External Beam Radiotherapy Planning Research Articles

Three-dimensional summation of rectal doses in brachytherapy combined with external beam radiotherapy for prostate cancer

Background and purposeTo determine the dose constraints for rectal bleeding in brachytherapy (BRT) combined with external beam radiotherapy (EBRT). Materials and methodsPost-BRT, pelvic computed tomography images were used for subsequent EBRT planning and BRT postplans in 37 patients. The physical doses for each plan were converted to biologically effective doses, and corresponding voxel doses were integrated to plot the summed dose-volume histogram (sum-DVH). Between 5 patients with (bled-pts) and 32 without (spared-pts) grade 2 or 3 rectal bleeding, the differences in the mean minimal dose (rDn) covering the rectal volume of 0.5–10.0cc and the rectal volume (rVn) receiving the calculated dose of 20–150Gy were compared. ResultsThe differences in the summed-rDn were determined by BRT exposure, while those of the summed-rVn were determined in the low-dose range and superimposed in the high-dose range by EBRT exposure. Of the 13 patients with rV150 of >1.2cc, 4 were bled-pts (30.8%). Of the 24 patients with rV150 of ≦1.2cc, 1 was a bled-pts (4.2%) (p=0.024; odds ratio, 10.2; CI (95%), 1.0–104.3). ConclusionsThe mono-scale DVH analysis is a promising method for exploring the threshold for rectal bleeding in combined radiotherapy.

The Equivalent Dose Contribution from High-Dose-Rate Brachytherapy to Pelvic Positive Lymph Nodes in Locally Advanced Cervical Cancer Patients

Definitive radiation therapy for locally advanced cervical cancer involves both external beam radiation therapy (EBRT) and high-dose-rate (HDR) brachytherapy. There remains controversy and practice pattern variation for the optimal radiation prescription dose to metastatic pelvic lymph nodes. This study investigates the contribution of the pelvic lymph node dose from HDR brachytherapy. We also examine the variation of the lymph node prescribed dose and actual delivered dose as determined from the EBRT and brachytherapy plans. From September 2007 to October 2011, 68 patients were treated with curative intent. Of these, 17 patients with 36 positive pelvic lymph nodes were included in this retrospective analysis. All patients were treated with EBRT to the pelvis with a supplemental boost to the involved pelvic node, plus HDR brachytherapy. Pathologically involved lymph nodes were contoured on the planning EBRT image as well as the 4 to 5 brachytherapy planning images. The mean received dose of each lymph node from the EBRT and brachytherapy plans was recorded. The Equivalent Dose in 2-Gray Fractions (EQD2) was calculated using the equation EQD2 = D × [(d + α/β)/2 Gy + α/β] where D is total dose, d is dose per fraction and α/β-ratio is the dose at which the linear and quadratic components are equal. A student t-test was performed to determine if the mean received dose was significantly different from the mean intended prescribed dose and the mean intended EQD2. The average prescribed dose from the EBRT, including the initial pelvic fields and boost contribution, was 54.09Gy. The average prescribed HDR dose to International Commission on Radiation Units (ICRU) point A was 26.81Gy. The average dose delivered to the involved pelvic lymph nodes from EBRT and brachytherapy were 54.25Gy and 4.31Gy, respectively, with the corresponding EQD2 of 53.45Gy and 4.00Gy. Therefore, there was no statistically significant difference between the means of the received individual lymph node dose and intended prescribed pelvic lymph node dose for the EBRT and brachytherapy plans (p < 0.05). The similar results between the received dose and the EQD2 were observed. The equivalent dose contribution to the involved pelvic lymph nodes in locally advanced cervical cancer from HDR brachytherapy was 4.00Gy. Our study shows that is the HDR contribution is 7% of the total EQD2 (57.45Gy). The HDR contribution needs to be accounted for when prescribing the EBRT boost dose to pelvic lymph nodes for the optimal therapeutic dose.

Endoscopic findings of rectal mucosal damage after pelvic radiotherapy for cervical carcinoma: correlation of rectal mucosal damage with radiation dose and clinical symptoms

PurposeTo describe chronic rectal mucosal damage after pelvic radiotherapy (RT) for cervical cancer and correlate these findings with clinical symptoms and radiation dose.Materials and MethodsThirty-two patients who underwent pelvic RT were diagnosed with radiation-induced proctitis based on endoscopy findings. The median follow-up period was 35 months after external beam radiotherapy (EBRT) and intracavitary radiotherapy (ICR). The Vienna Rectoscopy Score (VRS) was used to describe the endoscopic findings and compared to the European Organization for Research and Treatment of Cancer (EORTC)/Radiation Therapy Oncology Group (RTOG) morbidity score and the dosimetric parameters of RT (the ratio of rectal dose calculated at the rectal point [RP] to the prescribed dose, biologically effective dose [BED] at the RP in the ICR and EBRT plans, α/β = 3).ResultsRectal symptoms were noted in 28 patients (rectal bleeding in 21 patients, bowel habit changes in 6, mucosal stools in 1), and 4 patients had no symptoms. Endoscopic findings included telangiectasia in 18 patients, congested mucosa in 20, ulceration in 5, and stricture in 1. The RP ratio, BEDICR, BEDICR+EBRT was significantly associated with the VRS (RP ratio, median 76.5%; BEDICR, median 37.1 Gy3; BEDICR+EBRT, median 102.5 Gy3; p < 0.001). The VRS was significantly associated with the EORTC/RTOG score (p = 0.038).ConclusionThe most prevalent endoscopic findings of RT-induced proctitis were telangiectasia and congested mucosa. The VRS was significantly associated with the EORTC/RTOG score and RP radiation dose.

A multi-plane source model for out-of-field head scatter dose calculations in external beam photon therapy

Our purpose was to assess the out-of-field dose component related to head scatter radiation in high-energy photon therapy beams and then derive a multisource model for this dose component. For scattered photons, several planar sources have been defined, with number, location and tilt depending on the complexity of the field shape. In the absence of precise knowledge of out-of-field scattering characteristics, several assumptions are made to derive emission spectra and radiation intensity from measurements. Among these, the Compton formula is used to evaluate scattered photon energy and the Henyey–Greenstein phase function is used to evaluate the scattered photon angular distribution. For measured doses under out-of-field conditions, the average local difference between the calculated and measured photon dose is 10%, including doses as low as 0.01% of the maximum dose on the beam axis. This study demonstrates that the multi-plane source approach is suitable for accurate analytical modeling of the out-of-field dose component related to head scatter radiation. These results should be taken into account when evaluating doses to the remaining volume at risk in external beam radiotherapy planning.

Accelerated partial breast irradiation using external beam radiotherapy—A feasibility study based on dosimetric analysis

AimTo investigate the feasibility of using External Beam radiotherapy for accelerated partial breast irradiation by a comparative tumour and normal tissue dose volume analysis with that of high dose rate interstitial brachytherapy. BackgroundAccelerated Partial Breast Irradiation (APBI) is more clinically appealing because of the reduced treatment course duration and the irradiated area. Brachytherapy application is more dependent on the clinician's expertise when it is practised free hand without image guidance and a template. It happens to be an invasive procedure with the use of local anaesthesia which adds patient discomfort apart from its cost compared to External Beam Radiotherapy. But APBI with brachytherapy is more commonly practised procedure compared to EBRT owing to its previous reults. Hence in this research study, we intend to explore the use of EBRT with the radiobiological corrections for APBI in the place of brachytherapy. It is done as a dosimetric comparison of Brachytherapy treatment plans with that of EBRT plans. Materials and methodsThe computed tomography images of 15 patients undergoing ISBT planning were simulated with conformal photon fields. Various dose volume parameters of each structure were obtained from the DVH generated in the brachytherapy and the simulated external beam planning which can correlate well with the late toxicity. The plan quality indices such as conformity index and homogeneity index for the target volume were computed from the dosimetric factors. The statistical p values for CI, HI and normal tissue dosimetric parameters were calculated and the confidence levels achievable were analysed. The dose prescribed in brachytherapy was 3400cGy in ten fractions. The equivalent prescription dose for the external beam radiotherapy planning was 3000cGy in five fractions applied with radiobiological correction. ResultsAll the fifteen patients were with complete lung data and six were with left sided tumours having complete cardiac data. The lung dosimetry data and the cardiac dosimetry data of the patients were studied. Lower percentages of lung and cardiac V20 and V5 volumes were obtained with conformal planning. The conformity of radiation dose to the tumour volume was akin to the interstitial brachytherapy planning. Moreover the external beam planning resulted in more homogenous dose distribution. For the sampled population, the statistical analysis showed a confidence level of 95% for using EBRT as an alternate to multi catheter ISBT. ConclusionThe EBRT planning for Accelerated Partial Breast Irradiation was found to be technically feasible in the institution where the interstitial brachytherapy happens to be the only available technique as evident from the dose volume parameters and the statistical analysis.

Integration of FDG- PET/CT into external beam radiation therapy planning

SummaryThis work addresses the clinical adoption of FDG-PET/CT for image-guided radiation therapy planning (RTP). As such, important technical and methodological aspects of PET/CTbased RTP are reviewed and practical recommendations are given for routine patient management and clinical studies. First, recent developments in PET/CT hardware that are relevant to RTP are reviewed in the context of quality control and system calibration procedures that are mandatory for a reproducible adoption of PET/CT in RTP. Second, recommendations are provided on image acquisition and reconstruction to support the standardization of imaging protocols. A major prerequisite for routine RTP is a complete and secure data transfer to the actual planning system. Third, state-of-the-art tools for image fusion and co-registration are discussed briefly in the context of PET/CT imaging preand post-RTP. This includes a brief review of state-of-the-art image contouring algorithms relevant to PET/CT-guided RTP. Finally, practical aspects of clinical workflow and patient management, such as patient setup and requirements for staff training are emphasized. PET/ CT-guided RTP mandates attention to logistical aspects, patient set-up and acquisition parameters as well as an in-depth appreciation of quality control and protocol standardization. Conclusion: Upon fulfilling the requirements to perform PET/CT for RTP, a new dimension of molecular imaging can be added to traditional morphological imaging. As a consequence, PET/CT imaging will support improved RTP and better patient care. This document serves as a guidance on practical and clinically validated instructions that are deemed useful to the staff involved in PET/CT-guided RTP.

SU‐E‐T‐392: Using Deformable Registration to Evaluate Combined Biological Effective Dose in Patients Receiving Combination External Beam Radiotherapy and Brachytherapy of Prostate Cancer Patients

Purpose: To determine the feasibility of combining external beam radiotherapy (EBRT) and brachytherapy (BT) in terms of Biological Effective Dose (BED) using deformable image registration to evaluate treatment. Methods: This study analyzed combined EBRT and BT treatments of prostate cancer. Each patient received 45 Gy EBRT IMRT or VMAT technique prescribed to a planning target volume (PTV) followed by a 110 Gy or 100 Gy BT boost using I‐125 or Pd‐103, respectively. EBRT planning CT and post‐implant CT were co‐registered using rigid/deformable registration. The BT dose matrix was mapped via deformable transformation component to the EBRT CT study. The seed dose distribution was combined with the EBRT CT by the re‐sampling of the dose matrix. BED calculations were performed utilizing the linear quadratic model assuming &amp;#945;/&amp;#946; ratio of 2 to convert EBRT and BT dose distributions. This yields evaluable topographical dose volume histogram (DVH) for evaluation of dosage to the PTV and organs at risk (OAR). Results: Twenty seven patient plans were successfully reconstructed to yield combined BED information. The average EBRT BED was found to be 85 Gy and the BT BED average was to be 127 (range 100–155 Gy) for a combined total average dose of 212 (range 185–240 Gy). The combined V0.1cc and V2cc of OAR were evaluated in both conventional and a novel topographical technique. Conclusions: We found it feasible to combine EBRT and BT treatment plans for BED analysis of both target and OAR. This allows for a novel and dynamic evaluation of combined therapy. BED distribution can enable clinicians to identify areas where failure can occur and assess areas of potential toxicity, currently not possible using physical dose summation. It can also be used as a tool for physicians to objectively assess the quality of treatment plans and for multi institutional comparisons.

Three-Dimensional Dose Addition of External Beam Radiotherapy and Brachytherapy for Oropharyngeal Patients Using Nonrigid Registration

To develop and evaluate a method for adding dose distributions of combined external beam radiotherapy (EBRT) and brachytherapy (BT) for oropharyngeal patients. Two computed tomography (CT) scans were used for 5 patients: the EBRT CT, used for EBRT planning, and the BT CT, acquired after catheter implantation. For each scan, the salivary glands and the chewing and swallowing muscles were contoured, and a dose distribution was calculated. A nonrigid transformation was obtained by registering the organs' surfaces. Then the BT dose distribution was mapped onto the EBRT dose distribution by applying the transformation obtained. To account for differences in fractionation, the physical doses were converted to equivalent dose in 2 Gy (EQD(2)), and the total dose was found by adding dose voxel by voxel. The robustness of the dose addition was investigated by varying delineations and input parameters of the registration method and by varying the α/β parameter for EQD(2). The effect of the perturbations was quantified using dose-volume histograms (DVH) and gamma analyses (distance-to-agreement/dose-difference = 1 mm/1 Gy). The variations in input parameters and delineations caused only small perturbations in the DVH of the added dose distributions. For most organs the gamma index was low, and it was moderately elevated for organs lying in areas with a steep gradient (median gamma index ≤ 2.3 for constrictor muscles, ≤ 0.7 for all other organs). The presented method allows adding dose distributions of combined EBRT and BT for oropharyngeal patients. In general, the method is reliable and robust with respect to uncertainties in organ delineation, perturbations in input parameters of the method, and α/β values.

Fractionated radiotherapy for intracranial meningiomas

Fractionated external beam radiotherapy (EBRT) has multiple roles in the management of intracranial meningiomas. In multiple series post-operative EBRT has shown improved progression-free survival following subtotal resection and a reduction in long-term failures following an apparent gross total resection. In the definitive setting, the use of EBRT has increased as the growing utilization of neuro-imaging for various conditions identifies skull-based lesions which are not easily resectable. Optic nerve sheath meningiomas represent a classic example of the use of definitive EBRT, given the frequent visual sequelae of surgery or observation. EBRT planning is highly individualized and requires a detailed understanding of tumor grade, adjacent radiosensitive structures such as the anterior optic apparatus, and radiographic characteristics of the tumor such as hyperostosis.

SU‐GG‐T‐529: Fully Automated Patient Specific Collision Check for Novalis Radiosurgery System

Purpose: In Stereotactic treatment of cranial lesions multiple non‐coplanar beams or arcs are frequently used which can give rise to collision problem and consequently render a treatment plan undeliverable. In SBRT treatments for very large patients the same issue can also happen even if the treatment plan doesn't involve couch kick. We propose a easy‐to‐use, patient plan specific method to determine whether a certain plan will have collision problem and the parametric changes needed to avoid it. Method and Materials: Treatment couch dimension and relative position to immobilization device was measured, as well as the Novalis gantry head dimension and its clearance from the isocenter. A program was written to calculate, for a given gantry, couch, and collimator angle, the coordinates of the four corners of the front surface of the gantry head in the patient CT coordination system. Thus the collision can be checked by simply looking up the corresponding CT slice images with the treatment couch added. The projection of gantry head front surface on all slices are calculated and checked to assure that there's no collision with the couch or patient body. Results: We tested several cases of different disease sites and techniques and the method proposed here can detect the potential collision problem and also offer the advice regarding how much change needs to be made. Conclusion: The method proposed here can be easily implemented to provide institution customized, patient specific collision check for external beam radiation therapy plans, saving the trouble of manually checking for collision. Furthermore, it can be implemented with matlab or integrated with iPlan software to automatically check the collision and find correct setup way to avoid collision in SBRT cases.

Decreasing Temporal Lobe Dose With Five-Field Intensity-Modulated Radiotherapy for Treatment of Pituitary Macroadenomas

To compare temporal lobe dose delivered by three pituitary macroadenoma irradiation techniques: three-field three-dimensional conformal radiotherapy (3D-CRT), three-field intensity-modulated radiotherapy (3F IMRT), and a proposed novel alternative of five-field IMRT (5F IMRT). Computed tomography-based external beam radiotherapy planning was performed for 15 pituitary macroadenoma patients treated at New York University between 2002 and 2007 using: 3D-CRT (two lateral, one midline superior anterior oblique [SAO] beams), 3F IMRT (same beam angles), and 5F IMRT (same beam angles with additional right SAO and left SAO beams). Prescription dose was 45 Gy. Target volumes were: gross tumor volume (GTV) = macroadenoma, clinical target volume (CTV) = GTV, and planning target volume = CTV + 0.5 cm. Structure contouring was performed by two radiation oncologists guided by an expert neuroradiologist. Five-field IMRT yielded significantly decreased temporal lobe dose delivery compared with 3D-CRT and 3F IMRT. Temporal lobe sparing with 5F IMRT was most pronounced at intermediate doses: mean V25Gy (% of total temporal lobe volume receiving ≥25 Gy) of 13% vs. 28% vs. 29% for right temporal lobe and 14% vs. 29% vs. 30% for left temporal lobe for 5F IMRT, 3D-CRT, and 3F IMRT, respectively (p < 10(-7) for 5F IMRT vs. 3D-CRT and 5F IMRT vs. 3F IMRT). Five-field IMRT plans did not compromise target coverage, exceed normal tissue dose constraints, or increase estimated brain integral dose. Five-field IMRT irradiation technique results in a statistically significant decrease in the dose to the temporal lobes and may thus help prevent neurocognitive sequelae in irradiated pituitary macroadenoma patients.

SU‐FF‐T‐468: Comparison of Target Dose Inhomogeneity for Four Different Techniques of Breast Cancer Treatment

Purpose: To evaluate target dose inhomogeneity for four different breast cancer treatment techniques. Method and Materials: External beam radiotherapy (EBRT) was performed for 12 patients each using either whole or 3D conformal partial breast irradiation (WBI or PBI), 19 patients with high dose rate (HDR) MammoSite® brachytherapy and 13 patients with Contura® multi‐lumen applicator. The PTV_EVAL volume was defined by following NSABP B‐39/RTOG 0413 for PBI, MammoSite® and Contura® while retrospectively delineated for WBI. The differential dose volume histogram was evaluated using mean dose (Dm) and most probable dose (Dmp) relative to prescribed dose (Dpr) and root mean square deviation (RMSD). The biologically effective dose (BED) accounting for non‐uniform dose distribution was computed. Generalized equivalent uniform dose (gEUD) was calculated together with dose homogeneity index (DHI) and conformal index (COIN). Results: Compared to EBRT, the target received higher dose with HDR (Dm: 143% vs. 101%, Dmp: 111% vs. 101%) which increased BED values (77 Gy vs. 73 Gy for fibrosis, 56 Gy vs.47 Gy for erythema, and 63 Gy vs. 57 Gy for breast carcinoma, respectively) and dose inhomogeneity (RMSD: 12.1 vs. 1.8). Due to steeper dose fall‐off, HDR plans were more conformal than EBRT (COIN: 0.84 vs. 0.45). Compared to MammoSite®, Contura® yielded slightly higher dose (BED difference &lt; 0.5 Gy and 0.3 Gy higher in gEUD) which increased DHI by 5% and COIN by 1%. The PBI had large inter‐patient variability of BED values (2–8 times &gt; others) and the smallest BED and gEUD values. The WBI had large inter‐patient variability of gEUD values (14 times &gt; others) due to cold spots. Conclusion: Despite greater inhomogeneity, HDR plans have higher target dose conformality and are less patient‐specific than EBRT plans. However, based on the biological and dosimetric data, the four different techniques are clinically comparable.

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.

Sci‐YIS Fri ‐ 06: High spatial resolution magnetic resonance spectroscopic imaging of the brain at 3T for external beam radiation therapy planning

Recent research has shown that Magnetic Resonance Spectroscopic Imaging (MRSI) has good prospects for cancer detection and staging. Recent advancements in hardware in the form of RF coils and gradient sets have resulted in a good outlook for MRSI to be used in detection, localization, and classification of the lesions. Work done by other groups has shown that merging molecular imaging information from MRSI with anatomic scans used for treatment planning proved beneficial in delineating the tumor volume. MRSI involves defining an MR image volume which can be divided into a matrix of 3‐D sub‐volumes. Spectroscopic data is then acquired for all these sub‐volumes simultaneously. This leads to the quantification and localization of different levels of metabolites such as Choline, Creatine and N‐ acetylaspartate that are highly useful in detecting and possibly staging lesions. We focused on performing MRSI on the brain using a head transmit/receive (T/R) coil. Utilizing a reduced 2‐Dimensional Point Resolved Spectroscopy (2‐D PRESS) Turbo Spectroscopic Imaging (TSI) sequence to improve the spectral resolution of different metabolite peaks and the spatial resolution of the spectroscopic scan, good spectral/spatial information can be acquired revealing more accurate bio‐chemical imaging. Thus, an MRSI study could be easily used for improved treatment planning. Using 3T MRI we have improved the spatial resolution of the MRSI scans to 5×5×10mm3/voxel, meanwhile maintaining a good signal to noise ratio. This would increase the spatial relevance of the spectra acquired in the scan and in turn provide more information in the treatment planning phase.