Comparing conformal, arc radiotherapy and helical tomotherapy in craniospinal irradiation planning

Evolution of dosimetric treatment planning for pediatric total lymphoid irradiation (TLI): a single-institution experience

Background

Total lymphoid irradiation (TLI) is a conditioning regimen in allogeneic hematopoietic stem cell transplantation (allo-HSCT) which may reduce long-term toxicities attributed to other techniques, such as total body irradiation (TBI). At our institution, TLI treatments were first planned with the three-dimensional conformal radiation therapy (3D-CRT) technique and later with volumetric modulated arc therapy (VMAT). With the recent availability of a basic helical tomotherapy (HT), the possible dosimetric gain of the latter for TLI is studied.

Materials and methods

22 pediatric patients were planned for VMAT and HT, prescribed to 8 Gy in 4 fractions. VMAT was planned with template based on a single cost function, using the Monaco treatment planning system (TPS). HT plans were planned using Accuray Precision TPS for a basic HT without the dynamic jaws feature or VOLO-Ultra algorithm. Plan quality was analyzed based on four quality indices, mean and maximum doses to planning target volume (PTV) and organs at risk (OARs), dose gradient and integral doses. Differences were analyzed with Wilcoxon signed-rank test.

Results

HT plans resulted in improved conformity (CI) and homogeneity indices (HI) (p < 0.05) but less steep dose gradient (p = 0.181). VMAT plans created larger areas with high doses within the PTV, while comparable doses to OARs, except mainly for the spinal marrow, for which a reduction of 37.7% in D2% was obtained (p < 0.05). Integral dose for non-tumor tissue was 11.3% lower with the VMAT template (p < 0.05).

Conclusion

HT achieves better conformity and homogeneity even without its more advanced features. Nevertheless, the VMAT template achieves dosimetric results close to those of HT, both with similar clinical outcome.

Helical tomotherapy and two types of volumetric modulated arc therapy: dosimetric and clinical comparison for several cancer sites

Radiotherapy accelerators have undergone continuous technological developments. We investigated the differences between Radixact™ and VMAT treatment plans. Sixty patients were included in this study. Dosimetric comparison between the Radixact™ and VMAT plans was performed for six cancer sites: whole-brain, head and neck, lymphoma, lung, prostate, and rectum. The VMAT plans were generated with two Elekta linear accelerators (Synergy^® and Versa HD™). The planning target volume (PTV) coverage, organs-at-risk dose constraints, and four dosimetric indexes were considered. The deliverability of the plans was assessed using quality assurance (gamma index evaluation) measurements; clinical judgment was included in the assessment. The mean AAPM TG218 (3%-2 mm, global normalization) gamma index values were 99.4%, 97.8%, and 96.6% for Radixact™, Versa HD™, and Synergy®, respectively. Radixact™ performed better than Versa HD™ in terms of dosimetric indexes, hippocampi D_100%, spinal cord D_max, rectum V_{38.4  Gy}, bladder V_{30 Gy}, and V_{40 Gy}. Versa HD™ saved more of the (lungs-PTV) V_{5 Gy} and (lungs-PTV) D_mean, heart D_mean, breasts V_{4 Gy}, and bowel V_{45 Gy}. Regarding Synergy^®, the head and neck Radixact™ plan saved more of the parotid gland, oral cavity, and supraglottic larynx. From a clinical point of view, for the head and neck, prostate, and rectal sites, the Radixact™ and Versa HD™ plans were similar; Radixact™ plans were preferable for the head and neck and rectum to Synergy^® plans. The quality of linac plans has improved, and differences with tomotherapy have decreased. However, tomotherapy continues to be an essential add-on in multi-machine departments.

A Script-Based Automatic Intensity Modulated Radiation Therapy Planning Method With Robust Optimization for Craniospinal Irradiation

This report describes a script-based automatic planning method with robust optimization for craniospinal irradiation (CSI) to reduce sensitivity to field matching errors and increase planning efficiency. The data of 10 CSI patients with planning target volume (PTV) lengths between 49.8 and 85.0 cm were retrospectively studied. Robust intensity modulated radiation therapy plans with ±5-mm longitudinal position uncertainty were generated by the automatic planning script. A simple dose prediction model and a self-adjusting method were implied in the automatic plans. The plans' robustness against setup errors was evaluated by deliberately shifting the middle beamset ±5 mm in the superior-inferior direction. Manual and nonrobust plans were also created to evaluate the automatic robust plans' quality, efficiency, and robustness. There were no significant differences between the manual and automatic plans in terms of homogeneity index; conformity index; D1%, D2%, and D98% of PTV; and average doses of organs at risk. However, the D99% of the PTV in the automatic plans was slightly inferior to that in the manual plans. Compared with the manual plans, the automatic plans greatly increased efficiency, with a reduction in planning time of approximately 48%. When ±5-mm superior-inferior errors were introduced, the average deviations of the maximum dose D1% and minimum dose D99% to the spinal cord were 4.9% (±1.1%) and -3.4% (±1.3%), respectively. However, the corresponding values of the nonrobust plans were 20.0% (±5.4%) and -21.2 (±6.3%), respectively. The script-based automatic CSI planning method, combining robust optimization and a dose prediction model, efficiently created a good-quality plan that was robust to setup errors.

Tomotherapy for Cranio-Spinal Irradiation

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Tomotherapy is safe and effective for cranio-spinal irradiation, both in paediatric patients and in adults, with similar disease-specific outcomes and toxicities as other techniques such as 3DCRT or IMRT/VMAT.

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Tomotherapy offers several technical advantages when compared to other radiotherapy techniques such as higher target conformity and better dose homogeneity.

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Helical Tomotherapy provides good organ-at-risk sparing for several structures, especially the vertebrae, parotids, and optic system.

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Reported treatment time/ beam-on-time is longer with helical Tomotherapy compared to other techniques.

Tomotherapy is a method of delivering rotational IMRT offering various advantages, notably for complex and large targets such as the cranio-spinal axis. This systematic literature review reports on main clinical outcomes and toxicities in patients with various cancer types that received whole craniospinal axis irradiation (CSI) using Tomotherapy and offers a comprehensive comparison between Tomotherapy and other radiotherapy delivery techniques. Databases including PubMed, PubMed Central, Embase, and Cochrane were searched using the keywords “tomotherapy” AND “craniospinal”. Fifty-six papers were included in the review. Patient population was adult in 9 papers, paediatric in 26 papers and mixed in 14 papers. Patients treated with helical Tomotherapy had similar disease-specific clinical outcomes and toxicities as patients treated using other techniques. Compared to any other technique, Tomotherapy provides better target coverage, homogeneity, and conformity in 23, 34 and 22 reports. Tomotherapy showed better organ-at-risk sparing for the thyroid, parotids, cochlea, eyes, heart and esophagus. Beam-On-Time (BOT) was reported to be longer for Tomotherapy in most studies (Median BOT: HT = 11 min, VMAT = 5.49 min, 3DCRT = 1.46 min). In conclusion, Tomotherapy offers good cranio-spinal axis coverage with improved homogeneity and conformity compared to other techniques, but with a considerably longer treatment time. Clinical outcome and toxicities suggest using Tomotherapy for CSI is efficient and safe.

Volumetric Modulated Arc Therapy (VMAT) Craniospinal Irradiation (CSI) for Children and Adults: A Practical Guide for Implementation

PURPOSE

Volumetric modulated arc therapy (VMAT) craniospinal irradiation (CSI) has been shown to have significant dosimetric advantages compared to 3D-conformal therapy, but is a technically complex process. We sought to develop a guide for all aspects of the VMAT CSI process and report patient dosimetry results.

METHODS AND MATERIALS

We initiated VMAT CSI in 2017 and have regularly revised our standard operating procedure (SOP) for this process since then. Herein, we report a detailed template for the entire VMAT CSI process from initial patient setup and immobilization at time of CT simulation to contouring and treatment planning, quality assurance, and therapy delivery. The records of 12 patients who were treated with VMAT CSI were also retrospectively reviewed.

RESULTS

Patient age ranged from 2 to 59 years with 5 pediatric patients (age<18 years), 5 young adults (age 18-35 years) and 2 older adults (age>35 years). The majority of patients (67%) had medulloblastoma. CSI dose ranged from 21.6 Gy to 36 Gy, with a median of 36 Gy. The median CSI planning target volume (PTV) was 2383cc with a median V95% of 99.8% and median 0.03 cc hotspot of 112.5%. The average V107% was 7.4% and the average conformality index was 1.01.

CONCLUSIONS

VMAT CSI has potentially significant dosimetric and acute toxicity advantages compared to 3D-conformal. However, proper procedures need to be in place throughout the process in order to be able to realize these potential advantages. We herein describe our detailed SOP for VMAT CSI. Recognizing the scarcity of proton beam centers in many areas, VMAT CSI represents a feasible treatment with more widespread availability.

A novel inverse optimization based three-dimensional conformal radiotherapy technique in craniospinal irradiation

Our aim was to develop a novel inverse optimization-based three-dimensional conformal radiotherapy (i3DCRT) technique for craniospinal irradiation. The imaging data of 20 patients with medulloblastoma were used retrospectively. The first group included 10 pediatric patients with supine position treated under anesthesia/sedation, and the second group included 10 young adult/adult patients treated with prone position. Three different treatment plans were created for each patient via i3DCRT, forward-planned three-dimensional conformal radiotherapy (f3DCRT) and intensity-modulated radiotherapy (IMRT) techniques. A total dose of 36 Gy was prescribed in 20 fractions for all plans. The comparative evaluation was conducted by using the parameters of conformity-index, homogeneity-index, and doses to the target volumes and organs at risk (OARs). The plans created with i3DCRT technique achieved better conformity and homogeneity compared to f3DCRT. In terms of OARs sparing, we found pronounced dose reductions in esophagus and heart in i3DCRT compared to f3DCRT plans. i3DCRT technique also provided a well-conformed dose distribution not superior, but comparable, to IMRT without increase in the total monitor unit per fraction (MU/fx) with respect to f3DCRT. The average monitor unit per fraction (MU/fx) for i3DCRT, f3DCRT and IMRT plans were found as 379.3, 378.0 and 1051.7 MU for the first group and 577.4, 563.5 and 1368.7 MU for the second group, respectively. Novel i3DCRT technique solves the problems associated with field junctions and beam edge matching encountered in f3DCRT plans. Additionally, i3DCRT technique can create almost similar plans as with IMRT with lower total MU/fx.

Toxicity Reduction after Craniospinal Irradiation via Helical Tomotherapy in Patients with Medulloblastoma: A Unicentric Retrospective Analysis

Objectives: Recent trials with craniospinal irradiation (CSI) via helical Tomotherapy (HT) demonstrated encouraging medulloblastoma results. In this study, we assess the toxicity profile of different radiation techniques and estimate survival rates. Materials and Methods: We reviewed the records of 46 patients who underwent irradiation for medulloblastoma between 1999 and 2019 (27 conventional radiotherapy technique (CRT) and 19 HT). Patient, tumor, and treatment characteristics, as well as treatment outcomes-local control rate (LCR), event-free survival (EFS), and overall survival (OS)-were reviewed. Acute and late adverse events (AEs) were evaluated according to the Radiation Therapy Oncology Group and the European Organization for Research and Treatment of Cancer (RTOG/EORTC) criteria. Results: In total, 43 courses of CSI and three local RT were administered to the 46 patients: 30 were male, the median age was 7 years (range 1-56). A median total RT dose of 55 Gy (range 44-68) and a median CSI dose of 35 Gy (range, 23.4-40) was delivered. During follow-up (median, 99 months), six patients (13%) developed recurrence. The EFS rate after 5 years was 84%. The overall OS rates after 5 and 10 years were 95% and 88%, respectively. There were no treatment-related deaths. Following HT, a trend towards lower grade 2/3 acute upper gastrointestinal (p = 0.07) and subacute CNS (p = 0.05) toxicity rates was detected compared to CRT-group. The risk of late CNS toxicities, mainly grade 2/3, was significantly lower following HT technique (p = 0.003). Conclusion: CSI via HT is an efficacious treatment modality in medulloblastoma patients. In all, we detected a reduced rate of several acute, subacute, and chronic toxicities following HT compared to CRT.

Pediatric craniospinal irradiation with a short partial-arc VMAT technique for medulloblastoma tumors in dosimetric comparison

Background

This study aimed to contrast four different irradiation methods for pediatric medulloblastoma tumors in a dosimetric comparison regarding planning target volume (PTV) coverage and sparing of organs at risk (OARs).

Methods

In sum 24 treatment plans for 6 pediatric patients were realized. Besides the clinical standard of a 3D-conformal radiotherapy (3D-CRT) treatment plan taken as a reference, volumetric modulated arc therapy (VMAT) treatment plans (“VMAT_AVD” vs. “noAVD” vs. “FullArc”) were optimized and calculated for each patient. For the thoracic and abdominal region, the short partial-arc VMAT_AVD technique uses an arc setup with reduced arc-length by 100°, using posterior and lateral beam entries. The noAVD uses a half 180° (posterior to lateral directions) and the FullArc uses a full 360° arc setup arrangement. The prescription dose was set to 35.2 Gy.

Results

We identified a more conformal dose coverage for PTVs and a better sparing of OARs with used VMAT methods. For VMAT_AVD mean dose reductions in organs at risk can be realized, from 16 to 6.6 Gy, from 27.1 to 8.7 Gy and from 8.0 to 1.9 Gy for the heart, the thyroid and the gonads respectively, compared to the 3D-CRT treatment method. In addition we have found out a superiority of VMAT_AVD compared to the noAVD and FullArc trials with lower exposure to low-dose radiation to the lungs and breasts.

Conclusions

With the short partial-arc VMAT_AVD technique, dose exposures to radiosensitive OARS like the heart, the thyroid or the gonads can be reduced and therefore, maybe the occurrence of late sequelae is less likely. Furthermore the PTV conformity is increased. The advantages of the VMAT_AVD have to be weighed against the potentially risks induced by an increased low dose exposure compared to the 3D-CRT method.

Dosimetric comparison of integral dose for different techniques of craniospinal irradiation

Aim:

Comparison of the integral dose (ID) delivered to organs at risk (OAR), non-target body and target body by using different techniques of craniospinal irradiation (CSI).

Materials and methods:

Ten CSI patients (medulloblastoma) already planned and treated either with linear accelerator three-dimensional conformal radiation therapy (Linac-3DCRT) technique or with linear accelerator RapidArc (Linac-RapidArc) technique by Novalis-Tx Linac machine have been analysed. Retrospectively, these patients are again planned on Radixact-X9 Linac with Helical, Direct-3DCRT and Direct-intensity-modulated radiation therapy (Direct-IMRT) techniques. The dose prescription to planning target volume brain (PTV-Brain) and PTV-Spine is 36 Gy in 20 fractions and is kept the same for all techniques. The target body, non-target body, OARs and total body dose are compared.

Results:

ID is lowest in the RapidArc plan for every patient in comparison to Helical and Direct-IMRT. The ID for Body-PTV was found slightly higher in the RapidArc plan in comparison to 3DCRT plans. But there is better normal tissue sparing for most of the OARs in RapidArc plans if it compares with 3DCRT plans.

Findings:

RapidArc is a better alternative for the treatment of CSI. It provides better target coverage and better OARs sparing from any other treatment techniques.

Helical tomotherapy: Comparison of Hi-ART and Radixact clinical patient treatments at the Technical University of Munich

The helical tomotherapy (HT) Hi-ART system was installed at our department in April 2007. In July 2018 the first Radixact system in Germany has been launched for clinical use. We present differences, advantages and disadvantages and show future perspectives in patient treatment using two HT devices. We investigate patient characteristics, image quality, radiotherapy treatment specifications and analyze the time effort for treatments with the Hi-ART system from April 2010 until May 2017 and compare it to the data acquired in the first nine months of usage of the Radixact system. Comparing the Hi-ART and Radixact system, the unique option of integrated MVCT image acquisition has experienced distinct improvement in image quality. Time effort for irradiation treatment could be improved resulting in a mean beam on time for craniospinal axis treatment of 636.2 s for the Radixact system compared to 915.9 s for the Hi-ART system. The beneficial use of tomotherapy for complex target volumes is demonstrated by a head and neck tumor case and craniospinal axis treatment. With the Radixact system MVCT image quality has been improved allowing for fast and precise interfraction dose adaptation. The improved time effort for patient treatment could increase the accessibility for clinical usage.

Dosimetric comparison of short and full arc in spinal PTV in volumetric-modulated arc therapy-based craniospinal irradiation

Since 2011 when it was first described, the volumetric-modulated arc therapy (VMAT) technique for craniospinal irradiation (CSI) has always seen the use of large arc lengths for the spine fields ranging from 200° to 360°. This study was aimed to do a dosimetric comparison between the large and shorter spinal arc for CSI. For a cohort of 10 patients, 2 VMAT CSI plans were created for each patient, one using the conventional full 360° arc (VMAT_FA) for the spine and the other using 100° posterior arc (VMAT_PA) for 23.4 Gy and 35 Gy prescriptions. In both the plans, 360° arc fields were employed for treating cranial volume. Spillage dose (D_Body-PTV) to Body-PTV (D_Body-PTV: dose to body excluding planning target volume) was compared with VMAT_FA and VMAT_PA plans. In addition to these VMAT plans, a 3-dimensional conformal radiotherapy plan was also created for all these patients to compare the D_Body-PTV and target volume related dose constraints. Mean D95% difference between the two VMAT plans did not exceed 1.3% for cranial and spinal targets for both prescription levels. The conformity index (CI) was averaged over both prescription doses. Average CI shows a similar value for VMAT_FA (0.84 ± 0.04) and VMAT_PA (0.82 ± 0.05) plans. D95%, V110% and CI did not exhibit a statistically significant difference between partial and full-arc VMAT plans. However, the VMAT_PA plan exhibited a lower D_Body-PTV compared to VMAT_FA plans (0.007 ≤ p < 0.05) in the 1 to 5 Gy range. Nevertheless, partial arc plans could not offer a statistically significant dose reduction for delineated organs compared to full arc plans, except for bilateral kidneys.

Outcome and prognostic factors following palliative craniospinal irradiation for leptomeningeal carcinomatosis

Background

Leptomeningeal carcinomatosis (LC) is a severe complication of metastatic tumor spread to the central nervous system. Prognosis is dismal with a median overall survival (OS) of ~10–15 weeks. Treatment options include radiotherapy (RT) to involved sites, systemic chemo- or targeted therapy, intrathecal chemotherapy and best supportive care with dexamethasone. Craniospinal irradiation (CSI) is a more aggressive radiotherapeutic approach, for which very limited data exists. Here, we report on our 10-year experience with palliative CSI of selected patients with LC.

Patients and methods

Twenty-five patients received CSI for the treatment of LC at our institution between 2008 and 2018. Patients were selected individually for CSI based on clinical performance, presenting symptoms and estimated benefit. Median patient age was 53 years (IQR: 45–59), and breast cancer was the most common primary. Additional brain metastases were found in 18 patients (72.0%). RT was delivered at a TomoTherapy machine, using helical intensity-modulated radiotherapy (IMRT). The most commonly prescribed dose was 36 Gy in 20 fractions, corresponding to a median biologically equivalent dose of 40.8 Gy (IQR: 39.0–2.5). Clinical performance and neurologic function were assessed before and in response to therapy, and deficits were retrospectively quantified on the 5-point neurologic function scale (NFS). A Cox proportional hazards model with univariate and multivariate analyses was fitted for survival.

Results

Twenty-one patients died and four were alive at the time of analysis. Median OS from LC diagnosis was 19.3 weeks (IQR: 9.3–34.0, 95% CI: 11.0–32.0). In univariate analysis, a Karnofsky performance scale index (KPI) ≥70% (P=0.001), age ≤55 years at LC diagnosis (P=0.022), cerebrospinal fluid (CSF) protein <100 mg/dL (P=0.018) and no more than mild or moderate neurologic deficits (NFS ≤2; P=0.007) were predictive of longer OS. So were the neurologic response to treatment (P=0.018) and the application of systemic therapy after RT completion (P=0.029). The presence of CSF flow obstruction was predictive of shorter OS (P=0.026). In multivariate analysis, age at LC diagnosis (P=0.018), KPI (P<0.001) and neurologic response (P=0.037) remained as independent prognostic factors for longer OS. Treatment-associated toxicity was manageable and mostly grades I and II according to the Common Terminology Criteria for Adverse Events v4.0. Eight patients (32%) developed grade III myelosuppression. Neurologic symptom stabilization could be achieved in 40.0% and a sizeable improvement in 28.0% of all patients.

Conclusion

CSI for the treatment of LC is feasible and may have therapeutic value in carefully selected patients, alleviating symptoms or delaying neurologic deterioration. OS after CSI was comparable to the rates described in current literature for patients with LC. The use of modern irradiation techniques such as helical IMRT is warranted to limit toxicity. Patient selection should take into account prognostic factors such as age, clinical performance, neurologic function and the availability of systemic treatment options.

Acute toxicity of craniospinal irradiation with volumetric-modulated arc therapy in children with solid tumors

BACKGROUND

Craniospinal irradiation (CSI) is an important part of curative radiation therapy (RT) for many types of pediatric brain or solid tumors. After conventional CSI, long term survivors may experience sequelae due to unintended dose to normal tissue. Volumetric modulated arc therapy (VMAT) CSI reduces off-target doses at the cost of greater complexity and error risk, and we describe our initial experience in a group of pediatric patients with solid tumors presenting with disseminated or recurrent disease.

PROCEDURE

Pediatric patients with brain tumors were identified at Children's Hospital Los Angeles from 2013 to 2015. Clinical characteristics, acute toxicity, and radiotherapy data were abstracted from their medical records. We identified 19 patients who received VMAT CSI. Quality assurance was performed with a cylindrical detector array and ion chamber measurements at the arc junctions.

RESULTS

Patients had medulloblastoma or supratentorial primitive neuro-ectodermal tumor (n = 14, 11 high risk), germ cell tumors (two), relapsed neuroblastoma (two), and atypical teratoid/rhabdoid tumor (one). The most common acute toxicity was hematologic, including leukopenia (11% grade [Gr] 2, 26% Gr 3, and 63% Gr 4), anemia (89% Gr 2), and thrombocytopenia (16% Gr 1-2, 26% Gr 3, and 37% Gr 4). Despite leukopenia, we encountered only two Gr 3 infections (urinary tract and lung). The majority required blood products (89% red blood cells and 68% platelets). Weight loss was also common (47% Gr 1 and 26% Gr 2).

CONCLUSIONS

VMAT CSI, along with chemotherapy and anesthesia, is feasible with supportive care. Daily image-guided RT improves accuracy and reduces the risk of spinal cord overdose without increasing treatment time. Further research is needed to determine whether reducing doses to organs, such as thyroid, heart, or hippocampus, offsets the risk of increased volume of low-dose irradiation.

A dosimetric comparison of craniospinal irradiation using TomoDirect radiotherapy, TomoHelical radiotherapy and 3D conventional radiotherapy

Aim

The purpose of this study was to dosimetrically compare TomoDirect, TomoHelical and linear accelerator-based 3D-conformal radiotherapy (Linac-3DCRT) for craniospinal irradiation (CSI) in the treatment of medulloblastoma.

Methods

Five CSI patients were replanned with Linac-3DCRT, TomoHelical, TomoDirect-3DCRT and TomoDirect-intensity-modulated radiotherapy (IMRT). Dose of 36 Gy in 20 fractions was prescribed to the planning target volume (PTV). Homogeneity index (HI), non-target integral dose (NTID), dose–volume histograms, organs-at-risk (OARs)Dmax,Dmeanand treatment times were compared.

Results

TomoHelical achieved the best PTV homogeneity compared with Linac-3DCRT, TomoDirect-3DCRT and TomoDirect-IMRT (HI of 3·6 versus 20·9, 8·7 and 9·4%, respectively). TomoDirect-IMRT achieved the lowest NTID compared with TomoDirect-3DCRT, TomoHelical and Linac-3DCRT (141 J versus 151 J, 181 J and 250 J), indicating least biological damage to normal tissues. TomoHelical plans achieved the lowestDmaxin all organs except the breasts, and lowestDmeanfor most OARs, except in laterally situated OARs, where TomoDirect triumphed. Beam-on time was longest for TomoHelical, followed by TomoDirect and Linac-3DCRT.

Findings

TomoDirect has the potential to lower NTID and shorten treatment times compared with TomoHelical. It reduces PTV inhomogeneity and better spares OARs compared with Linac-3DCRT. Therefore, TomoDirect may be a CSI treatment alternative to TomoHelical and in place of Linac-3DCRT.

A low gradient junction technique of craniospinal irradiation using volumetric-modulated arc therapy and its advantages over the conventional therapy

A technique using volumetric-modulated arc therapy (VMAT) fields for craniospinal irradiation with low dose gradients at the field junction was tested for its sensitivity to positional inaccuracy. It was compared against the conventional three-dimensional (3D) conformal radiotherapy in terms of dose uniformity at the junction. Treatment plans generated for ten patients who received craniospinal irradiation (35Gy in 21 fractions) by VMAT technique at our centre were included in this study. For these patients, 3D conformal radiotherapy plans were also generated in addition to the VMAT treatment plans. Intentional shifting of the cranial field in the superior and then in the inferior directions was done, creating a gap or overlap between the fields. Consequent changes in dose distributions in these two plans to positional inaccuracies were studied. The 3D conformal radiotherapy plans showed large dose variations at the junction due to positional shifts as compared to the VMAT plans. With a 5mm superior shift of the cranial field isocentre creating a gap between the cranial and spinal fields, the magnitudes of under-dosing were 13.9±3.6Gy and 4.8±2.0Gy for 3D conformal radiotherapy and VMAT respectively. When the cranial field was moved by 5mm inferiorly creating an overlap between the fields, overdose to the effects of 10.3±4.0Gy and 4.9±1.3Gy were observed for the 3D conformal radiotherapy plans and VMAT plans respectively. The VMAT technique is insensitive to longitudinal setup errors (1-3mm) in patients because of the existence of low dose gradients at the junction between fields. This is unlike the 3D conformal radiotherapy plans which have steep dose gradients at the field edges and thus are highly sensitive to setup errors. Such an advantage for VMAT circumvents the need for dose feathering often practiced with the 3D conformal radiotherapy technique and makes the technique simpler to follow.

Universal field matching in craniospinal irradiation by a background-dose gradient-optimized method

Purpose

The gradient‐optimized methods are overcoming the traditional feathering methods to plan field junctions in craniospinal irradiation. In this note, a new gradient‐optimized technique, based on the use of a background dose, is described.

Methods

Treatment planning was performed by RayStation (RaySearch Laboratories, Stockholm, Sweden) on the CT scans of a pediatric patient. Both proton (by pencil beam scanning) and photon (by volumetric modulated arc therapy) treatments were planned with three isocenters. An ‘in silico’ ideal background dose was created first to cover the upper‐spinal target and to produce a perfect dose gradient along the upper and lower junction regions. Using it as background, the cranial and the lower‐spinal beams were planned by inverse optimization to obtain dose coverage of their relevant targets and of the junction volumes. Finally, the upper‐spinal beam was inversely planned after removal of the background dose and with the previously optimized beams switched on.

Results

In both proton and photon plans, the optimized cranial and the lower‐spinal beams produced a perfect linear gradient in the junction regions, complementary to that produced by the optimized upper‐spinal beam. The final dose distributions showed a homogeneous coverage of the targets.

Discussion

Our simple technique allowed to obtain high‐quality gradients in the junction region. Such technique universally works for photons as well as protons and could be applicable to the TPSs that allow to manage a background dose.

Impacts of lung and tumor volumes on lung dosimetry for nonsmall cell lung cancer

The purpose of this study was to determine the impacts of lung and tumor volumes on normal lung dosimetry in three-dimensional conformal radiotherapy (3DCRT), step-and-shoot intensity-modulated radiotherapy (ssIMRT), and single full-arc volumetric-modulated arc therapy (VMAT) in treatment of nonsmall cell lung cancers (NSCLC). All plans were designed to deliver a total dose of 66 Gy in 33 fractions to PTV for the 32 NSCLC patients with various total (bilateral) lung volumes, planning target volumes (PTVs), and PTV locations. The ratio of the lung volume (total lung volume excluding the PTV volume) to the PTV volume (LTR) was evaluated to represent the impacts in three steps. (a) The least squares method was used to fit mean lung doses (MLDs) to PTVs or LTRs with power-law function in the population cohort (N = 32). (b) The population cohort was divided into three groups by LTRs based on first step and then by PTVs, respectively. The MLDs were compared among the three techniques in each LTR group (LG) and each PTV group (PG). (c) The power-law correlation was tested by using the adaptive radiation therapy (ART) planning data of individual patients in the individual cohort (N = 4). Different curves of power-law function with high R² values were observed between averaged LTRs and averaged MLDs for 3DCRT, ssIMRT, and VMAT, respectively. In the individual cohort, high R² values of fitting curves were also observed in individual patients in ART, although the trend was highly patient-specific. There was a more obvious correlation between LTR and MLD than that between PTV and MLD.

Surgery Combined with Radiotherapy to Treat Spinal Tumors: A Review of Published Reports

Spinal tumors result in high morbidity and a high rate of lower limb paralysis. Both surgical therapy and radiation therapy (RT) are used to treat spinal tumors; however, how best to combine these two therapies to maximize the benefits and minimize the risks is still being debated. It is also difficult to decide the optimal timing, course and dose of RT, especially in pregnant women and children. The aim of this review is to assist surgeons who are dealing with spinal tumors by providing comprehensive information about advanced techniques for administering RT with greater precision and safety, and about the impact of various ways of combining surgery and RT on therapeutic outcomes. We here review published reports about treating spinal tumors with a combination of these two forms of therapy and attempt to draw appropriate conclusions concerning selection of optimal treatment protocols. Our conclusion is that postoperative radiotherapy, especially with high-precision, low-dose and multiple fractions, and brachytherapy are promising therapies to combined with surgery.

A Comparative Planning Analysis and Integral Dose of Volumetric Modulated Arc Therapy, Helical Tomotherapy, and Three-dimensional Conformal Craniospinal Irradiation for Pediatric Medulloblastoma

INTRODUCTION

The purpose of this study was to compare volumetric modulated arc therapy (VMAT) with helical tomotherapy (HT) and three-dimensional conformal radiation therapy (3D-CRT) for craniospinal irradiation (CSI) in children with medulloblastoma.

METHODS

Five children treated with 3D-CRT were retrospectively replanned with HT and VMAT. Tomotherapy plans used a single helical arc, thereby eliminating field junctions. VMAT plans used two arcs rotating alternatively clockwise and counterclockwise, respectively. Conformity and homogeneity indices, dose-volume histograms, integral doses, monitor units delivered, and beam-on times were compared.

RESULTS

VMAT showed an improved mean conformity index of 1.05 in comparison with 3D-CRT (1.58, P = .04) and HT (1.34, P = .04). The mean homogeneity index of VMAT (1.13) was not significantly different from 3D-CRT (1.16) but higher than HT (1.08, P = .04). For normal tissues, VMAT resulted in a lower mean dose to the skin, eyes, lenses, optic nerves, cochlea, esophagus, heart, peritoneal cavity, bladder, and rectum compared with 3D-CRT (all P = .04). There were few significant differences in dose-volume statistics for normal tissues between VMAT and HT. The mean nontarget tissue integral dose for VMAT of 80.8 J was significantly lower than for 3D-CRT (91.5 J, P = .04) and HT (95.6 J, P = .04). Body and nontarget tissue integral doses were lowest with VMAT in every patient.

CONCLUSIONS

For CSI, VMAT provides comparable normal tissue sparing with tomotherapy and may reduce the integral dose. Compared with 3D-CRT, VMAT improved normal tissue sparing at higher doses despite larger volumes receiving lower doses. These findings have potential implications in the risk of the development of late adverse effects and radiation-related second malignancies in children with curable primary disease.