Five-field Intensity-modulated Radiotherapy Research Articles

Performance of a knowledge-based planning model for optimizing intensity-modulated radiotherapy plans for partial breast irradiation.

PurposeTo evaluate a knowledge‐based (KB) planning model for RapidPlan, generated using a five‐field intensity‐modulated radiotherapy (IMRT) class solution beam strategy and rigorous dosimetric constraints for accelerated partial breast irradiation (APBI).Materials and methodsThe RapidPlan model was configured using 64 APBI treatment plans and validated for 120 APBI patients who were not included in the training dataset. KB plan dosimetry was compared to clinical plan dosimetry, the clinical planning constraints, and the constraints used in phase III APBI trials. Dosimetric differences between clinical and KB plans were evaluated using paired two‐tailed Wilcoxon signed‐rank tests.ResultsKB planning was able to produce IMRT‐based APBI plans in a single optimization without manual intervention that are comparable or better than the conventionally optimized, clinical plans. Comparing KB plans to clinical plans, differences in PTV, heart, contralateral breast, and ipsilateral lung dose–volume metrics were not clinically significant. The ipsilateral breast volume receiving at least 50% of the prescription dose was statistically and clinically significantly lower in the KB plans.ConclusionKB planning for IMRT‐based APBI provides equivalent or better dosimetry compared to conventional inverse planning. This model may be reliably applied in clinical practice and could be used to transfer planning expertise to ensure consistency in APBI plan quality.

Helical tomotherapy with a complete-directional-complete block technique effectively reduces cardiac and lung dose for left-sided breast cancer.

Objectives:To evaluate the feasibility and optimal restricted angle of the complete-directional-complete block (CDCB) technique in helical tomotherapy (HT) by including regional nodal irradiation (RNI) with the internal mammary node (IMN) in left-sided breast cancer.Methods:Ten left-sided breast cancer patients treated with 50 Gy in 25 fractions were compared with five-field intensity-modulated radiation therapy (5F-IMRT) and six types of HT plans. In the HT plans, complete block (CB), organ-based directional block (OBDB) and CDCB with different restricted angles were used.Results:The conformity index (CI) between the CDCB0,10,15,20 and 5F-IMRT groups was similar. Compared to CB, OBDB and 5F-IMRT, CDCB20 resulted in a decreased ipsilateral mean lung dose. The low-dose region (V5) of the ipsilateral lung in OBDB (84.0%) was the highest among all techniques (p < 0.001). The mean dose of the heart in CB was significantly reduced (by 11.5–22.4%) compared with other techniques. The V30 of the heart in CDCB20 (1.9%) was significantly lower than that of CB, OBDB and 5F-IMRT. Compared to the mean dose of the left anterior descending (LAD) artery of 5F-IMRT (27.0 Gy), CDCB0, CDCB10, CDCB15, CDCB20 and OBDB reduced the mean dose effectively by 31.7%, 38.3%, 39.6%, 42.0 and 56.2%, respectively. Considering the parameters of the organs-at-risk (OARs), CDCB10,15,20 had higher expectative values than the other techniques (p = 0.01).Conclusions:HT with the CDCB technique is feasible for treating left-sided breast cancer patients. The CDCB10-20 techniques not only achieved similar planning target volume coverage, homogeneity and dose conformity but also allowed better sparing of the heart and bilateral lungs.Advances in knowledge:For left-sided breast cancer patients whose RNI field includes the IMN, heart avoidance is an important issue. The CDCB technique achieved good PTV coverage, homogeneity and dose conformity and allowed better sparing of the mean dose of the lung, the LAD artery, and the heart and reduced the V30 of the heart.

Comparison of IMRT and VMAT Plan for Advanced Stage Non-Small Cell Lung Cancer Treatment

Background: Lungs and heart are the major dose-limiting organ during radiotherapy (RT) for lung cancer. This study compared Intensity-Modulated Radiotherapy (IMRT) with Volumetric Modulated Arc Therapy (VMAT) in reducing the dose to the lungs and heart. Methods: Ten patients with localized non-small-cell lung cancer underwent computed tomography (CT). The planning target volume (PTV) was defined and the organs at risk were outlined. Five-field coplanar IMRT plans and VMAT plans were generated for each patient. The planning objectives were to minimize the lung dose and heart dose while maintaining the dose to the PTV. Results: All IMRT plans, except for the three-field coplanar plans, improved the PTV90/V20 ratio significantly compared with the optimized 3D-CRT plan. Nine coplanar IMRT beams were significantly better than five or seven coplanar IMRT beams, with an improved PTV90/V20 ratio. Conclusions: The results of our study have shown that VMAT can reduce the dose to the heart compared with IMRT.

Comparison between helical tomotherapy and intensity-modulated radiotherapy on acute toxicity in patients with rectal cancer

Objective To compare acute toxicity for stage Ⅱ-Ⅲ patients with rectal cancer irradiated with helical tomotherapy (HT) and conventional five-field intensity-modulated radiotherapy (5-IMRT). Methods The data of 84 stage Ⅱ-Ⅲ patients with rectal adenocarcinoma treated with concurrent chemoradiotherapy (CRT) were retrospectively analyzed. 19 patients underwent postoperative CRT, and 65 patients underwent preoperative CRT. 43 patients received radiotherapy with HT and 41 patients with 5-IMRT. The delineation on clinical target volume (CTV) and gross tumor target (GTV) was similar for two groups. The CTV to plan tumor volume (PTV) margins were 1.0 cm for patients with 5-IMRT and 0.5 cm for patients with HT. For all patients, a dose of 45.0-50.4 Gy, in daily fractions of 1.8 Gy, was delivered to PTV. For 45 patients with high risk factors, simultaneous integrated boost (SIB) was given to the tumor or tumor bed of a total dose of 55.0-60.0 Gy, in daily fractions of 2.1-2.3 Gy. Before treatment, the patients treated with HT underwent scanning by the tomotherapy-integrated megavoltage computed tomography (MVCT) scan modality and were positioned by co-registration of these images to the original kilovoltage planning CT image set. Concurrent capecitabine every day 1 600 mg/m2, twice daily on every day in the week. Results The rates of grade ≥2 acute cystitis were 7.0 % (3 cases) in HT group and 2.4 % (1 case) in 5-IMRT group (P= 0.616), and ≥3 grade acute diarrhea were 4.7 % (2 cases) and 12.2 % (5 cases), respectively (P= 0.259). ≥2 grade leukopenia were 48.8 % (21 cases) and 19.5 % (8 cases), respectively (P= 0.005), ≥1 grade anemia were 34.9 % (15 cases) and 14.6 % (6 cases), respectively (P= 0.032), and ≥1 grade thrombocytopenia were 23.3 % (10 cases) and 14.6 % (6 cases), respectively (P= 0.314). Conclusions There is no significant difference in acute diarrhea and cystitis for patients treated with HT and 5-IMRT. Leukopenia and anemia in patients treated with HT are worse than those in patients with 5-IMRT, and thrombocytopenia is similar in the two groups. Key words: Rectal neoplasms; Chemoradiotherapy; Helical tomotherapy; Acute toxicity

A comparison of the acute toxicities using moderate hypo-fractionated intensity-modulated radiation therapy or volumetric modulated arc therapy for the treatment of early-stage prostate cancer

AbstractAimThis study compared the acute toxicities reported during radiotherapy treatment using either intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT) to deliver a moderate hypo-fractionated treatment for early-stage prostate cancer.Material and methodsAcute toxicities are routinely reported at the clinical site for all patients using the Common Terminology Criteria for Adverse Events. Toxicity assessment is performed on day 1 of treatment, then once weekly thereafter. The recorded toxicities of 40 cases treated with five-field IMRT, and 32 cases treated using VMAT were retrospectively compared. All cases were prescribed 73·68 Gy in 28 fractions. Eight symptoms were assessed; diarrhoea, proctitis, fatigue, pain, dermatitis, urinary frequency, urinary retention and urinary tract pain.ResultsIn terms of the overall toxicity recorded, VMAT was shown to reduce the toxicities of dermatitis, fatigue, pain and urinary frequency (p&amp;lt;0·05). Using IMRT, grade 2 toxicities were reported for proctitis, pain, urinary frequency, urinary retention and urinary tract pain. Using VMAT, grade 2 toxicities were reported for urinary frequency and urinary retention.FindingsThe research reported here is one of the first publications to demonstrate that VMAT is associated with decreased toxicities compared with IMRT for the treatment of early-stage prostate cancer.

Three-dimensional gamma analysis of dose distributions in individual structures for IMRT dose verification.

Our purpose in this study was to implement three-dimensional (3D) gamma analysis for structures of interest such as the planning target volume (PTV) or clinical target volume (CTV), and organs at risk (OARs) for intensity-modulated radiation therapy (IMRT) dose verification. IMRT dose distributions for prostate and head and neck (HN) cancer patients were calculated with an analytical anisotropic algorithm in an Eclipse (Varian Medical Systems) treatment planning system (TPS) and by Monte Carlo (MC) simulation. The MC dose distributions were calculated with EGSnrc/BEAMnrc and DOSXYZnrc user codes under conditions identical to those for the TPS. The prescribed doses were 76 Gy/38 fractions with five-field IMRT for the prostate and 33 Gy/17 fractions with seven-field IMRT for the HN. TPS dose distributions were verified by the gamma passing rates for the whole calculated volume, PTV or CTV, and OARs by use of 3D gamma analysis with reference to MC dose distributions. The acceptance criteria for the 3D gamma analysis were 3/3 and 2 %/2 mm for a dose difference and a distance to agreement. The gamma passing rates in PTV and OARs for the prostate IMRT plan were close to 100 %. For the HN IMRT plan, the passing rates of 2 %/2 mm in CTV and OARs were substantially lower because inhomogeneous tissues such as bone and air in the HN are included in the calculation area. 3D gamma analysis for individual structures is useful for IMRT dose verification.

Dosimetric and Radiobiological Consequences of Computed Tomography–Guided Adaptive Strategies for Intensity Modulated Radiation Therapy of the Prostate

To examine a range of scenarios for image-guided adaptive radiation therapy of prostate cancer, including different schedules for megavoltage CT imaging, patient repositioning, and dose replanning. We simulated multifraction dose distributions with deformable registration using 35 sets of megavoltage CT scans of 13 patients. We computed cumulative dose-volume histograms, from which tumor control probabilities and normal tissue complication probabilities (NTCPs) for rectum were calculated. Five-field intensity modulated radiation therapy (IMRT) with 18-MV x-rays was planned to achieve an isocentric dose of 76 Gy to the clinical target volume (CTV). The differences between D95, tumor control probability, V70Gy, and NTCP for rectum, for accumulated versus planned dose distributions, were compared for different target volume sizes, margins, and adaptive strategies. The CTV D95 for IMRT treatment plans, averaged over 13 patients, was 75.2 Gy. Using the largest CTV margins (10/7 mm), the D95 values accumulated over 35 fractions were within 2% of the planned value, regardless of the adaptive strategy used. For tighter margins (5 mm), the average D95 values dropped to approximately 73.0 Gy even with frequent repositioning, and daily replanning was necessary to correct this deficit. When personalized margins were applied to an adaptive CTV derived from the first 6 treatment fractions using the STAPLE (Simultaneous Truth and Performance Level Estimation) algorithm, target coverage could be maintained using a single replan 1 week into therapy. For all approaches, normal tissue parameters (rectum V(70Gy) and NTCP) remained within acceptable limits. The frequency of adaptive interventions depends on the size of the CTV combined with target margins used during IMRT optimization. The application of adaptive target margins (<5 mm) to an adaptive CTV determined 1 week into therapy minimizes the need for subsequent dose replanning.

Inverse planned constant dose rate volumetric modulated arc therapy (VMAT) as an efficient alternative to five-field intensity modulated radiation therapy (IMRT) for prostate

AbstractPurposeThe aim of this work was to determine if volumetric modulated arc therapy (VMAT) plans, created for constant dose-rate (cdrVMAT) delivery are a viable alternative to step and shoot five-field intensity modulated radiation therapy (IMRT).Materials and methodsThe cdrVMAT plans, inverse planned on a treatment planning system with no solution to account for couch top or rails, were created for delivery on a linear accelerator with no variable dose rate control system. A series of five-field IMRT and cdrVMAT plans were created using dual partial arcs (gantry rotating between 260° and 100°) with 4° control points for ten prostate patients with the average rectal constraint incrementally increased. Pareto fronts were compared for the planning target volume homogeneity and average rectal dose between the two techniques for each patient. Also investigated were tumour control probability and normal tissue complication probability values for each technique. The delivery parameters [monitor units (MU) and time] and delivery accuracy of the IMRT and VMAT plans were also compared.ResultsPareto fronts showed that the dual partial arc plans were superior to the five-field IMRT plans, particularly for the clinically acceptable plans where average rectal doses were less for rotational plans (p = 0·009) with no statistical difference in target homogeneity. The cdrVMAT plans had significantly more MU (p = 0·005) but the average delivery time was significantly less than the IMRT plans by 42%. All clinically acceptable cdrVMAT plans were accurate in their delivery (gamma 99·2 ± 1·1%, 3%3 mm criteria).ConclusionsAccurate delivery of dual partial arc cdrVMAT avoiding the couch top and rails has been demonstrated.

Coplanar intensity-modulated radiotherapy class solution for patients with prostate cancer with bilateral hip prostheses with and without nodal involvement

Dose distributions for prostate radiotherapy are difficult to predict in patients with bilateral hip prostheses in situ, due to image distortions and difficulty in dose calculation. The feasibility of delivering curative doses to prostate using intensity-modulated radiotherapy (IMRT) in patients with bilateral hip prostheses was evaluated. Planning target volumes for prostate only (PTV1) and pelvic nodes (PTV2) were generated from data on 5 patients. PTV1 and PTV2 dose prescriptions were 70Gy and 60Gy, respectively, in 35 fractions, and an additional nodal boost of 65Gy was added for 1 plan. Rectum, bladder, and bowel were also delineated. Beam angles and segments were chosen to best avoid entering through the prostheses. Dose-volume data were assessed with respect to clinical objectives. The plans achieved the required prescription doses to the PTVs. Five-field IMRT plans were adequate for patients with relatively small prostheses (head volumes<60cm3) but 7-field plans were required for patients with larger prostheses. Bowel and bladder doses were clinically acceptable for all patients. Rectal doses were deemed clinically acceptable, although the V50Gy objective was not met for 4/5 patients. We describe an IMRT solution for patients with bilateral hip prostheses of varying size and shape, requiring either localized or whole pelvic radiotherapy for prostate cancer.

Dosimetric Impact of Breathing Motion in Lung Stereotactic Body Radiotherapy Treatment Using Image-Modulated Radiotherapy and Volumetric Modulated Arc Therapy

The objective of this study was to investigate the influence of tumor motion on dose delivery in stereotactic body radiotherapy (SBRT) for lung cancer, using fixed field intensity- modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT). For each of 10 patients with stage I/II non-small-cell pulmonary tumors, a respiration-correlated four-dimensional computed tomography (4DCT) study was carried out. The internal target volume was delineated on the maximum intensity projection CT, which was reconstructed from the 4DCT dataset. A 5-mm margin was used for generation of the planning target volume. VMAT and five-field IMRT plans were generated using Pinnacle(3) SmartArc and direct machine parameter optimization, respectively. All plans were generated for an Elekta Synergy linear accelerator using 6-MV photons. Simulation was performed to study the interplay between multileaf collimator (MLC) sequences and target movement during the delivery of VMAT and IMRT. For each plan, 4D dose was calculated using deformable image registration of the 4DCT images. Target volume coverage and doses to critical structures calculated using 4D methodology were compared with those calculated using 3D methodology. For all patients included in this study, the interplay effect was found to present limited impact (less than 1% of prescription) on the target dose distribution, especially for SBRT, in which fewer fractions (three fractions) are delivered. Dose to the gross tumor volume (GTV) was, on average, slightly decreased (1% of prescription) in the 4D calculation compared with the 3D calculation. The motion impact on target dose homogeneity was patient-dependent and relatively small. Both VMAT and IMRT plans experienced negligible interplay effects between MLC sequence and tumor motion. For the most part, the 3D doses to the GTV and critical structures provided good approximations of the 4D dose calculations.

Comparison of Heart and Coronary Artery Doses Associated With Intensity-Modulated Radiotherapy Versus Three-Dimensional Conformal Radiotherapy for Distal Esophageal Cancer

To compare heart and coronary artery radiation exposure using intensity-modulated radiotherapy (IMRT) vs. four-field three-dimensional conformal radiotherapy (3D-CRT) treatment plans for patients with distal esophageal cancer undergoing chemoradiation. Nineteen patients with distal esophageal cancers treated with IMRT from March 2007 to May 2008 were identified. All patients were treated to 50.4 Gy with five-field IMRT plans. Theoretical 3D-CRT plans with four-field beam arrangements were generated. Dose-volume histograms of the planning target volume, heart, right coronary artery, left coronary artery, and other critical normal tissues were compared between the IMRT and 3D-CRT plans, and selected parameters were statistically evaluated using the Wilcoxon rank-sum test. Intensity-modulated radiotherapy treatment planning showed significant reduction (p < 0.05) in heart dose over 3D-CRT as assessed by average mean dose (22.9 vs. 28.2 Gy) and V30 (24.8% vs. 61.0%). There was also significant sparing of the right coronary artery (average mean dose, 23.8 Gy vs. 35.5 Gy), whereas the left coronary artery showed no significant improvement (mean dose, 11.2 Gy vs. 9.2 Gy), p = 0.11. There was no significant difference in percentage of total lung volume receiving at least 10, 15, or 20 Gy or in the mean lung dose between the planning methods. There were also no significant differences observed for the kidneys, liver, stomach, or spinal cord. Intensity-modulated radiotherapy achieved a significant improvement in target conformity as measured by the conformality index (ratio of total volume receiving 95% of prescription dose to planning target volume receiving 95% of prescription dose), with the mean conformality index reduced from 1.56 to 1.30 using IMRT. Treatment of patients with distal esophageal cancer using IMRT significantly decreases the exposure of the heart and right coronary artery when compared with 3D-CRT. Long-term studies are necessary to determine how this will impact on development of coronary artery disease and other cardiac complications.

Volumetric Modulated Arc Therapy for Advanced Pancreatic Cancer

Intensity-modulated radiotherapy (IMRT) allows for improved sparing of organs at risk (OARs) in advanced pancreatic cancer. A planning study evaluated if volumetric modulated arc therapy (RapidArc [RA]) could be used as an alternative to IMRT in such cases. In ten patients, five-field IMRT (5f-IMRT) plans with fixed gantry positions were compared to RA plans using similar constraints for planning target volume (PTV) and OARs. PTV coverage, conformity indices (CI), and OAR doses were compared. One patient was treated using RA and calculated dose distributions were measured in coronal planes in a solid-water phantom. RA plans showed superior mean CI of 1.09 +/- 0.02 (+/- 1 SD [standard deviation]) versus 1.20 +/- 0.10 in 5f-IMRT (p = 0.003). Both techniques achieved similar sparing of the right kidney, but RA significantly reduced left kidney doses with V(15) of 7.2% +/- 5.3% and 15.9% +/- 11.1%, respectively; p = 0.02. RA modestly decreased mean doses to liver (13.8 vs. 15.1 Gy; p = 0.003), stomach (16.7 vs. 17.9 Gy; p = 0.017), small bowel (19.8 vs. 22.1 Gy; p < 0.001), and duodenum (38.8 vs. 41.9 Gy; p = 0.004). Film dosimetry revealed excellent agreement between calculated and measured dose distributions. The delivery time for RA was < 3 min. RA planning achieved superior CI for pancreatic tumors compared to 5f-IMRT, and modestly reduced OAR doses. Fast treatment delivery using RA may decrease the risk of intrafractional organ motion.

Dosimetric evaluation of inspiration and expiration breath-hold for intensity-modulated radiotherapy planning of non-small cell lung cancer

The purpose of this study was to compare target coverage and lung tissue sparing between inspiration and expiration breath-hold intensity-modulated radiotherapy (IMRT) plans for patients with non-small cell lung cancer (NSCLC). In a prospective study, seven NSCLC patients gave written consent to undergo both moderate deep inspiration and end-expiration breath-hold computed tomography (CT), which were used to generate five-field IMRT plans. Dose was calculated with a scatter and an inhomogeneity correction algorithm. The percentage of the planning target volume (PTV) receiving 90% of the prescription dose (PTV90), the volume of total lung receiving ⩾ 10 Gy (V10) and ⩾ 20 Gy (V20) and the mean lung dose (MLD) were compared by the Student's paired t-test. Compared with the expiration plans, the mean ± SD reductions for V10, V20 and MLD on the inspiration plans were 4.0 ± 3.7% (p = 0.031), 2.5 ± 2.3% (p = 0.028) and 1.1 ± 0.7 Gy (p = 0.007), respectively. Conversely, a mean difference of 1.1 ± 1.1% (p = 0.044) in PTV90 was demonstrated in favour of expiration. When using IMRT, inspiration breath-hold can reduce the dose to normal lung tissue while expiration breath-hold can improve the target coverage. The improved lung sparing at inspiration may outweigh the modest improvements in target coverage at expiration.

Dosimetric comparison between intensity-modulated radiotherapy and conformal radiotherapy for upper thoracic esophageal carcinoma

Treatment planning for radiotherapy of upper thoracic esophageal carcinoma is challenging due to the anatomical features. The difficulty may be resolved by intensity-modulated radiotherapy (IMRT). This study was to compare the dosimetric advantages of IMRT to that of conformal radiotherapy (CRT) for upper thoracic esophageal carcinoma, and to explore the clinical application of IMRT. Eleven patients with upper thoracic esophageal carcinoma were enrolled. In addition to the actually used CRT plan, a five-field IMRT plan was generated for each case. The parameters of dose volume histogram for targets and organs at risk were compared between two techniques. For the planning target volume (PTV) of tumor and para-tumor tissues, the mean dose, maximal dose, doses covering 99% and 95% volume were similar in IMRT and CRT plans (P>0.05). However, IMRT plan had a higher conformity index than CRT plan (0.68+/-0.04 vs. 0.46+/-0.11, P<0.01). For the PTV of supraclavicular region, IMRT plan showed a better dose heterogeneity index than CRT plan (1.17+/-0.05 vs. 1.33+/-0.15, P=0.01). IMRT plan had lower maximal dose to the planning risk volume of the spinal cord (44.4 Gy vs. 52.5 Gy, P<0.05) and lower lung volume received dose of 10 Gy or higher [(32+/-6)% vs. (35+/-9)%, P<0.05] than CRT plan. For the upper thoracic esophageal carcinoma, IMRT has more conformal distribution of dose and better spinal cord sparing than CRT, and can reduce the volume of lung that received dose of 10 Gy or higher.

Dosimetric study of five-field intensity-modulated radiotherapy compared with conventional three-dimensional conformal radiotherapy for rectal cancer

Objective The aim of the study was to compare the difference of dose distribution in clinical target volume and organ at risk (OAR) between five-field intensity-modulated radiotherapy (IMRT) and conventional three-dimensional conformal radiotherapy (3DCRT) in the radiotherapy of rectal cancer.

Volumetric Modulated Arc Therapy: Planning and Evaluation for Prostate Cancer Cases

To develop an optimization method using volumetric modulated arc therapy (VMAT) and evaluate VMAT plans relative to the standard intensity-modulated radiotherapy (IMRT) approach in prostate cancer. A single gantry rotation was modeled using 177 equispaced beams. Multileaf collimator apertures and dose rates were optimized with respect to gantry angle subject to dose-volume-based objectives. Our VMAT implementation used conjugate gradient descent to optimize dose rate, and stochastic sampling to find optimal multileaf collimator leaf positions. A treatment planning study of 11 prostate cancer patients with a prescription dose of 86.4 Gy was performed to compare VMAT with a standard five-field IMRT approach. Plan evaluation statistics included the percentage of planning target volume (PTV) receiving 95% of prescribed dose (V95), dose to 95% of PTV (D95), mean PTV dose, tumor control probability, and dosimetric endpoints of normal organs, whereas monitor unit (MU) and delivery time were used to assess delivery efficiency. Patient-averaged PTV V95, D95, mean dose, and tumor control probability in VMAT plans were 96%, 82.6 Gy, 88.5 Gy, and 0.920, respectively, vs. 97%, 84.0 Gy, 88.9 Gy, and 0.929 in IMRT plans. All critical structure dose requirements were met. The VMAT plans presented better rectal wall sparing, with a reduction of 1.5% in normal tissue complication probability. An advantage of VMAT plans was that the average number of MUs (290 MU) was less than for IMRT plans (642 MU). The VMAT technique can reduce beam on time by up to 55% while maintaining dosimetric quality comparable to that of the standard IMRT approach.

Hypofractionated Intensity-Modulated Radiotherapy for Carcinoma of the Prostate: Analysis of Toxicity

Dose escalation for prostate cancer improves biological control but with a significant increase in late toxicity. Recent estimates of low alpha/beta ratio for prostate cancer suggest that hypofractionation may result in biological advantage. Intensity-modulated radiotherapy (IMRT) should enable dose escalation to the prostate while reducing toxicity to local organs. We report late toxicity data of a hypofractionated IMRT regime. Eligible men had T2-3N0M0 adenocarcinoma prostate, and either Gleason score >or= 7 or prostate-specific antigen 20-50 ng/L. Patients received 57-60 Gy to prostate in 19-20 fractions using five-field IMRT. All received hormonal therapy for 3 months before radiotherapy to a maximum of 6 months. Toxicity was assessed 2 years postradiotherapy using the RTOG criteria, LENT/SOMA, and UCLA prostate index assessment tools. Acute toxicity was favorable with no RTOG Grade 3 or 4 toxicity. At 2 years, there was 4% Grade 2 bowel and 4.25% Grade 2 bladder toxicity. There was no Grade 3 or 4 bowel toxicity; one patient developed Grade 3 bladder toxicity. UCLA data showed a slight improvement in urinary function at 2 years compared with pretreatment. LENT/SOMA assessments demonstrated general worsening of bowel function at 2 years. Patients receiving 60 Gy were more likely to develop problems with bowel function than those receiving 57 Gy. These data demonstrate that hypofractionated radiotherapy using IMRT for prostate cancer is well tolerated with minimal late toxicity at 2 years posttreatment. Ongoing studies are looking at the efficacy of hypofractionated regimes with respect to biological control.

Evaluation of Coplanar Partial Left Breast Irradiation Using Tomotherapy-Based Topotherapy

To investigate the use of topotherapy for accelerated partial breast irradiation through field-design optimization and dosimetric comparison to linear accelerator-based three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiation therapy (IMRT). Hypothetical 3-cm lumpectomy sites were contoured in each quadrant of a left breast by using dosimetric guidelines from the National Surgical Adjuvant Breast and Bowel Project B-39/Radiation Therapy Oncology Group 0413 protocol. Coplanar intensity-modulated topotherapy treatment plans were optimized by using two-, three-, four-, five-, and seven-field arrangements for delivery by the tomotherapy unit with fixed gantry angles. Optimized noncoplanar five-field 3D-CRT and IMRT were compared with corresponding topotherapy plans. On average, 99.5% +/- 0.5% of the target received 100% of the prescribed dose for all topotherapy plans. Average equivalent uniform doses ranged from 1.20-2.06, 0.79-1.76, and 0.10-0.29 Gy for heart, ipsilateral lung, and contralateral lung, respectively. Average volume of normal breast exceeding 90% of the prescription and average area of skin exceeding 35 Gy were lowest for five-field plans. Average uniformity indexes for five-field plans using 3D-CRT, IMRT, and topotherapy were 1.047, 1.050, and 1.040, respectively. Dose-volume histograms and calculated equivalent uniform doses of all three techniques illustrate clinically equivalent doses to ipsilateral breast, lung, and heart. This dosimetric evaluation for a single patient shows that coplanar partial breast topotherapy provides good target coverage with exceptionally low dose to organs at risk. Use of more than five fields provided no additional dosimetric advantage. A comparison of five-field topotherapy to 3D-CRT and IMRT for accelerated partial breast irradiation illustrates equivalent target conformality and uniformity.

Volumetric Modulated Arc Therapy for Delivery of Prostate Radiotherapy: Comparison With Intensity-Modulated Radiotherapy and Three-Dimensional Conformal Radiotherapy

Volumetric modulated arc therapy (VMAT) is a novel form of intensity-modulated radiotherapy (IMRT) optimization that allows the radiation dose to be delivered in a single gantry rotation of up to 360 degrees , using either a constant dose rate (cdr-VMAT) or variable dose rate (vdr-VMAT) during rotation. The goal of this study was to compare VMAT prostate RT plans with three-dimensional conformal RT (3D-CRT) and IMRT plans. The 3D-CRT, five-field IMRT, cdr-VMAT, and vdr-VMAT RT plans were created for 10 computed tomography data sets from patients undergoing RT for prostate cancer. The parameters evaluated included the doses to organs at risk, equivalent uniform doses, dose homogeneity and conformality, and monitor units required for delivery of a 2-Gy fraction. The IMRT and both VMAT techniques resulted in lower doses to normal critical structures than 3D-CRT plans for nearly all dosimetric endpoints analyzed. The lowest doses to organs at risk and most favorable equivalent uniform doses were achieved with vdr-VMAT, which was significantly better than IMRT for the rectal and femoral head dosimetric endpoints (p < 0.05) and significantly better than cdr-VMAT for most bladder and rectal endpoints (p < 0.05). The vdr-VMAT and cdr-VMAT plans required fewer monitor units than did the IMRT plans (relative reduction of 42% and 38%, respectively; p = 0.005) but more than for the 3D-CRT plans (p = 0.005). The IMRT and VMAT techniques achieved highly conformal treatment plans. The vdr-VMAT technique resulted in more favorable dose distributions than the IMRT or cdr-VMAT techniques, and reduced the monitor units required compared with IMRT.

The Effect of Changing Technique, Dose, and PTV Margin on Therapeutic Ratio During Prostate Radiotherapy

To quantify the dosimetric and radiobiological changes seen when using intensity-modulated radiation therapy (IMRT) or planning target volume (PTV) margin reduction with consistent planning parameters in a representative sample of localized prostate cancer patients. Twenty patients were randomly selected from a cohort that received 79.8 Gy using six-field conformal radiotherapy. Using the clinical contours, PTV margin, planning system, and dose constraints, five-field IMRT plans were generated for 79.8, 83.8, and 88.0 Gy. The 88.0-Gy IMRT plan was then reoptimized with a PTV margin reduced to 3 mm. These plans were then compared using various dosimetric and radiobiological endpoints calculated for various alpha/beta. Intensity-modulated RT resulted in greater conformity to the PTV (p < 0.001). No improvement in mean normal tissue complication probabilities in the rectal wall (NTCPrw) was seen, and the modified therapeutic ratio (TR(mod)) was largely unchanged between six-field conformal and IMRT for the majority of the patients. When IMRT was used to escalate dose, NTCPrw increased by 9% at each 5% prescription increase (p < 0.001). Reducing the posterior PTV margin from 7 mm to 3 mm for an IMRT plan reduced the mean NTCPrw by 12% (p < 0.001) and resulted in a trend toward increased TR(mod)(p = 0.005). Changes in TR(mod) between conformal and IMRT planning or PTV reduction showed large interpatient variability. Changing from conformal to IMRT, or from PTV(10-7) to PTV(3), did not produce a uniform interpatient increase in TR(mod)when the CTV contained the prostate alone. Radiobiological benefits of these two methods seem to be dependent on the particular anatomy of individual patients, supporting the use of patient-specific margin, planning, and dose prescription strategies.