Biologically Effective Uniform Dose Research Articles

SU‐E‐T‐488: Secondary Malignancy Risks in Lung Cancer Radiotherapy with Helical Tomotherapy, Intensity Modulated Radiotherapy, and Conformal Radiotherapy

Purpose: The aim of the study is to examine the risk of inducing secondary malignancies in association with the clinical effectiveness of treatment plans in terms of tumor control and normal tissue complication probabilities. Methods: Four patients having been treated for lung cancer were examined. For each of them, three treatment plans were developed based on the Helical Tomotherapy (HT), MLC‐based Intensity Modulated Radiation Therapy (IMRT), and 3D‐Conformal Radiation Therapy (CRT) radiation modalities. The different plans were evaluated using the complication‐free tumor control probability (P+), the overall probability of injury (PI), the overall probability of control/benefit (PB), and the biologically effective uniform dose (BEUD). The risks for secondary malignancies in the spinal cord, heart and contra‐lateral lung were calculated for the three radiation modalities. Results: Regarding the overall evaluation of the different radiation modalities based on the P+ index, the average values of the HT, IMRT and CRT are 67.3%, 61.2% and 68.2%, respectively. The corresponding average values of PB are 75.6%, 70.5% and 71.0%, whereas the average values of PI are 8.3%, 9.3% and 2.8%, respectively. Regarding the risk for secondary cancer, for spinal cord the CRT modality produces the lowest average risk (1.4%) compared with the HT (2.1%) and IMRT (1.6%) radiation modalities. In heart, the lowest average risk is produced by IMRT (3.8%) compared with the HT (5.1%) and CRT (4.7%), whereas the three radiation modalities show almost equivalent results regarding the contra‐lateral lung (0.8% for HT, 0.9% for IMRT and 0.9% for CRT, respectively). Conclusion: The plans that appear to be more effective for the treatment are prone to show the highest risk of secondary malignancy. Radiobiologically‐based treatment planning taking into account the risk of secondary cancer can be established as an effective clinical tool for treatment optimization.

SU-E-T-299: Sensitivity Analysis of the Radiobiological Parameters Used to Examine the Effectiveness of Different Fractionation Schedules in Prostate Cancer HDR Brachytherapy

Purpose: The aim of the present study is to evaluate the robustness of the effectiveness of different fractionation schemes of HDR brachytherapy (to be applied as monotherapy for low-risk prostate cancer) by using radiobiological models and dosimetric measures. Methods: In this study, the treatment plans of 12 patients who had undergone clinical implants for HDR brachytherapy of prostate cancer were evaluated using the response probabilities of the individual organs, the complication-free tumor control probability (P+), the total tumor control probability (PB), the total normal tissue complication probability (PI), the biologically effective uniform dose (BEUD) and the generalized equivalent uniform dose (gEUD) as measures. These indices use the D50, γ, s, α/β and alpha radiobiological parameters together with the corresponding tissue DVH data. The values of those parameters were varied around their reference values in order to examine the impact of their uncertainty on the values of the radiobiological measures in the evaluation of four fractionation schemes. Results: For the four examined fractionation schemes, the tumor control probabilities are 98.5% in 1×20Gy, 98.6% in 2×14Gy, 97.5% in 3×11Gy and 97.8% in 4x9.5Gy. The corresponding total normal tissue complication probabilities are 9.7% in 1×20Gy, 14.6% in 2×14Gy, 11.5% in 3×11Gy and 15.6% in 4×9.5Gy. The complication-free tumor control probabilities are 88.8% in 1x20Gy, 83.9% in 2×14Gy, 86.0% in 3×11Gy and 82.3% in 4×9.5Gy. The sensitivity analysis showed that the values of P+, PB, PI and BEUD varied by 6.1–7.3%, 5.8–9.3%, 5.6–7.2% and 7.6–9.0 Gy, respectively. Conclusion: The present analysis indicates that among the fractionation schemes of 1×20Gy, 2×14Gy, 3×11Gy and 4×9.5Gy the first scheme is more effective. The sensitivity analysis shows that the variation of the radiobiological parameters considerably affects the values of the response indices, especially the α/β parameter.

Complication probability model for subcutaneous fibrosis based on published data of partial and whole breast irradiation

PurposeTo extend the application of current radiation therapy (RT) based normal tissue complication probability (NTCP) models of radiation-induced fibrosis (RIF) of the breast to include the effects of fractionation, inhomogeneous dose, incomplete recovery, and time after the end of radiotherapy in partial breast irradiation (PBI). Materials and methodsAn NTCP Lyman model with biologically effective uniform dose (BEUD) with and without a correction for the effect of incomplete repair was used. The time to occurrence of RIF was also taken into account. The radiobiological parameters were determined by fitting incidences of moderate/severe RIF in published randomized studies on RT of the breast. The NTCP model was used to calculate the risk of toxicity in 35 patients treated with intensity modulated, non-accelerated PBI and the result was compared with observed incidence of RIF. ResultsWith α/β fixed at 3Gy the parameters of the model without correction for incomplete repair extracted from fitting were: 50% complication probability biologically effective dose BEUD50 = 107.2 Gy (95%CI = 95.9–118.6 Gy), volume parameter n = 0.06 (95%CI = 0–0.23), and slope of dose response m = 0.22, (95%CI = 0.20–0.23). After including the correction for incomplete repair with repair halftime for subcutaneous tissue of τ = 4.4 h we obtained BEUD50 = 105.8 Gy (95%CI = 96.9–114.6Gy), n = 0.15 (95%CI = 0–0.33), m = 0.22 (95%CI = 0.20–0.23). Average NTCP predicted by these models, 4.3% and 2.0% respectively, offered a good agreement with RIF incidence in our patients, 5.7%, after an average follow-up of 12 months. ConclusionThe NTCP models of RIF, incorporating the effects of fractionation, volume effect, and latency of toxicity look promising to model PBI. Clinical validation from a prospective PBI treatment study is under development and will help test this preliminary result.

A graphic user interface toolkit for specification, report and comparison of dose–response relations and treatment plans using the biologically effective uniform dose

A toolkit (BEUDcal) has been developed for evaluating the effectiveness and for predicting the outcome of treatment plans by calculating the biologically effective uniform dose (BEUD) and complication-free tumor control probability. The input for the BEUDcal is the differential dose-volume histograms of organs exported from the treatment planning system. A clinical database is built for the dose–response parameters of different tumors and normal tissues. Dose–response probabilities of all the examined organs are illustrated together with the corresponding BEUDs and the P + values. Furthermore, BEUDcal is able to generate a report that simultaneously presents the radiobiological evaluation together with the physical dose indices, showing the complementary relation between the physical and radiobiological treatment plan analysis performed by BEUDcal. Comparisons between treatment plans for helical tomotherapy and multileaf collimator-based intensity modulated radiotherapy of a lung patient were demonstrated to show the versatility of BEUDcal in the assessment and report of dose–response relations.

SU-FF-T-508: Utilizing Radiobiological Measures and Planned Adaptive Software to Evaluate Adaptive Tomotherapy Plans for Lung Cancer Patients

Purpose: To evaluate the radiobiological effects of the adaptive tomotherapy using the biologically effective uniform dose (BEUD) in addition to physical dose indices assessed by the Planned Adaptive software.Method and Materials: Three lungcancer patients who underwent helical tomotherapy were selected retrospectively. Daily megavoltage computed tomography (MVCT) scans were performed and registered with the planning kilovoltage CT (kVCT) images to correct the patient setup and internal organ motions. Evaluation on delivered dose in each treatment fraction of the tomotherapy was performed using the Planned Adaptive software. The cumulative dose difference between the planned total dose (i.e. fraction number × fraction dose) and the cumulative delivered dose was calculated. Among these three patients, one patient had two‐phase tomotherapy plans. The two‐phase tomotherapy of this patient contains the original plan and a second‐phase plan, which is made because of the obvious tumor shrinkage in the target observed during the treatment course and concern about high cumulative dose to the ipsilateral lung. The second‐phase tomotherapy plan of this patient could be deemed as an adaptive tomotherapy plan. Therefore, further investigation was performed to evaluate physical dose difference using DVH and incremental clinical effectiveness by the radiobiological index, BEUD. Results: The dose ratio between the planned and the delivered doses for the tomotherapy plans remained consistent (varied within 1%) for two patients without adaptive tomotherapy. However, there was a considerable increase in the delivered dose ratio of the second‐phase tomotherapy. Furthermore, significant rise in complication‐free tumor control rate (P +) of 15% in the second‐phase tomotherapy plan indicates the clinical effectiveness of the adaptive tomotherapy. Conclusion: The dosimetric impact and the clinical effect of the adaptive tomotherapy have been evaluated using the Planned Adaptive software plus the BEUD. The dosimetric effect of the adaptive tomotherapy planning was quantified into significant increase of P +

SU‐FF‐T‐99: Impact of Proper Bladder and Rectum Delineation in the Evaluation of the Effectiveness of IMRT in Prostate Cancer Radiotherapy

Purpose This study compares and evaluates different bladder and rectum delineation approaches using IMRT plans for prostate cases. A more comprehensive treatment plan evaluation can be performed using the biologically effective uniform dose (BEUD) together with the complication‐free tumor control probability (P+). Materials and Methods A single physician outlined the prostate planning target volume (PTV), rectum, bladder and femoral heads of 10 consecutive prostate patients. IMRT treatment plans were created with the Pinnacle treatment planning system (TPS). Two different bladder and rectum delineation approaches were examined. In the first approach the whole volume of bladder and rectum were delineated, whereas in the second approach, the delineation included only the volume of the organs lying in the range of 2 margins around the PTV. In the second case, the DVHs were normalized to their volume (2std normalized) and to the volume of the whole organ (2std relative to whole). Results At the optimum dose levels of the dose distributions using the whole volume of bladder and rectum, 2 std relative to the whole volume and 2 std normalized, respectively, the P+ is 67.7%, 51.2% and 32.7% for a BEUDPTV of 86.7 Gy, respectively. The respective total control probabilities, PB are 89.0%, 82.4% and 82.4% whereas the corresponding total complication probabilities, PI are 21.3%, 31.2% and 49.7%. More specifically, the response probabilities of the different tissues are 89.0%, 82.4% and 82.4% for the PTV, 0.0%, 0.0% and 0.01% for bladder and 21.3%, 31.2% and 49.7% for rectum. At the initially prescribed dose level (mean dose to the PTV = 79.4 Gy) the PI values become 6.7%, 12.4% and 27.8%. Conclusions The expected radiation induced bladder and rectum complications using different delineation approaches, should be estimated used appropriate dose‐response parameters, which should have been determined from studies of similar organ delineation methodology.

SU-GG-T-420: Radiobiological-Based Comparisons Among Conventional Radiotherapy and IMRT Delivery Techniques for Prostate Treatment Planning

Purpose: To apply biologically effective uniform dose (BEUD) calculation on prostate treatment plans developed using conventional radiotherapy and three IMRT techniques. Method and Materials: Ten prostate patients were chosen to be analyzed both physically and biologically. Conventional plans were developed using the four‐beam box and 3DCRT techniques for both 6MV and 18MV photon beams on Pinnacle3 treatment planning system. IMRT plans were constructed using the MLC‐based step‐and‐shoot IMRT technique (P3 IMRT) for both photon energies on Pinnacle3 treatment planning system. Plans for helical tomotherapy (HT) and serial tomotherapy were also made using the HiArt TomoTherapy and the Corvus6.3 treatment planning systems, respectively. Doses to the targets were normalized to assure that 95% of the PTV received 76Gy. For each prostate case, radiobiological measures were applied to comprehensively evaluate the suitability of four‐beam box treatment plans, 3DCRT plans and P3 IMRT plans developed using different photon beam energies. In addition, BEUD together with complication‐free tumorcontrol probability (P+) were calculated to compare plans with different delivery modalities. Results: 18MV photon beams delivered in conventional radiotherapy and IMRT plans, in general, resulted in higher P+ than 6MV beams. When applying RTOG0415 dose criteria to all plans, 3DCRT plans had a higher P+ of 37% than IMRT plans (25.8% for P3 IMRT and 29.2% for HT). By putting on stricter dose constraints to IMRT plans, higher P+ of 38.2% for P3 IMRT and 30.5% for HT were achieved. Conclusion: BEUD calculation provides a comprehensive evaluation on treatment plans with different delivery modalities. From results of radiobiological analysis, there were insignificantly different dose responses found between 6MV and 18MV treatment plans delivered using 3DCRT, four‐beam box and P3 IMRT techniques for prostate radiotherapy. Moreover, when comparing different treatment methodologies using radiobiological measures, IMRT plans turned out not necessarily superior to conventional treatment plans.

SU‐GG‐T‐431: Radiobiological Evaluation On the Four‐Dimensional Stereotactic Radiotherapy Plan

Purpose: To evaluate the four‐dimensional (4D) stereotactic radiotherapy plan for the lung patient using biologically effective uniform dose (BEUD) and to compare this 4D treatment plan with MLC‐based intensity modulated radiation therapy (IMRT) plans for fixed respiratory phases. Method and Materials: One patient with lung cancer, who was previously treated with stereotactic body radiotherapy (SBRT), was chosen to re‐planned with the 4D stereotactic radiotherapy technique using the Pinnacle3 treatment planning system. The 4D treatment plan was developed based on a set of 4DCT images divided into ten respiratory phases. Doses to the target were prescribed as 3 fractions of 16 Gy to 95% of planning target volume (PTV). BEUD calculation was performed to evaluate the final composite 4D dose distribution. Results: For this dose prescription, the complication‐free tumor control probability, P+ value, is 78.6% for the 4D stereotactic plan with a mean dose of 49.9 Gy to PTV and the BEUD of 49.9 Gy as well. The total control probability, PB, is 98.5% and the total complication probability, PI, is 20% due to high maximum dose to the lung, which is proximal to the PTV. When compared with fixed‐phase IMRT plans, the dose distributions were very similar; the P+ value of the 4D plan, however, was higher, but was not substantially different from values of fixed‐phase plans. Conclusion: From our radiobiological analysis of this lung SBRT case, the 4D plan was superior, but not significant improved from MLC‐based IMRT plans for fixed phases. Not only the mean doses to PTV of these plans were very close, but also were P+ and BEUDs of these plans. Dose distributions of the 4D plan can be further optimized to a maximum P+ of 86.5% when achieving BEUDB of 42.95 Gy by sparing the lung to make PI reach as low as 7.2%.

SU‐GG‐T‐429: Dose‐Mass‐Histogram (DMH) Vs. Dose‐Volume Histogram (DVH) in Predicting Lung Complications

Purpose: In radiotherapy for breast cancer, it is very important to estimate the expected lung complications. In this study, it is examined whether the Dose Mass Histogram (DMH) concept can be better associated with the expected lung complications than the widely used Dose Volume Histogram (DVH) concept. Method and Mataerials: The problem was investigated theoretically by applying two hypothetical dose distributions (Gaussian and Semi‐Gaussian shaped) on two lungs of uniform and varying densities. Furthermore, a group of breast cancer patients was used to clinically quantify the difference between DVHs and DMHs. These patients were treated with resection and irradiation with two tangential fields. The influence of the deviation between DVHs and DMHs on the clinical endpoint of radiation pneumonitis is estimated by using the Relative Seriality and LKB models. The biological equivalent of the corresponding difference in their mean doses was estimated by the Biologically Effective Uniform Dose (BEUD) and Equivalent Uniform Dose (EUD) concepts, respectively. Results: The relation of the DVHs and DMHs varies depending on the underlying cell density distribution and the applied dose distribution. The range of their deviation in terms of expected clinical outcome was large both for the theoretical and the clinical studies. For the group of patients, according to the DVH, lung receives 9.82 Gy, whereas according to the DMH it receives 8.06 Gy (1.76 Gy difference). Interpreting these figures in terms of lung response, DVH gives 0.30% probability for lung complications compared to 0.10% given by DMH for the Relative Seriality model. Similarly, for the LKB model the corresponding values are 2.62% and 1.85%, respectively. Conclusion: Concluding, the expected lung complications appear to be overestimated when using the DVH concept, whereas the effectiveness of the dose distribution is closer related to the radiation effects when using the DMH concept.

SU‐GG‐T‐423: Radiobiological Comparison of Helical Tomotherapy and MLC‐Based IMRT for Brain and Cranio‐Spinal Tumors

Purpose: In order to estimate better the clinical effectiveness of the Helical Tomotherapy and MLC‐based IMRT radiation modalities a radiobiological assessment was performed. This was achieved by employing additional physical and radiobiological criteria. Method and Materials: Two brain and cranio‐spinal cancers were investigated. For each cancer type, a linac MLC‐based step‐and‐shoot IMRT plan and a Helical Tomotherapy plan were developed. The treatment plans of the MLC‐based IMRT were developed on the Philips treatment planning station (Pinnacle 7.6 software release), whereas the dedicated Tomotherapy treatment planning station was used for the HT plans. The different treatment plans were compared using dosimetric criteria and the biologically effective uniform dose (BEUD) together with the complication‐free tumor control probability (P+). Results: The applied plan evaluation method shows that in the brain cancer case the HT treatment gives similar results with the MLC‐based IMRT (P+ of 66.0% and 63.4%, respectively). The total control probabilities, PB are 79.5% and 76.6%, whereas the total complication probabilities, PI are 13.4% and 13.1%. In both cases, the dose limiting tissue is the Speech Area. In the cranio‐spinal cancer case, the HT treatment plan is much better than the MLC‐based IMRT plan with P+ values of 84.1% and 28.4%, respectively. The PB values are 86.4% and 51.3%, whereas the PI values are 2.3% and 23.0%. In the case of HT, the lung is the dose limiting tissue (1.7%) whereas in the case of MLC‐based IMRT the dose limiting tissues are the lung (8.1%) and the left kidney (14.2%). Conclusion: Both MLC based‐IMRT and HT are suitable for treating often large PTVs while minimizing the volume of the organs at risk receiving high dose. However, in certain more complex clinical cases the HT radiation modality may show clearly better properties in producing very conformal and clinically effective dose distributions.

WE-C-AUD C-07: Expected Clinical Impact of the Differences Between Planned and Delivered Dose Distributions in Helical Tomotherapy

Purpose: To investigate the effectiveness of highly conformal radiation modalities in conjunction with a patient setup correction method, Helical Tomotherapy (HT) was employed using the Helical Megavoltage CT (MVCT) scanner of the tomotherapy unit. Any discrepancy between the planned and delivered dose distributions would likely affect the clinical outcome. Method and Materials: The case of a head and neck cancer was used to evaluate the accuracy of dose delivery. The right parotid, left parotid and spinal cord are the primary organs at risk proximal to the target volume. MVCT images were taken before and after the patient setup correction. MVCT images of the patient were acquired daily. The three dose distributions (planned, with and without patient setup correction) were compared by using the complication‐free tumor control probability (P +) and the biologically effective uniform dose (BEUD) concepts. Results: For the computerized treatment plan, the maximum value of P + is 88.3%, the total control probability, P B is 97.3% and the total risk for complications, P I is 9.3%. For the delivered dose distribution without patient setup correction, the value of P + is 79.8% and the probabilities P B and P I are 83.6% and 3.8%, respectively. Finally, for the delivered dose distribution with patient setup correction in every fraction the value of P + is 87.2% and the probabilities P B and P I are 92.7% and 5.5%, respectively. The expected clinical effectiveness dropped by a ΔP + of 1.1% and 8.5% in the cases with and without patient setup correction. Conclusion: Highly conformal treatment plans can deliver higher doses to the target allowing for increased control rates for the same or a reduced risk for complications. The results show that the effectiveness of the applied dose distribution drops between the treatment plan and the dose delivery with and without patient setup correction.

SU‐GG‐T‐425: Radiobiologically Quantified Treatment Setup Uncertainties Based On Megavoltage (MV) CT Imaging

Purpose: To evaluate and compare the expected effectiveness of the planned and delivered dose distributions in prostate cancer radiotherapy. The average setup uncertainties were determined by using the on‐board megavoltage computed tomography (MVCT) capabilities of the tomotherapy HiArt unit. Method and Materials: Co‐registrations between daily MVCT and planning CT were used. Before the delivery of each treatment an MVCT image was acquired. The therapists registered the MVCT image with the planning kilovoltage computed tomography (kVCT) images. The registration criteria were based on bony anatomy and contoured regions of interest. For a typical prostate cancer patient the dose distributions of the Helical Tomotherapy plan and that of the average shifted delivery registration were used. The dose distributions were compared based on dosimetric criteria and the biologically effective uniform dose (BEUD) together with the complication‐free tumor control probability (P+). Results: The average shifts that were observed are 10.7 mm for the vertical, 4.0 mm for the longitudinal and 0.5 mm for the lateral directions, respectively. At the optimum dose levels of the planned and delivered dose distributions, the P+ values are 84.7% and 84.0%, respectively. The total control probabilities, PB are 93.0% and 92.9%, whereas the total complication probabilities, PI are 8.3% and 8.9%. More specifically, the response probabilities of the different tissues are 95.6% and 95.5% for the GTV, 97.4% and 97.3% for the seminal vesicles, 0.8% and 0.7% for bladder and 7.6% and 8.3% for rectum. Conclusion: It is shown that the intra‐fraction movement of tumors can be reduced by using the MVCT co‐registration. This appears to be a powerful tool, which can result in improved sparing of critical structures, while delivering high doses to the target. The use of P+ — BEUD diagrams to compare similar treatment plans may show that in radiobiological terms they may be quite different.

SU-GG-T-421: Radiobiological Optimization of Breast Cancer Radiotherapy Taking Into Account Patient Positioning, Breathing and Radiation Pneumonitis Scoring

Purpose: Significant discrepancies in dose delivery can contribute to underdosage of the tumor or overdosage of normal tissue. To study the impact of patient positioning and internal organ motion in breast cancerradiotherapy, the setup and breathing uncertainties characterizing three different irradiation techniques are employed. Method and Materials: Fifteen breast cancer patients (5 resected with negative nodes (R−), 5 resected with positive nodes (R+) and 5 ablated), who were treated with three different irradiation techniques are examined. The positioning uncertainties in the anteroposterior (AP) and the craniocaudal (CC) directions are approximated by Gaussian distributions and breathing is assumed to be linear. The combined frequency distributions of the positioning and breathing distributions are obtained by convolution. The three radiation techniques are compared by using the complication‐free tumorcontrol probability, P + and the biologically effective uniform dose (BEUD). Results: For the R− case, at the optimum dose levels of the two dose distributions, the P + values are 97.9% and 97.3%, respectively. The respective total control probabilities, P B are 99.3% and 99.1%, whereas the corresponding total complication probabilities, P I are 1.4% and 1.8%. For the R+ case, the P + values are 94.2% and 93.0%, respectively. The P B values are 97.5% and 96.3%, whereas the P I values are 3.3% and 3.3%. For the Ablation case, the P + values are 96.9% and 89.4%, respectively. The P B values are 99.0% and 96.5%, whereas the P I values are 2.1% and 7.2%. In this case, for lungradiation pneumonitis Grade 1–2 the P + values would change to 69.3% and 37.7%, respectively. Conclusion: The combined effects of positioning uncertainties and breathing motion can introduce a significant deviation between the planned and delivered dose distributions to the lung in breast cancerradiotherapy. This inaccuracy in the delivered dose may lead to a significant underestimation of the expected lung complications.

SU‐GG‐T‐430: Radiobiological Investigation of the Dosimetric Effects of Daily Megavoltage CT Registration Techniques On Adaptive Radiotherapy with Helical Tomotherapy

Purpose: Pre‐treatment patient repositioning in highly conformal radiotherapy modalities is a prerequisite for reducing setup uncertainties. A MVCT image set has to be acquired to account for daily changes in the patient's internal anatomy and setup position. This study aims to investigate the expected effect of patient setup correction with the Hi‐Art tomotherapy system by using radiobiological measures. Method and Materials: Using the Planned Adaptive module (tomotherapy, Inc, Madison, WI), eventual dose discrepancies can be evaluated and corrected. In this study, patients treated for lung, pancreas and prostate carcinomas by Helical Tomotherapy plans are evaluated. In each cancer case, two dose distributions with and without patient setup correction were calculated using the MVCT image sets and they were evaluated using the complication‐free tumor control probability (P+) and biologically effective uniform dose (BEUD) concepts. Results: For the lung cancer case, at the optimum dose levels of the two dose distributions, the P+ value is 57.6% and 56.8% for a BEUDITV of 64.8 Gy, respectively. The respective total control probabilities, PB are 78.1% and 78.1%, whereas the corresponding total complication probabilities, PI are 20.5% and 21.3%. For the pancrease cancer case, the P+ value is 95.0% for a BEUDITV of 67.9 Gy and 97.5% for a BEUDITV of 69.9 Gy, respectively. The respective PB values are 97.8% and 98.7%, whereas the PI values are 2.9% and 1.2%. For the prostate cancer case, the P+ value is 57.7% for a BEUDITV of 90.2 Gy and 55.9% for a BEUDITV of 90.6 Gy, respectively. The respective PB values are 83.7% and 84.7%, whereas the PI values are 26.1% and 28.8%. Conclusion: According to our results, patient setup corrections during registration are adequate to produce the necessary target localization. Clinical cases, which look dosimetrically similar, can be quite different in radiobiological terms.

746 Poster Biologically effective uniform dose for appropriate dose prescription and treatment plan comparison

746 Poster Biologically effective uniform dose for appropriate dose prescription and treatment plan comparison