Dosimetry and efficiency comparison of knowledge-based and manual planning using volumetric modulated arc therapy for craniospinal irradiation
Article Category: Research Article
Data publikacji: 07 mar 2024
Zakres stron: 289 - 299
Otrzymano: 04 lis 2023
Przyjęty: 03 sty 2024
DOI: https://doi.org/10.2478/raon-2024-0018
Słowa kluczowe
© 2024 Wei-Ta Tsai et al., published by Sciendo
This work is licensed under the Creative Commons Attribution 4.0 International License.
Prophylactic or therapeutic craniospinal irradiation (CSI) is an option for managing certain primary brain tumors, such as medulloblastoma, or hematologic malignancies.1 Since the maximum field of the linear accelerator is 40 cm by 40 cm, the conventional three-dimensional conformal radiation therapy (3D-CRT) techniques for CSI use two opposed lateral craniocervical fields adjoined by two adjacent posterior spinal fields. In conventional CSI techniques, the fields are matched between the lateral and posterior fields, creating over- or underdosage within the spinal cord. To address this issue, 3D-CRT with the moving junction technique2,3, which involves changing different junction locations daily during the treatment course, is an option to blur the dose ununiform effect.
The moving junction technique in 3D-CRT requires the use of multiple treatment plans, which increases the complexity of treatment planning and daily treatment. Moreover, the CSI moving junction technique can only reduce the dose ununiform effect but cannot obtain dose homogeneity as a common treatment. With the development of commercial treatment planning system (TPS), volumetric modulated arc therapy (VMAT) with multi-isocenter optimization4 was introduced. VMAT with 360-degree beams can achieve higher conformity and better dispersion of normal organs compared to conventional 3D-CRT.5,6 The VMAT technique with large field overlaps for low-dose gradient junction could tolerate greater positional shifts while maintaining homogeneous dose.7,8 However, planning CSI using the high-precision VMAT technique is challenging and time-consuming for medical physicists due to the long treatment field from the brain to the lumbosacral region, which significantly exceeds the treatment field size of a linear accelerator and involves more than ten organs at risk. Because CSI treatment is relatively rare and only patients with possible malignancy tumor cells seeding in the craniospinal canal receive this treatment, medical physicists in many institutions are unfamiliar with this technique. The rarity of the expertise and complex planning processes make this process resource-intensive.
Knowledge-based planning (KBP) is based on a model of estimating dose-volume histograms (DVHs), which is configured by a library of historical treatment plans with the aim of improving planning efficiency.9 In previous studies, KBP has been adopted to treat patients with several cancer types, such as head and neck cancers and pelvic malignancies.10,11,12,13 KBP showed improved planning efficiency with well-reserved plan quality in those cancer sites. However, compared to those cancer sites, CSI would require more treatment isocenters and patients moving with junction feathering. Moreover, more organs at risk (OARs) needed to be considered in CSI than other treatment sites. Reviewing the literature, previous CSI studies have not compared the plan quality and cost-effectiveness of the general manual plan method and the KBP with and without re-optimization.
This study aimed to compare the plan quality and efficiency of the original manual plans (MP), KBP initial plans (RPI) (RapidPlanTM, Varian Medical Systems, Palo Alto, USA), and KBP final plans, which received further re-optimization (RPF) for CSI.
The Institutional Review Board of the Dalin Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation approved this study (approval number, B10804011-1) and waived the requirement for written informed consent from the patients involved because only anonymized images were retrospectively analyzed, and this study did not affect the actual treatments these patients received before.
This study retrospectively collected computed tomography (CT) image sets of 38 anonymized adults assessed between 2014 and 2019. All the image sets met the requirement of immobilization, supine position, and scan from head to pelvis. The slice thickness and matrix size were 3–5 mm and 512 × 512 voxels, respectively (Figure 1).
FIGURE 1.
Flowchart of the study design.
CSI = craniospinal irradiation; CT = computed tomography; KBP = knowledge-based planning; VMAT = volumetric modulated arc therapy
The clinical target volume (CTV) includes the whole brain and spinal cord, typically extended to the lumbar spine L3 level. Assembled CTV was separated into CTV-brain, CTV-spine-superior, and CTV-spine-inferior for the multiple field optimization (Figure 2). The PTV-brain was constructed by symmetrically extending the CTV-brain by 3 mm and by adding 5 mm margin to the spine area. The maximum and minimum lengths of the CTV were 77.83 cm and 65.40 cm, while those of the PTV were 78.80 cm and 66.38 cm. The mean lengths of the CTV and PTV were 71.15 ± 4.28 cm and 72.23 ± 4.16 cm, respectively. The mean CTV and PTV were 1413.40 ± 162.18 cm3 and 1823.93 ± 192.14 cm3, respectively. For planning evaluation purposes, the PTV-brain, PTV-spine-superior, and PTV-spine-inferior were combined as PTV.
FIGURE 2.
Example of the target and field setup.
The dose prescription was 36 Gy in 18 daily fractions. All plans were normalized so that 95% of the PTV received 100% of the prescribed dose.
The 38 CT image sets of anonymized adults were imported to Eclipse TPS version 13.6 (Varian Medical Systems, Palo Alto, CA, USA). Overall, six medical physicists were participated in this study. Plans for each patient were reviewed and approved by the same physician. A TrueBeam linear accelerator (Varian Medical Systems, Palo Alto, CA, USA) equipped with a 120-leaf multileaf collimator was selected. All plans were set as 6 megavoltage for the VMAT technique. Analytical Anisotropic Algorithm dose calculation algorithm, 2.5 mm dose calculation grid, and jaw tracking were used. The mean lateral field size for the brain field is 14.76 ± 0.08 cm, while the average lateral field size for the spine field is 12.42 ± 2.52 cm. These dimensions are adjusted to encompass the entire target within a reasonable rotation range. Jaw tracking technique is used to minimize the impact of transmission leakage dose to normal organ. The collimator rotation angle is set within a range of ± 35 degrees for the head and ± 12 degrees for the spine, according to the physicist’s discretion at the time.
The whole target length was more than 100 cm, whereas the maximum single-field size of a linear accelerator at the isocenter is 40 × 40 cm. Therefore, multiple fields and three isocenters were required. The PTV-brain used two full arcs, with the isocenter positioned at the center of the brain. For the PTV-spine, two or four partial arcs were used on the PTV-spine-superior, and PTV-spine-inferior to avoid the 60–120-degree and 240–300-degree direction for arm sparing. For the sake of clinical convenience, the three isocenters were aligned along the same X-axis (left-right). The spine isocenter shared the same X and Y coordinates, differing only along the Z-axis (craniocaudal) (Figure 2).
A total of 38 MPs were generated for the 38 patients, with 23 MPs used to train the RapidPlan (RP) model, and 15 MPs used for validation and comparison (Figure 1). Using RP, 15 RP initial plans (RPI) were generated without manual modification, on which we performed further manual re-optimization to generate 15 RP final plans (RPF). Finally, we compared the following three plan groups: MP, RPI, and RPF.
The RapidPlan is a commercial KBP program integrated within the Eclipse TPS. The KBP program references a library of previously clinically accepted treatment plans. It analyzes the geometric and dosimetric features, such as structure sets, field geometry, dose matrices and plan prescriptions of those plans to train a statistical model. This model is then used to predict an achievable range of DVHs and generate dose-volume objectives for a new plan.
The RapidPlan algorithm comprises two main components: model configuration and DVH estimation. The model configuration component is responsible for setting up new DVH estimation models, which are subsequently utilized in the DVH estimation component to generate estimates for an individual plan. The model configuration component encompasses two distinct phases: data extraction and model training. On the other hand, the DVH estimation component encompasses the phases of estimation generation and objective generation.
The minimum requirement of data extraction and model training was 20 plans with their targets and OARs. Among the 20 randomly selected plans for model training, the right lens of three plans were too small to evaluate. Therefore, we added three more plans to meet the training requirement.
The model training phase within the DVH estimation algorithm is dedicated to the creation of DVH estimation models. The estimation generation phase calculates for each supported structure the same metrics that were calculated during the data extraction of the DVH estimation model, except for the DVH. Once the estimation generation phase has derived the upper and lower bound DVHs, the optimization objectives placement phase translates them into optimization objectives.
There were 27 dosimetric goals of irradiated fields and OARs were evaluated for the three groups among 15 patients. One patient had previously undergone thyroidectomy, and his thyroid dose could not be evaluated. This resulted in a total of 404 items being calculated for model evaluation. Dosimetric characteristics, such as V95, V100, V107, Dmean, Dmax, and D2 of CTV, and PTV, were evaluated. In addition, conformity index (CI) and homogeneity index (HI) of the targets and dose gradient (Rx%) were compared.14 The Radiation Therapy Oncology Group (RTOG) criteria define CI values to be between 1.0 and 2.0 in accordance with the protocol, 2.0 to 2.5 and 0.9 to 1.0 as a minor deviation, and > 2.5 and < 0.9 as a major deviation from the protocol. The CI was defined as a ratio between the volume covered by the reference isodose (36 Gy) and the target volume, as in Equation [1].
The HI is the ratio between maximum isodose and reference isodose. The formula of HI was shown as Equation [2]. The ideal value is 1, which increases as the plan becomes less homogeneous.
The dose gradient (Rx%) formula is given below:
The pre-optimization, optimization, and re-optimization planning times were compared. The pre-optimization time included OARs contouring and field setup, and the re-optimization time was the time of further optimization and calculation until the plan was satisfied. Average monitor units (MUs) were also evaluated.
The Wilcoxon test was used to compare the differences between the three groups. The differences in the dose coverage, mean dose of the targets, and OARs were compared with a 95% confidence interval. All tests were two-sided. A
Table 1 shows the dosimetric results of targets. For the V100, V107, Dmax, and D2 of the CTV, both MP and RPF groups were significantly better than RPI (
Dosimetric comparison between manual plans, RapidPlan initial, and RapidPlan final
| V95 [%] | > 99 | 99.99 ± 0.03 | 99.98 ± 0.03 | 99.97 ± 0.03 | 0.36 | 0.03* | 0.09 |
| V100 [%] | > 99 | 99.20 ± 0.17 | 98.37 ± 0.33 | 99.37 ± 0.23 | < 0.01** | 0.07 | < 0.01** |
| V107 [%] | Minimize | 0.62 ± 0.59 | 2.94 ± 4.33 | 0.46 ± 0.66 | < 0.01** | 0.16 | < 0.01** |
| Dmean [Gy] | 36 | 37.23 ± 0.18 | 37.31 ± 0.21 | 37.22 ± 0.24 | 0.07 | 0.87 | 0.13 |
| Dmax [Gy] | Minimize | 39.38 ± 0.40 | 40.38 ± 0.57 | 39.42 ± 0.41 | < 0.01** | 0.78 | < 0.01** |
| D2 [%] | < 107 | 106.12 ± 0.73 | 106.95 ± 0.96 | 105.72 ± 0.84 | < 0.01** | 0.19 | < 0.01** |
| V95 [%] | > 98 | 99.68 ± 0.15 | 99.55 ± 0.23 | 99.24 ± 0.32 | 0.03* | < 0.01** | < 0.01** |
| V100 [%] | = 95 | 95.00 ± 0.00 | 95.00 ± 0.00 | 95.00 ± 0.00 | - | - | - |
| V107 [%] | Minimize | 0.62 ± 0.57 | 3.01 ± 4.12 | 0.44 ± 0.61 | < 0.01** | 0.17 | < 0.01** |
| Dmean [Gy] | 36 | 37.10 ± 0.16 | 37.22 ± 0.18 | 37.08 ± 0.20 | 0.05 | 0.73 | 0.01* |
| Dmax [%] | < 112 | 109.99 ± 1.17 | 112.89 ± 1.78 | 110.17 ± 1.14 | < 0.01** | 0.57 | < 0.01** |
| D2 [%] | < 107 | 106.09 ± 0.73 | 107.00 ± 0.93 | 105.71 ± 0.80 | < 0.01** | 0.21 | < 0.01** |
| CI | 1 | 0.98 ± 0.01 | 1.01 ± 0.01 | 1.00 ± 0.01 | < 0.01** | < 0.01** | 0.01* |
| HI | 1 | 1.10 ± 0.01 | 1.13 ± 0.02 | 1.10 ± 0.01 | < 0.01** | 0.57 | < 0.01** |
CI = conformity index; CTV = clinical target volume; Dx = minimum dose received by the hottest x% volume; HI = homogeneity index; MP = manual plan; PTV = planning target volume; RPI = RapidPlan initial; RPF = RapidPlan final; Vx = volume receiving at least x dose;
=
=
Furthermore, there were 14 OARs and 20 evaluation parameters for these OARs (Table 2). RPF and RPI had better dosimetric results than MP for the Dmean of optic nerves, parotid glands, heart, and esophagus, and Dmax of eyes (all
Dosimetric goals and results for organs at risk
| Dmax [Gy] | < 60 | 39.34 ± 0.39 | 40.24 ± 0.61 | 39.28 ± 0.37 | < 0.01** | 0.46 | < 0.01** |
| Dmax [Gy] | < 54 | 38.48 ± 0.41 | 39.03 ± 0.46 | 38.51 ± 0.28 | < 0.01** | 0.91 | < 0.01** |
| Dmean [Gy] | < 50 | 37.15 ± 0.35 | 37.10 ± 0.32 | 36.95 ± 0.32 | 0.69 | 0.07 | 0.06 |
| Dmax [Gy] | < 55 | 38.13 ± 0.40 | 38.73 ± 0.55 | 38.20 ± 0.26 | 0.01* | 0.46 | < 0.01** |
| Dmean [Gy] | < 50 | 27.61 ± 3.40 | 22.90 ± 2.39 | 22.42 ± 2.29 | < 0.01** | < 0.01** | 0.05 |
| Dmax [Gy] | < 55 | 37.13 ± 0.69 | 36.36 ± 1.72 | 36.15 ± 1.39 | 0.13 | 0.02* | 0.13 |
| Dmax [Gy] | < 50 | 25.55 ± 3.57 | 22.52 ± 3.83 | 21.60 ± 3.86 | 0.02* | 0.01* | 0.01* |
| Dmax [Gy] | < 10 | 8.40 ± 0.68 | 8.87 ± 1.00 | 8.10 ± 0.55 | 0.11 | 0.21 | < 0.01** |
| Dmean [Gy] | < 25 | 7.38 ± 2.52 | 5.16 ± 0.39 | 4.95 ± 0.39 | < 0.01** | < 0.01** | < 0.01** |
| Dmax [Gy] | < 50 | 38.93 ± 0.51 | 39.81 ± 0.67 | 39.04 ± 0.56 | < 0.01** | < 0.01** | < 0.01** |
| Dmax [Gy] | < 45 | 17.23 ± 4.04 | 16.68 ± 2.13 | 16.38 ± 2.04 | 0.59 | 0.36 | 0.07 |
| Dmean [Gy] | < 13 | 4.63 ± 0.30 | 4.95 ± 0.43 | 4.63 ± 0.24 | 0.03* | 0.73 | < 0.01** |
| V20Gy [%] | < 22 | 0.06 ± 0.11 | 0.04 ± 0.08 | 0.03 ± 0.04 | 0.64 | 0.44 | 0.33 |
| V5Gy [%] | < 42 | 36.48 ± 2.88 | 42.77 ± 5.62 | 37.11 ± 2.87 | 0.01* | 0.69 | < 0.01** |
| Dmean [Gy] | < 10 | 6.76 ± 1.47 | 5.53 ± 0.82 | 5.70 ± 0.93 | 0.01* | 0.02* | 0.33 |
| V40Gy [%] | < 3 | 0.00 ± 0.00 | 0.00 ± 0.00 | 0.00 ± 0.00 | - | - | - |
| V18Gy [%] | < 5 | 0.04 ± 0.10 | 0.01 ± 0.03 | 0.01 ± 0.02 | 0.31 | 0.23 | 0.41 |
| Dmean [Gy] | < 34 | 14.34 ± 1.62 | 13.23 ± 1.63 | 13.30 ± 1.74 | 0.01* | < 0.01** | 0.96 |
| Dmean [Gy] | < 30 | 4.82 ± 0.94 | 4.57 ± 0.73 | 4.45 ± 0.70 | 0.61 | 0.33 | < 0.01** |
| Dmean [Gy] | < 18 | 2.81 ± 1.17 | 2.47 ± 0.46 | 2.38 ± 0.43 | 0.96 | 0.73 | < 0.01** |
OAR = organ at risk; MP = manual plan; RPI = RapidPlan initial; RPF = RapidPlan final; Vx = volume receiving at least x dose;
=
=
Overall, the RPF group achieved superior or equal best results in 71.88% (23/32) of the 32 evaluation parameters of the targets (13) and OARs (19), which excluding the PTV V100% and heart V40Gy, because the volumes were the same in all three groups.
In this study, we evaluated the quality of the treatment plans for three groups of 15 patients each. We used 27 parameters to evaluate each plan, for a total of 404 parameters, due to one patient who did not have a thyroid gland. We did not include the parameters CTV V107%, CTV Dmean, CTV Dmax, PTV V107%, PTV Dmean, CI, and HI in the evaluation because they did not have specific goal values. The plan quality pass rate of the MP and RPF groups was 100% (404/404) according to the plan goals of targets and OARs. The RPI group pass rate was 89.36% (361/404). When evaluating the failures of the RPI group, although no patient in the RPI group passed the CTV V100 goal of 99%, the minimum and median values of RPI CTV V100 were 97.83% and 98.44%, respectively, and both the CTV V95 and the PTV V95 of RPI group reached the goals. The pass rates of CTV D2, PTV Dmax, and PTV D2, for the RPI group, were 66.67% (10/15), 33.33% (5/15), and 66.67% (10/15), respectively. In addition, in the OAR, the lens Dmax and lungs V5 of the RPI group did not meet the goals. The pass rate of the lens Dmax was 93.33% (14/15) for the RPI group. In one RPI plan, the lens Dmax was 10.98 Gy > 10 Gy. Lastly, the RPI lungs V5 pass rate was 53.33% (8/15).
Table 3 shows the mean dose of the 9 OARs. The highest OARs Dmean of the optic nerves, eyes, parotid glands, thyroid, heart, liver, and kidneys; and lens and lungs in these three groups were obtained in the MP group (78%, 7/9) and RPI group (22%, 2/9), respectively. The lowest OARs Dmean were mostly in the RPF group (89%, 8/9). Comparing RPI and MP, RPF and RPI, and RPF and MP groups, the RPI group significantly reduced the doses of optic nerves, eyes, parotid glands, and heart than the MP group; the RPF group further significantly reduced the doses of eyes, lenses, parotid glands, thyroid, lungs, liver, and kidneys than the RPI group (
The mean dose of the OARs outside the targets contours
| 22.90 ± 2.39 | 22.42 ± 2.29 | < 0.01** | < 0.01** | 0.05 | ||
| 10.16 ± 0.55 | 9.83 ± 0.74 | 0.01* | 0.01* | 0.02* | ||
| 7.09 ± 0.67 | 6.78 ± 0.39 | 0.43 | 0.16 | < 0.01** | ||
| 5.16 ± 0.39 | 4.95 ± 0.39 | < 0.01** | < 0.01** | < 0.01** | ||
| 9.00 ± 1.94 | 8.51 ± 2.07 | 0.06 | 0.04* | < 0.01** | ||
| 4.63 ± 0.30 | 4.63 ± 0.24 | 0.03* | 0.73 | < 0.01** | ||
| 5.53 ± 0.82 | 5.70 ± 0.93 | 0.01* | 0.02* | 0.33 | ||
| 4.57 ± 0.73 | 4.45 ± 0.70 | 0.61 | 0.33 | < 0.01** | ||
| 2.47 ± 0.46 | 2.38 ± 0.43 | 0.96 | 0.73 | < 0.01** | ||
Bold type = the highest Dmean in the three groups; MP = manual plan; RPI = RapidPlan initial; RPF = RapidPlan final; Underline mark = the lowest Dmean in the three groups;
=
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In the low-dose region of normal tissue, we employed R50%, R30%, and R10% as dose gradient indicators. The values for MP, RPI, and RPF at R50% were 2.27 ± 0.13, 2.26 ± 0.16, and 2.26 ± 0.14, respectively. For R30%, the values were 3.96 ± 0.31, 3.95 ± 0.32, and 3.94 ± 0.37, respectively. The corresponding values for R10% were 10.15 ± 1.93, 10.08 ± 1.69, and 10.00 ± 1.74. There were no statistically significant differences among the three groups (P > 0.05).
Figure 3A showed the population-averaged DVH of targets and OARs. In the DVH, the doses of optic nerves, eyes, lens, parotid glands, thyroid, liver, and kidneys in RPF or RPI were lower than those in MP. Furthermore, the DVH of RPF OARs was better than those of RPI OARs. Figure 3B shows the targets coverage of CTV and PTV. In the shoulder part of the DVH, with the 95% volume of targets, the MP and RPI groups had the same targets coverage, while the RPF group had a slightly better 95% volume dose coverage than the other two groups. The DVH tail part, the high dose in 5% volume, showed that the RPI had the highest dose in the craniospinal area. The population-averaged DVH showed that the RPF group had the best targets coverage, homogenous targets dose distribution, and OAR dose avoidance among these three groups.
FIGURE 3.
CTV = clinical target volume; MP = manual optimization plan; PTV = planning target volumes; RPI = RapidPlan initial; RPF = final RapidPlan after manual re-optimization
The pre-optimization time was the same in all three groups (146 minutes, Figure 4). The optimization process took a significantly longer time in the MP group than in the RPI and RPF groups with 111.45, 81.68, and 81.68 minutes (
FIGURE 4.
Comparison of the planning time for MP, RPI, and RPF. The error bar represents one standard deviation.
MP = manual optimization plan; RPI = RapidPlan initial; RPF = final RapidPlan after manual re-optimization
The average MU values with one standard deviation of MP, RPI, and RPF groups were 935.24 ± 128.44, 1013.22 ± 114.92, and 1026.46 ± 149.43, respectively, with no significant difference between these three groups (all
Our research discovered that by utilizing 23 plans to develop the KBP model in combination with RP and re-optimization in CSI, we were able to significantly shorten the planning time by half and enhance plan quality.
Incorporating more patients in the model libraries for model training have a possibility to lead to fewer outliers and more consistent plan quality.15,16,17 However, the application of the CSI technique in clinical practice is not common in most hospitals. In this study, because CSI treatment is relatively rare, we searched databases covering the previous 6 years and found only 38 CT image sets. The Varian accelerator company recommended a minimum of 20 to 25 treatment plans in training set for a specific target. According to the study by Jim P. Tol
The traditional CSI used patient prone position to reduce the OARs radiation dose via simple two lateral opposed and posterior-anterior (PA) fields. However, this technique can create dose ununiform in the field junction area. The commonly encountered pediatric CSI typically requires two fields and one junction to achieve coverage. This study aims to validate whether KBP can perform effectively in more complex scenarios, utilizing adult CSI as a test case. We used the VMAT technique to disperse the radiation dose in OARs and enhance the homogeneity of the targets dose. The VMAT technique delivers radiation from all angles, which causes it to be attenuated as it passes through the couch. Our medical physicist compensated for this effect by calculating the attenuation of the couch.19 Furthermore, cone beam computed tomography ensured an accurate treatment location. Therefore, in this study, all treatment plans were designed using the supine position, which could make patients more comfortable, relaxed, and stable during treatment.3,20
Although the plan parameter pass rate of RPI was only 89.36%, the RPI target coverage of minimum CTV V95 and PTV V95 values were ≥ 99.90% and ≥ 99.00%, respectively, which were both higher than 95%, the clinical common plan acceptable criteria.21 Compared with the traditional 3D-CRT technique, by which the high dose area might receive approximately twice the prescribed dose at the field overlapping sites, the highest PTV Dmax in RPI was 115.57% which was much lower than the traditional 3D-CRT technique. For OARs, all 14 plans in RPI achieved the goal (< 10 Gy) except for one plan with lens Dmax 10.98 Gy, which did not reach the goal. Table 2 shows that the heart Dmean in RPI was also the lowest of the three groups. Although, Uehara
The DVH distribution is one of the vital plan evaluation tools. The DVH of OARs (Figure 3) showed that most of the OARs in the MP group received higher doses than RPI and RPF, as shown by the Dmean and Dmax in Table 2. In the target DVH (Figure 3B), the RPF group had better 95% volume dose coverage and better performance at reducing high doses than the other two groups. According to our CI results, there was a minor deviation of the target in the MP group; however, RPI or RPF could have achieved the planning goal. Furthermore, HI values in this study show that MP and RPF groups had better homogeneity than did RPI. Previous studies on lung cancer or prostate cancer showed that KBP could reduce the OARs dose23; however, target coverage and dose homogeneity of KBP did not always have better results than the manual plan. Our study on CSI showed that RP improved the plan quality of OARs and that additional re-optimization after initial RP could improve the plan quality, as previous studies showed in other cancer sites.24,25,26,27
In terms of cardiac doses, all three plans (MP, RPI, and RPF) exhibited notably low V40Gy and V18Gy values, comfortably below the established cardiac dose constriants. It is pertinent to mention that the mean cardiac dose for RPI was already lower than that for MP. Therefore, the primary focus during the optimization process was not predominantly on further reducing cardiac dose. In the case of RPI, the lungs V5Gy value(42.77 ± 5.62%) surpassed the target threshold of 42%. Subsequently, in the ensuing RPF optimization, concerted efforts were undertaken to amplify the reduction of lungs V5Gy values, resulting in a dose shift towards the heart. Nevertheless, from a statistical perspective, the P-value for the comparison between RPI and RPF exceeded 0.05.
In our study, RPI and RPF reduced planning time compared to MP by 66.41% (450.14 minutes) and 54.59% (370.04 minutes), respectively. The result showed that KBP for CSI might save more planning time in complex plans with many OARs than in general cancer sites. Previously, Wells
This study used 23 plans to train the KBP CSI model and investigated the difference between MP and RP for the same patients and found that RP plans after re-optimization could halve the planning time and improve plan quality. According to our study result, medical physicists at low CSI patient volume hospitals could efficiently produce CSI plans by the KBP method.