Conventional Radiotherapy Plans Research Articles

Isotoxic investigation of 18F-FDG PET/CT-guided dose escalation with intensity-modulated radiotherapy for LA-NSCLC

Purpose This research compared differences of dosimetric and biological parameters between PET/CT-guided isotoxic SIB-IMRT plans and conventional radiotherapy plans for patients with LA-NSCLC, and it also evaluated the factors that affect dose escalation. Materials and methods This study consisted of a retrospective cohort of thirty patients with IIIA-IIIB NSCLC. SIB-IMRT (Plan_iso) and conventional radiotherapy (Plan_primary) plans were generated using auto-planning. Dosimetric parameters such as mean lung dose (MLD) and other indicators were compared. Tumor control probability (TCP) of PTV and normal tissue complication probability (NTCP) of total lung, heart, esophagus, and spinal cord were calculated. The relationships between dose escalation and 3 D length of PTV and other factors were analyzed. Paired-samples t-test, Mann-Whitney U test, and Chi-Square test were performed for comparisons between datasets. A P < .05 was considered statistically significant. Results The dosimetric parameters of PTV in Plan_iso were higher than those of PTV in Plan_primary, and there were significant differences (p < .05). Compared with Plan_primary, Plan_iso slightly increased dosimetric parameters of the total lung, heart, spinal cord, esophagus, and MUs. The absolute differences were small. TCPs of PTV in Plan_iso were significantly higher than those in Plan_primary. NTCPs of the total lung, esophagus, and spinal cord in Plan_iso were higher than those in Plan_primary. There were significant differences, but the absolute differences were small. NTCP of heart in Plan_iso was slightly higher than that in Plan_primary, but there was no statistical difference. Conclusions For LA-NSCLC, the SIB based on isotoxic radiotherapy can significantly increase TCP under the premise that the toxicity of OARs is comparable.

Conventional radiotherapy planning of cervical cancer in resource-constrained set-up: Utilizing soldering lead wire to delineate radiotherapy portal

Simulator for radiotherapy planning may not be available in resource-constrained set-up. Surface anatomy based planning has its own limitation in terms of adequately covering target due to variation of anatomy and tumor growth and spread pattern. Hence, improvisation of radiotherapy planning of cervical cancer, commonest malignancy among women in this set-up, utilizing locally available resource may improve treatment quality.Soldering lead wire, plumber’s measuring tape, diagnostic x-ray and transpore adhesive tape were utilized to delineate radiotherapy portals for management of cervical cancer. Delineation of radiotherapy portals for irradiation of different regions in selected patients of carcinoma cervix is feasible in resource-constrained set-up. Radiotherapy delivery by conventional 2-D technique through the portal designed by utilizing soldering lead wire and diagnostic x-ray was achievable. Radiotherapy portal so delineated need to be validated in future clinical studies.

Brachial plexus doses in locoregional radiotherapy for breast cancer

Background: Brachial plexopathy is a known issue following axillary radiotherapy in locally advanced breast cancer (LABC). We attempted to adapt Radiation Therapy Oncology Group (RTOG) guidelines on brachial plexus (BP) contouring (head and neck cancer) to breast cancer patients receiving post-mastectomy locoregional radiotherapy (LRRT), to determine (I) feasibility of identifying BP in the treatment position for breast cancer, and (II) radiation therapy dose received by BP with respect to the planned dose. Methods: Planning computed tomography (CT) sets (non-contrast) of 10 LABC patients, who had undergone mastectomy and subsequently completed LRRT including posterior axillary boost, were retrieved. Treatment included chest wall irradiation [50 gray (Gy) in 25 fractions, 6–10 Mega-electronVolt (MeV) electrons, 80–100% isodose], and supraclavicular and axillary RT with an anterior photon field [6 megavolts (MVs), 40 Gy in 20 fractions] and a posterior axillary field (6 MVs, 10 Gy in 5 fractions). Vertebral bodies C5–T1, anterior and middle scalene muscles (MS) were contoured and used as guide to identify probable location of BP. Results: Ten LABC patients received LRRT (50 Gy). Mean ipsilateral BP volume was 13.8 cc. Medians of maximum and mean BP doses were 54.65 and 36.62 Gy, respectively. Mean global dose maximum of the respective plans was 58.83 Gy. Mean BP volume receiving >50 Gy was 27.81% (range, 13.01–51.80%). Conclusions: BP contouring in LABC radiotherapy is feasible, with uncertainty in regions of altered anatomy (C5–6, shoulder). The maximum BP doses always exceeded prescribed dose, and although lower than tolerance dose (66 Gy) should be evaluated to reduce adverse events’ risk. This study establishes the feasibility of following RTOG guidelines for BP contouring even in altered treatment position in breast cancer radiotherapy planned on non-contrast CT scans. BP dose maxima in conventional radiotherapy planning are nearly 18–20% higher than prescription isodoses. Albeit safe in conventional terms, the risk of high doses leading to increased risk of plexopathy warrants consideration especially with regard to relation to tumor boost volumes as well as when using hypofractionated regimens which may be less forgiving for late effects.

Dosimetry study of 18F-FMISO + PET/CT hypoxia imaging guidance on intensity-modulated radiation therapy for non-small cell lung cancer.

This study was to evaluate the feasibility of simultaneous integrated boost on tumor hypoxia area by studying the dosimetric change of hypoxia imaging guidance on intensity-modulated radiation therapy for non-small cell lung cancer (NSCLC). Five NSCLC patients with large hypoxic volume participated in this study. FDG PET/CT images were fused with CT localization images to delineate gross tumor volume. FMISO PET/CT images were fused with CT localization images to delineate hypoxic biological target volume (BTV) (tissue maximum ratio ≥ 1.3) by threshold. BTV was irradiated with 72, 78 and 84Gy, respectively, 30 times. The dosimetry differences were compared in target volume and organ at risk between simultaneous integrated boost plans and conventional radiotherapy plans. Dosages on BTV of NSCLC hypoxic area were increased to 72, 78 and 84Gy, respectively, by simultaneous integrated boost intensity-modulated radiation therapy. There was no obvious difference in dosage distributions on original target volume compared with those in conventional radiotherapy. Dosages on main organ at risk in chest met the dosimetric constraint, and there was no significant difference compared with those in conventional radiotherapy. It is feasible in dosiology that the dosages in NSCLC hypoxic area were added to 72, 78 and 84Gy by simultaneous integrated boost with the guidance of 18F-FMISO PET/CT.

Value of single-photon emission computed tomography perfusion lung scintigraphy in radiotherapy optimization for non-small cell lung cancer

Objective To explore the relationship between functional dosimetric parameters of radiotherapy plans and radiation-induced lung injury using single-photon emission computed tomography (SPECT) perfusion lung scintigraphy, and to investigate the advantages of SPECT in optimizing radiotherapy plans. Methods From 2014 to 2015, 23 patients with non-small cell lung cancer (NSCLC) who received SPECT perfusion lung scintigraphy before radiotherapy were enrolled as subjects. The functional dose-volume histogram (fDVH) was generated and the relationship between fVx (the volume proportion of the functional lung tissue exposed to ≥x Gy of radiation in the whole functional lung tissue) and radiation-induced pneumonitis (RP) was explored. The radiotherapy plans were optimized based on SPECT and the dosimetric parameters were then compared between the optimized and conventional radiotherapy plans. The SPSS 13 software was used for chi-square test and receiver operating characteristic curve analysis. Comparison of DVH and fDVH between conventional and optimized radiotherapy plans was made by paired t test. Results The fV13 value for both lungs was most correlated with the incidence of grade ≥2 RP. The fV10, fV13, fV20, fV25, and fV40 values were significantly reduced and the conformity index was significantly improved after optimization (P=0.006, 0.007, 0.010, 0.036, 0.035, 0.040). Conclusions SPECT can be used to optimize radiotherapy plans. The fV13 value may be correlated with the incidence and severity of RP. Key words: Tomography, X-ray computed, single-photon emission; Pulmonary perfusion imaging; Radiation lung injury; Dose volume histogram

The comparison of dose distribution of different 3D conformal and conventional radiotherapy plans for gastric cancer

The comparison of dose distribution of different 3D conformal and conventional radiotherapy plans for gastric cancer

Validation of dose painting of lung tumours using alanine/EPR dosimetry

Biologic image guided radiotherapy (RT) with escalated doses to tumour sub volumes challenges today’s RT dose planning and delivery systems. In this phantom study, we verify the capability of a clinical dose planning and delivery system to deliver an 18F-FDG-PET based dose painted treatment plan to a lung tumour. Furthermore, we estimate the uncertainties of the dose painted treatment compared to conventional RT plans. An anthropomorphic thorax phantom of polystyrene and polyurethane was constructed based on CT images of a lung cancer patient. 101 EPR/alanine dosimeters were placed in separate cavities within the phantom. IMRT and VMAT plans were generated in Eclipse (version 10.0, Analytical Anisotropic Algorithm version 10.2.28, Varian Medical Systems, Inc.) for 6 and 15 MV photons, based on 18F-FDG-PET/CT images of the patient. A boost dose of 3.8 Gy/fraction was given to the 18F-FDG-avid region (biological planning volume; BTV), whereas 3.1 Gy/fraction was planned to the planning target volume (PTV, excluding the BTV). For the homogenous plans, 3.2 Gy/fraction was given to the PTV. Irradiation of the phantom was carried out at a Varian Trilogy linear accelerator (Varian Medical Systems, Inc.). Uncertainties involved in treatment planning and delivery were estimated from portal dosimetry gamma evalutation. Measured and calculated doses were compared by Bland–Altmann analysis. For all treatment plans, all dose-volume objectives could be achieved in the treatment planning system. The mean absolute differences between calculated and measured doses were small (<0.1 Gy) for BTV, PTV-BTV, lung and soft tissue. The estimated uncertainty of the planned doses was less than 3% for all plans, whereas the estimated uncertainty in the measured doses was less 2.3%. Our results show that planning and delivery of dose escalated lung cancer treatment on a clinical dose planning and delivery system has high dosimetric accuracy. The uncertainties associated with the dose escalated treatment plans are comparable to the conventional plans.

TH‐AB‐304‐03: Tumor Control Probability Applied to Lung Cancer: A Statistical Test of the Independence of Voxel Response

Purpose:Conventional radiotherapy planning uses simplified DVH‐derived metrics (e.g. D99, D95) as surrogates for tumor control probability when evaluating plan quality. While this has the advantage of providing an easily derived predictor variable, such metrics fail to consider critical aspects of the underlying radiobiology. Counter to observed radiobiological effects, there is a prevailing assumption of tumor subvolume independence. We tested this by introducing a parameter to capture departures from independence using a modified metric, termed the “generalized tumor dose” (gTD).Methods:For given dose distributions, cell survival was derived from a comprehensive biological model (Jeong, 2013 Phys. Med. Biol.). The gTD metric applied a generalized mean term, q, to subvolume survival values, with this term optimized according to its predictive power over the NSCLS cohort (N=316). Patients were treated 1.8–2.2 Gy/Fx in 28–39 Fxs (n=50), or 2.75 Gy/Fx in 24 fractions (n=266). Results were compared to other metrics according binary outcome and actuarial survival prediction.Results:Fitting model parameters to combined cohort data using log‐likelihood and actuarial methods, we derived an optimized generalized mean parameter q of −1.14 (95% confidence interval upper bound=0.08). Patient‐specific gTD values derived using this value showed superior performance to other clinical metrics. For gTD, normalized log‐likelihood=−0.471, AUC=0.634, and R^2=0.066, versus normalized log‐likelihood=−0.508/−0.504, AUC=0.473/0.462, and R^2=0.0011/0.0014 for D99/D95. Furthermore, when q wasn't incorporated into the model (q=1, implicitly), AUC decreased to 0.622, normalized log‐likelihood to −0.501 and R^2 to 0.0144.Conclusion:Negative q values suggest areas of highest dose play a greater role in determining outcome than expected based only on TCP.The biological origin of this effect could be of several potential causes, including bystander effects, genomic intra‐tumor heterogeneity, or tumor shrinkage. Accounting for these interactions, the gTD metric provides superior accuracy as a predictor of outcome.

Intensity-modulated whole pelvic radiotherapy provides effective dosimetric outcomes for cervical cancer treatment with lower toxicities

PurposeTo compare the efficacy of intensity-modulated radiotherapy, three-dimensional conformal radiotherapy, and conventional radiotherapy for cervical cancer treatment. Materials and methodsWhole pelvis intensity-modulated radiotherapy, three-dimensional conformal radiotherapy, and conventional radiotherapy plans were designed for 16 patients with stage IIB cervical cancer, each using the prescribed dose of 50.4Gy/28 fractions. Dose–volume histograms of the target volume and organs at risk were evaluated. ResultsCompared to the 3D conformal and conventional radiotherapy plans, the intensity-modulated radiotherapy plan demonstrated superior conformal treatment. The mean planning target volume dose of all three plans reached the target effective therapeutic dose. The planning target volume dose of the intensity-modulated radiotherapy plan was significantly higher than that of either the three-dimensional conformal radiotherapy or conventional radiotherapy plan (P<0.05). When more than 30Gy was administered in intensity-modulated radiotherapy, organs at risk including the small intestine, rectum, bladder, and bone marrow received a significantly reduced volume of radiation. In comparison of the average planning target volume doses, significant volume reductions in irradiation of organs at risk were obtained with full bladders. ConclusionsAn intensity-modulated radiotherapy plan with appropriate margins encompassing the primary tumour and potential microscopic pelvic disease reduces the dose to organs at risk without compromising target coverage. Intensity-modulated radiotherapy is an appropriate definitive treatment for patients with cervical cancer.

Volumetric modulated arc radiotherapy sparing the thyroid gland for early-stage glottic cancer: A dosimetrical analysis

Previous studies on advanced radiotherapy (RT) techniques for early stage glottic cancer have focused on sparing the carotid artery. However, the aim of the present study was to evaluate the dosimetric advantages of volumetric modulated arc therapy (VMAT) in terms of sparing the thyroid gland in early-stage glottic cancer patients. In total, 15 cT1N0M0 glottic cancer patients treated with definitive RT using VMAT were selected, and for dosimetric comparison, a conventional RT plan comprising opposed-lateral wedged fields was generated for each patient. The carotid artery, thyroid gland and spinal cord were considered organs at risk. The prescription dose was 63 Gy at 2.25 Gy per fraction. For the thyroid gland and carotid artery, all compared parameters were significantly lower with VMAT compared with conventional RT. For the thyroid gland, the median reduction rates of the mean dose (Dmean), the volume receiving ≥30% of the prescription dose (V30) and the V50 were 32.6, 40.9 and 46.0%, respectively. The Dmean was 14.7±2.6 Gy when using VMAT compared with 22.2±3.9 Gy when using conventional RT. The differences between the techniques in terms of planning target volume coverage and dose homogeneity were not significant. When considering a recent normal tissue complication probability model, which indicated the mean thyroid gland dose as the most significant predictor of radiation-induced hypothyroidism, the dosimetric advantage shown in this study may be valuable in reducing hypothyroidism following RT for early stage glottic cancer patients.

Re-Irradiation: Outcome, Cumulative Dose and Toxicity in Patients Retreated with Stereotactic Radiotherapy in the Abdominal or Pelvic Region

The purpose of the present study was to explore the outcome, cumulative dose in tumor and organs at risk and toxicity after extra-cranial stereotactic re-irradiation. Twenty-seven patients were evaluated who had been re-irradiated with stereotactic body radiotherapy (SBRT) after conventional radiotherapy (CRT). The dose summation of the SBRT and CRT plans was done by dose point calculations accounting for fraction size by the linear-quadratic model. Efficacy and toxicity was scored by looking at the reduction in tumor size, pain and bleeding. Symptomatic response was observed in 96% of the patients. The median maximum SBRT dose to the tumor was 90 Gy3 (range: 42-420 Gy3). The median cumulative dose for the rectum, bowel and bladder resulted in 104 Gy3, 98 Gy3 and 113 Gy3, respectively. No grades 5, 4 and 3 acute and late toxicity was observed. In conclusion: re-irradiation to the same region using extra-cranial stereotactic radiotherapy is feasible and resulted in a 96% symptomatic response with low toxicity.

Conventional radiation therapy for brain metastases

Conventional radiotherapy in the form of whole brain radiation treatment has been a longstanding treatment for brain metastases, and it continues to provide effective palliation as monotherapy and in combination with local and systemic treatments. Advances in systemic therapy have improved survival with metastatic disease, and in those patients with better prognostic factors, more aggressive local therapeutic approaches for brain metastases appear to benefit their survival and intracranial tumor control. Increased treatment intensity and longer survival following treatment of brain metastases have raised concerns about persistent treatment-related neurocognitive toxicities and the resulting impact on quality of life. Technological advances in conventional radiotherapy planning and delivery have led to novel approaches that may increase intracranial tumor control while minimizing the treatment-related toxicities of therapy. These innovative approaches include intensity-modulated radiotherapy, new image-guidance techniques, and volumetric modulated arc therapy, which allow for the delivery of whole brain radiotherapy with integrated boost treatment to the visible disease while sparing the hippocampal regions or delivery of hypofractionated radiotherapy to larger metastatic targets that may not be amenable to radiosurgery boost or salvage treatment.

Effect of beam arrangement on oral cavity dose in external beam radiotherapy of nasopharyngeal carcinoma

This study compared the oral cavity dose between the routine 7-beam intensity-modulated radiotherapy (IMRT) beam arrangement and 2 other 7-beam IMRT with the conventional radiotherapy beam arrangements in the treatment of nasopharyngeal carcinoma (NPC). Ten NPC patients treated by the 7-beam routine IMRT technique (IMRT-7R) between April 2009 and June 2009 were recruited. Using the same computed tomography data, target information, and dose constraints for all the contoured structures, 2 IMRT plans with alternative beam arrangements (IMRT-7M and IMRT-7P) by avoiding the anterior facial beam and 1 conventional radiotherapy plan (CONRT) were computed using the Pinnacle treatment planning system. Dose-volume histograms were generated for the planning target volumes (PTVs) and oral cavity from which the dose parameters and the conformity index of the PTV were recorded for dosimetric comparisons among the plans with different beam arrangements. The dose distributions to the PTVs were similar among the 3 IMRT beam arrangements, whereas the differences were significant between IMRT-7R and CONRT plans. For the oral cavity dose, the 3 IMRT beam arrangements did not show significant difference. Compared with IMRT-7R, CONRT plan showed a significantly lower mean dose, V30 and V-40, whereas the V-60 was significantly higher. The 2 suggested alternative beam arrangements did not significantly reduce the oral cavity dose. The impact of varying the beam angles in IMRT of NPC did not give noticeable effect on the target and oral cavity. Compared with IMRT, the 2-D conventional radiotherapy irradiated a greater high-dose volume in the oral cavity.

Intensity-modulated radiotherapy increases dose to the brachial plexus compared with conventional radiotherapy for head and neck cancer

The preferential use of intensity-modulated radiotherapy (IMRT) over conventional radiotherapy (CRT) in the treatment of head and neck cancer has raised concerns regarding dose to non-target tissue. The purpose of this study was to compare dose-volume characteristics with the brachial plexus between treatment plans generated by IMRT and CRT using several common treatment scenarios. The brachial plexus was delineated on radiation treatment planning CT scans from 10 patients undergoing IMRT for locally advanced head and neck cancer using a Radiation Therapy Oncology Group-endorsed atlas. No brachial plexus constraint was used. For each patient, a conventional three-field shrinking-field plan was generated and the dose-volume histogram (DVH) for the brachial plexus was compared with that of the IMRT plan. The mean irradiated volumes of the brachial plexus using the IMRT vs the CRT plan, respectively, were as follows: V50 (18±5 ml) vs (11±6 ml), p = 0.01; V60 (6±4 ml) vs (3±3 ml), p = 0.02; V66 (3±1 ml) vs (1±1 ml), p = 0.04, V70 (0±1 ml) vs (0±1 ml), p = 0.68. The maximum point dose to the brachial plexus was 68.9 Gy (range 62.3-78.7 Gy) and 66.1 Gy (range 60.2-75.6 Gy) for the IMRT and CRT plans, respectively (p = 0.01). Dose to the brachial plexus is significantly increased among patients undergoing IMRT compared with CRT for head and neck cancer. Preliminary studies on brachial plexus-sparing IMRT are in progress.

Dosimetric Comparison of Three Different Involved Nodal Irradiation Techniques for Stage II Hodgkin's Lymphoma Patients: Conventional Radiotherapy, Intensity-Modulated Radiotherapy, and Three-Dimensional Proton Radiotherapy

To compare the dose distribution to targeted and nontargeted tissues in Hodgkin's lymphoma patients using conventional radiotherapy (CRT), intensity-modulated RT (IMRT), and three-dimensional proton RT (3D-PRT). CRT, IMRT, and 3D-PRT treatment plans delivering 30 cobalt Gray equivalent (CGE)/Gy to an involved nodal field were created for 9 Stage II Hodgkin's lymphoma patients (n = 27 plans). The dosimetric endpoints were compared. The planning target volume was adequately treated using all three techniques. The IMRT plan produced the most conformal high-dose distribution; however, the 3D-PRT plan delivered the lowest mean dose to nontarget tissues, including the breast, lung, and total body. The relative reduction in the absolute lung volume receiving doses of 4-16 CGE/Gy for 3D-PRT compared with CRT ranged from 26% to 37% (p < .05), and the relative reduction in the absolute lung volume receiving doses of 4-10 CGE/Gy for 3D-PRT compared with IMRT was 48-65% (p < .05). The relative reduction in absolute total body volume receiving 4-30 CGE/Gy for 3D-PRT compared with CRT was 47% (p < .05). The relative reduction in absolute total body volume receiving a dose of 4 CGE/Gy for 3D-PRT compared with IMRT was 63% (p = .03). The mean dose to the breast was significantly less for 3D-PRT than for either IMRT or CRT (p = .03) The mean dose and absolute volume receiving 4-30 CGE/Gy for the heart, thyroid, and salivary glands were similar for the three modalities. In this favorable subset of Hodgkin's lymphoma patients without disease in or below the hila, 3D-PRT significantly reduced the dose to the breast, lung, and total body. These observed dosimetric advantages might improve the clinical outcomes of Hodgkin's lymphoma patients by reducing the risk of late radiation effects related to low-to-moderate doses in nontargeted tissues.

Dosimetric study on conventional mantle-field irradiation and intensity-modulated radiotherapy for Hodgkin's lymphoma

Objective To compare the dose distribution of mantle-field radiotherapy using conven-tional radiotherapy(CRT) and four intensity-modulated radiotherapy(IMRT) techniques in stage Ⅰ and Ⅱ Hodgkin's lymphoma(HL). Methods Ten patients with patholocally proved early stage HL underwent CT simulation. Then both CRT and IMRT planning performed using ECLIPS treatment planning system(TPS). The dosimetric parameters of different irradiation plans were analyzed, including conformal index (CI), homo-geneity index (HI), D_(95) and V_(95) of planning target volume (PTV), D_(max),D_(mean),D_(min),V_5,V_(10),V_(20) and V_(30) of the lung, as well as Dmax of the spinal cord. Results The isodose distribution and homogeneity of PTV were better in IMRT plans when compared with CRT plans. Target coverage, target dose conformity and homogene-ity were similar among all the four IMRT techniques. The V_(30) of the lung using IMRT was lower than using CRT,but the low-dose volume of the lung was higher. Among the four IMRT technique plans,the lung V_(20) and V_(30) were lower in plans with more-field technique,but the V_5 and V_(10) were higher. The D_(max) of the spinal cord using IMRT was all lower than that using CRT. Conclusions IMRT is better than CRT in target cov-erage, conformity, homogeneity and normal tissue sparing, especially in protecting the spinal cord and decrea-sing high-dose lung volume,though the low-dose lung volume is higher. Seven-field IMRT technique for man-de-field radiotherapy is recommanded. Key words: Lymphoma/conventional radiotherapy; Lymphoma/intensity modulated radiothera-py; Treatment planning system; Dosimetry

2379: Can IMRT Spare Carotid Vessels in Patients With Head and Neck Cancer?

Several studies have indicated that radiotherapy (RT) to the neck increases the risk of carotid stenosis and stroke. Because of improved target volume coverage and reduced dose to critical structures, IMRT has been widely accepted as a better treatment modality for head and neck cancer than conventional RT (CRT). IMRT plans contain more dose heterogeneity within the tumor volume than CRT plans. Since the carotids are often included in the treatment volume, it is essential to understand the impact of IMRT on carotid dose.

SU-FF-T-38: A New Software Tool for Plan Analysis and Comparison

Purpose: To develop a simple software tool which allows quantitative analysis and comparison of multiple treatment plans using physical and biological parameters. Method and Materials: When comparing multiple IMRT and/or conventional radiotherapy plans, it is often difficult to choose the best plan by visual inspection of DVHs and associated statistics such as “hot spots” and “cold spots”. Comparison of multiple rival IMRT and 3D plans can become a cumbersome process, particularly if different planning systems are used for each. To overcome these problems, we developed a Java-based software tool called MPACT (Multi-parameter Plan Analysis and Comparison Tool) to evaluate treatment plans using physical and biological parameters. MPACT directly imports patient and DVH information from the treatment planning system(s) and calculates gEUD (generalized Equivalent Uniform Dose), HI (Homogeneity Index), and CI (Conformity Index). The user may import as many plans as desired and compare these parameters for all plans on one screen. Results: MPACT has been used to assess the clinical advantage of breast IMRT for the first 10 patients treated at our center. While DVH analysis did not often reveal significant differences or provide an easy means for quantitative comparison, MPACT revealed that IMRT provided an 8% increase in the average target gEUD, 3% and 1% decreases in lung and heart gEUD, respectively, and a 3% increase in the average HI and CI in comparison to conventional compensator plans. Conclusion: MPACT provides a convenient mechanism for plan comparison for any treatment site, and facilitates an objective, quantitative decision-making process. It has proven to be a valuable tool for comparison of conventional and IMRT radiotherapy plans or multiple competing IMRT plans. The addition of TCP and NTCP calculation functionality is currently underway, and MPACT will ultimately serve as a platform for a plan optimization system using these calculated parameters.

SU‐FF‐J‐17: Accuracy and Dosimetric Advantage of Target Localization Using Stereoscopic Image‐Guided Radiotherapy for Lung Cancer Treatment

Purpose: We analyzed the accuracy of stereoscopic image‐guided radiotherapy (S‐IGRT) with the ExacTrac® system (BrainLAB AG, Heimstetten, Germany), and demonstrated the dosimetric advantage for lung cancer treatment. Methods: The accuracy of target localization using the ExacTrac system was analyzed by re‐scanning ten patients immobilized in the Vac‐loc bag with BB tags put on the isocenter marks determined by the ExacTrac system. The re‐scanned CT data from each patient was fused and compared to the isocenter locations on the original CT used for the treatment planning. The Active Breathing Coordinator™ (Elekta, Norcross, GA) was employed to minimize the breathing motion effect on S‐IGRT. The dosimetric advantage of S‐IGRT was demonstrated by comparing the normal lung volume receiving 15%, 30% and 50% of the prescription dose (V15%, V30% and V50%) between the plans with smaller margins in the S‐IGRT and those with normal margins in the conventional radiotherapy for the ten patients. Results: The average isocenter shifts using S‐IGRT were within 3.4 ±1.7mm in the lateral, 3.6±1.9mm in the anterior/posterior, and 2.2±3.2mm in the superior/inferior directions. The added margins around the CTV to create the PTV were chosen to be 10mm in the superior/inferior and 5mm in radial direction for the lung cancer treatment planning in S‐IGRT. For the ten patients with CTV volume from 8.3cm3 to 43.4cm3 and lung volume from 2736cm3 to 3640cm3, the averages of V15%, V30% and V50% were 17.4%, 9.8%, 5.9% for the S‐IGRT plans, and 33.4%, 18.2%, 12.8% for the conventional radiotherapy plans with 2cm margins in the all directions. Conclusion: The S‐IGRT with the ExacTrac system provided highly accurate tumor localization. The margins from CTV to PTV in S‐IGRT treatment planning could be reduced significantly due to the accurate target localization which will reduce the lung volume receiving doses in the medium and low ranges.

LQ-Based Model for Biological Radiotherapy Planning

Despite the increasing accumulation of radiobiological data, radiotherapy planning does not take into account the α/β values of normal irradiated tissues. The importance of the fact that the dose per fraction outside the 100% isodose area is not at all identical to the one inside the tumor area is also underestimated. Altered fractionation regimens further complicate the reliability of the conventional radiotherapy plans. In this study we report a theoretical application of the Macejewski’s concept of “normalised total dose” that could make feasible the integration of α/β and dose per fraction values in everyday radiotherapy practice. The concept of cumulative normalised total dose permits the preparing of radiotherapy plans with normalised isodose areas (the cumulative isodose area maps) for chosen ranges of radiation normalised doses. The effect of overall treatment time and interfraction interval is also taken into account. The present study suggests some guidelines that could be of value for the elaboration of a computer program for biological radiotherapy planning.