A comprehensive evaluation of the quality and complexity of prostate IMRT and VMAT plans generated by an automated inverse planning tool

Introduction: The Pinnacle3 Auto-Planning (AP) package is an automated inverse planning tool employing a multi-sequence optimisation algorithm. The nature of the optimisation aims to improve the overall quality of radiotherapy plans but at the same time may produce higher modulation, increasing plan complexity and challenging linear accelerator delivery capability. Methods and materials: Thirty patients previously treated with intensity-modulated radiotherapy (IMRT) to the prostate with or without pelvic lymph node irradiation were replanned with locally developed AP techniques for step-and-shoot IMRT (AP-IMRT) and volumetric-modulated arc therapy (AP-VMAT). Each case was also planned with VMAT using conventional inverse planning. The patient cohort was separated into two groups, those with a single primary target volume (PTV) and those with dual PTVs of differing prescription dose levels. Plan complexity was assessed using the modulation complexity score. Results: Plans produced with AP provided equivalent or better dose coverage to target volumes whilst effectively reducing organ at risk (OAR) doses. For IMRT plans, the use of AP resulted in a mean reduction in bladder V50Gy by 4·2 and 4·7 % (p ≤ 0·01) and V40Gy by 4·8 and 11·3 % (p < 0·01) in the single and dual dose level cohorts, respectively. For the rectum, V70Gy, V60Gy and V40Gy were all reduced in the dual dose level AP-VMAT plans by an average of 2·0, 2·7 and 7·3 % (p < 0·01), respectively. A small increase in plan complexity was observed only in dual dose level AP plans. Findings: The automated nature of AP led to high quality treatment plans with improvement in OAR sparing and minimised the variation in achievable dose planning metrics when compared to the conventional inverse planning approach.

The Influence of Lobe-based Radiotherapy Plan Optimization Method on Different Lymph Node Irradiation Schemes for Operable LA-NSCLC Patients

Purpose Various target volume delineation schemes differ greatly for stage IIIa NSCLC radiotherapy. Although tightened target volume may give patients the opportunity to receive radiotherapy, it is not absolutely safe to narrow the irradiation area. For IIIa NSCLC patients who will undergo lobectomy, a new neoadjuvant radiotherapy based on sparing preserved lung lobes may improve the dose distribution of the preserved lobe, and provide freedom for physicians in optimizing treatment strategies. Materials and methods Computed tomography imaging data of 20 IIIA- p N2 NSCLC patients were used to produce conventional IMRT(IMRT) and Preserved Lobe based IMRT(P-IMRT) plan respectively according to two different target volume delineation schemes(OPT1 and OPT2). Dose results of target coverage, Total lung, Ipsilateral lung, Preserved Total Lung, Preserved Ipsilateral Lung, Contralateral Lung, Resected Lobe and other OARs in the four groups were analyzed. Results All plans met dose limits. Lobe-based IMRT significantly reduce the irradiated dose of Lung lobes, especially Preserved Total Lung and Preserved Ipsilateral Lung, for both delineation schemes. Mean Dose of Preserved Total Lung decreased from 819.93 cGy to 690.98 cGy (OPT1) and 542.47 cGy to 469.62 cGy (OPT2), Mean Dose of Preserved Ipsilateral Lung decreased from 1282.95 cGy to 1068.55 cGy (OPT1) and 955.83 cGy to 795.97 cGy (OPT2), respectively. While the dose indices of Resected Lobe increased slightly for only about 1%. Comparing the four groups of plans, it’s more effective in optimizing the dose of lung lobes by this method for the delineation scheme with a large target volume. The lung dose metrics in P-IMRTOPT1 can be reduced to a value very close to that in IMRTOPT2, and some values are even lower than that in IMRTOPT2. Conclusion For IIIA-N2 NSCLC patients who will undergo lobectomy, no matter which target delineation scheme is chosen, preoperative neoadjuvant radiotherapy using a lobe -based planning can significantly reduce the radiation dose that preserves the lobes. Especially for the large-scale lymph node irradiation scheme, this method can also reduce the dose of preserved lung lobe to a level that is comparable to or lower than that of the conventional IMRT small-area lymph node irradiation scheme, and reduce the obstacles for clinicians in selecting the optimal individualized scheme.

Discussion on the Necessity of Bilateral Inguinal Lymphatic Area Irradiation for Cervical Cancer with Invasion of the Lower One Third of Vagina

Background The rate of inguinal lymph node metastasis is relatively low in cervical cancer patients.According to the NCCN (National Comprehensive Cancer Network) guidelines for cervical cancer,patients with cervical cancer invading the lower 1/3 of the vagina require bilateral inguinal lymphatic area preventive irradiation. But do they need preventive inguinal area irradiation? Methods A total of 184 patients with cervical cancer accompanied by the lower 1/3 of the vagina invasion were selected as the study subjects.In this study, a trial and control method was used to select 180 patients without inguinal lymph node metastasis.The patients were divided into preventive radiotherapy group (109 cases) and non-preventive radiotherapy group (71 cases). During and after treatment, the occurrence of inguinal skin damage, lower extremity edema and femoral head necrosis was observed. Results Thirteen cases (7.07%) of 184 patients were found with inguinal lymph node enlargement by imaging examination, and only 4 cases (2.17%) were further confirmed by pathology.In prophylaxis irradiation group, there were 26(23.85%) cases of side injury.In the follow-up of two groups after treatment there was no recurrence in the inguinal lymph nodes. Conclusion The inguinal lymph node metastasis rate in patients with cervical cancer invading the lower third of the vagina is 2.17%.In order to avoid such a low incidence, we carry out preventive irradiation, which will cause 23.85% of local secondary injuries .And even if we do not perform preventive inguinal lymph node irradiation, there is no difference in the recurrence rate of inguinal lymph nodes between the two groups. Preventive inguinal lymph node irradiation isn’t necessary for these patients.

Comparison of Dose Distribution in Regional Lymph Nodes in Whole-Breast Radiotherapy vs. Whole-Breast Plus Regional Lymph Node Irradiation: An In Silico Planning Study in Participating Institutions of the Phase III Randomized Trial (KROG 1701)

The purpose of the current in silico planning study is to compare radiation doses of whole-breast irradiation (WBI) and whole-breast plus regional lymph node irradiation (WBI+RNI) administered to the regional lymph nodes (RLN) in pN1 breast cancer. Twenty-four participating institutions were asked to create plans of WBI and WBI+RNI for two dummy cases. To compare target coverage between the participants, an isodose line equal to 90% of the prescribed dose was converted to an isodose contour (contour90% iso). The relative nodal dose (RND) was obtained using the ratio of RLN dose to the target dose. The Fleiss’s kappa values which represent inter-observer agreement of contour90% iso were over 0.68. For RNI, 6 institutions included axillary lymph node (ALN), supraclavicular lymph node (SCN), and internal mammary lymph node (IMN), while 18 hospitals included only ALN and SCN. The median RND between the WBI and WBI+RNI were as follows: 0.64 vs. 1.05 (ALN level I), 0.27 vs. 1.08 (ALN level II), 0.02 vs. 1.12 (ALN level III), 0.01 vs. 1.12 (SCN), and 0.54 vs. 0.82 (IMN). In all nodal regions, the RND was significantly lower in WBI than in WBI+RNI (p < 0.01). In this study, we could identify the nodal dose difference between WBI and WBI+RNI.