Implementation of Photon Treatment Back-up Workflow at a High-Volume Proton Center: Safety, Quality, and Patient Considerations.

PURPOSE: A successful proton beam therapy (PBT) center relies heavily on the proper function and maintenance of a proton beam therapy machine. However, when a PBT machine is non-operational, a proton facility is hindered with delays that can potentially lead to inferior treatment outcome due to treatment interruption. This article reports a viable solution for a photon back-up plan in a proton down event. METHODS AND MATERIALS: The implementation of a workflow for which proton plans are converted to photon plans so that patients can be treated using photons has been a successful strategy to reduce delays and mitigate its effect on patient care. This workflow was established through collaboration of physicians, physicists, dosimetrists, therapists, nurses, and schedulers. RESULTS AND CONCLUSIONS: A tiered system established by disease site, number of fractions, and individualized circumstances is used to prioritize patients. Proton-photon backup planning strategy and physics check details were described. This article provides an overview of workflow of conversion of PBT to photon when the PBT machine is down. Specific needs of patients undergoing proton beam therapy are addressed.

Beam angle comparison for distal esophageal carcinoma patients treated with intensity-modulated proton therapy.

PURPOSE: To compare the dosimetric performances of intensity-modulated proton therapy (IMPT) plans generated with two different beam angle configurations (the Right-Left oblique posterior beams and the Superior-Inferior oblique posterior beams) for the treatment of distal esophageal carcinoma in the presence of uncertainties and interplay effect. METHODS AND MATERIALS: Twenty patients' IMPT plans were retrospectively selected, with 10 patients treated with the R-L oblique posterior beams (Group R-L) and the other 10 patients treated with the S-I oblique posterior beams (Group S-I). Patients in both groups were matched by their clinical target volumes (CTVs-high and low dose levels) and respiratory motion amplitudes. Dose-volume-histogram (DVH) indices were used to assess plan quality. DVH bandwidth was calculated to evaluate plan robustness. Interplay effect was quantified using four-dimensional (4D) dynamic dose calculation with random respiratory starting phase of each fraction. Normal tissue complication probability (NTCP) for heart, liver, and lung was calculated, respectively, to estimate the clinical outcomes. Wilcoxon signed-rank test was used for statistical comparison between the two groups. RESULTS: Compared with plans in Group R-L, plans in Group S-I resulted in significantly lower liver Dmean and lung V30Gy[RBE] with slightly higher but clinically acceptable spinal cord Dmax . Similar plan robustness was observed between the two groups. When interplay effect was considered, plans in Group S-I performed statistically better for heart Dmean and V30Gy[RBE] , lung Dmean and V5Gy[RBE] , and liver Dmean , with slightly increased but clinically acceptable spinal cord Dmax . NTCP for liver was significantly better in Group S-I. CONCLUSIONS: IMPT plans in Group S-I have better sparing of liver, heart, and lungs at the slight cost of spinal cord maximum dose protection, and are more interplay-effect resilient compared to IMPT plans in Group R-L. Our study supports the routine use of the S-I oblique posterior beams for the treatments of distal esophageal carcinoma.

Dosimetric comparison of distal esophageal carcinoma plans for patients treated with small-spot intensity-modulated proton versus volumetric-modulated arc therapies.

BACKGROUND: Esophageal carcinoma is the eighth most common cancer in the world. Volumetric-modulated arc therapy (VMAT) is widely used to treat distal esophageal carcinoma due to high conformality to the target and good sparing of organs at risk (OAR). It is not clear if small-spot intensity-modulated proton therapy (IMPT) demonstrates a dosimetric advantage over VMAT. In this study, we compared dosimetric performance of VMAT and small-spot IMPT for distal esophageal carcinoma in terms of plan quality, plan robustness, and interplay effects. METHODS: 35 distal esophageal carcinoma patients were retrospectively reviewed; 19 patients received small-spot IMPT and the remaining 16 of them received VMAT. Both plans were generated by delivering prescription doses to clinical target volumes (CTVs) on phase-averaged 4D-CT's. The dose-volume-histogram (DVH) band method was used to quantify plan robustness. Software was developed to evaluate interplay effects with randomized starting phases for each field per fraction. DVH indices were compared using Wilcoxon rank-sum test. For fair comparison, all the treatment plans were normalized to have the same CTVhigh D95% in the nominal scenario relative to the prescription dose. RESULTS: In the nominal scenario, small-spot IMPT delivered statistically significantly lower liver Dmean and V30Gy[RBE] , lung Dmean , heart Dmean compared with VMAT. CTVhigh dose homogeneity and protection of other OARs were comparable between the two treatments. In terms of plan robustness, the IMPT and VMAT plans were comparable for kidney V18Gy[RBE] , liver V30Gy[RBE] , stomach V45Gy[RBE] , lung Dmean , V5Gy[RBE] , and V20Gy[RBE] , cord Dmax and D 0.03 c m 3 , liver Dmean , heart V20Gy[RBE] , and V30Gy[RBE] , but IMPT was significantly worse for CTVhigh D95% , D 2 c m 3 , and D5% -D95% , CTVlow D95% , heart Dmean , and V40Gy[RBE] , requiring careful and experienced adjustments during the planning process and robustness considerations. The small-spot IMPT plans still met the standard clinical requirements after interplay effects were considered. CONCLUSIONS: Small-spot IMPT decreases doses to heart, liver, and total lung compared to VMAT as well as achieves clinically acceptable plan robustness. Our study supports the use of small-spot IMPT for the treatment of distal esophageal carcinoma.

Small-spot intensity-modulated proton therapy and volumetric-modulated arc therapies for patients with locally advanced non-small-cell lung cancer: A dosimetric comparative study.

PURPOSE: To compare dosimetric performance of volumetric-modulated arc therapy (VMAT) and small-spot intensity-modulated proton therapy for stage III non-small-cell lung cancer (NSCLC). METHODS AND MATERIALS: A total of 24 NSCLC patients were retrospectively reviewed; 12 patients received intensity-modulated proton therapy (IMPT) and the remaining 12 received VMAT. Both plans were generated by delivering prescription doses to clinical target volumes (CTV) on averaged 4D-CTs. The dose-volume-histograms (DVH) band method was used to quantify plan robustness. Software was developed to evaluate interplay effects with randomized starting phases of each field per fraction. DVH indices were compared using Wilcoxon rank sum test. RESULTS: Compared with VMAT, IMPT delivered significantly lower cord Dmax , heart Dmean , and lung V5 Gy[ RBE ] with comparable CTV dose homogeneity, and protection of other OARs. In terms of plan robustness, the IMPT plans were statistically better than VMAT plans in heart Dmean , but were statistically worse in CTV dose coverage, cord Dmax , lung Dmean , and V5 Gy[ RBE ] . Other DVH indices were comparable. The IMPT plans still met the standard clinical requirements with interplay effects considered. CONCLUSIONS: Small-spot IMPT improves cord, heart, and lung sparing compared to VMAT and achieves clinically acceptable plan robustness at least for the patients included in this study with motion amplitude less than 11 mm. Our study supports the usage of IMPT to treat some lung cancer patients.

Impact of Spot Size and Spacing on the Quality of Robustly Optimized Intensity Modulated Proton Therapy Plans for Lung Cancer.

PURPOSE: To investigate how spot size and spacing affect plan quality, robustness, and interplay effects of robustly optimized intensity modulated proton therapy (IMPT) for lung cancer. METHODS AND MATERIALS: Two robustly optimized IMPT plans were created for 10 lung cancer patients: first by a large-spot machine with in-air energy-dependent large spot size at isocenter (σ: 6-15 mm) and spacing (1.3 σ), and second by a small-spot machine with in-air energy-dependent small spot size (σ: 2-6 mm) and spacing (5 mm). Both plans were generated by optimizing radiation dose to internal target volume on averaged 4-dimensional computed tomography scans using an in-house-developed IMPT planning system. The dose-volume histograms band method was used to evaluate plan robustness. Dose evaluation software was developed to model time-dependent spot delivery to incorporate interplay effects with randomized starting phases for each field per fraction. Patient anatomy voxels were mapped phase-to-phase via deformable image registration, and doses were scored using in-house-developed software. Dose-volume histogram indices, including internal target volume dose coverage, homogeneity, and organs at risk (OARs) sparing, were compared using the Wilcoxon signed-rank test. RESULTS: Compared with the large-spot machine, the small-spot machine resulted in significantly lower heart and esophagus mean doses, with comparable target dose coverage, homogeneity, and protection of other OARs. Plan robustness was comparable for targets and most OARs. With interplay effects considered, significantly lower heart and esophagus mean doses with comparable target dose coverage and homogeneity were observed using smaller spots. CONCLUSIONS: Robust optimization with a small spot-machine significantly improves heart and esophagus sparing, with comparable plan robustness and interplay effects compared with robust optimization with a large-spot machine. A small-spot machine uses a larger number of spots to cover the same tumors compared with a large-spot machine, which gives the planning system more freedom to compensate for the higher sensitivity to uncertainties and interplay effects for lung cancer treatments.

Treatment planning for dose escalation in non-small cell lung cancer (NSCLC).

This study was performed to examine potential field arrangements for irradiating non-small cell lung cancer (NSCLC) on a dose escalation study. An example patient was chosen and 7 coplanar treatment plans were created to treat a NSCLC. Two plans included prophylactic nodal irradiation (PNRT) and 5 did not. Four plans used 4 fields, 2 plans used 5 fields, and 1 plan included dynamic conformal 360 degrees rotational therapy. All plans delivered 80 Gy to the isocenter with 10-MV x-rays. Each plan was initially created without dose inhomogeneity corrections and then was recalculated with these corrections, maintaining the same weighting and number of monitor units. Avoiding PNRT spared a considerable volume of normal tissue from radiation. Plans with 5 fields generally spared normal tissues better than 4-field plans. There was no benefit to the dynamic conformal 360 degrees rotational plan. Inhomogeneity corrections revealed that higher doses were delivered to both the tumor and normal structures. Seven beam arrangements for the treatment of NSCLC were compared to develop potential beam arrangements that would be applicable to treating NSCLC on a multi-institutional dose escalation study. We favor the use of at least 5 beams in most situations. It is possible that the use of more fields would further improve plans up to a point of diminishing returns, as exemplified by the lack of benefit seen with the dynamic conformal 360 degrees rotational plan. It is possible that the use of noncoplanar fields or intensity-modulated radiation therapy (IMRT) may further improve the therapeutic ratio.