Feasibility study of automatic uARC planning for esophageal cancer using simultaneous integrated boost radiotherapy / 中华放射肿瘤学杂志

Objective:To compare dosimetric and radiobiological parameters between automatic and manual uARC plans in the treatment of esophageal cancer patients, aiming to provide reference for clinical application.Methods:High-quality uARC plans of 100 patients with esophageal cancer were selected, and the mean values of the dosimetric parameters in the target area and organs at risk (OAR) were counted, and the goal table of uRT-TPOIS intelligent plan was established. Automatic and manual uARC plans were generated with UIH (United Imaging) treatment planning system (TPS) for 21 esophageal cancer patients. The differences in mean dose (D mean), approximate minimum (D 98%) and maximum (D 2%) dose of planning target volume (PTV), homogeneity index (HI) and conformity index (CI), dose of OAR, mean planning time, monitor unit (MU), tumor control probability (TCP) and normal tissue complication probability (NTCP) were compared between automatic and manual uARC plans. Normally distributed data between two groups were compared by paired t-test, and non-normally distributed data were assessed by nonparametric Wilcoxon test. Results:The D 98% (PTV 60 Gy: P<0.001, PTV 54 Gy: P=0.001) , CI (PTV 60 Gy: P<0.001, PTV 54 Gy: P=0.002) and target volume of area covered by prescription dose (V 54 Gy: P<0.001) of the automatic uARC plans were better than those of manual uARC plans (all P<0.05). There was no significant difference in D mean or HI between the two plans [PTV 54 Gy (59.32±1.87) Gy vs. (59.13±1.64) Gy, (0.19±0.02) vs. (0.18±0.02), all P>0.05]. The D mean and D max of spinal cord of the automatic plan were better than those of the manual plan [(13.22±4.27) Gy vs. (13.75±4.44) Gy, P=0.020 and (36.99±1.67) Gy vs. (38.14±1.31) Gy, P=0.011]. There was no significant difference in the mean dose of V 20 Gy of the lung between two plans ( P>0.05), whereas the mean doses of V 5 Gy and V 10 Gy of the lung of the manual plan were less than those of the automatic plan ( both P<0. 001). Automatic uARC plan had a significantly shorter mean planning time than manual uARC plan [(11.79±1.71) min vs. (53.36±8.23) min, P<0.001]. MU did not significantly differ between two plans [(762.84±74.83) MU vs. (767.41±80.63) MU, P>0.05]. The TCP of the automatic plan was higher than that of the manual plan (PTV 60 Gy 89.15%±0.49% vs. 86.75%±6.46%, P=0.004 and PTV 54 Gy 79.79%±3.48% vs. 77.51%±5.04%, P=0.006). However, manual plan had a lower NTCP of the lung than automatic uARC plan (0.46%±0.40% vs. 0.35%±0.32%, P<0.001). There was no significant difference in NTCP of heart and spinal cord between two plans (all P>0.05). Conclusion:It is feasible to generate automatic uARC plan with uRT-TPOIS TPS for esophageal cancer patients, which can increase the target CI and shorten the plan design time.

Evaluating different radiotherapy treatment plans, in terms of critical organ scoring index, conformity index, tumor control probability, and normal tissue complication probability calculations in early glottic larynx carcinoma

Purpose: In this study, it is aimed to compare three different radiotherapy treatment planning techniques in terms of critical organ scoring index (COSI), two different conformity index (CI), tumor control probability (TCP), and normal tissue complication probability (NTCP) calculations in early (T1) glottic larynx carcinoma (T1GL). Furthermore, it is aimed to investigate these parameters compliance with dose-volume histograms (DVH) parameters. Materials and Methods: Ten T1GL patients were immobilized in a supine position with a head and neck thermoplastic mask. Treatment plans were created with opposed lateral fields (OLAFs) and intensity-modulated radiation therapy (IMRT) techniques with a total dose of 66 Gy in 33 fraction with 2 Gy/day. IMRT fields were selected as five fields (5IMRT) and seven fields (7IMRT). Dosimetric evaluation of three different treatment plans for T1GL carcinoma was performed in two consequential steps. First step was the assessment of planning target volume (PTV), all organs at risks (OARs), and normal tissue (NT) dose calculations according to given dose constraint directions and comparing the plans via DVH. In the second step, for PTV, the compatibility of DVH data with CIs-TCP was investigated where COSI-NTCP was compared with DVH for OARs. The DVH data were considered as reference in all evaluations. Results: The CIRTOG mean values were significantly closer to 1 with IMRT plans when compared to OLAF plans (P = 0.005). The CIPADDICK mean values revealed that OLAF plans were significantly worse than IMRT plans (P = 0.005). No statistically significant difference was found between all three plans in terms of homogeneity index mean values (P = 0.076). The calculated mean TCP values were significantly better for 7IMRT plans when compared to OLAF and 5IMRT plans (P = 0.007 and P = 0.017, respectively). Both NTCP and COSI evaluations, which is compatible with DVH, significantly favored OLAF plan for spinal cord and 7IMRT for thyroid gland. The COSI evaluations, which are compatible with DVH, significantly favored 7IMRT plan for carotid arteries and 5IMRT plan for NT. Conclusion: Our results demonstrated that CIPADDICK-TCP calculations for PTV and COSI-NTCP calculations for OARs were compatible with DVH in T1 GL plans. Therefore, we suggest such parameters as valuable tools for choosing the feasible one among multiple plans and even with different treatment machines

Uncertainty of small bowel dose?volume and normal tissue complication probability assessment due to small bowel motility during intensity?modulated radiotherapy for rectal cancer / 中华放射肿瘤学杂志

Objective To evaluate the uncertainty of the small bowel dose?volume and the normal tissue complication probability (NTCP) during intensity?modulated radiotherapy (IMRT) for rectal cancer, and to provide a reference for the dose limit and protection of the small bowel during IMRT for rectal cancer. Methods A total of 20 patients with rectal cancer who received postoperative adjuvant radiotherapy from March 2014 to August 2015 were enrolled in this study, including 10 patients receiving CT scan in the supine position and 10 patients in the prone position. All patients received computed tomography ( CT) scan before the treatment and at weeks 1, 2, 3, and 4 of treatment, and they were defined as Plan, 1W, 2W, 3W, and 4W CT groups, respectively. The small bowel loop ( BL ) and peritoneal space ( PS ) were delineated on the images. The IMRT plan based on the Plan CT was copied to the 1W, 2W, 3W, and 4W CT groups, and then the small bowel dose?volume and NTCP were assessed for all CT groups. The paired t?test was used for comparison between groups. The Pearson method was used to analyze the correlation between NTCPC(chronic NTCP) and dose?volume. Results A total of 89 CT images of 20 patients were obtained. In all the patients, the volumes of BL and PS were 25121 cm3 and 132416 cm3 , respectively, and the shift% was 2315% and 1134%, respectively. The V15 of BL and PS was 18486 cm3 and 79245 cm3 , respectively, and the shift% was 3169% and 370%, respectively. The V30 of BL and PS was 8801 cm3 and 64573 cm3 , respectively, and the shift% was 3766% and 1049%, respectively. The V15 of BL in 35% of patients and V15 of PS in 20% of patients, the Dmax of BL in 50% of patients, and the NTCP of 15% of patients in the course of treatment exceeded the safety limits. The 1?4W CT groups had a significantly higher NTCPC than the Plan CT group (402% vs. 320%, P=0104), and their SD% was 4168%. There was a significant correlation between NTCPC and V30?V50 of BL (R>0400, P=0000). The NTCPA ( acute NTCP ) and NTCP C in the supine position were significantly higher than those in the prone position ( 6230% vs. 5674%, P=0061;488% vs. 322%, P=0145 ) . Conclusions Small bowel motility leads to an uncertainty of the adverse event assessment during IMRT for rectal cancer. The change in BL is significantly larger than that in PS and the change in BL and PS in the supine position is significantly larger than that in the prone position. Using the prone position and minimizing V15 and V30 when designing the treatment plan can reduce the NTCP A and NTCP C in the small bowel.

Establishment of the NTCP model for radiation-induced lung injury in patients with non-small cell lung cancer / 中华放射肿瘤学杂志

Objective To examine the incidence of radiation-induced lung injury(RILI)after involved-field intensity-modulated radiation therapy(IMRT)in patients with locally advanced non-small cell lung cancer(NSCLC),and to evaluate the predictability of different models.Methods The clinical data of 242 inoperable or unresectable stage Ⅲ NSCLC patients treated in our hospital from 2007 to 2011 were reviewed. Grade 2 and grade 3 RILI that occurred within 6 months after IMRT were selected as outcome events in this study. The principal component analysis(PCA)model,Lyman-Kutcher-Burman(LKB)model,and mean lung dose(MLD)model were each used to establish a predictive model of normal tissue complication probability (NTCP)for evaluating the dosimetric parameters of IMRT. Results Four principal components were used in the PCA model. The areas under the receiver operating characteristic curve(AUCs)of grade 2 and grade 3 RILI were 0.652 and 0.611,respectively. For the LKB model, the fitted parameters were m=0.46, n=1.35, and D50=23.59 Gy for grade 2 RILI,and m=0.36,n=0.27,and D50=72.67 Gy for grade 3 RILI. The AUCs of grade 2 and grade 3 RILI in the LKB model were 0.607 and 0.585, respectively. For the MLD model, the estimated parameters were γ50=1.073 and D50=24.66 Gy for grade 2 RILI,and γ50=0.97 and D50=48.45 Gy for grade 3 RILI.The AUCs of grade 2 and grade 3 RILI in the MLD model were 0.604 and 0.569,respectively. Conclusions The use of large data set from a single patient population with the same mode of treatment is very important for improving model predictability and stability. Both the LKB model and PCA model can predict the probability of RILI,whereas the MLD model is less effective in predicting grade 3 RILI.

Feasibility of placing a dose constraint to peritoneal space instead of bowel loop in protection of the small intestine during intensity-modulated radiotherapy for rectal cancer / 中华放射肿瘤学杂志

Objective To compare the dose volume and normal tissue complication probability (NTCP) of small intestine between intensity-modulated radiotherapy (IMRT) with dose constraints to the peritoneal space (PS) and the bowel loop (BL) in the treatment of rectal cancer,and to investigate the feasibility of placing a dose constraint to the PS instead of the BL in protection of the small intestine.Methods A total of 24 patients with rectal cancer undergoing postoperative adjuvant radiotherapy were enrolled as subjects.In the 24 patients,12 were treated in supine position an.d 12 in prone position.The weekly computed tomography (CT) scans from pre-treatment to weeks 1-4 of treatment were defined as Plan,1 W,2 W,3 W,and 4 W.Contours of PS and BL were delineated on all CT images.Based on the Plan CT images,two IMRT plans,PPS and PBL,were designed with dose constraints to the PS and BL,respectively.The method was applied to 1-4 W CT images.For each CT scan,the dose volume and NTCP of the small intestine were evaluated in PPs and PBL.Results A total of 109 sets of CT images were acquired from 24 patients,and 218 plans were designed and copied.The median volume of the PS and BL was 1339.28 and 250.27 cm3,respectively.For the Plan CT scans,V15 values of the PS in PPs plan and the BL in PBL plan were 918.96 and 199.57 em3,respectively.For all CT scans,the dose volume of the small intestine in PPs,in most cases,was lower than that in PBL,while V15 values in Ps and PBL were 170.07 and 178.58 cm3 (P=0.000).The dose volume of the small intestine was correlated with V15 (P=0.000).PPs had significantly lower NTCP of chronic and acute adverse reactions than PBL(2.80％ vs.3.00％,P=0.018;57.32％ vs.58.64％,P=0.000).In patients with prone and supine treatment positions,most of the dose volume and NTCP of the small intestine in Ps were significantly lower than those in PBL(P＜0.05 for V10,V15,V30,and NTCP of acute adverse reactions).Conclusions It is feasible to place a dose constraint to the PS instead of the BL for protection of the small intestine during IMRT for rectal cancer.V15＜830 cm3 can be referred to as the objective function of dose restraint.

Difference in normal tissue complication probability of lower cranial nerves between target volumes recommended by Radiation Therapy Oncology Group and China in intensity-modulated radiotherapy for T1-2 nasopharyngeal carcinoma / 中华放射肿瘤学杂志

Objective To investigate the difference in normal tissue complication probability (NTCP) of lower cranial nerves (LCNs) between target volumes recommended by Radiation Therapy Oncology Group (RTOG) and China in intensity-modulated radiotherapy (IMRT) for T1-2 nasopharyngeal carcinoma (NPC),and to provide the evidence of dose-volume effect for the protection of LCNs in IMRT for NPC.Methods A total of 20 patients with T1-2 NPC who were treated from 2013 to 2015 were enrolled,and LCNs were delineated on CT images.Target volume delineation and treatment plan designing were performed according to the method recommended by RTOG0225 (RTOG target volume delineation method) or the Chinese Working Committee for Clinical Staging of NPC in 2010 (Chinese target volume delineation method),and the differences in the dose to LCNs and NTCP were calculated.Results In the RTOG and Chinese methods for target volume delineation,Dmax to the left and right LCNs was 7 450±273 cGy/7294±309 cGy and 7 361± 160 cGy/7 190±395 cGy,respectively (P=0.018 and 0.042),Dmean was 6735±285 cGy/6 660±333 cGy and 6 446±429 cGy/6 299±467 cGy,respectively (both P=0.000),and the NTCP was 60％±10％/57％±13％ and 51％±15％/45％±17％,respectively (both P=0.000).Conclusions It is feasible to precisely delineate target volume with the LCNs as a routine OAR and predict NTCP in IMRT for T1-2 NPC.The NTCP of the LCNs is closely associated with target volume dose and irradiated volume.The dose to the LCNs and NTCP determined by the Chinese target volume delineation method are significantly lower than those determined by the RTOG method.

Dosimetric evaluation and clinical outcome in post-operative patients of carcinoma vulva treated with intensity-modulated radiotherapy.

BACKGROUND: To compare dosimetric parameters of intensity‑modulated radiation therapy (IMRT) with 3D conformal radiotherapy (3DCRT) in post‑operative patients of vulvar cancer and to assess clinical outcome and toxicity with IMRT. MATERIALS AND METHODS: A total of 8 post‑operative patients of vulvar cancer were treated with IMRT. All patients were also planned by 3DCRT for comparison with IMRT. The two plans were compared in terms of conformity index, homogeneity index, tumor control probability (TCP) and normal tissue complication probability (NTCP) for the planning target volume and organs at risk (OAR). RESULTS: IMRT resulted in significantly lesser doses to rectum, bladder, bowel and femoral head as compared with 3DCRT plans. Mean conformity and homogeneity indices were better and within range with IMRT. The TCP was comparable between the two treatment plans and NTCP for rectum, bladder, bowel and femoral head was significantly less with IMRT as compared with 3DCRT. Treatment was well‑tolerated and none of the patients developed Grade 3 or higher toxicity. CONCLUSION: IMRT yielded superior plans with respect to target coverage, homogeneity and conformality while lowering dose to adjacent OAR as compared with 3DCRT. Thus, IMRT offers a reduction in NTCP while maintaining TCP.

Comparison of before and after CBCT image registration based on the lung cancer intensity-modulated planning / 中华放射肿瘤学杂志

Objective To study the CBCT image registration of PTV enlarging distance and IMRT planning(CT-1) for patients with lung cancer,and evaluate their characters.Methods Ten patients with lung cancer were included in the study.Two sets image,before and after radiotherapy,were acquired every week.Then delineated the targeted volume and made the planning (CT-2) according the enlarging distance data.To comparize the parameters of DVH for lung and spinal cord,volumes and dose of PTV and NTCP with CT-1 and CT-2.The difference of two plan was analyzed by covariance analysis or Wilcoxson's z-test.Results The max,min and mean dose of PTV,the lung V5,V10,V20,V30,V50 were similar in both plans (P =0.242-0.663).There was superiority in CT-2 of PTV and lung's mean dose(P =0.049,0,035).The NTCP had the decent tendency followed by the increasing of lung Vs,V10,V20(P =0.146,0.053,0.000).Conclusions CBCT based image registration can reduce PTV,the mean dose of lung,NTCP,and increase PTV dose.This provides a tool for exploring acurate radiotherapy strategies.

Parotid gland sparing effect by computed tomography-based modified lower field margin in whole brain radiotherapy

PURPOSE: Parotid gland can be considered as a risk organ in whole brain radiotherapy (WBRT). The purpose of this study is to evaluate the parotid gland sparing effect of computed tomography (CT)-based WBRT compared to 2-dimensional plan with conventional field margin. MATERIALS AND METHODS: From January 2008 to April 2011, 53 patients underwent WBRT using CT-based simulation. Bilateral two-field arrangement was used and the prescribed dose was 30 Gy in 10 fractions. We compared the parotid dose between 2 radiotherapy plans using different lower field margins: conventional field to the lower level of the atlas (CF) and modified field fitted to the brain tissue (MF). RESULTS: Averages of mean parotid dose of the 2 protocols with CF and MF were 17.4 Gy and 8.7 Gy, respectively (p or =20 Gy were observed in 15 (28.3%) for CF and in 0 (0.0%) for MF. The whole brain percentage volumes receiving >98% of prescribed dose were 99.7% for CF and 99.5% for MF. CONCLUSION: Compared to WBRT with CF, CT-based lower field margin modification is a simple and effective technique for sparing the parotid gland, while providing similar dose coverage of the whole brain.

Development of the DVH management software for the biologically-guided evaluation of radiotherapy plan

PURPOSE: To develop the dose volume histogram (DVH) management software which guides the evaluation of radiotherapy (RT) plan of a new case according to the biological consequences of the DVHs from the previously treated patients. MATERIALS AND METHODS: We determined the radiation pneumonitis (RP) as an biological response parameter in order to develop DVH management software. We retrospectively reviewed the medical records of lung cancer patients treated with curative 3-dimensional conformal radiation therapy (3D-CRT). The biological event was defined as RP of the Radiation Therapy Oncology Group (RTOG) grade III or more. RESULTS: The DVH management software consisted of three parts (pre-existing DVH database, graphical tool, and Pinnacle3 script). The pre-existing DVH data were retrieved from 128 patients. RP events were tagged to the specific DVH data through retrospective review of patients' medical records. The graphical tool was developed to present the complication histogram derived from the pre-existing database (DVH and RP) and was implemented into the radiation treatment planning (RTP) system, Pinnacle3 v8.0 (Phillips Healthcare). The software was designed for the pre-existing database to be updated easily by tagging the specific DVH data with the new incidence of RP events at the time of patients' follow-up. CONCLUSION: We developed the DVH management software as an effective tool to incorporate the phenomenological consequences derived from the pre-existing database in the evaluation of a new RT plan. It can be used not only for lung cancer patients but also for the other disease site with different toxicity parameters.

Analysis on the Calculated Dose in the Lung Radiation Surgery Planning Using TomoTherpay / 의학물리

The applicability and feasibility of TomoTherapy in the lung radiation surgery was analyzed by comparison of the calculated dose distribution in TomoTherapy planning with the results of conventional IMRS (intensity modulated radiation surgery) using LINAC (linear accelerator). The acquired CT (computed tomograph) images of total 10 patients whose tumors' motion were less than 5 mm were used in the radiation surgery planning and the same prescribed dose and the same dose constraints were used between TomoTherapy and LINAC. The results of TomoTherapy planning fulfilled the dose requirement in GTV (gross tumor volume) and OAR (organ at risk) in the same with the conventional IMRS using LINAC. TomoTherapy was superior in the view point of low dose in the normal lung tissue and conventional LINAC was superior in the dose homogeneity in GTV. The calculated time for treatment beam delivery was long more than two times in TomoTherapy compared with the conventional LINAC. Based on the results in this study, TomoTherapy can be evaluated as an effective way of lung radiation surgery for the patients whose tumor motion is little when the optimal planning is produced considering patient's condition and suitability of dose distribution.

A Dose Volume Histogram Analyzer Program for External Beam Radiotherapy / 대한방사선종양학회지

PURPOSE: To provide a simple research tool that may be used to analyze a dose volume histogram from different radiation therapy planning systems for NTCP (Normal Tissue Complication Probability), OED (Organ Equivalent Dose) and so on. MATERIALS AND METHODS: A high-level computing language was chosen to implement Niemierko's EUD, Lyman-Kutcher-Burman model's NTCP, and OED. The requirements for treatment planning analysis were defined and the procedure, using a developed GUI based program, was described with figures. The calculated data, including volume at a dose, dose at a volume, EUD, and NTCP were evaluated by a commercial radiation therapy planning system, Pinnacle (Philips, Madison, WI, USA) for comparison. RESULTS: The volume at a special dose and a dose absorbed in a volume on a dose volume histogram were successfully extracted using DVH data of several radiation planning systems. EUD, NTCP and OED were successfully calculated using DVH data and some required parameters in the literature. CONCLUSION: A simple DVH analyzer program was developed and has proven to be a useful research tool for radiation therapy.

Development of Model Plans in Three Dimensional Conformal Radiotherapy for Brain Tumors / 대한방사선종양학회지

PURPOSE: Three dimensional conformal radiotherapy planning is being used widely for the treatment of patients with brain tumor. However, it takes much time to develop an optimal treatment plan, therefore, it is difficult to apply this technique to all patients. To increase the efficiency of this technique, we need to develop standard radiotherapy plans for each site of the brain. Therefore we developed several 3 dimensional conformal radiotherapy plans (3D plans) for tumors at each site of brain, compared them with each other, and with 2 dimensional radiotherapy plans. Finally model plans for each site of the brain were decided. MATERIALS AND METHODS: Imaginary tumors, with sizes commonly observed in the clinic, were designed for each site of the brain and drawn on CT images. The planning target volumes (PTVs) were as follows; temporal tumor-5.7x8.2x7.6 cm, suprasellar tumor-3x4x4.1 cm, thalamic tumor-3.1x5.9x3.7 cm, frontoparietal tumor-5.5x7x5.5 cm, and occipitoparietal tumor-5x5.5x5 cm. Plans using parallel opposed 2 portals and/or 3 portals including fronto-vertex and 2 lateral fields were developed manually as the conventional 2D plans, and 3D noncoplanar conformal plans were developed using beam's eye view and the automatic block drawing tool. Total tumor dose was 54 Gy for a suprasellar tumor, 59.4 Gy and 72 Gy for the other tumors. All dose plans (including 2D plans) were calculated using 3D plan software. Developed plans were compared with each other using dose-volume histograms (DVH), normal tissue complication probabilities (NTCP) and variable dose statistic values (minimum, maximum and mean dose, D5, V83, V85 and V95). Finally a best radiotherapy plan for each site of brain was selected. RESULTS: 1) Temporal tumor; NTCPs and DVHs of the normal tissue of all 3D plans were superior to 2D plans and this trend was more definite when total dose was escalated to 72 Gy (NTCPs of normal brain 2D plans : 27%, 8% 3D plans : 1%, 1%). Various dose statistic values did not show any consistent trend. A 3D plan using 3 noncoplanar portals was selected as a model radiotherapy plan. 2) Suprasellar tumor; NTCPs of all 3D plans and 2D plans did not show significant difference because the total dose of this tumor was only 54 Gy. DVHs of normal brain and brainstem were significantly different for different plans. D5, V85, V95 and mean values showed some consistent trend that was compatible with DVH. All 3D plans were superior to 2D plans even when 3 portals (fronto-vertex and 2 lateral fields) were used for 2D plans. A 3D plan using 7 portals was worse than plans using fewer portals. A 3D plan using 5 noncoplanar portals was selected as a model plan. 3) Thalamic tumor; NTCPs of all 3D plans were lower than the 2D plans when the total dose was elevated to 72 Gy. DVHs of normal tissues showed similar results. V83, V85, V95 showed some consistent differences between plans but not between 3D plans. 3D plans using 5 noncoplanar portals were selected as a model plan. 4) Parietal (fronto- and occipito-) tumors; all NTCPs of the normal brain in 3D plans were lower than in 2D plans. DVH also showed the same results. V83, V85, V95 showed consistent trends with NTCP and DVH. 3D plans using 5 portals for frontoparietal tumor and 6 portals for occipitoparietal tumor were selected as model plans. CONCLUSION: NTCP and DVH showed reasonable differences between plans and were thought to be useful for comparing plans. All 3D plans were superior to 2D plans. Best 3D plans were selected for tumors in each site of brain using NTCP, DVH and finally by the planner's decision.

Dose Planning of Forward Intensity Modulated Radiation Therapy for Nasopharyngeal Cancer using Compensating Filters / 대한방사선종양학회지

PURPOSE: To improve the local control of patients with nasopharyngeal cancer, we have implemented 3-D conformal radiotherapy and forward intensity modulated radiation therapy (IMRT) to used of compensating filters. Three dimension conformal radiotherapy with intensity modulation is a new modality for cancer treatments. We designed 3-D treatment planning with 3-D RTP (radiation treatment planning system) and evaluation dose distribution with tumor control probability (TCP) and normal tissue complication probability (NTCP). MATERIALS AND METHODS: We have developed a treatment plan consisting four intensity modulated photon fields that are delivered through the compensating filters and block transmission for critical organs. We get a full size CT imaging including head and neck as 3 mm slices, and delineating PTV (planning target volume) and surrounding critical organs, and reconstructed 3D imaging on the computer windows. In the planning stage, the planner specifies the number of beams and their directions including non-coplanar, and the prescribed doses for the target volume and the permissible dose of normal organs and the overlap regions. We designed compensating filter according to tissue deficit and PTV volume shape also dose weighting for each field to obtain adequate dose distribution, and shielding blocks weighting for transmission. Therapeutic gains were evaluated by numerical equation of tumor control probability and normal tissue complication probability. The TCP and NTCP by DVH (dose volume histogram) were compared with the 3-D conformal radiotherapy and forward intensity modulated conformal radiotherapy by compensator and blocks weighting. Optimization for the weight distribution was performed iteration with initial guess weight or the even weight distribution. The TCP and NTCP by DVH were compared with the 3-D conformal radiotherapy and intensitiy modulated conformal radiotherapy by compensator and blocks weighting. RESULTS: Using a four field IMRT plan, we have customized dose distribution to conform and deliver sufficient dose to the PTV. In addition, in the overlap regions between the PTV and the normal organs (spinal cord, salivary grand, pituitary, optic nerves), the dose is kept within the tolerance of the respective organs. We evaluated to obtain sufficient TCP value and acceptable NTCP using compensating filters. Quality assurance checks show acceptable agreement between the planned and the implemented MLC (multi-leaf collimator). CONCLUSION: IMRT provides a powerful and efficient solution for complex planning problems where the surrounding normal tissues place severe constraints on the prescription dose. The intensity modulated fields can be efficaciously and accurately delivered using compensating filters.

The Use of Normal Tissue Complication Probability to Predict Radiation Hepatitis / 대한방사선종양학회지

PURPOSE: Although It has been known that the tolerance of the liver to external beam irradiation depends on the irradiated volume and dose, few data exist which quantify this dependence. However, recently, with the development of three dimensional (3-D) treatment planning, have the tools to quantify the relationships between dose, volume, and normal tissue complications become available. The objective of this study is to investigate the relationships between normal tissue complication probability (NTCP) and the risk of radiation hepatitis for patients who received variant dose partial liver irradiation. MATERIALS AND METHOD: From March 1992 to December 1994, 10 patients with hepatoma and 10 patients with bile duct cancer were included in this study. Eighteen patients had normal hepatic function, but 2 patients (prothrombin time 73%, 68%) had mild liver cirrhosis before irradiation. Radiation therapy was delivered with 10MV linear accelerator, 180~200 cGy fraction per day. The total dose ranged from 3,960 cGy to 6,000 cGy (median dose 5,040 cGy). The normal tissue complication probability was calculated by using Lyman's model. Radiation hepatitis was defined as the development of anicteric elevation of alkaline phosphatase of at least two fold and non-malignant ascites in the absence of documented progressive. RESULTS: The calculated NTCP ranged from 0.001 to 0.840 (median 0.05). Three of the 20 patients developed radiation hepatitis. The NTCP of the patients with radiation hepatitis were 0.390, 0.528, 0.844 (median : 0.58+/-0.23), but that of the patients without radiation hepatitis ranged from 0.001 to 0.308 (median : 0.09+/-0.09). When the NTCP was calculated by using the volume factor of 0.32, a radiation hepatitis was observed only in patients with the NTCP value more than 0.39. By contrast, clinical results of evolving radiation hepatitis were not well correlated with NTCP value calculated when the volume factor of 0.69 was applied. On the basis of these observations, the volume factor of 0.32 was more correlated to predict a radiation hepatitis. CONCLUSION: The risk of radiation hepatitis was increased above the cut-off value. Therefore the NTCP seems to be used for predicting the radiation hepatitis.