Optimizing the prescription isodose level in stereotactic volumetric-modulated arc radiotherapy of lung lesions as a potential for dose de-escalation

Abstract

BackgroundTo derive and exploit the optimal prescription isodose level (PIL) in inverse optimization of volumetric modulated arc radiotherapy (VMAT) as a potential approach to dose de–escalation in stereotactic body radiotherapy for non–small cell lung carcinomas (NSCLC).MethodsFor ten patients, inverse Monte Carlo dose optimization was performed to cover 95% PTV by varying prescription isodose lines (PIL) at 60 to 80% and reference 85%. Subsequently, these were re–normalized to the median gross tumor volume dose (GTV–based prescription) to assess the impacts of PTV and normal tissue dose reduction.ResultsWith PTV–based prescription, GTV mean dose was much higher with the optimized PIL at 60% with significant reduction of normal lung receiving 30 to 10 Gy (V30–10Gy), and observable but insignificant dose reduction to spinal cord, esophagus, ribs, and others compared with 85% PIL. Mean doses to the normal lung between PTV and GTV was higher with 60–70% PIL than 85%. The dose gradient index was 5.0 ± 1.1 and 6.1 ± 1.4 for 60 and 85% PIL (p < 0.05), respectively. Compared with the reference 85% PIL plan using PTV–base prescription, significant decreases of all normal tissue doses were observed with 60% and 70% PIL by GTV–based prescription. Yet, the resulting biological effective (BED) mean doses of PTV remain sufficiently high, ranging 104.2 to 116.9 Gy α/β = 10.ConclusionsOptimizing the PIL with VMAT has notable advantage of improving the dosimetric quality of lung SBRT and offers the potential of dose de–escalation for surrounding tissues while increasing the GTV dose simultaneously. The clinical implication of re–normalizing plans from PTV–prescription at 60–70% to the GTV median dose requires further investigations.

A physically meaningful relationship between R50% and PTV surface area in lung SBRT

“…DISCUSSION4.A | R50% dependence on PTV D avThe observed R50% local minimum in PTV D av seen inFig. 4can also be seen in the results of previous work 12,21. However, these One process dominates at the high end where PTV D av is large while a different process dominates when PTV D av is low.…”

Automated planning through robust templates and multicriterial optimization for lung VMAT SBRT of lung lesions

“…A recently published pooled analysis of 57 studies, 31 identified the maximum dose to chest wall (dose to 0.5 cm 3 and 5 cm 3 ) to be significantly associated with chest wall pain and rib fractures. Looking at the quality of our plans, gradient indexes are comparable to the values reported by Chan and colleagues 30 for lower prescription isodoses (5.0 ± 1.1 and 6.1 ± 1.4 for 60% and 85%, respectively) and doses to OARs are far below the constraints reported in literature.…”

“…Inhomogeneous dose distributions are generally considered to be advantageous for increasing the integral GTV dose and for OARs sparing. 30 However, the PTVs of the patients' sample selected in our study are very near or partly overlapped to the chest wall, so the maximum dose was limited in order to reduce chest wall toxicity. A recently published pooled analysis of 57 studies, 31 identified the maximum dose to chest wall (dose to 0.5 cm 3 and 5 cm 3 ) to be significantly associated with chest wall pain and rib fractures.…”

A study of minimum segment width parameter on VMAT plan quality, delivery accuracy, and efficiency for cervical cancer using Monaco TPS

“…Over the last decade, volumetric modulated arc therapy (VMAT) has been explored and implemented to treat a variety of cancers including in the prostate, head and neck, lung, and spine 1, 2, 3, 4. VMAT is a dynamic treatment technique in which the radiation dose rates, gantry speeds, and movements of the multi‐leaf collimator and jaws are simultaneously varied while the beam is on 5.…”