Dose Prescription Methods in Stereotactic Body Radiotherapy for Small Peripheral Lung Tumors: Approaches Based on the Gross Tumor Volume Are Superior to Prescribing a Dose That Covers 95% of the Planning Target Volume.

ABSTRACT

BACKGROUND AND PURPOSE: We aimed to validate the usefulness of prescriptions based on gross tumor volume for stereotactic body radiotherapy for small peripheral lung tumors. MATERIALS AND METHODS: Radiotherapy treatment planning data of 50 patients with small peripheral lung tumors (adenocarcinoma 24, squamous cell carcinoma 10, other 1, unknown 15) receiving breath-hold computed tomography-guided stereotactic body radiotherapy at our institution during 2013-2016 were analyzed. For each case, 3 dose prescription methods were applied one based on 95% (PTVD95%) of the planning target volume, one based on 50% of the gross tumor volume (GTVD50%), and one based on 98% (GTVD98%) of the gross tumor volume. The maximum (GTVDmax), minimum (GTVDmin), and mean gross tumor volume dose (GTVDmean) and the dose covering 98% of the gross tumor volume were calculated to evaluate variations in the gross tumor volume dose. RESULTS: Upon switching to GTVD50%, the variations in GTVDmax and GTVDmean decreased significantly, compared with variations observed for PTVD95% (p < 0.01), but the variation in GTVDmin increased significantly (p < 0.01). Upon switching to the GTVD98%, the variation in GTVDmean decreased significantly compared with that observed for PTVD95% (p < 0.01). CONCLUSION: Switching from prescriptions based on 95% of the planning target volume to those based on 98% of the gross tumor volume decreased variations among cases in the overall gross tumor volume dose. Overall, prescriptions based on 98% of the gross tumor volume appear to be more suitable than those based on 95% of the planning target volume in cases of small peripheral lung tumors treated with stereotactic body radiotherapy.