Abstract
Simple SummaryDose prescription for the inhomogeneous dosing in spatially fractionated radiation therapy (SFRT) is challenging, and further hampered by the inability of several planning systems to incorporate complex SFRT dose patterns. We developed dosing reference tables for an inventory of tumour scenarios and tested their accuracy with water phantom measurements of GRID therapy, delivered by a standard commercial GRID collimator. We find that dose heterogeneity parameters and EUD modeling are consistent across tumour sizes, configurations, and treatment depths. These results suggest that the developed reference tables can be used as a practical clinical resource for clinical decision-making on GRID therapy and to facilitate heterogeneity dose estimates in clinical patients when this commercially available GRID device is used.Computations of heterogeneity dose parameters in GRID therapy remain challenging in many treatment planning systems (TPS). To address this difficulty, we developed reference dose tables for a standard GRID collimator and validate their accuracy. The .decimal Inc. GRID collimator was implemented within the Eclipse TPS. The accuracy of the dose calculation was confirmed in the commissioning process. Representative sets of simulated ellipsoidal tumours ranging from 6–20 cm in diameter at a 3-cm depth; 16-cm ellipsoidal tumours at 3, 6, and 10 cm in depth were studied. All were treated with 6MV photons to a 20 Gy prescription dose at the tumour center. From these, the GRID therapy dosimetric parameters (previously recommended by the Radiosurgery Society white paper) were derived. Differences in D5 through D95 and EUD between different tumour sizes at the same depth were within 5% of the prescription dose. PVDR from profile measurements at the tumour center differed from D10/D90, but D10/D90 variations for the same tumour depths were within 11%. Three approximation equations were developed for calculating EUDs of different prescription doses for three radiosensitivity levels for 3-cm deep tumours. Dosimetric parameters were consistent and predictable across tumour sizes and depths. Our study results support the use of the developed tables as a reference tool for GRID therapy.
Highlights
Fractionated radiation therapy (SFRT) is a specially designed radiation therapy modality characterized by the delivery of a high and intentionally heterogeneous dose using megavoltage x-ray or proton beams for the management of patients with bulky tumours
A large nominal dose of Spatially fractionated radiation therapy (SFRT) did not reduce the patients’ radiation tolerance even when followed by full-dose conventional radiation therapy [5,14]. These clinical outcomes suggest that hypofractionated GRID therapy can be safely incorporated into the definitive management of both bulky recurrent/metastatic and likely far-advanced primary tumours
Tables were derived for the array of tumour depths, sizes, 3 of 17and geometries from the established planning system Eclipse, and subsequently calculated for their peak/valley dose ratio (PVDR), the doses covering 95%, 90%, ..., 10%, and 5% of tumour volume (D95, D90, ..., D10, D5) and equivalent uniform dose (EUD)
Summary
Fractionated radiation therapy (SFRT) is a specially designed radiation therapy modality characterized by the delivery of a high and intentionally heterogeneous dose using megavoltage x-ray or proton beams for the management of patients with bulky tumours. While a complete understanding of the radiobiological underpinnings of the observed SFRT responses is still an area of continued investigation, both shallow and deep-seated bulky tumours have consistently shown high symptomatic response rates to collimator-based GRID therapy [1,2,5,7,8,9,10,11,12,13,14,15,16] These encouraging clinical outcomes of SFRT were seen initially in palliative therapy, showing response rates in excess of 90% in patients with bulky refractory metastases and recurrences from various primary tumours [1]. A large nominal dose of SFRT did not reduce the patients’ radiation tolerance even when followed by full-dose conventional radiation therapy [5,14] These clinical outcomes suggest that hypofractionated GRID therapy can be safely incorporated into the definitive management of both bulky recurrent/metastatic and likely far-advanced primary tumours. These promising pilot results, in conjunction with the continued technical advances in radiotherapy dose modeling and delivery technologies, have spawned an accelerated interest in SFRT and growth in newly established centers aiming to initiate SFRT as a treatment modality for their patients
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