Cord Dose Research Articles

Optimal plan target in cases with locally advanced nasopharyngeal cancer: Comparison of VMAT, IMRT, hybrid, and tomotherapy results.

In locally advanced nasopharyngeal cancer (NC), the spread of the disease, proximity to critical structures, and high dose requirement for tumor control may complicate the treatment plan. In this study, VMAT/IMRT/hybrid/tomotherapy plans were made to reach the safest and most effective dose distribution for each of the patients and the results were compared. Double volumetric-modulated arc therapy (VMAT) and 7- and 9-field intensity-modulated radiation therapy (IMRT) plans were made to 21 locally advanced NCs with Varian Trilogy System. It was observed that appropriate dose distributions could not be achieved with IMRT or VMAT, and hybrid IMRT-VMAT plans were made. All cases were also planned with Tomotherapy Precision System, and the data of four different techniques were compared retrospectively. For normal tissue tolerances in 73 structures could not be obtained with VMAT and 38 structures with IMRT whereas the desired tolerance was provided with the hybrid plan. Hybrid plans were made with an average of 14 VMATs and 20 IMRTs. The maximum brainstem and spinal cord doses were found significantly lower in hybrid and tomotherapy techniques. Homogeneity index (HI) and conformity index (CI) values were the best in hybrid plans. No statistically significant difference between the hybrid plan and tomotherapy in terms of normal tissue tolerance doses and HI whereas a significant difference was found in the hybrid plan for CI. It was observed that the most ideal plans for the locally advanced NC could be obtained with tomotherapy and hybrid plan techniques that the better protection in critical structures and desired dose distribution at target volumes.

4DCT ventilation function image-based functional lung protection for esophageal cancer radiotherapy.

4DCT (four-dimensional computed tomography) can effectively obtain functional lung ventilation images for patients and integrate them into radiotherapy treatment planning. Studies have not been performed on esophageal cancer, and there is no clear consensus on the optimal functional lung threshold for functional lung. Functional lung images were generated for 11patients with esophageal cancer. The correlation between the dose-volume parameters of functional lung (FL) as defined by different thresholds and the change of PFT/PDFT (pulmonary [diffusion] function test) metrics before and after radiotherapy were evaluated. FL-sparing planning was generated for each patient to preserve the functional lung and compared to conventional anatomical CT (non-sparing) planning. There was asignificant positive correlation between the FL0.8 (defined Jacobian value ≤ 0.8), FL0.84, and FL0.9 dose-volume parameters and ΔFEV1/FVC (reduction before and after radiotherapy), and the FL0.8‑V30 correlation was the strongest (r = 0.819, P < 0.01). The FL-sparing planning had atarget area conformity index and homogeneity index comparable to the non-sparing planning (P > 0.05). For FL, the FL-sparing planning achieved lower FL-MLD (6.30 ± 2.14 Gy vs. 7.83 ± 2.70 Gy), V10 (17.13 ± 7.70% vs. 27.40 ± 9.48%), and V20 (6.96 ± 3.85% vs. 11.63 ± 7.19%) compared to the non-sparing planning (P < 0.05), while heart and spinal cord doses were not significantly different between the two planning groups. The 4DCT-based FL irradiation dose for esophageal cancer was significantly associated with adecrease in FEV1/FVC. The optimal FL defined as a Jacobian value ≤ 0.8 or about 21% of the whole lung volume may be a good choice. FL-sparing planning significantly reduced the FL dose without compromising target area coverage.

Dynamic conformal arc radiotherapy for locally advanced lung cancer: a comparison with static-beam conformal radiotherapy.

This study investigated whether the dose distribution of lung cancer can be improved by dynamic arc conformal radiotherapy (dynamic CRT) compared with static multiple-beam radiotherapy (static CRT). A dummy study of static CRT and dynamic CRT was performed, designed to meet the predetermined dose constraints. A dose of 60 Gy in 30 fractions was administered using two dose prescription methods: dose prescribed to the isocenter (IC prescription), and dose prescribed to > 50% of the planning target volume (D50 prescription). Dose-volume parameters were compared between the plans. Among 20 patients with locally advanced lung cancer, dose conformity was significantly better with dynamic CRT than static CRT (median conformity index: 1.3 vs. 2.2; p < 0.01). As for the lung dose, compared with static CRT, dynamic CRT did not increase the percentage lung volume receiving ≥ 20 Gy (18.9% vs. 19.3%, p = 0.09). The maximum spinal cord dose was significantly reduced by dynamic CRT (static vs. dynamic CRT: 44.1 vs. 25.2 Gy, p < 0.001). With the change from IC to D50 prescription, the 95% isodose volume increased by 18.3 cc in static CRT and by 4.1 cc in dynamic CRT, while doses to the lung and spinal cord remained within the acceptable ranges. The dynamic CRT technique showed better target coverage and lower doses to the spinal cord in exchange for increased low-dose lung area, compared with static CRT. Dynamic CRT with D50 prescription instead of prescription to the isocenter has excellent dose distribution profiles without compromising doses to organs at risk for lung cancer at favorable locations.

Preliminary Evaluation of Postoperative Radiotherapy between Small T-Shaped Field and All Regional Lymph Nodes Field in Thoracic Esophageal Squamous Cell Carcinoma

<h3>Purpose/Objective(s)</h3> The optimal extent of clinical target volume (CTV) for postoperative radiotherapy in complete resection thoracic esophageal squamous cell carcinoma (ESCC) patients remains controversial. This study aimed to evaluate the preliminary results of postoperative radiotherapy with standard all regional lymph nodes field and adjusted small T-shaped field. <h3>Materials/Methods</h3> A total of 75 thoracic ESCC patients were enrolled from April 2017 to March 2021, retrospectively. Among them were 63 males and 12 females, with an average age of 64.28 (range, 49-82) years. All patients received intensity-modulated radiotherapy (IMRT) at a dose of 45-50.4Gy/25-28F after radical resection of esophageal carcinoma, of which 39 cases were small T-shaped field (including bilateral supraclavicular lymph nodes, upper and middle mediastinal lymph nodes, small T group),36 cases were all regional lymph nodes field (including tumor bed, bilateral supraclavicular lymph nodes, all mediastinal lymph nodes, left gastric lymph nodes and celiac lymph nodes, control group). 24 cases (32%) received concurrent chemotherapy and 57 cases (76%) received adjuvant chemotherapy. The median follow-up period was 31(range, 15-57) months. <h3>Results</h3> At the end of follow-up period, 7 (17.9%) cases had locoregional recurrence (LRR) and 8(20.5%) had distant metastasis (DM) in small T group, while 9 (25%) cases had LRR and 9 (25%) had DM in control group. There was no significant difference in LRR rate (p=0.456) and DM rate (p=0.643) between the two groups. There was also no significant difference in the total OS rate between the two groups (p=0.146). In terms of radiotherapy parameters, in small T group, the median values of V5, V20 and average dose of the lungs were 37.31%, 16.43% and 8.11Gy, respectively. The median value of the maximum dose of spinal cord was 29.95Gy. For the heart, the median value of the average dose and V30 were 5.13Gy and 2.64%. And the median value of V40 of the stomach was 34.32%. In control group, the median values of V5, V20 and average dose of the lungs were 53.49%, 22.08% and 11.41Gy. The median value of the maximum dose of spinal cord was 36Gy. For the heart, the median value of the average dose and V30 were 27.52Gy and 37.39%. And the median value of V40 of the stomach was 63%. All of the above parameters in small T group were significantly lower than those in control group (p<0.05). In addition, we observed grade 2 radiation pneumonitis and grade 2 radiation esophagitis in both groups:9 cases of radiation pneumonia with grade 2 or above in control group and only 1 case in small T group (p<0.001). There were 15 cases of radiation esophagitis with grade 2 or above in control group and 6 cases in small T group (p=0.024). <h3>Conclusion</h3> In conclusion, radiotherapy with small T-shaped field might be a feasible and efficacious postoperative approach for ESCC patients.

Dosimetric Analysis of Online Adaptive Radiation Therapy in the Adjuvant Setting for Head and Neck Cancer

<h3>Purpose/Objective(s)</h3> Online adaptive radiotherapy (OnART) system designed to deliver re-optimized plans in real time using on-board cone beam CT and artificial intelligence has enabled frequent adaptation. Given the paucity of data on the role of adaptive radiotherapy (RT) and its frequency in the treatment of post-operative patients with head and neck squamous cell carcinoma (HNSCC), a dosimetric study was performed to assess the potential benefits of a single vs weekly OnART in this setting. <h3>Materials/Methods</h3> Twelve patients receiving conventionally fractionated RT (CFRT) over 6 weeks and 12 patients receiving hypofractionated RT (HFRT) over 3 weeks on a clinical trial between 2020 and 2021 were analyzed. The OnART plan was generated to meet the same quality as the original clinical plan and the OnART emulator was used to virtually conduct adaptive RT based on the patient's cone beam CT. The PTV coverage, dose heterogeneity, and cumulative dose to the organs-at-risk of a single mid-treatment OnART (at week 4 for CFRT and week 2 for HFRT) and weekly OnART were compared to the non-adapted plan. <h3>Results</h3> In total, 13, 8, and 3 patients had oral cavity, oropharynx, and larynx primaries, respectively, with 11 of the 24 patients receiving ipsilateral RT only. The average absolute and % weight loss during treatment were 5.7 lb and 3.1%, respectively. In the CFRT cohort, weekly OnART led to a significant improvement in high risk PTV (PTVHR) and standard risk PTV (PTVSR) V100 coverage (9.9% and 3.4% absolute) as well as hot spot (-1.3 Gy), max cord dose (-3.4 Gy), and mean oral cavity dose (-1.3 Gy), while the mean contralateral parotid dose increased modestly (0.76 Gy) (Table). When adapted once, only PTVHR coverage was improved (3.3%). For the HFRT cohort, weekly OnART resulted in a significant improvement in PTVHR/PTVSR coverage (3.7%/2.0%), hot spot (-0.82 Gy), and max cord dose (-2.5 Gy) (Table). When adapted once, mean oral cavity dose decreased (-1.4 Gy) and mean contralateral parotid dose increased (1.1 Gy). <h3>Conclusion</h3> There was a limited benefit of one-time OnART, but weekly adaptations improved the dosimetry, predominantly in PTV coverage and dose heterogeneity for patients receiving adjuvant RT for HNSCC. A prospective study is ongoing to determine the potential benefit in clinical and patient-reported outcomes of OnART in this setting.

Safety and Efficacy of Dose-Escalated Radiotherapy with a Simultaneous Integrated Boost for the Treatment of Spinal Metastases

<h3>Purpose/Objective(s)</h3> Dose-escalated radiotherapy (RT) using a spinal simultaneous integrated boost (SSIB) has been recently utilized for treatment of metastatic lesions not amenable to spine stereotactic radiosurgery (SSRS). Prior reports have utilized small sample sizes with short follow-up times. Our goal was to characterize the long-term efficacy and safety of this technique in a large cohort of patients with long term follow-up. <h3>Materials/Methods</h3> We reviewed 58 patients with 63 spinal metastatic sites that were treated with RT using a SSIB between 2012 and 2021. All patients received 30 Gy to the clinical tumor volume (CTV)and 40 Gy to the gross tumor volume, each delivered simultaneously in 10 fractions (GTV). Acute and late toxicities were noted for each patient. Local control (LC) was defined as having no progression on magnetic resonance imaging (MRI) at the SSIB-treated site. Overall survival (OS) was defined as the time from initiation of SSIB to death or last follow up, and was estimated using the Kaplan-Meier method. Multivariable Cox analysis was performed to identify associations with OS and LC. <h3>Results</h3> In our cohort, the median Karnofsky Performance Score (KPS) prior to RT was 80 (interquartile range [IQR], 80-90). Tumor histology was considered to be radioresistant in 81% of patients. Most patients had paraspinal involvement (65%) and epidural extension (82%). The median follow-up was 31 months with a median OS of 18 months (95% confidence interval [CI], 13-27 months). OS at 1, 2, and 3 years were 64%, 45%, and 24%, respectively. Actuarial LC was 98% (CI, 95-100%) and 95% (CI, 89-100%) at 1 and 2 years, respectively. The median GTV and CTV doses were 4123 cGy (range, 3400-4318 cGy) and 3641 cGy (range, 3302-4089 cGy), respectively. The mean cord dose was 2401 cGy (range 59-3168 cGy). The most commonly observed acute toxicities were fatigue (41%), pain (38%), esophagitis (8%), and nausea (8%). However, only one patient (2%) experienced Grade 3 or higher toxicity (pain). At last follow-up, no patients had developed myelopathy and all patients maintained ambulation. Following RT, pain improvement was achieved in 82% with a median pain score of 2 (IQR, 1-4) out of 10 from a pre-RT baseline of 4 (IQR, 3-6). Multivariable Cox analysis revealed that higher KPS score prior to RT (hazard ratio [HR], 0.40, 95%, CI, 0.20-0.84; <i>P</i>=0.016) was associated with longer OS, whereas increased size of PTV (HR 1.003, CI 1.001-1.005; <i>P</i>=0.017) was associated with shorter survival. <h3>Conclusion</h3> Our data show that the use of RT with SSIB provides favorable LC and OS with improved pain relief for selected patients that are not amenable for SSRS. Importantly, there were limited acute toxicities with no observed instances of radiation-induced myelopathy. Multi-institutional validation is warranted.

Dosimetric analysis and biological evaluation between proton radiotherapy and photon radiotherapy for the long target of total esophageal squamous cell carcinoma.

ObjectiveThe purpose of this study is to compare the dosimetric and biological evaluation differences between photon and proton radiation therapy.MethodsThirty esophageal squamous cell carcinoma (ESCC) patients were generated for volumetric modulated arc therapy (VMAT) planning and intensity-modulated proton therapy (IMPT) planning to compare with intensity-modulated radiation therapy (IMRT) planning. According to dose–volume histogram (DVH), dose–volume parameters of the plan target volume (PTV) and homogeneity index (HI), conformity index (CI), and gradient index (GI) were used to analyze the differences between the various plans. For the organs at risk (OARS), dosimetric parameters were compared. Tumor control probability (TCP) and normal tissue complication probability (NTCP) was also used to evaluate the biological effectiveness of different plannings.ResultsCI, HI, and GI of IMPT planning were significantly superior in the three types of planning (p < 0.001, p < 0.001, and p < 0.001, respectively). Compared to IMRT and VMAT planning, IMPT planning improved the TCP (p<0.001, p<0.001, respectively). As for OARs, IMPT reduced the bilateral lung and heart accepted irradiation dose and volume. The dosimetric parameters, such as mean lung dose (MLD), mean heart dose (MHD), V 5, V 10, and V 20, were significantly lower than IMRT or VMAT. IMPT afforded a lower maximum dose (D max) of the spinal cord than the other two-photon plans. What’s more, the radiation pneumonia of the left lung, which was caused by IMPT, was lower than IMRT and VMAT. IMPT achieved the pericarditis probability of heart is only 1.73% ± 0.24%. For spinal cord myelitis necrosis, there was no significant difference between the three different technologies.ConclusionProton radiotherapy is an effective technology to relieve esophageal cancer, which could improve the TCP and spare the heart, lungs, and spinal cord. Our study provides a prediction of radiotherapy outcomes and further guides the individual treatment.

Risk-adapted stereotactic body radiotherapy for patients with cervical spinal metastases.

Owing to the complex anatomical structure and biomechanics, the current standard palliative treatments for cervical spinal metastases are associated with a high risk of recurrence and complications. Stereotactic body radiotherapy (SBRT) can provide radical dose to tumors while protecting normal organs to the maximum extent. However, the efficacy and safety of SBRT for cervical spinal metastases is not well characterized. Data from 71 patients with cervical spine metastases who were treated with SBRT using CyberKnife between 2006 and 2021 were obtained from our prospectively maintained database. Primary endpoint was pain response at 12 weeks following SBRT completion; secondary endpoints included local control (LC), overall survival (OS), and adverse events. Standard-risk patients were planned to receive 30 Gy (range 21-36) with median fractions of 3 (range 1-3) and high-risk patients 35 Gy (range 24-50) with median fractions of 5 (range 4-5) according to the spinal cord and esophagus dose constraints. The median follow-up time was 17.07 months (range 3.1-118.9). After 12 weeks of SBRT completion, 54 (98.2%) of 55 patients with baseline pain achieved pain response and 46 (83.6%) achieved complete pain response. LC rates were 93.1% and 90% at 1 year and 2 year, respectively. The 1-year and 2-year OS rates were 66.2% and 37.4%, respectively. Eight patients experienced grades 1-4 adverse events (six vertebral compression fracture [VCF], five of them had VCF before SBRT; and two hemiparesis). No grade 5 adverse events were observed. Therefore, risk-adapted SBRT for cervical spine metastases achieved high pain control and LC rates with acceptable adverse events.

Investigation of four-dimensional (4D) Monte Carlo dose calculation in real-time tumor tracking stereotatic body radiotherapy for lung cancers.

To investigate the dosimetric variations and radiobiological impacts as a consequence of delivering treatment plans of 3D nature in 4D manner based on the 4D Monte Carlo treatment planning framework implemented on Cyberknife. Dose distributions were optimized on reference 3D images at end of exhale phase of a 4DCT dataset for twenty-five lung cancer patients treated with 60 Gy / 3Fx or 48 Gy / 4Fx. Deformable image registrations (DIR) between individual 3DCT images to the reference 3DCT image in the 4DCT study were performed to interpolate doses calculated on multiple anatomical geometries back on to the reference geometry to compose a 4D dose distribution that included the tracking beam motion and organ deformation. The 3D and 4D dose distributions that were initially calculated with the equivalent path-length (EPL) algorithm (3DEPL dose and 4DEPL dose) were recalculated with the Monte Carlo algorithm (3DMC dose and 4DMC dose). Dosimetric variations of V60Gy / 48Gy and D99 of GTV, mean doses to the lung and the heart and maximum dose (D1 ) of the spinal cord as a consequence of tracking beam motion in deforming anatomy, dose calculation algorithm, and both were quantified by the relative change from 4DMC to 3DMC doses, from 4DMC to 4DEPL doses, and from 4DMC to 3DEPL doses, respectively. Comparing 4DMC to 3DEPL plans, V60Gy / 48Gy and D99 of GTV decreased considerably by 13 ± 22% (mean ± 1SD) and 9.2 ± 5.5 Gy but changes of normal tissue doses were not more than 0.5 Gy on average. The generalized equivalent uniform dose (gEUD) and tumor control probability (TCP) were reduced by 14.3 ± 8.8 Gy and 7.5 ± 5.2%, and normal tissue complication probability (NTCP) for myelopathy and pericarditis were close to zero and NTCP for radiation pneumonitis was reduced by 2.5 ± 4.1%. Comparing 4DMC to 4DEPL plans found decreased V60Gy / 48Gy and D99 by 12.3 ± 21.6% and 7.3 ± 5.3 Gy, the normal tissues doses by 0.5 Gy on average, gEUD and TCP by 13.0 ± 8.6 Gy and 7.1 ± 5.1%. Comparing 4DMC to 3DMC doses, V60Gy / 48Gy and D99 of GTV was reduced by 5.2 ± 8.8 %and 2.6 ± 3.3 Gy, and normal tissues hardly changed from 4DMC to 3DMC doses. The corresponding decreases of gEUD and TCP were 2.8 ± 4.0 Gy and 1.6 ± 2.4%. The large discrepancy between original 3DEPL plan and benchmarking 4DMC plan is predominately due to dose calculation algorithms as the tracking beam motion and organ deformation hardly influenced doses of normal tissues and moderately decreased V60Gy / 48Gy and D99 of GTV. It is worth to make a thoughtful weight of the benefits of full 4D MC dose calculation and consider 3D MC dose calculation as a compromise of 4D MC dose calculation considering the multifold computation time. This article is protected by copyright. All rights reserved.

Dosimetric analysis of MR-LINAC treatment plans for salvage spine SBRT re-irradiation.

PurposeWe investigated the feasibility of thoracic spine stereotactic body radiotherapy (SBRT) using the Elekta Unity magnetic resonance‐guided linear accelerator (MRL) in patients who received prior radiotherapy. We hypothesized that Monaco treatment plans can improve the gross tumor volume minimum dose (GTVmin) with spinal cord preservation and maintain consistent plan quality during daily adaptation.MethodsPinnacle clinical plans for 10 patients who underwent thoracic spine SBRT (after prior radiotherapy) were regenerated in the Monaco treatment planning system for the Elekta Unity MRL using 9 and 13 intensity‐modulated radiotherapy (IMRT) beams. Monaco adapt‐to‐position (ATP) and adapt‐to‐shape (ATS) workflow plans were generated using magnetic resonance imaging with a simulated daily positional setup deviation, and these adaptive plans were compared with Monaco reference plans. Plan quality measures included target coverage, Paddick conformity index, gradient index, homogeneity index, spinal cord D0.01cc, esophagus D0.01cc, lung V10, and skin D0.01cc.ResultsGTVmin values from the Monaco 9‐beam and 13‐beam plans were significantly higher than those from Pinnacle plans (p < 0.01) with similar spinal cord dose. Spinal cord D0.01cc, esophagus D0.01cc, and lung V10 did not statistically differ among the three plans. The electron‐return effect did not induce remarkable dose effects around the lungs or skin. While in the ATP workflow, a large increase in GTVmin was observed at the cost of a 10%–50% increase in spinal cord D0.01cc, in the ATS workflow, the spinal cord dose increase was maintained within 3% of the reference plan.ConclusionThese findings show that MRL plans for thoracic spine SBRT are safe and feasible, allowing tumor dose escalation with spinal cord preservation and consistent daily plan adaptation using the ATS workflow. Careful plan review of hot spots and lung dose is necessary for safe MRL‐based treatment.

Dose rate and dose robustness for proton transmission FLASH-RT treatment in lung cancer.

To evaluate the plan quality and robustness of both dose and dose rate of proton pencil beam scanning (PBS) transmission FLASH delivery in lung cancer treatment. An in-house FLASH planning platform was used to optimize 10 lung cancer patients previously consecutively treated with proton stereotactic body radiation therapy (SBRT) to receive 3 and 5 transmission beams (Trx-3fds and Trx-5fds, respectively) to 34 Gy in a single fraction. Perturbation scenarios (n=12) for setup and range uncertainties (5mm and 3.5%) were introduced, and dose-volume histogram and dose-rate-volume histogram bands were generated. Conventional proton SBRT clinical plans were used as a reference. RTOG 0915 dose metrics and 40 Gy/s dose rate coverage (V40Gy/s) were used to assess the dose and dose rate robustness. Trx-5fds yields a comparable iCTV D2% of 105.3%, whereas Trx-3fds resulted in inferior D2% of 111.9% to the clinical SBRT plans with D2% of 105.6% (p<0.05). Both Trx-5fds and Trx-3fds plans had slightly worse dose metrics to organs at risk than SBRT plans. Trx-5fds achieved superior dosimetry robustness for iCTV, esophagus, and spinal cord doses than both Trx-3fds and conventional SBRT plans. There was no significant difference in dose rate robustness for V40Gy/s coverage between Trx-3fds and Trx-5fds. Dose rate distribution has similar distributions to the dose when perturbation exists. Transmission plans yield overall modestly inferior plan quality compared to the conventional proton SBRT plans but provide improved robustness and the potential for a toxicity-sparing FLASH effect. By using more beams (5- versus 3-field), both dose and dose rate robustness for transmission plans can be achieved.

Radiation myelopathy following stereotactic body radiation therapy for spine metastases.

Stereotactic body radiation therapy (SBRT) is now considered a standard of care treatment option in the management of spine metastases. One of the most feared complications of spine SBRT is radiation myelopathy (RM). We provided a narrative review of RM following spine SBRT based on review of the published literature, including data on spinal cord dose constraints associated with the risk of RM, strategies to mitigate the risk, and management options for RM. There are limited published data of cases of RM following spine SBRT with detailed spinal cord dosimetry. The HyTEC report provided recommendations for the point maximal dose (Dmax) for the spinal cord that is associated with a < 5% risk of RM for 1-5 fractions spine SBRT. In the setting of spine SBRT reirradiation after previous conventional external beam radiation therapy (cEBRT), factors associated with RM are: SBRT spinal cord Dmax, cumulative spinal cord Dmax, and the time interval between previous RT and SBRT reirradiation. There are various strategies to mitigate the risk of RM, including accurate delineation of the spinal cord (or thecal sac), strict adherence to the recommended spinal cord dose constraints, and robust treatment immobilisation set-up and delivery. Limited effective treatment options are available for patients who develop RM, and these include corticosteroids, hyperbaric oxygen, and bevacizumab; however, none have been supported by high quality evidence. RM is a rare but devastating complication following SBRT for spine metastases. There are strategies to minimise the risk of RM to ensure safe delivery of spine SBRT.

RONC-05. Peri-transplant Radiation Therapy for Young Children Treated with High-Dose Chemotherapy for Primary Brain Tumors

PURPOSE: The role of peri-transplant radiation therapy (RT) in young children with primary brain tumors is unclear. We characterized our institutional practice patterns and patient outcomes. MATERIALS AND METHODS: The cohort included all patients treated with high-dose chemotherapy for primary brain tumors at our institution from 2011-2017. Rates of local control (LC), progression-free survival (PFS), overall survival (OS), and radiation-associated injury were assessed. RESULTS: Of 37 eligible patients, 29 (78%) received peri-transplant RT at a median age of 4 years. Patients treated with RT were more likely to have metastatic (p=0.0121) and incompletely resected (p=0.056) disease, and to have high-risk histologies including atypical teratoid rhabdoid tumor, nongerminomatous germ cell tumor, pineoblastoma, primitive neuro-ectodermal tumor, glioneuronal tumor and group 3 medulloblastoma. Of those treated with RT, 13 (45%) received craniospinal irradiation (CSI) and 16 (55%) received focal RT. The median CSI dose was 23.4 Gy (IQR: 18-36; boost median 54 Gy [IQR: 53.7-55.8]) and focal RT dose was 50.4 Gy (IQR: 50.4-54.5). Compared to the focal RT group, patients treated with CSI were older (p=0.0499) and more likely to have metastatic disease (p=0.0004). For the complete cohort, at a median follow-up of 3.8 years, the 2-year rate of LC was 82% (95% CI: 70-96%), PFS was 63% (95% CI: 49-81%), and OS was 65% (95% CI: 51-82%). These rates did not differ significantly between patients treated with and without peri-transplant RT. Two cases of fatal myelopathy were observed after spinal cord doses within the highest tertile (41.4 CGE and 36 Gy); both cases occurred in patients who received RT before high-dose chemotherapy. CONCLUSION: Peri-transplant RT was used for high-risk disease. Oncologic outcomes after RT were encouraging. However, 2 cases of grade 5 myelopathy were observed. If used cautiously, RT may contribute to durable remission in patients at high risk of relapse.

Induction chemotherapy using carboplatin and paclitaxel followed by hypofractionated radiation therapy in locally advanced hypopharyngeal and laryngeal squamous cell cancer.

e18039 Background: Head and neck cancer (HNC) is one of the most common cancers in Pakistan due to excessive use of chewable tobacco. Locoregional control is not optimum due to advanced stage at presentation and suboptimal cancer treatment facilities. Innovations in treatment schedules are of utmost importance to tackle the problem of overburden of patients and shortage of resources for radiation therapy in the country. The aim of the study is to assess the efficacy of induction chemotherapy with carboplatin and paclitaxel (CP) followed by hypofractionated radiotherapy (HRT) in patients with locally advanced laryngeal and hypopharyngeal cancers. Methods: A total of 68 patients with biopsy proven HNC were included. Patients having primary tumor in larynx (35) and hypopharynx (33) with TNM stage III to IVB were selected. The patients were planned for three cycles of CP every three weeks in a dose of AUC = 5 and 175 mg/m² on day 1 of each cycle respectively. After three cycles of chemotherapy, patients were planned for hypofractionated radiotherapy (HRT). A total of 55 Gray (Gy) was planned with 2.75 Gy per fraction and five fractions a week. Spinal cord dose was limited to 33 Gy. Response Evaluation Criteria in Solid Tumor (RECIST) was used to assess various response rates using computed tomography (CT) six weeks after completion of HRT. Patients were followed for a median of 27.4 months to assess disease free survival (DFS) and overall survival (OS). Results: 61 patients (90%) were available for assessment. Others were excluded due to inability to complete the planned treatment. Eight patients (12%) showed disease progression during treatment and were switched to other form of treatment. Seven patients (10%) showed grade 3 mucosal toxicity and needed treatment interruption. Thirteen patients (19%) showed hematological related grade 1-2 toxicity. The complete response (CR) was seen in 18 (35%), partial response (PR) in 27 (52%) and stable disease SD in 7 (13%) patients. Three year DFS and OS were 45% and 58% respectively. Mean and median DFS (year) were 3.67±0.13 (95% confidence interval [CI] 3.19-3.94) and 4.24±0.43 (CI 3.46-4.52) respectively. Mean and median OS (year) were 3.89±0.11 (CI 3.72-4.15) and 4.12±0.23 (CI 3.87-4.38) respectively. Conclusions: Induction CP followed by HRT is a reasonable in locally advanced laryngeal and hypopharyngeal cancer. A larger phase III randomized trial will be better to define its role before routinely recommending this schedule in these patients.

PO-1516 Change in spinal cord dose of treatment plan using CT myelography image in spine SBRT

PO-1516 Change in spinal cord dose of treatment plan using CT myelography image in spine SBRT

Organ-at-risk dose prediction using a machine learning algorithm: Clinical validation and treatment planning benefit for lung SBRT.

ObjectiveTo quantify the clinical performance of a machine learning (ML) algorithm for organ‐at‐risk (OAR) dose prediction for lung stereotactic body radiation therapy (SBRT) and estimate the treatment planning benefit from having upfront access to these dose predictions.MethodsML models were trained using multi‐center data consisting of 209 patients previously treated with lung SBRT. Two prescription levels were investigated, 50 Gy in five fractions and 54 Gy in three fractions. Models were generated using a gradient‐boosted regression tree algorithm using grid searching with fivefold cross‐validation. Twenty patients not included in the training set were used to test OAR dose prediction performance, ten for each prescription. We also performed blinded re‐planning based on OAR dose predictions but without access to clinically delivered plans. Differences between predicted and delivered doses were assessed by root‐mean square deviation (RMSD), and statistical differences between predicted, delivered, and re‐planned doses were evaluated with one‐way analysis of variance (ANOVA) tests.ResultsANOVA tests showed no significant differences between predicted, delivered, and replanned OAR doses (all p ≥ 0.36). The RMSD was 2.9, 3.9, 4.3, and 1.7Gy for max dose to the spinal cord, great vessels, heart, and trachea, respectively, for 50 Gy in five fractions. Average improvements of 1.0, 1.4, and 2.0 Gy were seen for spinal cord, esophagus, and trachea max doses in blinded replans compared to clinically delivered plans with 54 Gy in three fractions, and 1.8, 0.7, and 1.5 Gy, respectively, for the esophagus, heart and bronchus max doses with 50 Gy in five fractions. Target coverage was similar with an average PTV V100% of 94.7% for delivered plans compared to 97.3% for blinded re‐plans for 50 Gy in five fractions, and respectively 98.4% versus 99.2% for 54 Gy in three fractions.ConclusionThis study validated ML‐based OAR dose prediction for lung SBRT, showing potential for improved OAR dose sparing and more consistent plan quality using dose predictions for patient‐specific planning guidance.

Risk of radiculopathy caused by second course of spine stereotactic body radiotherapy.

Stereotactic body radiotherapy is used to treat spinal metastases; however, 10% of patients experience local failure. We aimed to clarify the outcomes of the second course of stereotactic body radiotherapy for spinal metastases with a uniform fractionation schedule at our institution. Data of patients treated with a second salvage stereotactic body radiotherapy course at the same spinal level or adjacent level from July 2018 to December 2020 were retrospectively reviewed. The initial prescribed dose was 24Gy in two fractions, and the second dose 30 or 35Gy in five fractions. The spinal cord dose constraint at the second course was 15.5Gy at the maximum point dose. The endpoints were local failure and adverse effects. Local failure was defined as tumor progression using imaging. We assessed 19 lesions in 17 patients, with radioresistant lesions in 14 (74%) cases, the second stereotactic body radiotherapy to the same/adjacent spinal level in 13/6 cases, the median interval between stereotactic body radiotherapy of 23 (range, 6-52) months, and lesions compressing the cord in 5 (26%) cases. The median follow-up period was 19months. The 12- and 18-month local failure rates were 0% and 8%, respectively. Radiation-induced myelopathy, radiculopathy and vertebral compression fractures were observed in 0 (0%), 4 (21%) and 2 (11%) lesions, respectively. Three patients with radiculopathy experienced almost complete upper or lower limb paralysis. The second course of salvage stereotactic body radiotherapy for spinal metastases achieved good local control with a reduced risk of myelopathy. However, a high occurrence rate of radiation-induced radiculopathy has been confirmed.

SEAFARER – A new concept for validating radiotherapy patient specific QA for clinical trials and clinical practice

BackgroundThe quality of radiotherapy delivery has been shown to significantly impact clinical outcomes including patient survival. To identify errors, institutions perform Patient Specific Quality Assurance (PSQA) assessing each individual radiotherapy plan prior to starting patient treatments. Externally administered Dosimetry Audits have found problems despite institutions passing their own PSQA. Hence a new audit concept which assesses the institution’s ability to detect errors with their routine PSQA is needed. MethodsPurposefully introduced edits which simulated treatment delivery errors were embedded into radiation treatment plans of participating institutions. These were designed to produce clinically significant changes yet were mostly within treatment delivery specifications. Actual impact was centrally assessed for each plan. Institutions performed PSQA on each plan, without knowing which contained errors. ResultsSeventeen institutions using six radiation treatment planning systems and two delivery systems performed PSQA on twelve plans each. Seventeen erroneous plans (across seven institutions) passed PSQA despite causing >5% increase in spinal cord dose relative to the original plans. Six plans (from four institutions) passed despite a >10% increase. ConclusionsThis novel audit concept evolves beyond testing an institution’s ability to deliver a single test case, to increasing the number of errors caught by institutions themselves, thus increasing quality of radiation therapy and impacting every patient treated. Administered remotely this audit also provides advantages in cost, environmental impact, and logistics.

Less Time Is Less Motion: Analysis of Practical Efficiencies Gained With a Modified Workflow Integrating Planar kV Midimaging With CBCT for Spine Stereotactic Body Radiation Therapy

PurposeOur purpose was to optimize an image guided radiation therapy (IGRT) workflow to achieve practical setup accuracy in spine stereotactic body radiation therapy (SBRT). We assessed the time-saving efficiencies gained from incorporating planar kV midimaging as a surrogate for cone beam computed tomography (CBCT) for intrafraction motion monitoring. Methods and MaterialsWe selected 5 thoracic spine SBRT patients treated in 5 fractions and analyzed patient shifts captured by a modified IGRT workflow using planar kV midimaging integrated with CBCT to maintain a tolerance of 1 mm and 1°. We determined the frequency at which kV midimaging captured intrafraction motion as validated on repeat CBCT and assessed the potential time and dosimetric advantages of our modified IGRT workflow. ResultsPatient motion, detected as out-of-tolerance shifts on planar kV midimaging, occurred during 6 of 25 fractions (24%) and were validated on repeat CBCT 100% of the time. Observed intrafraction absolute shifts (mean ± standard deviation) for the 25 fractions were 0.39 ± 0.21, 0.56 ± 0.22, and 0.45 ± 0.21 mm for lateral-longitude-vertical translations and 0.38 ± 0.12°, 0.32 ± 0.09°, and 0.47 ± 0.14° for pitch-roll-yaw rotation, which if uncorrected, could have significantly affected target coverage and increased spinal cord dose. The average times for pretreatment imaging, midtreatment verification, and total treatment time were 8.94, 2.81, and 16.21 minutes. Our modified IGRT workflow reduced the total number of CBCTs required from 120 to 35 (70%) and imaging dose from 126.2 to 43.4 cGy (65.6%) while maintaining high fidelity for our patient population. ConclusionsAccurate patient positioning was effectively achieved with use of multiple 2-dimensional-3-dimensional kV images and an average of 1 verification CBCT scan per fraction. Integration of planar kV midimaging can effectively reduce treatment time associated with spine SBRT delivery and minimize the potential dosimetric effect of intrafraction motion on target coverage and spinal cord dose.

Quantifying the dosimetric effects of neck contour changes and setup errors on the spinal cord in patients with nasopharyngeal carcinoma: establishing a rapid estimation method

The purpose of this study was to quantify the effect of neck contour changes and setup errors on spinal cord (SC) doses during the treatment of nasopharyngeal carcinoma (NPC) and to establish a rapid dose estimation method. The setup errors and contour changes in 60 cone-beam computed tomography (CBCT) images of 10 NPC patients were analysed in different regions of the neck (C1–C3, C4–C5 and C6–C7). The actual delivered dose to the SC was calculated using the CBCT images, and univariate simulations were performed using the planning CT to evaluate the dose effects of each factor, and an index n}{}{mathrm{Dmax}}_{mathrm{displaced}} was introduced to estimate the SC dose. Compared with the planned dose, the mean (maximum) Dmax increases in the C1–C3, C4–C5 and C6–C7 regions of the SC were 2.1% (12.3%), 1.8% (8.2%) and 2.5% (9.2%), respectively. The simulation results showed that the effects of setup error in the C1–C3, C4–C5 and C6–C7 regions were 1.5% (9.7%), 0.9% (8.2%) and 1.3% (6.3%), respectively, and the effects of contour change were 0.4% (1.7%), 0.7% (2.5%) and 1.5% (4.9%), respectively. The linear regression model can be used to estimate the dose effect of contour changes (R2 > 0.975) and setup errors (R2 = 0.989). Setup errors may lead to a significant increase in the SC dose in some patients. This study established a rapid dose estimation method, which is of great significance for the daily dose evaluation and the adaptive re-planning trigger of the SC.