DVH Parameters Research Articles

Applicator reconstruction and applicator shifts in 3D MR-based PDR brachytherapy of cervical cancer

Purpose To evaluate the methods of applicator reconstruction in 3D MR-based planning for brachytherapy of cervical cancer, and to investigate applicator shifts and changes in DVH parameters during PDR treatment. Methods For each application MR scans with applicator in situ were made: three T2-weighted (4.5 mm slices) Turbo Spin Echo (TSE) scans and a balanced Steady State Free Precession scan (1.5 mm). Three observers tested two applicator reconstruction methods: (A) directly on the bSSFP scan and (B) on a resampled combination of the three T2-weighted scans. For 10 patients MR imaging was repeated on the second day of each PDR fraction to determine applicator shifts and changes in DVH parameters. Results For both applicator reconstruction methods the interobserver variation for the DVH parameters was comparable (average <1.5% in dose). Differences between the two methods were larger (up to 6.4% for target) and were related to position differences during MR scanning. The average applicator shift relative to the pelvic structures was 5–6 mm into the ventral direction and 3–4 mm cranially. For a single PDR fraction, the average D90 (HR-CTV) on ‘day 2’ was 0.2 (SD 2.0) Gy lower than that for day 1. The average increase in D 2cc (bladder) was 1.0 (SD 3.0) Gy αβ3 for a single PDR fraction. If the effect of both fractions was combined, for 1 patient a total decrease of D90 of 7 Gy αβ10 was found, whereas for another patient the total increase in bladder dose was 12 Gy αβ3. Conclusions Applicator reconstruction on MR data is feasible. In the overall accuracy during PDR brachytherapy the reconstruction uncertainty is of minor importance. Applicator and/or organ movement during the course of the PDR fraction produce larger uncertainties.

SU‐FF‐T‐135: Dosimetric and Delivery Advantages of a New 160‐Leaf MLC

Purpose: To conduct a measurement and treatment planning study on dosimetric and delivery advantages of a new 160 leaf MLC (160MLC, Siemens). Methods and Materials: The uses of 160MLC were compared with a commonly used 58‐leaf MLC (Siemens) and Cerrobend blocks. Radiation leakages and penumbra were measured using films and using a small‐size ionization chamber. A treatment planning system (Xio, CMS) was used to generate (1) isodose distributions for a series of single circular and square fields defined by the MLCs or blocks, and (2) 3DCRT plans for a pituitary adenoma case with a small target volume and closely adjacent organs at risks. Static IMRT plans for a variety of prostate and head and neck cases using Xio and another planning system (Panther, Prowess) were generated and delivered. Results: The 160MLC has lower radiation leakage (0.5% for 160MLC vs. 2% for 58MLC) and narrower penumbra (5–6 mm for 160MLC vs. 9–14 mm for 58MLC calculated between 80/20% isodose lines for a 10×10cm2 field with various MLC rotations), and slightly wider penumbra (within 1 mm) than the blocks. The dose conformity between using 160MLC and blocks determined for a series of circular fields is similar, and higher than that 58MLC. The 3DCRT plans for 160MLC and blocks are comparable and more conformal than that for 58MLC as assessed by DVH parameters. The use of 160MLC reduces the numbers of segments and MU by 13% versus the 58MLC. The average delivery time for the Prowess IMRT plans with 160MLC was 5 minutes. Conclusion: The 160MLC offers several dosimetric and delivery advantages including low leakage, narrow penumbra, conformal dose distributions similar to divergent blocks, reduced numbers of IMRT segments and MU, and reduced IMRT delivery time. These advantages lead to reduced normal tissue doses, without need of Cerrobend blocks, and improved treatment delivery.

Spatial distribution and DVH parameters correlation of additional rectal/sigmoid mucosal points, in high-dose-rate intracavitary brachytherapy for carcinoma of the cervix – A dosimetric study

Purpose: Late rectal and sigmoid toxicities seen in cervical cancer patients are attributed to brachytherapy despite rectal doses within tolerance limits. In an attempt to identify and document doses, correlate with DVH parameters and evaluate the spatial distribution of the additional rectal and sigmoid points, we undertook this dosimetric study.

Related factors in radiation pneumonitis

Radiation pneumonitis(RP) not only lowers the patients' life quality, but also is one of the common dose-limiting complications in thoracic radiotherapy. RP is the result of many factors, which interacts with each other. DVM parameters can be used to evaluate the treatment plan and to predict RP. But its reliabil- ity is not quite sure. Associating other predict factors such as cytokines with DVH parameters to estimate RP has become the current research focus. Key words: Radiation pneumonitis; Dose volume histogram parameters; Cytokines

Correlation of dose–volume parameters, endoscopic and clinical rectal side effects in cervix cancer patients treated with definitive radiotherapy including MRI-based brachytherapy

Purpose Correlation of dosimetric parameters for MRI-based 3D treatment planning with rectoscopic findings and clinical rectal side effects. Methods and materials Rectosigmoidoscopy and rectal morbidity assessment were performed on 35 cervical cancer patients treated with external beam radiotherapy (EBRT) and HDR-intracavitary brachytherapy (ICB). The total doses, normalised to 2 Gy fractions (EQD2, α/ β = 3 Gy), in 0.1, 1.0 and 2.0 cm 3 ( D 0.1cc, D 1cc, D 2cc) of rectum were determined by summation of EBRT and ICB plans. Correlation analysis between clinical symptoms (LENT/SOMA) and rectoscopic changes (Vienna Rectoscopy Score, VRS) was performed. For dose–response analyses, the logit model was applied. Results Mean follow-up was 18 months. LENT/SOMA score was 1 in 4 patients, 2 in 8 patients, 4 in 1 patient. Telangiectasia was found in 26 patients (74%), five of them had ulceration corresponding to the 0.1 cm 3 volume (anterior wall). Mean values D 0.1cc, D 1cc, and D 2cc were 81 ± 13, 70 ± 9 and 66 ± 8 Gy, respectively. The ED50 values for VRS ⩾ 3 and for LENT/SOMA ⩾ 2 significantly increased with decreasing volumes. D 2cc was higher in patients with VRS ⩾ 3 compared to VRS < 3 (72 ± 6 vs 62 ± 7 Gy; p < 0.001) and in symptomatic vs asymptomatic patients (72 ± 6 vs 63±8 Gy; p < 0.001). VRS correlated with the LENT/SOMA score. Conclusions Rectosigmoidoscopy is sensitive in detecting mucosal changes, independent of clinical symptoms. The localization of these changes corresponds to the high dose volumes as defined by imaging. The development of mucosal and clinical changes in the rectum follows a clear dose–effect and volume–effect. DVH parameters could be established.

Inter- and intraobserver variation in HR-CTV contouring: Intercomparison of transverse and paratransverse image orientation in 3D-MRI assisted cervix cancer brachytherapy

Aim To analyze agreement between target volumes, delineated by two observers on transverse (T) and paratransverse (perpendicular to the long cervical axis – PT) MR images for cervix cancer brachytherapy. Materials and methods In 13 patients, High Risk-CTV (HR-CTV) was outlined by two observers in T and PT MR image plane, respecting the GYN GEC-ESTRO recommendations for 3D-image based cervix cancer brachytherapy [1]. Contouring time was measured. HR-CTV sizes were compared, and conformity index (CI) was assessed. Interobserver variations in contour-extent along eight radial directions were compared between delineation planes. After applying a standard treatment plan, an intercomparison of DVH-parameters V100, D90, and D100 for the HR-CTV was carried out. Results Contouring time was slightly longer in T than PT orientation. Interplane CI did not differ significantly between observers (0.72 vs. 0.71), nor did the interobserver CI between planes (0.79 vs. 0.78). Variations in contour-extent between different radial directions and interplane deviations in DVH parameters were non-significant. Conclusion Contouring in PT, as compared to T plane, allows for a “circumferential view of the cervix” and facilitates comprehensive understanding of spatial relations between the applicator and patho-anatomical structures. It is marked by a lower contouring difficulty and leads to a comparable outcome in terms of DVH parameters. Interobserver inconsistencies can be minimized by systematic training and following the published recommendations.

Consequences of random and systematic reconstruction uncertainties in 3D image based brachytherapy in cervical cancer

Background and purpose The purpose of this study was to evaluate the impact of random and systematic applicator reconstruction uncertainties on DVH parameters in brachytherapy for cervical cancer. Material and methods Dose plans were analysed for 20 cervical cancer patients with MRI based brachytherapy. Uncertainty of applicator reconstruction was modelled by translating and rotating the applicator. Changes in DVH parameters per mm of applicator displacement were evaluated for GTV, CTV, bladder, rectum, and sigmoid. These data were used to derive patient population based estimates of delivered dose relative to expected dose. Results Deviations of DVH parameters depend on direction of reconstruction uncertainty. The most sensitive organs are rectum and bladder where mean DVH parameter shifts are 5–6% per mm applicator displacement in ant–post direction. For other directions and other DVH parameters, mean shifts are below 4% per mm. By avoiding systematic reconstruction errors, uncertainties on DVH parameters can be kept below 10% in 90% of a patient population. Systematic errors of a few millimetres can lead to significant deviations. Conclusion Comprehensive quality control of afterloader, applicators and imaging procedures should be applied to prevent systematic errors in applicator reconstruction. Random errors should be minimised by using small slice thickness. With careful reconstruction procedures, reliable DVH parameters for target and OAR’s can be obtained.

SU‐GG‐T‐464: Comparison of Dose Gradient in The Critical Normal Structures Between CyberKnife and IMRT Treatment of Prostate Cancer

Purpose: This study aims to investigate dose gradient or fall‐off with distance on the critical normal structures using CyberKnife and IMRT delivery for hypofractionated stereotactic prosate radiotherapy. Method and Materials: Eight cases of prostate cancer patient treated with the CyberKnife (CK) were used in this study. Based on the identical contour sets, treatment plan for each patient was generated on IMRT system. To calculate dose fall‐off, CTV (where CTV was prostate itself) contour was expanded 30 mm posteriorly and 50 mm uniformly for all patient cases with CK and IMRT planning systems. Plans were normalized such that 95% of the CTV received 100% of the prescribed dose. DVH parameters were used to analyze and compare doses to CTV and its posterior and uniform extension, bladder, rectum and urethra. Results: All plans satisfied the specified requirements with an exception in CTV dose conformity indices (CI). A number of IMRT plans show prescribed CTV isodose curve bulged out transversely. CI value for Cyberknife plans is 1.18±0.08 and 1.44±0.11 for IMRT. Dose fall‐off study showed that percent dose falloff/ mm (pdf/mm) are 3.75±1.58 and 3.15±1.88 posteriorly, and 3.60±3.97 and 3.62±4.30 in 20 mm uniformly expanded region for CK and IMRT, respectively. An attempt was made to recalculate pdf/mm for 5 mm split regions. For (0–5), (5–10), (10–15), and (15–20) mm regions, pdf/mm are 5.71±1.02, 4.49±0.56, 2.77±0.35, 2.05±0.19, and 5.61±1.26, 3.81±0.53, 2.07±0.46, 1.13±0.16 posteriorly, and 9.01±4.91, 2.67±0.59, 1.58±0.21, 1.13±0.11, and 9.62±5.08, 2.47±0.71, 1.32±0.16, 1.06±0.03 uniformly for CK and IMRT, respectively. Conclusion: CyberKnife and IMRT plans produced equivalent target dose coverage while CyberKnife plans show CTV dose is more conformal than IMRT. Dose fall‐off is slightly faster posteriorly for CyberKnife plans than IMRT plans. Conflict of Interest: Data was presented in CyberKnife User's Meeting 2008, Scottsdale, AZ.

The missing link between different DVH parameters for rectum and urethra in prostate brachytherapy

The missing link between different DVH parameters for rectum and urethra in prostate brachytherapy

MRI-Guided 3D Optimization Significantly Improves DVH Parameters of Pulsed-Dose-Rate Brachytherapy in Locally Advanced Cervical Cancer

To compare dose-volume histogram parameters of standard Point A and magnetic resonance imaging-based three-dimensional optimized dose plans in 21 consecutive patients who underwent pulsed-dose-rate brachytherapy (PDR-BT) for locally advanced cervical cancer. All patients received external beam radiotherapy (elective target dose, 45 Gy in 25-30 fractions; tumor target dose, 50-60 Gy in 25-30 fractions). PDR-BT was applied with a tandem-ring applicator. Additional ring-guided titanium needles were used in 4 patients and a multichannel vaginal cylinder in 2 patients. Dose planning was done using 1.5 Tesla T(1)-weighted and T(2)-weighted paratransversal magnetic resonance imaging scans. T(1)-weighted visible oil-containing tubes were used for applicator reconstruction. The prescribed standard dose for PDR-BT was 10 Gy (1 Gy/pulse, 1 pulse/h) for two to three fractions to reach a physical dose of 80 Gy to Point A. The total dose (external beam radiotherapy plus brachytherapy) was normalized to an equivalent dose in 2-Gy fractions using alpha/beta = 10 Gy for tumor, alpha/beta = 3 Gy for normal tissue, and a repair half-time of 1.5 h. The goal of optimization was dose received by 90% of the target volume (D(90)) of > or =85 Gy(alpha/beta10) in the high-risk clinical target volume (cervix and remaining tumor at brachytherapy), but keeping the minimal dose to 2 cm(3) of the bladder and rectum/sigmoid at <90 and <75 Gy(alpha/beta3), respectively. Using three-dimensional optimization, all dose-volume histogram constraints were met in 16 of 21 patients compared with 3 of 21 patients with two-dimensional library plans (p < 0.001). Optimization increased the minimal target dose (D(100)) of the high-risk clinical target volume (p < 0.007) and decreased the minimal dose to 2 cm(3) for the sigmoid significantly (p = 0.03). For the high-risk clinical target volume, D(90) was 91 +/- 8 Gy(alpha/beta10) and D(100) was 76 +/- 5 Gy(alpha/beta10). The minimal dose to 2 cm(3) for the bladder, rectum, and sigmoid was 73 +/- 6, 67 +/- 6, and 69 +/- 6 Gy(alpha/beta3), respectively. The results of our study have shown that magnetic resonance imaging-guided optimization of PDR-BT for locally advanced cervical cancer significantly improved the dose-volume histogram parameters.

Present status and future of high-precision image guided adaptive brachytherapy for cervix carcinoma

Introduction. Image guided adaptive brachytherapy (IGABT) for cervical cancer, using mainly MRI, is an evolving method, increasingly replacing the 2D approach based on conventional radiography. During the complex 4D chain of this procedure image-assistance is provided for disease assessment, provisional treatment planning (“pre-planning”), applicator placement and reconstruction, as well as for contouring, definitive treatment planning and quality control of dose delivery. With IGABT changes of topography adjacent to the applicator, caused by tumour regression, oedema, organ changes and dilation are identified. Thus, the CTV for IGABT is primarily based on the tumour volume at the time of BT and takes into account both time and spatial domains. IGABT requires systematic concepts for target, OAR, biological modelling, DVH analysis, and dose-volume-adaptation. Methods and Results. This report focuses on the advantages and uncertainties, dose-effect relations and clinical results of the IGABT procedure addressing the current status and future perspectives. Uncertainties during the 4D chain of IGABT are mainly related to target contouring, applicator reconstruction, as well as to inter-fraction, intra-fraction and inter-application variability, as caused by tumour response and organ changes. Different from EBRT where set-up uncertainties are compensated by adding a margin to the CTV, no margins to the lateral and anterior-posterior directions can be used for IGABT. Discussion. By 3D treatment planning for IGABT significant improvement of the DVH parameters is achieved compared to 2D library plans. In small tumours the benefit is primarily obtained by a decrease of dose to nearby OAR while in large tumours the use of supplementary interstitial techniques and optimization may double the target volume that can be treated at a therapeutic dose level. The clinical impact of IGABT could recently be demonstrated by the establishment of some correlations between target- and organ-related DVH parameters versus disease control and side effects, which need further clarification. Overall, a very high local control rate can be achieved with minor treatment related morbidity. This favourable therapeutic ratio seems to be now reproducible under different conditions at various treatment centres. These results have to be validated within the upcoming multi-centre prospective IntErnational study on MRI-guided brachytherapy in locally advanced cervical cancer (EMBRACE).

The next step in patient-specific QA: 3D dose verification of conformal and intensity-modulated RT based on EPID dosimetry and Monte Carlo dose calculations

Background and purpose A method was evaluated to reconstruct the 3D dose distribution in patients using their planning CT-scan in combination with a Monte Carlo calculation, and the energy fluence of the actual treatment beams measured pre-treatment with an EPID without the patient or a phantom in the beam. Materials and methods Nine plans of lung cancer patients treated with a 3D conformal technique, calculated using a simple convolution algorithm (CA), as well as five IMRT treatments of head-and-neck cancer patients, calculated with a more advanced superposition algorithm (SA), were verified. Differences between planned and reconstructed dose distributions were quantified in terms of DVH parameters. Results For the lung cancer group, differences between the reconstructed mean PTV dose and the values calculated with the TPS were 5.0 ± 4.2% (1SD) and −1.4 ± 1.5% for the CA and SA algorithm, respectively. No large differences in the lung and spinal cord DVH parameters were found. For the IMRT treatments, the average dose differences in the PTV were generally below 3%. The reconstructed mean parotid gland dose was 3.2 ± 1.2% lower, while the maximum spinal cord dose was on average 3.1 ± 1.9% higher. Conclusions EPID dosimetry combined with 3D dose reconstruction is a useful procedure for patient-specific QA of complex treatments. DVH parameters can be used to interpret the dose distribution delivered to the patient in the same way as during standard treatment plan evaluation.

Late swallowing dysfunction and dysphagia after radiotherapy for pharynx cancer: Frequency, intensity and correlation with dose and volume parameters

Background and purpose Dysphagia and swallowing problems are common in pharynx cancer patients treated with radiotherapy. Dysfunction of the upper aerodigestive tract may lead to reduced quality of life, malnutrition and aspiration pneumonia. The aim of the current study was to describe swallowing function after radiotherapy and examine its correlation with irradiated volume and dose. Patients and methods All recurrence free patients treated for pharynx cancer with radical radiotherapy at our institution, between 1998 and 2002, were invited to participate, 35 (55% of eligible) agreed. Patients were examined with EORTC quality of life questionnaires and functional endoscopic evaluation of swallowing. Organs at risk were delineated on planning CT scans, available for 25 patients. Results Eighty-three percent of patients had some degree of dysphagia. Reduced sensitivity was observed in 94%, residues in 88%, penetration in 59% and aspiration in 18% of patients. Several significant correlations were found between both subjective and objective swallowing problems and DVH parameters of the upper aerodigestive tract. Doses less than 60 Gy to the supraglottic region, the larynx and upper esophageal sphincter resulted in a low risk of aspiration. Discussion Both subjective and objective swallowing problems were frequent and severe after radiotherapy for pharynx cancer. Swallowing dysfunction was correlated with dose and volume parameters of the upper aerodigestive tract.

SU-FF-J-81: Estimation of Dose Variations During Prostate Radiation Treatment Due to Elastic Deformations of Soft Tissues

Objective: The true dose distribution is subject to change due to organ shifts and also deformations. The goal of this work is to estimate the effect of the elastic organ deformations on the dose distribution for the average prostate IMRT treatment. Methods: A prostate patient was surveyed during the radiation treatment (IRB approved). The original treatment plan was created based on the planning CT. On-board cone beam computed tomography (CBCT) images were taken before treatments for the first 5 days and once a week therafter. The prostate, seminal vesicles (SV), bladder and rectum segmented on each CBCT were deformably registered against the planning CT. The analysis was conducted with the help of C++ ITK image registration and segmentation package. Initially, a volume (e.g., prostate and bladder) segmented on the planning CT scan was aligned against corresponding volume on the daily CBCT scan using a translational filter. Then, the aligned volume on CBCT was elastically deformed (Finite Element elastic deformation method), and the computed deformation vector field was used to propagate the true delivered radiation dose distribution to the original CT-based volume of the patient. Results: For the plan with a planning target volume (PTV) defined as a combination of both prostate and SV with a 5-mm margin, the DVH parameters fluctuated as follows (Vx denotes percent volume above x% of the prescription dose): prostate mean V100 76%, mean V95 97%, compared to the original prostate 98.15% and 100%, rectum and bladder mean V50 49% and 75% correspondingly, compared to the original rectum and bladder 50% and 29%. Conclusions: This study shows that some deviations from the planned dose may occur due to elastic distortion of soft tissue geometry. The developed suite of applications can be used to monitor actual delivered dose to the targets and critical structures.

Dose volume histogram parameters for organs at risk are influenced by differences in 3D image-based brachytherapy treatment planning for cervix cancer

Purpose: 3D image-guided brachytherapy for cervical cancer is emerging in select US and European centers. The GYN GEC ESTRO Working Group recommended a target concept based on MRI and DVH analysis for organs at risk (OARs). CT-based planning has been used at the Medical College of Wisconsin (MCW) since 2004. The purpose of this study was to retrospectively report the MCW DVH parameters for OARs and compare them to the data published by the Vienna group, inlight of differences in treatment planning approaches.

3D image-guided HDR brachytherapy in locally advanced cervix cancer—comparison of intracavitary and interstitial treatment

Purpose: For cervix cancer patients with extensive parametrial infiltration (the commonest presentation in this part of world), interstitial brachytherapy is supposed to yield better target coverage than intracavitary (ICRT) alone. There are a paucity of data of a randomized comparison of HDR interstitial treatment and ICRT. The aim of this study was to compare DVH parameters and treatment outcome of these two arms of HDR brachytherapy in III B cervix cancer.

Factors influencing bowel sparing in intensity modulated whole pelvic radiotherapy for gynaecological malignancies

Background and purpose To evaluate the influence of uterus and bladder size on large and small bowel sparing with intensity modulated whole pelvic radiotherapy (IM-WPRT) in gynecologic patients. Patients and methods Twenty patients were selected; 10 women with cervical cancer treated with definitive radiotherapy (group ‘DEF’) and 10 endometrial cancer patients treated postoperatively (group ‘POST’). Bladder, rectal wall, small (SB) and large bowel (LB) were delineated as organs at risk. A conformal four field technique and a seven field IMRT plan (prescription dose 50.4 Gy) were compared in terms of DVH and various target parameters. Results At doses between 40 and 50.4 Gy statistically significant improvements ( P<0.05) were observed for IM-WPRT for irradiated volume of rectal wall and bladder. In both patient groups, with IMRT the average irradiated volume of SB was reduced by a factor of 6 at 50.4 Gy. This ratio was 2 for LB. In the DEF group the effect of SB-sparing with IMRT correlated with bladder size (correlation coefficient 0.70) while it did not correlate in the postoperative group. The effect of LB-sparing decreased with increasing bladder size in both groups but the impact of IMRT was larger for postoperative patients. Conclusions IMRT significantly reduced the absolute volume of rectal wall, bladder and bowel irradiated at the prescribed dose level in gynaecologic patients. Main differences between POST and DEF patients receiving IM-WPRT were absolute volumes of LB irradiated to doses between 35 and 50 Gy, suggesting an impact of intact uterus on LB volume in the pelvis. POST patients seem to benefit most from elective nodal IMRT. Bladder filling is an important co-factor influencing the benefit of IMRT with respect to OAR sparing.

Aggravation of dyspnea in stage I non-small cell lung cancer patients following stereotactic body radiotherapy: Is there a dose-volume dependency?

In SBRT for NSCLC, highly potent radiation doses are delivered to patients with frequent pre-irradiatory compromise of pulmonary function. For the risk of pulmonary toxicity to be minimized during SBRT planning, data on its dose-volume dependency is needed. In the present study, we analyse the association of dose-volume histogram parameters with changes in dyspnea. The study concerns 28 medically inoperable stage I NSCLC patients that received SBRT at our department between 2000 and 2003. A central dose of 45 Gy/3 fractions was delivered in 5–8 days. WHO toxicity scoring of dyspnea was prospectively performed at baseline and during a 6-month follow-up post-SBRT. DVH parameters for pulmonary tissue were retrieved from the 3-D dose distributions.Aggravated dyspnea was registered in 11 patients (40%). We found no association between DVH parameters and changes in dyspnea. Nor did we find any consistent temporal variations of dyspnea after SBRT. We identified COPD as the factor showing the closest association with aggravation of dyspnea. The observed aggravation of dyspnea following SBRT reflects habitual exacerbations of COPD rather than treatment-related toxicity. Concern about pulmonary toxicity should not be prohibitive for future studies targeting limitations to dose and volume.

952 PUBLICATION Long-term results of radiotherapy for recurrent cervical carcinoma following surgery

To compare two methods of DVH parameter determination for combined external beam and brachytherapy treatment of cervical cancer.Clinical treatment plans from five patients were used in this study. We simulated two applications given with PDR (32 × 60 cGy per application, given hourly) or HDR (4 × 7 Gy in two applications; each application of two fractions of 7 Gy, given within 17 h) standard and optimised treatment plans, all combined with IMRT (25 × 1.8 Gy). Additionally, we simulated an external beam (EBRT) boost to pathological lymph nodes or the parametrium (7 × 2 Gy).We determined D90 of the high-risk CTV (HR-CTV) and D2cc of bladder and rectum in EQD2 in two ways. (1) ‘Parameter adding’: assuming a uniform contribution of the EBRT dose distribution and adding the values of DVH parameters for the two brachytherapy insertions, and (2) ‘distributions adding’: summing 3D biological dose distributions of IMRT and brachytherapy plans and subsequently determining the values of the DVH parameters. We took α/β = 10 Gy for HR-CTV, α/β = 3 Gy otherwise and half-time of repair 1.5 h.Without EBRT boost, ‘parameter adding’ yielded a good approximation. With an EBRT boost to lymph nodes, the total D90 HR-CTV was underestimated by 2.6 (SD 1.3)% for PDR and 2.8 (SD 1.4)% for HDR. This was even worse with a parametrium boost: 9.1 (SD 6.2)% for PDR and 9.9 (SD 6.2)% for HDR.Without an EBRT boost ‘parameter adding’, as proposed by the GEC-ESTRO, yielded accurate results for the values for DVH parameters. If an EBRT boost is given ‘distributions adding’ should be considered.

NTCP modeling for acute esophagitis in patients treated with conformal radiation therapy for non-small cell lung cancer (NSCLC)

NTCP modeling for acute esophagitis in patients treated with conformal radiation therapy for non-small cell lung cancer (NSCLC)