Abstract
Purpose/objectivesTo evaluate the plan quality and treatment delivery efficiency of single‐isocenter/two‐lesions volumetric modulated arc therapy (VMAT) lung stereotactic body radiation therapy (SBRT).Materials/methodsEight consecutive patients with two peripherally located early stage nonsmall‐cell‐lung cancer (NSCLC) lung lesions underwent single‐isocenter highly conformal noncoplanar VMAT SBRT treatment in our institution. A single‐isocenter was placed between the two lesions. Doses were 54 or 50 Gy in 3 and 5 fractions respectively. Patients were treated every other day. Plans were calculated in Eclipse with AcurosXB algorithm and normalized to at least 95% of the planning target volume (PTV) receiving 100% of the prescribed dose. For comparison, two‐isocenter plans (isocenter placed centrally in each target) were retrospectively created. Conformity indices (CIs), heterogeneity index (HI), gradient index (GI), gradient distance (GD), and D2cm were calculated. The normal lung V5, V10, V20, mean lung dose (MLD) and other organs at risk (OARs) doses were evaluated. Total number of monitor units (MUs), beam‐on time, and patient‐specific quality assurance (QA) results were recorded.ResultsThe mean isocenter to tumor distance was 6.7 ± 2.3 cm. The mean combined PTV was 44.0 ± 23.4 cc. There was no clinically significant difference in CI, HI, GD, GI, D2cm, and V20 including most of the OARs between single‐isocenter and two‐isocenter lung SBRT plans, evaluated per RTOG guidelines. However, for single‐isocenter plans as the distance between the lesions increased, the V5, V10, and MLD increased, marginally. The total number of MUs and beam‐on time was reduced by a factor of 1.5 for a single‐isocenter plan compared to a two‐isocenter plan. The single‐isocenter/two‐lesions VMAT lung SBRT QA plans demonstrated an accurate dose delivery of 98.1 ± 3.2% for clinical gamma passing rate of 3%/3 mm.ConclusionThe SBRT treatment of two peripherally located lung lesions with a centrally placed single‐isocenter was dosimetrically equivalent to two‐isocenter plans. Faster treatment delivery for single‐isocenter treatment can improve patient compliance and reduce the amount of intrafraction motion errors for well‐suited patients.
Highlights
For medically inoperable stage I/II nonsmall‐cell lung cancer (NSCLC) patients, several Phase I/II trials have shown that the use of stereotactic body radiation therapy (SBRT) treatment for solitary lung lesions representing the primary tumor mass is safe, effective, and has a high cure rate comparable to surgery.[1,2,3,4,5,6,7] In these studies, medically inoperable patients with early‐stage nonsmall‐cell‐lung cancer (NSCLC) who underwent SBRT had 3‐yr primary tumor local control rates of up to 98% and a low risk of treatment‐related toxicity.In the setting of either multiple primary lung cancers or limited metastatic lesions to the lungs, SBRT presents a relatively new treatment opportunity
There was no clinically significant difference in Conformity indices (CIs), heterogeneity index (HI), gradient distance (GD), gradient index (GI), D2cm, and V20 including most of the organs at risk (OARs) between single‐isocenter and two‐isocenter lung SBRT plans, evaluated per Radiation Therapy Oncology Group (RTOG) guidelines
The total number of monitor units (MUs) and beam‐on time was reduced by a factor of 1.5 for a single‐isocenter plan compared to a two‐isocenter plan
Summary
In the setting of either multiple primary lung cancers or limited metastatic lesions to the lungs (oligometastastic), SBRT presents a relatively new treatment opportunity. Multiple metachronous or synchronous lung cancers are relatively common and have been managed by SBRT.[8] Based on Phase I/II trials of SBRT in the management of oligometastastic lung lesions, for patients with one to three tumors, up to five tumors (with curative intent) and more than five tumors with palliative treatment have been reported.[9,10] Rusthoven and colleagues treated 38 patients, 63 total tumors, with lung SBRT of total dose of 48–60 Gy in 3 fractions. Actuarial local control rates at 1‐ and 2‐yr after SBRT was 100% and 96% respectively.[10]
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