Tangent-based volumetric modulated arc therapy for advanced left breast cancer

Improving organ dose sparing in left-sided breast cancer with yaw-limited volumetric modulated arc therapy: A dosimetric comparison to conventional and intensity modulated radiation therapy approaches

BACKGROUND

To assess the dose-sparing capabilities of a yaw-limited volumetric modulated arc therapy (YL_VMAT) beam setup for adjacent organs at risk (OAR) in comparison with 3D-conventional radiation therapy (3D-CRT), intensity-modulated radiation therapy (IMRT) and conventional VMAT for radiation therapy in left-sided breast cancer patients.

METHODS

In total, 80 treatment plans for 20 patients, of which 10 patients underwent CT-scans in deep inspiration breath-hold (DIBH) and 10 patients in free-breathing (FB) technique. Besides generally tangential-weighted static and IMRT beams, VMAT treatment plans with approximately 270° arc length have been compared and analyzed to a multi-field, yaw-adapted, unconventional partial VMAT technique retrospectively. The prescription dose was set to 40.05 Gy in 15 fractions.

RESULTS

We achieved a more pronounced steeper dose falloff directed from the thoracic wall to the adjacent lung tissue resulting in a significantly better ipsilateral lung and considerably cardiac dose sparing using the YL_VMAT method in general. Compared with standard techniques (IMRT, VMAT, 3D-CRT), YL-VMAT in combination with DIBH can achieve lower mean doses for the heart (1.05 Gy vs. 1.73 Gy, 2.16 Gy and 1.44 Gy), the left anterior descending (LAD) artery (3.68 Gy vs. 6.53 Gy, 5.13 Gy and 8.64 Gy) and the left lung (3.59 Gy vs. 5.39 Gy, 4.79 Gy and 5.87 Gy), respectively. Also with FB, the corresponding mean doses for the left lung and cardiac structures were lower with the YL-VMAT method than with IMRT (heart: 1.70 Gy vs. 2.44 Gy; LAD: 6.50 Gy vs. 11.97 Gy; left lung: 3.10 Gy vs. 4.72 Gy), VMAT (heart: 1.70 Gy vs. 2.52 Gy; LAD: 6.50 Gy vs. 9.06 Gy; left lung: 3.10 Gy vs. 4.46 Gy) and 3D-CRT (heart: 1.70 Gy vs. 2.78 Gy; LAD: 6.50 Gy vs. 15.09 Gy; left lung: 3.10 Gy vs. 5.77 Gy). In addition, we found out superiority of YL_VMAT for the V5, V10, and V20 Gy to the left lung. For DIBH and FB, all differences for the left lung were significant, with p < 0.05.

CONCLUSIONS

With the YL_VMAT technique, dose exposures to radiosensitive OARs like the lung, heart and LAD artery can be reduced considerably to very low values in comparison to already established planning methods. The benefits must be weighed against the potential risks induced by an increased dose exposure to the contralateral breast.

Improvement of treatment plan quality with modified fixed field volumetric modulated arc therapy in cervical cancer

PURPOSE

This study aims to introduce modified fixed field volumetric modulated arc therapy (MF-VMAT) which manually opened the field size by fixing the jaws and comparing it to the typical planning technique, auto field volumetric modulated arc therapy (AF-VMAT) in cervical cancer treatment planning.

METHODS AND MATERIALS

Previously treated twenty-eight cervical cancer plans were retrospectively randomly selected and replanned in this study using two different planning techniques: AF-VMAT and MF-VMAT, resulting in a total of fifty-six treatment plans. In this study, we compared both planning techniques in three parts: (1) Organ at Risk (OARs) and whole-body dose, (2) Treatment plan efficiency, and (3) Treatment plan accuracy.

RESULTS

For OARs dose, bowel bag (p-value = 0.001), rectum (p-value = 0.002), and left femoral head (p-value = 0.001) and whole-body (p-value = 0.000) received a statistically significant dose reduction when using the MF-VMAT plan. Regarding plan efficiency, MF-VMAT exhibited a statistically significant increase in both number of monitor units (MUs) and control points (p-values = 0.000), while beam-on time, maximum leaf travel, average maximum leaf travel, and maximum leaf travel per gantry rotation were statistically significant decreased (p-values = 0.000). In terms of plan accuracy, the average gamma passing rate was higher in the MF-VMAT plan for both absolute dose (AD) (p-value = 0.001, 0.004) and relative dose (RD) (p-value = 0.000, 0.000) for 3%/3 and 3%/2 mm gamma criteria, respectively.

CONCLUSION

The MF-VMAT planning technique significantly reduces OAR doses and decreases the spread of low doses to normal tissues in cervical cancer patients. Additionally, this planning approach demonstrates efficient plans with lower beam-on time and reduced maximum leaf travel. Furthermore, it indicates higher plan accuracy through an increase in the average gamma passing rate compared to the AF-VMAT plan. Consequently, MF-VMAT offers an effective treatment planning technique for cervical cancer patients.

Minimizing normal tissue low dose bath for left breast Volumetric Modulated Arc Therapy (VMAT) using jaw offset

PURPOSE

With proper beam setup and optimization constraints in the treatment planning system, volumetric modulated arc therapy (VMAT) can improve target dose coverage and conformity while reducing doses to adjacent structures for whole breast radiation therapy. However, the low-dose bath effect on critical structures, especially the heart and the ipsilateral lung, remains a concern. In this study, we present a VMAT technique with the jaw offset VMAT (JO-VMAT) to reduce the leakage and scatter doses to critical structures for whole breast radiation therapy.

MATERIALS AND METHODS

The data of 10 left breast cancer patients were retrospectively used for this study. CT images were acquired on a CT scanner (GE, Discovery) with the deep-inspiration breath hold (DIBH) technique. The planning target volumes (PTVs) and the normal structures (the lungs, the heart, and the contralateral breast) were contoured on the DIBH scan. A 3D field-in-field plan (3D-FiF), a tangential VMAT (tVMAT) plan, and a JO-VMAT plan were created with the Eclipse treatment planning system. An arc treatment field with the x-jaw closed across the central axis creates a donut-shaped high-dose distribution and a cylinder-shaped low-dose volume along the central axis of gantry rotation. Applying this setup with proper multi-leaf collimator (MLC) modulation, the optimized plan potentially can provide sufficient target coverage and reduce unnecessary irradiation to critical structures. The JO-VMAT plans involve 5-6 tangential arcs (3 clockwise arcs and 2-3 counterclockwise arcs) with jaw offsets. The plans were optimized with objective functions specified to achieve PTV dose coverage and homogeneity; For organs at risk (OARs), objective functions were specified individually for each patient to accomplish the best achievable treatment plan. For tVMAT plans, optimization constraints were kept the same except that the jaw offset was removed from the initial beam setup. The dose volume histogram (DVH) parameters were generated for dosimetric evaluation of PTV and OARs.

RESULTS

The D95% to the PTV was greater than the prescription dose of 42.56 Gy for all the plans. With both VMAT techniques, the PTV conformity index (CI) was statistically improved from 0.62 (3D-FiF) to 0.83 for tVMAT and 0.84 for JO-VMAT plans. The difference in the homogeneity index (HI) was not significant. The Dmax to the heart was reduced from 12.15 Gy for 3D-FiF to 8.26 Gy for tVMAT and 7.20 Gy for JO-VMAT plans. However, a low-dose bath effect was observed with tVMAT plans to all the critical structures including the lungs, the heart, and the contralateral breast. With JO-VMAT, the V5Gy and V2Gy of the heart were reduced by 32.7% and 15.4% compared to 3D-FiF plans. Significantly, the ipsilateral lung showed a reduction in mean dose (4.65-3.44 Gy) and low dose parameters (23.4% reduction for V5Gy and 10.7% reduction for V2Gy) for JO-VMAT plans compared to the 3D-FiF plans. The V2Gy dose to the contralateral lung and breast was minimal with JO-VMAT techniques.

CONCLUSION

A JO-VMAT technique was evaluated in this study and compared with 3D-FiF and tVMAT techniques. Our results showed that the JO-VMAT technique can achieve clinically comparable coverage and homogeneity and significantly improve dose conformity within PTV. Additionally, JO-VMAT eliminated the low-dose bath effect at all OARs evaluation metrics including the ipsilateral/contralateral lung, the heart, and the contralateral breast compared to 3D-FiF and tVMAT. This technique is feasible for the whole breast radiation therapy of left breast cancers.

Hybrid planning techniques for early-stage left-sided breast cancer: dose distribution analysis and estimation of projected secondary cancer-relative risk

PURPOSE

The purpose of this study was to evaluate three techniques of irradiation of left-sided breast cancer patients, three-dimensional conformal radiotherapy (3D-CRT), hybrid Intensity-Modulated Radiotherapy (h-IMRT), and hybrid Volumetric-Modulated Arc Therapy (h-VMAT, h-ARC), in terms of dose distribution in the planning target volume (PTV) and organs at risk (OARs). The second aim was to estimate the projected relative risk of radiation-induced secondary cancers for hybrid techniques.

MATERIALS AND METHODS

Three treatment plans were prepared in 3D-CRT, h-IMRT, and h-VMAT techniques for each of the 40 patients, who underwent CT simulation in deep inspiration breath-hold (DIBH). For hybrid techniques, plans were created by combining 3D-CRT and dynamic fields with an 80%/20% dose ratio for 3D-CRT and IMRT or VMAT. Cumulative dose-volume histograms were used to compare dose distributions within the PTV and OARs (heart, left anterior descending coronary artery [LAD], left and right lung [LL, RL], right breast [RB]). Projected risk ratios for secondary cancers were estimated relative to 3D-CRT using the organ equivalent dose (OED) concept for the Schneider's linear exponential, plateau, and full mechanistic dose-response model.

RESULTS

All plans fulfilled the PTV criterium: V95%≥95%. Compared to 3D-CRT, both hybrid techniques showed significantly better target coverage (PTV: V95%>98%, p < 0.001), and the best conformality was achieved by h-ARC plans (CI: 1.18 ± 0.09, p < 0.001). Compared to 3D-CRT and h-ARC, h-IMRT increased the average sum of monitor units (MU) over 129.9% (p < 0.001). H-ARC increased the mean dose of contralateral organs and the LL V5Gy parameter (p < 0.001). Both hybrid techniques significantly reduced the Dmax of the heart by 5 Gy. Compared to h-IMRT, h-ARC increased secondary cancer projected relative risk ratios for LL, RL, and RB by 18, 152, and 81%, respectively.

CONCLUSIONS

The results confirmed that both hybrid techniques provide better target quality and OARs sparing than 3D-CRT. Hybrid VMAT delivers less MU compared to hybrid IMRT but may increase the risk of radiation-induced secondary malignancies.

Robustness of VMAT to setup errors in postmastectomy radiotherapy of left-sided breast cancer: Impact of bolus thickness

BACKGROUND

Volumetric modulated arc therapy (VMAT) with varied bolus thicknesses has been employed in postmastectomy radiotherapy (PMRT) of breast cancer to improve superficial target coverage. However, impact of bolus thickness on plan robustness remains unclear.

METHODS

The study enrolled ten patients with left-sided breast cancer who received radiotherapy using VMAT with 5 mm and 10 mm bolus (VMAT-5B and VMAT-10B). Inter-fractional setup errors were simulated by introducing a 3 mm shift to isocenter of the original plans in the anterior-posterior, left-right, and inferior-superior directions. The plans (perturbed plans) were recalculated without changing other parameters. Dose volume histograms (DVH) were collected for plan evaluation. Absolute dose differences in DVH endpoints for the clinical target volume (CTV), heart, and left lung between the perturbed plans and the original ones were used for robustness analysis.

RESULTS

VMAT-10B showed better target coverage, while VMAT-5B was superior in organs-at-risk (OARs) sparing. As expected, small setup errors of 3 mm could induce dose fluctuations in CTV and OARs. The differences in CTV were small in VMAT-5B, with a maximum difference of -1.05 Gy for the posterior shifts. For VMAT-10B, isocenter shifts in the posterior and right directions significantly decreased CTV coverage. The differences were -1.69 Gy, -1.48 Gy and -1.99 Gy, -1.69 Gy for ΔD95% and ΔD98%, respectively. Regarding the OARs, only isocenter shifts in the posterior, right, and inferior directions increased dose to the left lung and the heart. Differences in VMAT-10B were milder than those in VMAT-5B. Specifically, mean heart dose were increased by 0.42 Gy (range 0.10 ~ 0.95 Gy) and 0.20 Gy (range -0.11 ~ 0.72 Gy), and mean dose for the left lung were increased by 1.02 Gy (range 0.79 ~ 1.18 Gy) and 0.68 Gy (range 0.47 ~ 0.84 Gy) in VMAT-5B and VMAT-10B, respectively. High-dose volumes in the organs were increased by approximate 0 ~ 2 and 1 ~ 3 percentage points, respectively. Nevertheless, most of the dosimetric parameters in the perturbed plans were still clinically acceptable.

CONCLUSIONS

VMAT-5B appears to be more robust to 3 mm setup errors than VMAT-10B. VMAT-5B also resulted in better OARs sparing with acceptable target coverage and dose homogeneity. Therefore 5 mm bolus is recommended for PMRT of left-sided breast cancer using VMAT.

Three-dimensional conformal radiotherapy (3D-CRT) vs. volumetric modulated arc therapy (VMAT) in deep inspiration breath-hold (DIBH) technique in left-sided breast cancer patients-comparative analysis of dose distribution and estimation of projected secondary cancer risk

PURPOSE

The purpose of this study was to compare two techniques of irradiation of left-sided breast cancer patients who underwent breast-conserving surgery, three-dimensional conformal radiotherapy technique (3D-CRT) and volumetric modulated arc therapy (VMAT), in terms of dose distribution in the planning target volume (PTV) and organs at risk (OARs). The second aim of the study was estimation of the projected risk of radiation-induced secondary cancer for both radiotherapy techniques.

MATERIALS AND METHODS

For 25 patients who underwent CT simulation in deep inspiration breath-hold (DIBH), three treatment plans were generated: one using a three-dimensional conformal radiotherapy technique and two using volumetric modulated arc therapy. First VMAT-DIBH geometry consisted of three partial arcs (ARC-DIBH 3A) and second consisted of four partial arcs (ARC-DIBH 4A). Cumulative dose-volume histograms (DVHs) were used to compare dose distributions within the PTV and OARs (heart, left anterior descending coronary artery [LAD], ipsilateral and contralateral lung [IL, CL], and contralateral breast [CB]). Normal tissue complication probabilities (NTCPs) and organ equivalent doses (OEDs) were calculated using the differential DVHs. Excess absolute risks (EARs) for second cancers were estimated using Schneider's full mechanistic dose-response model.

RESULTS

All plans fulfilled the criterium for PTV V95% ≥ 95%. The PTV coverage, homogeneity, and conformity indices were significantly better for VMAT-DIBH. VMAT showed a significantly increased mean dose and V5Gy for all OARs, but reduced LAD D_max by 15 Gy. For IL, CL, and CB, the 3D-CRT DIBH method achieved the lowest values of EAR: 28.38 per 10,000 PYs, 2.55 per 10,000 PYs, and 4.48 per 10,000 PYs (p < 0.001), compared to 40.29 per 10,000 PYs, 15.62 per 10,000 PYs, and 23.44 per 10,000 PYs for ARC-DIBH 3A plans and 41.12 per 10,000 PYs, 15.59 per 10,000 PYs, and 22.73 per 10,000 PYs for ARC-DIBH 4A plans. Both techniques provided negligibly low NTCPs for all OARs.

CONCLUSION

The study shows that VMAT-DIBH provides better OAR sparing against high doses. However, the large low-dose-bath (≤ 5 Gy) is still a concern due to the fact that a larger volume of normal tissues exposed to lower doses may increase a radiation-induced risk of secondary cancer.

Comprehensive nodal breast VMAT: solving the low-dose wash dilemma using an iterative knowledge-based radiotherapy planning solution

INTRODUCTION

Aimed to develop a simple and robust volumetric modulated arc radiotherapy (VMAT) solution for comprehensive lymph node (CLN) breast cancer without increase in low-dose wash.

METHODS

Forty CLN-breast patient data sets were utilised to develop a knowledge-based planning (KBP) VMAT model, which limits low-dose wash using iterative learning and base-tangential methods as benchmark. Another twenty data sets were employed to validate the model comparing KBP-generated ipsilateral VMAT (ipsi-VMAT) plans against the benchmarked hybrid (h)-VMAT (departmental standard) and bowtie-VMAT (published best practice) methods. Planning target volume (PTV), conformity/homogeneity index (CI/HI), organ-at-risk (OAR), remaining-volume-at-risk (RVR) and blinded radiation oncologist (RO) plan preference were evaluated.

RESULTS

Ipsi- and bowtie-VMAT plans were dosimetrically equivalent, achieving greater nodal target coverage (P < 0.05) compared to h-VMAT with minor reduction in breast coverage. CI was enhanced for a small reduction in breast HI with improved dose sparing to ipsilateral-lung and humeral head (P < 0.05) at immaterial expense to spinal cord. Significantly, low-dose wash to OARs and RVR were comparable between all plan types demonstrating a simple VMAT class solution robust to patient-specific anatomic variation can be applied to CLN breast without need for complex beam modification (hybrid plans, avoidance sectors or other). This result was supported by blinded RO review.

CONCLUSIONS

A simple and robust ipsilateral VMAT class solution for CLN breast generated using iterative KBP modelling can achieve clinically acceptable target coverage and OAR sparing without unwanted increase in low-dose wash associated with increased second malignancy risk.

Tangential Volumetric Modulated Arc Therapy for Locally Advanced Breast Cancer

Cardiovascular toxicity from breast radiotherapy is a concern to patients and providers. Here we present a cardiac-sparing strategy utilizing tangential VMAT (tVMAT) in comparison to standard 3DCRT. Ten patients with left-sided breast cancer previously treated with adjuvant RT covering breast, axillary, and supraclavicular nodal regions were selected for the study. For each patient two plans were created: 1) a dual-isocenter three-field 3DCRT plan and 2) a monoisocentric tVMAT plan. The prescription for both techniques was 50 Gy in 25 fractions to the breast and nodal target volumes. Compared to 3DCRT, tVMAT provided more uniform coverage to breast and regional lymph nodes (mean conformity index was 1.42 for tVMAT versus 2.42 for 3DCRT, p<0.01) and the max point dose for tVMAT was lower on average (112.8% for tVMAT versus 121.5% for 3DCRT, p<0.001). Coverage to lymph nodes was superior for tVMAT (average minimum-coverage to 95% of entire nodal target volumes was 99.5% of the prescribed dose for tVMAT versus 94.9% for 3DCRT, p <0.001). OAR sparing was improved with tVMAT, with a lower average V20_Gy for the left lung (15.0% for tVMAT versus 24.6% for 3DCRT, p<0.01), and lower mean heart dose (156 cGy for tVMAT versus 200 cGy for 3DCRT, p<0.01). In conclusion, tangential VMAT is a promising technique for the treatment of intact breast and regional lymphatics and may improve target coverage and OAR avoidance compared to 3D conformal techniques.

Non-coplanar volumetric modulated arc therapy for locoregional radiotherapy of left-sided breast cancer including internal mammary nodes

Background

Non-coplanar volumetric modulated arc therapy (ncVMAT) is proposed to reduce toxicity in heart and lungs for locoregional radiotherapy of left-sided breast cancer, including internal mammary nodes (IMN).

Patients and methods

This retrospective study included 10 patients with left-sided breast cancer who underwent locoregional radiotherapy after breast-conserving surgery. For each patient, the ncVMAT plan was designed with four partial arcs comprising two coplanar arcs and two non-coplanar arcs, with a couch rotating to 90°. The prescribed dose was normalized to cover 95% of planning target volume (PTV), with 50 Gy delivered in 25 fractions. For each ncVMAT plan, dosimetric parameters were compared with the coplanar volumetric modulated arc therapy (coV-MAT) plan.

Results

T here were improvements in conformity index, homogeneity index and V₅₅ of total target volume (PTVall) comparing ncVMAT to coVMAT (p < 0.001). Among the organs at risk, the average V₃₀, V₂₀, V₁₀, V₅, and mean dose (D_mean) of the heart decreased significantly (p < 0.001). Furthermore, ncVMAT significantly reduced the mean V₂₀, V₁₀, V₅, and D_mean of left lung and the mean V₁₀ and V₅ and D_mean of contralateral lung (p < 0.001). An improved sparing of the left anterior descending coronary artery and right breast were also observed with ncVMAT (p < 0.001).

Conclusions

Compared to coVMAT, ncVMAT provides improved conformity and homogeneity of whole P TV, better dose sparing of the heart, bilateral lungs, left anterior descending coronary artery (LAD), and right breast for locoregional radiotherapy of left-sided breast cancer with IMN, potentially reducing the risk of normal tissue damage.

Half-beam volumetric-modulated arc therapy in adjuvant radiotherapy for gynecological cancers

PURPOSE

The purpose of this study is to introduce half-beam volumetric-modulated arc therapy (HVMAT), an innovative treatment planning technique from our work, for reducing dose to the organs at risk (OAR) during adjuvant radiotherapy for gynecological cancers.

METHODS AND MATERIALS

Seventy-two treatment plans of 36 patients with gynecological cancers receiving adjuvant radiotherapy were assessed. Among them, 36 plans were designed using HVMAT and paired with the other 36 traditional volumetric-modulated arc therapy (VMAT) plans for each patient. The main uniqueness of the HVMAT designs was that it consisted of two opposite-shielded half-beam fields rotated inversely in two coplanar arcs, collocating with the specially-devised avoidance structures to enhance the control of the OAR doses. The dose distributions in HVMAT and VMAT were evaluated and compared using the random effects model.

RESULTS

The ratios of OAR doses in HVMAT compared with VMAT showed a comprehensive OAR dose reduction when using HVMAT (V_20Gy : bladder, 0.92; rectum, 0.95; V_30Gy : bowel, 0.91; femoral heads, 0.66), except for the ilium (V_30Gy : 1.12). The overall mean difference for each OAR across V_40Gy , V_30Gy , V_20Gy , and bowel V_15Gy was statistically significant (almost all p < 0.001). In addition, HVMAT promoted a better conformity index, homogeneity index, D_2% , and V_107% of the planning target volume (all p < 0.001).

CONCLUSIONS

HVMAT is capable of generating deep double-concave dose distributions with the advantage of reducing dose to several OARs simultaneously. It is highly recommended for pelvic irradiation, especially for treating gynecological cancers in adjuvant radiotherapy.

Auxiliary Structures-Assisted Radiotherapy Improvement for Advanced Left Breast Cancer

Background

To improve the quality of plan for the radiation treatment of advanced left breast cancer by introducing the auxiliary structures (ASs) which are used to spare the regions with no intact delineated structures adjacent to the target volume.

Methods

CT data from 20 patients with left-sided advanced breast cancer were selected. An AS designated as A1 was created to spare the regions of the aorta, pulmonary artery, superior vena ava, and contralateral tissue of the upper chest and neck, and another, designated as A2, was created in the regions of the cardia and fundus of the stomach, left liver lobe, and splenic flexure of the colon. IMRT and VMAT plans were created for cases with and without the use of the AS dose constraints in plan optimization. Dosimetric parameters of the target and organs at risk (OARs) were compared between the separated groups.

Results

With the use of AS dose constraints, both the IMRT and VMAT plans were clinically acceptable and deliverable, even showing a slight improvement in dose distribution of both the target and OARs compared with the AS-unused plans. The ASs significantly realized the dose sparing for the regions and brought a better conformity index (p < 0.05) and homogeneity index (p < 0.05) in VMAT plans. In addition, the volume receiving at least 20 Gy (V₂₀) for the heart (p < 0.05), V₄₀ for the left lung (p < 0.05), and V₄₀ for the axillary-lateral thoracic vessel juncture region (p < 0.05) were all lower in VMAT plans.

Conclusion

The use of the defined AS dose constraints in plan optimization was effective in sparing the indicated regions, improving the target dose distribution, and sparing OARs for advanced left breast cancer radiotherapy, especially those that utilize VMAT plans.

Feasibility study: spot-scanning proton arc therapy (SPArc) for left-sided whole breast radiotherapy

BACKGROUND

This study investigated the feasibility and potential clinical benefit of utilizing a new proton treatment technique: Spot-scanning proton arc (SPArc) therapy for left-sided whole breast radiotherapy (WBRT) to further reduce radiation dose to healthy tissue and mitigate the probability of normal tissue complications compared to conventional intensity modulated proton therapy (IMPT).

METHODS

Eight patients diagnosed with left-sided breast cancer and treated with breast-preserving surgery followed by whole breast irradiation without regional nodal irradiation were included in this retrospective planning. Two proton treatment plans were generated for each patient: vertical intensity-modulated proton therapy used for clinical treatment (vIMPT, gantry angle 10°-30°) and SPArc for comparison purpose. Both SPArc and vIMPT plans were optimized using the robust optimization of ± 3.5% range and 5 mm setup uncertainties. Root-mean-square deviation dose (RMSD) volume histograms were used for plan robustness evaluation. All dosimetric results were evaluated based on dose-volume histograms (DVH), and the interplay effect was evaluated based on the accumulation of single-fraction 4D dynamic dose on CT50. The treatment beam delivery time was simulated based on a gantry rotation with energy-layer-switching-time (ELST) from 0.2 to 5 s.

RESULTS

The average D1 to the heart and LAD were reduced to 53.63 cGy and 82.25 cGy compared with vIMPT 110.38 cGy (p = 0.001) and 170.38 cGy (p = 0.001), respectively. The average V5Gy and V20Gy of ipsilateral lung was reduced to 16.77% and 3.07% compared to vIMPT 25.56% (p = 0.001) and 4.68% (p = 0.003). Skin3mm mean and maximum dose were reduced to 3999.38 cGy and 4395.63 cGy compared to vIMPT 4104.25 cGy (p = 0.039) and 4411.63 cGy (p = 0.043), respectively. A significant relative risk reduction (RNTCP = NTCP_SPArc/NTCP_vIMPT) for organs at risk (OARs) was obtained with SPArc ranging from 0.61 to 0.86 depending on the clinical endpoint. The RMSD volume histogram (RVH) analysis shows SPArc provided better plan robustness in OARs sparing, including the heart, LAD, ipsilateral lung, and skin. The average estimated treatment beam delivery times were comparable to vIMPT plans when the ELST is about 0.5 s.

CONCLUSION

SPArc technique can further reduce dose delivered to OARs and the probability of normal tissue complications in patients treated for left-sided WBRT.

In search of a one plan solution for VMAT post-mastectomy chest wall irradiation

PURPOSE

This study was designed to evaluate skin dose in both VMAT and tangent treatment deliveries for the purpose of identifying suitable bolus use protocols that should produce similar superficial doses.

METHODS

Phantom measurements were used to investigate skin dose in chest wall radiotherapy with and without bolus for 3D and rotational treatment techniques. Optically stimulated luminescence dosimeters (OSLDs) with and without housing and EBT3 film were used. Superflab (3, 5, and 10 mm) and brass mesh were considered. Measured doses were compared with predictions by the Eclipse treatment planning system. Patient measurements were also performed and the bolusing effect of hospital gowns and blankets were highlighted. The effect of flash for VMAT plans was considered experimentally by using 2 mm couch shifts.

RESULTS

For tangents, average skin doses without bolus were 0.64 (EBT3), 0.62 (bare OSLD), 0.77 (jacketed OSLD), and 0.68 (Eclipse) as a fraction of prescription. For VMAT, doses without bolus were 0.53 (EBT3), 0.53 (bare OSLD), 0.64 (jacketed OSLD), and 0.60 (Eclipse). For tangents, the average doses with different boluses as measured by EBT3 were 0.99 (brass mesh), 1.02 (3 mm), 1.03 (5 mm), and 1.07 (10 mm). For VMAT with bolus, average doses as measured by EBT3 were 0.83 (brass), 0.96 (3 mm), 1.03 (5 mm), and 1.04 (10 mm). Eclipse doses agreed with measurements to within 5% of measurements for all Superflab thicknesses and within 15% of measurements for no bolus. The presence of a hospital gown and blanket had a bolusing effect that increased the surface dose by approximately 10%.

CONCLUSIONS

Results of this work allow for consideration of different bolus thicknesses, materials, and usage schedules based on desired skin dose and choice of either tangents or an arc beam techniques.

Using Robust Optimization for Skin Flashing in Intensity Modulated Radiation Therapy for Breast Cancer Treatment: A Feasibility Study

PURPOSE

To study the feasibility and the effectiveness of a novel implementation of robust optimization on 2 sets of computed tomography (CT) data simultaneously for skin flashing in intensity modulated radiation therapy for breast cancer.

METHOD AND MATERIALS

Five patients who received treatment to the breast and regional lymphatics were selected for this study. For each patient, 3 plans were generated using 3 different skin-flashing methods, including (1) a manual flash plan with optimization on the nominal planning target volume (PTV) not extending beyond the skin that required manually postplanning the opening of the multi-leaf collimator and jaw to obtain flash; (2) an expanded PTV plan with optimization on an expanded PTV that included the target in the air beyond the skin; and (3) a robust-optimized (RO) plan using robust optimization that simultaneously optimizes on the nominal CT data set and a simulated geometry error CT data set. The feasibility and the effectiveness of the robust optimization approach was investigated by comparing it with the 2 other methods. The robustness of the plan against target position variations was studied by simulating 0-, 5-, 10-, and 15-mm geometry errors.

RESULTS

The RO plans were the only ones able to meet acceptable criteria for all patients in both the nominal and simulated geometry error scenarios. The expanded PTV plans developed major deviation on the maximum dose to the PTV for 1 patient. For the manual flash plans, every patient developed major deviation either on 95% of the dose to the PTV or the maximum dose to the PTV in the simulated geometry error scenarios. The RO plan demonstrated the best robustness against the target position variation among the 3 methods of skin flashing. The doses to the lung and heart were comparable for all 3 planning techniques.

CONCLUSION

Using robust optimization for skin flash in breast intensity modulated radiation therapy planning is feasible. Further investigation is warranted to confirm the clinical effectiveness of this novel approach.

Left breast irradiation with tangential intensity modulated radiotherapy (t-IMRT) versus tangential volumetric modulated arc therapy (t-VMAT): trade-offs between secondary cancer induction risk and optimal target coverage

Background

Adjuvant radiotherapy is the standard treatment after breast-conserving surgery. According to meta-analyses, adjuvant 3d-conventional irradiation reduces the risk of local recurrence and thereby improves long-term survival by 5–10%. However, there is an unintended exposure of organs such as the heart, lungs and contralateral breast. Irradiation of the left breast has been related to long-term effects like increased rates of coronary events as well as second cancer induction. Modern radiotherapy techniques such as tangential intensity modulated radiotherapy (t-IMRT) and tangential volumetric modulated arc therapy (t-VMAT) and particularly deep inspiration breath hold (DIBH) technique have been developed in order to improve coverage of target volume and to reduce dose to normal tissue. The aim of this study was to compare t-IMRT-plans with t-VMAT-plans in DIBH position for left-sided breast irradiation in terms of normal tissue exposure, i.e. of lungs, heart, left anterior descending coronary artery (LADCA), as well as homogeneity (HI) and conformity index (CI) and excess absolute risk (EAR) for second cancer induction for organs at risk (OAR) after irradiation.

Methods

Twenty patients, diagnosed with left-sided breast cancer and treated with breast-preserving surgery, were included in this planning study. For each patient DIBH-t-IMRT plan using 5 to 7 beams and t-VMAT plan using four rotations were generated to achieve 95% dose coverage to 95% of the volume. Data were evaluated on the basis of dose-volume histograms: Cardiac dose and LADCA (mean and maximum dose, D25% and D45%), dose to ipsilateral and contralateral lung (mean, D20%, D30%), dose to contralateral breast (mean dose), total monitor units, V5% of total body and normal tissue integral dose (NTID). In addition, homogeneity index and conformity index, as well as the excess absolute risk (EAR) to estimate the risk of second malignancy were calculated.

Results

T-IMRT showed a significant reduction in mean cardiac dose of 26% (p = 0.002) compared to t-VMAT, as well as a significant reduction in the mean dose to LADCA of 20% (p = 0.03). Following t-IMRT, mean dose to the left lung was increased by 5% (p = 0.006), whereas no significant difference was found in the mean dose to the right lung and contralateral breast between the two procedures. Monitor units were 31% (p = 0.000004) lower for t-IMRT than for t-VMAT. T-IMRT technique significantly reduced normal tissue integral dose (NTID) by 19% (p = 0.000005) and the V5% of total body by 24% (p = 0.0007). In contrast, t-VMAT improved CI and HI by 2% (p = 0.001) and 0.4% (p = 0.00001), respectively. EAR with t-IMRT was significantly lower, especially for contralateral lung and contralateral breast (2–5/10,000 person years) but not for ipsilateral lung.

Conclusion

Compared to t-VMAT, t-IMRT in left-sided breast irradiation significantly reduced dose to organs at risk as well as normal tissue integral dose, and V5% total body. EAR with t-IMRT was significantly lower for contralateral lung and contralateral breast. T-VMAT, however, achieved better homogeneity and conformity. This may be relevant in individual cases where sufficient coverage of medial lymphatic target volumes is warranted.