Left Parotids Research Articles

The clinical feasibility and effect of online cone beam computer tomography-guided intensity-modulated radiotherapy for nasopharyngeal cancer

Background and purpose Online adaptive correction in image-guided intensity-modulated radiotherapy appeared to be a promising approach for precision radiation treatment in head and neck tumors. This protocol was designed to evaluate the clinical feasibility and effect of online cone beam computed tomography (CBCT) guidance in IMRT of nasopharyngeal cancer (NPC). Methods and materials The Elekta Synergy system, which integrates an X-ray volumetric imager (XVI), was used to deliver radiation treatment for 22 cases of NPC. The acquired CBCT was registered to the planning CT for online and offline analysis. The systematic and random setup errors, as well as planning target volume (PTV) margin, were calculated at different correction threshold levels. The impact of online setup correction on dosimetry was evaluated by simulation of pre-correction errors. Results The correction-of-setup-errors frequencies for 1, 2 and 3 mm thresholds were 41.3–53.9%, 12.7–21.2% and 6.3–10.3%, respectively. Online correction was effective at the 2 mm threshold level for all three axes. The pre-correction systematic errors for the whole group ranged 1.1–1.3 mm, and the random errors were also 1.1–1.3 mm. After online correction, the systematic and random errors ranged 0.4–0.5 mm and 0.7–0.8 mm, respectively, in the three directions. The PTV margins for the pre-correction, pretreatment and post-treatment positions were 3.5–4.2 mm, 1.6–1.8 mm and 2.5–3.2 mm, respectively, in three directions. Analysis of hypothetical dosimetric change due to a translational isocenter shift of 3 mm showed that if no correction was applied, the mean maximum dose to both the brain stem and spinal cord would be increased by 10 Gy, the mean dose to the left and right parotids would be increased by 7.8 and 8.5 Gy, respectively, and the dose to target volumes would be decreased: 4 Gy for 95% GTV and 5.6 Gy for 95% CTV 60. Conclusions CBCT-based online correction increased the accuracy of IMRT for NPC and reduced irradiated margins, by decreasing both the systematic and random errors. Online CBCT correction reduces the radiation dose to normal tissue and creates room for further dose escalation of tumors.

Moving from 2D to 3D conformal radiotherapy (3DCRT) in locally advanced head and neck cancer: A dosimetric comparison

16530 Background: The aim of this study is to evaluate the dosimetric parameters of 3D CRT in head and neck tumors, to compare with hypothetical 2D plans, and to evaluate the acute toxicity. Methods: A total of 33 patients with median age of 62 years (range: 23–87 ) and with histologically proven head and neck cancer were consecutively treated with 3D CRT using a 6-field photon beam technique. 9 patients had supraglottic carcinoma, 5 - glottic carcinoma, 4- nasopharyngeal carcinoma, 4 - thyroid carcinoma, 2- oropharyngeal cancer, 3 - carcinoma of oral cavity, 1- carcinoma of hypopharynx, 1- maxillary sinus carcinoma, 3- unknown primary, 1- recurrent laryngeal carcinoma. 28 patients received concomitant chemotherapy and 13 were treated with neoadjuvant chemotherapy, 5 patients received postoperative radiotherapy and 28 received definitive radiotherapy. A comparative analysis of dose distributions and dose-volume histograms (DVH) between 2D and 3D plans for 11 patients with glottic and supraglottic carcinoma for the initial 50 Gy (since the 20 Gy boost was given almost identical in both technique) was carried out. Toxicity analysis was determined according to RTOG/EORTC toxicity criteria. Results: The mean dose coverage V45 (%) of the primary planning target volume for 2D and 3D plans was 89.6% and 94.8%, respectively (p=0.005). The mean volumes of the hot spots ( 110% of prescribed dose) for primary target volumes for 2D and 3D plans were: 61cc (range: 8.7–130.2 cc) and 26.2 cc (range: 0–49.8 cc), respectively (p=0.005). The mean dose to the parotid glands was significantly lower with 3D CRT (22.1 Gy and 24.7 Gy) compared to 2D technique (45.2 Gy and 46.4 Gy) for right and left parotids, respectively (p=0.003). The maximal spinal cord dose was: mean 45.3 Gy and 41.6 Gy for 2D and 3D CRT, respectively (p=0.003). Gr3 acute toxicity was observed in 3 patients (9%) , and Gr 4 toxicity in 6 patients ( 18%). Treatment was interrupted in 3 patients only. Conclusions: 3DCRT in head and neck cancer permits good coverage of the PTV .The low rate of acute toxicity can be explained by improving the dosimetric parameters of organs of risk and reducing the volume of hot spots in the target. Using 3D CRT for laryngeal carcinoma allows parotid sparing with a mean parotic dose of less than 26 Gy No significant financial relationships to disclose.

The impact of dental metal artifacts on head and neck IMRT dose distributions

Background and purposes To quantify the cold or hot spot induced in IMRT treatment plans due to the presence of metal artifact in CT image data sets stemming from dental work. Patients and methods Metal artifact corrected image data sets of five patients have been analyzed. IMRT plans were generated using five different planning image data sets: (a) uncorrected (UC) (b) homogeneous uncorrected (HUC), (c) sinogram completion corrected (SCC), (d) minimum value corrected (MVC), and (e) image set (d) subsequently corrected with a streak artifacts reduction algorithm (SAR–MVC). The SAR–MVC data set is assumed to be the closest approximation to the absence of metal artifacts and has therefore been taken as the reference image data set. An IMRT plan was generated for each of the image datasets (a)–(e). The resulting IMRT treatment plans for data sets (a)–(d) were then projected onto the reference data set (e) and recalculated. The reference dose distribution (e) was then subtracted from these recalculated dose distributions. Using dose difference analysis, the cold and hot spots in organs at risk (OARs) and the target volumes (TVs) were quantified. Results When compared to the reference dose distribution, the UC, HUC, and SCC plans exhibited hot spots showing on average more than 1.0 Gy hot dose in the left and right parotids. For the UC, HUC, and SCC recalculated plans, subvolumes of the clinical target volumes (CTV) were under dosed on average by more than 0.9 Gy. On the other hand, the MVC plan showed less than 0.3 Gy hot dose in both parotids, and the cold dose in the CTVs were reduced by up to 0.8 Gy. Conclusions The presence of dental metal artifacts in head and neck planning CT data sets can lead to relative hot spots in OARs and relative cold spots in regions of the TVs when compared to the reference data set that more closely approximates the patient anatomy. This effect can be reduced if a simple minimum value correction (MVC) method for the dental metal artifacts is employed.

SU-FF-J-55: Cumulative Dose Calculation Using Deformable Image Registration

Purpose: To use deformable image registration to calculate cumulative dose distributions received by a radiotherapy patient in order to evaluate the dosimetric impact of anatomical variations during the course of treatment. Method and Materials: An intensity-based deformable registration algorithm was developed to register the anatomy between the planning CT image and the daily CT images acquired from an in-room CT-on-rails system. After the transformation from daily CT to planning CT was found, daily treatment doses delivered to an organ can be meaningfully accumulated. For one head-and-neck patient, the treatment plan was transferred to 15 daily CT scans using bony registration, and the dose distributions were calculated for the daily anatomy without daily setup errors. Using deformable image registration, these daily dose distributions were mapped back to the planning CT image. The cumulative dose was calculated and compared to the original plan using dose-volume histograms (DVHs). Results: The dose delivered to the patient had minimal changes from the plan. Dose coverage for clinical target volumes at 70Gy, 63Gy, and 56Gy, left and right parotids at 25Gy, and mandible at 70Gy were evaluated. At these dose levels, the DVHs showed less than 1% difference, except for the left parotid, which had a 6% volume difference. The maximum dose in brainstem was 1.4% less than planned, the maximum dose in spinal cord was 2.2% higher than planned. The mean doses in left and right parotid were 4.4% higher and 2.5% lower than planned. Conclusion: In this case, we found little dosimetric differences due to changing anatomy during the course of treatment. Future studies will include daily setup errors. Deformable image registration is proven to be an effective approach for calculating cumulative dose distributions delivered to the patient, which can be used to evaluate the quality of treatment execution.

TU-C-J-6B-09: Automatic Contour Delineation On Subsequent CT Images Using Deformable Registration

Purpose: To implement a deformable registration algorithm to automatically delineate regions of interest (ROIs) on daily CT images by transforming the corresponding ROIs from a reference CT image. Method and Materials: An intensity-based ‘Demons’ deformable registration algorithm was used to find the correspondence between planning CT image and daily CT image. After reference ROIs were delineated manually on the reference CT image, the reference ROIs can be mapped onto each daily CT image. We tested this method on one head-and-neck patient (tonsil tumor). The patient received 3 CT scans per week prior to treatment for a total of 16 CT scans. The deformed ROIs were visually evaluated by a radiation oncologist. The dose-volume histograms (DVHs) of the deformed left and right parotids were calculated and compared with the planned DVHs. In addition, a cumulative dose distribution was calculated by mapping the daily dose distribution from each of the daily CT images back to the planning CT using the deformable registration method. Thus, the DVHs from the cumulative dose distribution can be calculated to represent the final “delivered” dose distribution. The volumetric changes during the elapsed treatment days for targets and critical structures were also investigated. Results: The deformed contours reasonably matched with gross anatomy presented by the CT images. The daily DVHs showed a large variation during the course of treatment due to both setup errors and internal organ deformation. In spite of large variation in DVHs of the parotids in daily CT images, the DVHs of the cumulative dose agreed reasonably well with the planned DVHs for both parotids in this case. Conclusion: We demonstrated that an intensity-based deformable registration algorithm can be used effectively to map the planning ROIs to subsequent CT images acquired during treatment. This allows effortless replanning in an adaptive CT-guided radiotherapy strategy.

Optimized radiotherapy in a locally advanced oropharyngeal carcinoma: Comparison of IMRT and proton beam

Curative treatment of oropharyngeal carcinoma with conventional radiation is limited by the tolerance of adjacent normal structures and the severity of acute reactions. Our aim was to compare the isodose distribution and dose volume histograms of two state of the art radiotherapy modalities, IMRT and proton beam radiation therapy in a patient with an advanced oropharyngeal carcinoma. Treatment plans were independently generated for a patient with T4N2c SCC of the right tongue base. Following standard head immobilization, 2.5 mm axial images were obtained with contrast enhancement using a GE CT-simulator. An MRI was also obtained before treatment planning. The contrast-enhanced tumor, entire base of tongue, and involved lymph nodes were contoured as GTV. The rest of the lymphatic system including supraclavicular lymph nodes contoured as CTV. The CTV also included a 1 cm margin around the GTV in the oropharynx. Spinal cord, brain stem, mandible, right and left parotids were delineated as Organs At Risk (OAR). The GTV and CTV were prescribed to 70.2 and 59.4 Gy respectively at 1.8 Gy per fraction, with 5 mm margins. Normal tissue constraints were 44, 54, and 60 Gy for spinal cord, brainstem and mandible respectively. Parotid doses were kept as low as possible. The same volumes, target doses and dose constraints were used for both treatment plans. The most significant finding was the uniformity of dose within the two target volumes and in normal tissues proximal to the CTV. The dose encompassing the GTV and CTV was much more homogeneous and conformal in the proton beam plan. The proton DVH for the GTV was steeper than that of IMRT and resulted in almost all of GTV uniformly receiving the prescribed dose of 70.2 Gy. In the IMRT plan, most of the GTV received a dose in excess of what was prescribed, 50 % of the GTV received a dose of >75 Gy and 25 % >78 Gy. The CTV coverage with protons was also better than with IMRT. Protons had more sparing of non-target tissues. Doses in the IMRT plan were spread out beyond the target volumes producing unwanted radiation at the non-target tissues such as the anterior oral cavity. The DVH for OAR, mandible and spinal cord also demonstrated a better distribution with protons. The median dose to the mandible was less than 10 Gy with protons while 47 Gy with IMRT. Fifty percent of the spinal cord volume received less than 30 Gy with protons, in contrast, 90% received >30 Gy with IMRT (see Figure). Because of the proximity of lymphatic CTV to both parotid glands, there was little difference in parotid doses between IMRT and protons. Protons produced superior dose distributions to the GTV and CTV with less dose to OAR and non-target tissues than IMRT in an advanced oropharyngeal cancer. The inhomogeneity of dose and the location of hot spots within the oropharynx with IMRT is problematic. This can cause an excessive mucositis and compromise the delivery of concurrent chemo radiotherapy and possibly lead to late morbidity. Even though the IMRT plan provided acceptable OAR doses, there is less organ dose with protons and potential risk of late injury.

Three-dimensional intensity-modulated radiotherapy in the treatment of nasopharyngeal carcinoma: the University of California–San Francisco experience

Purpose: To review our experience with three-dimensional intensity-modulated radiotherapy (IMRT) in the treatment of nasopharyngeal carcinoma. Methods and Materials: We reviewed the records of 35 patients who underwent 3D IMRT for nasopharyngeal carcinoma at the University of California–San Francisco between April 1995 and March 1998. According to the 1997 American Joint Committee on Cancer staging classification, 4 (12%) patients had Stage I disease, 6 (17%) had Stage II, 11 (32%) had Stage III, and 14 (40%) had Stage IV disease. IMRT of the primary tumor was delivered using one of the following three techniques: ( 1) manually cut partial transmission blocks, ( 2) computer-controlled autosequencing static multileaf collimator (MLC), and ( 3) Peacock system using a dynamic multivane intensity-modulating collimator (MIMiC). A forward 3D treatment-planning system was used for the first two methods, and an inverse treatment planning system was used for the third method. The neck was irradiated with a conventional technique using lateral opposed fields to the upper neck and an anterior field to the lower neck and supraclavicular fossae. The prescribed dose was 65–70 Gy to the gross tumor volume (GTV) and positive neck nodes, 60 Gy to the clinical target volume (CTV), and 50–60 Gy to the clinically negative neck. Eleven (32%) patients had fractionated high-dose-rate intracavitary brachytherapy boost to the primary tumor 1–2 weeks following external beam radiotherapy. Thirty-two (91%) patients also received cisplatin during, and cisplatin and 5-fluorouracil after, radiotherapy. Acute and late normal tissue effects were graded according to the Radiation Therapy Oncology Group (RTOG) radiation morbidity scoring criteria. Local-regional progression-free, distant metastasis-free survival and overall survival were estimated using the Kaplan–Meier method. Results: With a median follow-up of 21.8 months (range, 5–49 months), the local-regional progression-free rate was 100%. The 4-year overall survival was 94%, and the distant metastasis-free rate was 57%. The worst acute toxicity was Grade 2 in 16 (46%) patients, Grade 3 in 18 (51%) patients and Grade 4 in 1 (3%) patient. The worst late toxicity was Grade 1 in 15 (43%), Grade 2 in 13 (37%), and Grade 3 in 5 (14%) patients. Only 1 patient had a transient Grade 4 soft-tissue necrosis. At 24 months after treatment, 50% of the evaluated patients had Grade 0, 50% had Grade 1, and none had Grade 2 xerostomia. Analysis of the dose–volume histograms (DVHs) showed that the average maximum, mean, and minimum dose delivered were 79.5 Gy, 75.8 Gy, and 56.5 Gy to the GTV, and 78.9 Gy, 71.2 Gy, and 45.4 Gy to the CTV, respectively. An average of only 3% of the GTV and 2% of the CTV received less than 95% of the prescribed dose. The average dose to 5% of the brain stem, optic chiasm, and right and left optic nerves was 48.3 Gy, 23.9 Gy, 15.0 Gy, and 14.9 Gy, respectively. The average dose to 1 cc of the cervical spinal cord was 41.7 Gy. The doses delivered were within the tolerance of these critical normal structures. The average dose to 50% of the right and left parotids, pituitary, right and left T-M joints, and ears was 43.2 Gy, 41.0 Gy, 46.3 Gy, 60.5 Gy, 58.3 Gy, 52.0 Gy, and 52.2 Gy, respectively. Conclusion: 3D intensity-modulated radiotherapy provided improved target volume coverage and increased dose to the gross tumor with significant sparing of the salivary glands and other critical normal structures. Local-regional control rate with combined IMRT and chemotherapy was excellent, although distant metastasis remained unabated.

中耳手術後の耳下腺唾液流量の測定

Parotid salivary flow in 53 patients with chronic otitis media and in 20 normal control subjects was measured pre- and postoperatively. There were no statistically significant differences between the right and left parotids. Neither chronic otitis media nor cholesteatoma disturbed parotid salivary flow. Resection of Jacobson's nerve or the chorda tympani reduced parotid salivary flow. Resection of both nerves doubled the reduction of parotid salivary flow. These results suggest that the chorda tympani affects parotid secretion. The chorda tympani may contain secretory fibers to the parotid gland or autonomic nerve fibers which influence the parotid salivary secretion. However, this assumption is difficult to confirm, partly because of species differences or even differences in a single species of the innervations to the parotid gland. In our study contralateral parotid salivary flow did not reveal significant changes postoperatively. Postoperative reduction of parotid salivary flow was nearly fully restored approximately 9 months after middle ear surgery.