Radiosurgery of functioning pituitary adenomas: Comparison of different treatment techniques including dynamic and conformal arcs, shaped beams, and IMRT

Consensus guideline for the diagnosis and management of pituitary adenomas in childhood and adolescence: Part 1, general recommendations

Tumours of the anterior part of the pituitary gland represent just 1% of all childhood (aged <15 years) intracranial neoplasms, yet they can confer high morbidity and little evidence and guidance is in place for their management. Between 2014 and 2022, a multidisciplinary expert group systematically developed the first comprehensive clinical practice consensus guideline for children and young people under the age 19 years (hereafter referred to as CYP) presenting with a suspected pituitary adenoma to inform specialist care and improve health outcomes. Through robust literature searches and a Delphi consensus exercise with an international Delphi consensus panel of experts, the available scientific evidence and expert opinions were consolidated into 74 recommendations. Part 1 of this consensus guideline includes 17 pragmatic management recommendations related to clinical care, neuroimaging, visual assessment, histopathology, genetics, pituitary surgery and radiotherapy. While in many aspects the care for CYP is similar to that of adults, key differences exist, particularly in aetiology and presentation. CYP with suspected pituitary adenomas require careful clinical examination, appropriate hormonal work-up, dedicated pituitary imaging and visual assessment. Consideration should be given to the potential for syndromic disease and genetic assessment. Multidisciplinary discussion at both the local and national levels can be key for management. Surgery should be performed in specialist centres. The collection of outcome data on novel modalities of medical treatment, surgical intervention and radiotherapy is essential for optimal future treatment.

Intensity-Modulated Radiosurgery: Improving Dose Gradients and Maximum Dose Using Post Inverse-Optimization Interactive Dose Shaping

Intensity-modulated radiosurgery (IMRS) for brain metastases and arterio-venous malformations (AVM) using a serial tomotherapy system (Nomos Corp., Cranberry Township, PA) has been delivered in >150 cases over the last 5 years. A new software tool provided within the Corvus inverse planning software (ActiveRx) allows for post inverse planning re-optimization and individualization of the dose distribution. We analyzed this tool with respect to increasing the steepness of the dose gradient and in-target dose inhomogeneity while maintaining conformity. Fifteen clinically delivered IMRS plans for solitary brain metastases provided the basis for this analysis. The clinical IMRS plans were copied and the ActiveRx module was opened. The toolset in ActiveRx includes a hot spot eraser, a pencil tool to redefine isodose lines and a drag and drop tool, allowing reshaping of existing isodose lines. To assess changes in the steepness of the dose gradient and dose homogeneity, the 100%, 90%, 50% and 25% isodose volume, the volume of the target, maximum dose and mean dose to the target were recorded. We also recorded total monitor units and calculated treatment delivery times. Target volumes ranged from 0.6 to 14.1 cm3 (mean/median 3.9/1.8 cm3). Mean RTOG conformity index (CI) of plans clinically delivered was 1.23±0.31; mean homogeneity index (HI) was 115±5%. After using the ActiveRx tool-set, the mean CI was slightly improved to 1.14±0.1, with an associated increase in HI to 141±10%. The average, respective Ian Paddick CI for the 100%, 90% 50% and 25% isodose lines were 0.79 vs. 0.83, 0.44 vs. 0.59, 0.12 vs. 0.19, and 0.04 vs. 0.07, representing significant improvements after using ActiveRx post-optimization. Total MU were reduced by a mean of 12.3% using ActiveRx, shortening estimated treatment delivery times by 3.2 minutes on average. A post inverse planning optimization tool for IMRS plans allowed for statistically significant improvements in the steepness of the dose gradient, and increased maximum and mean target doses compared to clinically delivered plans that were already considered excellent. Gains were especially pronounced in the reduction of normal brain tissue included into the 90%, and 50% isodose lines. We have since made this process part of the clinical routine for all cranial IMRS procedures.

Radiotherapy for prolactin-secreting pituitary tumors

Review the medical and surgical management of patients with prolactinomas and provide an in-depth appraisal of the role of radiotherapy in the treatment of prolactinomas. A thorough review of the pertinent literature was carried out and relevant topics were identified. Topics covered in this comprehensive review include: indications for the use of radiotherapy, choice between conventional radiotherapy and stereotactic radiosurgery, as well as the benefits and potential complications associated with each modality. Due to the excellent response rates with medical management, and rapid symptom relief afforded by resection or debulking surgery in patients who do not respond or tolerate medical therapy, radiotherapy is reserved for patients who do not respond to dopamine agonists and surgery. Both external beam radiotherapy and stereotactic radiosurgery retain important roles in the treatment of refractory or recurrent prolactinomas. Choosing the optimal approach is crucial in maximizing tumor control outcomes and minimizing the risks associated with treatment. The primary determinants of optimal radiation approach are proximity of the tumor to the optic apparatus and tumor size, with radiosurgery being our recommended treatment of choice unless the tumor is larger than 3-4 cm or within 3 mm of the optic nerves, chiasm or tracts. Optimal multidisciplinary management requires the identification of appropriate candidates for radiotherapy in order to take full advantage of treatment options available for each patient.

Characterisation of dose distribution in linear accelerator-based intracranial stereotactic radiosurgery with the dynamic conformal arc technique: consideration of the optimal method for dose prescription and evaluation

OBJECTIVES

The purpose of this study was to characterise dose distribution in linear accelerator-based intracranial stereotactic radiosurgery using the dynamic conformal arc technique, and to validate the pertinence of dose prescription to the specific percentage isodose surface (IDS).

METHODS

73 plans for brain metastases were reviewed and replanned with a uniform method for target definition and treatment planning.

RESULTS

In all cases except 1 the dose prescription to the 80% IDS satisfied the criteria of the standardised prescription IDS as previously proposed. However, both of the planning target volume (PTV) coverage values for the 80% and 90% IDSs and the PTV D99 and D95 (IDS receiving at least 99% or 95% of the PTV) were inconsistent and significantly increased as a function of the PTV size. The 80% IDS for a PTV of more than 5 cm(3) achieved adequate PTV coverage without a leaf margin. The dose conformity for 80% IDS gradually worsened as the PTV increased, whereas that for the PTV D99 or D95 improved as a function of the PTV size. The addition of a leaf margin attained 100% PTV coverage for 80% IDS, while leading to a poorer dose conformity.

CONCLUSION

The dose prescription to the specific percentage IDS does not necessarily guarantee consistent target coverage, D99 and D95, and desirable dose conformity in proportion to the target volume. The dose prescription and evaluation at the specific target coverage would therefore be preferable as an objective method in order to report the "marginal dose" and to clearly compare the planning parameters with those from other modalities.

Impact of the high-definition multileaf collimator on linear accelerator-based intracranial stereotactic radiosurgery

OBJECTIVES

The impact of two multileaf collimator (MLC) systems for linear accelerator-based intracranial stereotactic radiosurgery (SRS) was assessed.

METHODS

68 lesions formed the basis of this study. 2.5 mm leaf width plans served as reference. Comparative plans, with identical planning parameters, were based on a 5 mm leaf width MLC system. Two collimation strategies, with collimation fixed at 0° or 90° and optimised per arc or beam, were also assessed. Dose computation was based on the pencil beam algorithm with allowance for tissue heterogeneity. Plan normalisation was such that 100% of the prescription dose covered 95% of the planning target volume. Plan evaluation was based on target coverage and normal tissue avoidance criteria.

RESULTS

The median conformity index difference between the MLC systems ranged between 0.8% and 14.2%; the 2.5 mm MLC exhibited better dose conformation. The median reduction of normal tissue exposed to ≥100%, ≥50% and ≥25% of the prescription dose ranged from 13.4% to 29.7%, favouring the 2.5 mm MLC system. Dose fall-off was steeper for the 2.5 mm MLC system with an overall median absolute difference ranging from 0.4 to 1.2 mm. The use of collimation optimisation resulted in a decrease in differences between the MLC systems. The results demonstrated the dosimetric merit of the 2.5 mm leaf width MLC system over the 5 mm leaf width system, albeit small, for the investigated range of intracranial SRS targets.

CONCLUSION

The clinical significance of these results warrants further investigation to determine whether the observed dosimetric advantages translate into outcome improvements.

Dosimetric comparison of intensity-modulated stereotactic radiotherapy with other stereotactic techniques for locally recurrent nasopharyngeal carcinoma

PURPOSE

Locally recurrent nasopharyngeal carcinoma (NPC) patients can be salvaged by reirradiation with a substantial degree of radiation-related complications. Stereotactic radiotherapy (SRT) is widely used in this regard because of its rapid dose falloff and high geometric precision. The aim of this study was to examine whether the newly developed intensity-modulated stereotactic radiotherapy (IMSRT) has any dosimetric advantages over three other stereotactic techniques, including circular arc (CARC), static conformal beam (SmMLC), and dynamic conformal arc (mARC), in treating locally recurrent NPC.

METHODS AND MATERIALS

Computed tomography images of 32 patients with locally recurrent NPC, previously treated with SRT, were retrieved from the stereotactic planning system for contouring and computing treatment plans. Treatment planning of each patient was performed for the four treatment techniques: CARC, SmMLC, mARC, and IMSRT. The conformity index (CI) and homogeneity index (HI) of the planning target volume (PTV) and doses to the organs at risk (OARs) and normal tissue were compared.

RESULTS

All four techniques delivered adequate doses to the PTV. IMSRT, SmMLC, and mARC delivered reasonably conformal and homogenous dose to the PTV (CI <1.47, HI <0.53), but not for CARC (p < 0.05). IMSRT presented with the smallest CI (1.37) and HI (0.40). Among the four techniques, IMSRT spared the greatest number of OARs, namely brainstem, temporal lobes, optic chiasm, and optic nerve, and had the smallest normal tissue volume in the low-dose region.

CONCLUSION

Based on the dosimetric comparison, IMSRT was optimal for locally recurrent NPC by delivering a conformal and homogenous dose to the PTV while sparing OARs.

Does intensity-modulated stereotactic radiotherapy achieve superior target conformity than conventional stereotactic radiotherapy in different intracranial tumours?

AIMS

To compare the dosimetric outcome of various conventional stereotactic radiotherapy (SRT) techniques with intensity-modulated stereotactic radiotherapy (IMSRT) in brain tumours of varying shape, size, location and proximity to organs at risk (OARs).

MATERIALS AND METHODS

Fused computed tomography and magnetic resonance imaging datasets of four patients with different brain tumours previously treated with non-coplanar static conformal fields (SCF) were re-planned on the BrainScan treatment planning system using non-coplanar conformal arcs (CA), dynamic conformal arcs (DCA) and IMSRT with coplanar (IMSRT_CP) or non-coplanar (IMSRT_NCP) beam arrangement. Beam shaping and intensity modulation were carried out using a BrainLab micromultileaf collimator. The primary objective for each plan was to encompass >or=99% of the planning target volume (PTV) by >95% of the prescribed dose while minimising the dose to OARs.

RESULTS

The mean PTV coverage in SCF, CA, DCA, IMSRT_NCP and IMSRT_CP was 99.2, 99.5, 99.4, 99.2 and 99.2%, respectively. The highest dose within the target was <107% of the prescribed dose in all plans. Conformity was found to vary depending on the shape and location of the target. The best mean conformity index, ranging from 0.74 (CA) to 0.84 (IMSRT_NCP) was observed in spherical tumours. Among the three conventional SRT techniques, DCA and SCF appeared comparable (mean conformity index 0.72 and 0.71, respectively) and more conformal than CA (mean conformity index 0.67). In all cases, IMSRT showed better target conformity than conventional SRT techniques with a mean conformity index of 0.83 for non-coplanar and 0.81 for coplanar beam arrangement. The maximum improvement in conformity index was observed for IMSRT_NCP in complex, concave and irregularly shaped targets. The volume of normal brain and other OARs irradiated to high (>or=80%) and low (>or=30%) dose varied depending on the tumour shape, size, and location, but was essentially comparable in all three conventional SRT techniques. IMSRT (both coplanar as well as non-coplanar) reduced the volume of normal brain being irradiated to moderate to high doses compared with conventional SRT techniques, more so for large and irregular targets.

CONCLUSIONS

DCA and SCF are preferred conventional SRT techniques in terms of target conformity and reduction of doses to OARs. The use of IMSRT_NCP further improves conformity and reduces doses to OARs in a range of brain tumours commonly considered for stereotactic irradiation.

Stereotactic radiotherapy of intracranial tumors: a comparison of intensity-modulated radiotherapy and dynamic conformal arc

PURPOSE

Intensity-modulated radiotherapy (IMRT) and dynamic conformal arc (DCA) are two state-of-the-art techniques for linac-based stereotactic radiotherapy (SRT) using the micromultileaf collimator. The purpose of this planning study is to examine the relative merits of these techniques in the treatment of intracranial tumors.

MATERIALS AND METHODS

SRT treatment plans were made for 25 patients with a glioma or meningioma. For all patients, we made an IMRT and a DCA plan. Plans were evaluated using: target coverage, conformity index (CI), homogeneity index (HI), doses in critical structures, number of monitor units needed, and equivalent uniform dose (EUD) in planning target volume (PTV) and critical structures.

RESULTS

In the overall comparison of both techniques, we found adequate target coverage in all cases; a better mean CI with IMRT in concave tumors (p = 0.027); a better mean HI with DCA in meningiomas, complex tumors, and small (< 92 mL) tumors (p = 0.000, p = 0.005, and p = 0.005, respectively); and a higher EUD in the PTV with DCA in convex tumors (gliomas) and large tumors (p = 0.000 and p = 0.003, respectively). In all patients, significantly more monitor units were needed with IMRT. The results of the overall comparison did not enable us to predict the preference for one of the techniques in individual patients. The DCA plan was acceptable in 23 patients and the IMRT plan in 19 patients. DCA was preferred in 18 of 25 patients.

CONCLUSIONS

DCA is our preferred SRT technique for most intracranial tumors. Tumor type, size, or shape do not predict a preference for DCA or IMRT.

Advances in stereotactic radiosurgery in the treatment of pituitary adenomas

PURPOSE OF REVIEW

Stereotactic radiosurgery has become the preferred radiation treatment modality for secreting and nonsecreting pituitary adenomas, although randomized studies comparing delivery systems, fractionation and dose have not been performed.

RECENT FINDINGS

The technical achievement of radiosurgery delivery systems has minimized the radiation dose to surrounding normal tissue compared with external beam radiotherapy. With a reduction in acute and chronic side effects, the total dose to abnormal tissue can be increased allowing for greater tumor control.

SUMMARY

The radiobiology, control rates and normal tissue tolerances of stereotactic radiosurgery in the treatment of pituitary adenomas is reviewed.