Biomedical subjects

Radhe Mohan

Publications and source records attributed to Radhe Mohan.

At least 19 recordsLinked to original sources

PubMed2006

Dosimetric comparison of four target alignment methods for prostate cancer radiotherapy.

PURPOSE: The aim of this study was to compare the dosimetric consequences of 4 treatment delivery techniques for prostate cancer patients treated with intensity-modulated radiotherapy (IMRT). METHODS AND MATERIALS: During an 8-week course of radiotherapy, 10 patients underwent computed tomography (CT) scans 3 times per week (243 total) before daily treatment with a CT-linear accelerator. Treatment delivery was simulated by realigning a fixed-margin treatment plan on each CT scan and calculating doses. The alignment methods were those based on the following: skin marks, bony registration, ultrasonography (US), and in-room CT. For the last two methods, prostate was the alignment target. The dosimetric effects of these alignment methods on the prostate, seminal vesicles, rectum, and bladder were compared. The average daily minimum dose to 0.1 cm3 was used as the metric for target coverage. RESULTS: Skin and bone alignments provided acceptable prostate coverage for only 70% of patients, US alignment for 90%, and CT alignment for 100%. CT-based alignment of the prostate provided seminal vesicle (SV) coverage of > or = 69 Gy for all patients; US and bone alignments provided SV coverage of > or = 60 Gy. This SV coverage may be acceptable for early-stage cancer (equivalent SV dose = 55.8 Gy at 1.8 Gy per fraction), but unacceptable for late-stage cancer (SV dose = 75.6 Gy). At 75.6 Gy, the acceptable rate for SV coverage was 40% for skin and bone alignments, 70% for US, and 80% for CT. CONCLUSIONS: Direct target alignment methods (US and CT) provided better target coverage. CT-guided alignment provided the best and most consistent dosimetric coverage. A larger planning target volume margin is needed for SV coverage when the alignment target is the prostate.

Algorithms↗

PubMed2006

Dosimetric verification for intensity-modulated radiotherapy of thoracic cancers using experimental and Monte Carlo approaches.

PURPOSE: To investigate the dosimetric accuracy of commercial treatment planning systems used in intensity-modulated radiotherapy (IMRT) for thoracic cancer. METHODS AND MATERIALS: Clinical IMRT plans for lung and esophageal cancers and mesothelioma were used to investigate the accuracy of dose calculations from two commercial treatment planning systems (Pinnacle and Corvus systems). Dose distributions were measured with ion chambers and thermoluminescent dosimeters for individual IMRT fields and composite treatment plans in water phantoms and anthropomorphic phantoms. A Monte Carlo-based system was established to compute three-dimensional dose distributions to compare with the treatment planning system calculations. RESULTS: Dose calculations from the Pinnacle system were acceptable within 5% of the local dose or a 5-mm distance-to-agreement for 80% of the points measured with ion chambers, 74% of the points measured with thermoluminescent dosimeters, and 96% of the points compared with the Monte Carlo calculations. For the Corvus system, 89% of the points agreed with the measured dose and 98% agreed with the Monte Carlo calculations. Underestimation of the dose from the treatment planning system was found in the low-dose regions (<50% of the prescribed dose), possibly caused by inadequate modeling of the multileaf collimators. CONCLUSION: The Pinnacle and Corvus dose calculations were acceptable for thoracic IMRT in high-dose regions. Beam modeling is likely the most critical factor for the accuracy of IMRT dose calculations.

Algorithms↗

PubMed2006

Dose-volume modeling of the risk of postoperative pulmonary complications among esophageal cancer patients treated with concurrent chemoradiotherapy followed by surgery.

PURPOSE: The aim of this study was to investigate the effect of radiation dose distribution in the lung on the risk of postoperative pulmonary complications among esophageal cancer patients. METHODS AND MATERIALS: We analyzed data from 110 patients with esophageal cancer treated with concurrent chemoradiotherapy followed by surgery at our institution from 1998 to 2003. The endpoint for analysis was postsurgical pneumonia or acute respiratory distress syndrome. Dose-volume histograms (DVHs) and dose-mass histograms (DMHs) for the whole lung were used to fit normal-tissue complication probability (NTCP) models, and the quality of fits were compared using bootstrap analysis. RESULTS: Normal-tissue complication probability modeling identified that the risk of postoperative pulmonary complications was most significantly associated with small absolute volumes of lung spared from doses > or = 5 Gy (VS5), that is, exposed to doses < 5 Gy. However, bootstrap analysis found no significant difference between the quality of this model and fits based on other dosimetric parameters, including mean lung dose, effective dose, and relative volume of lung receiving > or = 5 Gy, probably because of correlations among these factors. The choice of DVH vs. DMH or the use of fractionation correction did not significantly affect the results of the NTCP modeling. The parameter values estimated for the Lyman NTCP model were as follows (with 95% confidence intervals in parentheses): n = 1.85 (0.04, infinity), m = 0.55 (0.22, 1.02), and D50 = 17.5 Gy (9.4 Gy, 102 Gy). CONCLUSIONS: In this cohort of esophageal cancer patients, several dosimetric parameters including mean lung dose, effective dose, and absolute volume of lung receiving < 5 Gy provided similar descriptions of the risk of postoperative pulmonary complications as a function of the radiation dose distribution in the lung.

Analysis of Variance↗

PubMed2006

Comparison of outcomes for patients with medically inoperable Stage I non-small-cell lung cancer treated with two-dimensional vs. three-dimensional radiotherapy.

PURPOSE: This retrospective analysis was performed to assess the outcomes of three-dimensional (3D) conformal radiotherapy and two-dimensional (2D) planning. METHODS AND MATERIALS: Between 1978 and 2003, 200 patients with Stage I non-small-cell lung cancer (NSCLC) were treated with radiotherapy alone at M.D. Anderson Cancer Center. Eighty-five patients were treated with 3D conformal radiotherapy. For the 3D group, median age, radiation dose, and follow-up was 73 (range, 50-92), 66 Gy (range, 45-90.3 Gy), and 19 months (range, 3-77 months), respectively; and for the 2D group, 69 (range, 44-88), 64 Gy (range, 20-74 Gy), 20 months (range, 1-173 months), respectively. Overall survival (OS), disease-specific survival (DSS), disease-free survival (DFS), locoregional control (LRC), and distant metastasis-free survival (DMFS) rates were analyzed. RESULTS: There was no statistically significant difference in patient and tumor characteristics between 2D and 3D groups, except the 3D patients were older (p = 0.006). The OS, DSS, and LRC rates were significantly higher in patients who were treated by 3D conformal radiotherapy. Two- and 5-year OS for the 3D group were 68% and 36%, respectively, and 47% and 10% in the 2D group (p = 0.001). DSS at 2 and 5 years for the 3D group were 83% and 68%, respectively, vs. 62% and 29% in the 2D group (p < 0.001). LRC rates at 2 and 5 years for patients in the 3D group were 77% and 70% and 53% and 34% in the 2D group (p < 0.001). On univariate analysis elective, nodal irradiation was associated with decreased OS, DSS, and LRC. On multivariate analysis, 3D conformal radiotherapy was associated with increased OS and DSS. Male sex, age > or =70, weight loss > or =5%, and tumor size > or =4 cm were associated with decreased OS and DSS. CONCLUSIONS: This study demonstrates that 3D conformal radiotherapy improves outcomes in patients with medically inoperable Stage I NSCLC compared with 2D treatment and is an acceptable treatment for this group of patients.

Aged↗

PubMed2006

Geometric accuracy of a real-time target tracking system with dynamic multileaf collimator tracking system.

PURPOSE: Dynamically compensating for target motion during radiotherapy will increase treatment accuracy. A laboratory system for real-time target tracking with a dynamic MLC has been developed. In this study, the geometric accuracy limits of this DMLC target tracking system were evaluated. METHODS AND MATERIALS: A motion simulator was programmed to follow patient-derived tumor motion paths, parallel to the leaf motion direction. A target attached to the simulator was optically tracked, and the leaf positions adjusted to continually align the DMLC beam aperture to the target. Analysis of the tracking accuracy was based on video images of the target and beam alignment. The system response time was determined and the tracking error measured. Response time-corrected tracking accuracy was also calculated to investigate the accuracy limits of an improved system. RESULTS: The response time of the system is 160 +/- 2 ms. The geometric precision for tracking patient motion is 0.6 to 1.1 mm (1 sigma) for the 3 patient datasets tested, with tracking errors relative to the original patient motion of 35, 40, and 100%. CONCLUSIONS: A DMLC target tracking system has been developed that can account for detected motion parallel to the leaf motion direction. The tracking error has a negligible systematic component. Reducing the response time will further increase the overall system accuracy.

Calibration↗

PubMed2006

Risk factors for acute esophagitis in non-small-cell lung cancer patients treated with concurrent chemotherapy and three-dimensional conformal radiotherapy.

PURPOSE: To determine the risk factors for acute esophagitis (AE) in non-small-cell lung cancer (NSCLC) patients treated with concurrent chemotherapy (CCT) and three-dimensional conformal radiotherapy (3D-CRT). METHODS AND MATERIALS: Clinical data were retrospectively analyzed for 215 NSCLC patients treated with CCT and 3D-CRT during 2000-2003, 127 of whom also had induction chemotherapy (ICT). Carboplatin and paclitaxel were the most commonly used agents for both ICT and CCT. The median prescription dose of radiotherapy was 63.5 Gy in 35 fractions. AE was graded during each treatment week and 1-month follow-up visits. The factors related to clinical and disease characteristics, CCT and 3D-CRT treatments, and treatment planning were reviewed and analyzed for their association with Grade > or =3 AE using univariate and multivariate logistic tests. RESULTS: The rate of any grade AE was 93.0% and of Grade > or =3 was 20.5%. Univariate analyses showed that none of the clinical factors was significantly associated with Grade > or =3 AE. However, the mean radiation dose to the esophagus, the absolute esophageal volume treated above 15 Gy (aV15) through aV45 Gy, and the relative esophagus volume treated above 10 Gy (rV10) through rV45 Gy were significant risk factors for Grade > or =3 AE. Only rV20 was retained as the single risk factor in multivariate analyses. CONCLUSIONS: The risk of AE in the NSCLC patients treated with CCT and 3D-CRT was primarily determined by dosimetric factors. These factors should be carefully considered during treatment planning to minimize the incidence of AE.

Acute Disease↗

PubMed2006

Audio-visual biofeedback for respiratory-gated radiotherapy: impact of audio instruction and audio-visual biofeedback on respiratory-gated radiotherapy.

PURPOSE: Respiratory gating is a commercially available technology for reducing the deleterious effects of motion during imaging and treatment. The efficacy of gating is dependent on the reproducibility within and between respiratory cycles during imaging and treatment. The aim of this study was to determine whether audio-visual biofeedback can improve respiratory reproducibility by decreasing residual motion and therefore increasing the accuracy of gated radiotherapy. METHODS AND MATERIALS: A total of 331 respiratory traces were collected from 24 lung cancer patients. The protocol consisted of five breathing training sessions spaced about a week apart. Within each session the patients initially breathed without any instruction (free breathing), with audio instructions and with audio-visual biofeedback. Residual motion was quantified by the standard deviation of the respiratory signal within the gating window. RESULTS: Audio-visual biofeedback significantly reduced residual motion compared with free breathing and audio instruction. Displacement-based gating has lower residual motion than phase-based gating. Little reduction in residual motion was found for duty cycles less than 30%; for duty cycles above 50% there was a sharp increase in residual motion. CONCLUSIONS: The efficiency and reproducibility of gating can be improved by: incorporating audio-visual biofeedback, using a 30-50% duty cycle, gating during exhalation, and using displacement-based gating.

Adult↗

PubMed2006

Beam angle optimization and reduction for intensity-modulated radiation therapy of non-small-cell lung cancers.

PURPOSE: To optimize beam angles and reduce the number of beams used for intensity-modulated radiation therapy (IMRT) of non-small-cell lung cancer (NSCLC). METHODS AND MATERIALS: An exhaustive search scheme was used to perform beam angle optimization (BAO) for IMRT of NSCLC. This approach involved intercomparison of all possible beam angle combinations and selection of the best angles based on the scores or costs of the objective functions used in the treatment plan optimization. Ten Stage III NSCLC cases were selected to evaluate the BAO algorithm and dosimetry benefits of IMRT-BAO. IMRT plans using five or seven coplanar beams were optimized and compared with those using nine equal-spaced beams. Results of BAO were also compared between plans using different numbers of beams with or without fluence modulation. RESULTS: Each anatomic structure, e.g., tumor or lung, had its own preferred beam angles. Thus, BAO required appropriate balance of competing objective functions. Plans using fewer angles (five or seven beams) could achieve plan quality similar to those using nine equal-spaced beams, however with reduced monitor units and field segments. The number of beams used for the treatment (five vs. seven) and the fluence modulation (open or IMRT beams) did not have a significant impact on the results of the BAO. CONCLUSIONS: Use of fewer beams (e.g., five) for lung IMRT could result in acceptable plan quality but improved treatment efficiency. A multiresolution search scheme could be developed for BAO using fewer and nonmodulated beams to reduce the computation cost of BAO.

Algorithms↗

PubMed2006

Significant reduction of normal tissue dose by proton radiotherapy compared with three-dimensional conformal or intensity-modulated radiation therapy in Stage I or Stage III non-small-cell lung cancer.

PURPOSE: To compare dose-volume histograms (DVH) in patients with non-small-cell lung cancer (NSCLC) treated by photon or proton radiotherapy. METHODS AND MATERIALS: Dose-volume histograms were compared between photon, including three-dimensional conformal radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT), and proton plans at doses of 66 Gy, 87.5 Gy in Stage I (n=10) and 60-63 Gy, and 74 Gy in Stage III (n=15). RESULTS: For Stage I, the mean total lung V5, V10, and V20 were 31.8%, 24.6%, and 15.8%, respectively, for photon 3D-CRT with 66 Gy, whereas they were 13.4%, 12.3%, and 10.9%, respectively, with proton with dose escalation to 87.5 cobalt Gray equivalents (CGE) (p=0.002). For Stage III, the mean total lung V5, V10, and V20 were 54.1%, 46.9%, and 34.8%, respectively, for photon 3D-CRT with 63 Gy, whereas they were 39.7%, 36.6%, and 31.6%, respectively, for proton with dose escalation to 74 CGE (p=0.002). In all cases, the doses to lung, spinal cord, heart, esophagus, and integral dose were lower with proton therapy even compared with IMRT. CONCLUSIONS: Proton treatment appears to reduce dose to normal tissues significantly, even with dose escalation, compared with standard-dose photon therapy, either 3D-CRT or IMRT.

Carcinoma, Non-Small-Cell Lung↗

PubMed2006

Multiple regions-of-interest analysis of setup uncertainties for head-and-neck cancer radiotherapy.

PURPOSE: To analyze three-dimensional setup uncertainties for multiple regions of interest (ROIs) in head-and-neck region. METHODS AND MATERIALS: In-room computed tomography (CT) scans were acquired using a CT-on-rails system for 14 patients. Three separate bony ROIs were defined: C2 and C6 vertebral bodies and the palatine process of the maxilla. Translational shifts of 3 ROIs were calculated relative to the marked isocenter on the immobilization mask. RESULTS: The shifts for all 3 ROIs were highly correlated. However, noticeable differences on the order of 2-6 mm existed between any 2 ROIs, indicating the flexibility and/or rotational effect in the head-and-neck region. The palatine process of the maxilla had the smallest right-left shifts because of the tight lateral fit in the face mask, but the largest superior-inferior movement because of in-plane rotation and variations in jaw positions. The neck region (C6) had the largest right-left shifts. The positioning mouthpiece was found effective in reducing variations in the superior-inferior direction. There was no statistically significant improvement for using the S-board (8 out of 14 patients) vs. the short face mask. CONCLUSIONS: We found variability in setup corrections for different regions of head-and-neck anatomy. These relative positional variations should be considered when making setup corrections or designing treatment margins.

Algorithms↗

PubMed2006

Dosimetric properties of photon beams from a flattening filter free clinical accelerator.

Basic dosimetric properties of 6 MV and 18 MV photon beams from a Varian Clinac 21EX accelerator operating without the flattening filter have been measured. These include dose rate data, depth dose dependencies and lateral profiles in a water phantom, total scatter factors and transmission factors of a multileaf collimator. The data are reviewed and compared with measurements for the flattened beams. The unflattened beams have the following: a higher dose rate by factors of 2.3 (6 MV) and 5.5 (18 MV) on the central axis; lower out-of-field dose due to reduced head scatter and softer spectra; less variation of the total scatter factor with field size; and less variation of the shape of lateral dose profiles with depth. The findings suggest that with a flattening filter free accelerator better radiation treatments can be developed, with shorter delivery times and lower doses to normal tissues and organs.

Particle Accelerators↗

PubMed2006

Cluster model analysis of late rectal bleeding after IMRT of prostate cancer: a case-control study.

PURPOSE: Cluster models are newly developed normal-tissue complication probability models in which the spatial aspects of radiation-induced injury are taken into account by considering the size of spatially contiguous aggregates of damaged tissue units. The purpose of this study was to test the validity of a two-dimensional cluster model of late rectal toxicity based on maximum cluster size of damage to rectal surface. METHODS AND MATERIALS: A paired case-control study was performed in which each of 9 patients experiencing Grade 2 or higher late rectal toxicity after intensity-modulated radiation therapy of localized prostate cancer was paired with a patient having a similar rectal dose-surface histogram but free of rectal toxicity. Numeric simulations were performed to determine the distribution of maximum cluster size on each rectal surface for each of many different choices of possible model parameters. RESULTS: Model parameters were found for which patients with rectal toxicity were consistently more likely to have a significantly larger mean maximum cluster size than their matched controls. These parameter values correspond to a 50% probability of tissue-unit damage at doses near 30 Gy. CONCLUSIONS: This study suggests that a cluster model based on maximum cluster size of damage to rectal surface successfully incorporates spatial information beyond that contained in the rectal dose-surface histogram and may therefore provide a useful new tool for predicting rectal normal-tissue complication probability after radiotherapy.

Case-Control Studies↗

PubMed2006

Displacement-based binning of time-dependent computed tomography image data sets.

Respiration can cause tumors in the thorax or abdomen to move by as much as 3 cm; this movement can adversely affect the planning and delivery of radiation treatment. Several techniques have been used to compensate for respiratory motion, but all have shortcomings. Manufacturers of computed tomography (CT) equipment have recently used a technique developed for cardiac CT imaging to track respiratory-induced anatomical motion and to sort images according to the phase of the respiratory cycle they represent. Here we propose a method of generating CT images that accounts for respiratory-induced anatomical motion on the basis of displacement, i.e., displacement-binned CT image sets. This technique has shown great promise, however, it is not fully supported by currently used CT image reconstruction software. As an interim solution, we have developed a method for extracting displacement-binned CT image data sets from data sets assembled on the basis of a prospectively determined breathing phase acquired on a multislice helical CT scanner. First, the projection data set acquired from the CT scanner was binned at small phase intervals before reconstruction. The manufacturer's software then generated image sets identified as belonging to particular phases of the respiratory cycle. All images were then individually correlated to the displacement of an external fiducial marker. Next, CT image data sets were resorted on the basis of the displacement and assigned an appropriate phase. Finally, displacement-binned image data sets were transferred to a treatment-planning system for analysis. Although the technique is currently limited by the phase intervals allowed by the CT software, some improvement in image reconstruction was seen, indicating that this technique is useful at least as an interim measure.

Algorithms↗

PubMed2006

MCNPX simulation of a multileaf collimator.

Our purpose in this work was to validate a very detailed Monte Carlo model, developed in MCNPX, of a Millennium 120 multileaf collimator integrated into a Varian Clinac 21EX treatment head. The Monte Carlo results were compared with measurements for both the 6-MV and 18-MV photon modes. The following comparisons were performed: depth-dose curves, lateral profiles, multileaf collimator leakage, the tongue-and-grove test, and the round leaf-end test. The good agreement between the Monte Carlo simulations and measurements showed that our model is accurate. Consequently, the benchmarks provided by our study can be used in future Monte Carlo studies.

Computer Simulation↗

PubMed2006

Development and commissioning of a multileaf collimator model in monte carlo dose calculations for intensity-modulated radiation therapy.

A multileaf collimator (MLC) model, "MATMLC," was developed to simulate MLCs for Monte Carlo (MC) dose calculations of intensity-modulated radiation therapy (IMRT). This model describes MLCs using matrices of regions, each of which can be independently defined for its material and geometry, allowing flexibility in simulating MLCs from various manufacturers. The free parameters relevant to the dose calculations with this MLC model included MLC leaf density, interleaf air gap, and leaf geometry. To commission the MLC model and its free parameters for the Varian Millennium MLC-120 (Varian Oncology Systems, Palo Alto, CA), we used the following leaf patterns: (1) MLC-blocked fields to test the effects of leaf transmission and leakage; (2) picket-fence fields to test the effects of the interleaf air gap and tongue-groove design; and (3) abutting-gap fields to test the effects of rounded leaf ends. Transmission ratios and intensity maps for these leaf patterns were calculated with various sets of modeling parameters to determine their dosimetric effects, sensitivities, and their optimal combinations to give the closest agreement with measured results. Upon commissioning the MLC model, we computed dose distributions for clinical IMRT plans using the MC system and verified the results with those from ion chamber and thermoluminescent dosimeter measurements in water phantoms and anthropomorphic phantoms. This study showed that the MLC transmission ratios were strongly dependent on both leaf density and the interleaf air gap. The effect of interleaf air gap and tongue-groove geometry can be determined most effectively through fence-type MLC patterns. Using the commissioned MLC model, we found that the calculated dose from the MC system agreed with the measured data within clinically acceptable criteria from low- to high-dose regions, showing that the model is acceptable for clinical applications.

Humans↗

PubMed2006

Monte Carlo study of photon fields from a flattening filter-free clinical accelerator.

In conventional clinical linear accelerators, the flattening filter scatters and absorbs a large fraction of primary photons. Increasing the beam-on time, which also increases the out-of-field exposure to patients, compensates for the reduction in photon fluence. In recent years, intensity modulated radiation therapy has been introduced, yielding better dose distributions than conventional three-dimensional conformal therapy. The drawback of this method is the further increase in beam-on time. An accelerator with the flattening filter removed, which would increase photon fluence greatly, could deliver considerably higher dose rates. The objective of the present study is to investigate the dosimetric properties of 6 and 18 MV photon beams from an accelerator without a flattening filter. The dosimetric data were generated using the Monte Carlo programs BEAMnrc and DOSXYZnrc. The accelerator model was based on the Varian Clinac 2100 design. We compared depth doses, dose rates, lateral profiles, doses outside collimation, total and collimator scatter factors for an accelerator with and without a flatteneing filter. The study showed that removing the filter increased the dose rate on the central axis by a factor of 2.31 (6 MV) and 5.45 (18 MV) at a given target current. Because the flattening filter is a major source of head scatter photons, its removal from the beam line could reduce the out-of-field dose.

Computer Simulation↗

PubMed2006

Properties of unflattened photon beams shaped by a multileaf collimator.

Several studies have shown that removal of the flattening filter from the treatment head of a clinical accelerator increases the dose rate and changes the lateral profile in radiation therapy with photons. However, the multileaf collimator (MLC) used to shape the field was not taken into consideration in these studies. We therefore investigated the effect of the MLC on flattened and unflattened beams. To do this, we performed measurements on a Varian Clinac 21EX and MCNPX Monte Carlo simulations to analyze the physical properties of the photon beam. We compared lateral profiles, depth dose curves, MLC leakages, and total scatter factors for two energies (6 and 18 MV) of MLC-shaped fields and jaw-shaped fields. Our study showed that flattening filter-free beams shaped by a MLC differ from the jaw-shaped beams. Similar differences were also observed for flattened beams. Although both collimating methods produced identical depth dose curves, the penumbra size and the MLC leakage were reduced in the softer, unflattened beam and the total scatter factors showed a smaller field size dependence.

Computer Simulation↗

PubMed2006

A sensitivity-guided algorithm for automated determination of IMRT objective function parameters.

Optimizing intensity-modulated radiotherapy (IMRT) plans involves tradeoffs that balance normal-tissue objectives against each other and against tumor objectives. Adjusting the parameters that determine the appropriate contributions of individual anatomic structures to the objective functions through trial and error is time consuming and may not produce the best achievable plans. We have developed a sensitivity-guided parameter optimization (SGPO) method to assist in the automatic determination of parameters to drive the IMRT optimization to better achieve, or even exceed, specified planning goals. The method is based on the trade-off relationships among multiple objectives: In a globally optimal plan (or within a convex subspace of the plan objectives), any attempt to improve the achievement of goals for a structure will result in sacrificing the goals for at least one other structure. However, different objectives may have different sensitivities to the overall goal of an IMRT plan. For instance, changes in dose distribution, hence the subscore corresponding to an objective for a given normal structure, may minimally impact the target dose distribution. Stated differently, the target coverage is insensitive to the changes in dose distribution of the specific normal structure. A lung cancer treatment plan designed with the SGPO method was used to demonstrate that IMRT plans could be designed to favor a structure with the highest target sensitivity and spare the structures with the least target sensitivity without compromising the target coverage. Using one case each of prostate and paranasal sinus cancers, we also demonstrated that several alternative optimal solutions could be designed with the SGPO algorithm favoring different structures. Finally, we applied the method to eight oropharyngeal cancer cases to obtain objective function parameters that satisfied the Radiation Therapy Oncology Group RTOG-H-0022 protocol. The eight plans optimized using the computer-generated objective function parameters met the protocol's scoring criteria with no or only minor protocol violations. Our preliminary study indicates that the SGPO method may be an effective and practical way to improve IMRT planning.

Artificial Intelligence↗