Dependence of Induced Biological Damage on the Energy Distribution and Intensity of Clinical Intra-Operative Radiotherapy Electron Beams.

The survival fraction of epithelial HaCaT cells was analysed to assess the biological damage caused by intraoperative radiotherapy electron beams with varying energy spectra and intensities. These conditions were achieved by irradiating the cells at different depths in water using nominal 6 MeV electron beams while consistently delivering a dose of 5 Gy to the cell layer. Furthermore, a Monte Carlo simulation of the entire irradiation procedure was performed to evaluate the molecular damage in terms of molecular dissociations induced by the radiation. A significant agreement was found between the molecular damage predicted by the simulation and the damage derived from the analysis of the survival fraction. In both cases, a linear relationship was evident, indicating a clear tendency for increased damage as the averaged incident electron energy and intensity decreased for a constant absorbed dose, lowering the dose rate. This trend suggests that the radiation may have a more pronounced impact on surrounding healthy tissues than initially anticipated. However, it is crucial to conduct additional experiments with different target geometries to confirm this tendency and quantify the extent of this effect.

Evaluation of a high resolution diode array for CyberKnife quality assurance.

PURPOSE: The CyberKnife quality assurance (QA) program relies mainly on the use of radiochromic film (RCF). We aimed at evaluating high-resolution arrays of detectors as an alternative to films for CyberKnife machine QA. METHODS: This study will test the SRS Mapcheck (Sun Nuclear, Melbourne, Florida, USA) diode array and its own software, which allows three tests of the CyberKnife QA program to be performed. The first one is a geometrical accuracy test based on the delivery of two orthogonal beams (Automated Quality Assurance, AQA). Besides comparing the constancy and repeatability of both methods, known errors will be introduced to check their sensitivity. The second checks the constancy of the iris collimator field sizes (Iris QA). Changes in the field sizes will be introduced to study the array sensitivity. The last test checks the correct positioning of the multileaf collimator (MLC). It will be tested introducing known systematic displacements to whole banks and to single leaves. RESULTS: The results of the RCF and diode array were equivalent (maximum differences of 0.18 ± 0.14 mm) for the AQA test, showing the array a higher reproducibility. When known errors were introduced, both methods behaved linearly with similar slopes. Regarding Iris QA, the array measurements are highly linear when changes in the field sizes are introduced. Linear regressions show slopes of 0.96-1.17 with r2 above 0.99 in all field sizes. Diode array seems to detect changes of 0.1 mm. In MLC QA, systematic errors of the whole bank of leaves were not detected by the array, while single leaf errors were detected. CONCLUSIONS: The diode array is sensitive and accurate in the AQA and Iris QA tests, which give us the possibility of substituting RCF with a diode array. QA would be performed faster than using the film procedure, obtaining reliable results. Regarding the MLC QA, the inability to detect systematic displacements make it difficult to confidently use the detector.

The use of a thin guide-wire for urethral definition in prostate SBRT treatments with Cyberknife.

PURPOSE: To study and analyze the effect of the use of a thin guide-wire instead of a Foley catheter for urethral definition in prostate stereotactic body radiation therapy (SBRT) treatments and to compare treatment parameters in both situations. MATERIAL AND METHODS: Thirty-seven prostate SBRT patients were employed in this study. A Foley catheter was employed in nine of them, and a guide-wire was employed in the other 28 patients. For each of the 28 patients in which the guide-wire was employed, a comparison between urethral positions in both situations was performed, allowing for a margin definition of the urethra when a Foley catheter was employed. Displacements of the prostate during treatment were obtained, allowing for an analysis of prostate positions in both situations. Also, different treatment parameters such as the number of treatment interruptions, couch movements performed, and x-rays needed were gathered. RESULTS: Large differences between urethral positions can be found in the anterior-posterior (AP) directions compared to those in the lateral (LAT) direction. Differences are also larger in areas closer to the base of the prostate, where margins applied in the case of using a Foley catheter are 16 mm with a mean displacement of 6 mm in the posterior direction. No differences in the treatment parameters were found during treatment in both situations. The difference found in absolute prostate pitch rotations suggests that the Foley catheter provokes a shift of the prostate position, which does not occur when employing the guide-wire. CONCLUSIONS: Foley catheters shift the urethral position, making them a wrong surrogate of the urethra when no catheters are present. The margins needed to assess uncertainties introduced by the use of a Foley catheter are larger than those usually applied. The use of a Foley catheter did not present any additional difficulty during treatment delivery in terms of images employed or interruptions produced.

Definition of internal target volumes based on planar X-ray fluoroscopic images for lung and hepatic stereotactic body radiation therapy. Comparison to inhale/exhale CT technique.

PURPOSE: To compare tumor motion amplitudes measured with 2D fluoroscopic images (FI) and with an inhale/exhale CT (IECT) technique MATERIALS AND METHODS: Tumor motion of 52 patients (39 lung patients and 13 liver patients) was obtained with both FI and IECT. For FI, tumor detection and tracking was performed by means of a software developed by the authors. Motion amplitude and, thus, internal target volume (ITV), were defined to cover the positions where the tumor spends 95% of the time. The algorithm was validated against two different respiratory motion phantoms. Motion amplitude in IECT was defined as the difference in the position of the centroid of the gross tumor volume in the image sets of both treatments. RESULTS: Important differences exist when defining ITVs with FI and IECT. Overall, differences larger than 5 mm were obtained for 49%, 31%, and 9.6% of the patients in Superior-Inferior (SI), Anterior-Posterior (AP), and Lateral (LAT) directions, respectively. For tumor location, larger differences were found for tumors in the liver (73.6% SI, 27.3% AP, and 6.7% in LAT had differences larger than 5 mm), while tumors in the upper lobe benefitted less using FI (differences larger than 5 mm were only present in 27.6% (SI), 36.7% (AP), and 0% (LAT) of the patients). CONCLUSIONS: Use of FI with the linac built-in CBCT system is feasible for ITV definition. Large differences between motion amplitudes detected with FI and IECT methods were found. The method presented in this work based on FI could represent an improvement in ITV definition compared to the method based on IECT due to FI permits tumor motion acquisition in a more realistic situation than IECT.

On the use of Bayesian statistics in the application of adaptive setup protocols in radiotherapy.

PURPOSE: To propose adaptive setup protocols using Bayesian statistics that facilitate, based on a prediction of coverage probability, making a decision on which patients should follow daily imaging prior to treatment delivery. MATERIALS AND METHODS: The suitability of the treatment margins was assessed combining interfraction variability measurements of the first days of treatment with previous data gathered from our patient population. From this information, we decided if a patient needs an online imaging protocol to perform daily isocenter correction before each treatment fraction. We applied our method to five different datasets. Protocol parameters were selected from each dataset based on coverage probability, the expected imaging workload of the treatment unit, and the accuracy of patient classification. Time trends were assessed and included in the proposed protocols. To validate the accuracy of the protocols, they were applied to a validation dataset of prostate cancer patients. RESULTS: Adaptive setup protocols lead expected population coverage >97% in all datasets analyzed when time trends were considered. The reduction in imaging workload ranged from 40% in lung treatments to 28.5% in prostate treatments. Results of the protocol on the validation dataset were very similar to those previously predicted. CONCLUSIONS: The adaptive setup protocols based on Bayesian statistics presented in this study enable the optimization of imaging workload in the treatment unit ensuring that appropriate dose coverage remains unchanged.

Predictive value of PAK6 and PSMB4 expression in patients with localized prostate cancer treated with dose-escalation radiation therapy and androgen deprivation therapy.

PURPOSE: The present study analyzed the expression by immunochemistry of the novel markers P21-activated protein kinase 6 (PAK6) and proteasome beta-4 subunit (PSMB4) in men with localized prostate cancer (PC) who were treated with dose-escalation radiotherapy (RT) and androgen deprivation therapy. MATERIALS AND METHODS: Between 1996 and 2004, a cohort of 129 patients with PC who underwent diagnostic biopsies pretreatment and 24 to 36 months following RT were enrolled in this study. Suitable archival diagnostic tissue was obtained from 89 patients. Median follow-up was 129 months (48-198). Correlation analysis was done to assess association between PAK6 and PSMB4 expression and clinical outcome. RESULTS: PAK6 and PSMB4 were expressed in the cytoplasm in 62% and 96.7% of diagnostic biopsies, respectively. Increased staining for PAK6 was significantly (P = 0.04) correlated with higher Gleason scores. In the multivariate analysis, the intensity of PSMB4 staining was an independent predictor of local relapse (hazard ratio = 8.6, P = 0.04). CONCLUSIONS: To our knowledge, this is the first description of PAK6 and PSMB4 expression in the diagnostic specimens of men with PC who were treated with RT. If confirmed by further studies, increased expression of these genes could be used to identify patients at a high risk of developing local failure following high-dose RT, thus better tailoring treatments for the individual patient.

Long-term results of two prospective bladder-sparing trimodality approaches for invasive bladder cancer: neoadjuvant chemotherapy and concurrent radio-chemotherapy.

OBJECTIVE: To report long-term outcomes of selective organ preservation for muscle-invasive bladder cancer (MIBC) using 2 bladder-sparing trimodality approaches. MATERIALS AND METHODS: From 1990 to 2010, 80 patients with T2-T4 bladder cancer were prospectively enrolled in 2 successive bladder-sparing protocols. Forty-one patients were treated with neoadjuvant methotrexate, cisplatin, and vinblastine (MCV) chemotherapy followed by radiotherapy (60 Gy) in complete responders (protocol 1 [P1]) and 39 patients were treated with weekly cisplatin concurrent with radiotherapy (64.8 Gy) (protocol 2 [P2]). RESULTS: The median follow-up was 72 months (range, 9-204 months). Five and 10-year cumulative overall survival for all series were 73% and 60% and the corresponding numbers for cancer-specific survival were 82% and 80%, respectively. Of all surviving patients, 83% maintained their own bladder. Although there were no significant differences in overall survival (P = .820), cancer-specific survival (P = .688) and distant metastasis (P = .417) between protocols, complete response rates (P = .003), and disease-free survival (P = .031) were significantly higher in P2 treatment. CONCLUSION: Trimodality therapy with bladder preservation represents a real alternative to radical cystectomy (RC) in selected patients. Overall survival and cancer-specific survival rates are encouraging with more than 80% of survivors retaining functional bladders.

Sensitivity of a helical diode array device to delivery errors in IMRT treatment and establishment of tolerance level for pretreatment QA.

The aim of this study is to determine the gantry angle and multileaf collimator (MLC) gap error-detection threshold of a diode helical array with an inserted micro-ionization chamber in order to use this device for the pretreatment quality assurance (QA) of intensity-modulated radiation therapy (IMRT) treatments. Implications on the dose-volume histograms (DVHs) of the patient treatments will also be considered for the establishment of a QA protocol with a reasonable tolerance level. Three dynamic IMRT HN (head and neck) and prostate treatments were studied. Random and systematic variations of gantry angle and systematic errors in MLC gap width of the clinical treatments were analyzed in order to establish the detection sensitivity of the array. The associated clinical significance was studied introducing the same errors in the treatment plan based on the patients' computed tomography (CT) and calculating the corresponding DVHs. The Gamma (3%/3 mm) presented a 4% variation in failure rate for a rotation error of 1° for both types of treatment. Both systematic and random errors in gantry rotation angle have little effect on the patients' DVHs. MLC gap width errors of 1 mm and 2 mm in the prostate treatments imply a mean variation in isocenter-measured absorbed dose of 2.1% and 4.1%, respectively. In the case of HN, these errors entail a change in measured isocenter dose of 4.7% and 8.6%, respectively. The variation observed in the DVHs of the patients was, basically, a global displacement of the curves proportional to the isocenter dose variation caused by the gap width error. According to the array sensitivity to the analyzed errors and its implication in patient DVHs, a tolerance of 95% point passing rate for the gamma criterion 3%/2 mm and an agreement of 2% in isocenter absolute dose have been established as tolerance criteria for our pretreatment IMRT QA protocol.

Long-term results after high-dose radiotherapy and adjuvant hormones in prostate cancer: how curable is high-risk disease?

PURPOSE: To analyze long-term outcome and prognostic factors for high-risk prostate cancer defined by National Comprehensive Cancer Network criteria treated with high-dose radiotherapy and androgen deprivation in a single institution. METHODS AND MATERIALS: A total of 306 patients treated between 1995 and 2007 in a radiation dose-escalation program fulfilled the National Comprehensive Cancer Network high-risk criteria. Median International Commission on Radiation Units and Measurements radiation dose was 78 Gy (range, 66.0-84.1 Gy). Long-term androgen deprivation (LTAD) was administered in 231 patients, short-term androgen deprivation (STAD) in 59 patients, and no hormones in 16 patients. The Phoenix (nadir plus 2 ng/mL) consensus definition was used for biochemical control. Multivariate analysis was performed to determine the independent prognostic impact of clinical and treatment factors. Median follow-up time was 64 months (range, 24-171 months). RESULTS: The actuarial overall survival at 5 and 10 years was 95.7% and 89.8%, respectively, and the corresponding biochemical disease-free survival (bDFS) was 89.5% and 67.2%, respectively. Fourteen patients (4.6%) developed distant metastasis. Multivariate analysis showed that Gleason score>7 (p=0.001), pretreatment prostate-specific antigen (PSA) level>20 ng/mL (p=0.037), higher radiation dose (p=0.005), and the use of adjuvant LTAD vs. STAD (p=0.011) were independent prognostic factors affecting bDFS in high-risk disease. The 5-year bDFS for patients treated with LTAD plus radiotherapy dose>78 Gy was 97%. CONCLUSIONS: For high-risk patients the present series showed that the use of LTAD in conjunction with higher doses (>78 Gy) of radiotherapy was associated with improved biochemical tumor control. We observed that the presence of Gleason sum>7 and pretreatment PSA level>20 ng/mL in the same patient represents a 6.8 times higher risk of PSA failure. These men could be considered for clinical trials with addition of novel agents.

Post-treatment prostate biopsies in the era of three-dimensional conformal radiotherapy: what can they teach us?

BACKGROUND: The ability to discriminate between therapeutic success and failure after radiotherapy (RT) for prostate cancer (PCa) remains a clinical challenge. Post-treatment biopsies would seem ideal for evaluating innovations such as dose escalation protocols or combination treatments involving brachytherapy or hormones. OBJECTIVE: Correlate post-treatment biopsy results with prostate-specific antigen (PSA) and clinical outcome in PCa patients treated with three-dimensional conformal radiotherapy (3DCRT) in a dose-escalation study. DESIGN, SETTING, AND PARTICIPANTS: This study included 160 patients with clinical stage T1c to T3b PCa treated between 1995 and 2005 in Hospital Universitario la Princesa with 3DCRT who consented to and underwent a transrectal ultrasound (TRUS)-guided prostate biopsy 24-36 mo after RT. The median follow-up was 78 mo (range 27-171 mo). INTERVENTION: The median radiation dose was 74 gray (Gy; range 66.0-84.1). Risk-adapted short-term androgen deprivation (STAD) and long-term androgen deprivation (LTAD) were associated in 25 and 106 patients, respectively. Right and left systematic biopsies were carried out by the same urologist and were examined by a genitourinary pathologist. MEASUREMENTS: Biochemical disease-free survival (bDFS) according to American Society for Therapeutic Radiology and Oncology (ASTRO) 1997 and Phoenix definition criteria as well as histologic control using post-treatment prostate biopsies. RESULTS: Twenty-one percent of patients (34 of 160) had post-treatment-positive biopsies (PB). The 5-yr bDFS according to the Phoenix definition was 87%, 65%, and 92% for the whole series (PB and negative biopsies [NB] patients, respectively [p<0.001]). Multivariate analysis showed that biopsy status at 24-36 mo was an independent predictor of bDFS (p<0.0005) and of clinical failure-free survival (p=0.043). CONCLUSION: The results of the present study show a strong correlation between a post-treatment PB and the 5-yr probability of bDFS, confirming that PSA control can be an adequate surrogate for local control, as assessed by post-treatment biopsies.

Study of the uncertainty in the determination of the absorbed dose to water during external beam radiotherapy calibration.

To achieve a good clinical outcome in radiotherapy treatment, a certain accuracy in the dose delivered to the patient is required. Therefore, it is necessary to keep the uncertainty in each of the steps of the process inside some acceptable values, which implies a global uncertainty as low as possible. This work is focused on the uncertainty evaluation of absorbed dose to water in the routine calibration for clinical beams, in the range of energies used in external radiotherapy. With this aim, different uncertainty components (corrected electrometer reading, calibration factor, beam quality correction factor and reference conditions) associated to beam calibration have been considered. Results show a typical uncertainty in the determination of absorbed dose to water during beam calibration around 1.3% for photon beams and 1.5% for electron beams (k=1 in both cases) when the N(D,w) formalism is used and is theoretically calculated. These values may be different depending on the uncertainty provided by the standards laboratory for calibration factor, which is shown in the work. If the total application of the N(D,w) formalism, that is to say, specific calibrations of each chamber in the user's beam qualities, is taken into account the uncertainty in this step of the process could be placed close to 1.0%. Furthermore, the possibility of an uncertainty reduction with the absorbed dose to water formalism adoption against the air kerma one is discussed.

Is hormone therapy a protective factor for late hematuria after high-dose radiotherapy in prostate cancer?

OBJECTIVES: To identify potential clinical and dosimetric factors predictive of a higher risk of grade 2 or higher late hematuria in patients with prostate cancer treated with high-dose radiotherapy. METHODS: For this purpose, we have analyzed 229 T1c-T3b prostate cancer patients treated with 3-dimensional conformal radiotherapy (3DCRT) in a prospective dose escalation study and with a minimum follow-up of 1 year. The mean radiation dose was 79 Gy (range 72.1 to 84.14 Gy) and the mean follow-up was 47 months (range 14 to 95). One hundred eighteen patients also received androgen deprivation (AD) for high-risk disease. Univariate and multivariate analysis (MVA) were performed to identify variables significantly associated with late hematuria. RESULTS: Of the 31 (14%) patients with grade 2 or higher genitourinary toxicity, hematuria was the main symptom in 24 (10.5%) with only 1 patient (0.5%) experiencing grade 3 hematuria. On statistical analysis, all the dosimetric parameters failed to show a significant correlation with grade 2 or higher hematuria. On MVA, prior transurethral resection of the prostate (TURP) was significantly associated with a higher risk of late hematuria (relative risk [RR] = 2.8; P = 0.026), whereas long-term AD was correlated with a significantly decreased risk (RR = 0.21; P = 0.019). CONCLUSIONS: TURP was a relevant factor increasing 3 times the risk of late hematuria in prostate cancer patients treated with 3DCRT. Conversely, long-term AD resulted in a protective factor decreasing 5 times the risk of late hematuria. To our knowledge, this is the first study reporting a protecting effect of long-term hormones in late toxicity after radiotherapy.

Statistical analysis of dose-volume and dose-wall histograms for rectal toxicity following 3D-CRT in prostate cancer.

The purpose of this paper is to determine the correlation between dose-volume histogram (DVH) and dose wall-histogram (DWH) in the evaluation of rectal complications for prostate cancer patients treated with three-dimensional conformal radiotherapy (3D-CRT). A retrospective analysis of DVHs and DWHs of a subset of 25 prostate cancer patients treated with 3D-CRT was performed. For every patient the rectum and the rectal wall (inner and outer surface) were contoured. Median ICRU radiation dose of 79.4 Gy was administered. Correlation between DVHs and DWHs parameters was investigated by the nonparametric Spearman test and by linear regression analysis. The results showed a statistically significant linear correlation between pairs of DVH and DWH dosimetric parameters with Spearman correlation values (S) bigger than 0.8, with p values better than 0.0005 (two-sided) when the emptied rectum is considered. The variation of S and linear fit slope values [b(1)] showed a very similar functional shape with a minimum at 91% ICRU dose [S =0.83, b(1)=0.65]. The present study confirms a high correlation (>80%) between DVH and DWH of the rectum following 3D-CRT for prostate cancer. The derived advantage is that the contouring of inner surface of rectum could be obviated in almost 90% of patients when performing predictive models for rectal complications based on dosimetric variables under the standard treatment conditions specified in this study.

Clinical impact of the detector size effect in 3D-CRT.

OBJECTIVE: The detector size artificially increases the measured penumbra of radiotherapy fields. The aim of this work is to determine the influence of the detector size when planning three-dimensional conformal radiation therapy (3D-CRT) treatments. MATERIAL AND METHODS: Two anatomical sites of interest in 3D-CRT were studied: prostate and hypophysis chordoma. Conventional 3D-CRT treatments for two cases in these locations were planned with a FOCUS 4.0.0 (Computerized Medical Systems, USA) treatment planning system (TPS) equipped with Fast Fourier Transform Convolution (FFTC) and Multigrid Superposition (MGS) algorithms, making use of beams modelled from radiation profiles measured either with a 2.0 mm diameter detector (PFD(3G) diode) or with a 5.5 mm diameter detector (PTW-31002 ionisation chamber). These detectors cover up the range of detector sizes commonly used to measure radiation profiles for 3D-CRT. Dose-volume histograms (DVHs), radiobiological indexes, tumor control probability (TCP) and normal tissue complication probability (NTCP) were analysed and compared for planning target volumes (PTVs) and organs at risk (OAR) studied. RESULTS: Important differences in DVH were found. OAR received higher dose levels when a 5.5 mm detector was used to measure profiles compared to the case in which a 2.0 mm detector was used. A 2 Gy increment in the mean rectal dose was found when the larger detector was used. In the same way, NTCP of brain stem in hypophysis chordoma treatments was doubled when this detector was used. CONCLUSION: The current use of ionisation chambers of about 5 mm active diameter to get the necessary data to model treatment machines in radiotherapy treatment planning systems (TPS) implies a significant overirradiation of OAR close to the PTV in 3D-CRT treatments due to errors in the measured penumbra of beam profiles. To avoid this overirradiation, the measured profiles should either being acquired with a suitable detector size (2-3 mm active diameter) or being deconvoluted.

Impact of mean rectal dose on late rectal bleeding after conformal radiotherapy for prostate cancer: dose-volume effect.

PURPOSE: To identify the clinical and dosimetric factors predictive of a greater risk of Grade 2 or worse late rectal bleeding in patients with localized prostate cancer treated with three-dimensional conformal radiotherapy in a prospective dose-escalation study. METHODS AND MATERIALS: We performed a retrospective analysis of the clinical records and dose-volume histograms of 107 patients with Stage T1c-T3 prostate cancer treated at our institution with three-dimensional conformal radiotherapy who had a minimal follow-up of 1 year. Of the 107 patients, 21 were treated at dose level 1 (70.0 Gy), 57 at dose level 2 (72.0 Gy), and 29 at dose level 3 (75.6 Gy). The mean International Commission on Radiation Units and Measurements reference dose was 76.5 Gy (range, 69.8-82.6 Gy). RESULTS: The 4-year actuarial incidence of Grade 2 or worse late rectal bleeding was 7.7% +/- 2.5%. The results of the multivariate analysis indicated that the mean rectal dose (rectal D(mean); p = 0.003) and the percentage of rectum receiving >60 Gy (Vr(60); p = 0.002) correlated with Grade 2 or worse rectal bleeding. The receiver operating characteristic curve analysis showed that this logistic regression model using both Vr(60) and rectal D(mean) had good reliability to predict the risk of late rectal bleeding. The area under the curve for Vr(60) and rectal D(mean) was 0.889 and 0.892, respectively. CONCLUSION: The results of the present study provide clear evidence of a dose-volume effect and the importance of intermediate doses (60.0 Gy) on the risk of rectal bleeding at this prescription dose level. On the basis of these results, new constraints have been implemented in our institution to keep the risk of developing Grade 2 rectal bleeding reasonably low (rectal D(mean) 50.0 Gy and Vr(60) 42%).

Experimental validation tests of fast Fourier transform convolution and multigrid superposition algorithms for dose calculation in low-density media.

BACKGROUND AND PURPOSE: Modern conformal radiotherapy treatments require accurate dose calculation in any relevant clinical situation. One of these situations is the treatment of lung tumors, where irradiation has to be planned under challenging conditions for dose calculation. In this study we assess the errors in dose values predicted by fast Fourier transform convolution (FFTC) and multigrid superposition (MGS) algorithms implemented in a commercial treatment planning system (TPS). MATERIALS AND METHODS: FFTC and MGS algorithms were used in a FOCUS 3.0.0 (Computerized Medical Systems, USA) to calculate doses in treatment plans using photon beams of 6 and 25 MV nominal energy from a Saturne 43 linac (GE Medical Systems, USA). A 10x10-cm beam irradiating a mediastinum-lung and a thoracic wall-lung-thoracic wall modeled geometry was assessed. The calculated data were compared with measurements performed with radiographic films and ionization chamber. RESULTS: FFTC algorithm leads to an average deviation from ionometric dose measurements of over 10%. Discrepancies between measured and calculated beam fringe values (distance between 50 and 90% isodose lines) of up to 8 mm were observed. For MGS algorithm, all the points assessed in both geometries fulfilled the 3%-3 mm accuracy criteria and the average deviation of absolute dose was about 1%. A maximum of 3 mm deviation in the beam fringe for any depth was found and was within 2 mm beyond the buildup region. Deviations between ionometric and film measurements were within 3%. CONCLUSIONS: MGS algorithm assesses with reasonable accuracy dose distributions and absolute dose in inhomogeneous regions like the lung region. Therefore, and respecting the inhomogeneity dose calculation, the system could be used in routine clinical practice and in dose-escalation programs. This is not true in the case of FFTC algorithm which leads to errors greater than 10% in the absolute dose calculation and underestimates the beam fringe by up to 8 mm.