Reduction of organ motion by combined cardiac gating and respiratory gating

PURPOSE: To investigate whether the effect of organ motion can be further reduced with the application of a cardiac gating technique, together with respiratory gating. METHODS AND MATERIALS: Axial and coronal images through the heart and liver were continuously scanned with fast cine magnetic resonance imaging scans at three different gating settings: (1) without respiratory and cardiac gating; (2) with respiratory gating, but without cardiac gating; and (3) with both respiratory and cardiac gating. The effect of motion for either the heart or liver was analyzed with probability maps. RESULTS: With the application of respiratory gating only, the marginal region on the probability map was reduced by 10.0% in the axial slice and 19.8% in the coronal slice for the heart. It was reduced by 5.2% in the axial slice and 20.8% in the coronal slice for the liver. With the application of cardiac gating together with respiratory gating, the marginal region on the probability map was reduced further. The reduction was 8.0% in the axial slice and 13.6% in the coronal slice for the heart and 5.9% in the axial slice and 7.0% in the coronal slice for the liver. CONCLUSION: The effect of organ motion can be further reduced with the application of cardiac gating together with respiratory gating. The potential application to treatment planning merits further investigation.     

Interventions to reduce organ motion effects in radiation delivery

Because organ motion during a radiation treatment fraction can be substantial, with resultant alterations in organ volume definition and dosimetry, interventions to reduce the impact of intratreatment organ motion are required for many patients if dose escalation and reduction of dose to normal tissue are treatment goals. Before radiation delivery, fluoroscopy, cine computed tomography scans and magnetic resonance imaging can be used to measure the magnitude of organ motion for an individual patient. Strategies to minimize organ motion caused by breathing during radiation include altering breathing patterns, treating during voluntary or controlled breath holds, gating the radiation beam or tracking it with organ motion. Here the first 2 interventions will be primarily discussed. Approaches to minimize nonrespiratory organ motion include maintaining the same preparative regimen before each treatment and ensuring comfortable immobilization and short overall treatment time.     

Reduction of organ motion in lung tumors with respiratory gating

We evaluated the ability of a commercial respiratory gating system to assure the reproducibility of internal anatomy in respiration synchronized CT (RS-CT) scans. This passive system uses an infrared sensitive camera to track the motion of reflective markers mounted on the abdomen. Eighteen patients, nine with lung tumors and nine with liver tumors, were selected for evaluation of the Varian Real-Time Position Monitor respiratory gating system. Liver tumors were chosen as surrogate for lower lobe tumors. Each patient underwent at least two identical RS-CT scans, at end-inspiration (EI) or end-expiration (EE), to assess intra-fraction reproducibility. Twelve patients also underwent a free breathing scan and an opposed-respiration phase synchronized scan (EI if the two first were an EE and vice versa). On each CT, a physician contoured the liver, the kidneys, the spleen, and the diaphragms for the liver patients; and similarly, the lungs, the gross tumor volume (GTV), the trachea, the heart and the diaphragms for the lung patients. After registering the different CT images using bony anatomy, the changes of each structure between the respective data sets were quantified in terms of its volume, the displacement of its center of mass (COM), and an "index" coefficient of reproducibility. An analysis of the CT scans obtained at EI and EE phases yielded an average superior-inferior (SI) difference of the diaphragm position of 14.4 mm (range: 45.9-0.9). A similar analysis of CT scans acquired at the same breathing phase yielded 0.7 mm (range: 3.1-0, p=0.0001). Similar conclusions were derived in analysis of COM positions of the following structures: lungs, heart, lung's GTV, liver, spleen and kidneys. Evaluation of volume changes for lungs, liver, and spleen confirmed reproducibility of RS-CT while the "index" coefficient confirmed reproducibility of RS-CT of all organs. A commercial gating system using external markers for RS-CT significantly improves the positional reproducibility of thoracic and upper abdominal structures. This reproducible decrease in organ motion will allow a reduction of the margin of expansion facilitating increase in target dose beyond that allowed by conventional radiation treatments.     

Nasopharyngeal carcinoma. Treatment planning with IMRT and 3D conformal radiotherapy

The study was undertaken in order to compare dose plans for intensity-modulated radiotherapy (IMRT) with 3D conformal radiotherapy (3D-CRT) dose plans in patients with nasopharyngeal carcinoma (NPC). Clinical data from 20 consecutive patients treated with IMRT are presented. For 11 patients 3D-CRT plans were made and compared to the IMRT plans with respect to doses to the planning target volumes (PTVs) and to organs at risk (OARs). For comparison of the conformation of dose to defined target volumes the conformity index (CI) was used. Target volume coverage and critical organ protection were significantly improved with IMRT compared to 3D-CRT. One-year loco-regional control, distant metastasis-free survival, and overall survival were 79%, 72%, and 80%. Two patients have had recurrence in the clinical target volume (CTV) only and seven patients have relapsed in distant organs and/or in head-and-neck areas outside the target areas. The study confirms that IMRT is superior to 3D-CRT in the treatment of NPC. As locoregional control of NPC improves we are facing an increasing number of recurrences outside the irradiated area.     

Animation and radiobiological analysis of 3D motion in conformal radiotherapy.

PURPOSE: To allow treatment plans to be evaluated against the range of expected organ motion and set up error anticipated during treatment. METHODS: Planning tools have been developed to allow concurrent animation and radiobiological analysis of three dimensional (3D) target and organ motion in conformal radiotherapy. Surfaces fitted to structures outlined on CT studies are projected onto pre-treatment images or onto megavoltage images collected during the patient treatment. Visual simulation of tumour and normal tissue movement is then performed by the application of three dimensional affine transformations, to the selected surface. Concurrent registration of the surface motion with the 3D dose distribution allows calculation of the change in dose to the volume. Realistic patterns of motion can be applied to the structure to simulate inter-fraction motion and set-up error. The biologically effective dose for the structure is calculated for each fraction as the surface moves over the course of the treatment and is used to calculate the normal tissue complication probability (NTCP) or tumour control probability (TCP) for the moving structure. The tool has been used to evaluate conformal therapy plans against set up measurements recorded during patient treatments. NTCP and TCP were calculated for a patient whose set up had been corrected after systematic deviations from plan geometry were measured during treatment, the effect of not making the correction were also assessed. RESULTS: TCP for the moving tumour was reduced if inadequate margins were set for the treatment. Modelling suggests that smaller margins could have been set for the set up corrected during the course of the treatment. The NTCP for the rectum was also higher for the uncorrected set up due to a more rectal tissue falling in the high dose region. CONCLUSION: This approach provides a simple way for clinical users to utilise information incrementally collected throughout the whole of a patient's treatment. In particular it is possible to test the robustness of a patient plan against a range of possible motion patterns. The methods described represent a move from the inspection of static pre-treatment plans to a review of the dynamic treatment.     

Deep inspiration breath hold and respiratory gating strategies for reducing organ motion in radiation treatment

We examine 2 strategies for reducing respiration-induced organ motion in radiation treatment: deep inspiration breath hold (DIBH) and respiratory gating. DIBH is a controlled breathing technique in which the patient performs a supervised breath hold during treatment. The technique offers 2 benefits: reduced respiratory motion from the breath hold and increased normal tissue sparing from the increased lung volume. In respiratory-gated treatment, a device external to the patient monitors breathing and allows delivery of radiation only during certain time intervals, synchronous with the patient's respiratory cycle. Gated treatment offers reduced respiratory motion with less patient effort than DIBH. We briefly survey the development of these 2 strategies, describe their clinical implementation for treatment of thoracic and liver tumors at the Memorial Sloan-Kettering Cancer Center, and discuss their advantages and limitations.     

Accelerated partial breast irradiation using 3D conformal radiation therapy (3D-CRT)

PURPOSE: We present a novel three-dimensional conformal radiation therapy (3D-CRT) technique to treat the lumpectomy cavity, plus a 1.5-cm margin, in patients with early-stage breast cancer and study its clinical feasibility. METHODS AND MATERIALS: A 3D-CRT technique for partial-breast irradiation was developed using archived CT scans from 7 patients who underwent an active breathing control study. The clinical feasibility of this technique was then assessed in 9 patients who were prospectively enrolled on an Investigational Review Board-approved protocol of partial-breast irradiation. The prescribed dose was 34 Gy in 5 patients and 38.5 Gy in 4 patients, delivered in 10 fractions twice daily over 5 consecutive days. The impact of both breathing motion and patient setup uncertainty on clinical target volume (CTV) coverage was studied, and an appropriate CTV-to-PTV (planning target volume) margin was calculated. RESULTS: By adding a CTV-to-PTV "breathing-only" margin of 5 mm, 98%-100% of the CTV remained covered by the 95% isodose surface at the extremes of normal inhalation and normal exhalation. The "total" CTV-to-PTV margin employed to accommodate organ motion and setup error (10 mm) was found to be sufficient to accommodate the observed uncertainty in the delivery precision. Patient tolerance was excellent, and acute toxicity was minimal. No skin changes were noted during treatment, and at the initial 4-8-week follow-up visit, only mild localized hyperpigmentation and/or erythema was observed. No instances of symptomatic radiation pneumonitis have occurred. CONCLUSIONS: Accelerated partial-breast irradiation using 3D-CRT is technically feasible, and acute toxicity to date has been minimal. A CTV-to-PTV margin of 10 mm seems to provide coverage for most patients. However, more patients and additional studies will be needed to validate the accuracy of this margin, and longer follow-up will be needed to assess acute and chronic toxicity, tumor control, and cosmetic results.     

3D conformal radiation therapy for prostate cancer in elderly patients.

BACKGROUND AND PURPOSE: The aim of this study was to evaluate if conformal radiation therapy for localized prostate cancer with doses of 70 Gy is well tolerated in patients aged 75 years or older, and if the side effects and the biochemical recurrence free (bNED) survival are comparable to younger patients. PATIENTS AND METHODS: Eighty patients>or=75 years received definitive conformal radiotherapy for prostate cancer. Acute and late side effects as well as bNED survival (ASTRO criteria) were compared to 221 patients younger than 75 years who were treated during the same period of time. RESULTS: Median dose to the prostate was 70 Gy in both groups. There were no significant differences in acute or late side effects between age groups. The frequency of grade III late symptoms was low and ranged between 0 and 4% for the evaluated symptoms irrespective of age group. Older patients had a better bNED survival than younger patients (bNED survival at 4 years: 76 vs. 61%, P=0.042). CONCLUSIONS: High-dose conformal radiation therapy for prostate cancer is well tolerated in patients aged 75 years or older. In terms of bNED survival radiation treatment is at least as effective as it is for younger patients.     

A study of the effects of internal organ motion on dose escalation in conformal prostate treatments.

BACKGROUND AND PURPOSE: To assess the effect of internal organ motion on the dose distributions and biological indices for the target and non-target organs for three different conformal prostate treatment techniques. MATERIALS AND METHODS: We examined three types of treatment plans in 20 patients: (1) a six field plan, with a prescribed dose of 75.6 Gy; (2) the same six field plan to 72 Gy followed by a boost to 81 Gy; and (3) a five field plan with intensity modulated beams delivering 81 Gy. Treatment plans were designed using an initial CT data set (planning) and applied to three subsequent CT scans (treatment). The treatment CT contours were used to represent patient specific organ displacement; in addition, the dose distribution was convolved with a Gaussian distribution to model random setup error. Dose-volume histograms were calculated using an organ deformation model in which the movement between scans of individual points interior to the organs was tracked and the dose accumulated. The tumor control probability (TCP) for the prostate and proximal half of seminal vesicles (clinical target volume, CTV), normal tissue complication probability (NTCP) for the rectum and the percent volume of bladder wall receiving at least 75 Gy were calculated. RESULTS: The patient averaged increase in the planned TCP between plan types 2 and 1 and types 3 and 1 was 9.8% (range 4.9-12.5%) for both, whereas the corresponding increases in treatment TCP were 9.0% (1.3-16%) and 8.1% (-1.3-13.8%). In all patients, plans 2 and 3 (81 Gy) exhibited equal or higher treatment TCP than plan 1 (75.6 Gy). The maximum treatment NTCP for rectum never exceeded the planning constraint and percent volume of bladder wall receiving at least 75 Gy was similar in the planning and treatment scans for all three plans. CONCLUSION: For plans that deliver a uniform prescribed dose to the planning target volume (PTV) (plan 1), current margins are adequate. In plans that further escalate the dose to part of the PTV (plans 2 and 3), in a fraction of the cases the CTV dose increase is less than planned, yet in all cases the TCP values are higher relative to the uniform dose PTV (plan 1). Doses to critical organs remain within the planning criteria.     

食管癌三维适形放射治疗剂量学与放射性肺炎发生相互关系的研究

目的:通过食管癌常规放射治疗与三维适形放射治疗的技术对比研究,比较应用不同外照射技术时肿瘤靶区适形指数的差异,以及肺等正常组织受照射容积剂量与放射性肺炎并发症发生概率(NTCP)的关系.方法:应用三维治疗计划系统,对28例胸中段EPC分别设计三种照射技术(A:常规3野;B:适形3野;C:适形5野).比较在同一处方剂量(66 Gy)时肿瘤靶区的适形指数,全肺受照射剂量与肺的NTCP的差异.结果:A、B、C三种照射技术比较:1)靶区的适形指数从0.55±0.09提高至0.76±0.04 和 0.78±0.06.2)肺平均剂量从(16.54±2.35) Gy降低至(13.26±1.93) Gy和(3.38±1.61) Gy;肺的V20从(32.95±6.43)%降低至(23.01±6.25)%和(24.8±4.47)%;肺的V30从(17.25±4.96)% 降低至(12.18±3.66)%和(6.75±2.93)%.3)肺的 NTCP从(6.9±6.86)%降低至(1.14±1.11)%和(1±1.02)%.A、B和C三种照射技术比较差异均有统计学意义,P=0.000.结论:三维适形放射治疗技术的靶区剂量分布较理想,显著降低正常肺的照射体积和剂量,减少放射性肺炎NTCP.     

The sensitivity of dose distributions for organ motion and set-up uncertainties in prostate IMRT.

BACKGROUND AND PURPOSE: To determine the effect of organ motion and set-up uncertainties on IMRT dose distributions for prostate. METHODS: For five patients, IMRT techniques were designed to irradiate the CTV (prostate plus seminal vesicles). Technique I delivered 78 Gy to PTV1 (CTV+10 mm margin). Technique II delivered 68 Gy to PTV1, and a 10 Gy boost to PTV2 (CTV+an anisotropic margin of 0 to 5 mm). Technique III delivered 68 Gy to PTV1 and simultaneously 78 Gy to PTV2. Uncertainties were simulated using population statistics of organ motion and set-up accuracy. The average TCP (TCPpop) of the CTV and average NTCP (NTCPpop) of the rectal wall were calculated. RESULTS: The planning TCP was a good predictor for TCPpop for Techniques I and II. Technique III was sensitive for geometrical uncertainties, reducing TCPpop by 0.8 to 2.4% compared to planning. NTCPpop was reduced for Technique III by a factor 2.6 compared to Technique I. For all plans, the planning NTCP was strongly correlated with NTCPpop. CONCLUSIONS: Dose distributions created with Techniques I and II are insensitive for geometrical uncertainties, while Technique III resulted in a reduction of TCPpop. This reduction can be compensated by a small dose escalation, while still resulting in an NTCPpop of the rectal wall that is lower or comparable to Technique I.     

腺癌保乳术后调强放疗与三维适形放疗的疗效比较

目的 比较乳腺癌保乳术后调强放疗(IMRT)与三维适形放疗(3D-CRT)的疗效、不良反应及对基质金属蛋白酶-9(MMP-9)和基质金属蛋白酶组织抑制剂-1(TIMP-1)的影响.方法 选择96例接受乳腺癌保乳术的女性患者,按照随机数字表法将患者随机分为对照组和观察组,每组各48例.对照组予以3D-RCT,观察组予以IMRT,处方剂量均为50 Gy/25次.比较两组的照射剂量、不良反应、美容效果及治疗前后的血清MMP-9和TIMP-1水平.结果 观察组计划靶区(PTV)的V105%、V110%及V115%明显低于对照组(P﹤0.01),观察组患侧肺脏及左侧病灶者心脏接受的照射剂量明显低于对照组(P﹤0.01);观察组的皮肤反应率为12.5%(6/48),低于对照组的29.2%(14/48),差异有统计学意义(P﹤0.05);观察组美容优良率为97.9%(47/48),高于对照组的83.3%(40/48),差异有统计学意义(P﹤0.05).放疗后,两组患者的MMP-9及MMP-9/TIMP-1均较本组治疗前降低,但组间比较差异无统计学意义(P﹥0.05).结论 与3D-CRT相比,IMRT的PTV适形度和剂量均匀性较好,可降低危及器官的受照剂量,皮肤反应较少且美容效果好,值得临床推广.     

Dosimetry and radiobiologic model comparison of IMRT and 3D conformal radiotherapy in treatment of carcinoma of the prostate

INTRODUCTION: Intensity-modulated radiotherapy (IMRT) has introduced novel dosimetry that often features increased dose heterogeneity to target and normal structures. This raises questions of the biologic effects of IMRT compared to conventional treatment. We compared dosimetry and radiobiologic model predictions of tumor control probability (TCP) and normal tissue complication probability (NTCP) for prostate cancer patients planned for IMRT as opposed to standardized three-dimensional conformal radiotherapy (3DCRT). METHODS AND MATERIALS: Segmented multileaf collimator IMRT treatment plans for 32 prostate cancer patients were compared to 3DCRT plans for the same patients. Twenty-two received local-field irradiation (LFI), and 10 received extended-field irradiation (EFI) that included pelvic lymph nodes. For LFI, IMRT was planned for delivery of 2 Gy minimum dose to the prostate (> or =99% volume coverage) for 35 fractions. The 3DCRT plans, characterized by more homogenous dose to the target, were designed according to a different protocol to deliver 2 Gy to the center of the prostate for 37 fractions. Mean total dose from 35 fractions of IMRT was equal to mean total dose from 37 fractions of 3DCRT. For EFI, both IMRT and 3DCRT were planned for 2 Gy per fraction to a total dose of 50 Gy to prostate and pelvic lymph nodes, followed by 2 Gy per fraction to 20 Gy to the prostate alone. Treatment dose for EFI-IMRT was defined as minimum dose to the target, whereas for EFI-3DCRT, it was defined as dose to the center of the prostate. TCP was calculated for the prostate in the linear-quadratic model for two choices of alpha/beta. NTCP was calculated with the Lyman model for organs at risk, using Kutcher-Burman dose-volume histogram reduction with Emami parameters. RESULTS AND CONCLUSIONS: Dose to the prostate, expressed as mean +/- standard deviation, was 74.7 +/- 1.1 Gy for IMRT vs. 74.6 +/- 0.3 Gy for 3D for the LFI plans, and 74.8 +/- 0.6 Gy for IMRT vs. 71.5 +/- 0.6 Gy for 3D for the EFI plans. For the studied protocols, TCP was greater for IMRT than for 3D across the full range of target sensitivity, for both localized- and extended-field irradiation. For LFI, this was due to the smaller number of fractions (35 vs. 37) used for IMRT, and for EFI, this was due to the greater mean dose for IMRT, compared to 3D. For all organs, mean NTCP tended to be lower for IMRT than for 3D, although NTCP values were very small for both 3D and IMRT. Differences were statistically significant for rectum (LFI and EFI), bladder (EFI), and bowel (EFI). For both LFI and EFI, the calculated NTCPs qualitatively agreed with early published clinical data comparing genitourinary and gastrointestinal complications of IMRT and 3D. Present calculations support the hypothesis that accurately delivered IMRT for prostate cancer can limit dose to normal tissue by reducing treatment margins relative to conventional 3D planning, to allow a reduction in complication rate spanning several sensitive structures while maintaining or increasing tumor control probability.     

Dosimetric implications of changes in patient repositioning and organ motion in conformal radiotherapy for prostate cancer.

PURPOSE: To assess the influence of patient repositioning and organ motion on dose distribution within the prostate and the seminal vesicles (clinical target volume, (CTV)). MATERIAL AND METHODS: Nine patients were simulated and treated in the supine position, with an empty bladder, and without immobilization devices. While on treatment, patients underwent weekly pelvic computed tomography (CT) scans under conditions identical to those at simulation. Patients were aligned using lasers on anterior and lateral skin tattoos, onto which lead markers were placed. After each CT scan (n=53) the CTV was redefined by contouring, and a new isocenter was obtained. A six-field technique was used. The field margins around the CTV were 20 mm in the cranio-caudal axis, and 13 mm in the other axes, except in the lateral fields where a 10 mm posterior margin was used. Dose-volume histograms (DVHs) for each organ were compared with those determined at simulation, using the notion of the proportional change in the area under the CTV-DVH curve resulting from a change in treatment plan (cDVH). RESULTS: The reproducibility of the dose distribution was good for the prostate (%cDVH, mean+/-SD: -0.97+/-2.11%) and less than optimal for the seminal vesicles (%cDVH, mean+/-SD: -4.66+/-10.45%). When correlating prostate %cDVH variations with displacements of the isocenter in the Y axis (antero-posterior) the %cDVH exceeded (-)5% in only two dosimetries, both with an isocenter shift of >10 mm. For the seminal vesicles, however, ten out of 53 dosimetries showed a %cDVH exceeding (-) 5%. In nine of these ten dose distribution studies the posterior shift of the isocenter exceeded 8 mm. CONCLUSIONS: Precise targeting of prostate radiotherapy is primarily dependent on careful daily set-up and on random changes in rectal geometry. Margins no less than 10 mm around the prostate and at least 15 mm around the seminal vesicles are probably necessary to insure adequate target coverage with a six-field technique.     

Influence of organ motion on conformal vs. intensity-modulated pelvic radiotherapy for prostate cancer

PURPOSE: To compare an intensity-modulated radiotherapy (IMRT) planning approach for prostate pelvic RT with a conformal RT (CRT) approach taking into account the influence of organ-at-risk (OAR) motion. METHODS AND MATERIALS: A total of 20 male patients, each with one planning computed tomography scan and five to eight treatment computed tomography scans, were used for simulation of IMRT and CRT for delivery of a prescribed dose of 50 Gy to the prostate, seminal vesicles, and pelvic lymph nodes. Planning was done in Eclipse without correcting for OAR motion. Evaluation was performed using the CRT and IMRT dose matrices and the planning and treatment OAR outlines. The generalized equivalent uniform dose (gEUD) was calculated for 894 OAR volumes using a volume-effect parameter of 4, 12, and 8 for bowel, rectum and bladder, respectively. For the bowel, the gEUD was normalized to a reference volume of 200 cm(3). For each patient and each OAR, an average of the treatment gEUDs (gEUD(treat)) was calculated for CRT and IMRT. The paired t test was used to compare IMRT with CRT and gEUD(treat) with gEUD(plan). RESULTS: The mean gEUD(treat) was reduced from 43 to 40 Gy, 47 to 46 Gy, and 48 to 45 Gy with IMRT for the bowel, rectum, and bladder, respectively (p < 0.001). Differences between the gEUD(plan) and gEUD(treat) were not significant (p > 0.05) for any OAR but was >6% for the bowel in 6 of 20 patients. CONCLUSION: Intensity-modulated RT reduced the bowel, rectum, and bladder gEUDs also under influence of OAR motion. Neither CRT nor IMRT was robust against bowel motion, but IMRT was not less robust than CRT.     

The cost effectiveness of 3D conformal radiation therapy compared with conventional techniques for patients with clinically localized prostate cancer

Background: We previously demonstrated the advantages of three-dimensional conformal radiation therapy (3DCRT) in improved rates of biochemical (bNED) control in certain subsets of patients with clinically localized prostate cancer. However, in this era of cost consciousness and limited resources, the cost effectiveness of 3DCRT compared with conventional external beam irradiation (CRT) remains unexamined.

Methods and Materials: Between October 1, 1987 and November 30, 1991, 193 patients with clinically localized prostate cancer received definitive external beam irradiation at Fox Chase Cancer Center. The 1998 Medicare fee schedule was used to determine treatment charges and to provide a reference for a national comparison. Complete charges for pretreatment work-up, treatment, and follow-up were tabulated for each patient. The mean total charges (MTC) using the Lin method of estimating medical costs was used to analyze and compare costs between groups. A matched case/control analysis was performed to further evaluate the effect of cost between techniques. The median follow-up was 72 months (range 3–118).

Results: The overall 5-year actuarial rate of bNED control was 41% and 53%, respectively, for the CRT and 3DCRT patients (p = 0.03). The MTC for the CRT patients was $10,544.53. For the 3DCRT patients, the MTC was $8,955.48. The sample mean of the total costs from the observed deaths for the two patient groups by follow-up interval ranged from $9,800.63 to $59,635.01 for the CRT patients to $17,259.00 to $24,250.38 for the 3DCRT patients. No statistically significant difference in cost was observed between groups using the matched case/control analysis.

Conclusion: Initial work-up and treatment costs were greater for patients treated with 3DCRT compared with patients treated with conventional techniques. However, with longer follow-up, the mean total cost of treatment was not statistically different between the two treatment groups. Because of improved rates of bNED control for these patients and the increased costs associated with the treatment of a greater fraction of patients with recurrent disease following CRT, 3DCRT was cost effective for patients with clinically localized prostate cancer.