Hotspots

The NRG Oncology template for the radiation section of a conventionally fractionated lung trial. Its imaging section allows PET/CT or MRI for structure definition but asks that the final contours be confirmed on the planning CT, follows AAPM TG-132 for deformable registration, and notes that PET can help separate tumor from atelectasis. For plan evaluation it defines the prescription as the dose covering 95% of the PTV, with a protocol-specific D99% requirement, and asks that any dose above 105% of the prescription fall within the PTV rather than in normal tissue outside it.

The template NRG Oncology gives investigators for writing the radiation section of a lung SBRT trial. Its imaging section allows PET/CT or MRI for structure definition, asks that the images be registered accurately to the planning scan (following AAPM TG-132 for deformable registration), notes that PET may be needed to separate tumor from atelectasis or fibrosis, and suggests an extra margin when a fused image is the primary image for the GTV. Its target and planning sections (5.2.4 and 5.2.6–5.2.8) define the plan-quality measures for lung SBRT trials: the prescription as the dose covering 95% of the PTV, a D99% requirement, R100% (prescription isodose volume ÷ PTV), R50% (50% prescription isodose volume ÷ PTV) and D2cm (maximum dose at 2 cm from the PTV in any direction, as a percentage of the prescription), with a table of allowable dose spillage by PTV volume. It describes a 20 mm PTV expansion structure used to control intermediate dose spillage, asks that dose above 105% of prescription be avoided outside the PTV, describes a deliberately heterogeneous dose with the hotspot in the central GTV, defines the maximum dose on a 0.03 cc volume, and ranks planning priorities when target coverage and organ limits conflict.

The NRG Oncology template for the radiation section of a brain radiosurgery trial. Its example text asks for CT slices of 1.25 mm or less, strongly encourages MRI (contrast T1 and a 3D gradient-echo sequence) for target delineation, recommends fusing FDG-PET/CT when available, and asks that the fusion be done by a medical physicist and reviewed by the attending physician. Its plan-evaluation section defines the conformity index (CI, or R100%) as the prescription isodose volume ÷ PTV volume, R50% as the 50% prescription isodose volume ÷ target volume ("R50% defines dose falloff outside the target"), a heterogeneity index D5% ÷ D95%, and coverage as the PTV volume receiving the prescription dose ÷ PTV volume, and notes that criteria such as the CI should account for target size and treatment technology.

ICRU report on prescribing, recording and reporting intensity-modulated photon therapy. DoseLab has not read the report itself (it is sold by the ICRU). Its homogeneity index, (D2% − D98%) / D50%, is checked as quoted in the open-access Yan 2019 paper.

Retrospective study of 99 plans comparing five homogeneity index formulas. Its introduction summarizes the RTOG index (maximum isodose in the target ÷ reference isodose), D5%/D95%, and (D2% − D98%) ÷ prescribed dose, and explains that D2% and D98% are used because true point maximum and minimum doses are sensitive to calculation grid size and placement. Full text read in Europe PMC (PMC3532749).