Volumetric-modulated arc therapy in postprostatectomy radiotherapy patients: A planning comparison study

Dosimetric and radiobiological comparison of prostate VMAT plans optimized using the photon and progressive resolution algorithm

This study compared the dosimetric and radiobiological parameters of prostate volumetric modulated arc therapy (VMAT) plans using different prescriptions optimized by the photon optimization (PO) and progressive resolution optimization (PRO) algorithm. A total of 20 prostate patients were selected retrospectively and divided into 2 groups of VMAT plans using prescriptions of 60 Gy/20 fx and 79 Gy/38 fx. Inverse treatment planning optimized by the PO and PRO algorithm based on the dual-arc technique was carried out by the Eclipse treatment planning system. The maximum dose, minimum dose, mean dose, dose-volume points, and dose-volume indices of the targets and organs at risk (OAR) were calculated from the plans. In addition, radiobiological parameters such as tumor control probability (TCP), normal tissue complication probability (NTCP), and equivalent uniform dose (EUD) of the targets and OAR were determined based on their dose-volume histograms (DVHs). A paired Student's t-test was carried out to compare the difference between mean dose-volume points, radiobiological parameters, and dose-volume indices. Two-tailed p < 0.05 was defined as having statistical difference. For prostate VMAT plans optimized by the PO algorithm, equal or slightly larger mean dose and TCP of the PTV (1% for 60 Gy/20 fx and 0.2% for 78 Gy/39 fx) were found by comparing to the PRO. These were followed by finding the slightly larger conformity index (CI; 0.927 vs 0.895 and 0.910 vs 0.904), larger or equal homogeneity index (HI; 0.054 vs 0.052 and 0.058 vs 0.058), and smaller gradient index (GI; 1.366 vs 2.288 and 1.585 vs 1.742) of the PTV using plans optimized by the PO vs PRO using prescriptions of 60 Gy/20 fx and 78 Gy/39 fx. For the OAR, we found that the mean doses, NTCPs, and EUDs of the rectum, bladder, and femur were slightly larger for plans optimized by the PO algorithm compared to the PRO, though both optimization algorithms satisfied all the dose-volume criteria and objectives in the inverse planning. Both the PO and PRO algorithm can generate prostate VMAT plans fulfilling the required dose-volume criteria. It is concluded that plans optimized by the PO algorithm can produce prostate plan with very similar quality compared to PRO.

Big Data Readiness in Radiation Oncology: An Efficient Approach for Relabeling Radiation Therapy Structures With Their TG-263 Standard Name in Real-World Data Sets

Purpose

To prepare for big data analyses on radiation therapy data, we developed Stature, a tool-supported approach for standardization of structure names in existing radiation therapy plans. We applied the widely endorsed nomenclature standard TG-263 as the mapping target and quantified the structure name inconsistency in 2 real-world data sets.

Methods and Materials

The clinically relevant structures in the radiation therapy plans were identified by reference to randomized controlled trials. The Stature approach was used by clinicians to identify the synonyms for each relevant structure, which was then mapped to the corresponding TG-263 name. We applied Stature to standardize the structure names for 654 patients with prostate cancer (PCa) and 224 patients with head and neck squamous cell carcinoma (HNSCC) who received curative radiation therapy at our institution between 2007 and 2017. The accuracy of the Stature process was manually validated in a random sample from each cohort. For the HNSCC cohort we measured the resource requirements for Stature, and for the PCa cohort we demonstrated its impact on an example clinical analytics scenario.

Results

All but 1 synonym group (“Hydrogel”) was mapped to the corresponding TG-263 name, resulting in a TG-263 relabel rate of 99% (8837 of 8925 structures). For the PCa cohort, Stature matched a total of 5969 structures. Of these, 5682 structures were exact matches (ie, following local naming convention), 284 were matched via a synonym, and 3 required manual matching. This original radiation therapy structure names therefore had a naming inconsistency rate of 4.81%. For the HNSCC cohort, Stature mapped a total of 2956 structures (2638 exact, 304 synonym, 14 manual; 10.76% inconsistency rate) and required 7.5 clinician hours. The clinician hours required were one-fifth of those that would be required for manual relabeling. The accuracy of Stature was 99.97% (PCa) and 99.61% (HNSCC).

Conclusions

The Stature approach was highly accurate and had significant resource efficiencies compared with manual curation.

Dose-volume and radiobiological dependence on the calculation grid size in prostate VMAT planning

This study evaluated the effects of dose-volume and radiobiological dependence on the calculation grid size in prostate volumetric-modulated arc therapy (VMAT) planning. Ten patients with prostate cancer were selected for this retrospective treatment planning study. Prostate VMAT plans were created for the patients using the 6 MV photon beam produced by a Varian TrueBEAM linac with the calculation grid size equal to 1, 2, 2.5, 3, 4, and 5 mm. Dose-volume histograms (DVHs) of targets and organs at risk were generated for different grid sizes. We calculated the radiobiological parameters of the tumor control probability (TCP) of clinical target volume (CTV) and planning target volume (PTV), and the normal tissue complication probability (NTCP) of organs at risk (rectal wall, rectum, bladder wall, bladder, left femur, and right femur). The homogeneity, conformity, and gradient indexes of CTV and PTV were calculated for different grid sizes. The TCP of PTV was found decreasing with a rate of 0.06%/mm when the calculation grid size increased from 1 to 5 mm. On the other hand, both NTCPs of rectal wall and rectum were found decreasing with rates of 0.03%/mm and 0.05%/mm, respectively, with an increase of grid size. The homogeneity index of PTV increased with a rate of 0.57/mm of the calculation grid size, whereas the conformity index of PTV decreased with a rate of 0.0075/mm. The gradient index of PTV was found increasing with a rate equal to 0.05/mm. In prostate VMAT planning, variations of dose-volume and radiobiological parameters with calculation grid size on PTV, rectal wall, and rectum were more significant than those of CTV and other organs at risk such as bladder wall, bladder, and femurs. Results in this study are important in the treatment planning quality assurance when the calculation grid size is varied to compromise a shorter dose computing time.

Dosimetric and radiobiological characterizations of prostate intensity-modulated radiotherapy and volumetric-modulated arc therapy: A single-institution review of ninety cases

This study reviewed prostate volumetric-modulated arc therapy (VMAT) plans with intensity-modulated radiotherapy (IMRT) plans after prostate IMRT technique was replaced by VMAT in an institution. Characterizations of dosimetry and radiobiological variation in prostate were determined based on treatment plans of 40 prostate IMRT patients (planning target volume = 77.8–335 cm³) and 50 VMAT patients (planning target volume = 120–351 cm³) treated before and after 2013, respectively. Both IMRT and VMAT plans used the same dose-volume criteria in the inverse planning optimization. Dose-volume histogram, mean doses of target and normal tissues (rectum, bladder and femoral heads), dose-volume points (D_99% of planning target volume; D_30%, D_50%, V_{30 Gy} and V_{35 Gy} of rectum and bladder; D_5%, V_{14 Gy}, V_{22 Gy} of femoral heads), conformity index (CI), homogeneity index (HI), gradient index (GI), prostate tumor control probability (TCP), and rectal normal tissue complication probability (NTCP) based on the Lyman-Burman-Kutcher algorithm were calculated for each IMRT and VMAT plan. From our results, VMAT plan was found better due to its higher (1.05%) CI, lower (0.83%) HI and (0.75%) GI than IMRT. Comparing doses in normal tissues between IMRT and VMAT, it was found that IMRT mostly delivered higher doses of about 1.05% to the normal tissues than VMAT. Prostate TCP and rectal NTCP were found increased (1%) for VMAT than IMRT. It is seen that VMAT technique can decrease the dose-volume evaluation criteria for the normal tissues. Based on our dosimetric and radiobiological results in treatment plans, it is concluded that our VMAT implementation could produce comparable or slightly better target coverage and normal tissue sparing with a faster treatment time in prostate radiotherapy.