was, respectively, 67.0% (range 39–81%), 73.0% (range 56–94%), and 81.0% (range 54–93%). Minimum doses to PTV1 were 85, 80, and 88 Gy with the three respective techniques, while dose maxima were 89, 101, and 100 Gy. NTCPs of lung were 45.0% (range 11–75%) for 3D, 19.5% (range 8–59%) for BIM1, and 24.5% (range 3–61%) for BIM2. NTCPs of heart and spinal cord were comparable for all techniques. ULCPs were 37.0% (range 9–73%), 52.5% (range 22–86%), and 60.0% (range 20–85%), respectively. Applying physical limits to ensure clinical safety, minimum doses at PTV1 were recalculated. These were 72, 71, and 74 Gy for 3D, BIM1, and BIM2, respectively.Conclusion: The BIM2 plan is a candidate class solution for dose escalation studies in centrally located Stage III NSCLC.     

Hybrid IMRT for treatment of cancers of the lung and esophagus

PURPOSE: To report on a hybrid intensity-modulated radiation therapy (IMRT; static plus IMRT beams treated concurrently) technique for lung and esophageal patients to reduce the volume of lung treated to low doses while delivering a conformal dose distribution. METHODS: Treatment plans were analyzed for 18 patients (12 lung and 6 esophageal). Patients were treated with a hybrid technique that concurrently combines static (approximately two-thirds dose) and IMRT (approximately one-third dose) beams. These plans were compared with conventional three-dimensional (3D; non-IMRT) plans and all IMRT plans using custom four- and five-field arrangements and nine equally spaced coplanar beams. Plans were optimized to reduce V13 and V5 values. Dose-volume histograms were calculated for the planning target volume, heart, and the ipsilateral, contralateral, and total lung. Lung volumes V5, V13, V20, V30; mean lung dose (MLD); and the generalized equivalent uniform dose (gEUD) were calculated for each plan. RESULTS: Hybrid plans treated significantly smaller total and contralateral lung volumes with low doses than nine-field IMRT plans. Largest reductions were for contralateral lung V5, V13, and V20 values for lung (-11%, -15%, -7%) and esophageal (-16%, -20%, -7%) patients. Smaller reductions were found also for 3D and four- and five-field IMRT plans. MLD and gEUDs were similar for all plan types. The 3D plans treated much larger extra planning target volumes to prescribed dose levels. CONCLUSIONS: Hybrid IMRT demonstrated advantages for reduction of low-dose lung volumes in the thorax for reducing low dose to lung while also reducing the potential magnitude of dose deviations due to intrafraction motion and small field calculation accuracy.     

Reduction of normal lung irradiation in locally advanced non-small-cell lung cancer patients, using ventilation images for functional avoidance

PURPOSE: To investigate the ability of four-dimensional computed tomography (4D-CT)-derived ventilation images to identify regions of highly functional lung for avoidance in intensity-modulated radiotherapy (IMRT) planning in locally advanced non-small-cell lung cancer (NSCLC). METHODS AND MATERIALS: The treatment-planning records from 21 patients with Stage III NSCLC were selected. Ventilation images were generated from the 4D-CT sets, and each was imported into the treatment-planning system. Ninetieth percentile functional volumes (PFV90), constituting the 10% of the lung volume where the highest ventilation occurs, were generated. Baseline IMRT plans were generated using the lung volume constraint on V20 (<35%), and two additional plans were generated using constraints on the PFV90 without a volume constraint. Dose-volume and dose-function histograms (DVH, DFH) were generated and used to evaluate the planning target volume coverage, lung volume, and functional parameters for comparison of the plans. RESULTS: The mean dose to the PFV90 was reduced by 2.9 Gy, and the DFH at 5 Gy (F5) was reduced by 9.6% (SE = 2.03%). The F5, F10, V5, and V10 were all significantly reduced from the baseline values. We identified a favorable subset of patients for whom there was a further significant improvement in the mean lung dose. CONCLUSIONS: Four-dimensional computed tomography-derived ventilation regions were successfully used as avoidance structures to reduce the DVH and DFH at 5 Gy in all cases. In a subset, there was also a reduction in the F10 and V10 without a change in the V20, suggesting that this technique could be safely used.     

应用4D-CT技术确定肝癌内靶体积及相关剂量学研究

背景与目的:由于肝脏肿瘤的位移受呼吸运动的影响显著,三维适形放射治疗(three-dimensionaI confomal radiotherapy,3D CRT)难以准确定位靶区.本研究应用4D-CT技术确定个体化肝癌内靶体积(internal target volume,ITV),比较3D计划与4D计划的计划靶体积(planning target volume,PTV)及相关剂量学差异,并评价4D-CT的优势.方法:选择7例原发性肝癌患者,行4D-CT门控扫描,在10个相位的CT图像中分别勾画大体肿瘤体积(gross tumor volume,GTV)和临床靶体积(clinical target volume,CTV).在20%呼吸时相CT图像中利用三维治疗计划系统根据PTV-3D、PTV-4D为每例患者设计两套放疗计划:3D计划与4D计划.PTV-3D由CTV外扩常规的安全边界得到;PTV-4D由10个时相的CTV融合形成的ITV-4D外扩摆位边界(SM)得到.两套计划的处方剂量、射野方式均相同.比较两套计划中靶区体积、靶区与危及器官的剂量学、正常组织并发症概率的差异.结果:PTV-3D、PTV-4D的体积分别为(417.60±197.70)cm3、(331.90±183.10)cm3,后者体积减少20.50%(12.60%～34.40%);两者靶区覆盖率与剂量分布均匀性无显著性差异;4D计划中危及器官(肝、肾、胃、小肠)的受照剂量均较3D计划降低,以肝最为显著.肝V30、V40分别由38.77%、27.32%降至33.59%、22.62%;正常肝平均剂量由24.13 Gy下降为21.50 Gy;肝并发症概率由21.57%下降为15.86%;在不增加正常组织并发症的前提下,4D计划的处方剂量可由(50.57±1.51)Gy提升至(54.86±2.79)Gy,平均提高9.72%(4.00%～16.00%).结论:3D计划存在遗漏靶区或过度扩大靶区的缺陷.应用4D-CT技术可在3D CRT的基础上准确定位肝癌靶区,进一步减少正常组织的受照剂量,并提升靶区剂量.     

Protons offer reduced bone marrow,small bowel,and urinary bladder exposure for patients receiving neoadjuvant radiotherapy for resectable rectal cancer

Background

To assess the potential benefit of proton therapy (PT) over photon therapy, we compared 3-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT), and PT plans in patients undergoing neoadjuvant chemoradiation for resectable rectal cancer at our institution.

Methods

Eight consecutive patients with resectable (T2-T3) rectal cancers underwent 3DCRT, IMRT, and 3-dimensional conformal PT treatment planning. Initial target volumes (PTV1) were contoured using the Radiation Therapy Oncology Group anorectal atlas guidelines. Boost target volumes (PTV2) consisted of the gross rectal tumor plus a uniform 2-cm expansion. Plans delivered 45 Gray (Gy) or Cobalt Gray Equivalent (CGE) to the PTV1 and a 5.4-Gy (CGE) boost to the PTV2. Ninety-five percent of the PTVs received 100% of the target dose and 100% of the PTVs received 95% of the target dose. Standard normal-tissue constraints were utilized. Wilcoxon paired t-tests were performed to compare various dosimetric points between the 3 plans for each patient.

Results

All plans met all normal-tissue constraints and were isoeffective in terms of PTV coverage. The proton plans offered significantly reduced median normal-tissue exposure over the 3DCRT and IMRT plans with respect to pelvic bone marrow at the V5Gy, V10Gy, V15Gy, and V20Gy levels and the small bowel space at the V10Gy and V20Gy levels. The proton plans also offered significantly reduced median normal-tissue exposure over the 3DCRT plans with respect to the small bowel at the V30Gy and V40Gy levels and the urinary bladder at the V40Gy level.

Conclusions

By reducing bone marrow exposure, PT may reduce the acute hematologic toxicity of neoadjuvant chemoradiation and increase the likelihood of uninterrupted chemotherapy delivery. Bone marrow sparing may also facilitate the delivery of salvage chemotherapy for patients who subsequently develop hematogenous metastasis. Reduced small bowel exposure using PT may also reduce toxicity and possibly facilitate the use of more-aggressive chemotherapy with radiotherapy.     

准直器角度对宫颈癌 VMAT 的剂量学影响

目的：比较两种不同准直器角度对晚期宫颈癌 VMAT 计划的剂量学影响,为晚期宫颈癌 VMAT 计划的设计提供临床参考。方法：选择11例晚期宫颈癌患者,每例病人分别设计两种不同准直器角的双弧 VMAT计划,计划 A 和计划 B 的准直器角度分别为15°／345°和0°／90°。PTV 处方剂量为45Gy／（25f·1．8Gy）。所有计划都满足95％的靶区体积达到处方剂量要求。比较每个计划 PTV 的适形性指数（CI）与均匀性指数（HI）以及膀胱、直肠、股骨头和双肾的体积剂量（V30、V40、V50和 V18）和平均剂量（Dmean ）等参数。结果：两组计划靶区覆盖均能满足临床要求,但 B 计划的 CI 明显优于 A 组计划（0．75±0．03 vs 0．66±0．06;P ＜0．05）,并且有相似的均匀性指数。与 A 计划相比,B 计划在危及器官的体积剂量和平均剂量均明显低于前者（P ＜0．05）或者两者没有差别（P ＞0．05）。计划 A、B 两组膀胱和直肠的平均剂量（Dmean ）和体积剂量 V40分别为：（4500．70±218．28）cGy vs （4168．56±212．62）cGy（P ＝0．000）和（83．43％±11．73％）vs（61．46％±9．47％）（P ＝0．000）;（4836．12±313．33）cGy vs （4719．27±182．24）cGy（P＝0．121）和（97．05％±3．29％）vs （93．78％±6．60％）（P ＝0．066）。结论：对于晚期宫颈癌 VMAT 计划的设计,准直器角度为0°／90°的计划结果优于15°／345°的计划。不仅 PTV 的剂量分布有更好的适形性,而且能更好地保护危及器官。因此推荐使用0°／90°的准直器角度设计晚期宫颈癌的 VMAT 计划。